Different Physiological Changes on Carbonated Localized Bathing of Hands and Feet in Healthy Males

Physiological changes induced by the localized bathing of hands, feet, and simultaneous hand-foot baths were studied and compared with each other in order to elucidate the physiological mechanism of hand and foot baths. Fifteen healthy adult males (32±10years old) took hand, foot, and simultaneous hand-foot carbonated (module mixture type artificial carbonated bath, at a CO2, concentration of 1,100±100 ppm, pH 4.8) and freshwater baths (pH 7.4) at 38°C, and assumed a control sitting position following a randomized controlled design. They took 7 kinds of localized baths mentioned above at 1-week intervals. Each localized bathing session involved a 5-minute rest in a sitting position, the 30-minute bathing, followed by a 10-minute rest. Subjects’physiological parameters, such as the heart rate, blood pressure, near infrared spectroscopy of the forehead, laser Doppler flowmetric findings for immersed (foot) and non-immersed (shoulder muscle) body surface capillary fiow, as well as the body temperature of sublingual and tympanic membranes were monitored. While no physiological changes occurred during the proximal 5-10 minutes after starting simultaneous hand-foot baths, the body temperature, cerebral tissue circulation, cutaneous blood flow of the non-bathed skin, and heart rate increased and the diastolic pressure decreased in the distal half of 30-minute carbonated and freshwater baths. These physiological changes would probably be due to the thermal effect. However, the proximal 5-10 minutes after staning hand and foot carbonated baths showed opposite autonomic changes, which disappeared in the simultaneous hand-foot carbonated baths. Freshwater localized hand and foot baths did not lead to such differences. The cutaneous blood flow of bathed skin of the hands and feet was also significantly different only in the carbonated baths, while no differences were obtained in the freshwater hand and foot baths. Taken together, 38 °C and 1,100 ppm carbonated localized baths (hands and feet) showed opposing heart rate variability just after staning bathing, and they induced different cutaneous blood flow changes during bathing. These physiological differences in hand and foot bathing may be due to somato-autonomic and axonal refiexes induced by skin nociceptive ion channels with different sensitivities and reactions due to the varying pH of the bathing medium, and due to different hydrostatic pressures of the hand and foot baths.