Resistance to breathing during exercise-induced asthma attacks.

Exercise-induced wheezing attacks in young adults with asthma were studied using methods that measure airway resistance or total pulmonary resistance. Running up and down stairs for eight minutes provoked an average increase in airway resistance to 310 per cent more than the highest control values. The attacks were relieved by inhalation of isoproterenol aerosol and by inhalation of 6 per cent to 8 per cent carbon dioxide in air, but not by injected atropine. They differed in time course and response to pharmacologic agents from the reflex bronchoconstriction that followed forced breathing maneuvers or inhalation of dilute histamine aerosols in the same subjects.