Efficacy of body ventilation system for reducing strain in warm and hot climates.

This study determined whether a torso-vest forced ambient air body ventilation system (BVS) reduced physiological strain during exercise-heat stress. Seven heat-acclimated volunteers attempted nine, 2-h treadmill walks at 200 W m(-2) in three environments, -40 degrees C, 20% rh (HD), 35 degrees C, 75% rh (HW), and 30 degrees C, 50% rh, (WW) wearing the Army Combat Uniform, interceptor body armor (IBA) and Kevlar helmet. Three trials in each environment were BVS turned on (BVS(On)), BVS turned off (BVS(Off)), and no BVS (IBA). In HD, BVS(On) significantly lowered core temperature (T (re)), heart rate (HR), mean skin temperature (T (sk)), mean torso skin temperature (T (torso)), thermal sensation (TS), heat storage (S), and physiological strain index (PSI), versus BVS(Off) and IBA (P < 0.05). For HW (n = 6), analyses were possible only through 60 min. Exercise tolerance time (min) during HW was significantly longer for BVS(On) (116 +/- 10 min) versus BVS(Off) (95 +/- 22 min) and IBA (96 +/- 18 min) (P < 0.05). During HW, BVS(On) lowered HR at 60 min versus IBA, T (sk) from 30 to 60 min versus BVS(Off) and IBA, and PSI from 45 to 60 min versus BVS(Off) and at 60 min versus IBA (P < 0.05). BVS(On) changes in T (re) and HR were lower in HD and HW. During WW, BVS(On) significantly lowered HR, T (sk), and T (torso) versus BVS(Off) and IBA (P < 0.05) during late exercise. Sweating rates were significantly lower for BVS(On) versus BVS(Off) and IBA in both HD and WW (P < 0.05), but not HW. These results indicate that BVS(On) reduces physiological strain in all three environments by a similar amount; however, in hot-dry conditions the BVS(Off) increases physiological strain.