Critical Environmental Limits for Prolonged Work in the Heat Using a Simulated Burn Injury Model

Abstract

Following a deep burn injury, excision of devitalized skin and subsequent grafting impair sweat production within grafted sites. Since the capacity for whole‐body evaporative heat dissipation is dependent on sweat production and the total non‐injured skin area available for heat dissipation, burn injuries likely reduce the capacity for whole‐body heat dissipation in proportion to the size of the burn injury during heat stress. To test this possibility, four healthy subjects (1 female; 28 ± 7 years, 71.1 ± 9.0 kg, 1.87 ± 0.12 m2) visited the laboratory on separate days to complete an incremental humidity protocol while cycling at a fixed metabolic heat production (5 W/kg, equivalent to ~35% maximum oxygen uptake) in 40°C with and without simulated burn injuries of 20%, 40%, or 60% of total body surface area. During each trial, exercise was performed at an initial relative humidity (RH) of 25% for 30 min to achieve thermal equilibrium, after which exercise continued as RH was increased by 3% every 5 min up to 90 min. A ‘critical’ RH was identified as the RH value above which a steady‐state esophageal temperature could no longer be maintained, thus providing an indication of maximum evaporative heat dissipation. Burn injuries were simulated by covering skin on the torso, arms, and legs with highly absorbent, vapor‐impermeable material that prevents sweat evaporation. The results show that the average critical RH declined with the size of the simulated burn injury up to 40% (0%: 44.1 ± 2.4%; 20%: 41.8 ± 2.3%; 40%: 31.4 ± 5.1%), with significant reductions in the critical RH at 40% vs. 0% and 20% simulated burn injuries (P=0.009). However, a critical RH value could not be discerned in one subject with a 40% simulated burn injury or in any subject with a 60% simulated burn injury, indicating physiologically uncompensable conditions throughout the experimental protocol. These preliminary data suggest that under the current environmental conditions, burn survivors with injuries of ≥40% have a substantially attenuated capacity for heat dissipation, placing them at greater risk of heat‐related illness during prolonged work and heat stress. Such information may be incorporated into exposure guidelines for burn survivors working under severe occupational heat stress such as military personnel.Support or Funding InformationFunding: Department of Defense – US Army, W81XWH‐15‐1‐0647This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.