Human thermoregulation: separating thermal and nonthermal effects on the body's capacity to dissipate heat

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Temperature regulation is a vital aspect of human survival as relatively small deviations in internal body temperature can lead to profound disruptions in whole-body heat balance. Prolonged exposure to hot environments/processes and/or performing strenuous exercise can heat the body causing significant increases in internal body temperature. To offset this increase powerful and highly developed behavioral and autonomic thermoregulatory responses are activated to enhance whole-body heat loss. Inherent to this response is the concept of set-point about which internal body temperature is regulated. The body's temperature regulatory center is located in the hypothalamus of the central nervous system. Input to this center comes from temperature sensitive receptors in both the skin and the internal core regions of the body. Changes in skin and/or core temperature initiates a series of physiological actions aimed at enhancing heat dissipation. This heat is lost by contact with cool air and by sweat production, which cools your body as the sweat evaporates. However, when the body is unable to cool itself by sweating, several heat-induced illnesses such as heat stress or heat exhaustion and the more severe heat stroke can occur, and can result in death. Independent of thermal control (i.e., by changes in skin and/or core temperatures) of heat loss responses, there is increasing evidence demonstrating that nonthermal factors can have profound consequences on the body's ability to dissipate heat during heat stress. These nonthermal factors include those associated with the activation of the body's sensory receptors (i.e., baroreceptors, metaboreceptors, mechanoreceptors, etc.) as well as personal factors such as sex, aging, acclimation, etc. However, little is known about the mechanism underlying the nonthermal influence on human heat dissipation. My proposed study program is directed at understanding the separate and combined contribution of these factors during thermal challenges to human heat balance associated with elevations in environmental and metabolic (exercise) heat load. To achieve an advanced understanding of the role that nonthermal factors may play, we will study the mechanisms underlying the nonthermal modulation of the body's heat loss response from both a local and whole-body perspective. We will use the world's only whole-body calorimeter (a device for measuring heat emitted by the body) to precisely measure changes in the body's capacity to dissipate heat as function of these different factors. Moreover, in order to acquire a better understanding of the integration and coordination (interplay) of the human response to heat stress, the evaluation of thermoregulatory function will also be paralleled by the simultaneous measures of different physiological systems. By understanding the precise combination of environmental and metabolic heat loads where physiological differences in the body's capacity to dissipate heat occur in relation to these nonthermal factors, we can begin to develop a better understanding of how heat stress develops. Such information will have important practical benefits for many sectors of our society including the military, industry, sporting organizations and the general public. By understanding the interplay between thermal and nonthermal controllers on human thermoregulation, we can develop/improve management tools to control or eliminate heat stress conditions and protect the health and safety of individuals/workers during heat-stress conditions. Moreover, this knowledge can be used to stimulate the development of new technologies and solutions that will improve industry process efficiencies (e.g. ventilation and refrigeration, spot cooling techniques, new clothing designs, etc.).