Exercise-induced asthma.

Exercise-induced asthma is the phenomenon of transient airflow obstruction, typically 5 to 15 minutes after physical exertion. The increased airway resistance produces a 15% or greater decrease in the forced expiratory volume in 1 second, or in peak expiratory flow rate. Exercise-induced asthma occurs in 90% of individuals with asthma, representing 12% to 15% of the population world-wide. The prevalence of exercise-induced asthma among athletes ranges between 3% and 11%. Several theories of the etiology exist: respiratory heat or water loss (or both), hyperventilation causing discharge of bronchospastic chemical mediators or rebound rewarming of the blood in airway tissues. Treatment is either by pharmacologic or nonpharmacologic means, but medication continues to be the cornerstone of therapy for exercise-induced asthma. beta 2-Specific agonists remain the drugs of choice. Cromolyn sodium and nedocromil sodium are alternatives to the beta 2-agonists, and the combined use of the two classes of agents can provide additive benefits.