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

Abstract

Key points: A recent 30 year prospective study showed that lifelong sauna use reduces cardiovascular-related and all-cause mortality; however, the specific cardiovascular adaptations that cause this chronic protection are currently unknown. We investigated the effects of 8 weeks of repeated hot water immersion ('heat therapy') on various biomarkers of cardiovascular health in young, sedentary humans. We showed that, relative to a sham group which participated in thermoneutral water immersion, heat therapy increased flow-mediated dilatation, reduced arterial stiffness, reduced mean arterial and diastolic blood pressure, and reduced carotid intima media thickness, with changes all on par or greater than what is typically observed in sedentary subjects with exercise training. Our results show for the first time that heat therapy has widespread and robust effects on vascular function, and as such, could be a viable treatment option for improving cardiovascular health in a variety of patient populations, particularly those with limited exercise tolerance and/or capabilities.

Abstract: 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 haemodynamics, 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 on biomarkers of vascular function in young, sedentary subjects. Twenty young, sedentary subjects were assigned to participate in 8 weeks (4-5 times per 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). Eight weeks of heat therapy increased flow-mediated dilatation from 5.6 ± 0.3 to 10.9 ± 1.0% (P < 0.01) and superficial femoral dynamic arterial compliance from 0.06 ± 0.01 to 0.09 ±0.01 mm(2) 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 s(-1) (P = 0.03), carotid intima media thickness from 0.43 ± 0.01 to 0.37 ± 0.01 mm (P < 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 dilatation. Heat therapy improved endothelium-dependent dilatation, 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.

© 2016 The Authors. The Journal of Physiology © 2016 The Physiological Society.

Figures

Figure 1

Progress through the phases of the study

Figure 2. Changes in brachial artery flow‐mediated dilatation (FMD)

FMD presented as a percentage change from baseline diameter (A), and shear‐corrected FMD (B), over 8 weeks of heat therapy (closed symbols) or thermoneutral water immersion (sham; open symbols). Data are mean ± SEM. Symbols denote results of post hoc analyses when significant main effects were observed. *P < 0.05 from 0 weeks (within group). ‡P < 0.05 from 4 weeks (within group). †P < 0.05 vs sham group at the same time point. SRAUC, area under the curve of the shear rate stimulus for vasodilatation.

Figure 3. Dynamic cross‐sectional arterial compliance, β‐stiffness index and aortic pulse wave velocity

Changes in dynamic cross‐sectional arterial compliance (A), β‐stiffness index (B) and aortic pulse wave velocity (C) over 8 weeks of heat therapy (closed symbols) or thermoneutral water immersion (sham; open symbols). Data are mean ± SEM. Symbols denote results of post hoc analyses when significant main effects were observed. *P < 0.05 from 0 weeks (within group). †P < 0.05 vs sham group at the same time point.

Figure 4. Arterial wall thickness

Changes in arterial wall thickness in the common carotid (A) and superficial femoral arteries (B) over 8 weeks of heat therapy (closed symbols) or thermoneutral water immersion (sham; open symbols). Data are mean ± SEM. Symbols denote results of post hoc analyses when significant main effects were observed. *P < 0.05 from 0 weeks (within group). †P < 0.05 vs sham group at the same time point.