Comparison of low-concentration carbon dioxide-enriched and tap water immersion on body temperature after passive...

Because carbon dioxide (CO₂)-enriched water causes cutaneous vasodilation, immersion in CO₂-enriched water facilitates heat transfer from the body to the water or from the water to the body. Consequently, immersion in CO₂-enriched water raises or reduces body temperature faster than immersion in fresh water. However, it takes time to dissolve CO₂ in tap water and because the dissolved CO₂ concentration decreases over time, the actual CO₂ concentration is likely lower than the stated target concentration. However, it is unclear whether water containing a lower CO₂ concentration would also cool the body faster than fresh water after body temperature had been increased.

Ten healthy males (mean age = 20 ± 1 years) participated in the study. Participants were first immersed for 15 min in a tap water bath at 40 °C to raise body temperature. They then moved to a tap water or CO₂-enriched water bath at 30 °C to reduce body temperature. The CO₂ concentration was set at 500 ppm. The present study measured cooling time and cooling rate (slope of the regression line relating auditory canal temperature (T_ac) to cooling time) to assess the cooling effect of CO₂-enriched water immersion.

Immersion in 40 °C tap water caused T_ac to rise 0.64 ± 0.25 °C in the tap water session and 0.62 ± 0.27 °C in the CO₂-enriched water session (P > 0.05). During the 30 °C water immersion, T_ac declined to the baseline within 13 ± 6 min in tap water and 10 ± 6 min in CO₂-enriched water (P > 0.05). Cooling rates were 0.08 ± 0.06 °C/min in tap water and 0.08 ± 0.04 °C/min in CO₂-enriched water (P > 0.05).

CO₂-enriched water containing 500 ppm CO₂ did not cool faster than tap water immersion. This suggests that when the water temperature is 30 °C, a CO₂ concentration of 500 ppm is insufficient to obtain the advantageous cooling effect during water immersion after body temperature has been increased.