Effects of CO2-bath immersion (100ppm) on thermoregulatory responses in humans

Thermoregulation and thermal sensation during whole-body water immersion at different water temperatures in healthy individuals: A scoping review

BACKGROUND

Severe thermal discomfort may increase risk of drowning due to hypothermia or hyperthermia from prolonged exposure to noxious water temperatures. The importance of using a behavioral thermoregulation model with thermal sensation may predict the thermal load that the human body receives when exposed to various immersive water conditions. However, there is no thermal sensation "gold standard" model specific for water immersion. This scoping review aims to present a comprehensive overview regarding human physiological and behavioral thermoregulation during whole-body water immersion and explore the feasibility for an accepted defined sensation scale for cold and hot water immersion.

METHODS

A standard literary search was performed on PubMed, Google Scholar, and SCOPUS. The words "Water Immersion," "Thermoregulation," "Cardiovascular responses" were used either as independent searched terms and MeSH terms (Medical Subject Headings) or in combination with other text words. The inclusion criteria for clinical trials terms to thermoregulatory measurements (core or skin temperature), whole-body immersion, 18-60 years old and healthy individuals. The prementioned data were analyzed narratively to achieve the overall study objective.

RESULTS

Twenty-three published articles fulfilled the review inclusion/exclusion criteria (with nine measured behavioral responses). Our outcomes illustrated a homogenous thermal sensation in a variety of water temperatures ranges, that was strongly associated with thermal balance, and observed different thermoregulatory responses. This scoping review highlights the impact of water immersion duration on human thermoneutral zone, thermal comfort zone, and thermal sensation.

CONCLUSION

Our findings enlighten the significance of thermal sensation as a health indicator for establishing a behavioral thermal model applicable for water immersion. This scoping review provides insight for the needed development of subjective thermal model of thermal sensation in relation to human thermal physiology specific to immersive water temperature ranges within and outside the thermal neutral and comfort zone.

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

Background

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.

Methods

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.

Results

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).

Conclusions

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.