A comparison of endogenous versus exogenous heating on the subsequent development of hypothermia.

Abstract

This study investigated the effect of endogenous and exogenous heating on body core cooling rate, afterdrop and re-warming rate in humans during subsequent cold-water immersion. On three separate days, following 30 min baseline resting at an ambient temperature of 25°C, seven subjects were either: (1) seated upright for 15 min rest (Control); (2) exercised 15 min on a cycle ergometer at 70% VO2 max (Exercise); or, (3) immersed 16.8 +/- 6.2 min in warm water (40°C) (Warm-water immersion) to an esophageal temperature (TES) similar to that of end of exercise. Subjects were then cooled in water (7°C) to a TES of 34.5°C and rewarmed by spontaneous shivering (shivering thermogenesis) in air. There was a 1.3-fold increase in the overall body core cooling rate during Exercise as compared to Control (P < 0.01). Warm-water immersion demonstrated the largest difference in overall cooling rate above Exercise and Control with a 2.5- and 3.3-fold increase, respectively (P < 0.01). The greatest difference between trials occurred within the initial 15 min (i.e., a 2.0- and 4.9-fold increase above Control for Exercise and Warm-water immersion, respectively). There was no significant difference in the TES afterdrop (∼0.5°C) nor afterdrop duration (∼15 min). Similarly, rewarming rates were almost identical under all conditions (∼3.1°C·h-1). These data show that pre-warming can have a detrimental effect on survival time during a subsequent cold-water immersion.