Influence of heat and humidity on the airway obstruction induced by exercise in asthma.

We examined the degree of airway obstruction that developed in eight asthmatics who exercised while breathing air under four conditions: (a) ambient room temperature and water content; (b) body temperature and ambient water content; (c) ambient room temperature fully saturated; and (d) body temperature fully saturated. These test conditions were performed in random order. Multiple aspects of pulmonary mechanics were measured before and 5 min after exercise. When air at ambient conditions was inhaled, the expected airway obstruction developed after exercise, and all variables changes significantly from their pre-challenge values. Heating the air to body temperature did not influence this response. Increasing the humidity at ambient temperatures significantly blunted the response, and by inhaling body temperature, fully saturated air completely prevented it from occurring. Thus, the water content of inspired air is an important variable in the development of exercise induced asthma.