Alveolar-Arterial Oxygen Pressure Gradient in Normal Dogs

Abstract

Measurements of alveolar and arterial O2 tension were made by Riley''s technique in 23 normal anesthetized dogs breathing room air. The alveolar-arterial O2 gradient ranged from 0 to 29 mm. Hg, depending upon the magnitude of the alveolar ventilation. Exptl. increase of alveolar ventilation caused an increase in the size of the gradient; exptl. decrease of alveolar ventilation caused a decrease in the gradient. Ten measurements of the alveolar-arterial O2 gradient in 3 normal wakeful dogs revealed a mean gradient of 18 mm. Hg. 19 expts. performed on 14 anesthetized dogs breathing 8-10% O2 revealed a mean alveolar-arterial gradient of 3 mm.Hg. 16 measurements of the arterial O2 tension by a polarographic technique during the inspiration of 100% O2 revealed negligible a-a gradients. It is concluded that the alveolar-arterial gradient in normal dogs is due to uneven ventilation of the lungs and that no gradient results either from imperfect diffusion across the alveolar membrane or from venous admixture to arterialized blood.