Prevalence and characteristics of late asthmatic responses to exercise.

The prevalence and characteristics of late asthmatic responses to exercise were studied in an adult asthmatic population. Twenty-four subjects (eight male and 16 female), aged 17 to 39 years (mean, 23.7 years), performed a 6-minute exercise on a bicycle ergometer at 75% of their maximum oxygen intake. FEV1 was measured at regular time intervals up to 8 hours after exercise. Seven subjects demonstrated a late asthmatic reaction defined as a fall in FEV1 greater than 10% between 2 to 8 hours. Bronchial reactivity to histamine was unchanged 24 hours after the exercise, compared to baseline. On a control day, a fall in FEV1 similar to the one observed after exercise was induced by methacholine inhalation. Measurements of FEV1 were done at the same time intervals as on exercise day. Neutrophil chemotactic activity was measured in the serum of 15 subjects, on exercise day for early responders, and on the 3 test days for subjects with a dual response. There was no difference between subjects with an isolated early or late response for age, sex, or atopic status. Baseline expiratory flows and nonspecific bronchial reactivity to histamine were similar in both groups. These results demonstrate the occurrence of a late asthmatic response in 30.4% of the population studied. There was no significant change of nonspecific bronchial responsiveness after the late asthmatic response to exercise. No significant increase in neutrophil chemotactic activity could be observed.