Effects of hot and humid environments

There was severe physiologic sweating in subjects under humid heat exposure, resulting in water loss that could cause electrolyte imbalance, which could lead to an increase in core temperature. To rule out this influence, subjects were given saline supplementation at regular intervals during the test: 200 mL of saline was provided after subjects entered the environmental chamber and completed each segment of the cognitive test, respectively. Drinking water was strictly prohibited during the experimental test. In addition, behavioral thermoregulatory activities (e.g., adding or subtracting clothing, borrowing a fan to dissipate heat, etc.) were not allowed during the test. A portable cardiopulmonary monitor was used to monitor the heart rate and respiratory frequency of the subjects in real time during the test to avoid the risk of heat stress. The study involved human subjects in accordance with the Declaration of Helsinki (Ethical Principles for Medical Research Involving Human Subjects), and all subjects were allowed to withdraw from the trial at any time.

First, the decrease in cognitive performance with increasing ambient temperature found in this study is consistent with the results of previous studies, so it can be inferred that ambient temperature has a negative effect on cognitive performance; second, the decrease in cognitive performance did not appear to be statistically significant when the ambient temperature was higher than 35 ℃, which may be due to the fact that after the ambient temperature was higher than 35 ℃, the body's level of environmental stress appeared to be adapted to change to ensure the The reason for this may be that after the ambient temperature is higher than 35 ℃, the body's level of environmental stress is adapted to ensure physiological homeostasis (e.g., enhanced autonomic thermoregulation), and at this time the maintenance of cognitive level is no longer the body's primary choice. Therefore, the average relative cognitive performance of subjects at ambient temperatures above 35 ℃ was significantly lower than that at 32 ℃.

The results differ from other previous studies on human cognitive performance. The possible reasons for the U-shaped distribution of relative cognitive performance are: the higher the ambient temperature, the earlier the adaptive changes of the human body to the environmental stress appeared to prioritize the balance of the human physiological level, while ignoring the priority level of the cognitive task; however, after the lowest cognitive performance appeared, with the continuation of the cognitive task, the subjects may have a compensatory effect at the mental level, which is manifested by the increase of sympathetic excitability and the production of the fight-flight effect; at the same time, the increase in body temperature caused by the moist heat exposure may cause an increase in the level of arousal, and its relative cognitive performance increased, and the trend of attenuation remained unchanged even at 150 min. It should be noted that the reason for the high cognitive performance during the 120th to 150th min (test 5) may also be related to the scallop effect at the psychological level. The high cognitive performance at this time may only exist for a short period of time, which is a benign stress response, and may decrease rapidly after a short period of high cognitive performance.

This study used an experimental approach to explore changes in human cognitive performance under multiple cognitive task stimuli during sustained exposure to a hot and humid environment. The most salient findings of this study are that human cognitive performance does not decrease monotonically with exposure time under sustained hot and humid exposure.

(1) Subjects' mean reaction time increased with increasing ambient temperature, whereas mean correctness decreased with increasing ambient temperature, but the rate of decrease began to plateau at 35-38 °C.

(2) The average correct rate and average reaction time in the first three segments of the cognitive test continued to decrease, but the correct rate and average reaction time began to increase and become shorter in the last two segments.

(3) The average relative cognitive performance tended to decrease with increasing ambient temperature, but surprisingly, it was found that the relative cognitive performance showed a U-shaped distribution throughout the exposure period, and the higher the ambient temperature, the earlier the lowest point of the U-shaped curve (i.e., the lowest point of the cognitive level) corresponded to the time. The elevation of relative cognitive performance in the latter part of the exposure time may be related to the increased arousal level induced by high temperature, as well as psychological factors such as the scallop effect and the fight-and-flight effect.

This study is of theoretical guidance to the evaluation of cognitive ability and work efficiency of people under moist heat exposure, and the scientific formulation of work plans, such as drawing on this test method can be used to evaluate the cognitive ability of people under long-term moist heat exposure and to judge the feasibility of their continued work. Or it can be used for the scientific formulation of the work plan of people under moist heat exposure to ensure that the cognitive minimum point of the operating personnel is shifted forward during the operating period, so as to ensure that most of the working time is in the period of high cognitive level in order to guarantee a higher working efficiency.

The limitation of this study is that 14 right-handed young male subjects were selected as the test sample. On the one hand, the sample size is limited, and the pattern of cognitive change obtained needs to be verified by a larger sample size; on the other hand, since the sample is all male subjects, the generalizability of the findings needs to be examined, and whether they are applicable to left-handedness, different genders, and different age groups needs to be supplemented in future studies.