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Repeated moderate heat exposure improves limb endothelial function in humans

Limited reports suggest that sauna baths or dry sauna may improve vascular function in patients with peripheral artery disease or heart failure. However, it is unclear if repeated moderate heat exposure (RMHE) with regular warm water baths can improve endothelial function in normal aged individuals. We assessed limb endothelial‐dependent function via measuring brachial flow‐mediated dilation (FMD) in 6 elder volunteers (5 M and 1 F, 59 ± 3 yrs, 177 ± 4 cm, 88 ± 10 kg) after 4 weeks (5 days/week) of warm baths (39–42 °C for 30 min). During each bath, subjects were in the recumbent position in the bathtub with water up to their mid chest, while their forearms were not kept in water. On the days of prior, 1 day post 4 weeks of RMHE and 1 week after end of RMHE, FMD was measured with Doppler ultrasound following 5 minutes of forearm ischemia in a laboratory at ~23 °C. Endothelium‐independent vasodilation was quantified by measuring the brachial artery dilator response to sublingual nitroglycerin (0.4 mg). RMHE led to significant increases in FMD (one‐way repeated measures ANOVA, P=0.019). Compared with prior RMHE (Δ4.98 ± 0.98% from prior ischemia baseline), the FMD increased in all subjects after 4 weeks of RMHE (Δ8.48 ± 1.33%, P=0.033), and returned to baseline diameters one week after completion of RMHE (Δ5.71 ± 0.68%, P=0.915). In contrast, RMHE did not induce significant changes in the dilator response to sublingual nitroglycerin (prior, post, post 1‐wk: Δ11.91 ± 0.70%, Δ11.84 ± 1.05%, Δ11.21 ± 0.33%, P=0.684). These data suggest that repeated moderate heat exposure improves limb endothelial‐dependent function, and does not alter endothelium‐independent vasodilation in normal aged individuals. We speculate the increased blood flow seen with heat exposure may increase vessel shear stress and eNOS activity, which may in turn contribute to the improved chronic endothelial function by the repeated heat exposures. The mechanism(s) should be examined in future studies.