Examining biophysical and physiological factors modulating human temperature regulation

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Humans are exposed to various forms of heat stress, such as during extreme heat events, occupational tasks, and physical activity. The human thermoregulatory system mitigates fatal rises in internal temperature during heat stress by initiating behavioural responses and physiological heat loss mechanisms such as sweating and vasodilation. Since perturbations in either core and/or skin temperature influence sweating and cutaneous vasodilation, the prevailing understanding of thermoregulatory control has been in relationship to core or mean body temperature (a composite of core and skin temperature). The fundamental assumption has remained that the initiation, and amplitude, of heat loss responses are proportional to elevations in core and/or mean body temperature, and any deviation is suggestive of altered thermoregulatory function. However, this oversimplification of the thermoregulatory control does not consider that changes in core and/or skin temperature are purely due to imbalances in heat transfer between the body and surrounding environment. Recent evidence has suggested that thermoregulatory responses such as sweating may not be determined by the absolute, or change, in core and/or skin temperature - highlighting the need to advance our understanding of temperature regulation in humans. Human physiological, and to an extent behavioural, thermoregulation is a complex and coordinated response including afferent thermoreceptors, central integration, efferent sympathetic activity, and end organ function. While work over the last couple decades has assessed how factors such as sex and age modify end organ function (e.g., sweat glands, cutaneous blood vessels), much less is known about thermoreceptor integration and function. Therefore, the purpose of this proposal is to evaluate how physiological and biophysical factors influence specific components of the thermoregulatory control loop. With technological advances, innovative protocols, and incorporation of thermopharmacology, these studies will provide a unique opportunity to examine the thermoregulatory control loop in humans, with particular emphasis on the impacts of age and sex on thermosensory integration. Combining these methodological approaches during passive and active heat stress will enable comprehensive evaluations of human temperature regulation. We aim to provide novel insights into the underlying mechanisms surrounding internal and peripheral temperature sensation in humans, and how this afferent information is integrated to produce a sufficient heat loss response to achieve heat balance. The results from these studies will enhance our current understanding of thermoregulatory control in humans throughout the lifespan during heat stress.