Effects of repeated carbon dioxide-rich water bathing on core temperature, cutaneous blood flow and thermal sensation

Abstract.

We examined the effects of repeated artificial CO₂ (1,000 ppm) bathing on tympanic temperature (T _ty), cutaneous blood flow, and thermal sensation in six healthy males. Each subject was immersed in CO₂-rich water at a temperature of 34°C up to the level of the diaphragm for 20 min. The CO₂-rich water was prepared using a multi-layered composite hollow-fiber membrane. The CO₂ bathing was performed consecutively for 5 days. As a control study, subjects bathed in fresh water at 34°C under the same conditions. T _ty was significantly lowered during CO₂ bathing (P<0.05). Cutaneous blood flow in the immersed skin (right forearm) was significantly increased during CO₂ bathing compared with that during fresh-water bathing (P<0.05), whereas cutaneous blood flow in the non-immersed skin (chest) was not different between CO₂ and fresh-water bathing. Subjects reported a "warm" sensation during the CO₂ bathing, whereas they reported a "neutral" sensation during the fresh-water bathing. The effects of the repeated CO₂ bathing were not obvious for core temperature and cutaneous blood flow, but the thermal sensation score during the CO₂ bathing was reduced sequentially by repeated CO₂ bathing (P<0.05). These thermal effects of CO₂ bathing could be ascribed largely to the direct action of CO₂ on vascular smooth muscles and to the activity of thermoreceptors in the skin. Serial CO₂ bathing may influence the activity of thermoreceptors in the skin.