CONTINUOUS AND INTERMITTENT PERSONAL MICROCLIMATE COOLING STRATEGIES

A comparison was made between two personal auxiliary cooling approache s for the relief of thermal stress while wearing the standard USAF Che mical Defense Ensemble (CDE). Subjects exercised at approximately 40% VO(2)max in either warm (28/24/34 degrees C) or hot (38/26/43 degrees C) environmental conditions, (Tdb/Twb/Tbg degrees C, respectively). Du ring each of three trials, four hours of intermittent work (four work/ rest cycles) were attempted. Microclimate air cooling was applied in t wo different fashions and compared with a control trial during which n o cooling was received (NC). In one trial, conditioned air cooling (Ti n approximately 20 degrees Cdb) was delivered during rest periods only (intermittent cooling, IC), while during the second trial, ambient ai r cooling was also applied during the work period in addition to the c onditioned air delivered during rest periods (continuous cooling, CC). During the warm condition, exposure cycle time was 45 min work and 15 min rest, while under the hot conditions, exposure cycle time was 30 min work and 30 min rest. Both CC and IC trials resulted in significan tly extended work times, lower final rectal temperatures, heart rates, and sweat production (SP) than in the NC trial. Additionally, CC resu lted in significantly lower SP, higher % sweat evaporation, and lower ratings of perceived exertion (RPE) and thermal comfort (TC) than IC a t both warm and hot temperatures. Moreover, subjects were better able to maintain thermal equilibrium (i.e., cumulative heat balance) over t ime using CC compared to IC in the warm environment. The physiological significance of these findings, in some cases, was secondary to the i mprovement in subjective measures of TC and RPE. In conclusion, the ad dition of ambient air, microclimate cooling during work in these envir onments is effective in lowering thermal strain for subjects exercisin g in the heat while wearing the CDE.