Pulmonary gas exchange in asymptomatic smokers and nonsmokers.

Pulmonary gas exchange has been studied in 14 healthy smokers and 16 healthy nonsmokers (mean age: 36 years) breathing hypoxic, normoxic and hyperoxic gas mixtures, in a sitting position, at rest and on exercise. Alveolar-arterial oxygen tension difference is increased in smokers in hypoxia, at rest and on exercise, and the pulmonary diffusing capacity for oxygen is decreased. In normoxia the alveolar-arterial oxygen tension difference is increased on exercise. There is no difference between the two groups in hyperoxia. For the whole group there exists a negative relationship between (A-a)DO2 in normoxia and the diffusion indices measured on exercise. Arterio-alveolar carbon dioxide tension difference and the ratio physiological dead space/tidal volume are almost identical in both groups in any condition. A diffusion defect seems to be the more constant alteration of gas exchange in asymptomatic smokers.