Passive heat therapy improves endothelial function, arterial stiffness and blood pressure in sedentary humans

The majority of cardiovascular diseases are characterized by disorders of the arteries, predominantly caused by endothelial dysfunction and arterial stiffening. Intermittent hot water immersion ("heat therapy") results in elevations in core temperature and changes in cardiovascular hemodynamics, such as cardiac output and vascular shear stress, that are similar to exercise, and thus, may provide an alternative means of improving health which could be utilized by patients with low exercise tolerance and/or capabilities. We sought to comprehensively assess the effects of 8 weeks of heat therapy biomarkers of vascular function in young, sedentary subjects. Methods: Twenty young, sedentary subjects were assigned to participate in 8 weeks (4-5x/week) of heat therapy (N = 10; immersion in a 40.5°C bath sufficient to maintain rectal temperature ≥ 38.5°C for 60 min per session) or thermoneutral water immersion (N = 10; sham). Results: Eight weeks of heat therapy increased flow-mediated dilation from 5.6 ± 0.3{%} to 10.9 ± 1.0{%} (P {\textless} 0.01) and superficial femoral dynamic arterial compliance from 0.06 ± 0.01 to 0.09 ±0.01 mm2 mmHg-1 (P = 0.03), and reduced (i.e., improved) aortic pulse wave velocity from 7.1 ± 0.3 to 6.1 ± 0.3 m sec-1 (P = 0.03), carotid intima media thickness from 0.43 ± 0.01 to 0.37 ± 0.01 mm (P {\textless} 0.001), and mean arterial blood pressure from 83 ± 1 to 78 ± 2 mmHg (P = 0.02). No changes were observed in the sham group or for carotid arterial compliance, superficial femoral intima media thickness or endothelium-independent dilation. Conclusions: Heat therapy improved endothelium-dependent dilation, arterial stiffness, intima media thickness, and blood pressure, indicating improved cardiovascular health. These data suggest heat therapy may provide a simple and effective tool for improving cardiovascular health in various populations.