Bub-KAO tablet (50g) consisting of equimolar bicarbonate salt and succinate made it possible to use easily CO₂ bath at home. Since the obtained CO₂ concentration was not so high, we studied the circulatory effects of usual concentration of Bub-KAO bath in normal and hypertensive men.
Seven Bub-KAO tablets (KAO Co., Tokyo, Japan) were put into 350 l of 41°C simple hot spring bath (CO₂ conc. ≈300ppm). Eight normotensive subjects (32.2±4.2yrs) and 13 hypertensive patients (67.8±11.3yrs) took this artificial CO₂ bath for 10min. As a control, 12 normotensives (38.1±8.8yrs) and 12 hypertensives (51.0±8.2yrs) were immersed in 41°C simple hot spring bath for 10min. Hemodynamic functions and blood gas were followed before and after bathing for 30min in the supine position.
In normotensives, blood pressure (BP) was unchanged either by Bub-KAO or simple bath. The increase in heart rate (HR) and cardiac output (CO) and the decrease in total peripheral resistance (TPRi) after Bub-KAO bath were slightly but significantly greater than those of simple bath. In hypertensives, BP was significantly decrased after Bub-KAO bath (-17.2±6.4/-6.8±2.1mmHg) compared to simple bath. Although the increase in HR and CO (+0.55±0.22l/min) after Bub-KAO bath were not so remarkable, decrease in TPRi (-9.3±3.6 unit) was significantly greater than simple bath. Venous blood obtained 10min after Bub-KAO bath became fresh red showing a significant increase in pO₂ and pH (alkalosis) and significant decrease in pCO₂. In arterial blood, although pO₂ was unchanged, slight decrease in pCO₂ and increase in pH were also observed.
These results indicated that artificial CO₂ bath made by usual amounts of Bub-KAO tablets significantly reduced BP of the hypertensives due to vasodilating effect. Vasodilation by CO₂ bath was considered to be derived from the peripheral action of CO₂ as blood pCO₂ was rather reduced. As a basic mechanism of vasodilation by CO₂, we proposed the inhibitory effect on tissue enerqy metabolism of CO₂ as a product inhibtor of TCA cycle and subsequently, the onset of vascular autoregulation mechanism.

The effects of single bathing of the artificial mineral spring (Basukurin: Tsumura Juntendo Inc. Japan), equivalent mixture of sodium sulfate and sodium bicarbonate, were studied in 13 normal and 22 hypertensive subjects comparing with natural simple hot spring (Kirisima spa).
Blood pressure (BP: automatic sphygmomanometer), heart rate (HR), cardiac output (CO: earpiece type dye-dilution densisometer), total peripheral resistance (TPR: mean BP/cardiac index), forehead deep body temperature (DBT: Core Temp CTM 204) plasma renin activity (PRA: RIA by Habar's method), plasma norepinephrine (NE) and blood gas partial pressure (pO₂ and pCO₂) and pH were measured before and after bathing. Mineral concentration of simple hot spring and Basukurin bath (120g powder/360l simple hot spring) were 0.019% and 0.052%, respectively. The temperature and duration of bathing were both 41°C for 10min.
In normotensives, only systolic BP and TPR were significantly decreased 30min after the simple and Basukurin bathing by the same degree. HR was significantly increased throughout 30min after both bathing. CO was increased only after 10min of Basuku rin bathing. In hypertensives, systolic and diastolic BP and TPR were significantly decreased throughout 30min after simple and Basukurin bathing. The decrement in BP and TPR, however were significantly greater in Basukurin bathing. HR and CO were significantly increased after both bathing. Forehead DBT was significantly elevated after both bathing and gradually decreased throughout 30min of observation. In Basukurin bathing, although the increment in DBT was greater than simple hot spring bathing, the decrease was slower than simple hot spring bathing suggsting the protection from heat radiation by Basukurin bathing. PRA and plasma NE concentration examined in hypertensive subjects after 30min of bathing were significantly elevated only in Basukurin bathing. Although arterial gas concentration and pH were not changed after bathing, venous blood pO₂ and pH were significantly increased and pCO₂ was significantly decreased after 10min of Basukurin bathing.
These data indicates that single Basukurin bathing has more potent hypotensive effect due to vasodilation than simple hot spring. Enhanced vasodilation by Basukurin bathing is probably derived from the protection of heat radiation from the skin by the formtion of thin mineral film on the skin. Increased venous blood pO₂ and pH and decreased pCO₂ represents also the improvement of peripheral circulation assisted by vasodilation and elevated CO.