Skin temperature feedback optimizes microclimate cooling

A novel pulsed cooling paradigm (PCskin) integrating mean skin temperature (Tsk) feedback was compared with constant cooling (CC) or time-activated pulsed cooling (PC). Eight males exercised while wearing personal protective equipment (PPE) in a warm, dry environment (dry bulb temperature: 30 degrees C; dew-point temperature: 11 degrees C) in each of the tests. Treadmill exercise was performed (approximately 225 W x m(-2)) for 80 min. A liquid cooling garment (LCG) covered 72% of the body surface area. Core temperature (Tc), local skin temperatures, heart rate, inlet and outlet LCG perfusate temperatures, flow, and electrical power to the LCG and metabolic rate were measured during exercise. At 75 min of exercise Tsk was higher (33.9 +/- 0.2 degrees C) in PCskin, than in PC (33.1 +/- 0.5 degrees C) or CC (32.0 +/- 0.6 degrees C) and PC > CC. The changes in Tc and heart rate during the tests were not different. Tc at 75 min was not different among the cooling paradigms (37.6 +/- 0.3 degrees C in PCskin, 37.6 +/- 0.2 degrees C in PC and 37.6 +/- 0.2 degrees C in CC). Heart rate averaged 124 +/- 10 bpm in PCskin, 120 +/- 9 bpm in PC and 117 +/- 9 bpm in CC. Total body insulation (degrees C x W(-1) x m(-2)) was significantly reduced in PCskin (0.020 +/- 0.003) and PC (0.024 +/- 0.004) from CC (0.029 +/- 0.004). Electrical power in PCskin was reduced by 46% from CC and by 28% from PC. Real-time Tsk feedback to control cooling optimized LCG efficacy and reduced electrical power for cooling without significantly changing cardiovascular strain in exercising men wearing PPE.