Limb blood flow while wearing aircrew chemical defense ensembles in the heat with and without auxiliary cooling.

The effect of auxiliary air cooling on endurance time and limb blood flow in the heat (37 degrees C, 50% r.h., target time = 150 min) while wearing aircrew chemical defense (CD) ensembles was examined. Eight males were dressed in aircrew CD ensembles with or without an air-cooled vest. After an initial 10 min treadmill walk and 20 min of seated rest, the subjects alternately rested and exercised on a cycle ergometer (10 min rest, 10 min exercise) resulting in an overall metabolic rate of 240 W. Arm and leg blood flow (ABF, LBF), determined by venous occlusion plethysmography, were significantly lower with air cooling (AC) than with no cooling (NC) during the same time period (p less than 0.05). Endurance time was much greater with AC than with NC (150 min AC vs. 92 +/- 0.08 min NC, p less than 0.01). Arm and calf skin temperatures, rectal temperature and heart rate were all significantly lower with AC than with NC (p less than 0.05) after the onset of the cycle exercise. The results show that the use of the air-cooled vest under these conditions was able to increase heat tolerance and reduce blood flow to the periphery.