History of exercise-induced asthma.

Strenuous exercise prolonged for several minutes can cause airway obstruction in asthmatic subjects. Initial obstruction becomes most extreme 5-10 min after the completion of exercise and usually remits within a few minutes but may recur 3-6 h later. The response to exercise depends upon the type of exercise. Swimming is less likely to cause exercise-induced asthma than running. Recent exercise or pretreatment with a bronchodilator or cromolyn can inhibit exercise-induced asthma. Nasal breathing or inhalation of warm, fully humidified air during exercise can minimize exercise-induced asthma. Local changes in osmolarity or cooling of mast cells probably causes release of mediators that cause airway obstruction.