[Pulmonary diffusing capacity in normal smoking Chinese].

Single-breath carbon monoxide diffusing capacity parameters including DLCO, VA and DLCO/VA were studied in 131 asymptomatic healthy smoking Chinese men aged 25-70 years. Measurements were conducted with a rolling-sealed, computer-based pulmonary function analyzer and were in accordance with testing procedures recommended by the American Thoracic Society. Diffusing capacity in smokers was compared with that in normal nonsmoking adults. Cigarette smoking caused a reduction in DLCO and DLCO/VA, but not in VA. Therefore, the change in diffusing capacity was not related to a decrease in lung volume. Twenty-one percent of all smoking subjects showed an abnormally low DLCO value. The onset of this defect in pulmonary diffusion appears to occur early in cigarette smokers. Since older smokers with evidence suggestive of pulmonary emphysema or chronic bronchitis were excluded due to their respiratory symptoms, the accumulated effect of smoking on DLCO cannot be demonstrated in this study. The prediction equations of DLCO, VA and DLCO/VA were generated for Chinese male smokers, using age, height and weight as the independent variables. The present study was unable to include any tobacco smoking parameters in the regressing equations. It is postulated that the modest increase in carboxyhemoglobin (COHb %) in smokers may explain the immediately lower DLCO values observed in smokers shortly after they begin smoking.