Studies on the effects of heating as well as the mineral components of hot spring water have been conducted to investigate the effects of balneotherapy. However, few studies have been conducted on the effects of hydrostatic pressure and buoyancy during water immersion. Therefore, we investigated the effect of water immersion up to the neck at thermoneutral temperature on hemostatic activity.
Nine healthy men aged 22 to 34 were immersed up to the neck in the standing position in thermoneutral water (34.0±0.5°C) for two hours. The heart rate decreased immediately after starting water immersion and remained low during the immersion. Hematocrit values (Ht) of the blood samples taken from the ante-cubital vein decreased by 3.4% in average. The decrease in Ht was more prominent in the blood samples taken from the earlobe (4.0%), suggesting that hemodilution due to fluid shift was stronger in the upper part of the body. The time until euglobulin clot lysis shortened immediately after starting the immersion. Although fibrinolytic activity was enhanced, the concentration of tissue plasminogen activator (t-PA) antigen in the blood decreased gradually during the immersion and tended to return to the original level 30 minutes after immersion. A larger decrease in the concentration of plasminogen activator inhibitor-1 (PAI-1) antigen in the blood was observed immediately after starting the immersion, and it remained low for 30 minutes after immersion. An increase in fibrinolytic activity due to the decrease in PAI-1, not in t-PA, was observed during water immersion at thermoneutral temperature and the activation of fibrinolytic system without activation of the coaguration system was also observed.

Effects of 38°C 30-minute bathing on hemostatic function and autonomic nervous function were studied in 15 48-to-72-year-old patients with cerebral infarction. Blood samples were collected three times: immediately before the bathing, at the end of 30 minutes of bathing, and 30 minutes after the bathing. Hematocrit values and fibrinogen concentrations decreased during bathing and returned to the pre-bathing levels 30 minutes after bathing. This indicates that bathing caused hemodilution due to the fluid shift. During bathing, noradrenaline decreased at a rate significantly higher than that of hemodilution while the sympathetic nervous function, which was evaluated by spectral analysis of sequential variation in arterial blood pressure, was not suppressed. The autonomic nervous system seemed to be inactive in these patients. Coagulation time (PT and APTT) and platelet factor (β-TG and PF4) showed few changes. In the fibrinolytic system, however, tissue plasminogen activator (t-PA) antigen levels increased and plasminogen activator inhibitor type-1 (PAI-1) levels decreased after 30 minutes of bathing. This suggests that fibrinolytic activity was enhanced by 38°C bathing for 30 minutes. Thus, subthermal bathing with comfort may be useful in preventing cerebral infarction.