Exercise-induced asthma. Assessment of current etiologic concepts.

Airflow limitation in exercise-induced asthma is related to the thermal events in the intrathoracic airways. This article reviews the present knowledge about the exchange of respiratory heat and water. The evidence for the various theories proposed for the basic mechanisms involved in exercise-induced asthma are discussed. The evidence suggests that exercise-induced airways obstruction may be a vascular phenomenon dependent on the rapidity and magnitude of airway rewarming. Obstruction is induced if a thermal gradient exists at the end of exercise and the greater the gradient the greater the resultant hyperemia and edema. The basic mechanism of control of reactivity is still not known and directions for future research are outlined.