Effects of hot water immersion on autonomic activity and hemodaynamics

It has been reported that the incidence of sudden death is high in the bathroom, especially in the elderly. We hypothesize that imbalance of autonomic activity during hot water immersion could result in the dysregulation of hemodynamic parameters which could predispose to cardiovascular accidents. To explore this hypothesis, we investigated alteration of autonomic nervous activity, as well as hemodynamic changes during hot water immersion in healthy elderly and young subjects. Healthy eight elderly female (mean age 65±1.8) and eight young female (mean age 20±0.7) were participated. They had hot water immersion and hot water shower with 40 degree of water temperature for 10 minutes after 10 minutes of baseline measurements. Changes in blood pressure (BP) and heart rate were measured continuously using peripheral arterial tonometry during the whole protocol. Autonomic nervous activity was evaluated by means of power spectral analysis of heart rate and blood pressure variability. Systolic BP was significantly increased in the elderly subjects by immersion (112±16 mmHg to 121±15 mmHg, p=0.007), while that change in young subjects was not significant (97±11 mmHg to 104±14 mmHg, p=0.67). Thereafter, in each group, the systolic BP was returned to basal levels. In the elderly subjects secondary overshoot of systolic BP was observed (110±20 mmHg to 121±15 mmHg, p=0.021), and the BP levels were kept during hot water immersion. Both high frequency area (HF) and low frequency area (LF) of heart rate variability were significantly increased in response to immersion in elderly as well as young subjects. However, increase in HF in response to immersion was less prominent in elderly subjects (66±52 ms2/Hz to 114±184 ms2/Hz, p=0.266) compared with young subjects (87±68 ms2/Hz to 314±309 ms2/Hz, p=0.031). Secondary overshoot of systolic BP observed in the elderly was associated with an increase in LF/HF (0.7±0.4 ms2/Hz to 2.1±5.1 ms2/Hz, p=0.068). Similar changes were observed during hot water shower, however changes were not significant in either groups. The large fluctuation of BP related to imbalance of autonomic nervous activity observed in the elderly subjects may underlie the sudden death in the bathroom. Am J Hypertens (2004) 17, 234A–234A; doi: 10.1016/j.amjhyper.2004.03.625