Mechanism of postural hypoxemia in asymptomatic smokers.

Abstract

Ventilatory function, lung volumes, flow-volume curves, and alveolar-arterial oxygen tension gradients were measured in 24 smokers and nonsmokers by standard methods. Ventilatory tests and lung volumes were normal in both groups. As compared to nonsmokers, the smokers had a slightly smaller residual volume and functional residual capacity, (FRC), particularly in the supine position, and their flow-volume curves were less favorable. As a result, the forced expiratory flow rate at FRC in the supine position was significantly less in smokers than in nonsmokers. Alveolar-arterial oxygen tension gradients while breathing room air were larger in smokers than in nonsmokers, more so in the supine (P < 0.01) than in the erect position. When pure oxygen or 14 per cent oxygen was breathed, the alveolar-arterial oxygen tension gradients were identical in both groups; this indicates that maldistribution caused postural hypoxemia. Alveolar-arterial oxygen tension gradients, measured while the subjects were breathing ro...