Graduate School of Fisheries and Environmental Sciences, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki, 852-8521, Japan.
J Physiol Anthropol. 2020 Feb 4;39(1):2. doi: 10.1186/s40101-020-0212-3.
This study examined the effects of immersion in stirred, high-concentration, artificial carbonic acid water on body cooling.
Seven healthy male students (23 ± 2 years old) participated in the experiment. Signed informed consent was obtained from all subjects before the experiment. The subjects changed into shorts and T-shirts and entered an experimental room (with room temperature controlled at 30 °C and relative humidity maintained at 70%) at least 30 min before starting the experiment. After starting the experiment, the subjects were asked to rest on an exercise bike for 5 min and then pedal for 20 min. The exercise load was set to reach 50% of each subject's presumed maximum oxygen intake at 5 min after starting exercise. Subjects then continued pedaling for 1 min to cool down. After this exercise, subjects sat on a chair and immersed forearms in tap water or artificial carbonic acid water (CO water) at 25 °C for 20 min. During immersion, tap water or CO water was stirred slowly with a pump. After immersion, subjects rested for 10 min. Skin temperature and skin blood flow (left forearm), as well as heart rate and ear canal temperature, were measured continuously. Thermal sensation and thermal comfort were measured intermittently.
Skin blood flow of the immersed forearms was higher in CO water than in tap water during immersion. The blood flow in the last 5 min (average at rest was 100%) was significantly higher in CO water (290.85 ± 84.81%) than in tap water (104.80 ± 21.99%). Thermal sensation and thermal comfort were not different between conditions. Ear canal temperature significantly declined more in CO water (- 0.56 ± 0.31 °C) than in tap water (- 0.48 ± 0.30 °C) during immersion.
Our study suggests that immersion of the forearms in slowly stirred CO water at 25 °C reduces core temperature elevated by heat stress or exercise more effectively than does tap water at the same temperature. Immersion of the forearms in stirred CO water at 25 °C could be useful as a preventive measure against heat stroke from summer work or exercise.
本研究旨在探究浸泡于搅拌式高浓度人工碳酸水中对身体降温的影响。
7 名健康男性学生（23±2 岁）参与了本实验。所有受试者在实验前均签署了知情同意书。受试者在实验前至少 30min 换上短裤和 T 恤，进入实验房间（室温控制在 30°C，相对湿度保持在 70%）。实验开始后，受试者先在健身车上休息 5min，然后蹬车 20min。运动负荷设定为运动后 5min 达到每个受试者预计最大耗氧量的 50%。然后，受试者继续蹬车 1min 以降温。运动结束后，受试者坐在椅子上，将前臂浸泡在 25°C 的自来水中或人工碳酸水中 20min。在浸泡过程中，通过泵缓慢搅拌自来水或人工碳酸水。浸泡后，受试者休息 10min。连续测量皮肤温度和皮肤血流量（左前臂）、心率和耳道温度，间歇性测量热感觉和热舒适度。
浸泡过程中，浸泡于人工碳酸水中的前臂皮肤血流量高于浸泡于自来水中的皮肤血流量。在最后 5min（平均休息时为 100%），CO 水（290.85±84.81%）中的血流量明显高于自来水（104.80±21.99%）。两种条件下的热感觉和热舒适度无差异。浸泡过程中，耳道温度在 CO 水中下降更明显（-0.56±0.31°C），而在自来水中下降较少（-0.48±0.30°C）。
我们的研究表明，与相同温度的自来水相比，25°C 下缓慢搅拌的人工碳酸水浸泡前臂可更有效地降低因热应激或运动引起的核心体温升高。25°C 下搅拌的 CO 水浸泡前臂可能有助于预防夏季工作或运动引起的中暑。
