Water temperature affects heart rate and core body temperature during whole body immersion

Abstract

Background Whole body immersion (WI) is one of the oldest therapeutic concepts of medicine and still constitutes a significant role in the area of CAM as well as in rehabilitation facilities. Medical baths have strong effects on the cardiovascular regulation and the autonomic nervous system, mainly mediated by buoyancy, hydrostatic pressure and water temperature. However, scientific literature with respect to this medical practice is limited. In particular, little is known about the effects of different water temperatures on heart rate, heart rate variability (HRV) and body core temperature. Hence, we investigated the effects of WI with water temperatures of 33 and 36 °C (indifferent temperature) and 39 °C on heart rate, HRV and core body temperature before, during and after bathing. Methods In total 21 healthy subjects (average age: 24.3±2.3 years, 11 female, 10 male) underwent WI with water temperatures of 33 °C (WI33), 36 °C (WI36), 39 °C (WI39). “Dry-bath”(DB; bathtub without water to assure same body position as during WI) was used as a control. The procedure consisted of three successive intervals: 30 min resting in a supine position, 20 min WI and 30 min rest in the supine position. The recording of an electrocardiogram was started after 20 min of rest before WI. It was continued throughout the rest of the procedure. In addition, core body temperature was recorded using a rectal sensor. Here, we report on the effects with respect to the last 60 s at the end of each interval. Results During WI33, WI36 and DB the average heart rate was not affected (70.2, 74.2, and 67.2 beats/min) compared to baseline before WI. Correspondingly, the standard deviation of normal-to-normal heartbeats (SDNN) did not change (68, 63, 62 ms). Furthermore, the core body temperature was not affected (36.9, 37.0, 37.0 °C). However, during WI39 the heart rate increased to 97 beats/min and SDNN decreased to 24 ms. At the same time the core body temperature increased to 37.5 °C. During rest after WI39 the core body temperature stayed at 37.5 °C, but the heart rate decreased to 73.9 beats/min and SDNN increased to 60 ms. Conclusion WI with a water temperature of 39 °C increased heart rate and core body temperature and decreased HRV. Hence, WI at this temperature induces moderate cardiovascular stress and moderate hyperthermia. Spectral components of HRV and more specific analysis of temperature regulation may reveal more subtle changes during WI at different water temperatures.