An experiment was conducted to investigate the effects of bathing in artificial CO₂ spa water (CO₂ 260ppm, at 38°C for 10 minutes) on the autonomic nervous system of man in comparison with those of bathing in plain water. The heart rate, coefficient of variation of R-R intervals of ECG (CV_RR), blood pressure, and pulse wave were measured, and dynamic autonomic nervous function tests as described by Nishijo et al. were performed on eight gealthy volunteers (female).
The results obtained showed that the heart rate and height of pulse wave increased and blood pressure decreased during bathing both in artificial CO₂ spa water and plain water. However, the systolic blood pressure increased after bathing in plain water but did not increase after bathing in artificial CO₂ spa water. Though CV_RR decreased during and after bathing in plain water, it did not decrease after bathing in artificial CO₂ spa water. Furthermore, the related degree of sympathetic and parasympathetic nervous functions increased after bathing in artificial CO₂ spa water (as measured after 40 minutes and 50 minutes). These results suggest that bathing in artificial CO₂ spa water can enhance the functions of the autonomic nervous system.