A MINISWINE MODEL OF ACUTE EXERTIONAL HEAT EXHAUSTION

Method: We examined the thermoregulatory and hemodynamic responses of 12 miniswine (31 +/- 3.9 kg) during 25-30 min of treadmill exercise (5 .4 km . h(-1), 5% grade) under cool (10 degrees C), moderate (20 degre es C) and warm (30 degrees C) ambient temperature (Ta) conditions. Res ults: Within 15-20 min of exercise at Ta = 30 degrees C, the miniswine demonstrated significant hyperventilation, hypersalivation, and unste ady gait. Exercise-heat endurance time (T) at Ta = 30 degrees C decrea sed by 35% and 40% in comparison to T at Ta = 20 degrees C and 10 degr ees C, respectively. This resulted from a significant rise in heat str ain (S)-defined as the rate of change in rectal temperature. Averaged throughout exercise, S increased from 0.04 +/- 0.01 degrees C . min(-1 ) and 0.05 +/- 0.02 degrees C . min(-1) at Ta = 10 degrees C and 20 de grees C, respectively, to 0.10 +/- 0.03 degrees C . min(-1) at Ta = 30 degrees C. Due to the comparatively large storage capacity of the por cine spleen relative to humans, splenectomized miniswine were used. Th is permitted calculation of percentage changes in plasma volume (%Delt a PVc) from hematocrit (HCT) and hemoglobin (HGB) without the confound ing effects oi splenic red cells released into the circulation during exercise. Independent of Ta, preexercise PVc decreased 3%-5% (p less t han or equal to 0.05) within the first 10 min of exercise, but increas ed 5%-9% (p less than or equal to 0.05) by 10 min post-exercise. Concl usion: We conclude that the poor thermoregulatory ability of miniswine manifested in insignificant sweating and restricted evaporative cooli ng, may make them an appropriate model for acute exertional heat exhau stion in humans working in hot, humid conditions and/or wearing imperm eable protective clothing. Further, evaluation of plasma volume change s from HCT and HGB in a miniswine model should consider the merit ai a splenectomized design.