Referential equations for pulmonary diffusing capacity using GAMLSS models derived from Japanese individuals with near-normal lung function

Objective To generate appropriate reference values for the single-breath diffusing capacity of the lungs for carbon monoxide (D-LCO), alveolar volume (V-A), and the transfer coefficient of the lungs for carbon monoxide (K-CO, often denoted as D-LCO/V-A) in the Japanese population. We also intended to assess the applicability of these values for the Japanese population by comparing them to those published by the Global Lung Function Initiative in 2017 (GLI-2017) and previous values. Methods In this retrospective study, we measured the spirometric indices, D-LCO, V-A, and K-CO of the Japanese population aged 16-85 years. The lambda, mu, and sigma (LMS) method and the generalized additive models for the location, scale, and shape program in R were used to generate the reference values. Results We conducted a total of 390 tests. The GLI-2017 z-scores of D-LCO were approximately zero, whereas those of K-CO and V-A were far from zero. In the present study, the mean square errors of the D-LCO, V-A, and K-CO reference values were lower than the reference values derived from GLI-2017 and previous linear regression equations. Conclusions Reference values obtained in this study were more appropriate for our sample than those reported in GLI-2017. Differences between the two equations were attributed to underestimating K-CO (D-LCO / V-A) and overestimating V-A, respectively, by the GLI-2017 for the Japanese population.

Automated summary

The objective of this study was to generate appropriate reference values for lung function parameters in the Japanese population and assess their applicability compared to existing values. The results showed that the reference values obtained in this study were more suitable for the Japanese population than those reported by the Global Lung Function Initiative in 2017. Differences in the equations were attributed to underestimation of the transfer coefficient and overestimation of alveolar volume in the GLI-2017 guidelines for the Japanese population.