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Wang H, Wang W, Gao X, Wu D, Lu Q, Li C, Zheng S, Wang H. Effects of Postural Resonance on Skin Sympathetic Nerve Activity and Blood Pressure: A Pilot Study Evaluating Vascular Tone Baroreflex Stimulation Through Biofeedback. Appl Psychophysiol Biofeedback 2024; 49:205-218. [PMID: 38159163 DOI: 10.1007/s10484-023-09614-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/01/2023] [Indexed: 01/03/2024]
Abstract
Heart rate and vascular tension baroreflex exhibit resonance characteristics at approximately 0.1 and 0.03 Hz. In this study, we aimed to induce postural resonance (PR) through rhythmic postural adjustments. To assess the viability of this technique, we investigated the acute impacts of postural resonance on blood pressure, sympathetic nerve activity, and mood. Fifteen healthy study participants, consisting of 8 males and 7 females, were selected for this self-controlled study. Skin sympathetic nerve activity was continuously monitored during both the intervention and stress test on the experimental day. After PR intervention, the diastolic blood pressure and mean arterial pressure in the PR group exhibited significant reductions compared to the CON group (P = 0.032, CON = 71.67 ± 2.348, PR = 64.08 ± 2.35; P = 0.041, CON = 75.00 ± 2.17, PR = 81.67 ± 2.17). After PR intervention both left brachial ankle pulse wave velocity and right brachial ankle pulse wave velocity exhibited a significant reduction compared to pre-intervention levels (from 1115.86 ± 150.08 to 1048.43 ± 127.40 cm/s, p < 0.001; 1103.86 ± 144.35 to 1060.43 ± 121.35 cm/s, p = 0.018). PR intervention also led to a significant decrease in burst frequency and duration (P = 0.049; CON = 8.96 ± 1.17, PR = 5.51 ± 1.17) and a noteworthy decrease in burst amplitude and burst threshold during the cold-pressor test (P = 0.002; P = 0.002). Additionally, VAS scores exhibited a substantial increase following PR (P = 0.035, CON = 28.4 ± 4.49, PR = 42.17 ± 4.10). PR can induce resonance effects within the cardiovascular system, resulting in the effective reduction of blood pressure, skin sympathetic nerve activity and pulse wave velocity, and decreased burst amplitude and burst threshold of the sympathetic nerve during the cold-pressor test.
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Affiliation(s)
- Hao Wang
- Sports Rehabilitation Research Center, China Institute of Sport Science, Beijing, China
| | - Wendi Wang
- Sports Rehabilitation Research Center, China Institute of Sport Science, Beijing, China
| | - Xiaolin Gao
- Sports Rehabilitation Research Center, China Institute of Sport Science, Beijing, China.
| | - Dongzhe Wu
- Sports Rehabilitation Research Center, China Institute of Sport Science, Beijing, China.
| | - Qiaopei Lu
- Sports Training Center, Institute of Sport Science, Beijing, China
| | - Chuangtao Li
- Sports Rehabilitation Research Center, China Institute of Sport Science, Beijing, China
| | - Sainan Zheng
- School of Sport Science, Beijing Sport University, Beijing, China
| | - Haoruo Wang
- School of Sport Science, Beijing Sport University, Beijing, China
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Sawada T, Okawara H, Nakashima D, Aoki K, Namba M, Iwabuchi S, Katsumata Y, Nakamura M, Nagura T. Local alternating heat and cold stimulation affects hemodynamics and oxygenation in fatigued muscle tissue and autonomic nervous activity: a single-arm interventional study. J Physiol Anthropol 2024; 43:11. [PMID: 38528599 DOI: 10.1186/s40101-024-00358-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2023] [Accepted: 03/20/2024] [Indexed: 03/27/2024] Open
Abstract
BACKGROUND Local alternating heat and cold stimulation as an alternative to contrast bath may cause intermittent vasoconstriction and vasodilation, inducing a vascular pumping effect and consequently promoting increased tissue blood flow and oxygenation. This study aimed to examine the effects of local alternating heat and cold stimulation, using a wearable thermal device, on the hemodynamics of fatigued muscle tissue and autonomic nervous activity. METHODS Twenty healthy individuals experienced fatigue in the periarticular muscles of the shoulder joint due to a typing task. Local alternating heat and cold stimulations were then applied to the upper trapezius muscle. Muscle hardness was measured using a muscle hardness meter, and muscle tissue hemodynamics and oxygenation were evaluated using near-infrared spectroscopy before and after the stimulation. Autonomic nervous activity was also evaluated using heart rate variability. RESULTS Alternating heat and cold stimulation decreased muscle hardness of the fatigued trapezius muscle from 1.38 ± 0.15 to 1.31 ± 0.14 N (P < 0.01). The concentration of total hemoglobin in the trapezius muscle tissue increased from - 0.21 ± 1.36 to 2.29 ± 3.42 µmol/l (P < 0.01), and the tissue hemoglobin oxygen saturation also increased from 70.1 ± 5.4 to 71.1 ± 6.0% (P < 0.05). Additionally, the heart rate variability parameter, which is an index of sympathetic nervous activity, increased from 3.82 ± 2.96 to 6.86 ± 3.49 (P < 0.01). A correlation was found between increased tissue hemoglobin oxygen saturation and increased parameters of sympathetic nervous activity (r = 0.50, P < 0.05). CONCLUSIONS Local alternating heat and cold stimulation affected the hemodynamic response in fatigued muscle tissue and autonomic nervous activity. This stimulation is more efficient than conventional contrast baths in terms of mobility and temperature control and has potential as a new versatile therapeutic intervention for muscle fatigue. TRIAL REGISTRATION UMIN-CTR (UMIN000040087: registered on April 7, 2020, https://upload.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000045710 . UMIN000040620: registered on June 1, 2020, https://upload.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000046359 ).
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Affiliation(s)
- Tomonori Sawada
- Diagnosis and Treatment Division, Nagura Orthopedic Clinic, Chuo, Tokyo, Japan
- Department of Orthopaedic Surgery, Keio University School of Medicine, Shinjuku, Tokyo, Japan
| | - Hiroki Okawara
- Diagnosis and Treatment Division, Nagura Orthopedic Clinic, Chuo, Tokyo, Japan
- Department of Orthopaedic Surgery, Keio University School of Medicine, Shinjuku, Tokyo, Japan
| | - Daisuke Nakashima
- Diagnosis and Treatment Division, Nagura Orthopedic Clinic, Chuo, Tokyo, Japan.
- Department of Orthopaedic Surgery, Keio University School of Medicine, Shinjuku, Tokyo, Japan.
- Department of Clinical Biomechanics, Keio University School of Medicine, Shinjuku, Tokyo, Japan.
| | - Kentaro Aoki
- Department of Orthopaedic Surgery, Keio University School of Medicine, Shinjuku, Tokyo, Japan
| | - Mira Namba
- Department of Orthopaedic Surgery, Keio University School of Medicine, Shinjuku, Tokyo, Japan
| | - Shuhei Iwabuchi
- Department of Orthopaedic Surgery, Keio University School of Medicine, Shinjuku, Tokyo, Japan
| | - Yoshinori Katsumata
- Institute for Integrated Sports Medicine, Keio University School of Medicine, Shinjuku, Tokyo, Japan
- Department of Cardiology, Keio University School of Medicine, Shinjuku, Tokyo, Japan
| | - Masaya Nakamura
- Department of Orthopaedic Surgery, Keio University School of Medicine, Shinjuku, Tokyo, Japan
| | - Takeo Nagura
- Diagnosis and Treatment Division, Nagura Orthopedic Clinic, Chuo, Tokyo, Japan
- Department of Orthopaedic Surgery, Keio University School of Medicine, Shinjuku, Tokyo, Japan
- Department of Clinical Biomechanics, Keio University School of Medicine, Shinjuku, Tokyo, Japan
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3
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Bigalke JA, Greenlund IM, Nicevski JR, Tikkanen AL, Carter JR. Sympathetic neural reactivity to the Trier social stress test. J Physiol 2022; 600:3705-3724. [PMID: 35844138 PMCID: PMC9401978 DOI: 10.1113/jp283358] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2022] [Accepted: 07/04/2022] [Indexed: 01/05/2023] Open
Abstract
Sympathetic responsiveness to laboratory mental stress is highly variable, making interpretations of its role in stress reactivity challenging. The present study assessed muscle sympathetic nerve activity (MSNA, microneurography) responsiveness to the Trier social stress test (TSST), which employs an anticipatory stress phase, followed by a public speaking and mental arithmetic task. We hypothesized that sympathetic reactivity to the anticipatory phase would offer a more uniform response between individuals due to elimination of confounds (i.e. respiratory changes, muscle movement, etc.) observed during more common stress tasks. Participants included 26 healthy adults (11 men, 15 women, age: 25 ± 6 years, body mass index: 24 ± 3 kg/m2 ). Continuous heart rate (electrocardiogram) and beat-to-beat blood pressure (finger plethysmography) were recorded from all participants, while MSNA recordings were obtained in 20 participants. MSNA burst frequency was significantly reduced during anticipatory stress. During the speech, although burst frequency was unchanged, total MSNA was significantly increased. Changes in diastolic arterial pressure were predictive of changes in MSNA during anticipatory (β = -0.680, P = 0.001), but not the speech (P = 0.318) or mental maths (P = 0.051) phases. Lastly, sympathetic reactivity to anticipatory stress was predictive of subsequent reactivity to both speech (β = 0.740, P = 0.0002) and maths (β = 0.663, P = 0.001). In conclusion, anticipatory social stress may offer a more versatile means of assessing sympathetic reactivity to mental stress in the absence of confounds and appears to predict reactivity to subsequent mental stress paradigms. KEY POINTS: Cardiovascular reactivity to laboratory mental stress is predictive of future health outcomes. However, reactivity of the sympathetic nervous system to mental stress is highly variable. The current study assessed peripheral muscle sympathetic nerve activity in response to the Trier social stress test, a psychosocial stressor that includes anticipatory stress, public speaking and mental arithmetic. Our findings demonstrate that sympathetic neural activity is consistently reduced during anticipatory stress. Conversely, the classically observed inter-individual variability of sympathetic responsiveness was observed during speech and maths tasks. Additionally, sympathetic reactivity to the anticipatory period accurately predicted how an individual would respond to both speech and maths tasks, outlining the utility of anticipatory stress in future research surrounding stress reactivity. Utilization of the Trier social stress test in autonomic physiology may offer an alternative assessment of sympathetic responsiveness to stress with more consistent inter-individual responsiveness and may be a useful tool for further investigation of stress reactivity.
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Affiliation(s)
- Jeremy A. Bigalke
- Department of Health and Human Development, Montana State University, Bozeman, Montana,Department of Psychology, Montana State University, Bozeman, Montana
| | - Ian M. Greenlund
- Department of Health and Human Development, Montana State University, Bozeman, Montana,Department of Psychology, Montana State University, Bozeman, Montana
| | - Jennifer R. Nicevski
- Department of Health and Human Development, Montana State University, Bozeman, Montana
| | - Anne L. Tikkanen
- Department of Health and Human Development, Montana State University, Bozeman, Montana
| | - Jason R. Carter
- Department of Health and Human Development, Montana State University, Bozeman, Montana,Department of Psychology, Montana State University, Bozeman, Montana
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4
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Cui J, Gao Z, Leuenberger UA, Blaha C, Luck JC, Herr MD, Sinoway LI. Repeated warm water baths decrease sympathetic activity in humans. J Appl Physiol (1985) 2022; 133:234-245. [PMID: 35736952 DOI: 10.1152/japplphysiol.00684.2021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Acute whole-body heat stress evokes sympathetic activation. However, the chronic effects of repeated moderate heat exposure (RMHE) on muscle sympathetic nerve activity (MSNA) in healthy individuals remains unclear. We performed RMHE with 4 weeks (5 days/week) warm baths (~40 °C, for 30 min) in 9 healthy older (59 ± 2 yrs) volunteers. Hemodynamic variables and MSNA were examined prior, 1 day after and 1 week following 4 weeks of RMHE in a laboratory at ~23 °C. Cold pressor test and handgrip exercise were performed during the tests. Under normothermic condition, the resting MSNA burst rate (prior, post, post 1-wk: 31.6 ± 2.0, 25.2 ± 2.0, 27.7 ± 1.7 bursts/min; P < 0.001) and burst incidence (P < 0.001) significantly decreased after RMHE. Moreover, the resting heart rate significantly decreased after RMHE (62.3 ± 1.6, 59.5 ± 2.0, 58.2 ± 1.6 beats/min, P = 0.031). The low frequency to high frequency ratio of heart rate variability, an index of sympathovagal balance, also decreased after RMHE. The sensitivity of baroreflex control of MSNA and heart rate were not altered by RMHE, although the operating points were reset. The MSNA and hemodynamic responses (i.e. changes) to handgrip exercise or cold pressor test were not significantly altered. These data suggest that the RMHE evoked by warm baths decreases resting sympathetic activity and HR, which can be considered beneficial effects. The mechanism(s) should be examined in future studies.
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Affiliation(s)
- Jian Cui
- Penn State Heart and Vascular Institute, Pennsylvania State University, Hershey, PA, United States
| | - Zhaohui Gao
- Penn State Heart and Vascular Institute, Pennsylvania State University, Hershey, PA, United States
| | - Urs A Leuenberger
- Penn State Heart and Vascular Institute, Pennsylvania State University, Hershey, PA, United States
| | - Cheryl Blaha
- Penn State Heart and Vascular Institute, Pennsylvania State University, Hershey, PA, United States
| | - Jonathan Carter Luck
- Penn State Heart and Vascular Institute, Pennsylvania State University, Hershey, PA, United States
| | - Michael D Herr
- Penn State Heart and Vascular Institute, Pennsylvania State University, Hershey, PA, United States
| | - Lawrence I Sinoway
- Penn State Heart and Vascular Institute, Pennsylvania State University, Hershey, PA, United States
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5
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Bigalke JA, Carter JR. Sympathetic Neural Control in Humans with Anxiety-Related Disorders. Compr Physiol 2021; 12:3085-3117. [PMID: 34964121 DOI: 10.1002/cphy.c210027] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Numerous conceptual models are used to describe the dynamic responsiveness of physiological systems to environmental pressures, originating with Claude Bernard's milieu intérieur and extending to more recent models such as allostasis. The impact of stress and anxiety upon these regulatory processes has both basic science and clinical relevance, extending from the pioneering work of Hans Selye who advanced the concept that stress can significantly impact physiological health and function. Of particular interest within the current article, anxiety is independently associated with cardiovascular risk, yet mechanisms underlying these associations remain equivocal. This link between anxiety and cardiovascular risk is relevant given the high prevalence of anxiety in the general population, as well as its early age of onset. Chronically anxious populations, such as those with anxiety disorders (i.e., generalized anxiety disorder, panic disorder, specific phobias, etc.) offer a human model that interrogates the deleterious effects that chronic stress and allostatic load can have on the nervous system and cardiovascular function. Further, while many of these disorders do not appear to exhibit baseline alterations in sympathetic neural activity, reactivity to mental stress offers insights into applicable, real-world scenarios in which heightened sympathetic reactivity may predispose those individuals to elevated cardiovascular risk. This article also assesses behavioral and lifestyle modifications that have been shown to concurrently improve anxiety symptoms, as well as sympathetic control. Lastly, future directions of research will be discussed, with a focus on better integration of psychological factors within physiological studies examining anxiety and neural cardiovascular health. © 2022 American Physiological Society. Compr Physiol 12:1-33, 2022.
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Affiliation(s)
- Jeremy A Bigalke
- Department of Psychology, Montana State University, Bozeman, Montana, USA
| | - Jason R Carter
- Department of Psychology, Montana State University, Bozeman, Montana, USA.,Department of Health and Human Development, Montana State University, Bozeman, Montana, USA
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Manfredi LH. Overheating or overcooling: heat transfer in the spot to fight against the pandemic obesity. Rev Endocr Metab Disord 2021; 22:665-680. [PMID: 33000381 DOI: 10.1007/s11154-020-09596-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 09/17/2020] [Indexed: 12/25/2022]
Abstract
The prevalence of obesity has nearly doubled worldwide over the past three and a half decades, reaching pandemic status. Obesity is associated with decreased life expectancy and with an increased risk of metabolic, cardiovascular, nervous system diseases. Hence, understanding the mechanisms involved in the onset and development of obesity is mandatory to promote planned health actions to revert this scenario. In this review, common aspects of cold exposure, a process of heat generation, and exercise, a process of heat dissipation, will be discussed as two opposite mechanisms of obesity, which can be oversimplified as caloric conservation. A common road between heat generation and dissipation is the mobilization of Free Faty Acids (FFA) and Carbohydrates (CHO). An increase in energy expenditure (immediate effect) and molecular/metabolic adaptations (chronic effect) are responses that depend on SNS activity in both conditions of heat transfer. This cycle of using and removing FFA and CHO from blood either for heat or force generation disrupt the key concept of obesity: energy accumulation. Despite efforts in making the anti-obesity pill, maybe it is time to consider that the world's population is living at thermoneutrality since temperature-controlled places and the lack of exercise are favoring caloric accumulation.
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Affiliation(s)
- Leandro Henrique Manfredi
- Graduate Program in Biomedical Sciences, Federal University of Fronteira Sul, Chapecó, Santa Catarina, Brazil.
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7
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Ferreira FC, Vaz Padilha MCS, Tobadini E, Carandina A, Montano N, Soares PPDS, Rodrigues GD. The interplay between heated environment and active standing test on cardiovascular autonomic control in healthy individuals. Physiol Meas 2021; 42. [PMID: 34261052 DOI: 10.1088/1361-6579/ac1497] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2021] [Accepted: 07/14/2021] [Indexed: 01/03/2023]
Abstract
Objective.To investigate the interplay between active standing and heat stress on cardiovascular autonomic modulation in healthy individuals.Approach.Blood pressure (BP) and ECG were continuously recorded during 30 min in supine (SUP) and 6 min in orthostatic position (ORT) under thermal reference (TC; ∼24 °C) or heated environment (HOT; ∼36 °C) conditions, in a randomized order. All data collection was performed during the winter and spring seasons when typical outdoor temperatures are ∼23 °C. Spectral analysis was employed by the autoregressive model of R-R and systolic blood pressure (SBP) time series and defined, within each band, in low (LF, 0.04 to 0.15 Hz) and high (0.15-0.40 Hz) frequencies. The indices of cardiac sympathetic (LF) and cardiac parasympathetic (HF) were normalized (nu) dividing each band power by the total power subtracted the very-low component (<0.04 Hz), obtaining the cardiac autonomic balance (LF/HF) modulation. The gain of the relationship between SBP and R-R variabilities within the LF band was utilized for analysis of spontaneous baroreflex sensitivity (alpha index;αLF). Nonlinear analysis was employed through symbolic dynamics of R-R, which provided the percentage of sequences of three heart periods without changes in R-R interval (0V%; cardiac sympathetic modulation) and two significant variations (2UV% and 2LV%; cardiac vagal modulation).Main results.HOT increased 0V% and HR, and decreasedαLF and 2UV% during SUP compared to TC. During ORT, HOT provokes a greater increment on HR, LF/HF and 0V%, indexes compared to ORT under TC.Significance.At rest, heat stress influences both autonomic branches, increasing sympathetic and decreasing vagal modulation and spontaneous baroreflex sensitivity. The augmented HR during active standing under heat stress seems to be mediated by a greater increment in cardiac sympathetic modulation, showing an interplay between gravitational and thermal stimulus.
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Affiliation(s)
- Felipe Castro Ferreira
- Laboratory of Experimental and Applied Exercise Physiology, Department of Physiology and Pharmacology, Fluminense Federal University, Niterói, Brazil
| | | | - Eleonora Tobadini
- Department of Internal Medicine, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, I-20122 Milan, Italy.,Department of Clinical Sciences and Community Health, University of Milan, I-20122 Milan, Italy
| | - Angelica Carandina
- Department of Internal Medicine, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, I-20122 Milan, Italy
| | - Nicola Montano
- Department of Internal Medicine, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, I-20122 Milan, Italy.,Department of Clinical Sciences and Community Health, University of Milan, I-20122 Milan, Italy
| | - Pedro Paulo da Silva Soares
- Laboratory of Experimental and Applied Exercise Physiology, Department of Physiology and Pharmacology, Fluminense Federal University, Niterói, Brazil
| | - Gabriel Dias Rodrigues
- Laboratory of Experimental and Applied Exercise Physiology, Department of Physiology and Pharmacology, Fluminense Federal University, Niterói, Brazil.,Department of Clinical Sciences and Community Health, University of Milan, I-20122 Milan, Italy
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8
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Brochu P, Ménard J, Marchand A, Haddad S. Cardiopulmonary values and organ blood flows before and during heat stress: data in nine subjects at rest in the upright position. Can J Physiol Pharmacol 2021; 99:1148-1158. [PMID: 34062083 DOI: 10.1139/cjpp-2021-0044] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Physiological changes associated with thermoregulation can influence the kinetics of chemicals in the human body, such as alveolar ventilation (VA) and redistribution of blood flow to organs. In this study, the influence of heat stress on various physiological parameters was evaluated in nine male volunteers during sessions of exposure to wet blub globe temperatures (WBGT) of 21, 25 and 30°C for four hours. Skin and core temperatures and more than twenty cardiopulmonary parameters were measured. Liver, kidneys, brain, skin and muscles blood flows were also determined based on published measurements. Results show that most subjects (8 out of 9) have been affected by the inhalation of hot and dry air at the WBGT of 30°C. High respiratory rates, superficial tidal volumes and low VA values were notably observed. The skin blood flow has increased by 2.16-fold, whereas the renal blood flow and liver blood flow have decreased by about by 11 and 18% respectively. A complete set of key cardiopulmonary parameters in healthy male adults before and during heat stress was generated for use in PBPK modeling. A toxicokinetic studies are ongoing to evaluate the impact of heat stress on the absorption, biotransformation and excretion rates of volatile xenobiotics.
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Affiliation(s)
- Pierre Brochu
- Université de Montréal, 5622, Environmental and Occupational Health, School of Public Health, Montreal, Quebec, Canada;
| | - Jessie Ménard
- Université de Montréal, 5622, Environmental and Occupational Health, School of Public Health, Montreal, Quebec, Canada.,Centre for Public Health Research (CReSP), Montréal, Quebec, Canada;
| | - Axelle Marchand
- Université de Montréal, 5622, Environmental and Occupational Health, School of Public Health, Montreal, Quebec, Canada.,Centre for Public Health Research (CReSP), Montréal, Quebec, Canada;
| | - Sami Haddad
- Université de Montréal, 5622, Environmental and Occupational Health, School of Public Health, Montreal, Quebec, Canada.,Centre for Public Health Research (CReSP), Montréal, Quebec, Canada;
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9
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Cui J, Gao Z, Blaha C, Luck JC, Brandt K, Sinoway LI. Moderate whole body heating attenuates the exercise pressor reflex responses in older humans. Am J Physiol Regul Integr Comp Physiol 2021; 320:R757-R769. [PMID: 33789459 DOI: 10.1152/ajpregu.00232.2020] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Prior reports show that whole body heat stress attenuates the pressor response to exercise in young healthy subjects. The effects of moderate whole body heating (WBH; e.g., increase in internal temperature Tcore of ∼0.4°C-0.5°C) or limb heating on sympathetic and cardiovascular responses to exercise in older healthy humans remain unclear. We examined the muscle sympathetic nerve activity (MSNA), mean arterial blood pressure (MAP), and heart rate (HR) in 14 older (62 ± 2 yr) healthy subjects during fatiguing isometric handgrip exercise and postexercise circulatory occlusion (PECO). The protocol was performed under normothermic, moderate WBH, and local limb (i.e., forearm) heating conditions during three visits. During the mild WBH stage (increase in Tcore of <0.3°C), HR increased, whereas BP and MSNA decreased from baseline. Under the moderate WBH condition (increase in Tcore of ∼0.4°C), BP decreased, HR increased, and MSNA was unchanged from baseline. Compared with the normothermic trial, the absolute MAP during fatiguing exercise and PECO was lower during the WBH trial. Moreover, MSNA and MAP responses (i.e., changes) to fatiguing exercise were also less than those seen during the normothermic trial. Limb heating induced a similar increase in forearm muscle temperature to that seen in the WBH trial (∼0.7°C-1.5°C). Limb heating did not alter resting MAP, HR, or MSNA. The MSNA and hemodynamic responses to exercise in the limb heating trial were not different from those in the normothermic trial. These data suggest that moderate WBH attenuates MSNA and BP responses to exercise in older healthy humans.
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Affiliation(s)
- Jian Cui
- Penn State Health, Penn State Heart and Vascular Institute, Hershey, Pennsylvania
| | - Zhaohui Gao
- Penn State Health, Penn State Heart and Vascular Institute, Hershey, Pennsylvania
| | - Cheryl Blaha
- Penn State Health, Penn State Heart and Vascular Institute, Hershey, Pennsylvania
| | - Jonathan Carter Luck
- Penn State Health, Penn State Heart and Vascular Institute, Hershey, Pennsylvania
| | - Kristen Brandt
- Penn State Health, Penn State Heart and Vascular Institute, Hershey, Pennsylvania
| | - Lawrence I Sinoway
- Penn State Health, Penn State Heart and Vascular Institute, Hershey, Pennsylvania
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10
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Convertino VA, Koons NJ, Suresh MR. Physiology of Human Hemorrhage and Compensation. Compr Physiol 2021; 11:1531-1574. [PMID: 33577122 DOI: 10.1002/cphy.c200016] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Hemorrhage is a leading cause of death following traumatic injuries in the United States. Much of the previous work in assessing the physiology and pathophysiology underlying blood loss has focused on descriptive measures of hemodynamic responses such as blood pressure, cardiac output, stroke volume, heart rate, and vascular resistance as indicators of changes in organ perfusion. More recent work has shifted the focus toward understanding mechanisms of compensation for reduced systemic delivery and cellular utilization of oxygen as a more comprehensive approach to understanding the complex physiologic changes that occur following and during blood loss. In this article, we begin with applying dimensional analysis for comparison of animal models, and progress to descriptions of various physiological consequences of hemorrhage. We then introduce the complementary side of compensation by detailing the complexity and integration of various compensatory mechanisms that are activated from the initiation of hemorrhage and serve to maintain adequate vital organ perfusion and hemodynamic stability in the scenario of reduced systemic delivery of oxygen until the onset of hemodynamic decompensation. New data are introduced that challenge legacy concepts related to mechanisms that underlie baroreflex functions and provide novel insights into the measurement of the integrated response of compensation to central hypovolemia known as the compensatory reserve. The impact of demographic and environmental factors on tolerance to hemorrhage is also reviewed. Finally, we describe how understanding the physiology of compensation can be translated to applications for early assessment of the clinical status and accurate triage of hypovolemic and hypotensive patients. © 2021 American Physiological Society. Compr Physiol 11:1531-1574, 2021.
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Affiliation(s)
- Victor A Convertino
- Battlefield Healthy & Trauma Center for Human Integrative Physiology, United States Army Institute of Surgical Research, JBSA San Antonio, Texas, USA
| | - Natalie J Koons
- Battlefield Healthy & Trauma Center for Human Integrative Physiology, United States Army Institute of Surgical Research, JBSA San Antonio, Texas, USA
| | - Mithun R Suresh
- Battlefield Healthy & Trauma Center for Human Integrative Physiology, United States Army Institute of Surgical Research, JBSA San Antonio, Texas, USA
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11
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Holwerda SW, Carter JR, Yang H, Wang J, Pierce GL, Fadel PJ. CORP: Standardizing methodology for assessing spontaneous baroreflex control of muscle sympathetic nerve activity in humans. Am J Physiol Heart Circ Physiol 2021; 320:H762-H771. [PMID: 33275522 PMCID: PMC8082800 DOI: 10.1152/ajpheart.00704.2020] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/26/2020] [Revised: 11/24/2020] [Accepted: 11/24/2020] [Indexed: 12/28/2022]
Abstract
The use of spontaneous bursts of muscle sympathetic nerve activity (MSNA) to assess arterial baroreflex control of sympathetic nerve activity has seen increased utility in studies of both health and disease. However, methods used for analyzing spontaneous MSNA baroreflex sensitivity are highly variable across published studies. Therefore, we sought to comprehensively examine methods of producing linear regression slopes to quantify spontaneous MSNA baroreflex sensitivity in a large cohort of subjects (n = 150) to support a standardized procedure for analysis that would allow for consistent and comparable results across laboratories. The primary results demonstrated that 1) consistency of linear regression slopes was considerably improved when the correlation coefficient was above -0.70, which is more stringent compared with commonly reported criterion of -0.50, 2) longer recording durations increased the percentage of linear regressions producing correlation coefficients above -0.70 (1 min = 15%, 2 min = 28%, 5 min = 53%, 10 min = 67%, P < 0.001) and reaching statistical significance (1 min = 40%, 2 min = 69%, 5 min = 78%, 10 min = 89%, P < 0.001), 3) correlation coefficients were improved with 3-mmHg versus 1-mmHg and 2-mmHg diastolic blood pressure (BP) bin size, and 4) linear regression slopes were reduced when the acquired BP signal was not properly aligned with the cardiac cycle triggering the burst of MSNA. In summary, these results support the use of baseline recording durations of 10 min, a correlation coefficient above -0.70 for reliable linear regressions, 3-mmHg bin size, and importance of properly time-aligning MSNA and diastolic BP. Together, these findings provide best practices for determining spontaneous MSNA baroreflex sensitivity under resting conditions for improved rigor and reproducibility of results.
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Affiliation(s)
- Seth W Holwerda
- Department of Anesthesiology, University of Kansas Medical Center, Kansas City, Kansas
| | - Jason R Carter
- Department of Health and Human Development, Montana State University, Bozeman, Montana
| | - Huan Yang
- Department of Neurology, Beth Israel Deaconess Medical Center/Harvard Medical School, Boston, Massachusetts
| | - Jing Wang
- College of Nursing, University of Texas at Arlington, Arlington, Texas
| | - Gary L Pierce
- Department of Health and Human Physiology, University of Iowa, Iowa City, Iowa
| | - Paul J Fadel
- Department of Kinesiology, University of Texas at Arlington, Arlington, Texas
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12
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Perry BG, Mündel T. Lower body positive pressure affects systemic but not cerebral haemodynamics during incremental hyperthermia. Clin Physiol Funct Imaging 2020; 41:226-233. [PMID: 33238075 DOI: 10.1111/cpf.12682] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2020] [Revised: 10/17/2020] [Accepted: 11/18/2020] [Indexed: 11/28/2022]
Abstract
Hyperthermia produces profound redistribution of blood and circulatory reflex function. We investigated the potential for lower body positive pressure (LBPP) to maintain or restore haemodynamics during graded hyperthermia. Eight healthy adults rested supine in a custom-made LBPP box, sealed distal to the iliac crest. Following 5 min of normothermic rest, 20 mmHg of LBPP was applied and repeated when core temperature (Tcore ) had increased passively by +0.5 and +1°C. Primary dependent variables included mean middle cerebral artery blood velocity (MCAvmean , transcranial Doppler), mean arterial blood pressure (MAP, finger photoplethysmography), heart rate (HR) and partial pressure of end-tidal carbon dioxide (PET CO2 ). The absolute increase in MAP during LBPP was lower at Tcore +1°C (2 ± 3 mmHg), compared with normothermia (7 ± 3 p = .01). The modest increase in MCAvmean was unchanged by Tcore (normothermia, 2 ± 3 cm/s; +0.5°C, 3 ± 3 cm/s and +1°C, 3 ± 4 cm/s, p = .74). By design, PET CO2 was unchanged in all conditions from normothermic baseline (42 ± 1, p = .81). LBPP-induced changes in HR were greater at +0.5°C (-13 ± 4 b/min) and +1°C (-12 ± 6 b/min) compared with normothermia (-3 ± 3 b/min, p = .01 and p = .01, respectively). These data indicate that despite a significant attenuation in MAP to LBPP with moderate hyperthermia, MCAvmean dynamics were unchanged among the thermal manipulations.
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Affiliation(s)
- Blake G Perry
- School of Health Sciences, Massey University, Wellington, New Zealand.,School of Sport, Exercise and Nutrition, Massey University, Palmerston North, New Zealand
| | - Toby Mündel
- School of Sport, Exercise and Nutrition, Massey University, Palmerston North, New Zealand
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13
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Sugawara J, Tomoto T. Effects of short-term warm water immersion on cardiac baroreflex sensitivity in healthy men. J Physiol Sci 2020; 70:34. [PMID: 32646375 PMCID: PMC10717741 DOI: 10.1186/s12576-020-00762-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2020] [Accepted: 07/03/2020] [Indexed: 11/10/2022]
Abstract
Warm water immersion (WWI) causes dizziness presumably due to a substantial drop of blood pressure. The aim of this study was to elucidate the effects of short-term WWI on cardiac baroreflex sensitivity (BRS) and the contribution of arterial stiffness to the cardiac BRS. Twelve apparent healthy men (44 ± 12 years) performed the single stand-up test after 5-min sitting in the bathtub without (Control) and with 41 °C warm water at the heart level (WWI). Cardiac BRS gain was evaluated by R-R interval response to the standing-induced drop of systolic blood pressure. In addition, before and 10 min after the single stand-up test, carotid arterial β-stiffness index was evaluated in the supine rest. BRS gain was blunted (2.9 ± 1.6 vs. 1.8 ± 1.1 ms/mmHg, P = 0.005), whereas β-stiffness index was not changed significantly after WWI. BRS gain correlated with β-stiffness index before (r = - 0.626, P = 0.028) and after WWI (r = - 0.672, P = 0.015). ANCOVA revealed that these slopes of linear regression lines remained unchanged after WWI (P = 0.350). These results indicate that a short-term WWI acutely deteriorates cardiac BRS. Individuals with stiffer arteries are relatively more susceptible to WWI because of their poor baseline BRS, which might be one of the causes of bathing-related falling in elderly persons as well as frailty.
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Affiliation(s)
- Jun Sugawara
- Human Informatics and Interaction Research Institute, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, Ibaraki, 305-8566, Japan.
| | - Tsubasa Tomoto
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, Dallas, TX, USA
- Department of Neurology and Neurotherapeutics, University of Texas Southwestern Medical Center, Dallas, TX, USA
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14
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Ott EP, Jacob DW, Baker SE, Holbein WW, Scruggs ZM, Shoemaker JK, Limberg JK. Sympathetic neural recruitment strategies following acute intermittent hypoxia in humans. Am J Physiol Regul Integr Comp Physiol 2020; 318:R961-R971. [PMID: 32267729 DOI: 10.1152/ajpregu.00004.2020] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We examined the effect of acute intermittent hypoxia (IH) on sympathetic neural firing patterns and the role of the carotid chemoreceptors. We hypothesized exposure to acute IH would increase muscle sympathetic nerve activity (MSNA) via an increase in action potential (AP) discharge rates and within-burst firing. We further hypothesized any change in discharge patterns would be attenuated during acute chemoreceptor deactivation (hyperoxia). MSNA (microneurography) was assessed in 17 healthy adults (11 male/6 female; 31 ± 1 yr) during normoxic rest before and after 30 min of experimental IH. Prior to and following IH, participants were exposed to 2 min of 100% oxygen (hyperoxia). AP patterns were studied from the filtered raw MSNA signal using wavelet-based methodology. Compared with baseline, multiunit MSNA burst incidence (P < 0.01), AP incidence (P = 0.01), and AP content per burst (P = 0.01) were increased following IH. There was an increase in the probability of a particular AP cluster firing once (P < 0.01) and more than once (P = 0.03) per burst following IH. There was no effect of hyperoxia on multiunit MSNA at baseline or following IH (P > 0.05); however, hyperoxia following IH attenuated the probability of particular AP clusters firing more than once per burst (P < 0.01). Acute IH increases MSNA by increasing AP discharge rates and within-burst firing. A portion of the increase in within-burst firing following IH can be attributed to the carotid chemoreceptors. These data advance the mechanistic understanding of sympathetic activation following acute IH in humans.
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Affiliation(s)
- Elizabeth P Ott
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri
| | - Dain W Jacob
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri
| | - Sarah E Baker
- Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota
| | | | | | - J Kevin Shoemaker
- School of Kinesiology, University of Western Ontario, London, Ontario, Canada
| | - Jacqueline K Limberg
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri.,Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota
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15
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Cutaneous warmth, but not touch, increases muscle sympathetic nerve activity during a muscle fatigue hand-grip task. Exp Brain Res 2020; 238:1035-1042. [PMID: 32198543 PMCID: PMC7181540 DOI: 10.1007/s00221-020-05779-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2019] [Accepted: 03/10/2020] [Indexed: 12/05/2022]
Abstract
In homeostasis, somatosensory C fibre afferents are hypothesised to mediate input to the brain about interactions with external stimuli and sympathetic efference provides the output that regulates bodily functions. We aimed to test this hypothesis and whether different types of innocuous somatosensory input have differential effects. Healthy volunteers performed a muscle fatigue (hand-grip) task to exhaustion, which produces increased muscle sympathetic nerve activity (MSNA), as measured through microneurography. Participants completed the muscle fatigue task without concurrent cutaneous sensory stimulation (control) or we applied skin warming (heat pack) as a C fibre stimulation, slow brush stroking as C and Aβ fibre stimulation, or vibration as Aβ fibre stimulation, to the participant’s forearm. We also measured heart rate, the duration of the hand-grip task, and ratings of pain at the end of the task. Concurrent skin warming showed increased MSNA compared to the other conditions. Tactile stimuli (brushing, vibration) were not significantly different to the control (no intervention) condition. Warming increased the pain from the muscle contraction, whereas the tactile stimuli did not. We interpret the effect of warming on MSNA as providing relevant afferent information during muscle contraction, which needed to be counteracted via vasoconstriction to maintain homeostasis. Brushing and vibration were less homeostatically relevant stimuli for the muscle contraction and hence had no significant effect. The findings add sensory specificity to our current understanding of homeostatic regulation through somatosensory afferent and sympathetic efferent pathways.
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16
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Hissen SL, Macefield VG, Brown R, Taylor CE. Sympathetic baroreflex sensitivity is inversely related to vascular transduction in men but not women. Am J Physiol Heart Circ Physiol 2019; 317:H1203-H1209. [PMID: 31675259 DOI: 10.1152/ajpheart.00501.2019] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Sympathetic baroreflex sensitivity (BRS) is a measure of how effectively the baroreflex buffers beat-to-beat changes in blood pressure through the modulation of muscle sympathetic nerve activity (MSNA). However, current methods of assessment do not take into account the transduction of sympathetic nerve activity at the level of the vasculature, which is known to vary between individuals. In this study we tested the hypothesis that there is an inverse relationship between sympathetic BRS and vascular transduction. In 38 (18 men) healthy adults, continuous measurements of blood pressure, MSNA and superficial femoral artery diameter and blood flow (Doppler ultrasound) were recorded during 10 min of rest. Spontaneous sympathetic BRS was quantified as the relationship between diastolic pressure and MSNA burst incidence. Vascular transduction was quantified by plotting the changes in leg vascular conductance for 10 cardiac cycles following each burst of MSNA, and taking the nadir. In men, sympathetic BRS was inversely related to vascular transduction (r = -0.49; P = 0.04). However, this relationship was not present in women (r = -0.17; P = 0.47). To conclude, an interaction exists between sympathetic BRS and vascular transduction in healthy men, such that men with high sympathetic BRS have low vascular transduction and vice versa. This may be to ensure that blood pressure is regulated effectively, although further research is needed to explore what mechanisms are involved and examine why this relationship was not apparent in women.NEW & NOTEWORTHY Evidence suggests that compensatory interactions exist between factors involved in cardiovascular control. This study was the first to demonstrate an inverse relationship between sympathetic BRS and beat-to-beat vascular transduction. Those with low sympathetic BRS had high vascular transduction and vice versa. However, this interaction was present in young men but not women.
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Affiliation(s)
- Sarah L Hissen
- School of Science and Health, Western Sydney University, Sydney, Australia
| | - Vaughan G Macefield
- School of Medicine, Western Sydney University, Sydney, Australia.,Neuroscience Research Australia, Sydney, Australia.,Baker Heart and Diabetes Institute, Melbourne, Australia
| | - Rachael Brown
- School of Medicine, Western Sydney University, Sydney, Australia.,Neuroscience Research Australia, Sydney, Australia
| | - Chloe E Taylor
- School of Science and Health, Western Sydney University, Sydney, Australia.,School of Medicine, Western Sydney University, Sydney, Australia
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17
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Wakeham DJ, Lord RN, Talbot JS, Lodge FM, Curry BA, Dawkins TG, Simpson LL, Shave RE, Pugh CJA, Moore JP. Upward resetting of the vascular sympathetic baroreflex in middle-aged male runners. Am J Physiol Heart Circ Physiol 2019; 317:H181-H189. [PMID: 31050557 DOI: 10.1152/ajpheart.00106.2019] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
This study focused on the influence of habitual endurance exercise training (i.e., committed runner or nonrunner) on the regulation of muscle sympathetic nerve activity (MSNA) and arterial pressure in middle-aged (50 to 63 yr, n = 23) and younger (19 to 30 yr; n = 23) normotensive men. Hemodynamic and neurophysiological assessments were performed at rest. Indices of vascular sympathetic baroreflex function were determined from the relationship between spontaneous changes in diastolic blood pressure (DBP) and MSNA. Large vessel arterial stiffness and left ventricular stroke volume also were measured. Paired comparisons were performed within each age category. Mean arterial pressure and basal MSNA bursts/min were not different between age-matched runners and nonrunners. However, MSNA bursts/100 heartbeats, an index of baroreflex regulation of MSNA (vascular sympathetic baroreflex operating point), was higher for middle-aged runners (P = 0.006), whereas this was not different between young runners and nonrunners. The slope of the DBP-MSNA relationship (vascular sympathetic baroreflex gain) was not different between groups in either age category. Aortic pulse wave velocity was lower for runners of both age categories (P < 0.03), although carotid β-stiffness was lower only for middle-aged runners (P = 0.04). For runners of both age categories, stroke volume was larger, whereas heart rate was lower (both P < 0.01). In conclusion, we suggest that neural remodeling and upward setting of the vascular sympathetic baroreflex compensates for cardiovascular adaptations after many years committed to endurance exercise training, presumably to maintain arterial blood pressure stability. NEW & NOTEWORTHY Exercise training reduces muscle sympathetic burst activity in disease; this is often extrapolated to infer a similar effect in health. We demonstrate that burst frequency of middle-aged and younger men committed to endurance training is not different compared with age-matched casual exercisers. Notably, well-trained, middle-aged runners display similar arterial pressure but higher sympathetic burst occurrence than untrained peers. We suggest that homeostatic plasticity and upward setting of the vascular sympathetic baroreflex maintains arterial pressure stability following years of training.
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Affiliation(s)
- Denis J Wakeham
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University , Cardiff , United Kingdom
| | - Rachel N Lord
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University , Cardiff , United Kingdom
| | - Jack S Talbot
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University , Cardiff , United Kingdom
| | - Freya M Lodge
- Cardiff and Vale University Health Board, University Hospital of Wales , Cardiff , United Kingdom
| | - Bryony A Curry
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University , Cardiff , United Kingdom
| | - Tony G Dawkins
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University , Cardiff , United Kingdom
| | - Lydia L Simpson
- Physical Activity for Health and Well-Being Centre, School of Sport, Health and Exercise Sciences, Bangor University , Bangor , United Kingdom
| | - Rob E Shave
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University , Cardiff , United Kingdom.,Centre for Heart, Lung, and Vascular Health, University of British Columbia Okanagan , Kelowna, BC , Canada
| | - Christopher J A Pugh
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University , Cardiff , United Kingdom
| | - Jonathan P Moore
- Physical Activity for Health and Well-Being Centre, School of Sport, Health and Exercise Sciences, Bangor University , Bangor , United Kingdom
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18
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Carter JR, Fonkoue IT, Greenlund IM, Schwartz CE, Mokhlesi B, Smoot CA. Sympathetic neural responsiveness to sleep deprivation in older adults: sex differences. Am J Physiol Heart Circ Physiol 2019; 317:H315-H322. [PMID: 31149842 DOI: 10.1152/ajpheart.00232.2019] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Our laboratory has previously reported that total sleep deprivation (TSD) modifies muscle sympathetic neural activity (MSNA) differently in young men and women. Because postmenopausal women are among the highest risk for hypertension, this study compares MSNA responses with TSD in older men and women. We hypothesized that TSD would alter MSNA in older adults, with greater sympathoexcitation in postmenopausal women. Twenty-seven participants (14 men and 13 women) between the ages of 55 and 75 yr were tested twice, once after 24-h TSD and once after normal sleep (randomized, crossover design). Our primary outcome measure of MSNA (microneurography) was successful across both conditions in 20 participants (10 men and 10 women). Secondary outcome measures included seated blood pressure, heart rate, and fasting plasma testosterone, estradiol, and progesterone. Age (60 ± 1 vs. 61 ± 2 yr) and BMI (27 ± 1 vs. 26 ± 1 kg/m2) were not different between groups. TSD increased systolic blood pressure in both men (124 ± 5 to 130 ± 4 mmHg) and women (107 ± 5 to 116 ± 4 mmHg), but the increases were not different between groups (condition, P = 0.014; condition × sex, P > 0.05). In contrast, TSD elicited divergent MSNA responses in older men and women. Specifically, MSNA burst frequency increased in postmenopausal women (28 ± 3 to 34 ± 3 burst/min), but not older men (38 ± 3 to 35 ± 3 bursts/min; condition × sex, P = 0.032). In conclusion, TSD elicited sympathoexcitation in postmenopausal women but not age-matched men. These findings provide new mechanistic insight into reported links between sleep deprivation and hypertension.NEW & NOTEWORTHY Epidemiological studies report that sleep deprivation is more strongly associated with hypertension in women than in men. In the present study, 24-h total sleep deprivation (TSD) increased blood pressure in postmenopausal women and age-matched men. In contrast, only women demonstrated increases in muscle sympathetic nerve activity after TSD. The sympathoexcitation observed in postmenopausal women suggests a potential contributing mechanism for epidemiological observations and advances our understanding of the complex relations between sleep, sex, and hypertension.
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Affiliation(s)
- Jason R Carter
- Department of Kinesiology and Integrative Physiology, Michigan Technological University, Houghton, Michigan
| | - Ida T Fonkoue
- Department of Kinesiology and Integrative Physiology, Michigan Technological University, Houghton, Michigan
| | - Ian M Greenlund
- Department of Kinesiology and Integrative Physiology, Michigan Technological University, Houghton, Michigan
| | | | - Babak Mokhlesi
- Sleep Research Center, Department of Medicine, University of Chicago, Chicago, Illinois
| | - Carl A Smoot
- Department of Kinesiology and Integrative Physiology, Michigan Technological University, Houghton, Michigan
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19
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Cui J, Drew RC, Muller MD, Blaha C, Gonzalez V, Sinoway LI. Habitual cigarette smoking raises pressor responses to spontaneous bursts of muscle sympathetic nerve activity. Am J Physiol Regul Integr Comp Physiol 2019; 317:R280-R288. [PMID: 31091152 DOI: 10.1152/ajpregu.00293.2018] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Smoking is a risk factor for cardiovascular diseases. Prior reports showed a transient increase in blood pressure (BP) following a spontaneous burst of muscle sympathetic nerve activity (MSNA). We hypothesized that this pressor response would be accentuated in smokers. Using signal-averaging techniques, we examined the BP (Finometer) response to MSNA in 18 otherwise healthy smokers and 42 healthy nonsmokers during resting conditions. The sensitivities of baroreflex control of MSNA and heart rate were also assessed. The mean resting MSNA, heart rate, and mean arterial pressure (MAP) were higher in smokers than nonsmokers. The MAP increase following a burst of MSNA was significantly greater in smokers than nonsmokers (Δ3.4 ± 0.3 vs. Δ1.6 ± 0.1 mmHg, P < 0.001). The baroreflex sensitivity (BRS) of burst incidence, burst area, or total activity was not different between the two groups. However, cardiac BRS was lower in smokers than nonsmokers (14.6 ± 1.7 vs. 24.6 ± 1.5 ms/mmHg, P < 0.001). Moreover, the MAP increase following a burst was negatively correlated with the cardiac BRS. These observations suggest that habitual smoking in otherwise healthy individuals raises the MAP increase following spontaneous MSNA and that the attenuated cardiac BRS in the smokers was a contributing factor. We speculate that the accentuated pressor increase in response to spontaneous MSNA may contribute to the elevated resting BP in the smokers.
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Affiliation(s)
- Jian Cui
- Penn State Heart and Vascular Institute, Penn State Hershey, Milton S. Hershey Medical Center, Hershey, Pennsylvania
| | - Rachel C Drew
- Penn State Heart and Vascular Institute, Penn State Hershey, Milton S. Hershey Medical Center, Hershey, Pennsylvania
| | - Matthew D Muller
- Penn State Heart and Vascular Institute, Penn State Hershey, Milton S. Hershey Medical Center, Hershey, Pennsylvania
| | - Cheryl Blaha
- Penn State Heart and Vascular Institute, Penn State Hershey, Milton S. Hershey Medical Center, Hershey, Pennsylvania
| | - Virginia Gonzalez
- Penn State Heart and Vascular Institute, Penn State Hershey, Milton S. Hershey Medical Center, Hershey, Pennsylvania
| | - Lawrence I Sinoway
- Penn State Heart and Vascular Institute, Penn State Hershey, Milton S. Hershey Medical Center, Hershey, Pennsylvania
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20
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De Maria B, Bari V, Cairo B, Vaini E, Esler M, Lambert E, Baumert M, Cerutti S, Dalla Vecchia L, Porta A. Characterization of the Asymmetry of the Cardiac and Sympathetic Arms of the Baroreflex From Spontaneous Variability During Incremental Head-Up Tilt. Front Physiol 2019; 10:342. [PMID: 31001137 PMCID: PMC6454064 DOI: 10.3389/fphys.2019.00342] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2018] [Accepted: 03/13/2019] [Indexed: 11/13/2022] Open
Abstract
Hysteresis of the baroreflex (BR) is the result of the different BR sensitivity (BRS) when arterial pressure (AP) rises or falls. This phenomenon has been poorly studied and almost exclusively examined by applying pharmacological challenges and static approaches disregarding causal relations. This study inspects the asymmetry of the cardiac BR (cBR) and vascular sympathetic BR (sBR) in physiological closed loop conditions from spontaneous fluctuations of physiological variables, namely heart period (HP) and systolic AP (SAP) leading to the estimation of cardiac BRS (cBRS) and muscle sympathetic nerve activity (MSNA) and diastolic AP (DAP) leading to the estimation of vascular sympathetic BRS (sBRS). The assessment was carried out in 12 young healthy subjects undergoing incremental head-up tilt with table inclination gradually increased from 0 to 60°. Two analytical methods were exploited and compared, namely the sequence (SEQ) and phase-rectified signal averaging (PRSA) methods. SEQ analysis is based on the detection of joint causal schemes representing the HP and MSNA burst rate delayed responses to spontaneous SAP and DAP modifications, respectively. PRSA analysis averages HP and MSNA burst rate patterns after aligning them according to the direction of SAP and DAP changes, respectively. Since cBRSs were similar when SAP went up or down, hysteresis of cBR was not detected. Conversely, hysteresis of sBR was evident with sBRS more negative when DAP was falling than rising. sBR hysteresis was no longer visible during sympathetic activation induced by the orthostatic challenge. These results were obtained via the SEQ method, while the PRSA technique appeared to be less powerful in describing the BR asymmetry due to the strong association between BRS estimates computed over positive and negative AP variations. This study suggests that cBR and sBR provide different information about the BR control, sBR exhibits more relevant non-linear features that are evident even during physiological changes of AP, and the SEQ method can be fruitfully exploited to characterize the BR hysteresis with promising applications to BR branches different from cBR and sBR.
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Affiliation(s)
| | - Vlasta Bari
- Department of Cardiothoracic, Vascular Anesthesia and Intensive Care, IRCCS Policlinico San Donato, Milan, Italy
| | - Beatrice Cairo
- Department of Biomedical Sciences for Health, University of Milan, Milan, Italy
| | - Emanuele Vaini
- Department of Cardiothoracic, Vascular Anesthesia and Intensive Care, IRCCS Policlinico San Donato, Milan, Italy
| | - Murray Esler
- Human Neurotransmitters Laboratory, Baker IDI Heart and Diabetes Institute, Melbourne, VIC, Australia
| | - Elisabeth Lambert
- Human Neurotransmitters Laboratory, Baker IDI Heart and Diabetes Institute, Melbourne, VIC, Australia.,Faculty of Health, Arts and Design, Iverson Health Innovation Research Institute, Swinburne University of Technology, Hawthorn, VIC, Australia
| | - Mathias Baumert
- School of Electrical and Electronic Engineering, The University of Adelaide, Adelaide, SA, Australia
| | - Sergio Cerutti
- Department of Electronics Information and Bioengineering, Politecnico di Milano, Milan, Italy
| | | | - Alberto Porta
- Department of Cardiothoracic, Vascular Anesthesia and Intensive Care, IRCCS Policlinico San Donato, Milan, Italy.,Department of Biomedical Sciences for Health, University of Milan, Milan, Italy
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21
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Crandall CG, Rickards CA, Johnson BD. Impact of environmental stressors on tolerance to hemorrhage in humans. Am J Physiol Regul Integr Comp Physiol 2018; 316:R88-R100. [PMID: 30517019 DOI: 10.1152/ajpregu.00235.2018] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Hemorrhage is a leading cause of death in military and civilian settings, and ~85% of potentially survivable battlefield deaths are hemorrhage-related. Soldiers and civilians are exposed to a number of environmental and physiological conditions that have the potential to alter tolerance to a hemorrhagic insult. The objective of this review is to summarize the known impact of commonly encountered environmental and physiological conditions on tolerance to hemorrhagic insult, primarily in humans. The majority of the studies used lower body negative pressure (LBNP) to simulate a hemorrhagic insult, although some studies employed incremental blood withdrawal. This review addresses, first, the use of LBNP as a model of hemorrhage-induced central hypovolemia and, then, the effects of the following conditions on tolerance to LBNP: passive and exercise-induced heat stress with and without hypohydration/dehydration, exposure to hypothermia, and exposure to altitude/hypoxia. An understanding of the effects of these environmental and physiological conditions on responses to a hemorrhagic challenge, including tolerance, can enable development and implementation of targeted strategies and interventions to reduce the impact of such conditions on tolerance to a hemorrhagic insult and, ultimately, improve survival from blood loss injuries.
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Affiliation(s)
- Craig G Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center , Dallas, Texas
| | - Caroline A Rickards
- Department of Physiology and Anatomy, University of North Texas Health Science Center , Fort Worth, Texas
| | - Blair D Johnson
- Department of Exercise and Nutrition Sciences, University at Buffalo , Buffalo, New York
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22
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El Sayed K, Macefield VG, Hissen SL, Joyner MJ, Taylor CE. Blood pressure reactivity at onset of mental stress determines sympathetic vascular response in young adults. Physiol Rep 2018; 6:e13944. [PMID: 30552755 PMCID: PMC6294720 DOI: 10.14814/phy2.13944] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2018] [Accepted: 11/22/2018] [Indexed: 11/24/2022] Open
Abstract
We have previously shown in young males that the rate of rise in blood pressure (BP) at the onset of mental stress determines whether or not muscle sympathetic nerve activity (MSNA) has a role in driving the pressor response. The aim of this study was to investigate these interactions in young females. BP and MSNA were recorded continuously in 19 females and 21 males during 2-min mental stressors (mental arithmetic and Stroop test). Physical stressor tasks (cold pressor, handgrip exercise, postexercise ischemia) were also performed. During the first minute of mental arithmetic, the rate of rise in mean arterial pressure (MAP) was significantly greater in negative responders (mean decrease in MSNA) compared with positive responders (mean increase in MSNA) in both males (1.9 ± 0.7 vs. 0.7 ± 0.3 mmHg/sec) and females (1.0 ± 0.3 vs. 0.5 ± 0.2 mmHg/sec). For the Stroop test, there was no significant difference in the rate of the rise in BP between positive and negative responders (P > 0.05). However, peak changes in MAP were significantly greater in negative responders compared with positive responders in both males (22 ± 6 vs. 13 ± 3 mmHg) and females (12 ± 2 vs. 6 ± 1 mmHg). Sympathetic baroreflex sensitivity was greater in negative responders and may contribute to the fall in MSNA experienced by these individuals during mental stress. During physical stressors there were consistent increases in BP and MSNA in males and females. The findings suggest that, in both males and females, BP reactivity at the onset of mental stress dictates whether or not there is an increase or decrease in MSNA.
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Affiliation(s)
- Khadigeh El Sayed
- School of MedicineWestern Sydney UniversitySydneyNew South WalesAustralia
| | - Vaughan G. Macefield
- School of MedicineWestern Sydney UniversitySydneyNew South WalesAustralia
- Neuroscience Research AustraliaSydneyNew South WalesAustralia
- Baker Heart and Diabetes InstituteMelbourneVictoriaAustralia
| | - Sarah L Hissen
- School of Science and HealthWestern Sydney UniversitySydneyNew South WalesAustralia
| | | | - Chloe E. Taylor
- School of MedicineWestern Sydney UniversitySydneyNew South WalesAustralia
- School of Science and HealthWestern Sydney UniversitySydneyNew South WalesAustralia
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23
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Hissen SL, Sayed KE, Macefield VG, Brown R, Taylor CE. The Stability and Repeatability of Spontaneous Sympathetic Baroreflex Sensitivity in Healthy Young Individuals. Front Neurosci 2018; 12:403. [PMID: 29962929 PMCID: PMC6010576 DOI: 10.3389/fnins.2018.00403] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2018] [Accepted: 05/25/2018] [Indexed: 01/18/2023] Open
Abstract
Spontaneous sympathetic baroreflex sensitivity (BRS) is a valuable tool for assessing how well the baroreflex buffers beat-to-beat changes in blood pressure. However, there has yet to be a study involving appropriate statistical tests to examine the stability of sympathetic BRS within an experimental session and the repeatability between separate sessions. The aim of this study was to use intra-class correlations, ordinary least products regression, and Bland–Altman analyses to examine the stability and repeatability of spontaneous sympathetic BRS assessment. In addition, the influence of recording duration on values of BRS was assessed. In eighty-four healthy young individuals (49 males, 35 females), continuous measurements of blood pressure, heart rate and muscle sympathetic nerve activity (MSNA) were recorded for 10 min. In a subgroup of 13 participants (11 male, 2 female) the measurements were repeated on a separate day. Sympathetic BRS was quantified using MSNA burst incidence (BRSinc) and total MSNA (BRStotal) for the first 5-min period, the second 5-min period, and a 2-min segment taken from the second 5-min period. Intra-class correlation coefficients indicated moderate stability in sympathetic BRSinc and BRStotal between the first and second 5-min periods in males (BRSincr = 0.63, BRStotalr = 0.78) and females (BRSincr = 0.61, BRStotalr = 0.47) with no proportional bias, but with fixed bias for BRSinc in females. When comparing the first 5-min with the 2-min period (n = 76), the intra-class correlation coefficient indicated poor to moderate repeatability in sympathetic BRSinc and BRStotal for males (BRSincr = -0.01, BRStotalr = 0.70) and females (BRSincr = 0.46, BRStotalr = 0.39). However, Bland–Altman analysis revealed a fixed bias for BRStotal in males and proportional bias for BRStotal in females, with lower BRS values for 5-min recordings. In the subgroup, intra-class correlations indicated moderate repeatability for measures of BRSinc (9 male, 2 female, r = 0.63) and BRStotal (6 male, 2 female, r = 0.68) assessed using 5-min periods recorded on separate days. However, Bland–Altman analysis indicated proportional bias for BRSinc and fixed bias for BRStotal. In conclusion, measures of spontaneous sympathetic BRS are moderately stable and repeatable within and between testing sessions in healthy young adults, provided that the same length of recording is used when making comparisons.
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Affiliation(s)
- Sarah L Hissen
- School of Science and Health, Western Sydney University, Sydney, NSW, Australia
| | - Khadigeh El Sayed
- School of Medicine, Western Sydney University, Sydney, NSW, Australia
| | - Vaughan G Macefield
- School of Medicine, Western Sydney University, Sydney, NSW, Australia.,Baker Heart and Diabetes Institute, Melbourne, VIC, Australia.,Neuroscience Research Australia, Sydney, NSW, Australia
| | - Rachael Brown
- School of Medicine, Western Sydney University, Sydney, NSW, Australia
| | - Chloe E Taylor
- School of Science and Health, Western Sydney University, Sydney, NSW, Australia.,School of Medicine, Western Sydney University, Sydney, NSW, Australia
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24
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Limberg JK, Ott EP, Holbein WW, Baker SE, Curry TB, Nicholson WT, Joyner MJ, Shoemaker JK. Pharmacological assessment of the contribution of the arterial baroreflex to sympathetic discharge patterns in healthy humans. J Neurophysiol 2018; 119:2166-2175. [PMID: 29488839 DOI: 10.1152/jn.00935.2017] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
To study how changes in baroreceptor afferent activity affect patterns of sympathetic neural activation, we manipulated arterial blood pressure with intravenous nitroprusside (NTP) and phenylephrine (PE) and measured action potential (AP) patterns with wavelet-based methodology. We hypothesized that 1) baroreflex unloading (NTP) would increase firing of low-threshold axons and recruitment of latent axons and 2) baroreflex loading (PE) would decrease firing of low-threshold axons. Heart rate (HR, ECG), arterial blood pressure (BP, brachial catheter), and muscle sympathetic nerve activity (MSNA, microneurography of peroneal nerve) were measured at baseline and during steady-state systemic, intravenous NTP (0.5-1.2 µg·kg-1·min-1, n = 13) or PE (0.2-1.0 µg·kg-1·min-1, n = 9) infusion. BP decreased and HR and integrated MSNA increased with NTP ( P < 0.01). AP incidence (326 ± 66 to 579 ± 129 APs/100 heartbeats) and AP content per integrated burst (8 ± 1 to 11 ± 2 APs/burst) increased with NTP ( P < 0.05). The firing probability of low-threshold axons increased with NTP, and recruitment of high-threshold axons was observed (22 ± 3 to 24 ± 3 max cluster number, 9 ± 1 to 11 ± 1 clusters/burst; P < 0.05). BP increased and HR and integrated MSNA decreased with PE ( P < 0.05). PE decreased AP incidence (406 ± 128 to 166 ± 42 APs/100 heartbeats) and resulted in fewer unique clusters (15 ± 2 to 9 ± 1 max cluster number, P < 0.05); components of an integrated burst (APs or clusters per burst) were not altered ( P > 0.05). These data support a hierarchical pattern of sympathetic neural activation during manipulation of baroreceptor afferent activity, with rate coding of active neurons playing the predominant role and recruitment/derecruitment of higher-threshold units occurring with steady-state hypotensive stress. NEW & NOTEWORTHY To study how changes in baroreceptor afferent activity affect patterns of sympathetic neural activation, we manipulated arterial blood pressure with intravenous nitroprusside and phenylephrine and measured sympathetic outflow with wavelet-based methodology. Baroreflex unloading increased sympathetic activity by increasing firing probability of low-threshold axons (rate coding) and recruiting new populations of high-threshold axons. Baroreflex loading decreased sympathetic activity by decreasing the firing probability of larger axons (derecruitment); however, the components of an integrated burst were unaffected.
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Affiliation(s)
- Jacqueline K Limberg
- Department of Nutrition and Exercise Physiology, University of Missouri , Columbia, Missouri.,Department of Anesthesiology and Perioperative Medicine, Mayo Clinic , Rochester, Minnesota
| | - Elizabeth P Ott
- Department of Nutrition and Exercise Physiology, University of Missouri , Columbia, Missouri
| | - Walter W Holbein
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic , Rochester, Minnesota
| | - Sarah E Baker
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic , Rochester, Minnesota
| | - Timothy B Curry
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic , Rochester, Minnesota
| | - Wayne T Nicholson
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic , Rochester, Minnesota
| | - Michael J Joyner
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic , Rochester, Minnesota
| | - J Kevin Shoemaker
- School of Kinesiology, University of Western Ontario , London, Ontario , Canada
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25
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Greaney JL, Kenney WL. Measuring and quantifying skin sympathetic nervous system activity in humans. J Neurophysiol 2017; 118:2181-2193. [PMID: 28701539 DOI: 10.1152/jn.00283.2017] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2017] [Revised: 07/10/2017] [Accepted: 07/10/2017] [Indexed: 01/23/2023] Open
Abstract
Development of the technique of microneurography has substantially increased our understanding of the function of the sympathetic nervous system (SNS) in health and in disease. The ability to directly record signals from peripheral autonomic nerves in conscious humans allows for qualitative and quantitative characterization of SNS responses to specific stimuli and over time. Furthermore, distinct neural outflow to muscle (MSNA) and skin (SSNA) can be delineated. However, there are limitations and caveats to the use of microneurography, measurement criteria, and signal analysis and interpretation. MSNA recordings have a longer history and are considered relatively more straightforward from a measurement and analysis perspective. This brief review provides an overview of the development of the technique as used to measure SSNA. The focus is on the utility of measuring sympathetic activity directed to the skin, the unique issues related to analyzing and quantifying multiunit SSNA, and the challenges related to its interpretation.
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Affiliation(s)
- Jody L Greaney
- Noll Laboratory, Department of Kinesiology, The Pennsylvania State University, University Park, Pennsylvania
| | - W Larry Kenney
- Noll Laboratory, Department of Kinesiology, The Pennsylvania State University, University Park, Pennsylvania
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26
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Effect of passive heat stress and exercise in the heat on arterial stiffness. Eur J Appl Physiol 2017; 117:1679-1687. [DOI: 10.1007/s00421-017-3658-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Accepted: 05/27/2017] [Indexed: 11/26/2022]
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27
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Cui J, Boehmer J, Blaha C, Sinoway LI. Muscle sympathetic nerve activity response to heat stress is attenuated in chronic heart failure patients. Am J Physiol Regul Integr Comp Physiol 2017; 312:R873-R882. [PMID: 28330967 DOI: 10.1152/ajpregu.00355.2016] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2016] [Revised: 03/13/2017] [Accepted: 03/16/2017] [Indexed: 01/26/2023]
Abstract
Heat stress evokes significant increases in muscle sympathetic nerve activity (MSNA) in healthy individuals. The MSNA response to heat stress in chronic heart failure (CHF) is unknown. We hypothesized that the MSNA response to heat stress is attenuated in CHF. Passive whole body heating was applied with water-perfused suits in 13 patients (61 ± 2 yr) with stable class II-III CHF, 12 age-matched (62 ± 2 yr) healthy subjects, and 14 young (24 ± 1 yr) healthy subjects. Mild heating (i.e., increases in skin temperature ΔTsk ~2-4°C, internal temperature ΔTcore <0.3°C) significantly decreased MSNA in CHF patients; however, it did not significantly alter the MSNA in the age-matched and young healthy subjects. Heat stress (i.e., ΔTsk ~4°C and ΔTcore ~0.6°C) raised MSNA in the age-matched (32.9 ± 3.2 to 45.6 ± 4.2 bursts/min; P < 0.001) and young (14.3 ± 1.7 to 26.3 ± 2.4 bursts/min; P < 0.001) controls, but not in CHF (46.2 ± 5.3 to 50.5 ± 5.3 bursts/min; P = 0.06). The MSNA increase by the heat stress in CHF (Δ4.2 ± 2.0 bursts/min) was significantly less than those seen in the age-matched (Δ12.8 ± 1.7 bursts/min, P < 0.05) and young (Δ12.0 ± 2.7 bursts/min, P < 0.05) control groups. These data suggest that the MSNA response to heat stress is attenuated in CHF patients. We speculate that the attenuated MSNA response to heat stress may contribute to impaired cardiovascular adjustments in CHF in a hot environment.
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Affiliation(s)
- Jian Cui
- Penn State Heart and Vascular Institute, Penn State Hershey, Milton S. Hershey Medical Center, Hershey, Pennsylvania
| | - John Boehmer
- Penn State Heart and Vascular Institute, Penn State Hershey, Milton S. Hershey Medical Center, Hershey, Pennsylvania
| | - Cheryl Blaha
- Penn State Heart and Vascular Institute, Penn State Hershey, Milton S. Hershey Medical Center, Hershey, Pennsylvania
| | - Lawrence I Sinoway
- Penn State Heart and Vascular Institute, Penn State Hershey, Milton S. Hershey Medical Center, Hershey, Pennsylvania
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28
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Cui J, Blaha C, Sinoway LI. Whole body heat stress attenuates the pressure response to muscle metaboreceptor stimulation in humans. J Appl Physiol (1985) 2016; 121:1178-1186. [PMID: 27763873 DOI: 10.1152/japplphysiol.00212.2016] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2016] [Revised: 10/04/2016] [Accepted: 10/04/2016] [Indexed: 01/20/2023] Open
Abstract
The effects of whole body heat stress on sympathetic and cardiovascular responses to stimulation of muscle metaboreceptors and mechanoreceptors remains unclear. We examined the muscle sympathetic nerve activity (MSNA), blood pressure, and heart rate in 14 young healthy subjects during fatiguing isometric handgrip exercise, postexercise circulatory occlusion (PECO), and passive muscle stretch during PECO. The protocol was performed under normothermic and whole body heat stress (increase internal temperature ~0.6°C via a heating suit) conditions. Heat stress increased the resting MSNA and heart rate. Heat stress did not alter the mean blood pressure (MAP), heart rate, and MSNA responses (i.e., changes) to fatiguing exercise. During PECO, whole body heat stress accentuated the heart rate response [change (Δ) of 5.8 ± 1.5 to Δ10.0 ± 2.1 beats/min, P = 0.03], did not alter the MSNA response (Δ16.4 ± 2.8 to Δ17.3 ± 3.8 bursts/min, P = 0.74), and lowered the MAP response (Δ20 ± 2 to Δ12 ± 1 mmHg, P < 0.001). Under normothermic conditions, passive stretch during PECO evoked significant increases in MAP and MSNA (both P < 0.001). Of note, heat stress prevented the MAP and MSNA responses to stretch during PECO (both P > 0.05). These data suggest that whole body heat stress attenuates the pressor response due to metaboreceptor stimulation, and the sympathetic nerve response due to mechanoreceptor stimulation.
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Affiliation(s)
- Jian Cui
- Penn State Health, Penn State Heart and Vascular Institute, Hershey, Pennsylvania
| | - Cheryl Blaha
- Penn State Health, Penn State Heart and Vascular Institute, Hershey, Pennsylvania
| | - Lawrence I Sinoway
- Penn State Health, Penn State Heart and Vascular Institute, Hershey, Pennsylvania
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29
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Marchi A, Bari V, De Maria B, Esler M, Lambert E, Baumert M, Porta A. Simultaneous Characterization of Sympathetic and Cardiac Arms of the Baroreflex through Sequence Techniques during Incremental Head-Up Tilt. Front Physiol 2016; 7:438. [PMID: 27746741 PMCID: PMC5041323 DOI: 10.3389/fphys.2016.00438] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2016] [Accepted: 09/14/2016] [Indexed: 11/17/2022] Open
Abstract
We propose a sympathetic baroreflex (sBR) sequence method for characterizing sBR from spontaneous beat-to-beat fluctuations of muscle sympathetic nerve activity (MSNA) and diastolic arterial pressure (DAP). The method exploits a previously defined MSNA variability quantifying the fluctuations of MSNA burst rate. The method is based on the detection of MSNA and DAP sequences characterized by the contemporaneous DAP increase and MSNA decrease or vice versa. The percentage of sBR sequences (SEQ%sBR) was taken as an indication of the degree of sBR solicitation and the average slope of the regression lines in the (DAP, MSNA) plane was taken as sBR sensitivity (sBRSSEQ) and expressed in bursts.s−1.mmHg−1. sBRSSEQ was compared to a more traditional estimate based on the baroreflex threshold analysis (sBRSBTA). An incremental head-up tilt protocol, carried out in 12 young healthy subjects (age: 20–36 yr, median = 22.5 yr, 9 females) sequentially tilted at 0, 20, 30, 40, 60° table inclinations, was utilized to set the sBR sequence method parameters. Traditional sequence analysis was exploited to estimate cardiac baroreflex (cBR) sensitivity (cBRSSEQ) and percentage of cBR sequences (SEQ%cBR). The head-up tilt induced the progressive increase of SEQ%sBR and SEQ%cBR and gradual decrease of both sBRSSEQ and cBRSSEQ, thus suggesting the gradual rise of the sBR and cBR solicitations and the progressive reduction of their effectiveness with the stimulus. sBRSSEQ was significantly associated with sBRSBTA. sBRSSEQ and cBRSSEQ were significantly correlated as well as SEQ%sBR and SEQ%cBR, even though the correlation was not strong, thus suggesting a certain degree of independence between the baroreflex arms. The proposed sBR sequence approach provides a dynamical characterization of the sBR alternative to more traditional static pharmacological and nonpharmacological methods and fully homogenous with the cBR sequence technique.
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Affiliation(s)
- Andrea Marchi
- Department of Electronics Information and Bioengineering, Politecnico di MilanoMilan, Italy; Department of Emergency and Intensive Care, San Gerardo HospitalMonza, Italy
| | - Vlasta Bari
- Department of Biomedical Sciences for Health, University of Milan Milan, Italy
| | - Beatrice De Maria
- Department of Electronics Information and Bioengineering, Politecnico di MilanoMilan, Italy; IRCCS Fondazione Salvatore MaugeriMilan, Italy
| | - Murray Esler
- Human Neurotransmitter Laboratory, Baker IDI Heart and Diabetes Institute Melbourne, VIC, Australia
| | - Elisabeth Lambert
- Human Neurotransmitter Laboratory, Baker IDI Heart and Diabetes Institute Melbourne, VIC, Australia
| | - Mathias Baumert
- School of Electrical and Electronic Engineering, University of Adelaide Adelaide, SA, Australia
| | - Alberto Porta
- Department of Biomedical Sciences for Health, University of MilanMilan, Italy; Department of Cardiothoracic, Vascular Anesthesia and Intensive Care, IRCCS Policlinico San DonatoMilan, Italy
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30
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Eckberg DL, Diedrich A, Cooke WH, Biaggioni I, Buckey JC, Pawelczyk JA, Ertl AC, Cox JF, Kuusela TA, Tahvanainen KUO, Mano T, Iwase S, Baisch FJ, Levine BD, Adams-Huet B, Robertson D, Blomqvist CG. Respiratory modulation of human autonomic function: long-term neuroplasticity in space. J Physiol 2016; 594:5629-46. [PMID: 27029027 DOI: 10.1113/jp271656] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2015] [Accepted: 03/14/2016] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS We studied healthy astronauts before, during and after the Neurolab Space Shuttle mission with controlled breathing and apnoea, to identify autonomic changes that might contribute to postflight orthostatic intolerance. Measurements included the electrocardiogram, finger photoplethysmographic arterial pressure, respiratory carbon dioxide levels, tidal volume and peroneal nerve muscle sympathetic activity. Arterial pressure fell and then rose in space, and drifted back to preflight levels after return to Earth. Vagal metrics changed in opposite directions: vagal baroreflex gain and two indices of vagal fluctuations rose and then fell in space, and descended to preflight levels upon return to Earth. Sympathetic burst frequencies (but not areas) were greater than preflight in space and on landing day, and astronauts' abilities to modulate both burst areas and frequencies during apnoea were sharply diminished. Spaceflight triggers long-term neuroplastic changes reflected by reciptocal sympathetic and vagal motoneurone responsiveness to breathing changes. ABSTRACT We studied six healthy astronauts five times, on Earth, in space on the first and 12th or 13th day of the 16 day Neurolab Space Shuttle mission, on landing day, and 5-6 days later. Astronauts followed a fixed protocol comprising controlled and random frequency breathing and apnoea, conceived to perturb their autonomic function and identify changes, if any, provoked by microgravity exposure. We recorded the electrocardiogram, finger photoplethysmographic arterial pressure, tidal carbon dioxide concentrations and volumes, and peroneal nerve muscle sympathetic activity on Earth (in the supine position) and in space. (Sympathetic nerve recordings were made during three sessions: preflight, late mission and landing day.) Arterial pressure changed systematically from preflight levels: pressure fell during early microgravity exposure, rose as microgravity exposure continued, and drifted back to preflight levels after return to Earth. Vagal metrics changed in opposite directions: vagal baroreflex gain and two indices of vagal fluctuations (root mean square of successive normal R-R intervals; and proportion of successive normal R-R intervals greater than 50 ms, divided by the total number of normal R-R intervals) rose significantly during early microgravity exposure, fell as microgravity exposure continued, and descended to preflight levels upon return to Earth. Sympathetic mechanisms also changed. Burst frequencies (but not areas) during fixed frequency breathing were greater than preflight in space and on landing day, but their control during apnoea was sharply altered: astronauts increased their burst frequencies from already high levels, but they could not modulate either burst areas or frequencies appropriately. Space travel provokes long-lasting sympathetic and vagal neuroplastic changes in healthy humans.
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Affiliation(s)
- Dwain L Eckberg
- Departments of Medicine and Physiology, Hunter Holmes McGuire Department of Veterans Affairs Medical Center, Virginia Commonwealth University School of Medicine, Richmond, VA, USA.
| | - André Diedrich
- Department of Medicine, Division of Clinical Pharmacology, Autonomic Dysfunction Center, Vanderbilt University School of Medicine, Vanderbilt University, Nashville, TN, USA
| | - William H Cooke
- Department of Kinesiology, Health, and Nutrition, University of Texas at San Antonio, San Antonio, TX, USA
| | - Italo Biaggioni
- Department of Medicine, Division of Clinical Pharmacology, Autonomic Dysfunction Center, Vanderbilt University School of Medicine, Vanderbilt University, Nashville, TN, USA
| | - Jay C Buckey
- Dartmouth Hitchcock Medical Centre, Lebanon, NH, USA
| | - James A Pawelczyk
- Department of Physiology, Pennsylvania State University, University Park and Hershey, PA, USA
| | - Andrew C Ertl
- Department of Medicine, Division of Clinical Pharmacology, Autonomic Dysfunction Center, Vanderbilt University School of Medicine, Vanderbilt University, Nashville, TN, USA
| | - James F Cox
- Departments of Medicine and Physiology, Hunter Holmes McGuire Department of Veterans Affairs Medical Center, Virginia Commonwealth University School of Medicine, Richmond, VA, USA
| | - Tom A Kuusela
- Department of Physics, Turku University, Turku, Finland
| | - Kari U O Tahvanainen
- Department of Clinical Physiology and Nuclear Medicine, South Karelia Central Hospital, Lappeenranta, Finland
| | - Tadaaki Mano
- Gifu University of Medical Science, 795-1 Nagamine Ichihiraga, Seki, Gifu, 501-3892, Japan
| | - Satoshi Iwase
- Department of Physiology, Aichi Medical University, Aichi, Japan
| | | | - Benjamin D Levine
- Department of Medicine, University of Texas Southwestern Medical Centre at Dallas, Dallas, TX, USA.,Institute for Exercise and Environmental Medicine, Texas Health Presbyterian, Hospital, Dallas, TX, USA
| | | | - David Robertson
- Department of Medicine, Division of Clinical Pharmacology, Autonomic Dysfunction Center, Vanderbilt University School of Medicine, Vanderbilt University, Nashville, TN, USA
| | - C Gunnar Blomqvist
- Department of Medicine, University of Texas Southwestern Medical Centre at Dallas, Dallas, TX, USA
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31
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Kim HG, Kim JK, Kim KA, Nho H, Lee S, Chang MJ, Choi HM. The role of metaboreceptor on exercise in hyperthermic environment with college basketball players. SPRINGERPLUS 2016; 5:365. [PMID: 27066375 PMCID: PMC4805669 DOI: 10.1186/s40064-016-1989-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/14/2015] [Accepted: 03/10/2016] [Indexed: 11/10/2022]
Abstract
The objective of this study is to review physiological differences of college basketball players cardiovascular responses and group IV metaboreceptor interactions appearing post muscular ischemia exercise (PEMI) caused by a static handgrip exercise (SHE). The subjects were placed in a temperature and moisture stabilized indoor environment for 2 h in order to measure blood pressure. For the SHE, maximal voluntary contraction of arms with a relative strength of 50 % of the maximum muscular strength was put into isometric training for 2 min. After completing the exercises, cuffs worn on the arms of the subjects were pressurized up to 200 mmHg by applying PEMI to block the artery and vein. In this way, the cardiovascular responses created by SHE and PEMI were measured. Blood samples of subjects were collected from the vein of each upper arm before SHE and after PEMI to measure the metabolite hormone and catecholamine in the blood. Results from the measurements showed a significant decrease of blood pressure under high temperature environments compared to normal temperature environments. With respect to PEMI, increases in blood pressure under the high temperature environment were significantly lower compared to the normal temperature environment. In conclusion, this study revealed that college basketball players with good physical strength had higher sensitivities of arterial baroreceptor. However, blood pressure was not increased accordingly because the increase of cutaneous vasoconstriction due to stimuli of the metaboreceptor under a high temperature environment could not be compensated by arterial baroreflex due to the increase of total vascular conductance.
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Affiliation(s)
- Hyun-Gook Kim
- Graduate School of Physical Education, KyungHee University, Seocheon-dong Giheung-gu, Yongin-si, Gyeonggi-do 446-701 Korea
| | - Jong-Kyung Kim
- Graduate School of Physical Education, KyungHee University, Seocheon-dong Giheung-gu, Yongin-si, Gyeonggi-do 446-701 Korea
| | - Kyung-Ae Kim
- Graduate School of Physical Education, KyungHee University, Seocheon-dong Giheung-gu, Yongin-si, Gyeonggi-do 446-701 Korea
| | - Hosung Nho
- Graduate School of Physical Education, KyungHee University, Seocheon-dong Giheung-gu, Yongin-si, Gyeonggi-do 446-701 Korea
| | - Sungchul Lee
- Graduate School of Physical Education, KyungHee University, Seocheon-dong Giheung-gu, Yongin-si, Gyeonggi-do 446-701 Korea
| | - Myoung-Jae Chang
- Graduate School of Physical Education, KyungHee University, Seocheon-dong Giheung-gu, Yongin-si, Gyeonggi-do 446-701 Korea
| | - Hyun-Min Choi
- Graduate School of Physical Education, KyungHee University, Seocheon-dong Giheung-gu, Yongin-si, Gyeonggi-do 446-701 Korea
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32
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Bain AR, Nybo L, Ainslie PN. Cerebral Vascular Control and Metabolism in Heat Stress. Compr Physiol 2016; 5:1345-80. [PMID: 26140721 DOI: 10.1002/cphy.c140066] [Citation(s) in RCA: 61] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
This review provides an in-depth update on the impact of heat stress on cerebrovascular functioning. The regulation of cerebral temperature, blood flow, and metabolism are discussed. We further provide an overview of vascular permeability, the neurocognitive changes, and the key clinical implications and pathologies known to confound cerebral functioning during hyperthermia. A reduction in cerebral blood flow (CBF), derived primarily from a respiratory-induced alkalosis, underscores the cerebrovascular changes to hyperthermia. Arterial pressures may also become compromised because of reduced peripheral resistance secondary to skin vasodilatation. Therefore, when hyperthermia is combined with conditions that increase cardiovascular strain, for example, orthostasis or dehydration, the inability to preserve cerebral perfusion pressure further reduces CBF. A reduced cerebral perfusion pressure is in turn the primary mechanism for impaired tolerance to orthostatic challenges. Any reduction in CBF attenuates the brain's convective heat loss, while the hyperthermic-induced increase in metabolic rate increases the cerebral heat gain. This paradoxical uncoupling of CBF to metabolism increases brain temperature, and potentiates a condition whereby cerebral oxygenation may be compromised. With levels of experimentally viable passive hyperthermia (up to 39.5-40.0 °C core temperature), the associated reduction in CBF (∼ 30%) and increase in cerebral metabolic demand (∼ 10%) is likely compensated by increases in cerebral oxygen extraction. However, severe increases in whole-body and brain temperature may increase blood-brain barrier permeability, potentially leading to cerebral vasogenic edema. The cerebrovascular challenges associated with hyperthermia are of paramount importance for populations with compromised thermoregulatory control--for example, spinal cord injury, elderly, and those with preexisting cardiovascular diseases.
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Affiliation(s)
- Anthony R Bain
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Kelowna, Canada
| | - Lars Nybo
- Department of Nutrition, Exercise and Sport Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Philip N Ainslie
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Kelowna, Canada
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Schlader ZJ, Wilson TE, Crandall CG. Mechanisms of orthostatic intolerance during heat stress. Auton Neurosci 2015; 196:37-46. [PMID: 26723547 DOI: 10.1016/j.autneu.2015.12.005] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2015] [Revised: 11/30/2015] [Accepted: 12/14/2015] [Indexed: 01/04/2023]
Abstract
Heat stress profoundly and unanimously reduces orthostatic tolerance. This review aims to provide an overview of the numerous and multifactorial mechanisms by which this occurs in humans. Potential causal factors include changes in arterial and venous vascular resistance and blood distribution, and the modulation of cardiac output, all of which contribute to the inability to maintain cerebral perfusion during heat and orthostatic stress. A number of countermeasures have been established to improve orthostatic tolerance during heat stress, which alleviate heat stress induced central hypovolemia (e.g., volume expansion) and/or increase peripheral vascular resistance (e.g., skin cooling). Unfortunately, these countermeasures can often be cumbersome to use with populations prone to syncopal episodes. Identifying the mechanisms of inter-individual differences in orthostatic intolerance during heat stress has proven elusive, but could provide greater insights into the development of novel and personalized countermeasures for maintaining or improving orthostatic tolerance during heat stress. This development will be especially impactful in occuational settings and clinical situations that present with orthostatic intolerance and/or central hypovolemia. Such investigations should be considered of vital importance given the impending increased incidence of heat events, and associated cardiovascular challenges that are predicted to occur with the ensuing changes in climate.
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Affiliation(s)
- Zachary J Schlader
- Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, NY, United States.
| | - Thad E Wilson
- Marian University College of Osteopathic Medicine, Indianapolis, IN, United States
| | - Craig G Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, TX, United States
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Greaney JL, Kenney WL, Alexander LM. Sympathetic regulation during thermal stress in human aging and disease. Auton Neurosci 2015; 196:81-90. [PMID: 26627337 DOI: 10.1016/j.autneu.2015.11.002] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2015] [Revised: 11/18/2015] [Accepted: 11/19/2015] [Indexed: 02/07/2023]
Abstract
Humans control their core temperature within a narrow range via precise adjustments of the autonomic nervous system. In response to changing core and/or skin temperature, several critical thermoregulatory reflex effector responses are initiated and include shivering, sweating, and changes in cutaneous blood flow. Cutaneous vasomotor adjustments, mediated by modulations in sympathetic nerve activity (SNA), aid in the maintenance of thermal homeostasis during cold and heat stress since (1) they serve as the first line of defense of body temperature and are initiated before other thermoregulatory effectors, and (2) they are on the efferent arm of non-thermoregulatory reflex systems, aiding in the maintenance of blood pressure and organ perfusion. This review article highlights the sympathetic responses of humans to thermal stress, with a specific focus on primary aging as well as impairments that occur in both heart disease and type 2 diabetes mellitus. Age- and pathology-related changes in efferent muscle and skin SNA during cold and heat stress, measured directly in humans using microneurography, are discussed.
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Affiliation(s)
- Jody L Greaney
- Department of Kinesiology, Noll Laboratory, The Pennsylvania State University, University Park, PA 16802, United States.
| | - W Larry Kenney
- Department of Kinesiology, Noll Laboratory, The Pennsylvania State University, University Park, PA 16802, United States
| | - Lacy M Alexander
- Department of Kinesiology, Noll Laboratory, The Pennsylvania State University, University Park, PA 16802, United States
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Taylor CE, Witter T, El Sayed K, Hissen SL, Johnson AW, Macefield VG. Relationship between spontaneous sympathetic baroreflex sensitivity and cardiac baroreflex sensitivity in healthy young individuals. Physiol Rep 2015; 3:3/11/e12536. [PMID: 26564059 PMCID: PMC4673619 DOI: 10.14814/phy2.12536] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Low baroreflex sensitivity (BRS) is associated with elevated cardiovascular risk. However, the evidence is based primarily on measurements of cardiac BRS. It cannot be assumed that cardiac or sympathetic BRS alone represent a true reflection of baroreflex control of blood pressure. The aim of this study was to examine the relationship between spontaneous sympathetic and cardiac BRS in healthy, young individuals. Continuous measurements of blood pressure, heart rate, and muscle sympathetic nerve activity (MSNA) were made under resting conditions in 50 healthy individuals (18–28 years). Sympathetic BRS was quantified by plotting MSNA burst incidence against diastolic pressure (sympathetic BRSinc), and by plotting total MSNA against diastolic pressure (sympathetic BRStotal). Cardiac BRS was quantified by plotting R-R interval against systolic pressure using the sequence method. Significant sympathetic BRSinc and cardiac BRS slopes were obtained for 42 participants. A significant positive correlation was found between sympathetic BRSinc and cardiac BRS (r = 0.31, P = 0.049). Among this group, significant sympathetic baroreflex slopes were obtained for 39 participants when plotting total MSNA against diastolic pressure. In this subset, a significant positive correlation was observed between sympathetic BRStotal and cardiac BRS (r = 0.40, P = 0.012). When males and females were assessed separately, these modest relationships only remained significant in females. Analysis by gender revealed correlations in the females between sympathetic BRSinc and cardiac BRS (r = 0.49, P = 0.062), and between sympathetic BRStotal and cardiac BRS (r = 0.57, P = 0.025). These findings suggest that gender interactions exist in baroreflex control of blood pressure, and that cardiac BRS is not appropriate for estimating overall baroreflex function in healthy, young populations. This relationship warrants investigation in aging and clinical populations.
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Affiliation(s)
- Chloe E Taylor
- School of Science and Health, University of Western Sydney, Sydney, Australia
| | - Trevor Witter
- Centre for Translational Physiology, University of Otago, Wellington, New Zealand
| | | | - Sarah L Hissen
- School of Science and Health, University of Western Sydney, Sydney, Australia
| | - Aaron W Johnson
- School of Medicine, University of Western Sydney, Sydney, Australia
| | - Vaughan G Macefield
- School of Medicine, University of Western Sydney, Sydney, Australia Neuroscience Research Australia, Sydney, Australia
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Hissen SL, Macefield VG, Brown R, Witter T, Taylor CE. Baroreflex modulation of muscle sympathetic nerve activity at rest does not differ between morning and afternoon. Front Neurosci 2015; 9:312. [PMID: 26388723 PMCID: PMC4557114 DOI: 10.3389/fnins.2015.00312] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2015] [Accepted: 08/19/2015] [Indexed: 11/22/2022] Open
Abstract
The incidence of cardiovascular events is significantly higher in the morning than other times of day. This has previously been associated with poor blood pressure control via the cardiac baroreflex. However, it is not known whether diurnal variation exists in vascular sympathetic baroreflex function, in which blood pressure is regulated via muscle sympathetic nerve activity (MSNA). The aim of this study was to compare vascular sympathetic baroreflex sensitivity (BRS) in the same participants between the morning and afternoon. In 10 participants (mean age 22 ± 2.9 years), continuous measurements of blood pressure, heart rate and MSNA were made during 10 min of rest in the morning (between 0900 and 1000 h) and afternoon (between 1400 and 1500 h). Spontaneous vascular sympathetic BRS was quantified by plotting MSNA burst incidence against diastolic pressure (vascular sympathetic BRSinc), and by plotting total MSNA against diastolic pressure (vascular sympathetic BRStotal). Significant vascular sympathetic BRSinc and vascular sympathetic BRStotal slopes were obtained for 10 participants at both times of day. There was no significant difference in vascular sympathetic BRSinc between morning (-2.2 ± 0.6% bursts/mmHg) and afternoon (-2.5 ± 0.2% bursts/mmHg; P = 0.68) sessions. Similarly, vascular sympathetic BRStotal did not differ significantly between the morning (-3.0±0.5 AU/beat/mmHg) and afternoon (-2.9 ± 0.4 AU/beat/mmHg; P = 0.89). It is concluded that in healthy, young individuals baroreflex modulation of MSNA at rest does not differ between the morning and afternoon. The results indicate that recording MSNA at different times of the day is a valid means of assessing sympathetic function.
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Affiliation(s)
- Sarah L. Hissen
- School of Science and Health, University of Western SydneySydney, NSW, Australia
| | - Vaughan G. Macefield
- School of Medicine, University of Western SydneySydney, NSW, Australia
- Neuroscience Research AustraliaSydney, NSW, Australia
| | - Rachael Brown
- School of Medicine, University of Western SydneySydney, NSW, Australia
| | - Trevor Witter
- Centre for Translational Physiology, University of OtagoWellington, New Zealand
| | - Chloe E. Taylor
- School of Science and Health, University of Western SydneySydney, NSW, Australia
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Abstract
Heat stress increases human morbidity and mortality compared to normothermic conditions. Many occupations, disease states, as well as stages of life are especially vulnerable to the stress imposed on the cardiovascular system during exposure to hot ambient conditions. This review focuses on the cardiovascular responses to heat stress that are necessary for heat dissipation. To accomplish this regulatory feat requires complex autonomic nervous system control of the heart and various vascular beds. For example, during heat stress cardiac output increases up to twofold, by increases in heart rate and an active maintenance of stroke volume via increases in inotropy in the presence of decreases in cardiac preload. Baroreflexes retain the ability to regulate blood pressure in many, but not all, heat stress conditions. Central hypovolemia is another cardiovascular challenge brought about by heat stress, which if added to a subsequent central volumetric stress, such as hemorrhage, can be problematic and potentially dangerous, as syncope and cardiovascular collapse may ensue. These combined stresses can compromise blood flow and oxygenation to important tissues such as the brain. It is notable that this compromised condition can occur at cardiac outputs that are adequate during normothermic conditions but are inadequate in heat because of the increased systemic vascular conductance associated with cutaneous vasodilation. Understanding the mechanisms within this complex regulatory system will allow for the development of treatment recommendations and countermeasures to reduce risks during the ever-increasing frequency of severe heat events that are predicted to occur.
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Affiliation(s)
- Craig G Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas Marian University College of Osteopathic Medicine, Indianapolis, Indiana
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Barbic F, Heusser K, Marchi A, Zamunér AR, Gauger P, Tank J, Jordan J, Diedrich A, Robertson D, Dipaola F, Achenza S, Porta A, Furlan R. Cardiovascular parameters and neural sympathetic discharge variability before orthostatic syncope: role of sympathetic baroreflex control to the vessels. Physiol Meas 2015; 36:633-41. [PMID: 25798786 DOI: 10.1088/0967-3334/36/4/633] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
We tested the hypothesis that altered sympathetic baroreceptor control to the vessels (svBRS) and disrupted coupling between blood pressure (BP) fluctuations and muscle sympathetic activity (MSNA) discharge pattern in the low frequency band (LF, around 0.1 Hz) precede vasovagal syncope. Seven healthy males underwent ECG, BP, respiratory, and MSNA recordings at baseline (REST) and during a 15 min 80° head-up tilt, followed by a -10 mmHg step wise increase of lower body negative pressure up to presyncope. Spectral and coherence analyses of systolic arterial pressure (SAP) and MSNA variability provided the indexes of vascular sympathetic modulation, LFSAP, and of the linear coupling between MSNA and SAP in the low frequency band (around 0.1 Hz), K(2)MSNA-SAP(LF). svBRS was assessed as the slope of the regression line between MSNA and diastolic arterial pressure (DAP). Data were analyzed at REST, during asymptomatic and presyncope periods of tilt. svBRS declined during presyncope period compared to REST and asymptomatic tilt. The presyncope period was characterized by a decrease of RR interval, LFMSNA, LFSAP, and K(2)MSNA-SAP(LF) values compared to the asymptomatic one, whereas MSNA burst rate was unchanged. The reduction of svBRS producing an altered coupling between MSNA and SAP variability at 0.1 Hz, may provoke circulatory changes leading to presyncope.
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Affiliation(s)
- Franca Barbic
- Internal Medicine, Humanitas Clinical and Research Center, Rozzano, BIOMETRA Department, University of Milan, Italy
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Porta A, Marchi A, Bari V, Heusser K, Tank J, Jordan J, Barbic F, Furlan R. Conditional symbolic analysis detects nonlinear influences of respiration on cardiovascular control in humans. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2015; 373:rsta.2014.0096. [PMID: 25548269 PMCID: PMC4281867 DOI: 10.1098/rsta.2014.0096] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
We propose a symbolic analysis framework for the quantitative characterization of complex dynamical systems. It allows the description of the time course of a single variable, the assessment of joint interactions and an analysis triggered by a conditioning input. The framework was applied to spontaneous variability of heart period (HP), systolic arterial pressure (SAP) and integrated muscle sympathetic nerve activity (MSNA) with the aim of characterizing cardiovascular control and nonlinear influences of respiration at rest in supine position, during orthostatic challenge induced by 80° head-up tilt (TILT) and about 3 min before evoked pre-syncope signs (PRESY). The approach detected (i) the exaggerated sympathetic modulation and vagal withdrawal from HP variability and the increased presence of fast MSNA variability components during PRESY compared with TILT; (ii) the increase of the SAP-HP coordination occurring at slow temporal scales and a decrease of that occurring at faster time scales during PRESY compared with TILT; (iii) the reduction of the coordination between fast MSNA and SAP patterns during TILT and PRESY; (iv) the nonlinear influences of respiration leading to an increased likelihood to observe the abovementioned findings during expiration compared with inspiration one. The framework provided simple, quantitative indexes able to distinguish experimental conditions characterized by different states of the autonomic nervous system and to detect the early signs of a life threatening situation such as postural syncope.
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Affiliation(s)
- Alberto Porta
- Department of Biomedical Sciences for Health, University of Milan, Milan, Italy IRCCS Galeazzi Orthopedic Institute, Milan, Italy
| | - Andrea Marchi
- Department of Anesthesia and Intensive Care Unit, Rozzano, Milan, Italy
| | - Vlasta Bari
- Department of Cardiothoracic-Vascular Anesthesia and Intensive Care, IRCCS Policlinico San Donato, Milan, Italy
| | - Karsten Heusser
- Institut für Klinische Pharmakologie, Medizinische Hochschule Hannover, Hannover, Germany
| | - Jens Tank
- Institut für Klinische Pharmakologie, Medizinische Hochschule Hannover, Hannover, Germany
| | - Jens Jordan
- Institut für Klinische Pharmakologie, Medizinische Hochschule Hannover, Hannover, Germany
| | - Franca Barbic
- Department of Internal Medicine, Humanitas Clinical and Research Center, Rozzano, Milan, Italy
| | - Raffaello Furlan
- Department of Medical Biotechnology and Translational Medicine, University of Milan, Milan, Italy Department of Internal Medicine, Humanitas Clinical and Research Center, Rozzano, Milan, Italy
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Abstract
Clinical reports have suggested that patients with heart diseases may be particularly vulnerable to heat injury. This review examines the effects of heat stress on cardiovascular and autonomic functions in patients with chronic heart failure (CHF). Laboratory investigations have shown that cutaneous vasodilator responses to heating are impaired in patients, whereas activation of skin sympathetic nerve activation is not attenuated in CHF as compared to controls. Attenuated cutaneous vasodilation may increase the risk of a heat related illness when CHF subjects are exposed to hyperthermic conditions.
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Taylor CE, Willie CK, Ainslie PN, Tzeng YC. Assessment of human baroreflex function using carotid ultrasonography: what have we learnt? Acta Physiol (Oxf) 2014; 211:297-313. [PMID: 24739079 DOI: 10.1111/apha.12302] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2014] [Accepted: 04/09/2014] [Indexed: 12/13/2022]
Abstract
The arterial baroreflex is critical to both short- and long-term regulation of blood pressure. However, human baroreflex research has been largely limited to the association between blood pressure and cardiac period (or heart rate) or indices of vascular sympathetic function. Over the past decade, emerging techniques based on carotid ultrasound imaging have allowed new means of understanding and measuring the baroreflex. In this review, we describe the assessment of the mechanical and neural components of the baroreflex through the use of carotid ultrasound imaging. The mechanical component refers to the change in carotid artery diameter in response to changes in arterial pressure, and the neural component refers to the change in R-R interval (cardiac baroreflex) or muscle sympathetic nerve activity (sympathetic baroreflex) in response to this barosensory vessel stretch. The key analytical concepts and techniques are discussed, with a focus on the assessment of baroreflex sensitivity via the modified Oxford method. We illustrate how the application of carotid ultrasound imaging has contributed to a greater understanding of baroreflex physiology in humans, covering topics such as ageing and diurnal variation, and physiological challenges including exercise, postural changes and mental stress.
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Affiliation(s)
- C. E. Taylor
- School of Science and Health; University of Western Sydney; Sydney NSW Australia
| | - C. K. Willie
- School of Health and Exercise Sciences; Centre for Heart Lung and Vascular Health; University of British Columbia Okanagan; Kelowna BC Canada
| | - P. N. Ainslie
- School of Health and Exercise Sciences; Centre for Heart Lung and Vascular Health; University of British Columbia Okanagan; Kelowna BC Canada
| | - Y.-C. Tzeng
- Cardiovascular Systems Laboratory; Centre for Translational Physiology; University of Otago; Wellington New Zealand
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Cerebral vasoreactivity: impact of heat stress and lower body negative pressure. Clin Auton Res 2014; 24:135-41. [PMID: 24706257 DOI: 10.1007/s10286-014-0241-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2013] [Accepted: 03/20/2014] [Indexed: 10/25/2022]
Abstract
OBJECTIVE Cerebrovascular reactivity represents the capacity of the cerebral circulation to raise blood flow in the face of increased demand, and may be reduced in some clinical and physiological conditions. We tested the hypothesis that the hypercapnia-induced increase in cerebral perfusion is attenuated during heat stress (HS) compared to normothermia (NT), and this response is further reduced during the combined challenges of HS and lower body negative pressure (LBNP). METHODS Ten healthy individuals (9 men) undertook rebreathing-induced hypercapnia during NT, HS, and HS + 20 mmHg LBNP (HSLBNP), while cerebral perfusion was indexed from middle cerebral artery blood velocity (MCA V mean). Cerebrovascular responses were calculated from the slope of the change in MCA V mean and cerebral vascular conductance (CVCi) relative to the increase in end tidal carbon dioxide ([Formula: see text]) during rebreathing. RESULTS MCA V mean was similar in HS (55 ± 19 cm s(-1)) and HSLBNP (52 ± 16 cm s(-1)), and both values were reduced relative to NT (66 ± 20 cm s(-1)), yet the rise in MCA V mean per Torr increase in [Formula: see text] during rebreathing was similar in each condition (NT: 2.5 ± 0.6 cm s(-1) Torr(-1); HS: 2.4 ± 0.8 cm s(-1) Torr(-1); HSLBNP: 2.1 ± 1.1 cm s(-1) Torr(-1)). Likewise, the rate of increase in CVCi was not different between conditions (NT: 2.1 ± 0.65 cm s(-1 )mmHg(-1)100 Torr(-1); HS: 2.4 ± 0.8 cm s(-1) mmHg(-1) 100 Torr(-1); HSLBNP: 2.0 ± 1.0 cm s(-1) mmHg(-1) 100 Torr(-1)). INTERPRETATIONS These data indicate that cerebrovascular reactivity is not compromised during whole-body heat stress alone or when combined with mild orthostatic stress relative to normothermic conditions.
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Bain AR, Morrison SA, Ainslie PN. Cerebral oxygenation and hyperthermia. Front Physiol 2014; 5:92. [PMID: 24624095 PMCID: PMC3941303 DOI: 10.3389/fphys.2014.00092] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2014] [Accepted: 02/18/2014] [Indexed: 12/04/2022] Open
Abstract
Hyperthermia is associated with marked reductions in cerebral blood flow (CBF). Increased distribution of cardiac output to the periphery, increases in alveolar ventilation and resultant hypocapnia each contribute to the fall in CBF during passive hyperthermia; however, their relative contribution remains a point of contention, and probably depends on the experimental condition (e.g., posture and degree of hyperthermia). The hyperthermia-induced hyperventilatory response reduces arterial CO2 pressure (PaCO2) causing cerebral vasoconstriction and subsequent reductions in flow. During supine passive hyperthermia, the majority of recent data indicate that reductions in PaCO2 may be the primary, if not sole, culprit for reduced CBF. On the other hand, during more dynamic conditions (e.g., hemorrhage or orthostatic challenges), an inability to appropriately decrease peripheral vascular conductance presents a condition whereby adequate cerebral perfusion pressure may be compromised secondary to reductions in systemic blood pressure. Although studies have reported maintenance of pre-frontal cortex oxygenation (assessed by near-infrared spectroscopy) during exercise and severe heat stress, the influence of cutaneous blood flow is known to contaminate this measure. This review discusses the governing mechanisms associated with changes in CBF and oxygenation during moderate to severe (i.e., 1.0°C to 2.0°C increase in body core temperature) levels of hyperthermia. Future research directions are provided.
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Affiliation(s)
- Anthony R Bain
- Centre for Heart Lung and Vascular Health, University of British Columbia Okanagan, BC, Canada
| | - Shawnda A Morrison
- Faculty of Professional Studies, Kinesiology, Acadia University Wolfville, NS, Canada
| | - Philip N Ainslie
- Centre for Heart Lung and Vascular Health, University of British Columbia Okanagan, BC, Canada
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Qian S, Jiang Q, Liu K, Li B, Li M, Li L, Yang X, Yang Z, Sun G. Effects of short-term environmental hyperthermia on patterns of cerebral blood flow. Physiol Behav 2014; 128:99-107. [PMID: 24530482 DOI: 10.1016/j.physbeh.2014.01.028] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2013] [Revised: 01/11/2014] [Accepted: 01/26/2014] [Indexed: 10/25/2022]
Abstract
Environmental hyperthermia is a very common risk factor for many occupations, however, its potential influences on cerebral circulation remain obscure. In this study, 20 participants underwent two simulated environmental thermal conditions (50 °C/25 °C, 1 h), and their cerebral blood flows (CBFs) were quantified using a pseudo-continuous arterial spin labeling (ASL) MR imaging. During the experiment, the physiological parameters, including rectal temperature, arterial blood pressure and weight loss, heart rate and respiration rate, were recorded, and a visual analog scale (VAS) test was performed during both conditions to evaluate the psychological state including vigilance, anxiety, vigor, confidence, anger, nervousness, drowsiness, and loquacity. After scanning, a highly-demanding attentional task--the psychomotor vigilance test (PVT) was performed for behavioral performance evaluation. Compared with that during normothermic condition, the global CBF (gCBF) during hyperthermic condition showed a tendency of decrease, but no significant differences. Regional CBFs (rCBFs) were significantly altered mainly in the prefrontal cortex, somatosensory areas and limbic system. Physiological detection revealed significantly decreased diastolic pressure and systolic pressure and accelerated respiration rate. Furthermore, linear multivariate regression analysis showed that altered rCBFs in several regions could be predicted by physiological (systolic pressure, rectal temperature) and psychological (vigilance, drowsiness, nervousness, anger) changes. And PVT revealed significantly slower attentional reaction during hyperthermia, and the longer reaction time was correlated with the altered rCBF in the left dorsolateral prefrontal cortex (DLPFC). These findings suggested that during short-term hyperthermia gCBF might remain relatively stable under the integrated effect of physiological changes and cerebral auto-regulation, rather than decreased solely dependently on hyperthermia-induced physiological changes. Furthermore, altered regional blood distribution might be accounted for neural activity of thermal sensation and regulation, mood state and cognitive changes.
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Affiliation(s)
- Shaowen Qian
- Department of Medical Imaging, Jinan Military General Hospital, Shandong, PR China
| | - Qingjun Jiang
- Department of Medical Imaging, Jinan Military General Hospital, Shandong, PR China
| | - Kai Liu
- Department of Medical Imaging, Jinan Military General Hospital, Shandong, PR China
| | - Bo Li
- Department of Medical Imaging, Jinan Military General Hospital, Shandong, PR China
| | - Min Li
- Department of Medical Imaging, Jinan Military General Hospital, Shandong, PR China
| | - Li Li
- Department of Medical Imaging, Jinan Military General Hospital, Shandong, PR China
| | - Xiao Yang
- Department of Medical Imaging, Jinan Military General Hospital, Shandong, PR China
| | - Zhen Yang
- Department of Medical Imaging, Jinan Military General Hospital, Shandong, PR China
| | - Gang Sun
- Department of Medical Imaging, Jinan Military General Hospital, Shandong, PR China.
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45
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Ikemura T, Hayashi N. Effects of heat stress on ocular blood flow during exhaustive exercise. J Sports Sci Med 2014; 13:172-9. [PMID: 24570622 PMCID: PMC3918555] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2013] [Accepted: 10/23/2013] [Indexed: 06/03/2023]
Abstract
The hypothesis that heat stress reduces the ocular blood flow response to exhaustive exercise was tested by measuring ocular blood flow, blood pressure, and end- tidal carbon dioxide partial pressure (PETCO2) in 12 healthy males while they performed cycle ergometer exercise at 75% of the maximal heart rate at ambient temperatures of 20°C (control condition) and 35°C (heat condition), until exhaustion. The blood flows in the retinal and choroidal vasculature (RCV), the superior temporal retinal arteriole (STRA) and the superior nasal retinal arteriole (SNRA) were recorded at rest and at 6 and 16 min after the start of exercise period and at exhaustion [after 16 ± 2 min (mean ± SE) and 24 ± 3 min of exercise in the heat and control condition, respectively]. The mean arterial pressure at exhaustion was significantly lower in the heat condition than in the control condition at both 16 min and exhaustion. The degree of PETCO2 reduction did not differ significantly between the two thermal conditions at either 16 min or exhaustion. The blood flow velocity in the RCV significantly increased from the resting baseline value at 6 min in both thermal conditions (32 ± 6% and 25 ± 5% at 20°C and 35°C, respectively). However, at 16 min the increase in RCV blood flow velocity had returned to the resting baseline level only in the heat condition. At exhaustion, the blood flows in the STRA and SNRA had decreased significantly from the resting baseline value in the heat condition (STRA: -19 ± 5% and SNRA: -30 ± 6%), and SNRA blood flow was lower than that in the control condition (-14 ± 6% vs -30 ± 6% at 20°C and 35°C, respectively), despite the finding that both thermal conditions induced the same reductions in PETCO2 and vascular conductance. These findings suggested that the heat condition decreases or suppresses ocular blood flow via attenuation of pressor response during exhaustive exercise. Key PointsThe ocular (retinal and choroidal) blood flow response to exhaustive exercise with heat stress is unknown.We hypothesized that the heat stress decreases ocular blood flow response to exhaustive exercise, since cerebral flow, which is regulated similarly to ocular flow, was reported to decrease during heat stress.To test this hypothesis, ocular blood flow was measured during exhaustive exercise at 20°C (control condition) and 35°C (heat condition).At exhaustion in the heat condition, the ocular flow response was suppressed or decreased with an attenuated pressor response.It is suggested that the heat condition decreases or suppresses the ocular blood flow to exhaustive exercise via attenuation of pressor response.
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Affiliation(s)
- Tsukasa Ikemura
- Graduate School of Human-Environment Studies, Kyushu University , Kasuga, Fukuoka, Japan ; Graduate School of Decision Science and Technology, Tokyo Institute of Technology , Ookayama, Meguro, Japan
| | - Naoyuki Hayashi
- Graduate School of Decision Science and Technology, Tokyo Institute of Technology , Ookayama, Meguro, Japan
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Ikemura T, Miyaji A, Kashima H, Yamaguchi Y, Hayashi N. Ocular blood flow decreases during passive heat stress in resting humans. J Physiol Anthropol 2013; 32:23. [PMID: 24314154 PMCID: PMC4029185 DOI: 10.1186/1880-6805-32-23] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2013] [Accepted: 11/19/2013] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Heat stress induces various physiological changes and so could influence ocular circulation. This study examined the effect of heat stress on ocular blood flow. FINDINGS Ocular blood flow, end-tidal carbon dioxide (P(ET)CO2) and blood pressure were measured for 12 healthy subjects wearing water-perfused tube-lined suits under two conditions of water circulation: (1) at 35 °C (normothermia) for 30 min and (2) at 50 °C for 90 min (passive heat stress). The blood-flow velocities in the superior temporal retinal arteriole (STRA), superior nasal retinal arteriole (SNRA), and the retinal and choroidal vessels (RCV) were measured using laser-speckle flowgraphy. Blood flow in the STRA and SNRA was calculated from the integral of a cross-sectional map of blood velocity. PETCO2 was clamped at the normothermia level by adding 5% CO2 to the inspired gas. Passive heat stress had no effect on the subjects' blood pressures. The blood-flow velocity in the RCV was significantly lower after 30, 60 and 90 min of passive heat stress than the normothermic level, with a peak decrease of 18 ± 3% (mean ± SE) at 90 min. Blood flow in the STRA and SNRA decreased significantly after 90 min of passive heat stress conditions, with peak decreases of 14 ± 3% and 14 ± 4%, respectively. CONCLUSION The findings of this study suggest that passive heat stress decreases ocular blood flow irrespective of the blood pressure or arterial partial pressure of CO2.
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Affiliation(s)
- Tsukasa Ikemura
- Graduate School of Human-Environment Studies, Kyushu University, Kasuga-koen 6-1, Kasuga, Fukuoka 816-8580, Japan
- Graduate School of Decision Science and Technology, Tokyo Institute of Technology, Ookayama 2-12-1-W9-1, Meguro, Tokyo 152-8552, Japan
| | - Akane Miyaji
- Graduate School of Human-Environment Studies, Kyushu University, Kasuga-koen 6-1, Kasuga, Fukuoka 816-8580, Japan
- Graduate School of Decision Science and Technology, Tokyo Institute of Technology, Ookayama 2-12-1-W9-1, Meguro, Tokyo 152-8552, Japan
| | - Hideaki Kashima
- Graduate School of Human-Environment Studies, Kyushu University, Kasuga-koen 6-1, Kasuga, Fukuoka 816-8580, Japan
| | - Yuji Yamaguchi
- Graduate School of Human-Environment Studies, Kyushu University, Kasuga-koen 6-1, Kasuga, Fukuoka 816-8580, Japan
| | - Naoyuki Hayashi
- Graduate School of Decision Science and Technology, Tokyo Institute of Technology, Ookayama 2-12-1-W9-1, Meguro, Tokyo 152-8552, Japan
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Greaney JL, Schwartz CE, Edwards DG, Fadel PJ, Farquhar WB. The neural interaction between the arterial baroreflex and muscle metaboreflex is preserved in older men. Exp Physiol 2013; 98:1422-31. [PMID: 23733520 DOI: 10.1113/expphysiol.2013.073189] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Sympathetic baroreflex sensitivity is increased during selective activation of the skeletal muscle metaboreflex with postexercise ischaemia (PEI) in young adults. However, to date, there are no data demonstrating this neural interaction between the arterial baroreflex and the muscle metaboreflex in healthy older adults. Therefore, the goal of the present study was to examine the influence of healthy ageing on the metabolic component of the exercise pressor reflex and its interaction with the arterial baroreflex in the control of sympathetic outflow. Postexercise ischaemia following static hand grip performed at 30% maximal voluntary contraction was used to isolate muscle metaboreflex activation in young [n = 10; 24 ± 1 years old; resting blood pressure (BP) 116 ± 3/64 ± 3 mmHg] and older men (n = 9; 59 ± 2 years old; resting BP 120 ± 2/77 ± 2 mmHg). Arterial BP (Finometer) and muscle sympathetic nerve activity (MSNA) were measured continuously. Weighted linear regression analysis between MSNA and diastolic BP was used to estimate arterial baroreflex MSNA gain. There were no age-related differences in the increase in mean BP (young, Δ14 ± 3 mmHg versus older, Δ15 ± 2 mmHg; P > 0.05) or MSNA burst frequency (young, Δ11 ± 2 bursts min(-1) versus older, Δ9 ± 1 bursts min(-1); P > 0.05) during PEI. Likewise, the gain of arterial baroreflex control of total MSNA increased to a similar extent in both groups during PEI (young, -4.2 ± 0.9 baseline versus -6.3 ± 1.1 PEI a.u. beat(-1) mmHg(-1); and older, -3.7 ± 1.1 baseline versus -6.7 ± 1.4 PEI a.u. beat(-1) mmHg(-1); P < 0.05 for both). Collectively, these findings indicate that the neural interaction between the arterial baroreflex and the skeletal muscle metaboreflex in the regulation of MSNA is preserved in healthy ageing.
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Affiliation(s)
- Jody L Greaney
- W. B. Farquhar: 541 South College Avenue, Fred Rust HPL - Office #143, Newark, DE 19716, USA.
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Yang H, Carter JR. Baroreflex sensitivity analysis: spontaneous methodology vs. Valsalva's maneuver. Clin Auton Res 2013; 23:133-9. [PMID: 23677496 DOI: 10.1007/s10286-013-0195-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2013] [Accepted: 04/16/2013] [Indexed: 11/29/2022]
Abstract
INTRODUCTION Spontaneous analysis techniques and Valsalva's maneuver (VM) are often used as a non-pharamcological approach to assess both sympathetic (sBRS) and cardiovagal (cBRS) baroreflex sensitivity. Despite their wide utilization, no studies have assessed the intra-individual reliability between these analysis techniques. Accordingly, we hypothesized that spontaneous BRS would be positively correlated to VM BRS. METHODS Heart rate (HR), blood pressure (BP), and muscle sympathetic nerve activity (MSNA) were measured in 26 healthy subjects (age, 22 ± 1 year; 14 men and 12 women) during 10 min supine rest and 3 VM at 40 mmHg expiratory pressure (15 s, 1 min recoveries). For spontaneous BRS, relations between diastolic BP and MSNA were used to determine sBRS, while relations between systolic BP and R-R interval were used to determine cBRS. During VM, sBRS was the ratio of MSNA and the maximum diastolic BP reduction during early phase II, and cBRS was derived from linear relations between systolic BP and R-R interval during early phase II (i.e., hypotensive stimulus) and phase IV (i.e., hypertensive stimulus). RESULTS Spontaneous sBRS was significantly correlated to VM sBRS (r = 0.516, p = 0.036). In contrast, spontaneous cBRS from up-up sequence was not correlated to VM phase IV cBRS (r = 0.274, p = 0.109). Similarly, spontaneous cBRS from down-down sequence was not correlated to VM phase II cBRS (r = 0.199, p = 0.207). CONCLUSION In conclusion, our findings demonstrate positive association between spontaneous sBRS and VM sBRS, but there is no correlation between spontaneous and VM cBRS.
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Affiliation(s)
- Huan Yang
- Department of Kinesiology and Integrative Physiology, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, USA
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Kenney WL, Stanhewicz AE, Bruning RS, Alexander LM. Blood pressure regulation III: what happens when one system must serve two masters: temperature and pressure regulation? Eur J Appl Physiol 2013; 114:467-79. [PMID: 23636697 DOI: 10.1007/s00421-013-2652-5] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2013] [Accepted: 04/19/2013] [Indexed: 11/25/2022]
Abstract
When prolonged intense exercise is performed at high ambient temperatures, cardiac output must meet dual demands for increased blood flow to contracting muscle and to the skin. The literature has commonly painted this scenario as a fierce competition, wherein one circulation preserves perfusion at the expense of the other, with the regulated maintenance of blood pressure as the ultimate goal. This review redefines this scenario as commensalism, an integrated balance of regulatory control where one circulation benefits with little functional effect on the other. In young, healthy subjects, arterial pressure rarely falls to any great extent during either extreme passive heating or prolonged dynamic exercise in the heat, nor does body temperature rise disproportionately due to a compromised skin blood flow. Rather, it often takes the superimposition of additional stressors--e.g., dehydration or simulated hemorrhage--upon heat stress to substantially impact blood pressure regulation.
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Affiliation(s)
- W Larry Kenney
- Department of Kinesiology and Physiology Program, The Pennsylvania State University, 102 Noll Laboratory, University Park, PA, 16802-6900, USA,
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Carter JR, Schwartz CE, Yang H, Joyner MJ. Fish oil and neurovascular reactivity to mental stress in humans. Am J Physiol Regul Integr Comp Physiol 2013; 304:R523-30. [PMID: 23408034 DOI: 10.1152/ajpregu.00031.2013] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Omega-3 fatty acids found in fish oil have been suggested to protect against cardiovascular disease, yet underlying mechanisms remain unclear. Despite the well-documented link between mental stress and cardiovascular risk, no study has examined neural cardiovascular reactivity to mental stress after fish oil supplementation. We hypothesized that fish oil would blunt the blood pressure, heart rate (HR), and muscle sympathetic nerve activity (MSNA) responsiveness to mental stress and/or augment limb vasodilation associated with mental stress. Blood pressure, HR, MSNA, forearm vascular conductance (FVC), and calf vascular conductance (CVC) responses were recorded during a 5-min mental stress protocol in 67 nonhypertensive subjects before and after 8 wk of fish oil (n = 34) or placebo supplementation (n = 33). Fish oil blunted HR reactivity to mental stress (group × condition × time interactions, P = 0.012) but did not alter blood pressure reactivity to mental stress (interactions, P > 0.05). Fish oil blunted total MSNA reactivity to mental stress (interaction, P = 0.039) but did not alter MSNA burst frequency and burst incidence reactivity (interactions, P > 0.05). Finally, fish oil significantly blunted CVC reactivity to mental stress (interaction, P = 0.013) but did not alter FVC reactivity (interaction, P > 0.05). In conclusion, 8 wk of fish oil supplementation significantly attenuated both HR and total MSNA reactivity to mental stress and elicited a paradoxical blunting of calf vascular conductance. These findings support and extend the growing evidence that fish oil may have positive health benefits regarding neural cardiovascular control in humans.
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Affiliation(s)
- Jason R Carter
- Department of Kinesiology and Integrative Physiology, Michigan Technological University, 1400 Townsend Dr., Houghton, MI 49931, USA.
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