Wijayanto Titis, Toramoto Sayo, Maeda Yasuhiko, Son Su-Young, Umezaki Sonomi, Tochihara Yutaka
Industrial Engineering Program, Faculty of Engineering, Universitas Gadjah Mada, Jl Grafika 2 Kampus UGM, Yogyakarta, 55281, Indonesia.
Department of Human Science, Kyushu University, 4-9-1, Shiobaru, Minami-ku, Fukuoka, 815-8540, Japan.
J Physiol Anthropol. 2017 Jan 5;36(1):8. doi: 10.1186/s40101-016-0124-4.
Heat acclimatization studies have reported that tropical natives have better physiological function to tolerate heat exposure compared to those from temperate natives, in which may result in a better ability to show a better resistance to performance losses during heat stress. In this study, we investigate whether the degree of heat acclimatization affects cognitive abilities during heat exposure by comparing heat acclimatization level of subjects from Southeast Asia and temperate natives from Japan.
Eleven tropical males from Southeast Asia and ten temperate males from Japan participated in this study and performed two types of cognitive task: short-term memory test and mental arithmetic test, under control and passive heat exposure conditions. Passive heat condition was stimulated through leg immersion protocol by immersing subjects' lower legs into a hot water maintained at 42 °C in a chamber controlled at 28 °C air temperature and 50% relative humidity.
The results show that the subjects in tropical group, who had smaller increase of rectal temperature, did not show any performance losses in both cognitive tests during heat exposure, while for Japanese group, there was performance decrement in mental arithmetic test during heat exposure (P < 0.05). We also found that the subjects in both tropical and Japanese groups tried to maintain their performance by increasing oxyhemoglobin in their prefrontal cortex area during performing the tasks during heat exposure. In addition, the subjects in the Japanese group showed higher increase of oxyhemoglobin when they performed the tasks during heat exposure than those when they performed the tasks in control condition (P < 0.05), while the subjects in tropical group did not show any differences in oxyhemoglobin during task performance between control and heating conditions.
In addition to a better ability to maintain their homeostasis during heat exposure, tropical natives from Southeast Asia showed better resistance to performance loss during heat exposure in comparison with temperate natives from Japan. The tropical natives also showed smaller increase of oxyhemoglobin indicating less cognitive effort to maintain performance.
热适应研究报告称，与温带地区的人相比，热带地区的本地人在耐受热暴露方面具有更好的生理功能，这可能使他们在热应激期间对表现下降具有更强的抵抗力。在本研究中，我们通过比较东南亚受试者和日本温带地区受试者的热适应水平，来探究热适应程度是否会影响热暴露期间的认知能力。
11名来自东南亚的热带男性和10名来自日本的温带男性参与了本研究，并在对照和被动热暴露条件下进行了两种认知任务：短期记忆测试和心算测试。被动热暴露条件通过腿部浸入方案来模拟，即将受试者的小腿浸入温度保持在42°C的热水中，实验舱内的空气温度控制在28°C，相对湿度控制在50%。
结果显示，热带组受试者的直肠温度升高幅度较小，在热暴露期间的两项认知测试中均未出现任何表现下降，而日本组在热暴露期间的心算测试中表现有所下降（P<0.05）。我们还发现，热带组和日本组的受试者在热暴露期间执行任务时，都试图通过增加前额叶皮质区域的氧合血红蛋白来维持表现。此外，日本组受试者在热暴露期间执行任务时的氧合血红蛋白增加幅度高于其在对照条件下执行任务时（P<0.05），而热带组受试者在任务执行期间，对照条件和热暴露条件下的氧合血红蛋白没有差异。
除了在热暴露期间具有更好的内稳态维持能力外，与来自日本温带地区的本地人相比，来自东南亚的热带本地人在热暴露期间对表现下降具有更强的抵抗力。热带本地人氧合血红蛋白的增加幅度也较小，表明维持表现所需的认知努力较少。
