Beyond Epidemiology: Understanding the Physiology of Vulnerability to Extreme Heat in At-Risk Populations

Abstract

The present thesis provides knowledge and evidence to increase the understanding of physiological vulnerability to extreme heat in at-risk populations. Specifically, Chapter 2 provides an overview of who is most at risk of heat-related morbidity and mortality during extreme heat, and how and why they may be at more risk. Chapter 3 systematically reviews and meta-analyses the experimental evidence of the effect of prescription or over-the-counter medications, previously identified by public health organizations as increasing risk, on the physiological capacity to regulate body temperature during exposure to heat stress. In Chapter 4, a double-blind, placebo-controlled, clinical trial is presented investigating the independent effect of a prescription medication, the antidepressant amitriptyline, taken as usually administered (dose and route of administration), on whole-body thermoregulatory responses to a passive, unencapsulated heat stress. Chapter 5 examines and synthesizes the experimental evidence present in the literature to better understand the role of skin blood flow, which is altered due to factors such as ageing and type 2 diabetes, on human-environmental heat exchange during heat exposure. Specifically, evidence in support of differences in skin blood flow between groups affecting heat exchange at the skin surface. Finally, in Chapter 6, biophysical modelling incorporating physiological experimental evidence is utilized to examine the environmental limits of electric fan-use in the context of the United States summer as a potential stay-at-home cooling strategy aligned with existing efforts to mitigate the spread of SARS-COV-2 – helping keep vulnerable populations such as older adults and those with co-morbidities safe during the two simultaneous health threats of extreme heat and COVID-19.