University of Arizona (1982–1985)
In 1982, I followed Dr. Jack Wilmore, another of my UC Davis professors, to the Department of Exercise Science at the University of Arizona where I accepted an academic position as assistant professor and continued to focus my research efforts on physiological impacts of exercising in the heat and adaptation to the microgravity environment of space. Living in the extreme desert heat of Tucson motivated research in my interest of physiological adaptation to heat. My graduate student, Chris Kirby, conducted an intense investigation where we were able to demonstrate that heat dissipation from sweat evaporation became more efficient following acclimatization to exercise in the heat because of an increase in the ability of the sweat glands to absorb sodium [4]. We also observed this improved ability to absorb water and sodium by the kidneys; our collection of total body water intake and output along with total caloric exchange over an acclimation period of 10 days allowed us for the first time to demonstrate that the expansion of plasma volume during heat acclimatization was the result of an expansion of total body water [5] rather than the hypothesized transfer of fluid from extravascular (interstitial) space to the intravascular space [6]. Ken McKeever, one of my doctoral students who worked in the Animal Sciences department, went on to conduct experiments in dogs and horses to demonstrate that plasma volume expansion during chronic exposure to extreme heat and physical activity appeared to be a universal adaptation across species. However, physiological mechanisms appeared to be species specific, since dogs relied mainly on fluid intake through thirst [7] while horses relied primarily on improved renal tubular reabsorption of urea [8] in contrast to renal tubular sodium and water reabsorption observed in humans.
In addition to research in the area of physiological adaptation to heat, I continued my collaborative research efforts with NASA on understanding the physiology underlying the orthostatic intolerance that accompanies prolonged exposure to low-gravity environments such as those of space. With Tom Sather, another of my doctoral students, we used lower body negative pressure (LBNP) to describe the underlying physiology responsible for the ability of some individuals who tolerated orthostatic stress quite well with robust abilities to compensate for the stress of standing in gravity (we called these individuals ‘high’ tolerant) compared to others who experienced instability and fainting symptoms [9].