Effects of short-term warm water immersion on cardiac baroreflex sensitivity in healthy men

Jun Sugawara,Tsubasa Tomoto

doi:10.1186/s12576-020-00762-1

Abstract

Warm water immersion (WWI) causes dizziness presumably due to a substantial drop of blood pressure. The aim of this study was to elucidate the effects of short-term WWI on cardiac baroreflex sensitivity (BRS) and the contribution of arterial stiffness to the cardiac BRS. Twelve apparent healthy men (44 ± 12 years) performed the single stand-up test after 5-min sitting in the bathtub without (Control) and with 41 °C warm water at the heart level (WWI). Cardiac BRS gain was evaluated by R–R interval response to the standing-induced drop of systolic blood pressure. In addition, before and 10 min after the single stand-up test, carotid arterial β-stiffness index was evaluated in the supine rest. BRS gain was blunted (2.9 ± 1.6 vs. 1.8 ± 1.1 ms/mmHg, P = 0.005), whereas β-stiffness index was not changed significantly after WWI. BRS gain correlated with β-stiffness index before (r = − 0.626, P = 0.028) and after WWI (r = − 0.672, P = 0.015). ANCOVA revealed that these slopes of linear regression lines remained unchanged after WWI (P = 0.350). These results indicate that a short-term WWI acutely deteriorates cardiac BRS. Individuals with stiffer arteries are relatively more susceptible to WWI because of their poor baseline BRS, which might be one of the causes of bathing-related falling in elderly persons as well as frailty.

Highlights

Passive heat therapy seems to be capable of inducing improvements in vascular health [4, 17]
Orthostatic challenge results in transient reductions of cardiac output and mean arterial pressure (MAP), and concomitant decreases in cerebral perfusion pressure and blood flow because blood is displaced from the thorax to the lower body [20]
The averaged value of two bouts was calculated as baroreflex sensitivity (BRS) gain in the control condition

Summary

Introduction

Passive heat therapy seems to be capable of inducing improvements in vascular health [4, 17]. Orthostatic challenge results in transient reductions of cardiac output and mean arterial pressure (MAP), and concomitant decreases in cerebral perfusion pressure and blood flow because blood is displaced from the thorax to the lower body [20]. In this situation, maintaining adequate blood pressure via baroreflex is likely to be an important regulatory mechanism in tolerating orthostatic hypotension and avoiding syncope [20].

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Discussion

Conclusion