Grading, time course, and incidence of exercise-induced airway obstruction and hyperinflation in asthmatic children.

We evaluated clinical status and pulmonary function in 60 perenially asthmatic and 11 normal children before and repeatedly after incrementally increasing bicycle ergometer exercise. The changes in clinical status and pulmonary function which were elicited by strenuous exercise were graded by an air exchange and a physiological grading system respectively. Normal children showed no significant clinical or physiological changes after exercise. Strenuous exercise elicited significant deteriorations in clinical and physiological measurements in 36% to 77% of asthmatic girls and 46% to 90% of asthmatic boys, the frequency depending on the test used to determine exercise-induced abnormalities. The incidence of exercise-induced asthma (EIA) was statistically significantly higher in asthmatic boys than girls. The higher incidence of EIA in boys was primarily due to a larger number of very severe attacks in boys than girls; mild and moderate EIA was about equally common in the two sexes. Most patients with EIA developed large and small airway obstruction, although large airway obstruction tended to be the predominant and the more severe abnormality. Clinical and physiological abnormalities, regardless of severity, were usually most marked during the first ten minutes after exercise and lessened thereafter. Mild EIA usually lasted for only 15 minutes or less; severe EIA improved, but usually did not resolve within 35 minutes of exercise. There were three patinets in whom the severity of EIA got worse after exercise and an additional seven in whom the improvement was minimal. In these ten patients isoproterenol aerosol terminated EIA, indicating that exercise-induced large and small airway obstruction in asthmatic children is primarily, if not solely, due to bronchospasm.