Effect of carbon dioxide breathing on specific airway conductance in normal and asthmatic subjects.

Abstract

The effect of breathing 2.5 to 10 per cent carbon dioxide in air on specific airway conductance was determined by plethysmography in 9 normal subjects and in 8 subjects with mild asthma. In 9 normal subjects, during breathing of 5, 7.5, and 10 per cent carbon dioxide, mean (± SE) values of specific airway conductance decreased by 15.8 ± 6.1, 24.4 ± 6.0, and 28.4 ± 7.9 per cent with increases in end-tidal carbon dioxide tension of 5.0 ± 1.6, 12.3 ± 2.3, and 20.2 ± 2.5 mm Hg, respectively. These changes were not significantly affected by prior administration of atropine or propranolol except that atropine prevented the decrease in specific airway conductance during 5 per cent carbon dioxide breathing. Isocapnic hyperventilation decreased specific airway conductance (15 ± 6 per cent) but to a lesser extent than during similar increases in ventilation due to breathing of 10 per cent carbon dioxide. In contrast, in 8 subjects with asthma, specific airway conductance did not change during carbon dioxide breathi...