Characterization of the late response in exercise-induced asthma.

Nine young adult subjects who developed asthma after a standard treadmill exercise test were studied. Pulmonary function tests were performed before and after exercise and serially for at least 6 hr afterwards. The subjects performed pulmonary function tests while breathing room air and after breathing an oxygen-helium mixture with each test. Although pulmonary function returned to normal within 3 hr after exercising in all subjects, eight of the nine had late asthmatic reactions 3 to 5 hr afterward. In general the late response was less severe than the initial response. Two subjects, however, noticed clinical asthma. In the immediate response, eight of the nine subjects were helium "responders," suggesting that the immediate response involved both large and small airways. In the late response, seven of eight subjects were helium "nonresponders," suggesting that the late response occurred primarily in small airways.