Physiological and perceptual responses of exposure to different thermal environments at low pressure (61.6 kPa)

In aerospace and military activities, people tend to encounter hypobaric and hypoxic extreme environments caused by the high-altitude, which can lead to physiological and perceptual changes of the human body, thus affecting work efficiency and health. In this study, ambient temperature is set at 21 °C, 26 °C, 30 °C, and altitude is set at 4000 m, with humidity of 40% and air velocity of less than 0.3 m/s. Besides, 13 healthy subjects were recruited to continuously measure their physiological parameters, including axillary temperature, local skin temperature, blood oxygen saturation, heart rate, and blood pressure, and the subjective parameters of overall and local thermal sensation. The main results are as follows: At 21 °C, the axillary temperature declined slightly over time. Also, there was a linear correlation between local skin temperature and thermal sensation. The heart rate and sweating rate under 30 °C were higher than under other conditions(P < 0.05). However, there was no significant difference in sweating rate between 21 °C and 26 °C(P = 0.99). Meanwhile, the sweat volume increased linearly with time under the three conditions(P < 0.001). The blood oxygen saturation was 82.2–83.6% at low pressure(61.6 kPa). Regarding thermal sensations, more than 84% of people felt neutral at 26 °C. This study found that the feet and calves were most sensitive to environmental temperature at 61.6 kPa. The human body's mean sensation thermal vote(MSTV) was kept in the range of −0.5∼+0.5, and the mean skin temperature in the thermal comfort zone was about 32.3–33.9 °C. Also, the recommended environmental temperature should be in the range of 23.3–28.6 °C.