[Dynamic analysis of airway temperature in dogs breathing cold air]

Exercise in cold, dry air induces bronchoconstriction. However, the time course of airway cooling during the breathing of cold air has not been investigated. In this study in dogs, the temperatures of tracheal gas and the tracheal wall were measured continuously while the animal was breathing cold air at approximately 4.5 degrees C. The temperature of the tracheal gas decreased during the inspiratory phase, increase slightly early in the expiratory phase, and then decreased to the level at end-expiration. The lowest temperature of the tracheal gas decreased significantly, from 29.7 +/- 2.4 degrees C (mean +/- SD) to 25.7 +/- 2.8 degrees C. The highest temperature also changed significantly, but the decrease was less than 1 degree C. The lowest temperature of the tracheal wall decreased from 31.1 +/- 2.6 degrees C to 30.5 +/- 2.5 degrees C during cold-air breathing, but the difference was not significant. When a dog inspired deeply during a cough, the temperature of tracheal gas did not decrease linearly with the progression of inspiration. However, the decrease in the tracheal wall temperature was almost directly proportional to inspiratory volume. We concluded that both the tracheal gas and the tracheal wall temperatures were resistant to cooling with cold-air breathing. It remains uncertain whether rapid, deep breathing during exercise decreased the tracheal wall temperature.