Understanding the interplay of thermal and non-thermal factors on whole-body heat exchange during heat stress

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Temperature regulation is a vital aspect of human survival. However, exposure to hot environments (higher ambient temperatures increase the requirements for the body to dissipate heat) and/or heat generated from metabolic processes (increases in metabolic rate augments the heat produced by the body and thus rate that heat must be dissipated) can lead to dangerous increases in body temperature. To offset this increase, highly developed autonomic thermoeffector responses (cutaneous vasodilation and sweating) are activated to facilitate whole-body heat loss during heat stress. However, physiological control of thermoeffector responses and therefore whole-body heat loss can vary as a function of: i) inter-individual (age, sex, other) and intra-individual factors both within (fitness, hydration, other) and beyond (number of exposures, sleep state, other) an individual's control, and ii) the actions of nonthermal factors associated with activation of sensory receptors (baroreceptors, metaboreceptors, osmoreceptors, etc.). Emerging evidence indicates that an interplay between these modulators of heat dissipation may have profound effects on an individual's physiological capacity to dissipate heat. However, our understanding of the interplay between factors remains incomplete. Thus, the main goals of this proposal is to expound the complex interplay of intra-individual factors (fitness, hydration, heat exposure duration) as well as the role of sensory receptor activation associated with baroreceptors, metaboreceptors and osmoreceptors on heat dissipation as a function of inter-individual factors of sex and age. This includes explicating the mechanisms mediating the nonthermal modulation of heat loss responses. These goals will be addressed using an experimental paradigm developed and studied at our research unit which uniquely integrates the use of our one-of-a-kind air calorimeter (device to accurately measure the heat dissipated and stored by the human body) to investigate the control mechanisms governing heat dissipation from a whole-body perspective. Characterizing the physiological interrelations of these factors on the body's physiological capacity to dissipate represents an important step toward advancing our understanding of human heat stress response. By obtaining a comprehensive understanding of the physiological factors affecting a person's ability to live and work in the heat we can generate novel heat protection strategies consisting of monitoring and management solutions and technologies that will provide the maximum level of protection to all Canadians and Canadian workers against the rising threat to human safety - heat. Importantly, the proposed research activities will attract a new cadre of trainees and drive a new generation and culture of scientific growth to address real-world challenges faced by industry and other sectors of our population affected by extreme heat spurred by a warming planet.