Thermal comfort and sensation in men wearing a cooling system controlled by skin temperature.

OBJECTIVE: The study was done to determine whether thermal comfort (TC), thermal sensation (TS), and subjective factors gauging environmental stress were negatively affected with different cooling methods in men exercising in chemical protective clothing. BACKGROUND: Previous studies have reported that intermittent regional cooling improved the efficacy of cooling as compared with constant cooling (CC), but no studies have addressed whether there is any improvement in thermal comfort. METHODS: Eight male volunteers exercised at moderate work intensity (425 W) in three microclimate cooling tests. The circulating fluid in the cooling garment was provided during exercise to the head (6% body surface area [BSA]), torso (22% BSA), and thighs (44% BSA) and manipulated under three methods: (a) CC, (b) pulsed cooling (PC), and (c) PC activated by mean skin temperature (T(sk)) control (PC(skin)). TC and TS ratings were recorded every 20 min during the 80-min test. RESULTS: TC and TS ratings were not different for PC(skin) and CC; thus the participants perceived PC(skin) as being similar to CC. TS was significantly warmer with PC than with PC(skin) and CC (p < .001). In PC(skin), T(sk) was significantly higher than in PC and CC (p < .001), and PC(skin) was rated as being not as warm as PC according to TS. CONCLUSION: This indicates that the PC(skin) method was perceived as being as cool as CC and cooler than PC. APPLICATION: These findings indicate that the PC(skin) cooling method is an acceptable alternative to CC and PC based on human perceptions.

Skin temperature feedback optimizes microclimate cooling.

INTRODUCTION: A novel pulsed cooling paradigm (PCskin) integrating mean skin temperature (Tsk) feedback was compared with constant cooling (CC) or time-activated pulsed cooling (PC). METHODS: Eight males exercised while wearing personal protective equipment (PPE) in a warm, dry environment (dry bulb temperature: 30 degrees C; dew-point temperature: 11 degrees C) in each of the tests. Treadmill exercise was performed (approximately 225 W x m(-2)) for 80 min. A liquid cooling garment (LCG) covered 72% of the body surface area. Core temperature (Tc), local skin temperatures, heart rate, inlet and outlet LCG perfusate temperatures, flow, and electrical power to the LCG and metabolic rate were measured during exercise. RESULTS: At 75 min of exercise Tsk was higher (33.9 +/- 0.2 degrees C) in PCskin, than in PC (33.1 +/- 0.5 degrees C) or CC (32.0 +/- 0.6 degrees C) and PC > CC. The changes in Tc and heart rate during the tests were not different. Tc at 75 min was not different among the cooling paradigms (37.6 +/- 0.3 degrees C in PCskin, 37.6 +/- 0.2 degrees C in PC and 37.6 +/- 0.2 degrees C in CC). Heart rate averaged 124 +/- 10 bpm in PCskin, 120 +/- 9 bpm in PC and 117 +/- 9 bpm in CC. Total body insulation (degrees C x W(-1) x m(-2)) was significantly reduced in PCskin (0.020 +/- 0.003) and PC (0.024 +/- 0.004) from CC (0.029 +/- 0.004). Electrical power in PCskin was reduced by 46% from CC and by 28% from PC. DISCUSSION/CONCLUSION: Real-time Tsk feedback to control cooling optimized LCG efficacy and reduced electrical power for cooling without significantly changing cardiovascular strain in exercising men wearing PPE.

Intermittent microclimate cooling during exercise-heat stress in US army chemical protective clothing.

The effectiveness of intermittent, microclimate cooling for men who worked in US Army chemical protective clothing (modified mission-oriented protective posture level 3; MOPP 3) was examined. The hypothesis was that intermittent cooling on a 2 min on-off schedule using a liquid cooling garment (LCG) covering 72% of the body surface area would reduce heat strain comparably to constant cooling. Four male subjects completed three experiments at 30 degrees C, 30% relative humidity wearing the LCG under the MOPP 3 during 80 min of treadmill walking at 224 +/- 5 W . m(-2). Water temperature to the LCG was held constant at 21 degrees C. The experiments were; 1) constant cooling (CC); 2) intermittent cooling at 2-min intervals (IC); 3) no cooling (NC). Core temperature increased (1.6 +/- 0.2 degrees C) in NC, which was greater than IC (0.5 +/- 0.2 degrees C) and CC (0.5 +/- 0.3 degrees C) ( p < 0.05). Mean skin temperature was higher during NC (36.1 +/- 0.4 degrees C) than IC (33.7 +/- 0.6 degrees C) and CC (32.6 +/- 0.6 degrees C) and mean skin temperature was higher during IC than CC ( p < 0.05). Mean heart rate during NC (139 +/- 9 b . min(-1)) was greater than IC (110 +/- 10 b . min(-1)) and CC (107 +/- 9 b . min(-1)) ( p < 0.05). Cooling by conduction (K) during NC (94 +/- 4 W . m(-2)) was lower than IC (142 +/- 7 W . m(-2)) and CC (146 +/- 4 W . m(-2)) ( p < 0.05). These findings suggest that IC provided a favourable skin to LCG gradient for heat dissipation by conduction and reduced heat strain comparable to CC during exercise-heat stress in chemical protective clothing.

Epidemiology of hospitalizations and deaths from heat illness in soldiers.

PURPOSE: Serious heat illness has received considerable recent attention due to catastrophic heat waves in the United States and Europe, the deaths of high-profile athletes, and military deployments. METHODS: This study documents heat illness hospitalizations and deaths for the U.S. Army from 1980 through 2002. Hospitalization data were obtained from the Total Army Injury Health Outcomes Database (TAIHOD) coded according to the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM). North Atlantic Treaty Organization Standardization Agreement codes were searched for heat injuries in an effort to detect cases that were not found during the ICD-9-CM search. RESULTS: Five-thousand two-hundred forty-six soldiers were hospitalized, and 37 died due to heat illness. Our results indicate: 1) approximately 60% reduction in hospitalization rates (fewer heat exhaustion cases) over the 22-yr period; 2) fivefold increase in heat stroke hospitalization rates (1.8 per 100,000 in 1980 to 14.5 per 100,000 in 2001); 3) heat stroke cases were associated with dehydration (17%), rhabdomyolysis (25%), and acute renal failure (13%); 4) lower hospitalizations rates among African and Hispanic Americans compared with Caucasians (incidence density ratio, 0.76 [95% confidence interval, 0.71-0.82]; 5) greater rates of hospitalizations and heat strokes among recruits from northern than southern states (incidence density ratio, 1.69 [95% confidence interval, 1.42-1.90]; and 6) greater rates of hospitalizations and heat strokes among women than men (incidence density ratio, 1.18 [95% confidence interval, 1.09-1.27]). CONCLUSIONS: Exertional heat illness continues to be a military problem during training and operations. Whereas the hospitalization rate of heat illness is declining, heat stroke has markedly increased.

Biotelemetry transmitter implantation in rodents: impact on growth and circadian rhythms.

The implantation of a biotelemetry transmitter for core body temperature (T(c)) and motor activity (MA) measurements is hypothesized to have effects on growth and circadian rhythmicity depending on animal body-to-transmitter (B:T) size ratio. This study examined the impact of transmitter implantation (TM) on body weight, food intake (FI), water intake (WI), and circadian T(c) and MA rhythms in mice (23.8 +/- 0.04 g) and rats (311.5 +/- 5.1 g) receiving no treatment (NT), anesthesia, laparotomy (LAP), and TM. The B:T size ratio was 6:1 and 84:1 for mice and rats, respectively. In mice, body weight required 14 days to recover to presurgical levels and never attained the level of the other groups. FI recovered in 3 days, whereas WI never reached presurgical levels. Rat body weight did not decrease below presurgical levels. FI and WI recovered to presurgical levels in rats by day 2 postsurgery. Anesthesia decreased mouse body weight for 1 wk, but was without effect in rats. LAP significantly decreased body weight for 5 days in mice and 1 day in rats, showing a significant effect of the surgical procedure in the absence of TM in both species. Circadian T(c) and MA rhythms were evident within the first week in both species, indicating dissociation between circadian rhythmicity and recovery of growth variables. Cosinor analysis showed a TM effect on T(c) min, T(c) max, mesor, amplitude, and period of mice, whereas only the amplitude of the rhythm was affected in rats. These data indicate that a large B:T size ratio is associated with minimization of the adverse effects of surgical implantation. We recommend that B:T size ratio, recovery of presurgical body weight, and display of a robust circadian T(c) and MA rhythm be established before collection of biotelemetry data collection under an experimental paradigm.