A Systematic Review of the Psychological Effects of Heat Stress on Subjects in Uncooled, Sealed, Environment Suits

Abstract

This review was performed to determine if current literature is sufficient to understand the cognitive effects of heat stress for individuals in uncooled pressure suits and the timeline when these effects would occur. Recent growth in the commercial spaceflight industry has led to renewed interest in environment suits to protect against decompression events. Such suits impair the body’s thermoregulatory mechanisms leading to heat stress.22 Because of this, space suits incorporate cooling mechanisms to offload stored heat.22,32,44 However, coolant system failures have been a recurrent problem for spacecraft, particularly those affecting the systems in pressure suits.3,4 Events that force crew members to stay in suits for extended periods of time, such as off nominal landings with a delayed rescue, or coolant failures on orbit could expose crew members to significant heat stress. While the physiological effects are well documented, the cognitive effects of heat stress, which could impair one’s ability to perform critical spaceflight tasks, are less well understood. A systematic review was performed via Ovid, Pubmed, the Defense Technical Information Center, the Institute for Scientific Information Web Of Science, and Google Scholar. The aim was to identify English language studies measuring performance ability, body temperature, and time in individuals wearing uncooled, sealed environment suits and performing limited physical activity under hot environmental conditions. These criteria were used to ensure both space suit based and analogue based studies were detected. Twenty-eight studies representing data from five hundred fifteen individuals met inclusion criteria. The studies tested multiple variables across a range of conditions. The results show evidence for increased fatigue, increased depression, increased hostility, decreased cognitive capacity, decreased vigilance, worsened task performance, decreased psychomotor abilities, increased anxiety, decreased perception, and decreased memory. Application of the results from this review to the spacefaring population are limited because most of the reviewed studies are in analogue populations that do not match current astronauts or expected commercial spaceflight participants. Many factors, such as demographics, suit type, health status of individuals, environmental exposures and activities differ between the conditions in these studies and those expected to be experienced in spaceflight.