The Air Calorimeter: an innovative tool for the scientific discovery of the human heat stress response in a warming planet

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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. This balance is easily disturbed during exposure to a hot environment and/or increases in metabolic heat production due to exercise. To offset this increase, highly developed autonomic thermoregulatory responses are activated to enhance whole-body heat loss. The Snellen air calorimeter housed at the University of Ottawa is the world's only active calorimeter capable of measuring this highly dynamic and powerful physiologic response. This unique scientific tool provides an accurate measure of the heat dissipated and stored by the body, thereby enabling leading-edge research on the human heat stress response. Without the benefit of whole-body calorimetry our ability to measure whole-body heat exchange can only be estimated by the measurement of local heat loss responses of skin blood flow and sweating (surrogate measures of whole-body heat loss) and/or body temperatures (proxy measure of body heat storage). As our research demonstrates, this can lead to misguided conclusions about an individual's level of thermal strain to a given heat stress. In this application, we are requesting the replacement of some aging instruments in imminent danger of failing permanently. We will replace these with newer, state-of-art components with greater operational responsiveness and/or measurement sensitivity that will improve our calorimetric measurement of whole-body heat exchange and body heat storage. These include i) recording system for the high-precision temperature sensors critical to the measurement of dry heat exchange and mass flow, ii) gas analysers to measure heat production and used to quantify body heat storage, and iii) Eddy current ergometer to regulate heat production during exercise. To enhance the operational capacity of our calorimeter we seek to install a load cell platform on the calorimeter floor that will permit the continuous measurement of sweat loss that with the concomitant measurement of whole-body evaporative heat loss will give us an unparalleled ability to measure whole-body sweating efficiency. Key to the improvement of the operational capability of our calorimeter will be the reconfiguration of the software platform that controls all mechanical components (heater, boiler, other) and instruments (ergometer, gas analyzers, physiological devices, other) of the calorimeter. The components requested in this application will ensure that the calorimeter remains functional to enable fundamental research in human thermoregulation leading to new discoveries in our understanding of the human heat stress response. Importantly, it 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.