Effects of simulated high altitude on body temperature and heart rate in pilot reserves during the hot-dry exposure.

Recent research has primarily focused on human thermoregulatory responses at high altitudes, but investigations involving extremely high-temperature and hypobaric compound environments are currently lacking. To address this gap in knowledge, this study aimed to enhance the prediction of human heat sensation for pilot reserves while operating in extremely hot cabins with decompression. To achieve this, an improved Predicted Heat Strain (PHS) model was developed by incorporating the influence of air pressure on metabolic rate. The model's validity was assessed through experiments conducted at different altitudes (0m, 5000m, and 8000m) and varying environmental conditions (26°C and 45 °C, 10% RH and 40% RH) within an environmental simulation cabin. During these experiments, local skin temperature, core temperature, heart rate, and blood oxygen saturation were measured. The findings revealed distinct variations in the skin temperature of the hand and foot segments across different experimental stages, and significant correlations were observed between heart rate, core temperature, and local skin temperatures. Furthermore, regression models were established to explore the relationship between heart rate and local skin temperatures. By comparing simulated and experimental core and local skin temperatures, the enhanced PHS model was successfully validated. The conclusions drawn from this study provide valuable insights for predicting thermal physiological indices accurately and conveniently in hot-dry and hypobaric environments.

Alteration of gut microbiota after heat acclimation may reduce organ damage by regulating immune factors during heat stress.

Introduction: Heat-related illnesses can lead to morbidity, which are anticipated to increase frequency with predictions of increased global surface temperatures and extreme weather events. Although heat acclimation training (HAT) could prevent heat-related diseases, the mechanisms underlying HAT-promoting beneficial changes in organ function, immunity, and gut microbes remain unclear. Methods: In the current study, we recruited 32 healthy young soldiers and randomly divided them into 4 teams to conduct HATs for 10 days: the equipment-assisted training team at high temperature (HE); the equipment-assisted training team under normal hot weather (NE); the high-intensity interval training team at high temperature (HIIT), and the control team without training. A standard heat tolerance test (HTT) was conducted before (HTT-1st) and after (HTT-2nd) the training to judge whether the participants met the heat acclimation (HA) criteria. Results: We found that the participants in both HE and NE teams had significantly higher acclimation rates (HA/total population) than whom in the HIIT team. The effects of HAT on the participants of the HE team outperformed that of the NE team. In the HA group, the differences of physiological indicators and plasma organ damage biomarkers (ALT, ALP, creatinine, LDH, α-HBDH and cholinesterase) before and after HTT-2nd were significantly reduced to those during HTT-1st, but the differences of immune factors (IL-10, IL-6, CXCL2, CCL4, CCL5, and CCL11) elevated. The composition, metabolism, and pathogenicity of gut microbes changed significantly, with a decreased proportion of potentially pathogenic bacteria (Escherichia-Shigella and Lactococcus) and increased probiotics (Dorea, Blautia, and Lactobacillus) in the HA group. Training for a longer time in a high temperature and humidity showed beneficial effects for intestinal probiotics. Conclusion: These findings revealed that pathogenic gut bacteria decrease while probiotics increase following HA, with elevated immune factors and reduced organ damage during heat stress, thereby improving the body's heat adaption.

Thermal response of human body with immersion suit in cold environment.

Hypothermia caused by cold water immersion is one of the main causes of death in marine accidents. Immersion suit is a kind of protective clothing when implementing flying tasks over the sea in cold seasons, with the main function to slow down the loss of human heat in water and prolong the survival time. In this study, the thermal properties and wearing types of immersion suit and underwear were analyzed. The subjects with internal- and external-wear immersion suit exposed to the experimental environments for 2 h in five working conditions. The core temperature, weighted average skin temperature, and average body temperature were measured and calculated. Both internal- and external-wear immersion suits could fulfil the cold protection requirements under the experimental conditions. The results of clothing parameter tests and physiological experiments both exhibit that the external-wear immersion suit has better thermal insulation effect. And the tolerance time in low-temperature water was predicted, which is crucial for effective and efficient rescue during shipwreck in adverse thermal scenarios. In future research, a comprehensive evaluation and analysis of the thermal insulation performance of immersion suit could be completed in combination with the water ingress of the clothing, the subjects' thermal comfort, and flexibility of the clothing.

Thermal protection study of bladder compensatory suit using a heat transfer model.

BACKGROUND: The bladder compensatory suit (BCS) is important individual protective equipment for pilots' activities in a high-flying environment. The layout and thermal diffusion ability of the bladder directly affects the thermal comfort of pilots in flight. OBJECTIVE: (1) Established and verified a human-compensatory suit-environment heat transfer model; (2) Used the model to study the human thermal variation of each segment in hot conditions and clothing. METHODS: To verify the two-dimensional heat transfer model, simulated data of body temperature were compared with experimental results under the same conditions (AT: 40/45°C, ordinary clothing). The model could be used to calculate the temperature variation of each body segment in three environments temperature (28°C, 35°C and 40°C) and three types of clothing (naked, ordinary clothing, BCS). RESULTS: The results showed that: (1) the bladder significantly affected sweating speed and skin temperature, as well as core temperature; (2) the skin temperature of the area covered by the bladder was difficult to reduce by the thermal regulation system. It was because sweat secretion was inhibited, thus, to limit evaporation. CONCLUSIONS: The model could be used as a reference for the thermal protection design of bladder compensatory suit. SUMMARY: The bladder compensatory suit (BCS) is important individual protective equipment for pilots activities in a high-flying environment, and its layout directly affects the thermal comfort. Based on a two-dimensional thermal regulation system model, a body-clothing-environment heat transfer model was established. The model was used to calculate the temperature and sweat variation of each body segment in different environments and clothing.

Mechanical and physiological effect of partial pressure suit: Experiment and numerical study.

BACKGROUND: During high-altitude flight, the protection of the pilot is vital. A partial pressure suit may affect human physiology, especially circulatory physiology. OBJECTIVE: The purpose of this study was to investigate how a partial pressure suit works. METHOD: Ten subjects took part in the flight simulation experiments. Counter pressure at the chest, abdomen, thigh and shank were detected, together with physiological parameters such as heart rate (HR), mean arterial pressure (MAP), stroke volume (SV), cardiac output (CO) and total peripheral resistance (TPR). A numerical model was also established to simulate hemo-physiological effects of the partial pressure suit. RESULTS: The experiment's results show the non-uniform counter pressure distribution in different parts of the body. There is a linear, proportional relation between TPR and the pressurizing level. HR and MAP increase along with that of the pressure level. SV and CO decrease with the increase of the pressure level. The numerical model simulated the physiological effect of a partial pressure suit. The results were verified by experiment data. The simulation estimated the change of blood flow with the pressure level. CONCLUSIONS: The numerical model provides a potential way to improve the protection of pilots.

Optimizing the physical ergonomics indices for the use of partial pressure suits.

This study developed an ergonomic evaluation system for the design of high-altitude partial pressure suits (PPSs). A total of twenty-one Chinese males participated in the experiment which tested three types of ergonomics indices (manipulative mission, operational reach and operational strength) were studied using a three-dimensional video-based motion capture system, a target-pointing board, a hand dynamometer, and a step-tread apparatus. In total, 36 ergonomics indices were evaluated and optimized using regression and fitting analysis. Some indices that were found to be linearly related and redundant were removed from the study. An optimal ergonomics index system was established that can be used to conveniently and quickly evaluate the performance of different pressurized/non-pressurized suit designs. The resulting ergonomics index system will provide a theoretical basis and practical guidance for mission planners, suit designers and engineers to design equipment for human use, and to aid in assessing partial pressure suits.

[Evaluation of operation ergonomics at high-temperature in the cockpit].

10 male subjects participated in the environmental simulation study to evaluate the operation ergonomics at high-temperature in the cockpit. Grip strength, perception, dexterity, reaction and intelligence were measured respectively during the tests at 40 degrees C and 45 degrees C, simulating the high-temperatures in a simulation cockpit chamber. Then the data obtained were compared to the combined index of heat stress (CIHS). The average values of each item of the subjects' performance at the two different temperatures are compared. The results indicated that CIHS exceeded the heat stress safety line after 45 min at 40 degrees C, grip strength decreased by 12%, and perception increased by 2.89 times. In contrast, at 45 degrees C, CIHS exceeded the safety line after 20 min, grip strength decreased by 3.2%, and perception increased by 4.36 times. However, Finger dexterity was less affected. Reaction ability was first accelerated, and then slowed down. The error rate in the intelligence test increased to a greater extent. At the high temperatures, the minimum perception was the most affected, followed by grip strength, reaction and finger dexterity were less affected, while the intelligence did not decline, but rise.