1
|
Søndergaard S. Observational study on passive leg raising and the autonomic nervous system. Physiol Rep 2022; 10:e15537. [PMID: 36541245 PMCID: PMC9768665 DOI: 10.14814/phy2.15537] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2022] [Revised: 11/05/2022] [Accepted: 11/21/2022] [Indexed: 06/17/2023] Open
Abstract
In the intensive care and perioperative setting, circulation is often supported by intravenous fluid preceded by prediction of fluid responsiveness during a passive leg raising (PLR) maneuver. An increase in stroke volume (SV) or cardiac output (CO) of 10%-15% indicates that the subject may increase the flow upon volume expansion. However, the semi-recumbent position as an initial position in PLR likely reduces SV by gravitational displacement of central blood volume (CBV) to lower extremities, thereby accentuating volume responsiveness during leg raising in healthy people. Coincident with gravitational perturbations in hemodynamics, remedial changes occur in the autonomic nervous system (ANS), as expressed in spectral power in heart rate variability (HRV). This study aims to clarify these concomitant changes during PLR. A convenience number of healthy volunteers (N = 11) were recruited by advertisement in university departments. The subjects were exposed to the established PLR sequence and the heart rate (HR), mean arterial pressure (MAP), SV, and CO were sampled at 1 Hz, while electrocardiogram was recorded at 1000 Hz. Relative powers reflecting autonomic nervous system activity were assessed from spectral analysis of HRV. In response to PLR, SV increased (12.4% ± 8.7%, p < 0.0026), while HR (-7.6% ± 4.7%, p < 0.0009) and MAP (-7.6% ± 6.9%, p < 0.01) decreased, with no change in CO (4.1% ± 12.8%, ns). The HRV low-frequency component was reduced (-34%; p < 0.0095), while the high-frequency activity increased (78.5%; p < 0.0013), with a 63% decrease in the low/high frequency ratio (p < 0.0078). Thus, HRV indicated a reduced sympathetic index (semi-recumbent 0.808 vs. PLR -0.177 a.u., p < 0.001) and an increased parasympathetic index (-0.141 to 0.996 a.u., p < 0.0001). Gravitational depletion and expansion of CBV during PLR were associated with a counterregulatory autonomic response. Healthy volunteers appeared volume responsive in terms of SV, but not CO. Responses to PLR are influenced by the ANS, and HRV analysis should be included in the assessment of the PLR test.
Collapse
Affiliation(s)
- Søren Søndergaard
- Department of Intensive Care and Neurointensive Stepdown Unit, Elective Surgery CentreSilkeborg Regional HospitalSilkeborgDenmark
| |
Collapse
|
2
|
Savioli G, Zanza C, Longhitano Y, Nardone A, Varesi A, Ceresa IF, Manetti AC, Volonnino G, Maiese A, La Russa R. Heat-Related Illness in Emergency and Critical Care: Recommendations for Recognition and Management with Medico-Legal Considerations. Biomedicines 2022; 10:2542. [PMID: 36289804 PMCID: PMC9599879 DOI: 10.3390/biomedicines10102542] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2022] [Revised: 09/22/2022] [Accepted: 10/06/2022] [Indexed: 11/30/2022] Open
Abstract
Hyperthermia is an internal body temperature increase above 40.5 °C; normally internal body temperature is kept constant through natural homeostatic mechanisms. Heat-related illnesses occur due to exposure to high environmental temperatures in conditions in which an organism is unable to maintain adequate homeostasis. This can happen, for example, when the organism is unable to dissipate heat adequately. Heat dissipation occurs through evaporation, conduction, convection, and radiation. Heat disease exhibits a continuum of signs and symptoms ranging from minor to major clinical pictures. Minor clinical pictures include cramps, syncope, edema, tetany, and exhaustion. Major clinical pictures include heatstroke and life-threatening heat stroke and typically are expressed in the presence of an extremely high body temperature. There are also some categories of people at greater risk of developing these diseases, due to exposure in particular geographic areas (e.g., hot humid environments), to unchangeable predisposing conditions (e.g., advanced age, young age (i.e., children), diabetes, skin disease with reduced sweating), to modifiable risk factors (e.g., alcoholism, excessive exercise, infections), to partially modifiable risk factors (obesity), to certain types of professional activity (e.g., athletes, military personnel, and outdoor laborers) or to the effects of drug treatment (e.g., beta-blockers, anticholinergics, diuretics). Heat-related illness is largely preventable.
Collapse
Affiliation(s)
- Gabriele Savioli
- Emergency Department, IRCCS Policlinico San Matteo, 27100 Pavia, Italy
- Doctoral Program Experimental Medicine, Department of Clinical-Surgical, Diagnostic and Pediatric Sciences, University of Pavia, 27100 Pavia, Italy
| | - Christian Zanza
- Foundation “Ospedale Alba-Bra”, Department of Emergency Medicine, Anesthesia and Critical Care Medicine, Michele and Pietro Ferrero Hospital, 12060 Verduno, Italy
| | - Yaroslava Longhitano
- Foundation “Ospedale Alba-Bra”, Department of Emergency Medicine, Anesthesia and Critical Care Medicine, Michele and Pietro Ferrero Hospital, 12060 Verduno, Italy
| | - Alba Nardone
- Department of Internal Medicine, Università degli Studi of Pavia, 27100 Pavia, Italy
| | - Angelica Varesi
- Department of Internal Medicine, Università degli Studi of Pavia, 27100 Pavia, Italy
| | | | - Alice Chiara Manetti
- Department of Surgical, Medical and Molecular Pathology and Critical Care Medicine, Institute of Legal Medicine, University of Pisa, 56126 Pisa, Italy
| | - Gianpietro Volonnino
- Department of Anatomy, Histology, Forensic Medicine and Orthopedics, Sapienza University, 00185 Rome, Italy
| | - Aniello Maiese
- Department of Surgical, Medical and Molecular Pathology and Critical Care Medicine, Institute of Legal Medicine, University of Pisa, 56126 Pisa, Italy
| | - Raffaele La Russa
- Department of Clinical and Experimental Medicine, University of Foggia, 71122 Foggia, Italy
| |
Collapse
|
3
|
Wang XR, Du HB, Wang HH, Zhang LM, Si YH, Zhang H, Zhao ZG. Mesenteric Lymph Drainage Improves Cardiac Papillary Contractility and Calcium Sensitivity in Rats with Hemorrhagic Shock. J Surg Res 2021; 266:245-253. [PMID: 34034059 DOI: 10.1016/j.jss.2021.04.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2020] [Revised: 03/29/2021] [Accepted: 04/01/2021] [Indexed: 10/21/2022]
Abstract
BACKGROUND Myocardial dysfunction is an important adverse factor of hemorrhagic shock that induces refractory hypotension, and post-hemorrhagic shock mesenteric lymph (PHSML) return is involved in this adverse effect. This study investigated whether mesenteric lymph drainage (MLD) improves PHSML return-induced cardiac contractile dysfunction via the restoration of cardiomyocyte calcium sensitivity. MATERIALS AND METHODS A hemorrhage shock model was established by using a controlled hemorrhage through the femoral artery that maintained a mean arterial pressure of 40 ± 2 mmHg for 3 h. MLD and mesenteric lymph duct ligation (MLDL) were performed from 1 to 3 h during hypotension. The papillary muscles of the heart were collected for measurement of calmodulin expression and for determining contractile responses to either isoprenaline or calcium. RESULTS The results showed that either MLD or MLDL reversed the hemorrhagic shock-induced downregulation of calmodulin expression, a marker protein of cardiomyocyte calcium sensitization, in papillary muscles. MLD also improved the decreased contractile response and ±df/dt of the papillary muscle strip to gradient isoprenaline or calcium caused by hemorrhagic shock. CONCLUSION These findings indicate that increased cardiac contractibility may be associated with the restoration of calcium sensitivity produced by PHSML drainage.
Collapse
Affiliation(s)
- Xiao-Rong Wang
- Institute of Microcirculation, Hebei North University, Zhangjiakou, China; Hebei Key Laboratory of Critical Disease Mechanism and Intervention, Hebei Medical University & Hebei North University, Shijiazhuang & Zhangjiakou, China
| | - Hui-Bo Du
- Institute of Microcirculation, Hebei North University, Zhangjiakou, China; Hebei Key Laboratory of Critical Disease Mechanism and Intervention, Hebei Medical University & Hebei North University, Shijiazhuang & Zhangjiakou, China
| | - Huai-Huai Wang
- Institute of Microcirculation, Hebei North University, Zhangjiakou, China; The Second Affiliated Hospital, Hebei North University, Zhangjiakou, China
| | - Li-Min Zhang
- Institute of Microcirculation, Hebei North University, Zhangjiakou, China; Hebei Key Laboratory of Critical Disease Mechanism and Intervention, Hebei Medical University & Hebei North University, Shijiazhuang & Zhangjiakou, China
| | - Yong-Hua Si
- Department of Pediatrics, Cangzhou City People's Hospital, Cangzhou, China
| | - Hong Zhang
- Institute of Microcirculation, Hebei North University, Zhangjiakou, China
| | - Zi-Gang Zhao
- Institute of Microcirculation, Hebei North University, Zhangjiakou, China; Hebei Key Laboratory of Critical Disease Mechanism and Intervention, Hebei Medical University & Hebei North University, Shijiazhuang & Zhangjiakou, China.
| |
Collapse
|
4
|
Luo D, Dai W, Lei L, Cai X. The clinical value of passive leg raising plus ultrasound to predict fluid responsiveness in children after cardiac surgery. BMC Pediatr 2021; 21:243. [PMID: 34011296 PMCID: PMC8132037 DOI: 10.1186/s12887-021-02703-2] [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] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/08/2020] [Accepted: 05/05/2021] [Indexed: 11/17/2022] Open
Abstract
Background There are few non-invasive monitoring methods that can reliably predict fluid responsiveness (FR) in children. Here, we interrogate the value of doppler ultrasound evaluation of passive leg raising (PLR)-induced changes in stroke volume (SV) and cardiac output (CO) as a predictor of FR in children with mechanical ventilation after congenital cardiac surgery. Methods A total of 40 children with mechanical ventilation following congenital cardiac surgery, who required volume expansion (VE) were included in this study. Hemodynamic parameters such as heart rate (HR), mean arterial pressure (MAP), SV, and central venous pressure (CVP) were monitored before and after PLR and VE. Besides, we assessed changes in SV and CO by bedside ultrasound. Patients showing > 10 % increase in SV in response to VE were considered to be responders (26 patients), while the rest (14 patients) were defined as non-responders. Results Our data demonstrated that ΔSV-PLR and ΔCO- PLR were positively correlated with ΔSV-VE (r = 0.683, p < 0.001 and r = 0.374, p = 0.017, respectively), and the area under the ROC curve (AUC) of ΔSV-PLR was 0.879 (95 % CI [0.745 1.000], p < 0.001). The best cut-off value for ΔSV-PLR in predicting FR was 13 %, with its sensitivity and specificity were 81.8 and 86.3 %, respectively. ΔCVP, ΔHR, and ΔMAP were weak predictors of FR in the children. Conclusions Our study demonstrated that SV changes, as evaluated by noninvasive ultrasound combined with PLR, could effectively evaluate FR in children under mechanical ventilation after congenital cardiac surgery.
Collapse
Affiliation(s)
- Deqiang Luo
- Department of Intensive Care Unit, The First Affiliated Hospital of Nanchang University, No. 17 Yongwaizheng Street,Dong Lake District, 330000, Nanchang City, Jiangxi Province, China.,Department of Intensive Care Unit, The Fifth People's Hospital of Shangrao City, No.1, Jiannan Road, 334000, Shangrao City, Jiangxi province, China
| | - Wei Dai
- Department of Intensive Care Unit, The Fifth People's Hospital of Shangrao City, No.1, Jiannan Road, 334000, Shangrao City, Jiangxi province, China
| | - Lei Lei
- Department of Animal Science, Hubei Vocational College Of Bio-Technology, No.1, Yezihu Lake, Hongshan District, 430070, Wuhan City, Hubei province, China
| | - Xueying Cai
- Department of Intensive Care Unit, The First Affiliated Hospital of Nanchang University, No. 17 Yongwaizheng Street,Dong Lake District, 330000, Nanchang City, Jiangxi Province, China. .,Department of Intensive Care Unit, Affiliated Hangzhou First People's Hospital, Zhejiang University School of Medicine, No. 261 Huansha Road, Shangcheng District, 310006, Hangzhou City, Zhejiang Province, China.
| |
Collapse
|
5
|
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.
Collapse
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
| |
Collapse
|
6
|
Trachsel LD, Barry H, Gravel H, Behzadi P, Henri C, Gagnon D. Cardiac function during heat stress: impact of short-term passive heat acclimation. Am J Physiol Heart Circ Physiol 2020; 319:H753-H764. [DOI: 10.1152/ajpheart.00407.2020] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A lower heart rate during heat exposure is a classic marker of heat acclimation (HA). It remains unknown if improved cardiac function contributes to this response. A 7-day passive HA protocol did not alter cardiac systolic function during passive heating, whereas it improved some indexes of diastolic function in young adults. Nonetheless, heart rate during heating was unaffected by HA. These results suggest that passive HA induces limited adaptations in cardiac function during passive heating.
Collapse
Affiliation(s)
- Lukas D. Trachsel
- Cardiovascular Prevention and Rehabilitation Center, Montreal Heart Institute, Montreal, Canada
- Department of Medicine, Université de Montréal, Montreal, Canada
- University Clinic for Cardiology, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland
| | - Hadiatou Barry
- Cardiovascular Prevention and Rehabilitation Center, Montreal Heart Institute, Montreal, Canada
- Department of Pharmacology and Physiology, Université de Montréal, Montreal, Canada
| | - Hugo Gravel
- Cardiovascular Prevention and Rehabilitation Center, Montreal Heart Institute, Montreal, Canada
- Department of Pharmacology and Physiology, Université de Montréal, Montreal, Canada
| | - Parya Behzadi
- Cardiovascular Prevention and Rehabilitation Center, Montreal Heart Institute, Montreal, Canada
- Department of Pharmacology and Physiology, Université de Montréal, Montreal, Canada
| | - Christine Henri
- Department of Medicine, Université de Montréal, Montreal, Canada
- Research Centre, Montreal Heart Institute, Montreal, Canada
| | - Daniel Gagnon
- Cardiovascular Prevention and Rehabilitation Center, Montreal Heart Institute, Montreal, Canada
- Department of Pharmacology and Physiology, Université de Montréal, Montreal, Canada
- Research Centre, Montreal Heart Institute, Montreal, Canada
- School of Human Kinetics and Exercise Science, Université de Montréal, Montreal, Canada
| |
Collapse
|
7
|
|
8
|
Gagnon D, Romero SA, Ngo H, Sarma S, Cornwell WK, Poh PYS, Stoller D, Levine BD, Crandall CG. Healthy aging does not compromise the augmentation of cardiac function during heat stress. J Appl Physiol (1985) 2016; 121:885-892. [PMID: 27609201 DOI: 10.1152/japplphysiol.00643.2016] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2016] [Accepted: 09/06/2016] [Indexed: 11/22/2022] Open
Abstract
During heat stress, stroke volume is maintained in young adults despite reductions in cardiac filling pressures. This is achieved by a general augmentation of cardiac function, highlighted by a left and upward shift of the Frank-Starling relation. In contrast, healthy aged adults are unable to maintain stroke volume during heat stress. We hypothesized that this would be associated with a lack of shift in the Frank-Starling relation. Frank-Starling relations were examined in 11 aged [69 ± 4 (SD) yr, 4 men/7 women] and 12 young (26 ± 5 yr, 6 men/6 women) adults during normothermic and heat stress (1.5°C increase in core temperature) conditions. During heat stress, increases in cardiac output were attenuated in aged adults (+2.5 ± 0.3 (95% CI) vs. young: +4.5 ± 0.5 l/min, P < 0.01) because of an attenuated chronotropic response (+30 ± 4 vs. young: +42 ± 5 beats/min, P < 0.01). In contrast to our hypothesis, a leftward shift of the Frank-Starling relation maintained stroke volume during heat stress in aged adults (76 ± 8 vs. normothermic: 74 ± 8 ml, P = 0.38) despite reductions in cardiac filling pressure (6.6 ± 1.0 vs. normothermic: 8.9 ± 1.1 mmHg, P < 0.01). In a subset of participants, volume loading was used to return cardiac filling pressure during heat stress to normothermic values, which resulted in a greater stroke volume for a given cardiac filling pressure in both groups. These results demonstrate that the Frank-Starling relation shifts during heat stress in healthy young and aged adults, thereby preserving stroke volume despite reductions in cardiac filling pressures.
Collapse
Affiliation(s)
- Daniel Gagnon
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas; Cardiovascular Prevention and Rehabilitation Centre (ÉPIC), Montreal Heart Institute Research Centre, Montreal, Quebec, Canada; and Département de physiologie moléculaire et intégrative, Faculté de Médecine, Université de Montréal, Montreal, Quebec, Canada
| | - Steven A Romero
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
| | - Hai Ngo
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
| | - Satyam Sarma
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
| | - William K Cornwell
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
| | - Paula Y S Poh
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
| | - Douglas Stoller
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
| | - Benjamin D Levine
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
| | - Craig G Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas;
| |
Collapse
|
9
|
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.
Collapse
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
| |
Collapse
|
10
|
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: 46] [Impact Index Per Article: 5.1] [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.
Collapse
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
| |
Collapse
|
11
|
Greaney JL, Stanhewicz AE, Proctor DN, Alexander LM, Kenney WL. Impairments in central cardiovascular function contribute to attenuated reflex vasodilation in aged skin. J Appl Physiol (1985) 2015; 119:1411-20. [PMID: 26494450 PMCID: PMC4683344 DOI: 10.1152/japplphysiol.00729.2015] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2015] [Accepted: 10/20/2015] [Indexed: 01/08/2023] Open
Abstract
During supine passive heating, increases in skin blood flow (SkBF) and cardiac output (Qc) are both blunted in older adults. The aim here was to determine the effect of acutely correcting the peripheral vasodilatory capacity of aged skin on the integrated cardiovascular responses to passive heating. A secondary aim was to examine the SkBF-Qc relation during hyperthermia in the presence (upright posture) and absence (dynamic exercise) of challenges to central venous pressure. We hypothesized that greater increases in SkBF would be accompanied by greater increases in Qc. Eleven healthy older adults (69 ± 3 yr) underwent supine passive heating (0.8°C rise in core temperature; water-perfused suit) after ingesting sapropterin (BH4, a nitric oxide synthase cofactor; 10 mg/kg) or placebo (randomized double-blind crossover design). Twelve young (24 ± 1 yr) subjects served as a comparison group. SkBF (laser-Doppler flowmetry) and Qc (open-circuit acetylene wash-in) were measured during supine heating, heating + upright posture, and heating + dynamic exercise. Throughout supine and upright heating, sapropterin fully restored the SkBF response of older adults to that of young adults but Qc remained blunted. During heat + upright posture, SkBF failed to decrease in untreated older subjects. There were no age- or treatment-related differences in SkBF-Qc during dynamic exercise. The principal finding of this study was that the blunted Qc response to passive heat stress is directly related to age as opposed to the blunted peripheral vasodilatory capacity of aged skin. Furthermore, peripheral impairments to SkBF in the aged may contribute to inapposite responses during challenges to central venous pressure during hyperthermia.
Collapse
Affiliation(s)
- Jody L Greaney
- Department of Kinesiology, Noll Laboratory, The Pennsylvania State University, University Park, Pennsylvania
| | - Anna E Stanhewicz
- Department of Kinesiology, Noll Laboratory, The Pennsylvania State University, University Park, Pennsylvania
| | - David N Proctor
- Department of Kinesiology, Noll Laboratory, The Pennsylvania State University, University Park, Pennsylvania
| | - Lacy M Alexander
- Department of Kinesiology, Noll Laboratory, The Pennsylvania State University, University Park, Pennsylvania
| | - W Larry Kenney
- Department of Kinesiology, Noll Laboratory, The Pennsylvania State University, University Park, Pennsylvania
| |
Collapse
|
12
|
Frost H, Mortensen CR, Secher NH, Nielsen HB. Postoperative volume balance: does stroke volume increase in Trendelenburg's position? Clin Physiol Funct Imaging 2015; 37:314-316. [PMID: 26519213 DOI: 10.1111/cpf.12306] [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: 06/19/2015] [Accepted: 08/18/2015] [Indexed: 11/30/2022]
Abstract
In healthy humans, stroke volume (SV) and cardiac output (CO) do not increase with expansion of the central blood volume by head-down tilt or administration of fluid. Here, we exposed 85 patients to Trendelenburg's position about one hour after surgery while cardiovascular variables were determined non-invasively by Modelflow. In Trendelenburg's position, SV (83 ± 19 versus 89 ± 20 ml) and CO (6·2 ± 1·8 versus 6·8 ± 1·8 l/min; both P<0·05) increased, while heart rate (75 ± 15 versus 76 ± 14 b min-1 ) and mean arterial pressure were unaffected (84 ± 15 versus 84 ± 16 mmHg). For the 33 patients (39%) with a > 10% increase in SV (from 78 ± 16 to 90 ± 17 ml) corresponding to an increase in CO from 5·9 ± 1·5 to 6·9 ± 1·6 l min-1 (P<0·05) when tilted head-down, administration of 250 ml Ringer's lactate solution increased SV (to 88 ± 18 ml) and CO (to 6·8 ± 1·7 l min-1 ). In conclusion, determination of SV and/or CO in Trendelenburg's position can be used to evaluate whether a patient is in need of IV fluid as here exemplified after surgery.
Collapse
Affiliation(s)
- H Frost
- Department of Anaesthesia, The Abdominal Center, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
| | - C R Mortensen
- Department of Anaesthesia, The Abdominal Center, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
| | - N H Secher
- Department of Anaesthesia, The Abdominal Center, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
| | - H B Nielsen
- Department of Anaesthesia, The Abdominal Center, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
| |
Collapse
|
13
|
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.
Collapse
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
| | | |
Collapse
|