To clarify possible involvement of hot spring bathing in the occurrence of acute myocardial infarction and cerebral infarction at Kusatsu, its effects on blood pressure, heart rate, plasma cortisol and hematocrit were examined in 9 healthy young men. Abrupt increase in systolic blood pressure was observed immediately after starting a 3-minute 47°C or a 10-minute 42°C hot-spring bath. Both systolic and diastolic blood pressure were abruptly decreased one minute after completing either 47°C or 42°C bathing. The heart rate was increased gradually after the start of either 47°C or 42°C bathing and was decreased gradually after the completion of either 47°C or 42°C bathing. It was considered that the plasma Cortisol level was increased 15 minutes after starting 47°C bathing and the hematocrit was increased 15 minutes after starting 42°C bathing. We have already reported that fibrinolytic activity was decreased and platelet function was activated by 47°C bathing. Taken together, it is suggested that the mechanism of the occurrence of thrombotic diseases after hot spring bathing may be explained by considering transient changes in blood pressure, heart rate, blood viscosity, fibrinolytic activity and platelet function induced by hyperthermal stress.

A total of 422 patients who were hospitalized in the Division of Rehabilitation, Kusatsu Branch Hospital of the Gunma University Hospital from 1986 to 1996 was analysed with respect to the patients' sex, age, place of residence, disease, complications, day from onset to admission to our hospital, days of treatment in the hospital, outcome, reason to receive rehabilitation, persons who took care of the patient, and family members. Of the 422 cases, 262 (62.1%) were 65 or more years old. 193 patients (45.7%) were residents of Kusatsu, and 143 patients (33.9%) were from outside Gunma Prefecture.
With respect to diseases, cerebral diseases had the highest percentage (148 cases, 35.1%) and 277 (65.6%) cases had complications. The mean days of treatment in the hospital were 73 days. Hot-spring bathing was used for rehabilitation in 351 (83.2%) cases, resulting in improvement of clinical symptoms and quality of life in almost all cases. As to reason to receive rehabilitation in our hospital, 202 (47.9%) came of own will, 79 (18.7%) were recommended by doctors of other hospitals, and 68 (16.1%) were emergency admissions. Most patients lived alone or had only one family member of an old age and 83.2% of the persons who took care of patients were female family members. Many patients still wanted to receive rehabilitation even long after the onset of their impairment. These findings suggest that hot-spring bathing is effective for rehabilitation of various kinds of diseases. Although it has been found that many patients came to our hospital from various areas in the country expecting to rehabilitation using hot-spring water, it is difficult to follow up on them and to contact their family members for instructions.

The change in the skin surface temperature after taking a 3-minute 47°C hot-spring bath was examined in five healthy male volunteers whose mean age was 29.5 years and body mass index was 22.6kg/m², As a control, they took a 10-minute 42°C hot-spring bath after 4 days. Skin surface temperature was measured by a thermotracer in a room where the ambient temperature was maintained at 25°C and relative humidity at 38%. To eliminate any effect of diurnal variation in skin surface temperature, the experiment was started at 1 p.m. of each day. There was no significant difference in the highest value of skin surface temperature of the face, chest, arm, hand, leg and foot between both bathings. However, the abdominal skin surface temperature was slightly higher after the 3-minute 47°C bath than after the 10-minute 42°C bath. The skin surface temperature of the chest was transiently decreased after the 3-minute 47°C bath. The highest value of skin surface temperature of all areas examined after the 3-minute 47°C bath was about 34°C and did not differ from that after the 10-minute 42°C bath. These findings suggest that external heat stress gives no influence on the skin surface temperature and the transient decline of the skin surface temperature of the chest after the 3-minute 47°C bath may be due to some pathophysiological change in the vascular and respiratory systems.

The effect of hot spring bathing on nocturnal blood pressure was investigated in 6 normotensive young individuals at Kusatsu. Blood pressure and heart rate were measured at 1-hour intervals from 18:00 one day until 12:00 the following day. The experiments were performed on 2 consecutive days. Three subjects took a 10-minute 42°C hot-spring bath at 20:00 on the first experimental day but did not on the second experimental day. The order of experiments was inverted in the other 3 subjects. While not statistically significant, the nocturnal blood pressure on the “bathing” day tended to be decreased more than that on the control day. However, there was no difference in the heart rate. These findings may suggest possible involvement of hot spring bathing in the initiation of thrombotic diseases occurred in the morning hours at Kusatsu.

Effect of carbon dioxide bath on cardiovascular functions and peripheral circulation were studied using a new system of carbon dioxide bath. The subjects consisted of 13 males and 17 females, ranging from 50 to 84 years old, 67.4±8.3 in average, having the complaints resulting mainly from arteriosclerosis such as coldness on extremities or exertional pains of lower extremities. Each subject took a bath in plain water (PW) on the first experimental day and then a bath in carbon dioxide (CO₂) at the same time on the second experimental day. Both baths were done for 10min. at 39°C of water temperature. The results obtained were as follows.
1) Mean blood pressure (MBP) was elevating during bath and lowered below prebath level immediately after bath in both PW and CO₂ groups. However, MBP in CO₂ group was lower significantly (p<0.05) than in PW group 20 and 30min after bath.
2) Both body and skin temperatures were similarly elevated at all points to be measured directly after bath, and then lowerd gradually thereafter. There was no significance in changes between both groups.
4) An increase in cutaneous blood flow was observed at the same grade in both groups during and after bath, though no showing significant difference between both groups.
5) PO₂ in venous blood increased after bath, while PCO₂ decreased. However, no significant difference in these changes was observed between both groups.
6) Tendency to increase in CV R-R was observed during and after bath, though no significant difference was showed between both groups.
7) Relating to the feeling to bath, all subjects had the feeling of “warmness” at the beginning of bath and also of comfortableness during and after bath in both PW and CO₂ groups. However, there was no difference in the intensity of these feelings between both groups.
8) No side reaction due to an inhalation of carbon dioxide during bath was observed in all subjects.
From these results, it is expected that a new carbon dioxide bath results in benefit for patients with disturbance of peripheral circulation.

Effects of hot-spring bathing on plasma concentrations of diuresis-related hormones were examined. Four healthy males were asked to bath in either 47°C hot-spring water for 3 minutes (jikan-yu) or 42°C hot-spring water for 10 min. Plasma levels of human atrial natriuretic polypeptide (HANP), anti-diuretic hormone (ADH), aldosterone (ALD), and endothelin (ET) were measured at 0, 5, 15, and 30 minutes after the start of the immersion. A transient rise was found only in plasma HANP at 5 minutes in the 42°C bath, which may have been induced by the hydrostatic pressure. Plasma concentrations of ADH, ALD, and ET hormones showed no remarkable change.
These results suggest that a few minutes of hot-spring bathing may have little influence on the amount of these hormones secreted.

Effects of hyperthermia on the formation of platelet-derived microparticles (MP) and the expression of surface CD62 antigen were examined in normal human platelets. Venous blood from healthy subjects, anticoagulated with 1 volume of 3.8% sodium citrate, was heated at 37°C (control), 42°C and 47°C for 15 minutes. Then 2μl of each sample was incubated with FITC or PE-conjugated anti-human CD42b or CD62 antibodies, and assayed for MP and CD62 by flow cytometry. The percentage of MP after the incubation was not significantly different from that before the incubation nor that of control (9.9±0.6% before incubation, 10.2±0.6% at 37°C, 10.8±0.4% at 42°C and 10.3±0.3% at 47°C), CD62 positive-platelets slightly increased after the incubation, but no significant differences were observed between the control value and the values at 42°C and 47°C (1.6±0.3% at 37°C, 1.9±0.5% at 42°C and 1.7±0.3% at 47°C). These data suggest that hyperthermia has only a weak stimulatory effect on platelets and is unable to induce MP formation.