Chronic Heat Therapy for Improving Biomarkers of Vascular Health in Young, Healthy, Humans

Exercise training is a potent means of improving cardiovascular (CV) risk; however, exercise is challenging for many patient populations. Passive heat therapy may provide a simple and effective alternative to exercise for improving CV health, and no one has yet studied the physiological benefits of chronic heat exposure in humans. Heat exposure induces the expression of heat shock proteins, which can have a multitude of beneficial effects on the CV system, many of which are common to exercise training. In particular, these benefits include upregulation of many cellular pathways associated with improved vascular function, a predominant contributor to CV health. The goal of the study is to determine the effects of chronic passive heat therapy on vascular function in young, healthy, able-bodied individuals. The investigators will perform a randomized-controlled trial in which subjects participate in 8 weeks of either heat therapy or thermoneutral water immersion (sham). Heat therapy will entail 8 weeks of hot water immersion sufficient to raise core temperature >38.5°C for 1h, 4-5 times per week. Thermoneutral water immersion will entail 8 weeks of immersion in 36°C water for the same duration as heat therapy. In both subject groups, the investigators will measure various well-established biomarkers of vascular function before and after 8 weeks of heat therapy, including measures of arterial stiffness (arterial compliance, beta-stiffness, and pulse wave velocity), endothelium-dependent dilation (flow-mediated dilation), and intima media thickness. The investigators will investigate the effects of heat therapy on the microvasculature and on the mechanisms behind improvements in vascular function in the cutaneous microcirculation, an ideal site for pharmacodissecting the molecular pathways involved, using microdialysis paired with laser-Doppler flowmetry. If successful, these studies will serve as a basis for developing heat therapy as a novel means of improving CV risk, which has the potential to reshape the treatment of patient populations with limited exercise capabilities.