Cold air inhalation and esophageal temperature in exercising humans.

This study was performed to examine the dynamics and localization of respiratory heat exchange in exercising humans breathing cold air. Eight normal individuals performed 10 min of exercise at 80% of their predicted Vo2max with inspired air at 22 degrees C, saturated with water vapor; or at -40 degrees C, dry. Rectal temperature (Tre) and temperature at various locations along the length of the esophagus were measured during the exercise period. Temperature in the lower third of the esophagus was in close agreement with Tre and was unaffected by the level of respiratory heat exchange. Upper esophageal temperature decreased substantially during exercise, the magnitude of the decrease being dependent upon proximity to intrathoracic airways and the level of respiratory heat exchange (RHE). We conclude that with high levels of RHE, the capacity of the nasopharynx and upper airways to completely condition inspired air is exceeded. As a consequence, heat and water exchange occur in regions of the respiratory tract not normally involved in this function.