Prediction Equations for Single-Breath Carbon Monoxide Diffusing Capacity from a Chinese Population

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Abstract
Most available prediction equations for the single breath carbon monoxide diffusing capacity, or DLCO, are based on white populations and do not account for racial differences. We performed this test on 436 Chinese adults. The method of measurement essentially followed the American Thoracic Society recommendations. Data on 306 subjects who had two technically acceptable test results provided prediction equations and upper and lower 95% confidence limits for healthy nonsmokers. Simple linear equations using age, height, and body weight as independent variables were generated and compared with nonlinear models. The use of nonlinear models did not add to the predictability of standard linear regressions. The distribution of residuals (predicted-measured values) was Gaussian with simple linear regressions. A comparison of predicted values for DLCO, calculated from different equations in an independent group of healthy subjects, revealed that the present set of equations had the smallest residual mean and standard deviation rankings compared with other equations for white subjects. These are the first DLCO equations proposed for Chinese men and women aged 20 to 70 yr. The predicted values from this study for DLCO and alveolar volume (VA), were significantly lower than those of most equations for white subjects, but were not for DLCO/VA. Although a portion of the differences may be explained by the additive effects of technical factors, the discrepancies can also be attributed to the smaller body size in this ethnic group, and consequently to the smaller lung volumes. Equations derived from whites, with inclusion of smokers, provided predicted values comparable to, or even lower than, those from this study.(ABSTRACT TRUNCATED AT 250 WORDS)