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The decrease in pulmonary function, expressed as peak expiratory flow, which is seen in some asthmatics after exercise (exercise-induced asthma (EIA)), has been studied under conditions standardized with regard to ventilation during exercise, room temperature and relative humidity of the inhaled air. Exercise was performed under four different conditions. 1) temperature (T) 15 degrees C and relative humidity (RH) 30%, and 2) T 15 degrees C and RH 70%, 3) T 30 degrees C and RH 30% and 4) T 30 degrees C and RH 70%. Treadmill running was performed on four succeeding days at the same time of day with the four different combined conditions. Identical ventilation during the exercise was secured on each day by monitoring respiratory frequency, tidal volume, minute ventilation and accumulated ventilation. A significantly smaller decrease in pulmonary function occurred when both T and RH were high, whereas the decrease in pulmonary function after exercise was identical when either temperature or relative humidity, or both, were low. It is concluded that the water concentration of the inspired air is negatively correlated to the decrease in pulmonary function after exercise in asthmatics.

Eleven adult patients with exercise-induced asthma (EIA) were subjected to swimming and bicycle exercise under controlled conditions regarding temperature and relative humidity of the inhaled air, the respiratory frequency, tidal volume, minute ventilation and the accumulated ventilation. Swimming for 6 min was performed on the first day, and the next day the patients performed bicycle exercise. On both days the temperature of the inhaled air was 23% C and the relative humidity 15%. The average accumulated ventilation for the 6 min of exercise was 404 l for bicycle exercise and 419 l for swimming. The decrease in pulmonary function was 31% after bicycle exercise and 30% after swimming. It is concluded that the stimuli for EIA are equally effective whether exercise is performed in the form of swimming or bicycling.