Reduction in central blood pressure after bathing in hot water

BACKGROUND: We evaluated the reduction in central blood pressure (BP) that occurs after bathing in hot water. METHODS: We subjected 28 Japanese hypertensive patients receiving treatment to 24 h ambulatory central BP monitoring. Japanese often bathe in hot water, and BP measurements were obtained on both bathing and nonbathing days. The patients removed the BP monitors by themselves before bathing and reattached them afterwards. RESULTS: The patients' mean age was 65.5±9.7 years (men: 46.4%) and their mean office BP was 131.2±12.6/73.0±7.5 mmHg. The mean temperature of the bathing water was 40.6±1.5°C. The postbathing reduction in central systolic BP (N=20; 140.7±26.7 to 127.7±18.4 mmHg, reduction: 13.0±22.6 mmHg; P=0.019) was greater than the equivalent reductions in brachial systolic and diastolic BP (N=28; systolic/diastolic 139.1±21.0/80.3±14.4 to 131.1±16.2/72.0±10.7 mmHg, reduction: 8.0±17.5/8.3±9.6 mmHg; P=0.023 and P<0.001, respectively). The patients' mean brachial BP decreased significantly after bathing (8.5±12.1 mmHg, P=0.001), but their brachial pulse pressure did not (-1.0±9.7 mmHg, P=0.60). Multivariate analysis showed that the postbathing reduction in central BP was affected by the reduction in the augmentation index, even after adjusting for the associated decrease in the mean brachial BP. However, the patients' night-time brachial and central BP levels did not differ significantly between bathing and nonbathing days. CONCLUSION: The postbathing decrease in central BP was 5 mmHg greater than that in brachial BP and was influenced by the reduction in wave reflection. However, night-time brachial and central BP did not differ between bathing days and nonbathing days.