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Chapman CL, Johnson BD, Hostler DP, Schlader ZJ. Diagnostic accuracy of thermal, hydration, and heart rate assessments in discriminating positive acute kidney injury risk following physical work in the heat. JOURNAL OF OCCUPATIONAL AND ENVIRONMENTAL HYGIENE 2024; 21:326-341. [PMID: 38512776 DOI: 10.1080/15459624.2024.2315161] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/23/2024]
Abstract
Occupational heat stress increases the risk of acute kidney injury (AKI). This study presents a secondary analysis to generate novel hypotheses for future studies by investigating the diagnostic accuracy of thermal, hydration, and heart rate assessments in discriminating positive AKI risk following physical work in the heat in unacclimatized individuals. Unacclimatized participants (n = 13, 3 women, age: ∼23 years) completed four trials involving 2 h of exercise in a 39.7 ± 0.6 °C, 32 ± 3% relative humidity environment that differed by experimental manipulation of hyperthermia (i.e., cooling intervention) and dehydration (i.e., water drinking). Diagnostic accuracy was assessed via receiver operating characteristic curve analysis. Positive AKI risk was identified when the product of concentrations insulin-like growth factor binding protein 7 and tissue inhibitor of metalloproteinase-2 [IGFBP7∙TIMP-2] exceeded 0.3 (ng∙mL-1)2∙1000-1. Peak absolute core temperature had the acceptable discriminatory ability (AUC = 0.71, p = 0.009), but a relatively large variance (AUC 95% CI: 0.57-0.86). Mean body temperature, urine specific gravity, urine osmolality, peak heart rate, and the peak percent of both maximum heart rate and heart rate reserve had poor discrimination (AUC = 0.66-0.69, p ≤ 0.051). Mean skin temperature, percent change in body mass and plasma volume, and serum sodium and osmolality had no discrimination (p ≥ 0.072). A peak increase in mean skin temperature of >4.7 °C had a positive likelihood ratio of 11.0 which suggests clinical significance. These data suggest that the absolute value of peak core temperature and the increase in mean skin temperature may be valuable to pursue in future studies as a biomarker for AKI risk in unacclimatized workers.
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Affiliation(s)
- Christopher L Chapman
- Military Performance Division, U.S. Army Research Institute of Environmental Medicine, Natick, Massachusetts
- Thermal and Mountain Medicine Division, U.S. Army Research Institute of Environmental Medicine, Natick, Massachusetts
- Oak Ridge Institute for Science and Education, Oak Ridge, Tennessee
| | - Blair D Johnson
- Department of Kinesiology, School of Public Health-Bloomington, Indiana University, Bloomington, Indiana
| | - David P Hostler
- Department of Exercise & Nutrition Sciences, University at Buffalo, Buffalo, New York
| | - Zachary J Schlader
- Department of Kinesiology, School of Public Health-Bloomington, Indiana University, Bloomington, Indiana
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2
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Watanabe K, Koch Esteves N, Gibson OR, Akiyama K, Watanabe S, González-Alonso J. Heat-related changes in the velocity and kinetic energy of flowing blood influence the human heart's output during hyperthermia. J Physiol 2024; 602:2227-2251. [PMID: 38690610 DOI: 10.1113/jp285760] [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: 10/03/2023] [Accepted: 04/03/2024] [Indexed: 05/02/2024] Open
Abstract
Passive whole-body hyperthermia increases limb blood flow and cardiac output (Q ̇ $\dot Q$ ), but the interplay between peripheral and central thermo-haemodynamic mechanisms remains unclear. Here we tested the hypothesis that local hyperthermia-induced alterations in peripheral blood flow and blood kinetic energy modulate flow to the heart andQ ̇ $\dot Q$ . Body temperatures, regional (leg, arm, head) and systemic haemodynamics, and left ventricular (LV) volumes and functions were assessed in eight healthy males during: (1) 3 h control (normothermic condition); (2) 3 h of single-leg heating; (3) 3 h of two-leg heating; and (4) 2.5 h of whole-body heating. Leg, forearm, and extracranial blood flow increased in close association with local rises in temperature while brain perfusion remained unchanged. Increases in blood velocity with small to no changes in the conduit artery diameter underpinned the augmented limb and extracranial perfusion. In all heating conditions,Q ̇ $\dot Q$ increased in association with proportional elevations in systemic vascular conductance, related to enhanced blood flow, blood velocity, vascular conductance and kinetic energy in the limbs and head (all R2 ≥ 0.803; P < 0.001), but not in the brain. LV systolic (end-systolic elastance and twist) and diastolic functional profiles (untwisting rate), pulmonary ventilation and systemic aerobic metabolism were only altered in whole-body heating. These findings substantiate the idea that local hyperthermia-induced selective alterations in peripheral blood flow modulate the magnitude of flow to the heart andQ ̇ $\dot Q$ through changes in blood velocity and kinetic energy. Localised heat-activated events in the peripheral circulation therefore affect the human heart's output. KEY POINTS: Local and whole-body hyperthermia increases limb and systemic perfusion, but the underlying peripheral and central heat-sensitive mechanisms are not fully established. Here we investigated the regional (leg, arm and head) and systemic haemodynamics (cardiac output:Q ̇ $\dot Q$ ) during passive single-leg, two-leg and whole-body hyperthermia to determine the contribution of peripheral and central thermosensitive factors in the control of human circulation. Single-leg, two-leg, and whole-body hyperthermia induced graded increases in leg blood flow andQ ̇ $\dot Q$ . Brain blood flow, however, remained unchanged in all conditions. Ventilation, extracranial blood flow and cardiac systolic and diastolic functions only increased during whole-body hyperthermia. The augmentedQ ̇ $\dot Q$ with hyperthermia was tightly related to increased limb and head blood velocity, flow and kinetic energy. The findings indicate that local thermosensitive mechanisms modulate regional blood velocity, flow and kinetic energy, thereby controlling the magnitude of flow to the heart and thus the coupling of peripheral and central circulation during hyperthermia.
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Affiliation(s)
- Kazuhito Watanabe
- Division of Sport, Health and Exercise Sciences, Department of Life Sciences, Brunel University London, Uxbridge, UK
- Faculty of Education and Human Studies, Akita University, Akita, Japan
| | - Nuno Koch Esteves
- Division of Sport, Health and Exercise Sciences, Department of Life Sciences, Brunel University London, Uxbridge, UK
- Research Centre, University College of Osteopathy, London, UK
| | - Oliver R Gibson
- Division of Sport, Health and Exercise Sciences, Department of Life Sciences, Brunel University London, Uxbridge, UK
- Centre for Physical Activity in Health and Disease, Brunel University London, Uxbridge, UK
| | - Koichi Akiyama
- Department of Anesthesiology, Kindai University Hospital, Osaka, Japan
| | - Sumie Watanabe
- Division of Sport, Health and Exercise Sciences, Department of Life Sciences, Brunel University London, Uxbridge, UK
- Faculty of Education and Human Studies, Akita University, Akita, Japan
| | - José González-Alonso
- Division of Sport, Health and Exercise Sciences, Department of Life Sciences, Brunel University London, Uxbridge, UK
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De Vita A, Belmusto A, Di Perna F, Tremamunno S, De Matteis G, Franceschi F, Covino M. The Impact of Climate Change and Extreme Weather Conditions on Cardiovascular Health and Acute Cardiovascular Diseases. J Clin Med 2024; 13:759. [PMID: 38337453 PMCID: PMC10856578 DOI: 10.3390/jcm13030759] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2023] [Revised: 01/12/2024] [Accepted: 01/24/2024] [Indexed: 02/12/2024] Open
Abstract
Climate change is widely recognized as one of the most significant challenges facing our planet and human civilization. Human activities such as the burning of fossil fuels, deforestation, and industrial processes release greenhouse gases into the atmosphere, leading to a warming of the Earth's climate. The relationship between climate change and cardiovascular (CV) health, mediated by air pollution and increased ambient temperatures, is complex and very heterogeneous. The main mechanisms underlying the pathogenesis of CV disease at extreme temperatures involve several regulatory pathways, including temperature-sympathetic reactivity, the cold-activated renin-angiotensin system, dehydration, extreme temperature-induced electrolyte imbalances, and heat stroke-induced systemic inflammatory responses. The interplay of these mechanisms may vary based on individual factors, environmental conditions, and an overall health background. The net outcome is a significant increase in CV mortality and a higher incidence of hypertension, type II diabetes mellitus, acute myocardial infarction (AMI), heart failure, and cardiac arrhythmias. Patients with pre-existing CV disorders may be more vulnerable to the effects of global warming and extreme temperatures. There is an urgent need for a comprehensive intervention that spans from the individual level to a systemic or global approach to effectively address this existential problem. Future programs aimed at reducing CV and environmental burdens should require cross-disciplinary collaboration involving physicians, researchers, public health workers, political scientists, legislators, and national leaders to mitigate the effects of climate change.
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Affiliation(s)
- Antonio De Vita
- Università Cattolica del Cattolica del Sacro Cuore, 00168 Roma, Italy; (A.B.); (F.D.P.); (F.F.); (M.C.)
- Department of Cardiovascular Sciences, Fondazione Policlinico Universitario A. Gemelli, IRCCS, 00168 Roma, Italy;
| | - Antonietta Belmusto
- Università Cattolica del Cattolica del Sacro Cuore, 00168 Roma, Italy; (A.B.); (F.D.P.); (F.F.); (M.C.)
| | - Federico Di Perna
- Università Cattolica del Cattolica del Sacro Cuore, 00168 Roma, Italy; (A.B.); (F.D.P.); (F.F.); (M.C.)
| | - Saverio Tremamunno
- Department of Cardiovascular Sciences, Fondazione Policlinico Universitario A. Gemelli, IRCCS, 00168 Roma, Italy;
| | - Giuseppe De Matteis
- Department of Internal Medicine and Gastroenterology, Fondazione Policlinico Universitario A. Gemelli, IRCCS, 00168 Roma, Italy;
| | - Francesco Franceschi
- Università Cattolica del Cattolica del Sacro Cuore, 00168 Roma, Italy; (A.B.); (F.D.P.); (F.F.); (M.C.)
- Emergency Medicine, Fondazione Policlinico Universitario A. Gemelli, IRCCS, 00168 Roma, Italy
| | - Marcello Covino
- Università Cattolica del Cattolica del Sacro Cuore, 00168 Roma, Italy; (A.B.); (F.D.P.); (F.F.); (M.C.)
- Emergency Medicine, Fondazione Policlinico Universitario A. Gemelli, IRCCS, 00168 Roma, Italy
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Notley SR, Mitchell D, Taylor NAS. A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 3: Heat and cold tolerance during exercise. Eur J Appl Physiol 2024; 124:1-145. [PMID: 37796292 DOI: 10.1007/s00421-023-05276-3] [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: 01/26/2023] [Accepted: 07/04/2023] [Indexed: 10/06/2023]
Abstract
In this third installment of our four-part historical series, we evaluate contributions that shaped our understanding of heat and cold stress during occupational and athletic pursuits. Our first topic concerns how we tolerate, and sometimes fail to tolerate, exercise-heat stress. By 1900, physical activity with clothing- and climate-induced evaporative impediments led to an extraordinarily high incidence of heat stroke within the military. Fortunately, deep-body temperatures > 40 °C were not always fatal. Thirty years later, water immersion and patient treatments mimicking sweat evaporation were found to be effective, with the adage of cool first, transport later being adopted. We gradually acquired an understanding of thermoeffector function during heat storage, and learned about challenges to other regulatory mechanisms. In our second topic, we explore cold tolerance and intolerance. By the 1930s, hypothermia was known to reduce cutaneous circulation, particularly at the extremities, conserving body heat. Cold-induced vasodilatation hindered heat conservation, but it was protective. Increased metabolic heat production followed, driven by shivering and non-shivering thermogenesis, even during exercise and work. Physical endurance and shivering could both be compromised by hypoglycaemia. Later, treatments for hypothermia and cold injuries were refined, and the thermal after-drop was explained. In our final topic, we critique the numerous indices developed in attempts to numerically rate hot and cold stresses. The criteria for an effective thermal stress index were established by the 1930s. However, few indices satisfied those requirements, either then or now, and the surviving indices, including the unvalidated Wet-Bulb Globe-Thermometer index, do not fully predict thermal strain.
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Affiliation(s)
- Sean R Notley
- Defence Science and Technology Group, Department of Defence, Melbourne, Australia
- School of Human Kinetics, University of Ottawa, Ottawa, Canada
| | - Duncan Mitchell
- Brain Function Research Group, School of Physiology, University of the Witwatersrand, Johannesburg, South Africa
- School of Human Sciences, University of Western Australia, Crawley, Australia
| | - Nigel A S Taylor
- Research Institute of Human Ecology, College of Human Ecology, Seoul National University, Seoul, Republic of Korea.
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Alhummiany B, Sharma K, Buckley DL, Soe KK, Sourbron SP. Physiological confounders of renal blood flow measurement. MAGMA (NEW YORK, N.Y.) 2023:10.1007/s10334-023-01126-7. [PMID: 37971557 DOI: 10.1007/s10334-023-01126-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2023] [Revised: 09/26/2023] [Accepted: 10/12/2023] [Indexed: 11/19/2023]
Abstract
OBJECTIVES Renal blood flow (RBF) is controlled by a number of physiological factors that can contribute to the variability of its measurement. The purpose of this review is to assess the changes in RBF in response to a wide range of physiological confounders and derive practical recommendations on patient preparation and interpretation of RBF measurements with MRI. METHODS A comprehensive search was conducted to include articles reporting on physiological variations of renal perfusion, blood and/or plasma flow in healthy humans. RESULTS A total of 24 potential confounders were identified from the literature search and categorized into non-modifiable and modifiable factors. The non-modifiable factors include variables related to the demographics of a population (e.g. age, sex, and race) which cannot be manipulated but should be considered when interpreting RBF values between subjects. The modifiable factors include different activities (e.g. food/fluid intake, exercise training and medication use) that can be standardized in the study design. For each of the modifiable factors, evidence-based recommendations are provided to control for them in an RBF-measurement. CONCLUSION Future studies aiming to measure RBF are encouraged to follow a rigorous study design, that takes into account these recommendations for controlling the factors that can influence RBF results.
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Affiliation(s)
- Bashair Alhummiany
- Department of Biomedical Imaging Sciences, University of Leeds, Leeds, LS2 9NL, UK.
| | - Kanishka Sharma
- Department of Imaging, Infection, Immunity and Cardiovascular Disease, The University of Sheffield, Sheffield, UK
| | - David L Buckley
- Department of Biomedical Imaging Sciences, University of Leeds, Leeds, LS2 9NL, UK
| | - Kywe Kywe Soe
- Department of Imaging, Infection, Immunity and Cardiovascular Disease, The University of Sheffield, Sheffield, UK
| | - Steven P Sourbron
- Department of Imaging, Infection, Immunity and Cardiovascular Disease, The University of Sheffield, Sheffield, UK.
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Notley SR, Mitchell D, Taylor NAS. A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 1: Foundational principles and theories of regulation. Eur J Appl Physiol 2023; 123:2379-2459. [PMID: 37702789 DOI: 10.1007/s00421-023-05272-7] [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: 12/30/2022] [Accepted: 06/30/2023] [Indexed: 09/14/2023]
Abstract
This contribution is the first of a four-part, historical series encompassing foundational principles, mechanistic hypotheses and supported facts concerning human thermoregulation during athletic and occupational pursuits, as understood 100 years ago and now. Herein, the emphasis is upon the physical and physiological principles underlying thermoregulation, the goal of which is thermal homeostasis (homeothermy). As one of many homeostatic processes affected by exercise, thermoregulation shares, and competes for, physiological resources. The impact of that sharing is revealed through the physiological measurements that we take (Part 2), in the physiological responses to the thermal stresses to which we are exposed (Part 3) and in the adaptations that increase our tolerance to those stresses (Part 4). Exercising muscles impose our most-powerful heat stress, and the physiological avenues for redistributing heat, and for balancing heat exchange with the environment, must adhere to the laws of physics. The first principles of internal and external heat exchange were established before 1900, yet their full significance is not always recognised. Those physiological processes are governed by a thermoregulatory centre, which employs feedback and feedforward control, and which functions as far more than a thermostat with a set-point, as once was thought. The hypothalamus, today established firmly as the neural seat of thermoregulation, does not regulate deep-body temperature alone, but an integrated temperature to which thermoreceptors from all over the body contribute, including the skin and probably the muscles. No work factor needs to be invoked to explain how body temperature is stabilised during exercise.
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Affiliation(s)
- Sean R Notley
- Defence Science and Technology Group, Department of Defence, Melbourne, Australia
- School of Human Kinetics, University of Ottawa, Ottawa, Canada
| | - Duncan Mitchell
- Brain Function Research Group, School of Physiology, University of the Witwatersrand, Johannesburg, South Africa
- School of Human Sciences, University of Western Australia, Crawley, Australia
| | - Nigel A S Taylor
- Research Institute of Human Ecology, College of Human Ecology, Seoul National University, Seoul, Republic of Korea.
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7
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Meade RD, Notley SR, Akerman AP, McGarr GW, Richards BJ, McCourt ER, King KE, McCormick JJ, Boulay P, Sigal RJ, Kenny GP. Physiological responses to 9 hours of heat exposure in young and older adults. Part I: Body temperature and hemodynamic regulation. J Appl Physiol (1985) 2023; 135:673-687. [PMID: 37439239 DOI: 10.1152/japplphysiol.00227.2023] [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: 04/11/2023] [Revised: 06/23/2023] [Accepted: 07/10/2023] [Indexed: 07/14/2023] Open
Abstract
Aging is associated with an elevated risk of heat-related mortality and morbidity, attributed, in part, to declines in thermoregulation. However, comparisons between young and older adults have been limited to brief exposures (1-4 h), which may not adequately reflect the duration or severity of the heat stress experienced during heat waves. We therefore evaluated physiological responses in 20 young (19-31 yr; 10 females) and 39 older (61-78 yr; 11 females) adults during 9 h of rest at 40°C and 9% relative humidity. Whole body heat exchange and storage were measured with direct calorimetry during the first 3 h and final 3 h. Core temperature (rectal) was monitored continuously. The older adults stored 88 kJ [95% confidence interval (CI): 29, 147] more heat over the first 3 h of exposure (P = 0.006). Although no between-group differences were observed after 3 h [young: 37.6°C (SD 0.2°C) vs. older: 37.7°C (0.3°C); P = 0.216], core temperature was elevated by 0.3°C [0.1, 0.4] (adjusted for baseline) in the older group at hour 6 [37.6°C (0.2°C) vs. 37.9°C (0.2°C); P < 0.001] and by 0.2°C [0.0, 0.3] at hour 9 [37.7°C (0.3°C) vs. 37.8°C (0.3°C)], although the latter comparison was not significant after multiplicity correction (P = 0.061). Our findings indicate that older adults sustain greater increases in heat storage and core temperature during daylong exposure to hot dry conditions compared with their younger counterparts. This study represents an important step in the use of ecologically relevant, prolonged exposures for translational research aimed at quantifying the physiological and health impacts of hot weather and heat waves on heat-vulnerable populations.NEW & NOTEWORTHY We found greater increases in body heat storage and core temperature in older adults than in their younger counterparts during 9 h of resting exposure to hot dry conditions. Furthermore, the age-related increase in core temperature was exacerbated in older adults with common heat-vulnerability-linked health conditions (type 2 diabetes and hypertension). Impairments in thermoregulatory function likely contribute to the increased risk of heat-related illness and injury seen in older adults during hot weather and heat waves.
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Affiliation(s)
- Robert D Meade
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
- Harvard T.H. Chan School of Public Health, Harvard University, Boston, Massachusetts, United States
| | - Sean R Notley
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
| | - Ashley P Akerman
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
| | - Gregory W McGarr
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
| | - Brodie J Richards
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
| | - Emma R McCourt
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
| | - Kelli E King
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
| | - James J McCormick
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
| | - Pierre Boulay
- Faculty of Physical Activity Sciences, University of Sherbrooke, Sherbrooke, Quebec, Canada
| | - Ronald J Sigal
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
- Department of Medicine, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada
- Department of Cardiac Sciences, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada
- Department of Community Health Sciences, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada
- Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada
- Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, Ontario, Canada
| | - Glen P Kenny
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
- Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, Ontario, Canada
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Foster J, Mckenna ZJ, Atkins WC, Jarrard CP, Crandall CG. Aging Increases Enterocyte Damage during a 3-Hour Exposure to Very Hot and Dry Heat: A Preliminary Study. BIOLOGY 2023; 12:1088. [PMID: 37626974 PMCID: PMC10451985 DOI: 10.3390/biology12081088] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2023] [Revised: 08/01/2023] [Accepted: 08/02/2023] [Indexed: 08/27/2023]
Abstract
Profound heat stress can damage the gastrointestinal barrier, leading to microbial translocation from the gut and subsequent systemic inflammation. Despite the greater vulnerability of older people to heat wave-related morbidity and mortality, it is unknown if age modulates gastrointestinal barrier damage and inflammation during heat stress. Therefore, the aim of this study was to determine if aging impacted enterocyte damage and systemic inflammatory responses to a 3-h exposure to very hot and dry (47 °C, 15% humidity) heat with accompanying activities of daily living (intermittent activity at 3 METS). Data from 16 young (age 21 to 39 years) and 16 older (age 65 to 76 years) humans were used to address this aim. In each group, log-transformed plasma concentrations of intestinal fatty acid binding protein (I-FABPlog), interleukin-8 (IL-8log), and tissue factor (TFlog) were assessed as indices of enterocyte damage, systemic inflammation, and blood coagulation, respectively, before and after the 3-h heat exposure. In the younger cohort, I-FABPlog concentration did not increase from pre to post heat exposure (p = 0.264, d = 0.20), although it was elevated in the older group (p = 0.014, d = 0.67). The magnitude of the increase in I-FABPlog was greater in the older participants (p = 0.084, d = 0.55). Across all participants, there was no correlation between the change in core temperature and the change in IFABPlog. There was no change in IL-8log in the younger group (p = 0.193, d = 0.23) following heat exposure, but we observed a decrease in IL-8log in the older group (p = 0.047, d = 0.48). TFlog decreased in the younger group (p = 0.071, d = 0.41), but did not change in the older group (p = 0.193, d = 0.15). Our data indicate that I-FABPlog concentration (an index of enterocyte damage) is increased in older humans during a 3-h extreme heat exposure. Future studies should determine whether this marker reflects increased gastrointestinal barrier permeability in older individuals during heat exposure.
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Affiliation(s)
- Josh Foster
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, The University of Texas Southwestern Medical Center, Dallas, TX 75231, USA; (Z.J.M.); (W.C.A.); (C.P.J.); (C.G.C.)
- Centre for Human and Applied Physiological Sciences, Faculty of Life Sciences and Medicine, King’s College London, London SE1 1UL, UK
| | - Zachary J. Mckenna
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, The University of Texas Southwestern Medical Center, Dallas, TX 75231, USA; (Z.J.M.); (W.C.A.); (C.P.J.); (C.G.C.)
| | - Whitley C. Atkins
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, The University of Texas Southwestern Medical Center, Dallas, TX 75231, USA; (Z.J.M.); (W.C.A.); (C.P.J.); (C.G.C.)
| | - Caitlin P. Jarrard
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, The University of Texas Southwestern Medical Center, Dallas, TX 75231, USA; (Z.J.M.); (W.C.A.); (C.P.J.); (C.G.C.)
| | - Craig G. Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, The University of Texas Southwestern Medical Center, Dallas, TX 75231, USA; (Z.J.M.); (W.C.A.); (C.P.J.); (C.G.C.)
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9
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Wait SO, Charkoudian N, Skinner JW, Smith CJ. Combining hypoxia with thermal stimuli in humans: physiological responses and potential sex differences. Am J Physiol Regul Integr Comp Physiol 2023; 324:R677-R690. [PMID: 36971421 PMCID: PMC10202487 DOI: 10.1152/ajpregu.00244.2021] [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: 09/27/2021] [Revised: 03/08/2023] [Accepted: 03/20/2023] [Indexed: 03/29/2023]
Abstract
Increasing prevalence of native lowlanders sojourning to high altitudes (>2,500 m) for recreational, occupational, military, and competitive reasons has generated increased interest in physiological responses to multistressor environments. Exposure to hypoxia poses recognized physiological challenges that are amplified during exercise and further complicated by environments that might include combinations of heat, cold, and high altitude. There is a sparsity of data examining integrated responses in varied combinations of environmental conditions, with even less known about potential sex differences. How this translates into performance, occupational, and health outcomes requires further investigation. Acute hypoxic exposure decreases arterial oxygen saturation, resulting in a reflex hypoxic ventilatory response and sympathoexcitation causing an increase in heart rate, myocardial contractility, and arterial blood pressure, to compensate for the decreased arterial oxygen saturation. Acute altitude exposure impairs exercise performance, for example, reduced time to exhaustion and slower time trials, largely owing to impairments in pulmonary gas exchange and peripheral delivery resulting in reduced V̇o2max. This exacerbates with increasing altitude, as does the risk of developing acute mountain sickness and more serious altitude-related illnesses, but modulation of those risks with additional stressors is unclear. This review aims to summarize and evaluate current literature regarding cardiovascular, autonomic, and thermoregulatory responses to acute hypoxia, and how these may be affected by simultaneous thermal environmental challenges. There is minimal available information regarding sex as a biological variable in integrative responses to hypoxia or multistressor environments; we highlight these areas as current knowledge gaps and the need for future research.
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Affiliation(s)
- Seaver O Wait
- Department of Public Health and Exercise Science, Appalachian State University, Boone, North Carolina, United States
| | - Nisha Charkoudian
- United States Army Research Institute of Environmental Medicine, Natick, Massachusetts, United States
| | - Jared W Skinner
- Department of Public Health and Exercise Science, Appalachian State University, Boone, North Carolina, United States
| | - Caroline J Smith
- Department of Public Health and Exercise Science, Appalachian State University, Boone, North Carolina, United States
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Sixtus RP, Berry MJ, Gray CL, Dyson RM. A novel whole-body thermal stress test for monitoring cardiovascular responses in Guinea pigs. J Therm Biol 2023; 113:103500. [PMID: 37055107 DOI: 10.1016/j.jtherbio.2023.103500] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2022] [Revised: 01/27/2023] [Accepted: 02/04/2023] [Indexed: 03/12/2023]
Abstract
Cardiovascular disease is a leading cause of morbidity and mortality worldwide. Stress tests are frequently employed to expose early signs of cardiovascular dysfunction or disease and can be employed, for example, in the context of preterm birth. We aimed to establish a safe and effective thermal stress test to examine cardiovascular function. Guinea pigs were anaesthetized using a 0.8% isoflurane, 70% N2O mix. ECG, non-invasive blood pressure, laser Doppler flowmetry, respiratory rate, and an array of skin and rectal thermistors were applied. A physiologically relevant heating and a cooling thermal stress test was developed. Upper and lower thermal limits for core body temperature were set at 41.5 OC and 34 OC, for the safe recovery of animals. This protocol therefore presents a viable thermal stress test for use in guinea pig models of health and disease that facilitates exploration of whole-system cardiovascular function.
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Affiliation(s)
- Ryan P Sixtus
- Department of Paediatrics and Child Health, University of Otago, Wellington, New Zealand.
| | - Mary J Berry
- Department of Paediatrics and Child Health, University of Otago, Wellington, New Zealand
| | - Clint L Gray
- Department of Paediatrics and Child Health, University of Otago, Wellington, New Zealand
| | - Rebecca M Dyson
- Department of Paediatrics and Child Health, University of Otago, Wellington, New Zealand
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11
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Jacobsen AP, Khiew YC, Duffy E, O'Connell J, Brown E, Auwaerter PG, Blumenthal RS, Schwartz BS, McEvoy JW. Climate change and the prevention of cardiovascular disease. Am J Prev Cardiol 2022; 12:100391. [PMID: 36164332 PMCID: PMC9508346 DOI: 10.1016/j.ajpc.2022.100391] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2022] [Revised: 08/27/2022] [Accepted: 09/10/2022] [Indexed: 11/26/2022] Open
Abstract
Climate change is a worsening global crisis that will continue negatively impacting population health and well-being unless adaptation and mitigation interventions are rapidly implemented. Climate change-related cardiovascular disease is mediated by air pollution, increased ambient temperatures, vector-borne disease and mental health disorders. Climate change-related cardiovascular disease can be modulated by climate change adaptation; however, this process could result in significant health inequity because persons and populations of lower socioeconomic status have fewer adaptation options. Clear scientific evidence for climate change and its impact on human health have not yet resulted in the national and international impetus and policies necessary to slow climate change. As respected members of society who regularly communicate scientific evidence to patients, clinicians are well-positioned to advocate on the importance of addressing climate change. This narrative review summarizes the links between climate change and cardiovascular health, proposes actionable items clinicians and other healthcare providers can execute both in their personal life and as an advocate of climate policies, and encourages communication of the health impacts of climate change when counseling patients. Our aim is to inspire the reader to invest more time in communicating the most crucial public health issue of the 21st century to their patients.
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Affiliation(s)
- Alan P. Jacobsen
- Ciccarone Center for the Prevention of Cardiovascular Disease, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, United States
| | - Yii Chun Khiew
- Division of Gastroenterology, Department of Gastroenterology, MedStar Georgetown University Hospital, Washington, DC, United States
| | - Eamon Duffy
- Division of Cardiology, Department of Medicine, Columbia University Irving Medical Center, New York, NY, United States
| | - James O'Connell
- Department of Public Health, Health Service Executive West, Galway, Ireland
| | - Evans Brown
- Department of Medicine, Division of Hospital Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, United States
| | - Paul G. Auwaerter
- Sherrilyn and Ken Fisher Center for Environmental Infectious Diseases, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, United States
| | - Roger S. Blumenthal
- Ciccarone Center for the Prevention of Cardiovascular Disease, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, United States
| | - Brian S. Schwartz
- Department of Environmental Health and Engineering, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, United States
| | - John William McEvoy
- Ciccarone Center for the Prevention of Cardiovascular Disease, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, United States
- National Institute for Prevention and Cardiovascular Health, National University of Ireland Galway, Galway, Ireland
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12
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Chou TH, Coyle EF. Cardiovascular responses to hot skin at rest and during exercise. Temperature (Austin) 2022; 10:326-357. [PMID: 37554384 PMCID: PMC10405766 DOI: 10.1080/23328940.2022.2109931] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2022] [Revised: 07/25/2022] [Accepted: 07/30/2022] [Indexed: 10/15/2022] Open
Abstract
Integrative cardiovascular responses to heat stress during endurance exercise depend on various variables, such as thermal stress and exercise intensity. This review addresses how increases in skin temperature alter and challenge the integrative cardiovascular system during upright submaximal endurance exercise, especially when skin is hot (i.e. >38°C). Current evidence suggests that exercise intensity plays a significant role in cardiovascular responses to hot skin during exercise. At rest and during mild intensity exercise, hot skin increases skin blood flow and abolishes cutaneous venous tone, which causes blood pooling in the skin while having little impact on stroke volume and thus cardiac output is increased with an increase in heart rate. When the heart rate is at relatively low levels, small increases in heart rate, skin blood flow, and cutaneous venous volume do not compromise stroke volume, so cardiac output can increase to fulfill the demands for maintaining blood pressure, heat dissipation, and the exercising muscle. On the contrary, during more intense exercise, hot skin does not abolish exercise-induced cutaneous venoconstriction possibly due to high sympathetic nerve activities; thus, it does not cause blood pooling in the skin. However, hot skin reduces stroke volume, which is associated with a decrease in ventricular filling time caused by an increase in heart rate. When the heart rate is high during moderate or intense exercise, even a slight reduction in ventricular filling time lowers stroke volume. Cardiac output is therefore not elevated when skin is hot during moderate intensity exercise.
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Affiliation(s)
- Ting-Heng Chou
- Center for Regenerative Medicine, The Research Institute at Nationwide Children’s Hospital, Columbus, OH, USA
| | - Edward F. Coyle
- Department of Kinesiology and Health Education, The University of Texas at Austin, Texas, Tx, USA
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13
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Lloyd A, Fiala D, Heyde C, Havenith G. A mathematical model for predicting cardiovascular responses at rest and during exercise in demanding environmental conditions. J Appl Physiol (1985) 2022; 133:247-261. [PMID: 35652831 PMCID: PMC9342140 DOI: 10.1152/japplphysiol.00619.2021] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The present research describes the development and validation of a cardiovascular model (CVR Model) for use in conjunction with advanced thermophysiological models, where usually only a total cardiac output is estimated. The CVR Model detailed herein estimates cardio-dynamic parameters (changes in cardiac output, stroke volume, and heart rate), regional blood flow, and muscle oxygen extraction, in response to rest and physical workloads, across a range of ages and aerobic fitness levels, as well as during exposure to heat, dehydration, and altitude. The model development strategy was to first establish basic resting and exercise predictions for cardio-dynamic parameters in an "ideal" environment (cool, sea level, and hydrated person). This basic model was then advanced for increasing levels of altitude, heat strain, and dehydration, using meta-analysis and reaggregation of published data. Using the estimated altitude- and heat-induced changes in maximum oxygen extraction and maximum cardiac output, the decline in maximum oxygen consumption at high altitude and in the heat was also modeled. A validation of predicted cardiovascular strain using heart rate was conducted using a dataset of 101 heterogeneous individuals (1,371 data points) during rest and exercise in the heat and at altitude, demonstrating that the CVR Model performs well (R2 = 0.82-0.84) in predicting cardiovascular strain, particularly at a group mean level (R2 = 0.97). The development of the CVR Model is aimed at providing the Fiala thermal Physiology & Comfort (FPC) Model and other complex thermophysiological models with improved estimations of cardiac strain and exercise tolerance, across a range of individuals during acute exposure to environmental stressors.NEW & NOTEWORTHY The present research promotes the adaption of thermophysiological modeling to the estimation of cardiovascular strain in individuals exercising under acute environmental stress. Integration with advanced models of human thermoregulation opens doors for detailed numerical analysis of athletes' performance and physiology during exercise, occupational safety, and individual work tolerability. The research provides a simple-to-validate metric of cardiovascular function (heart rate), as well as a method to evaluate key principles influencing exercise- and thermoregulation in humans.
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Affiliation(s)
- Alex Lloyd
- 1Environmental Ergonomics Research Centre, Loughborough University, Loughborough, United Kingdom
| | - Dusan Fiala
- 2ERGONSIM—Human Thermal Modelling, Messstetten, Germany
| | | | - George Havenith
- 1Environmental Ergonomics Research Centre, Loughborough University, Loughborough, United Kingdom
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14
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Di Credico A, Perpetuini D, Izzicupo P, Gaggi G, Cardone D, Filippini C, Merla A, Ghinassi B, Di Baldassarre A. Estimation of Heart Rate Variability Parameters by Machine Learning Approaches Applied to Facial Infrared Thermal Imaging. Front Cardiovasc Med 2022; 9:893374. [PMID: 35656402 PMCID: PMC9152459 DOI: 10.3389/fcvm.2022.893374] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2022] [Accepted: 04/04/2022] [Indexed: 01/18/2023] Open
Abstract
Heart rate variability (HRV) is a reliable tool for the evaluation of several physiological factors modulating the heart rate (HR). Importantly, variations of HRV parameters may be indicative of cardiac diseases and altered psychophysiological conditions. Recently, several studies focused on procedures for contactless HR measurements from facial videos. However, the performances of these methods decrease when illumination is poor. Infrared thermography (IRT) could be useful to overcome this limitation. In fact, IRT can measure the infrared radiations emitted by the skin, working properly even in no visible light illumination conditions. This study investigated the capability of facial IRT to estimate HRV parameters through a face tracking algorithm and a cross-validated machine learning approach, employing photoplethysmography (PPG) as the gold standard for the HR evaluation. The results demonstrated a good capability of facial IRT in estimating HRV parameters. Particularly, strong correlations between the estimated and measured HR (r = 0.7), RR intervals (r = 0.67), TINN (r = 0.71), and pNN50 (%) (r = 0.70) were found, whereas moderate correlations for RMSSD (r = 0.58), SDNN (r = 0.44), and LF/HF (r = 0.48) were discovered. The proposed procedure allows for a contactless estimation of the HRV that could be beneficial for evaluating both cardiac and general health status in subjects or conditions where contact probe sensors cannot be used.
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Affiliation(s)
- Andrea Di Credico
- Department of Medicine and Aging Sciences, University "G. d'Annunzio" of Chieti - Pescara, Chieti, Italy.,Reprogramming and Cell Differentiation Lab, Center for Advanced Studies and Technology, University "G. d'Annunzio" of Chieti - Pescara, Chieti, Italy
| | - David Perpetuini
- Department of Neurosciences, Imaging and Clinical Sciences, University "G. d'Annunzio" of Chieti - Pescara, Chieti, Italy
| | - Pascal Izzicupo
- Department of Medicine and Aging Sciences, University "G. d'Annunzio" of Chieti - Pescara, Chieti, Italy
| | - Giulia Gaggi
- Department of Medicine and Aging Sciences, University "G. d'Annunzio" of Chieti - Pescara, Chieti, Italy.,Reprogramming and Cell Differentiation Lab, Center for Advanced Studies and Technology, University "G. d'Annunzio" of Chieti - Pescara, Chieti, Italy
| | - Daniela Cardone
- Department of Neurosciences, Imaging and Clinical Sciences, University "G. d'Annunzio" of Chieti - Pescara, Chieti, Italy
| | - Chiara Filippini
- Department of Neurosciences, Imaging and Clinical Sciences, University "G. d'Annunzio" of Chieti - Pescara, Chieti, Italy
| | - Arcangelo Merla
- Department of Engineering and Geology, University "G. d'Annunzio" of Chieti - Pescara, Chieti, Italy
| | - Barbara Ghinassi
- Department of Medicine and Aging Sciences, University "G. d'Annunzio" of Chieti - Pescara, Chieti, Italy.,Reprogramming and Cell Differentiation Lab, Center for Advanced Studies and Technology, University "G. d'Annunzio" of Chieti - Pescara, Chieti, Italy
| | - Angela Di Baldassarre
- Department of Medicine and Aging Sciences, University "G. d'Annunzio" of Chieti - Pescara, Chieti, Italy.,Reprogramming and Cell Differentiation Lab, Center for Advanced Studies and Technology, University "G. d'Annunzio" of Chieti - Pescara, Chieti, Italy
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15
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Li Z, Jiang W, Fan H, Yan F, Dong R, Bai T, Xu K. Reallocation of cutaneous and global blood circulation during sauna bathing through a closed-loop model. COMPUTER METHODS AND PROGRAMS IN BIOMEDICINE 2022; 221:106917. [PMID: 35640388 DOI: 10.1016/j.cmpb.2022.106917] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2021] [Revised: 05/20/2022] [Accepted: 05/25/2022] [Indexed: 06/15/2023]
Abstract
OBJECTIVE Sauna bathing (SB) is an important strategy in cardiovascular protection, but there is no mathematical explanation for the reallocation of blood circulation during heat-induced superficial vasodilation. We sought to reveal such reallocation via a simulated hemodynamic model. METHODS A closed-loop cardiovascular model with a series of electrical parameters was constructed. The body surface was divided into seven blocks and each block was modeled by a lumped resistance. These resistances were adjusted to increase skin blood flow (SBF), with the aim of reflecting heat-induced vasodilation during SB. Finally, the blood pressure was compared before and after SB, and the blood flow inside the aorta and visceral arteries were also analyzed. RESULTS With increasing SBF in this model, the systolic, diastolic, and mean blood pressure in the arterial trunk decreased by 13-29, 18-36, and 19-37 mmHg, respectively. Despite the increase in the peak and mean blood flow in the arterial trunk, the diastolic blood flow reversal in the thoracic and abdominal aortas increased significantly. Nevertheless, the blood supply to the heart, liver, stomach, spleen, kidney, and intestine decreased by at least 25%. Moreover, the pulmonary blood flow increased significantly. CONCLUSION Simulated heat-induced cutaneous vasodilation in this model lowers blood pressure, induces visceral ischemia, and promotes pulmonary circulation, suggesting that the present closed-loop model may be able to describe the effect of sauna bathing on blood circulation. However, the increase of retrograde flow in the aortas found in this model deserves further examination.
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Affiliation(s)
- Zhongyou Li
- Sichuan Province Biomechanical Engineering Laboratory, Chengdu, China; Department of Mechanical Science and Engineering, Sichuan University, Nan Yihuan Road No 24, Wuhou District, 610065, China
| | - Wentao Jiang
- Sichuan Province Biomechanical Engineering Laboratory, Chengdu, China; Department of Mechanical Science and Engineering, Sichuan University, Nan Yihuan Road No 24, Wuhou District, 610065, China.
| | - Haidong Fan
- Department of Mechanical Science and Engineering, Sichuan University, Nan Yihuan Road No 24, Wuhou District, 610065, China
| | - Fei Yan
- Chongqing University Three Gorges Hospital, Chongqing University, Chongqing, China
| | - Ruiqi Dong
- National Engineering Research Center for Biomaterials, Sichuan University, Chengdu, China
| | - Taoping Bai
- Sichuan Province Biomechanical Engineering Laboratory, Chengdu, China; Department of Mechanical Science and Engineering, Sichuan University, Nan Yihuan Road No 24, Wuhou District, 610065, China
| | - Kairen Xu
- Sichuan Province Biomechanical Engineering Laboratory, Chengdu, China; Department of Mechanical Science and Engineering, Sichuan University, Nan Yihuan Road No 24, Wuhou District, 610065, China
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16
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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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17
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James TJ, Corbett J, Cummings M, Allard S, Young JS, Towse J, Carey-Jones K, Eglin C, Hopkins B, Morgan C, Tipton M, Saynor ZL, Shepherd AI. Timing of acute passive heating on glucose tolerance and blood pressure in people with type 2 diabetes: a randomized, balanced crossover, control trial. J Appl Physiol (1985) 2021; 130:1093-1105. [PMID: 33411640 DOI: 10.1152/japplphysiol.00747.2020] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Type 2 diabetes mellitus (T2DM) is characterized by chronic hyperglycemia and progressive insulin resistance, leading to macro and microvascular dysfunction. Passive heating has potential to improve glucose homeostasis and act as an exercise mimetic. We assessed the effect of acute passive heating before or during an oral glucose tolerance test (OGTT) in people with T2DM. Twelve people with T2DM were randomly assigned to the following three conditions: 1) 3-h OGTT (control), 2) 1-h passive heating (40°C water) 30 min before an OGTT (HOT-OGTT), and 3) 1-h passive heating (40°C water) 30 min after commencing an OGTT (OGTT-HOT). Blood glucose concentration, insulin sensitivity, extracellular heat shock protein 70 (eHSP70), total energy expenditure (TEE), heart rate (HR), systolic blood pressure (SBP), and diastolic blood pressure (DBP) were recorded. Passive heating did not alter blood glucose concentration [control: 1,677 (386) arbitrary units (AU), HOT-OGTT: 1,797 (340) AU, and OGTT-HOT: 1,662 (364) AU, P = 0.28], insulin sensitivity (P = 0.15), or SBP (P = 0.18) but did increase eHSP70 concentration in both heating conditions [control: 203.48 (110.81) pg·mL-1; HOT-OGTT: 402.47 (79.02) pg·mL-1; and OGTT-HOT: 310.00 (60.53) pg·mL-1, P < 0.001], increased TEE (via fat oxidation) in the OGTT-HOT condition [control: 263 (33) kcal, HOT-OGTT: 278 (40) kcal, and OGTT-HOT: 304 (38) kcal, P = 0.001], increased HR in both heating conditions (P < 0.001), and reduced DBP in the OGTT-HOT condition (P < 0.01). Passive heating in close proximity to a glucose challenge does not alter glucose tolerance but does increase eHSP70 concentration and TEE and reduce blood pressure in people with T2DM.NEW & NOTEWORTHY This is the first study to investigate the timing of acute passive heating on glucose tolerance and extracellular heat shock protein 70 concentration ([eHSP70]) in people with type 2 diabetes. The principal novel findings from this study were that both passive heating conditions: 1) did not reduce the area under the curve or peak blood glucose concentration, 2) elevated heart rate, and 3) increased [eHSP70], which was blunted by glucose ingestion, while passive heating following glucose ingestion, 4) increased total energy expenditure, and 5) reduced diastolic blood pressure.
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Affiliation(s)
- Thomas J James
- School of Sport, Health and Exercise Science, Faculty of Science and Health, University of Portsmouth, United Kingdom.,Diabetes and Endocrinology Department, Portsmouth Hospitals University NHS Trust, Portsmouth, United Kingdom
| | - Jo Corbett
- School of Sport, Health and Exercise Science, Faculty of Science and Health, University of Portsmouth, United Kingdom
| | - Michael Cummings
- Diabetes and Endocrinology Department, Portsmouth Hospitals University NHS Trust, Portsmouth, United Kingdom
| | - Sharon Allard
- Diabetes and Endocrinology Department, Portsmouth Hospitals University NHS Trust, Portsmouth, United Kingdom
| | - John S Young
- School of Pharmacy and Biomedical Sciences, Faculty of Science and Health, University of Portsmouth, United Kingdom
| | - Jonathan Towse
- School of Pharmacy and Biomedical Sciences, Faculty of Science and Health, University of Portsmouth, United Kingdom
| | - Kathryn Carey-Jones
- School of Biological Sciences, Faculty of Science and Health, University of Portsmouth, United Kingdom.,Oaks Healthcare, Cowplain Family Practice, Waterlooville, United Kingdom
| | - Clare Eglin
- School of Sport, Health and Exercise Science, Faculty of Science and Health, University of Portsmouth, United Kingdom
| | - Billy Hopkins
- School of Sport, Health and Exercise Science, Faculty of Science and Health, University of Portsmouth, United Kingdom
| | - Connor Morgan
- School of Sport, Health and Exercise Science, Faculty of Science and Health, University of Portsmouth, United Kingdom
| | - Michael Tipton
- School of Sport, Health and Exercise Science, Faculty of Science and Health, University of Portsmouth, United Kingdom
| | - Zoe L Saynor
- School of Sport, Health and Exercise Science, Faculty of Science and Health, University of Portsmouth, United Kingdom.,Diabetes and Endocrinology Department, Portsmouth Hospitals University NHS Trust, Portsmouth, United Kingdom
| | - Anthony I Shepherd
- School of Sport, Health and Exercise Science, Faculty of Science and Health, University of Portsmouth, United Kingdom.,Diabetes and Endocrinology Department, Portsmouth Hospitals University NHS Trust, Portsmouth, United Kingdom
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18
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Brunt VE, Minson CT. Heat therapy: mechanistic underpinnings and applications to cardiovascular health. J Appl Physiol (1985) 2021; 130:1684-1704. [PMID: 33792402 DOI: 10.1152/japplphysiol.00141.2020] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Cardiovascular diseases (CVD) are the leading cause of death worldwide, and novel therapies are drastically needed to prevent or delay the onset of CVD to reduce the societal and healthcare burdens associated with these chronic diseases. One such therapy is "heat therapy," or chronic, repeated use of hot baths or saunas. Although using heat exposure to improve health is not a new concept, it has received renewed attention in recent years as a growing number of studies have demonstrated robust and widespread beneficial effects of heat therapy on cardiovascular health. Here, we review the existing literature, with particular focus on the molecular mechanisms that underscore the cardiovascular benefits of this practice.
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Affiliation(s)
- Vienna E Brunt
- Department of Integrative Physiology, University of Colorado Boulder, Boulder, Colorado.,Department of Human Physiology, University of Oregon, Eugene, Oregon
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19
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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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20
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Brengelmann GL. Reply to "Letter to the editor: The venous circulation actively alters flow: a brief evolutionary perspective". Am J Physiol Heart Circ Physiol 2021; 320:H471-H473. [PMID: 33448257 DOI: 10.1152/ajpheart.00910.2020] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- George L Brengelmann
- Department of Physiology and Biophysics, University of Washington, Seattle, Washington
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21
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Taylor NAS, Lee JY, Kim S, Notley SR. Physiological interactions with personal-protective clothing, physically demanding work and global warming: An Asia-Pacific perspective. J Therm Biol 2021; 97:102858. [PMID: 33863427 DOI: 10.1016/j.jtherbio.2021.102858] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Revised: 01/07/2021] [Accepted: 01/13/2021] [Indexed: 01/03/2023]
Abstract
The Asia-Pacific contains over half of the world's population, 21 countries have a Gross Domestic Product <25% of the world's largest economy, many countries have tropical climates and all suffer the impact of global warming. That 'perfect storm' exacerbates the risk of occupational heat illness, yet first responders must perform physically demanding work wearing personal-protective clothing and equipment. Unfortunately, the Eurocentric emphasis of past research has sometimes reduced its applicability to other ethnic groups. To redress that imbalance, relevant contemporary research has been reviewed, to which has been added information applicable to people of Asian, Melanesian and Polynesian ancestry. An epidemiological triad is used to identify the causal agents and host factors of work intolerance within hot-humid climates, commencing with the size dependency of resting metabolism and heat production accompanying load carriage, followed by a progression from the impact of single-layered clothing through to encapsulating ensembles. A morphological hypothesis is presented to account for inter-individual differences in heat production and heat loss, which seems to explain apparent ethnic- and gender-related differences in thermoregulation, at least within thermally compensable states. The mechanisms underlying work intolerance, cardiovascular insufficiency and heat illness are reviewed, along with epidemiological data from the Asia-Pacific. Finally, evidence-based preventative and treatment strategies are presented and updated concerning moisture-management fabrics and barriers, dehydration, pre- and post-exercise cooling, and heat adaptation. An extensive reference list is provided, with >25 recommendations enabling physiologists, occupational health specialists, policy makers, purchasing officers and manufacturers to rapidly extract interpretative outcomes pertinent to the Asia-Pacific.
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Affiliation(s)
- Nigel A S Taylor
- Research Institute of Human Ecology, College of Human Ecology, Seoul National University, Seoul, Republic of Korea.
| | - Joo-Young Lee
- Research Institute of Human Ecology, College of Human Ecology, Seoul National University, Seoul, Republic of Korea
| | - Siyeon Kim
- Human Convergence Technology R&D Department, Korea Institute of Industrial Technology, Ansan, Republic of Korea
| | - Sean R Notley
- School of Human Kinetics, University of Ottawa, Ottawa, Canada
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22
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Sivakorn C, Wilairatana P, Krudsood S, Schultz MJ, Techarang T, Kheawsawaung K, Dondorp AM. Severe orthostatic hypotension in otherwise uncomplicated Plasmodium vivax infection. Malar J 2021; 20:28. [PMID: 33413379 PMCID: PMC7792005 DOI: 10.1186/s12936-020-03564-3] [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: 10/28/2020] [Revised: 12/16/2020] [Accepted: 12/20/2020] [Indexed: 11/16/2022] Open
Abstract
Impaired autonomic control of postural homeostasis resulting in orthostatic hypotension has been described in falciparum malaria. However, severe orthostatic intolerance in Plasmodium vivax has been rarely reported. A case of non-immune previously healthy Thai woman presenting with P. vivax infection with well-documented orthostatic hypotension is described. In addition to oral chloroquine and intravenous artesunate, the patient was treated with fluid resuscitation and norepinephrine. During hospitalization, her haemodynamic profile revealed orthostatic hypotension persisting for another three days after microscopic and polymerase chain reaction confirmed parasite clearance. Potential causes are discussed.
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Affiliation(s)
- Chaisith Sivakorn
- Department of Clinical Tropical Medicine, Faculty of Tropical Medicine, Mahidol University, 420/6 Ratchawithi Road, Ratchathewi, 10400, Bangkok, Thailand.
| | - Polrat Wilairatana
- Department of Clinical Tropical Medicine, Faculty of Tropical Medicine, Mahidol University, 420/6 Ratchawithi Road, Ratchathewi, 10400, Bangkok, Thailand
| | - Srivicha Krudsood
- Department of Tropical Hygiene, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
| | - Marcus J Schultz
- Mahidol-Oxford Research Unit (MORU), Mahidol University, Bangkok, Thailand.,Department of Intensive Care, Academic Medical Center, and Laboratory of Experimental Intensive Care and Anesthesiology (L.E.I.C.A), University of Amsterdam, Amsterdam, The Netherlands.,Nuffield Department of Medicine, Oxford University, Oxford, UK
| | - Tachpon Techarang
- School of Medicine, Walailak University, Nakhon Si Thammarat, Thailand
| | - Khanittha Kheawsawaung
- Hospital for Tropical Diseases, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
| | - Arjen M Dondorp
- Mahidol-Oxford Research Unit (MORU), Mahidol University, Bangkok, Thailand.,Department of Intensive Care, Academic Medical Center, and Laboratory of Experimental Intensive Care and Anesthesiology (L.E.I.C.A), University of Amsterdam, Amsterdam, The Netherlands.,Nuffield Department of Medicine, Oxford University, Oxford, UK
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23
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Shen C, Wei D, Wang G, Kang Y, Yang F, Xu Q, Xia L, Liu J. Swine hemorrhagic shock model and pathophysiological changes in a desert dry-heat environment. PLoS One 2021; 16:e0244727. [PMID: 33400711 PMCID: PMC7785222 DOI: 10.1371/journal.pone.0244727] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2020] [Accepted: 12/15/2020] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND This study aimed to establish a traumatic hemorrhagic shock (THS) model in swine and examine pathophysiological characteristics in a dry-heat environment. METHODS Forty domestic Landrace piglets were randomly assigned to four study groups: normal temperature non-shock (NS), normal temperature THS (NTHS), desert dry-heat non-shock (DS), and desert dry-hot THS (DTHS) groups. The groups were exposed to either normal temperature (25°C) or dry heat (40.5°C) for 3 h. To induce THS, anesthetized piglets in the NTHS and DTHS groups were subjected to liver trauma and hypovolemic shock until death, and piglets in the NS and DS groups were euthanized at 11 h and 4 h, respectively. Body temperature, blood gas, cytokine production, and organ function were assessed before and after environmental exposure at 0 h and at every 30 min after shock to death. Hemodynamics was measured post exposure and post-shock at 0 h and at every 30 min after shock to death. RESULTS Survival, body temperature, oxygen delivery, oxygen consumption, and cardiac output were significantly different for traumatic hemorrhagic shock in the dry-heat groups compared to those in the normal temperature groups. Lactic acid and IL-6 had a marked increase at 0.5 h, followed by a progressive and rapid increase in the DTHS group. CONCLUSIONS Our findings suggest that the combined action of a dry-heat environment and THS leads to higher oxygen metabolism, poorer hemodynamic stability, and earlier and more severe inflammatory response with higher mortality.
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Affiliation(s)
- Caifu Shen
- Key Laboratory of Special Environmental Medicine of Xinjiang, General Hospital of Xinjiang Military Command of the Chinese People’s Liberation Army, Urumqi, China
| | - Dunhong Wei
- Key Laboratory of Special Environmental Medicine of Xinjiang, General Hospital of Xinjiang Military Command of the Chinese People’s Liberation Army, Urumqi, China
| | - Guangjun Wang
- Key Laboratory of Special Environmental Medicine of Xinjiang, General Hospital of Xinjiang Military Command of the Chinese People’s Liberation Army, Urumqi, China
| | - Yan Kang
- The 69240 Army Hospital of the Chinese People’s Liberation Army, Xinjiang, Urumqi, China
| | - Fan Yang
- Key Laboratory of Special Environmental Medicine of Xinjiang, General Hospital of Xinjiang Military Command of the Chinese People’s Liberation Army, Urumqi, China
| | - Qin Xu
- Key Laboratory of Special Environmental Medicine of Xinjiang, General Hospital of Xinjiang Military Command of the Chinese People’s Liberation Army, Urumqi, China
| | - Liang Xia
- Key Laboratory of Special Environmental Medicine of Xinjiang, General Hospital of Xinjiang Military Command of the Chinese People’s Liberation Army, Urumqi, China
| | - Jiangwei Liu
- Key Laboratory of Special Environmental Medicine of Xinjiang, General Hospital of Xinjiang Military Command of the Chinese People’s Liberation Army, Urumqi, China
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24
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Gravel H, Chaseling GK, Barry H, Debray A, Gagnon D. Cardiovascular control during heat stress in older adults: time for an update. Am J Physiol Heart Circ Physiol 2020; 320:H411-H416. [PMID: 33275528 DOI: 10.1152/ajpheart.00536.2020] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
It is generally accepted that older adults display an impaired cardiovascular response to heat stress, and it has been suggested that this impaired response contributes to their increased risk of mortality during extreme heat events. Seminal studies have shown that cutaneous vasodilation, the redistribution of blood flow from visceral organs, and the increase in cardiac output are blunted in older adults during passive heating. The blunted rise of cardiac output was initially attributed to an inability to maintain stroke volume, suggesting that cardiac systolic and/or diastolic function does not adequately respond to the constraints of heat stress in older adults. Recent studies evaluated potential mechanisms underlying these seminal findings and their results challenge some of these initial observations. Notably, stroke volume is maintained during heat exposure in older adults and studies have provided evidence for preserved cardiac systolic and diastolic functions in this population. Nonetheless, a blunted increase in cardiac output during heat exposure remains a consistent observation in older adults, although it is now attributed to a blunted increase in heart rate. Recent studies have also evaluated the possibility that the attenuated capacity of aged skin to vasodilate contributes to a blunted increase in cardiac output during heat stress. The objective of this Mini-Review is to highlight these recent advances and challenge the long-standing view that the control of stroke volume during heat exposure is compromised in older adults. By doing so, our intent is to stimulate future studies to evaluate several unanswered questions in this area of research.
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Affiliation(s)
- Hugo Gravel
- Cardiovascular Prevention and Rehabilitation Centre, Montreal Heart Institute, Montreal, Quebec, Canada.,Research Centre, Montreal Heart Institute, Montreal, Quebec, Canada.,Department of Pharmacology and Physiology, Université de Montréal, Montreal, Quebec, Canada
| | - Georgia K Chaseling
- Cardiovascular Prevention and Rehabilitation Centre, Montreal Heart Institute, Montreal, Quebec, Canada.,Research Centre, Montreal Heart Institute, Montreal, Quebec, Canada.,Department of Pharmacology and Physiology, Université de Montréal, Montreal, Quebec, Canada
| | - Hadiatou Barry
- Cardiovascular Prevention and Rehabilitation Centre, Montreal Heart Institute, Montreal, Quebec, Canada.,Research Centre, Montreal Heart Institute, Montreal, Quebec, Canada.,Department of Pharmacology and Physiology, Université de Montréal, Montreal, Quebec, Canada
| | - Amélie Debray
- Cardiovascular Prevention and Rehabilitation Centre, Montreal Heart Institute, Montreal, Quebec, Canada.,Research Centre, Montreal Heart Institute, Montreal, Quebec, Canada.,Department of Medicine, Université de Montréal, Montreal, Quebec, Canada
| | - Daniel Gagnon
- Cardiovascular Prevention and Rehabilitation Centre, Montreal Heart Institute, Montreal, Quebec, Canada.,Research Centre, Montreal Heart Institute, Montreal, Quebec, Canada.,Department of Pharmacology and Physiology, Université de Montréal, Montreal, Quebec, Canada.,School of Kinesiology and Exercise Science, Université de Montréal, Montreal, Quebec, Canada
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25
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Chapman CL, Johnson BD, Parker MD, Hostler D, Pryor RR, Schlader Z. Kidney physiology and pathophysiology during heat stress and the modification by exercise, dehydration, heat acclimation and aging. Temperature (Austin) 2020; 8:108-159. [PMID: 33997113 PMCID: PMC8098077 DOI: 10.1080/23328940.2020.1826841] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2020] [Revised: 09/17/2020] [Accepted: 09/17/2020] [Indexed: 02/06/2023] Open
Abstract
The kidneys' integrative responses to heat stress aid thermoregulation, cardiovascular control, and water and electrolyte regulation. Recent evidence suggests the kidneys are at increased risk of pathological events during heat stress, namely acute kidney injury (AKI), and that this risk is compounded by dehydration and exercise. This heat stress related AKI is believed to contribute to the epidemic of chronic kidney disease (CKD) occurring in occupational settings. It is estimated that AKI and CKD affect upwards of 45 million individuals in the global workforce. Water and electrolyte disturbances and AKI, both of which are representative of kidney-related pathology, are the two leading causes of hospitalizations during heat waves in older adults. Structural and physiological alterations in aging kidneys likely contribute to this increased risk. With this background, this comprehensive narrative review will provide the first aggregation of research into the integrative physiological response of the kidneys to heat stress. While the focus of this review is on the human kidneys, we will utilize both human and animal data to describe these responses to passive and exercise heat stress, and how they are altered with heat acclimation. Additionally, we will discuss recent studies that indicate an increased risk of AKI due to exercise in the heat. Lastly, we will introduce the emerging public health crisis of older adults during extreme heat events and how the aging kidneys may be more susceptible to injury during heat stress.
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Affiliation(s)
- Christopher L. Chapman
- Center for Research and Education in Special Environments, Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, NY, USA
- Department of Human Physiology, University of Oregon, Eugene, OR, USA
| | - Blair D. Johnson
- Department of Kinesiology, School of Public Health, Indiana University, Bloomington, IN, USA
| | - Mark D. Parker
- Department of Physiology and Biophysics, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, Buffalo, NY, USA
- Department of Ophthalmology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, Buffalo, NY, USA
| | - David Hostler
- Center for Research and Education in Special Environments, Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, NY, USA
| | - Riana R. Pryor
- Center for Research and Education in Special Environments, Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, NY, USA
| | - Zachary Schlader
- Department of Kinesiology, School of Public Health, Indiana University, Bloomington, IN, USA
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26
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Hyperthermia and dehydration: their independent and combined influences on physiological function during rest and exercise. Eur J Appl Physiol 2020; 120:2813-2834. [DOI: 10.1007/s00421-020-04493-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2020] [Accepted: 09/03/2020] [Indexed: 10/23/2022]
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27
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Taylor NAS, Notley SR, Lindinger MI. Heat adaptation in humans: the significance of controlled and regulated variables for experimental design and interpretation. Eur J Appl Physiol 2020; 120:2583-2595. [DOI: 10.1007/s00421-020-04489-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2020] [Accepted: 09/03/2020] [Indexed: 01/27/2023]
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28
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Foster J, Hodder SG, Lloyd AB, Havenith G. Individual Responses to Heat Stress: Implications for Hyperthermia and Physical Work Capacity. Front Physiol 2020; 11:541483. [PMID: 33013476 PMCID: PMC7516259 DOI: 10.3389/fphys.2020.541483] [Citation(s) in RCA: 55] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Accepted: 08/18/2020] [Indexed: 12/11/2022] Open
Abstract
Background Extreme heat events are increasing in frequency, severity, and duration. It is well known that heat stress can have a negative impact on occupational health and productivity, particularly during physical work. However, there are no up-to-date reviews on how vulnerability to heat changes as a function of individual characteristics in relation to the risk of hyperthermia and work capacity loss. The objective of this narrative review is to examine the role of individual characteristics on the human heat stress response, specifically in relation to hyperthermia risk and productivity loss in hot workplaces. Finally, we aim to generate practical guidance for industrial hygienists considering our findings. Factors included in the analysis were body mass, body surface area to mass ratio, body fat, aerobic fitness and training, heat adaptation, aging, sex, and chronic health conditions. Findings We found the relevance of any factor to be dynamic, based on the work-type (fixed pace or relative to fitness level), work intensity (low, moderate, or heavy work), climate type (humidity, clothing vapor resistance), and variable of interest (risk of hyperthermia or likelihood of productivity loss). Heat adaptation, high aerobic fitness, and having a large body mass are the most protective factors during heat exposure. Primary detrimental factors include low fitness, low body mass, and lack of heat adaptation. Aging beyond 50 years, being female, and diabetes are less impactful negative factors, since their independent effect is quite small in well matched participants. Skin surface area to mass ratio, body composition, hypertension, and cardiovascular disease are not strong independent predictors of the heat stress response. Conclusion Understanding how individual factors impact responses to heat stress is necessary for the prediction of heat wave impacts on occupational health and work capacity. The recommendations provided in this report could be utilized to help curtail hyperthermia risk and productivity losses induced by heat.
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Affiliation(s)
- Josh Foster
- Environmental Ergonomics Research Centre, Loughborough University, Loughborough, United Kingdom
| | - Simon G Hodder
- Environmental Ergonomics Research Centre, Loughborough University, Loughborough, United Kingdom
| | - Alex B Lloyd
- Environmental Ergonomics Research Centre, Loughborough University, Loughborough, United Kingdom
| | - George Havenith
- Environmental Ergonomics Research Centre, Loughborough University, Loughborough, United Kingdom
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29
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Cramer MN, Hieda M, Huang M, Moralez G, Crandall CG. Dietary nitrate supplementation does not influence thermoregulatory or cardiovascular strain in older individuals during severe ambient heat stress. Exp Physiol 2020; 105:1730-1741. [PMID: 32816341 DOI: 10.1113/ep088834] [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] [Received: 06/08/2020] [Accepted: 08/17/2020] [Indexed: 12/16/2022]
Abstract
NEW FINDINGS What is the central question of this study? Does dietary nitrate supplementation with beetroot juice attenuate thermoregulatory and cardiovascular strain in older adults during severe heat stress? What is the main finding and its importance? A 7-day nitrate supplementation regimen lowered resting mean arterial pressure in thermoneutral conditions. During heat stress, core and mean skin temperatures, vasodilatory responses, sweat loss, heart rate and left ventricular function were unchanged, and mean arterial pressure was only transiently reduced, post-supplementation. These data suggest nitrate supplementation with beetroot juice does not mitigate thermoregulatory or cardiovascular strain in heat-stressed older individuals. ABSTRACT This study tested the hypothesis that dietary nitrate supplementation with concentrated beetroot juice attenuates thermoregulatory and cardiovascular strain in older individuals during environmental heat stress. Nine healthy older individuals (six females, three males; aged 67 ± 5 years) were exposed to 42.5 ± 0.1°C and 34.0 ± 0.5% relative humidity conditions for 120 min before (CON) and after 7 days of dietary nitrate supplementation with concentrated beetroot juice (BRJ; 280 ml, ∼16.8 mmol of nitrate daily). Core and skin temperatures, body mass changes (indicative of whole-body sweat loss), skin blood flow and cutaneous vascular conductance, forearm blood flow and vascular conductance, heart rate, arterial blood pressures and indices of cardiac function were measured. The 7-day beetroot juice regimen increased plasma nitrate/nitrite levels from 27.4 ± 15.2 to 477.0 ± 102.5 μmol l-1 (P < 0.01) and lowered resting mean arterial pressure from 90 ± 7 to 83 ± 10 mmHg at baseline under thermoneutral conditions (P = 0.02). However, during subsequent heat stress, no differences in core and skin temperatures, skin blood flow and vascular conductance, forearm blood flow and vascular conductance, whole-body sweat loss, heart rate, and echocardiographic indices of systolic function and diastolic filling were evident following nitrate supplementation (all P > 0.05). Mean arterial pressure was lower in BRJ vs. CON during heat stress (treatment-by-time interaction: P = 0.02). Overall, these findings suggest that dietary nitrate supplementation with concentrated beetroot juice does not attenuate thermoregulatory or cardiovascular strain in older individuals exposed to severe ambient heat stress.
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Affiliation(s)
- Matthew N Cramer
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Michinari Hieda
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, TX, USA.,School of Medicine, Kyushu University, Fukuoka, Japan
| | - Mu Huang
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, TX, USA.,Applied Clinical Research, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Gilbert Moralez
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, TX, USA.,Applied Clinical Research, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Craig G Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, TX, USA
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30
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Ravanelli N, Barry H, Schlader ZJ, Gagnon D. Impact of passive heat acclimation on markers of kidney function during heat stress. Exp Physiol 2020; 106:269-281. [PMID: 32495481 DOI: 10.1113/ep088637] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2020] [Accepted: 06/01/2020] [Indexed: 12/15/2022]
Abstract
NEW FINDINGS What is the central question of this study? Does passive heat acclimation alter glomerular filtration rate and urine-concentrating ability in response to passive heat stress? What is the main finding and its importance? Glomerular filtration rate remained unchanged after passive heat stress, and heat acclimation did not alter this response. However, heat acclimation mitigated the reduction in urine-concentrating ability and reduced the incidence of albuminuria in young healthy adults after passive heat stress. Collectively, these results suggest that passive heat acclimation might improve structural integrity and reduce glomerular permeability during passive heat stress. ABSTRACT Little is known about the effect of heat acclimation on kidney function during heat stress. The purpose of this study was to determine the impact of passive heat stress and subsequent passive heat acclimation on markers of kidney function. Twelve healthy adults (seven men and five women; 26 ± 5 years of age; 72.7 ± 8.6 kg; 172.4 ± 7.5 cm) underwent passive heat stress before and after a 7 day controlled hyperthermia heat acclimation protocol. The impact of passive heat exposure on urine and serum markers of kidney function was evaluated before and after heat acclimation. Glomerular filtration rate, determined from creatinine clearance, was unchanged with passive heat stress before (pre, 133 ± 41 ml min-1 ; post, 127 ± 51 ml min-1 ; P = 0.99) and after (pre, 129 ± 46 ml min-1 ; post, 130 ± 36 ml min-1 ; P = 0.99) heat acclimation. The urine-to-serum osmolality ratio was reduced after passive heating (P < 0.01), but heat acclimation did not alter this response. In comparison to baseline, free water clearance was greater after passive heating before (pre, -0.86 ± 0.67 ml min-1 ; post, 0.40 ± 1.01 ml min-1 ; P < 0.01) but not after (pre, -0.16 ± 0.57 ml min-1 ; post, 0.76 ± 1.2 ml min-1 ; P = 0.11) heat acclimation. Furthermore, passive heating increased the fractional excretion rate of potassium (P < 0.03) but not sodium (P = 0.13) or chloride (P = 0.20). Lastly, heat acclimation reduced the fractional incidence of albuminuria after passive heating (before, 58 ± 51%; after, 8 ± 29%; P = 0.03). Collectively, these results demonstrate that passive heat stress does not alter the glomerular filtration rate. However, heat acclimation might improve urine-concentrating ability and filtration within the glomerulus.
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Affiliation(s)
- Nicholas Ravanelli
- Cardiovascular Prevention and Rehabilitation Centre, Montreal Heart Institute, Montreal, QC, Canada.,Research Centre, Montreal Heart Institute, Montreal, QC, Canada.,Department of Pharmacology and Physiology, Université de Montréal, Montreal, QC, Canada
| | - Hadiatou Barry
- Cardiovascular Prevention and Rehabilitation Centre, Montreal Heart Institute, Montreal, QC, Canada.,Research Centre, Montreal Heart Institute, Montreal, QC, Canada.,Department of Pharmacology and Physiology, Université de Montréal, Montreal, QC, Canada
| | - Zachary J Schlader
- Department of Kinesiology, School of Public Health, Indiana University, Bloomington, IN, USA
| | - Daniel Gagnon
- Cardiovascular Prevention and Rehabilitation Centre, Montreal Heart Institute, Montreal, QC, Canada.,Research Centre, Montreal Heart Institute, Montreal, QC, Canada.,Department of Pharmacology and Physiology, Université de Montréal, Montreal, QC, Canada
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Chapman CL, Benati JM, Johnson BD, Vargas NT, Lema PC, Schlader ZJ. Renal and segmental artery hemodynamics during whole body passive heating and cooling recovery. J Appl Physiol (1985) 2019; 127:974-983. [DOI: 10.1152/japplphysiol.00403.2019] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
High environmental temperatures are associated with increased risk of acute kidney injury, which may be related to reductions in renal blood flow. The susceptibility of the kidneys may be increased because of heat stress-induced changes in renal vascular resistance (RVR) to sympathetic activation. We tested the hypotheses that, compared with normothermia, increases in RVR during the cold pressor test (CPT, a sympathoexcitatory maneuver) are attenuated during passive heating and exacerbated after cooling recovery. Twenty-four healthy adults (22 ± 2 yr; 12 women, 12 men) completed CPTs at normothermic baseline, after passive heating to a rise in core temperature of ~1.2°C, and after cooling recovery when core temperature returned to ~0.2°C above normothermic baseline. Blood velocity was measured by Doppler ultrasound in the distal segment of the right renal artery (Renal, n = 24 during thermal stress, n = 12 during CPTs) or the middle portion of a segmental artery (Segmental, n = 12). RVR was calculated as mean arterial pressure divided by renal or segmental blood velocity. RVR increased at the end of CPT during normothermic baseline in both arteries (Renal: by 1.0 ± 1.0 mmHg·cm−1·s, Segmental: by 2.2 ± 1.2 mmHg·cm−1·s, P ≤ 0.03), and these increases were abolished with passive heating ( P ≥ 0.76). At the end of cooling recovery, RVR in both arteries to the CPT was restored to that of normothermic baseline ( P ≤ 0.17). These data show that increases in RVR to sympathetic activation during passive heating are attenuated and return to that of normothermic baseline after cooling recovery. NEW & NOTEWORTHY Our data indicate that increases in renal vascular resistance to the cold pressor test (i.e., sympathetic activation) are attenuated during passive heating, but at the end of cooling recovery this response returns to that of normothermic baseline. Importantly, hemodynamic responses were assessed in arteries going to (renal artery) and within (segmental artery) the kidney, which has not been previously examined in the same study during thermal and/or sympathetic stressors.
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Affiliation(s)
- Christopher L. Chapman
- Center for Research and Education in Special Environments, Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, New York
| | - Julia M. Benati
- Center for Research and Education in Special Environments, Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, New York
| | - Blair D. Johnson
- Center for Research and Education in Special Environments, Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, New York
| | - Nicole T. Vargas
- Center for Research and Education in Special Environments, Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, New York
| | - Penelope C. Lema
- Department of Emergency Medicine, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, Buffalo, New York
| | - Zachary J. Schlader
- Center for Research and Education in Special Environments, Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, New York
- Department of Kinesiology, School of Public Health–Bloomington, Indiana University, Bloomington, Indiana
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32
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The origin, significance and plasticity of the thermoeffector thresholds: Extrapolation between humans and laboratory rodents. J Therm Biol 2019; 85:102397. [DOI: 10.1016/j.jtherbio.2019.08.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2019] [Revised: 08/05/2019] [Accepted: 08/05/2019] [Indexed: 01/07/2023]
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33
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Affiliation(s)
- Rafael Dalmau
- Department of Anesthesiology, Hospital Español de Rosario, Rosario, Argentina
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34
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Abstract
In addition to its role as an environmental stressor, scientists have recently demonstrated the potential for heat to be a therapy for improving or mitigating declines in arterial health. Many studies at both ends of the scientific controls spectrum (tightly controlled, experimental vs. practical) have demonstrated the beneficial effects of heating on microvascular function (e.g., reactive hyperemia, cutaneous vascular conductance); endothelial function (e.g., flow-mediated dilation); and arterial stiffness (e.g., pulse-wave velocity, compliance, β-stiffness index). It is important to note that findings of beneficial effects are not unanimous, likely owing to the varied methodology in both heating protocols and assessments of outcome measures. Mechanisms of action for the effects of both acute and chronic heating are also understudied. Heat science is a very promising area of human physiology research, as it has the potential to contribute to approaches addressing the global cardiovascular disease burden, particularly in aging and at risk populations, and those for whom exercise is not feasible or recommended.
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Affiliation(s)
- Jem L Cheng
- Department of Kinesiology, McMaster University , Hamilton, Ontario , Canada
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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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Rozenbaum Z, Topilsky Y, Khoury S, Assi M, Balchyunayte A, Laufer-Perl M, Berliner S, Pereg D, Entin-Meer M, Havakuk O. Relationship between climate and hemodynamics according to echocardiography. J Appl Physiol (1985) 2018; 126:322-329. [PMID: 30462569 DOI: 10.1152/japplphysiol.00519.2018] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Studies performed in controlled laboratory conditions have shown that environmental thermal application may induce various circulatory changes. We aimed to demonstrate the effect of local climate on hemodynamics according to echocardiography. Echocardiographic studies conducted in ambulatory patients, 18 yr of age or older, between January 2012 and July 2016, at our medical center, for whom climate data on the day of the echocardiogram study were available, were retrospectively included in case climate data. Discomfort index, apparent temperature, temperature-humidity index, and thermal index were computed. Echocardiograms conducted in hotter months (June-November) were compared with those done in colder months (December-May). The cohort consisted of 11,348 individuals, 46.2% women, and mean age of 57.9 ± 18.1 yr. Climate indexes correlated directly with stroke volume ( r = 0.039) and e' (lateral r = 0.047; septal r = 0.038), and inversely with systolic pulmonary artery pressure (SPAP; r = -0.038) (all P values < 0.05). After adjustment for age and sex, echocardiograms conducted during June-November had a lower chance to show e' septal < 7 cm/s (odds ratio 0.88, 95% confidence interval 0.78-0.98, P = 0.017) and SPAP > 40 mmHg (odds ratio 0.81, 95% confidence interval 0.67-0.99, P = 0.04) compared with those conducted in other months. The authors concluded that climate may affect hemodynamics, according to echocardiographic assessment in ambulatory patients. NEW & NOTEWORTHY In the present study, we examined 11,348 individuals who underwent ambulatory echocardiography. Analyses of the echocardiographic studies demonstrated that environmental thermal stress, i.e., climate, may affect hemodynamics. Most notably were the effects on diastolic function. Higher values of mitral e', stroke volume, as well as ejection fraction, and lower values of systolic pulmonary artery pressure and tricuspid regurgitation were demonstrated on hotter days and seasons.
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Affiliation(s)
- Zach Rozenbaum
- Department of Cardiology, Tel Aviv Medical Center , Tel Aviv , Israel.,Sackler Faculty of Medicine, Tel Aviv University , Tel Aviv , Israel
| | - Yan Topilsky
- Department of Cardiology, Tel Aviv Medical Center , Tel Aviv , Israel.,Sackler Faculty of Medicine, Tel Aviv University , Tel Aviv , Israel
| | - Shafik Khoury
- Department of Cardiology, Tel Aviv Medical Center , Tel Aviv , Israel.,Sackler Faculty of Medicine, Tel Aviv University , Tel Aviv , Israel
| | - Milwidsky Assi
- Department of Cardiology, Tel Aviv Medical Center , Tel Aviv , Israel.,Sackler Faculty of Medicine, Tel Aviv University , Tel Aviv , Israel
| | - Asta Balchyunayte
- Department of Internal Medicine, Tel Aviv Medical Center , Tel Aviv , Israel.,Sackler Faculty of Medicine, Tel Aviv University , Tel Aviv , Israel
| | - Michal Laufer-Perl
- Department of Cardiology, Tel Aviv Medical Center , Tel Aviv , Israel.,Sackler Faculty of Medicine, Tel Aviv University , Tel Aviv , Israel
| | - Shlomo Berliner
- Department of Internal Medicine, Tel Aviv Medical Center , Tel Aviv , Israel.,Sackler Faculty of Medicine, Tel Aviv University , Tel Aviv , Israel
| | - David Pereg
- Department of Cardiology, Meir Medical Center, Kfar Saba, Israel.,Sackler Faculty of Medicine, Tel Aviv University , Tel Aviv , Israel
| | - Michal Entin-Meer
- Cardiovascular Research Laboratory, Tel Aviv Medical Center , Tel Aviv , Israel.,Sackler Faculty of Medicine, Tel Aviv University , Tel Aviv , Israel
| | - Ofer Havakuk
- Department of Cardiology, Tel Aviv Medical Center , Tel Aviv , Israel.,Sackler Faculty of Medicine, Tel Aviv University , Tel Aviv , Israel
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Caldwell JN, van den Heuvel AMJ, Kerry P, Clark MJ, Peoples GE, Taylor NAS. A vascular mechanism to explain thermally mediated variations in deep-body cooling rates during the immersion of profoundly hyperthermic individuals. Exp Physiol 2018; 103:512-522. [DOI: 10.1113/ep086760] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2017] [Accepted: 01/15/2018] [Indexed: 11/08/2022]
Affiliation(s)
- Joanne N. Caldwell
- Centre for Human and Applied Physiology, School of Medicine; University of Wollongong; Wollongong NSW 2522 Australia
| | - Anne M. J. van den Heuvel
- Centre for Human and Applied Physiology, School of Medicine; University of Wollongong; Wollongong NSW 2522 Australia
| | - Pete Kerry
- Centre for Human and Applied Physiology, School of Medicine; University of Wollongong; Wollongong NSW 2522 Australia
| | - Mitchell J. Clark
- Centre for Human and Applied Physiology, School of Medicine; University of Wollongong; Wollongong NSW 2522 Australia
| | - Gregory E. Peoples
- Centre for Human and Applied Physiology, School of Medicine; University of Wollongong; Wollongong NSW 2522 Australia
| | - Nigel A. S. Taylor
- Centre for Human and Applied Physiology, School of Medicine; University of Wollongong; Wollongong NSW 2522 Australia
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van den Heuvel AMJ, Haberley BJ, Hoyle DJR, Taylor NAS, Croft RJ. The independent influences of heat strain and dehydration upon cognition. Eur J Appl Physiol 2017; 117:1025-1037. [DOI: 10.1007/s00421-017-3592-2] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2016] [Accepted: 03/18/2017] [Indexed: 01/08/2023]
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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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Ravanelli NM, Gagnon D, Hodder SG, Havenith G, Jay O. The biophysical and physiological basis for mitigated elevations in heart rate with electric fan use in extreme heat and humidity. INTERNATIONAL JOURNAL OF BIOMETEOROLOGY 2017; 61:313-323. [PMID: 27473105 DOI: 10.1007/s00484-016-1213-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/07/2016] [Revised: 07/10/2016] [Accepted: 07/12/2016] [Indexed: 06/06/2023]
Abstract
Electric fan use in extreme heat wave conditions has been thought to be disadvantageous because it might accelerate heat gain to the body via convection. However, it has been recently shown that fan use delays increases in heart rate even at high temperatures (42 °C) in young adults. We here assess the biophysical and physiological mechanisms underlying the apparently beneficial effects of fan use. Eight males (24 ± 3 y; 80.7 ± 11.7 kg; 2.0 ± 0.1 m2) rested at either 36 °C or 42 °C, with (F) or without (NF) electric fan use (4.2 m/s) for 120 min while humidity increased every 7.5 min by 0.3 kPa from a baseline value of 1.6 kPa. Heart rate (HR), local sweat rate (LSR), cutaneous vascular conductance (CVC), core and mean skin temperatures, and the combined convective/radiative heat loss (C+R), evaporative heat balance requirements (Ereq) and maximum evaporative potential (Emax) were assessed. C+R was greater with fan use at 36 °C (F 8 ± 6, NF 2 ± 2 W/m2; P = 0.04) and more negative (greater dry heat gain) with fan use at 42 °C (F -78 ± 4, NF -27 ± 2 W/m2; P < 0.01). Consequently, Ereq was lower at 36 °C (F 38 ± 16, NF 45 ± 3 W/m2; P = 0.04) and greater at 42 °C (F 125 ± 1, NF 74 ± 3 W/m2; P < 0.01) with fan use. However, fan use resulted in a greater Emax at baseline humidity at both 36 °C (F 343 ± 10, NF 153 ± 5 W/m2; P < 0.01) and 42 °C (F 376 ± 13, NF 161 ± 4 W/m2; P < 0.01) and throughout the incremental increases in humidity. Within the humidity range that a rise in HR was prevented by fan use but not without a fan, LSR was higher in NF at both 36 °C (P = 0.04) and 42 °C (P = 0.05), and skin temperature was higher in NF at 42 °C (P = 0.05), but no differences in CVC or core temperatures were observed (all P > 0.05). These results suggest that the delayed increase in heart rate with fan use during extreme heat and humidity is associated with improved evaporative efficiency.
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Affiliation(s)
- Nicholas M Ravanelli
- School of Human Kinetics, University of Ottawa, 200 Lees Ave, Ottawa, K1N 6N5, Canada
- Thermal Ergonomics Laboratory, Faculty of Health Sciences, University of Sydney, Lidcombe, NSW, 2141, Australia
| | - Daniel Gagnon
- Cardiovascular Prevention and Rehabilitation Centre (ÉPIC), Montreal Heart Institute Research Centre, Department of Molecular and Integrative Physiology, Faculty of Medicine, Université de Montréal, Montréal, QC, Canada
| | - Simon G Hodder
- Environmental Ergonomics Research Centre, Loughborough Design School, Loughborough University, Leics, LE11 3TU, UK
| | - George Havenith
- Environmental Ergonomics Research Centre, Loughborough Design School, Loughborough University, Leics, LE11 3TU, UK
| | - Ollie Jay
- Thermal Ergonomics Laboratory, Faculty of Health Sciences, University of Sydney, Lidcombe, NSW, 2141, Australia.
- Charles Perkins Centre, University of Sydney, Camperdown, NSW, 2050, Australia.
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41
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Wilson TE. Renal sympathetic nerve, blood flow, and epithelial transport responses to thermal stress. Auton Neurosci 2016; 204:25-34. [PMID: 28043810 DOI: 10.1016/j.autneu.2016.12.007] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2016] [Revised: 11/28/2016] [Accepted: 12/20/2016] [Indexed: 12/12/2022]
Abstract
Thermal stress is a profound sympathetic stress in humans; kidney responses involve altered renal sympathetic nerve activity (RSNA), renal blood flow, and renal epithelial transport. During mild cold stress, RSNA spectral power but not total activity is altered, renal blood flow is maintained or decreased, and epithelial transport is altered consistent with a sympathetic stress coupled with central volume loaded state. Hypothermia decreases RSNA, renal blood flow, and epithelial transport. During mild heat stress, RSNA is increased, renal blood flow is decreased, and epithelial transport is increased consistent with a sympathetic stress coupled with a central volume unloaded state. Hyperthermia extends these directional changes, until heat illness results. Because kidney responses are very difficult to study in humans in vivo, this review describes and qualitatively evaluates an in vivo human skin model of sympathetically regulated epithelial tissue compared to that of the nephron. This model utilizes skin responses to thermal stress, involving 1) increased skin sympathetic nerve activity (SSNA), decreased skin blood flow, and suppressed eccrine epithelial transport during cold stress; and 2) increased SSNA, skin blood flow, and eccrine epithelial transport during heat stress. This model appears to mimic aspects of the renal responses. Investigations of skin responses, which parallel certain renal responses, may aid understanding of epithelial-sympathetic nervous system interactions during cold and heat stress.
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Affiliation(s)
- Thad E Wilson
- Division of Biomedical Sciences, Marian University College of Osteopathic Medicine, Indianapolis, IN, USA.
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42
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Nakajima Y. Controversies in the temperature management of critically ill patients. J Anesth 2016; 30:873-83. [PMID: 27351982 DOI: 10.1007/s00540-016-2200-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2015] [Accepted: 06/04/2016] [Indexed: 11/30/2022]
Abstract
Although body temperature is a classic primary vital sign, its value has received little attention compared with the others (blood pressure, heart rate, and respiratory rate). This may result from the fact that unlike the other primary vital signs, aging and diseases rarely affect the thermoregulatory system. Despite this, when humans are exposed to various anesthetics and analgesics and acute etiologies of non-infectious and infectious diseases in perioperative and intensive care settings, abnormalities may occur that shift body temperature up and down. A recent upsurge in clinical evidence in the perioperative and critical care field resulted in many clinical trials in temperature management. The results of these clinical trials suggest that aggressive body temperature modifications in comatose survivors after resuscitation from shockable rhythm, and permissive fever in critically ill patients, are carried out in critical care settings to improve patient outcomes; however, its efficacy remains to be elucidated. A recent, large multicenter randomized controlled trial demonstrated contradictory results, which may disrupt the trends in clinical practice. Thus, updated information concerning thermoregulatory interventions is essential for anesthesiologists and intensivists. Here, recent controversies in therapeutic hypothermia and fever management are summarized, and their relevance to the physiology of human thermoregulation is discussed.
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Affiliation(s)
- Yasufumi Nakajima
- Department of Anesthesiology and Intensive Care, Kansai Medical University, Shinmachi 2-3-1, Hirakata, Osaka, 573-1191, Japan.
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43
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Taylor NA, Peoples GE, Petersen SR. Load carriage, human performance, and employment standards. Appl Physiol Nutr Metab 2016; 41:S131-47. [DOI: 10.1139/apnm-2015-0486] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The focus of this review is on the physiological considerations necessary for developing employment standards within occupations that have a heavy reliance on load carriage. Employees within military, fire fighting, law enforcement, and search and rescue occupations regularly work with heavy loads. For example, soldiers often carry loads >50 kg, whilst structural firefighters wear 20–25 kg of protective clothing and equipment, in addition to carrying external loads. It has long been known that heavy loads modify gait, mobility, metabolic rate, and efficiency, while concurrently elevating the risk of muscle fatigue and injury. In addition, load carriage often occurs within environmentally stressful conditions, with protective ensembles adding to the thermal burden of the workplace. Indeed, physiological strain relates not just to the mass and dimensions of carried objects, but to how those loads are positioned on and around the body. Yet heavy loads must be borne by men and women of varying body size, and with the expectation that operational capability will not be impinged. This presents a recruitment conundrum. How do employers identify capable and injury-resistant individuals while simultaneously avoiding discriminatory selection practices? In this communication, the relevant metabolic, cardiopulmonary, and thermoregulatory consequences of loaded work are reviewed, along with concomitant impediments to physical endurance and mobility. Also emphasised is the importance of including occupation-specific clothing, protective equipment, and loads during work-performance testing. Finally, recommendations are presented for how to address these issues when evaluating readiness for duty.
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Affiliation(s)
- Nigel A.S. Taylor
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW 2522, Australia
| | - Gregory E. Peoples
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW 2522, Australia
| | - Stewart R. Petersen
- Faculty of Physical Education and Recreation, University of Alberta, Edmonton, AB T6G 2R3, Canada
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44
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Taylor NA. Overwhelming Physiological Regulation Through Personal Protection. J Strength Cond Res 2015; 29 Suppl 11:S111-8. [DOI: 10.1519/jsc.0000000000001030] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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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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Taylor NAS, Haberley BJ, Hoyle DJR. Thermal performance trials on the habitability of private bushfire shelters: part 1. INTERNATIONAL JOURNAL OF BIOMETEOROLOGY 2015; 59:983-993. [PMID: 25336107 DOI: 10.1007/s00484-014-0911-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/03/2014] [Revised: 10/10/2014] [Accepted: 10/12/2014] [Indexed: 06/04/2023]
Abstract
This communication is the first of two in which specifications for private bushfire shelters were evaluated during human trials. The purpose of this investigation (series 1) was to test the hypothesis that shelters capable of maintaining the internal environment at, or below, a modified discomfort index of 39 °C would prevent a deep-body temperature elevation of >2 °C. This was tested over 96 trials during which eight men and eight women were exposed at rest (60 min) to three regulated shelter conditions satisfying that standard: 40 °C and 70 % relative humidity, 45 °C and 50 % relative humidity and 50 °C and 30 % relative humidity. Subjects were tested twice in each condition following exercise- and heat-induced dehydration (2 % body mass reduction) and pre-heating to each of two deep-body thermal states (37.5 and 38.5 °C). Participants presented well rested and euhydrated, and pre-treatments successfully achieved the thermal and hydration targets prior to exposure. Auditory canal temperatures declined as exposures commenced, with subsequent rises of >0.5 °C not evident within any trial. However, each increment in air temperature elicited a significant elevation in the respective within-trial mean auditory canal temperature (37.4, 37.7 and 37.9 °C) and heart rate (103, 116 and 122 beats.min(-1)) when subjects were moderately hyperthermic (all P < 0.05). Nevertheless, on average, subjects successfully defended deep-body temperature at levels significantly below those associated with heat illness, and it was concluded that this thermal specification for bushfire shelters appeared adequate, providing the physical characteristics of the internal air remained stable.
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Affiliation(s)
- Nigel A S Taylor
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Northfields Avenue, Wollongong, NSW 2522, Australia,
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Taylor NAS, Haberley BJ. Thermal performance trials on the habitability of private bushfire shelters: part 2. INTERNATIONAL JOURNAL OF BIOMETEOROLOGY 2015; 59:995-1005. [PMID: 25361703 DOI: 10.1007/s00484-014-0912-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/03/2014] [Revised: 10/07/2014] [Accepted: 10/12/2014] [Indexed: 06/04/2023]
Abstract
In the preceding communication, an investigation was described in which the thermal specifications for the design of private bushfire shelters were evaluated. Since those trials were undertaken with the thermal characteristics of the air clamped, survival uncertainty persisted if the internal ambient conditions were progressively changing, as would occur within an air-tight shelter. Therefore, two further investigations were performed. In the first, changes in the physical properties of air within an air-tight shelter simulator (1.2 m(3)), initially equilibrated to 43.7 °C and 42.3 % relative humidity, were studied when pre-heated, well-hydrated males were sealed inside (N = 16; 60 min; experimental series 2). Air temperature and humidity moved sigmoidally to 40.5 °C (standard deviation (SD), 0.5) and 90.1 % (SD, 2.1). Oxygen and carbon dioxide fractional concentrations changed reciprocally, with respective terminal averages of 16.7 % (SD, 0.8) and 3.94 % (SD, 0.72). Deep-body temperature rose beyond the tenth minute to a terminal mean of 39.3 °C (SD, 0.2). In the third experimental series, these air temperature and humidity changes were reproduced in trials commencing at two different thermal states (40 °C and 70 % relative humidity; 45 °C and 50 % relative humidity). Sixteen pre-heated and slightly dehydrated men and women were investigated. In neither condition did the auditory canal temperature of any individual change by more than 2 °C or exceed 40 °C. It may be concluded, within the limits of these experiments, that the recommended thermal and dimensional specifications for bushfire shelters can provide tenable conditions for healthy, young adults.
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Affiliation(s)
- Nigel A S Taylor
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW 2522, Australia,
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48
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LEE JOSHUAF, CHRISTMAS KEVINM, MACHIN DANIELR, MCLEAN BLAKED, COYLE EDWARDF. Warm Skin Alters Cardiovascular Responses to Cycling after Preheating and Precooling. Med Sci Sports Exerc 2015; 47:1168-76. [DOI: 10.1249/mss.0000000000000539] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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49
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Chiesa ST, Trangmar SJ, Kalsi KK, Rakobowchuk M, Banker DS, Lotlikar MD, Ali L, González-Alonso J. Local temperature-sensitive mechanisms are important mediators of limb tissue hyperemia in the heat-stressed human at rest and during small muscle mass exercise. Am J Physiol Heart Circ Physiol 2015; 309:H369-80. [PMID: 25934093 PMCID: PMC4504966 DOI: 10.1152/ajpheart.00078.2015] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/02/2015] [Accepted: 04/27/2015] [Indexed: 11/30/2022]
Abstract
Limb tissue and systemic blood flow increases with heat stress, but the underlying mechanisms remain poorly understood. Here, we tested the hypothesis that heat stress-induced increases in limb tissue perfusion are primarily mediated by local temperature-sensitive mechanisms. Leg and systemic temperatures and hemodynamics were measured at rest and during incremental single-legged knee extensor exercise in 15 males exposed to 1 h of either systemic passive heat-stress with simultaneous cooling of a single leg (n = 8) or isolated leg heating or cooling (n = 7). Systemic heat stress increased core, skin and heated leg blood temperatures (Tb), cardiac output, and heated leg blood flow (LBF; 0.6 ± 0.1 l/min; P < 0.05). In the cooled leg, however, LBF remained unchanged throughout (P > 0.05). Increased heated leg deep tissue blood flow was closely related to Tb (R2 = 0.50; P < 0.01), which is partly attributed to increases in tissue V̇O2 (R2 = 0.55; P < 0.01) accompanying elevations in total leg glucose uptake (P < 0.05). During isolated limb heating and cooling, LBFs were equivalent to those found during systemic heat stress (P > 0.05), despite unchanged systemic temperatures and hemodynamics. During incremental exercise, heated LBF was consistently maintained ∼0.6 l/min higher than that in the cooled leg (P < 0.01), with LBF and vascular conductance in both legs showing a strong correlation with their respective local Tb (R2 = 0.85 and 0.95, P < 0.05). We conclude that local temperature-sensitive mechanisms are important mediators in limb tissue perfusion regulation both at rest and during small-muscle mass exercise in hyperthermic humans.
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Affiliation(s)
- Scott T Chiesa
- Centre for Sports Medicine and Human Performance, Brunel University London, Uxbridge, UK; and
| | - Steven J Trangmar
- Centre for Sports Medicine and Human Performance, Brunel University London, Uxbridge, UK; and
| | - Kameljit K Kalsi
- Centre for Sports Medicine and Human Performance, Brunel University London, Uxbridge, UK; and
| | - Mark Rakobowchuk
- Centre for Sports Medicine and Human Performance, Brunel University London, Uxbridge, UK; and
| | - Devendar S Banker
- Centre for Sports Medicine and Human Performance, Brunel University London, Uxbridge, UK; and Department of Anaesthetics, Ealing Hospital NHS Trust, Southall, UK
| | - Makrand D Lotlikar
- Centre for Sports Medicine and Human Performance, Brunel University London, Uxbridge, UK; and Department of Anaesthetics, Ealing Hospital NHS Trust, Southall, UK
| | - Leena Ali
- Centre for Sports Medicine and Human Performance, Brunel University London, Uxbridge, UK; and Department of Anaesthetics, Ealing Hospital NHS Trust, Southall, UK
| | - José González-Alonso
- Centre for Sports Medicine and Human Performance, Brunel University London, Uxbridge, UK; and
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Lee JB, Kim TW. Increased levels of FFA during passive heat loading after a 2-week repeated heat load in Koreans. INTERNATIONAL JOURNAL OF BIOMETEOROLOGY 2015; 59:473-475. [PMID: 24865598 DOI: 10.1007/s00484-014-0849-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2013] [Revised: 05/09/2014] [Accepted: 05/13/2014] [Indexed: 06/03/2023]
Abstract
The purpose of this study was to determine whether repeated heat load is closely related to circulating levels of free fatty acids (FFA) during repeated passive heat loading (PHL), defined as immersion of the lower body up to an umbilical level in hot water, 42 ± 0.5 °C (three times/week, 30 min/day) for 2 weeks. There were significant correlations between mean body temperature and FFA before and after repeated heat load (p < 0.001, respectively), and the level of FFA was significantly higher after repeated heat load during PHL (p < 0.01). The threshold of mean body temperature for lipolysis was lowered by repeated heat load and enhanced lipolysis during PHL. However, caution is needed for diabetic individuals.
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Affiliation(s)
- Jeong Beom Lee
- Department of Physiology, College of Medicine, Soonchunhyang University, 366-1 Ssangyong-dong, Cheonan, 331-946, Republic of Korea
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