Abstract des Autors

The purpose of this study was to assess an alteration of cardiac autonomic nerve activity during water immersion. Ten healthy young males (age: 21-28 yr) were immersed in water at the temperatures of 25øC, 30øC and 34øC. Subjects sat calmly for 20 minutes in sitting position before water immersion, and then were immersed in water at subaxillary level in sitting position for 15 minutes, performing controlled breathing (15 cycle/min). Electrocardiograms were recorded continuously. Autonomic nerve activity was estimated with the analysis of power spectral by using the Fast Fourier Transformation (FFT). High (HF; 0.15-0.50 Hz) and low (LF; 0.04-0.15 Hz) frequency areas and the ratio of LF to HF (LF/HF) were calculated as the indices of cardiac parasympathetic nerve activity, sympathetic nerve activity with parasympathetic modulation, and sympathetic nerve activity, respectively. During the water immersion at 25øC, 30øC and 34øC, HF was significantly increased, while the heart rate and LF/HF were significantly decreased. There were no statistically significant differences among both of HF and LF/HF during the immersion at 25øC, 30øC and 34øC, although the rate of change in HF at the temperature of 25øC appeared to be prominent compared to those at 30øC and 34øC and some subjects showed an exaggerated change in HF immediately after immersion. These results suggest that cardiac parasympathetic nerve activity is enhanced and cardiac sympathetic nerve activity is suppressed during a short time water immersion at the thermoneutral temperature (34øC) and the temperatures of 25øC and 30øC, which are the usual temperatures found in indoor pools. Verf.-Referat