Head cooling is desirable but not essential for preventing heat strain in pilots

Liquid-cooled garments (LCGs) are being considered for reducing heat strain in pilots. While head cooling has been shown to be thermally efficient and subjectively desirable, it is technically difficult to achieve. This laboratory study was carried out to see if head cooling in addition to torso cooling is a necessity. Six male subjects wore a cooling vest and cap under summer flight clothing on three occasions in a climatic chamber set at Tdb = 42 degrees C, Twb = 32 degrees C (RH = 50%), Tg = 52 degrees C at head position, WBGT = 35 degrees C. Cooling conditions were: control (CTRL), no fluid circulation; condition VEST, only torso cooling; condition HEAD, both torso and head cooling. Cooling fluid was circulated from a reservoir maintained at 10 degrees C. Subjective thermal comfort assessments confirmed the desirability of head cooling, but performance measurements and physiological measurements of thermal strain showed no statistically significant differences between conditions VEST and HEAD. It was concluded that head cooling is desirable but not essential.     

Heat strain during at-sea helicopter operations and the effect of passive microclimate cooling.

Twelve Navy H-3 helicopter aircrew members were monitored (heart rate, skin and rectal temperatures) in both microclimate cooling (ice) vest and non-vest conditions during at-sea operations in the high heat environment of the Persian Gulf. During all flights and flight phases, ambient dry bulb temperatures ranged from 31.0 degrees C (in-flight) to 48.6 degrees C (hover). Heart rate was greatest during hover and on-deck (range: 89.9 to 145.0 beats/min) without an ice vest, yet was significantly reduced with ice (range: 79.7 to 86.0 beats/min) (p less than 0.05). Rectal temperature was not found to be different between vest and non-vest conditions; however, change across flight phases in both conditions was significant (p less than 0.05). Analysis of variance demonstrated significantly lower mean weighted skin temperatures (p less than 0.05) when wearing the ice vest. These data suggest that wearing a protective cooling vest can reduce the heat strain associated with helicopter flight in high heat environments.     

Heat stress on helicopter pilots during ground standby.

We attempted to use measurements of ambient thermal conditions to characterize and then predict thermal conditions in the cockpit before takeoff and during an hour standby period in Bell 206 and Bell 212 helicopters with a crew of two and with the cockpit doors opened. Dry bulb, wet bulb, and globe temperatures were measured on 28 separate summer days. The wet bulb globe temperature index (WBGT) was used to estimate heat stress. Ambient WBGT at time 0 ranged from 13 degrees C to 31 degrees C. There was a 2.9 +/- 3.7 degree difference in WBGT between ambient and cockpit conditions at time 0 which increased to 7.2 +/- 3.5 degrees after 1 h. Because of the cooling effect of opening the helicopter cockpit doors, the cockpit WBGT actually decreased over the standby period when cockpit WBGT values were 30 degrees C or more at time 0. Thus, there was an inverse correlation between cockpit WBGT at time 0 and the change in cockpit WBGT over the 1-h period (r = -0.767, p less than 0.001). The mean WBGT in the cockpit over the 1-h standby period was positively correlated with the ambient WBGT at time 0 (r = 0.783, p less than 0.001). We conclude that the greenhouse effect results in a cockpit WBGT which is significantly higher than ambient conditions. Subsequent changes in cockpit WBGT depend on the balance between heat transfer from the pilot's bodies to the cockpit and the loss of heat after the doors of the helicopters are opened. Ambient thermal conditions can be used to predict heat stress during the ground standby period.     

Effectiveness of an air-cooled vest using selected air temperature and humidity combinations

We evaluated the effectiveness of an air-cooled vest in reducing thermal strain of subjects exercising in the heat (49 degrees C dry bulb (db), 20 degrees C dew point (dp] in chemical protective clothing. Four male subjects attempted 300-min heat exposures at two metabolic rates (175 and 315 W) with six cooling combinations--control (no vest) and five different db and dp combinations. Air supplied to the vest at 15 scfm ranged from 20-27 degrees C db, 7-18 degrees C dp; theoretical cooling capacities were 498-687 W. Without the vest, endurance times were 118 min (175 W) and 73 min (315 W). Endurance times with the vest were 300 min (175 W) and 242-300 min (315 W). The five cooling combinations were similarly effective in reducing thermal strain and extending endurance time, although there was a trend for the vest to be more effective when supplied with air at the lower dry bulb temperature. At 175 W, subjects maintained a constant body temperature; at 315 W, the vest's ability to extend endurance is limited to about 5 hours.     

Heat stress effects for USAF anti-G suits with and without a counter-pressure vest

BACKGROUND: Aircrew have reported increased heat stress when wearing the USAF Combined Advanced Technology Enhanced Design G-Ensemble or COMBAT EDGE (CE). The perceived thermal burden has been attributed to the fact that CE includes an inflatable counter-pressure vest to ease the work of positive pressure breathing during G (PBG). This study compared the heat load of CE with that of the standard USAF anti-G system (STD) without the vest, and measured heat stress effects on G-tolerance in both suits. METHODS: This study had 12 subjects (6 of them aircrew) who participated. Simulated preflight thermal stress (20 min walking at 35 degrees C with 85% relative humidity and radiant heat) was followed by return to a cooler environment (21 degrees C). G-tolerance and subjective stress levels were determined on the human centrifuge before and after the heat stress. Body weight, rectal and skin temperatures, and blood parameters were also assessed. RESULTS: Baseline relaxed tolerance for +Gz gradual onset runs (GORs) were (mean +/- SD) 7.6 +/- 1.3 G for CE and 7.1 +/- 0.8 G for STD (p < 0.05). Maximal rectal temperature following heat stress peaked at 38.1 +/- 0.4 degrees C for both CE and STD, and mean nude weight loss was 1.10 +/- 0.24 kg for both. Relaxed GOR tolerances after heat stress were 7.1 +/- 1.3 for CE and 6.3 +/- 0.9 for STD (p < 0.01). The heat stress significantly reduced G tolerance for both CE and STD (p < 0.01). CONCLUSIONS: Simulated preflight activity in hot conditions revealed no significant difference between CE and STD with regard to maximal core and skin temperature elevations or dehydration levels. CE supported a significantly higher baseline relaxed G-tolerance than STD, an advantage that persisted after heat stress and dehydration.     

载人航天器预冷温度的热生理学探讨

目的探讨载人舱室适宜的预冷温度 ,以预防或减缓发射、返回段航天器内高温对人体的不利影响。方法 5名健康男性青年按着航天服时不通风和以通风流率 1 0 0L/min(STPD)通风等不同着装条件 ,在舱温 1 5、l0、5℃环境中进行 2 5人次实验。测量直肠温度 (Tr)、平均皮温 (Tsk)和平均体温 (Tb)等热生理指标。结果在舱温 1 5℃航天服通风和不通风状态 ,实验 2h内人体直肠温度降低不显著 (从初始值 37.0± 0 .2℃降为 36.7± 0 .3℃ ) ,平均体温、平均皮温显著降低 (P <0 .0 5) ,受试者有局部的冷紧张 ;而在舱温和通风温度 1 0℃时 ,受试者热生理指标随时间延长不断降低 ,直肠温度从 37.0± 0 .3℃显著下降至 36.3± 0 .3℃ ,Tsk、Tb 显著低于初始值 (P <0 .0 5) ,受试者有全身性冷紧张。结论按人体热舒适状态无显著改变的要求 ,航天器座舱预冷后维持 1 5℃气温对人体较为适宜。     

Effect of acclimation on changes in water and electrolyte homeostasis in soldiers during exertional heat stress

BACKGROUND/AIM: Exertional heat stress is a common problem in military services. The aim of this study was to exemine changes in body water and serum concentrations of some electrolites in soldiers during exertional heat stress (EHST), as well as effects of 10-day passive or active acclimation in a climatic chamber. METHODS: Forty male soldiers with high aerobic capacity, performed EHST either in cool (20 degrees C, 16 degrees C WBGT-wet bulb globe temperature), or hot (40 degrees C, 25 degrees C WBGT) environment, unacclimatized, or after 10 days of passive or active acclimation. The subjects were allowed to drink tap water ad libitum during EHST. Mean skin (Tsk) and tympanic (Tty) temperatures and heart rates (HR) measured physiological strain, while sweat rate (SwR), and serum concentrations of sodium, potassium and osmolality measured changes in water and electrolite status. Blood samples were collected before and immediately after the EHST. RESULTS: Exertional heat stress in hot conditions induced physiological heat stress (increase in Tty, HR, and SwR), with significant decrease in serum sodium concentration (140.6 +/- 1.52 before vs. 138.5 +/- 1.0 mmol/l after EHST, p < 0.01) and osmolality (280.7 +/- 3.8 vs. 277.5 +/- 2.6 mOsm/kg, p < 0.05) in the unacclimatized group. The acclimated soldiers suffered no such effects of exertional heat stress, despite almost the same degree of heat strain, measured by Tty, HR and SwR. CONCLUSION: In the trained soldiers, 10-day passive or active acclimation in a climatic chamber can prevent disturbances in water and electrolitic balance, i.e. decrease in serum sodium concentrations and osmolality induced by exertional heat stress.     

Body temperature in sedentary adults during moderate exercise: no effect from exercise the day before

BACKGROUND: Epidemiological findings show a continued presence of exertional heat injury during military basic recruit training. Current guidelines do not consider the carry-over effects of prior exercise or exposure to high ambient temperatures on the risk of succumbing to heat illness. HYPOTHESIS: From the epidemiological evidence we hypothesized that both prior exercise and exposure to hot environments on the day before would increase the core temperature response during exercise the next day. METHODS: Seven sedentary and non heat-acclimated men and women each performed eight randomized exposures involving treadmill walking for a maximum of 2 h every 2 wk. Two separate control trials at a wet bulb globe temperature (WBGT) of 22.5 degrees C and 26.5 degrees C consisted of exercise during the morning only. Six experimental trials involved successive days of exercise with trials on the second day at either a WBGT of 22.5 degrees C or 26.5 degrees C. All of the experimental trials involved walking during the first morning at a WBGT of 22.5 degrees C. Further, four of these trials included additional exercise in the afternoon at either a WBGT of 22.5 degrees C (two trials) or 29.5 degrees C (two trials). RESULTS: There was no impact of prior exercise on the day preceding the tests at either WBGT for any of the dependent measures. Rectal temperatures increased to 38.0 degrees C at the WBGT of 22.5 degrees C and to 38.5 degrees C for trials at 26.5 degrees C. There were also no carry-over effects from exercise conducted during the preceding afternoon. CONCLUSIONS: Under situations where individuals are well hydrated, rested, and free of injury, illness, and drug use, repeated exercise bouts on successive days do not alter the thermoregulatory response to exercise.     

Effects of atropine on thermoregulatory responses to exercise in different environments

The thermoregulatory effects of atropine (2 mg im) were examined in six heat-acclimated subjects during exercise in three environments, which provided different evaporative capacities, but similar heat stress as indicated by the wet bulb, globe temperature index (WBGT). Subjects walked in environments of Ta = 42.3 degrees C, Tdp = 14.6 degrees C, WBGT = 29.1 degrees C (HD); Ta = 33.9 degrees C, Tdp = 23.5 degrees C, WBGT = 28.9 degrees C (WM); Ta = 30.4 degrees C, Tdp = 23.8 degrees C, WBGT = 27.4 degrees C, (WW) after atropine and saline injections. In comparison to saline, atropine elevated rectal temperature (Tre) (p less than 0.05) in HD. Additionally, atropine elevated (p less than 0.01) mean skin temperature (Tsk), and heart rate (HR) in all three environments relative to saline. Whole body sweating rate (msw) was 45% lower (p less than 0.01) in each environment after atropine relative to saline. Exercise time was reduced from saline values (p less than 0.05) by 26.5 min in the HD after atropine. Within the atropine treatments, Tre was higher (p less than 0.05) in HD (0.6 degrees C) than WW, and HR was higher (p less than 0.05) in HD (23 b X min-1) and WM (14 b X min-1) than WW. Tsk was higher (p less than 0.01) in WM than WW (1.2 degrees C) and in HD than WM (1.5 degrees C). Exercise time was 26.5 min longer (p less than 0.05) in WW than HD in the atropine experiments.(ABSTRACT TRUNCATED AT 250 WORDS)     

Heat shock protein 70 as a biomarker of heat stress in a simulated hot cockpit

BACKGROUND: Fighter pilots are frequently exposed to high temperatures during high-speed low-level flight. Heat strain can result in temporary impairment of cognitive functions and when severe, loss of consciousness and consequent loss of life and equipment. Induction of stress proteins is a highly conserved stress response mechanism from bacteria to humans. Induced stress protein levels are known to be cytoprotective and have been correlated with stress tolerance. Although many studies on the heat shock response mechanisms have been performed in cell culture and animal model systems, there is very limited information on stress protein induction in human subjects. HYPOTHESIS: Heat shock proteins (Hsp), especially Hsp70, may be induced in human subjects exposed to high temperatures in a hot cockpit designed to simulate heat stress experienced in low flying sorties. METHODS: Six healthy volunteers were subjected to heat stress at 55 degrees C in a high temperature cockpit simulator for a period of 1 h at 30% humidity. Physiological parameters such as oral and skin temperatures, heart rate, and sweat rate were monitored regularly during this time. The level of Hsp70 in leukocytes was examined before and after the heat exposure in each subject. CONCLUSIONS: Hsp70 was found to be significantly induced in all the six subjects exposed to heat stress. The level of induced Hsp70 appears to correlate with other strain indicators such as accumulative circulatory strain and Craig's modified index. The usefulness of Hsp70 as a molecular marker of heat stress in humans is discussed.     

Heat stress and carbon monoxide exposure during C-130 vehicle transportation

INTRODUCTION: Running gasoline engines in a confined space causes heat stress and carbon monoxide (CO) buildup. Loading the C-130 aircraft by driving the vehicles onto the platform may expose the C-130 cabin crew to these environmental hazards. This study was aimed at investigating heat stress and CO exposure in the C-130 cabin during vehicle airlift. METHODS: There were four summer flights (two two-vehicle, two three-vehicle; 2 d, 2 nights) studied. The cabin heat stress index (wet bulb globe temperature, WBGT) and CO levels before vehicle loading (control) were compared with those after vehicle loading. Furthermore, two- and three-vehicle transportations, as well as day and night transportations, were compared. RESULTS: Ground temperature ranged from 18.2 to 33.4 degrees C. Mean heat stress index was higher in vehicle transportation than control flights, the greatest difference being 5.9 degrees C (p < 0.001). The WBGT levels exceeded the recommended exposure limit in 28 of 38 measurements during day flights. The cabin heat stress increased sharply with vehicle loading, and continued to increase for a range of 60-140 min after loading. Elevated cabin CO levels were found in three-vehicle flights as compared with two, and in night flights as compared with day. CONCLUSIONS: In hot climates, C-130 vehicle transportation may exacerbate heat stress. The in-flight heat stress can be predicted by the ambient temperature, duration of the vehicle transportation, and number of transported vehicles. The cabin CO level is related to the number of transported vehicles. We recommend the use of effective environmental control systems during C-130 vehicle transportation in hot climates.     

Rapid cooling techniques in joggers experiencing heat strain

This study examined subjects that exercised on three occasions in a heated environment (WBGT = 39 degrees C] until they experienced heat strain. Since morbidity and mortality due to heat injury increase with the duration of elevated core temperature, it is important that techniques to lower core temperature be evaluated. Following three exercise sessions, subjects underwent each of three core cooling treatments in random order: 1) Torso immersion in cool water, 2) Hands and feet immersion in cool water, and 3) Sit-in-shade with a 1.5mph breeze provided. Subjects (n=5) consistently reached peak rectal temperatures of 38.8 (+/-0.1) degrees C following each exercise bout in the heated environment. Torso immersion produced a significantly (p<0.05) greater rate of decline in rectal temperature (0.25+/-0.10 degrees C/min) than the hands and feet immersion technique (0.16+/-0.05 degrees C/min) and the sit in the shade technique (0.11+/-0.04 degrees C/min). After only 10 minutes of cooling, the differences among cooling techniques were evident. Similar trends were observed for mean heart rate readings, albeit not significant (p>0.05). It was concluded that rectal temperatures can be reduced rapidly through the use of a cool water torso-immersion technique.     

Heat strain attenuation while wearing NBC clothing: dry-ice vest compared to water spray

BACKGROUND: While wearing impermeable nuclear, biological, and chemical (NBC) clothing, reduction of thermal stress is of primary importance. We compared the effect between two cooling methods on the attenuation of heat strain. METHODS: There were six male subjects who were divided into two groups of three and exposed on two consecutive days to 125 min of exercise in a high heat load (40 degrees C, 40% RH) wearing NBC clothing. They were cooled by one of two different cooling methods: an active cooling vest (CV) based on the sublimation of dry ice, or tap water spraying (TP). RESULTS: After 2 h, rectal temperature (Tre) was significantly higher for the CV compared with the TP (38.1 +/- 0.04 degrees C vs. 37.7 +/- 0.10 degrees C, respectively). Skin temperature (Tsk) was significantly higher for the CV compared with the TP (36.60 +/- 0.54 degrees C vs. 34.90 +/- 0.35 degrees C, respectively). In the second hour, heart rate (HR) was significantly higher for CV compared with TP (118 +/- 13 bpm vs. 104 +/- 64 bpm, respectively). Heat storage was significantly higher after the first and second hours for the CV compared with the TP. The physiological strain index (PSI) was higher for CV compared with TP in the second hour. Sweat rate (msw) was significantly higher for CV compared with TP (560 +/- 45 g x h(-1) vs. 409 +/- 84 g x h(-1), respectively). Subjective thermal comfort was not significantly different. CONCLUSIONS: TP was more effective than the CV in reducing heat strain under the conditions used in the study. Until a significant breakthrough in reducing heat strain while wearing NBC clothing in field conditions can be found, TP appears to be an effective and recommended cooling method.     

The effects of continuous hot weather training on risk of exertional heat illness

PURPOSE: To determine whether cumulative daily average wet-bulb globe temperature (WBGT) index, over one or two preceding days, is a better measure for predicting cases of exertional heat illness (EHI) than current daily average WBGT, which is the standard heat index used by the Marine Corps; and to identify the most accurate index of heat stress to prevent and predict future cases of EHI. METHODS: A case-crossover study was conducted in male and female Marine Corps recruits in basic training at Marine Corps Recruit Depot, Parris Island, SC. Weather measurements were obtained for 2069 cases of EHI during 1979-1997 and for randomly selected control periods before and after each EHI episode. RESULTS: The risk of EHI increased with WBGT (OR = 1.11 degrees F(-1); 95% CI, 1.10-1.13). EHI risk was associated not only with the WBGT at the time of the event (OR = 1.10 degrees F(-1); 95% CI, 1.08-1.11) but with the previous day's average WBGT as well (OR = 1.03 degrees F(-1); 95% CI, 1.02-1.05). Alternative combinations of WBGT components were identified that better predicted EHI risk. CONCLUSION: Our results provide evidence for a cumulative effect of previous day's heat exposure on EHI risk in these Marine Corps recruits. A simple index for use in predicting EHI risk is proposed that includes the dry-bulb temperature and the relative humidity.     

Optimising the acquisition and retention of heat acclimation

Heat acclimation (HA) often starts in a moderately hot environment to prevent thermal overload and stops immediately prior to athletic activities. The aims of this study were (1) to establish whether acclimation to a moderately hot climate is sufficient to provide full acclimation for extreme heat and (2) to investigate the physiological responses to heat stress during the HA decay period. 15 male subjects exercised for 9 consecutive days at 26° C Wet Bulb Globe Temperature (WBGT) and 3 days at 32° C WBGT on a cycle ergometer for up to 2?h per day and repeated the exercise 3, 7 and 18 days later in 26° C WBGT. Rectal temperature (T (re)) and heart rate (HR) were measured during 60?min of steady state exercise (～45% of maximum oxygen uptake). During days 1-9, end-exercise T (re) was reduced from 38.7±0.1 to a plateau of 38.2±0.1° C (p<0.05), HR was reduced from 156±10 to 131±11?bpm (p<0.05). No changes in HR and T (re) occurred during the 3 days in the very hot environment. However, T (re) during rest and exercise were significantly lower by 0.4-0.5° C after HA compared with day 9, suggesting that heat acclimation did not decay but resulted in further favourable adaptations.     

Heat and cold: what does the environment do to marathon injury?

The medical work load seems to increase both with heat and humidity, and with cold and rainy conditions. Heat tolerance during exercise is variable and heat intolerance may contribute to collapse and increase medical encounters. Exposure to cold, wet conditions results in increasing incidence of hypothermia in exhausted marathon runners. Finish-line encounters and course dropouts increase as conditions cool and warm away from the most advantageous conditions in the 4.4-15 degrees C (40-59 degrees F) wet bulb globe temperature (WBGT) range. The risk of requiring medical attention and not finishing rises considerably when the WBGT is >15.5 degrees C (60 degrees F). Comparing the correlation coefficients of the Boston Marathon and Twin Cities Marathon data suggests that the risks of medical problems and not finishing are associated with the warmest temperature of the race and not the start temperature. The community consequences of races conducted in hot and humid conditions can be significant, particularly when the WBGT is >15.5 degrees C. The emergency medical systems can be overwhelmed with a surge of patients, some very ill, and the emergency call response times drop to unacceptable levels blocking access for the citizens of the community. With respect to marathon encounters, heat stress increases both the finish-line medical encounter rate and the on course drop-out rate, and seems to increase the incidence of hyponatraemia and heat stroke. Cold conditions increase the drop-out rate along the course and, if associated with wet conditions, also increase the encounter rate.     

RPE drift during cycling in 18 degrees C vs 30 degrees C wet bulb globe temperature

AIM: The potential influence of a hotter vs cooler environment on ratings of perceived exertion (RPE) estimations during longer duration exercise is not well-understood. This study compared overall and differentiated RPEs during cycling in 18 degrees C vs 30 degrees C wet bulb globe temperature (WBGT). METHODS: Male volunteers (n=16) completed a maximal cycling trial (60 rev . min(-1), 25 Watts . min(-1)) to determine VO(2) max and ventilatory threshold (VT) before completing 2 (counterbalanced) longer duration cycling trials. At 30 degrees C WBGT (30C) and 18 degrees C WBGT (18C), subjects cycled 60 min (60 rev . min(-1), 90% individualized VT). Heart rate (HR, b . min(-1)) and rectal temperature (Tre, degrees C) were recorded every 5 min with corresponding RPE-overall (RPE-O), RPE-legs (RPE-L) and RPE-chest (RPE-C) estimations. RESULTS: HR was not significantly different at 5 min but was greater (P<0.05) for 30C at all other time points. During 30C, Tre was significantly greater (25, 30, 35, 40, 45, 50, 55 and 60 min), RPE-O was significantly greater (5, 40, 45, 50, 55 and 60 min), RPE-L was significantly greater (55 and 60 min) and RPE-C was significantly greater (35, 40, 45, 50, 55 and 60 min). CONCLUSIONS: Greater cardiovascular (HR) and thermal (Tre) strain partially explain greater perceptual ratings during 30C. Discernible RPE differences resulted mid-way through 60 min cycling with minimal differences initially. Results suggest RPEs are magnified in a 30 degrees C (vs 18 degrees C) environment beyond 30 min duration. Additionally, a 30 degrees C environment resulted in a less pronounced impact on RPE-L (vs RPE-C and RPE-O).     

Helicopter cockpit seat side and trapezius muscle metabolism with night vision goggles

INTRODUCTION: Documented neck strain among military helicopter aircrew is becoming more frequent and many militaries use helicopters that provide pilots with the option of sitting in the left or right cockpit seat during missions. PURPOSE: The purpose of this study was to use near infrared spectroscopy (NIRS) to investigate the physiological changes in trapezius muscle oxygenation and blood volume during night vision goggle (NVG) flights as a function of left and right cockpit seating. METHODS: There were 25 pilots who were monitored during NVG flight simulator missions (97.7 +/- 16.1 min). Bilateral NIRS probes attached to the trapezius muscles at C7 level recorded total oxygenation index (TOI, %), total hemoglobin (tHb), oxyhemoglobin (Hbo2), and deoxyhemo-globin (HHb). RESULTS: No significant differences existed between variables for pilots seated in the right cockpit seat as compared with the pilots seated in the left cockpit seat in either trapezius muscle (pTOI = 0.72; ptHb = 0.72; pHbo2 = 0.57; pHHb = 0.21). CONCLUSION: Alternating cockpit seats on successive missions is not a means to decrease metabolic stress for helicopter pilots using NVG. This suggests that cockpit layout and location of essential instruments with respect to the horizontal and the increased head supported mass of the NVG may be important factors influencing metabolic stress of the trapezius muscle.     

Heat strain evaluation of chemical protective garments

BACKGROUND: The purpose of this study was to compare thermoregulatory and subjective responses of 12 test subjects (10 male, 2 female) wearing 5 different Joint Service Lightweight Integrated Suit Technology (JSLIST) prototype and 3 different currently fielded control chemical/ biological (CB) protective overgarments. METHODS: The overgarments were compared while subjects attempted to complete 100 min of moderate exercise (400 W) in an environmental chamber (35 degrees C/50% rh). Rectal temperature (Tre), skin temperature, heart rate, sweating rate, and test time, as well as subjective symptoms of heat illness were measured. Data were analyzed for times earlier than 100 min because subjects were not usually able to complete the 100-min trials. RESULTS: At 50 min, of the 3 controls, the Army/Air Force Battledress Overgarment (BDO) imposed significantly greater heat strain (indicated by Tre 37.90 degrees C) than the Marine Saratoga (SAR) (Tre 37.68 degrees C) and Navy Chemical Protective Overgarment (CPO) (Tre 37.69 degrees C). The JSLIST prototype garments imposed heat strain (50 min Tre 37.73-37.86 degrees C) as well as subjective perception of heat strain, that ranged between the warmest and coolest controls. CONCLUSIONS: In the environmental and exercise test conditions of this study, we did not find the five JSLIST overgarments to be consistently different from one another. Subjects in the control garments were and felt generally warmer (BDO) or cooler (SAR, CPO) than in the JSLIST prototype garments.     

Effect of head or neck cooling used with a liquid-conditioned vest during simulated aircraft sorties

The effectiveness of head or neck cooling in reducing head sweating and increasing subject comfort when used in conjunction with a liquid-conditioned vest during simulated sorties in the European Fighter Aircraft was investigated. Six subjects underwent three 2-h exposures at 40 degrees C wearing Aircrew Chemical Defence clothing and one of three combinations of liquid-conditioned garments. In all three exposures, a liquid-conditioned vest was worn and, in two exposures, either a head-cooling cowl or a neck-cooling collar was worn in addition to the vest. All six subjects reported increased comfort and decreased head sweating with head cooling, a result supported by the data collected.