EFFECT OF EXERCISE RATE AND ROUTE OF INHALATION ON SULFUR-DIOXIDE-INDUCED BRONCHOCONSTRICTION IN ASTHMATIC SUBJECTS

Publisher Website
Google Scholar
Abstract
Nine asthmatic patients exercised at low, moderate and high work rates on a cycle ergometer while breathing filtered, humidified air with or without 0.5 ppm SO2 in a double-blind study. Subjects first performed these experiments breathing through a mouthpiece while wearing a noseclip (oral breathing) and then repeated the experiments breathing through a facemask that separated and permitted independent measurement of oral and nasal air flow (oronasal breathing). Specific airway resistance was determined before and after exercise by body plethysmography. Inhaled by mouthpiece, 0.5 ppm SO2 caused bronchoconstriction at moderate and high but not at low work rates. There was a dose-response relationship between the work rate performed and the degree of bronchoconstriction induced. Inhaled oronasally, 0.5 ppm SO2 caused bronchoconstriction only at the high work rate. SO2-induced bronchoconstriction is dependent on the work rate of exercise during exposure. Oronasal breathing is only partially effective in preventing the bronchoconstriction observed with oral breathing. Oronasal breathing is less effective in preventing bronchoconstriction with high than with moderate exercise at this concentration of SO2.