A 3-min bath in 47°C hot-spring water called ‘jikan-yu’ has been recommended for over 130 years at Kusatsu-spa. There is a traditional custom of pouring hot-spring water of the same temperature over the head before entering the bath to avert an afflux of blood to the brain. The medical significance of this custom was investigated in 8 healthy male volunteers (age 31±6 years and body mass index 22.4±1.6kg/m2). There were no significant differences in plasma levels of corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH), cortisol, and β-endorphin on a comparison of findings before and after the action of pouring 20 pails of 47°C hot-spring water over the parietal and occipital areas of the head. However, the direct effect of heat stress on the internal thermosensor in the anterior hypothalamus regulating heat loss and thermogenesis was not examined in this study. Thus, it is considered that the action does not provide a direct hyperthermal stimulus to the brain stem to release stress hormones but may dilate blood vessels of the head to prepare for the abrupt afflux into the cerebral circulation of blood heated by subsequent very hot hot-spring bathing.
In order to investigate the effects of the concentration of chemical components of sea water on thermoregulatory functions, rectal, skin and mean body temperatures were measured continuously before, during total body bathing as well as during recovery period on land. Eight healthy young men were subjected in the experiment. Their physical characteristics were in average 19.8±1.0yrs in age, 169.2±5.0cm in height, 57.1±3.1kg in weight and 14.0±2.6% in body fat fraction, respectively. Each subject bathed in sea water or in tap water for 15 minutes in the long-sitting position at 38.5°C of water temperature during bathing and took recovery on land for 60 minutes. Water bathing was conducted in individual subject with the concentration of chemical components of sea water at 0, 1, 3.5 and 7%, respectively. The rectal temperature increased during bathing and decreased gradually during recovery period on land. Statistically significant difference (p<.05) between 0 and 7% of the concentration of sea water was detected in the rectal temperature during bathing and recovery period. The mean skin temperature showed a continuous increase during bathing and showed a rapid decrease during 20 minutes in recovery, and a gradual decrease after then. Statistically significant difference (p<.05) between 0 and 7% of the concentration of sea water was detected in the mean skin temperatures during recovery period. The mean body temperature also showed a continuous increase during bathing and rapid decrease during the first 20 minutes in the recovery period, and decreased gradually thereafter. Statistically significant difference (p<.01) between 0 and 7% of the concentration of sea water was detected in the mean body temperature during bathing and recovery period.
To clarify a mechanism of psychologic relaxation by artificial hot spring, the effect of hot spring bathing on psychologic sweating was studied in 11 healthy subjects (1 female and 10 males, age 26±5.7 years). After lying in the supine position for 5 minutes, the subjects were asked to take a bath with plain water or artificial hot spring for 5 minutes in the sitting position. The temperature of the bath was 40°C. To prepare the artificial hot spring, sodium sulfate tablet (Tsumura & Co.) was solved in 200L of plain water. For the measurement of psychologic sweating, Perspiro (Suzuken, Co. Ltd) was used. Sensor was attached to the first finger by biphasic adhesive tape. The psychologic sweating was induced by deep respiration, mental arithmetic, hand grip, blood pressure measurement and blood sampling. There were no statistical significant differences of CV value, heart rate, blood pressures, catecholamine values and serum β endorphin levels before and after the bathing. The psychologic sweating markedly decreased after the bathing (11.5±19.6 to 1.1±2.7 for plain water bathing, 14.9±21.9 to 1.6±5.1 for artificial hot spring, N. S.). The decrease in psychologic sweating after bathing suggests the action of psychologic relaxation by bathing.