Relief of Hypoxia-Related Bronchoconstriction by Breathing 30 Per Cent Oxygen1–4

Airway resistance decreases when hypoxemic subjects with chronic obstructive pulmonary disease (COPD) breathe 30 % O2. To verify this finding and to localize the site of action of O2, flow volume curves on air and helium-O2mixtures were obtained before and after subjects breathed 30 % O2. Patients with COPD and hypoxemia showed an increase in flow rates and a decrease in the density dependence of flow while breathing 30 % O2. Atropine produced a similar change in flow rates and density dependence, but then no further change occurred with 30 % O2. Five control subjects with COPD, who performed the same sequence of tests without breathing 30 % O2, showed no change in flow rates or density dependence. Normal control subjects also showed no change in flow rates or density dependence while breathing 30 % O2. Breathing 30 % O2 relieves hypoxia-induced bronchoconstriction and appears to act on large airways.