EFFECT OF OXYGEN BREATHING ON DISTRIBUTION OF PULMONARY BLOOD FLOW IN CHRONIC OBSTRUCTIVE LUNG DISEASE

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Abstract
Serial changes in physiologic dead space/tidal volume (VD/VT) ratio and minute ventilation were measured in 58 subjects who had chronic obstructive lung disease, while breathing air, or O2 for 10-15 min. The ratio did not increase by more than 0.05 between 2 measurements when the subjects were breathing air. During O2 breathing, VD/VT ratio increased by more than 0.05 (and by up to 0.15) in 39 subjects, and by less than this amount in the other 19. Increases of VD/VT ratio were unrelated to changes in ventilation and reflected changes in the distribution of blood flow in the direction of increased blood flow through poorly ventilated regions of the lungs. The increase of VD/VT ratio may be due to reversal of pre-existing regional pulmonary vasoconstriction. The occurrence of this phenomenon in 2/3 of 58 patients with obstructive lung disease, is comparable with the previous demonstration that somewhat more than 1/2 of normal subjects re-producibly show brisk pulmonary vasoconstriction in response to hypoxia, and that the remainder show little or none. This intrinsic characteristic of different normal subjects may persist and be ex-aggerated in persons with obstructive lung disease.