Efficacy of Hot Water Immersion versus Aerobic Exercise Training in Lowering Blood Pressure and Improving Cardiovascular Function in Adults with Untreated Hypertension
Authors: Kaiser Brendan W. , Chapman Christopher L. , Larson Emily A. , Gibson Brandon M. , Reed Emma L. , Halliwill John R. , Minson Christopher T. 
Published: May 2022

INTRODUCTIONHypertension remains among the most prevalent cardiovascular disease risk factors world‐wide. Aerobic exercise training is the current gold‐standard non‐pharmacological intervention for lowering blood pressure, yet passive heat therapy is an effective alternative means of reducing blood pressure and improving cardiovascular health for individuals that are unable or unwilling to engage in traditional exercise training. However, the effectiveness of heat therapy versus exercise training has not been compared in adults with untreated hypertension. Therefore, the purpose of this ongoing clinical trial is to compare the effectiveness of hot water immersion (HWI) versus aerobic exercise training (EX) in lowering blood pressure and improving cardiovascular function. Data presented are preliminary (mid‐point) comparisons following 15 sessions of either HWI or EX.HYPOTHESISIt was hypothesized that hot water immersion would be more effective than traditional aerobic exercise training in reducing blood pressure and improving cardiovascular function in adults with untreated hypertension.METHODSPrior to randomization, all subjects (n=6, 1F) completed resting vascular function testing, including measurements of blood pressure (automated sphygmomanometer), cardiac output (acetylene wash‐in method), and carotid‐femoral pulse wave velocity (PWV). Systemic vascular conductance (SVC) was calculated as cardiac output/mean arterial pressure (MAP). Following pre‐testing (PRE), subjects were randomized into either HWI (n=4, 1F) or EX (n=2). During HWI, subjects were immersed to the level of the sternum in 40.5°C water for 45 minutes. EX consisted of upright cycling at 60% of heart rate reserve (HRR) for 40 min, with 5 min each for warm‐up and cool‐down at 30% of HRR. Participants completed 15 sessions of either HWI or EX prior to mid‐point (MID) testing. Combined data are presented as the change from PRE as mean ± SD and were analyzed using a paired‐samples t test. Group mean data for HWI versus EX are presented as the change from PRE as means ± SD and were analyzed using an unpaired two sample t‐test.RESULTSFollowing 15 sessions of either HWI or EX, systolic blood pressure tended to be reduced (‐5±4 mmHg; p=0.10). The change in systolic blood pressure (SBP) was directionally similar between HWI and EX (∆ from PRE, HWI vs. EX; ‐3±5 vs. ‐7±7 mmHg; p=0.59), whereas the change in diastolic blood pressure (DBP) was divergent between HWI and EX (‐3±8 vs. +5±10 mmHg; p=0.43). Accordingly, changes in MAP were disparate between HWI and EX (‐3±7 vs. +2±9 mmHg; p=0.61). Cardiac output was similar between HWI and EX (‐0.09±0.71 vs. ‐0.76±1.07 L/min; p=0.53), as were changes in SVC (‐0.3±6.6 vs. ‐7.6±15.9 mL•min‐1•mmHg‐1; p=0.63). Overall, PWV was reduced by both interventions (‐0.6±0.3 m/s; p=0.01) and changes in PWV were similar between HWI and EX (‐0.6±0.4 vs. ‐0.5±0.4 m/s; p=0.72).CONCLUSIONSPreliminary data from this ongoing clinical trial suggest both hot water immersion and exercise are similarly effective in lowering systolic blood pressure and reducing arterial stiffness in people with untreated hypertension.