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Thermal physiology, more relevant than ever before

2022; American Physiological Society; Volume: 133; Issue: 3 Linguagem: Inglês

10.1152/japplphysiol.00464.2022

8750-7587

W. Larry Kenney, George Havenith, Ollie Jay,

Spaceflight effects on biology

EditorialImpact of Climate Change on Health and PerformanceThermal physiology, more relevant than ever beforeW. Larry Kenney, George Havenith, and Ollie JayW. Larry KenneyPhysiology Program and Department of Kinesiology, The Pennsylvania State University, University Park, Pennsylvania, George HavenithEnvironmental Ergonomics Research Centre, Loughborough University, Loughborough, United Kingdom, and Ollie JayHeat and Health Research Incubator, Faculty of Medicine and Health, University of Sydney, Sydney, New South Wales, AustraliaPublished Online:13 Sep 2022https://doi.org/10.1152/japplphysiol.00464.2022This is the final version - click for previous versionMoreSectionsPDF (283 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat Extreme heat in the United States is already the nation’s top weather-related killer. On a global scale, the devastating direct and indirect health impacts of acute and chronic heat exposure are evident every year in places such as India, Pakistan, Australia, Japan, and Western Europe to name a few. As the warming effects of anthropogenic climate change continue to take hold, heat will be an enduring health hazard for decades to come. History has taught us that during heat extremes people with a low physiological and/or behavioral adaptative capacity are at the greatest risk. The most vulnerable groups include older adults, infants, people of all ages with chronic health conditions (e.g., cardiovascular disease), and outdoor workers (1).Physiology is the study of the function of living organisms. Applied physiology often involves the application of physiological knowledge to safeguard an organism’s homeostasis in the presence of perturbations, both internal (maturation, aging, disease, etc.) and external (the ambient environment, posture and movement, physical activity, etc.). The Journal of Applied Physiology, and the authors who publish their research in it, will therefore serve an essential role in 1) developing a better understanding of how future climate change will impact humans at the individual level, and 2) helping people from all walks of life find ways of surviving, and even potentially thriving, on an inevitably hotter planet.The ability of humans to regulate their body temperatures and the integrated effects of heat and humidity on the human body are unique among the animal kingdom. Heat stress impacts literally every physiological system. A deep knowledge of the separate and integrative effects of elevated body temperatures on cardiovascular, renal, respiratory, endocrine, and other systemic functions is paramount to understanding the fundamental causes of the high levels of heat-related mortality and morbidity reported among certain groups in the epidemiological literature and thus inform evidence-based solutions to protect the most vulnerable.In recent weeks and months, as heat waves have ravaged the planet, hundreds of journal articles across a variety of different disciplines, newspaper and magazine articles, and social media posts about human health consequences of heat stress have been published. Many such treatises are written by, or involve interviews with epidemiologists, meteorologists, climatologists, physicians from various specialties, or simply by media pundits. Yet often the inclusion of physiological expertise is absent, even though it is the complex physiological strain (not just heatstroke) that arises from extreme heat exposure that is ultimately responsible for most heat-related morbidity and mortality. The consequence is that incomplete or distorted pictures can emerge about the threat of extreme heat on human health and the solutions that will help.For example, heat stress risk is often assessed using only ambient temperature (which is measured fully aspirated in the shade) without full consideration for the three other environmental parameters (humidity, radiation, and wind) or the two personal parameters (activity and clothing) that define human heat stress risk (2). It is stated, without supporting physiological evidence (3), that pregnancy “compromises a woman’s ability to thermoregulate” and may thus be the cause of the elevated risk of negative birth outcomes in pregnant women following extreme heat exposure (4). A widely used and cited climatology-based model, developed by well-respected physical scientists, for assessing current and future impacts of extreme heat on human health (due to heatstroke) uses a wet-bulb temperature (Twb) of 35°C for extended periods as a threshold for human survival (5). Although the biophysical principles are sound—no skin surface heat dissipation whatsoever would be possible under such conditions, and the rapid storage of metabolic heat would inevitably lead to catastrophic hyperthermia in a matter of hours—an incorporation of physiological principles reveals that such an approach likely reaches overly conservative conclusions about the impact of future warming. Accounting for physiological phenomena, such as age-related decrements in the ability to fully wet the skin (6), climate-mediated effects on sweating efficiency and sweating requirements, as well as conditions such as hidromeiosis, almost certainly mean that the limits of human habitability are reached at substantially lower Twb values. Indeed, upper limits of heat balance in even young, healthy men and women occur closer to a Twb = 31.5°C in hot, humid environments (7, 8) when directly determined from actual human research subjects with their inherent physiological responses and variability. Biophysical modeling shows that in extreme hot, but dry environments, Twb limits for survival will even be lower than that.Similarly, despite a growing physiological basis to the contrary (9–12), public health organizations, such as the Centers for Disease Control and Prevention (13) and the New York State Department of Health (14) continue to state that simple cooling devices such as electric fans should not be used by anyone above 35°C (95°F). Although there are certainly environmental limits to the efficacy of great airflow for cooling, this advice is apparently based on an over-simplified understanding of human-environmental heat exchange that fails to acknowledge the ability of humans to sweat and thus augment skin surface evaporation, which under most circumstances is greatly accelerated with increased convection. Nevertheless, the same advice urges that fans should not be used because of their propensity to “accelerate dehydration.” We have also recently seen the World Economic Forum create a video for their 4.2 million Twitter followers in advance of a forthcoming heatwave describing the “5 of the best ways to cool down according to science”—the content of which appears to be primarily based on a media article citing as evidence nonsignificant findings and other media articles, and includes a warning against whole body cold water immersion [the advised treatment for exertional hyperthermia for maximizing the probability of survival according to the American College of Sports Medicine (15) and International Olympic Committee (16)] because of the supposed perils of “cold shock,” which physiologists will recognize as the main cause of drowning of normothermic people during sudden accidental immersion in cold open water, due to a gasping reflex and uncontrolled hyperventilation (17).Indeed, there is an entire subdiscipline of Thermal Physiology, which has a unique focus on how organisms, including humans, respond and adapt to environmental changes in temperature, including environmental extremes of heat and cold. To date, they have largely been an underused resource in research seeking to understand the impacts of current heat waves and future climate change. Although epidemiologists have taken enormous strides in helping us understand who is most vulnerable to the health impacts of extreme heat, thermal physiologists can help describe why, and subsequently, what can be done about it (18). Although climatologists can model future heatwave conditions according to different carbon emission scenarios, thermal physiologists can simulate those different futures in climate chambers and demonstrate their impact on the ability of people with different physiological profiles to work, play, and even survive.To misquote John Donne, “No discipline is an island.” Without doubt, inclusivity of different expertise areas and cross talk among scientific disciplines are essential. Silo-based scientific disciplines are clearly essential to the fundamental understanding of various aspects of climate change, but a team approach can accelerate the process. For example, adding a climate scientist with a background in biometeorology to our (WLK) research team of thermal physiologists has proved beneficial, and the establishment of the Heat and Health Research Incubator at the University of Sydney enabled us (OJ) to place thermal physiology at the center of multidisciplinary climate change research. Thermal physiology should be recognized and promoted as the optimal discipline for best describing the impact of global warming on the human body. We call on all physiologists to ensure that there is greater awareness and inclusion of their expertise, not only in the coverage of events such as heatwaves but in interdisciplinary research that is carried out in the future to develop the comprehensive solutions to the complex problems that we face as a consequence climate change.To that end, the Journal of Applied Physiology announces a Call for Papers on the Impact of Climate Change on Health and Performance.DISCLOSURESNo conflicts of interest, financial or otherwise, are declared by the authors.AUTHOR CONTRIBUTIONSW.L.K. and O.J. drafted manuscript; W.L.K., G.H., and O.J. edited and revised manuscript; W.L.K., G.H., and O.J. approved final version of manuscript.REFERENCES1. Ebi KL, Capon A, Berry P, Broderick C, de Dear R, Havenith G, Honda Y, Kovats RS, Ma W, Malik A, Morris NB, Nybo L, Seneviratne SI, Vanos J, Jay O. Hot weather and heat extremes: health risks. Lancet 398: 698–708, 2021. doi:10.1016/S0140-6736(21)01208-3. 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Crossref | PubMed | ISI | Google ScholarAUTHOR NOTESCorrespondence: W. L. Kenney ([email protected]edu). Download PDF Previous Back to Top Next FiguresReferencesRelatedInformation More from this issue > Volume 133Issue 3September 2022Pages 676-678 Crossmark Copyright & PermissionsCopyright © 2022 the American Physiological Society.https://doi.org/10.1152/japplphysiol.00464.2022PubMed35981733History Received 5 August 2022 Accepted 11 August 2022 Published online 13 September 2022 Published in print 1 September 2022 Keywordsclimate changeglobal warmingheat stress Metrics