Single-breath carbon monoxide diffusing capacity: effect of body size and age in healthy nonsmoking Chinese

Because of unanswered questions about reference values for single-breath carbon monoxide diffusing capacity (DLCO) in Chinese, standardized DLCO measurements were carried out in a selected sample of 257 healthy nonsmoking Chinese aged 20-70 years. The methods of measurement essentially followed the American Thoracic Society (ATS) recommendations. The measured DLCO was corrected to a standard hemoglobin value. Observed mean values for DLCO were 25.87 +/- 5.64 mL/min/mmHg in men and 21.16 +/- 3.88 mL/min/mmHg in women. Correlations of DLCO indices with anthropometric variables revealed that DLCO was best correlated with age in both sexes (r = -0.71 for men and r = -0.61 for women, p < 0.001). For alveolar volume (VA), the most significant correlation was found with height. For specific diffusing capacity (DLCO/VA), there was a significant negative relationship with age. Reference equations using age and body surface area (BSA) as independent variables for DLCO, VA and DLCO/VA were derived separately for men and women. An analysis of the distribution of residuals was Gaussian with simple linear regressions. Predicted values for DLCO and VA, as estimated in the present study, were much lower than equations derived from Caucasian populations. On the contrary, DLCO/VA values, as predicted by the present set of equations, were comparable to those of Caucasian equations. Therefore, differences in DLCO values between Chinese and Caucasians may be explained by differences in lung volume rather than by ethnic variations in the inherent characteristics of the alveolar capillary membrane. Predicted values for Chinese should be obtained from equations established from this study rather than extrapolated from those of Caucasians. The results of this study will be of value to clinical laboratories dealing with pulmonary function testing for Chinese patients.