Physical and physiological considerations for mitigating thermal stress

Abstract

To determine the type of intervention which best mitigates thermal stress within a given context, two important factors need to be taken into account: the specific characteristics of the ambient environment (temperature, humidity, air speed and mean radiant temperature) and how the thermoregulatory control system will detect and potentially physiologically compensate the applied intervention. The purpose of the present thesis was to further explore these concepts and apply newly generated knowledge to the presently pressing context of human adaptation to heatwaves. The purpose of Studies 1-3 was to further mechanistically explore and characterise how the body detects and counteracts exogenous cooling and heating loads applied internally. Specifically, study 1 sought to confirm the existence of visceral thermoreceptors, which limit the effectiveness of cold fluid ingestion to defend against heat stress, by investigating whether hot and cold fluid ingestion modifies cold-defense thermoeffectors, independently of differences in core and skin temperature. The aim of Study 2 was to determine whether these thermoreceptors could adequately detect and counteract the relatively large internal heat sink provided by ice slurry ingestion by reducing whole-body heat loss responses during exercise. Study 3, investigated whether hot and cold fluid ingestion prior to a bout of exercise could delay the onset of sweating and vasodilation responses, independently of differences in core and skin temperature. Next, study 4 examined how ambient temperature, humidity and air speed interact to modify heat balance in distinctly different, but commonly experienced, simulated heatwave conditions. Finally, study 5 combined the information from studies 1-4 in order to determine the optimal cooling strategies during hot-dry heatwave conditions which could be applied in isolation or in conjunction with electric fan use and readily-available tap water.