Portable, ambient air microclimate cooling in simulated desert and tropic conditions.

We examined the feasibility of providing ambient air during exercise and conditioned (cooled) air during rest on reducing physiological strain and optimizing tolerance time. Six male soldiers attempted 250-min exposures in hot/dry and hot/wet environments. Subjects wore chemical protective clothing over the combat vehicle crewman uniform and an air-cooled vest. They alternated between 50 min of treadmill walking (420 W) and 50 min of rest (105 W). During the walks, a backpack mounted blower provided a total of 10 or 18 cfm of air to the vest and face; while subjects received 18 cfm of conditioned air from an umbilical during rest. A control test with conditioned air during rest, but only a ventilated facepiece during work was also conducted in the hot/dry environment. In the hot/dry environment the ambient air backpack extended (p less than 0.05) tolerance time and significantly reduced rectal temperatures, heart rates and sweating rates compared to control; no differences were found between 10 and 18 cfm. In the hot/wet environment, tolerance time was extended compared to a predicted tolerance time assuming no microclimate cooling. We conclude that the ambient air backpack reduced physiological strain and improved tolerance time of combat vehicle crewmen during exercise in the heat.