The purpose of the study is to clarify the effects of thermal stimulation on the autonomic nervous system and the cardiovascular system using spectral analysis of the variability of heart rate and arterial pressure. In 15 healthy subjects, arterial pressure, heart rate and power spectral density of these parameters were measured during the immersion of the right hand in cold and warm water (at 5, 34, 48°C) for 2 minutes. Each parameter was unchanged in the immersion in the water at 34°C. In contrast, in the immersion in the water at 5 and 48°C, the high-frequency (0.15-0.40 Hz) power spectral density (HF) (msec²) of the heart rate variability was decreased, but the ratio of the low-frequency (0.04-0.15 Hz) power spectral density (msec²) to HF was increased. In parallel with these changes, the low-frequency (0.02-0.15 Hz) power spectral density (mmHg²) of the systolic arterial blood pressure was increased. The arterial blood pressure and the heart rate were also increased by the thermal stimulation.
　The mechanism of these responses was considered to be mediated through the somatosympathetic reflex, because the responses of these parameters occurred immediately after the immersion of the right hand in both the cold and warm water. These results indicate that thermal stimulation affects the cardiovascular system through the modulation of the autonomic nervous system in humans. Thus, the change in the environmental temperature might be one of the factors which cause myocardial infarction and sudden cardiac death.

DESCENTE SPORTS SCIENCE Vol.18/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE