Head and/or torso cooling during simulated cockpit heat stress

Liquid-conditioned garments (LCG's) may be useful in alleviating heat stress on aircrew members. This study evaluated the effects of a liquid-cooled vest and/or cap on subjects exposed to a thermal environment which simulated the stress of low-level flight in hot weather. The chamber was set at dry bulb temperature 35 degrees C, wet bulb temperature 26 degrees C, and black globe temperature 43 degrees C. Subjects were eight men, aged 23-45 yr. Each subject was studied in four 100-min exposures: uncooled control (XX); head cooling only (HX); torso cooling only (XT); and combined head and torso cooling (HT). Cooling effects were evaluated by using rectal temperature (Tre); heart rate (HR); sweat rate (SRF and SRT for forehead and total body, respectively); and subjective comfort. Uncooled runs (XX) produced final values: Tre = 37.8 degrees C, HR = 94 beats/min, SRT = 25 g/m2 X h and SRF = 45 g/m2 X h. Combined head and torso cooling maintained the subjects at nearly their initial (baseline) state. Cap effects per se were assessed by comparing HX to XX, and HT to XT. Head cooling proved 2-3 times as efficient as torso cooling, although limited by the small surface area involved. We conclude that the specific effects of head cooling in improving comfort and diminishing forehead sweating, as well as the efficient systemic cooling observed, justify further work on cockpit applications.