Effect of Palm Cooling on Heat Extraction During Exercise in a Hot Dry Environment

Abstract

Athletes, military personnel, astronauts, and firefighters are often required to perform in hot environments, increasing the risk of hyperthermia. Several methods of body cooling have been studied but most are dependent upon heavy equipment or an external power source, and may be impractical for use in the field. A portable palm cooling with negative pressure device (RTX) has been used to extract heat through the palm of the hand and attenuate hyperthermia. PURPOSE: To evaluate the effectiveness of the RTX in slowing the development of hyperthermia and associated symptoms to three other conditions [hand immersed in water bath (WB), water-perfused vest (VEST), no-cooling condition (NC)] in subjects exercising in a hot environment wearing summer fatigues, a backpack and body armor. METHODS: 10 subjects (age 25 ± 3 yrs; weight 74 ± 6 kg; height 177 ± 6 cm; VO2max 54 ± 9 mL kg-1.min-1) performed four heat stress tests in a counter-balanced order (NC / RTX/WB/VEST). The protocol consisted of two bouts [1st and 2nd bouts were terminated at a core temperature (TC) of 38.5°C and 39°C, respectively] of treadmill walking (at 50% VO2max), separated by a 41 -min cooling and rehydration period in a hot, dry environment (42°C, 30% rh). Time duration, rate of rise in core temperature (Tcslope) and heart rate (HR) were evaluated using a 2-way repeated-measures ANO VA. RESULTS: The time to reach the pre-determined TC in the 1st and 2nd bouts were not different among RTX (mean ± SD; 52 ± 14 and 42 ± 12 min respectively), NC (49 ± 13 and 41 ± 14 min respectively), and WB (54 ± 14 and 55 ± 20 min respectively), but was longer for the VEST (85 ± 30, and 65 ± 12 min respectively) in both bouts (p<0.05). The Tcslope (°C/min) was significantly lower for VEST in the 1st and 2nd bouts versus the other conditions (p<0.05), and no differences were observed during recovery. HR was not different at 10, 20 and 30 minutes of exercise in the 1st bout among RTX, NC, and WB, but was lower for VEST in the 1st bout (p<0.05). HR was not different among conditions in the 2nd bout. CONCLUSION: The RTX was not effective in slowing the development of hyperthermia in the present protocol. Aspects related to hand vasoconstriction and the severe work/heat stress conditions used in the present study possibly prevented the expected heat extraction. Supported by DARPA grant # W911NF-06-1 -0025