Referential equations for pulmonary diffusing capacity generated from the Japanese population using the Lambda, Mu, or Sigma method and their comparisons with prior referential equations

Abstract

Background: This study aimed to establish reference equations for single-breath lung carbon monoxide diffusing capacity (D_LCO), alveolar volume (V_A), and transfer coefficient of the lungs for carbon monoxide (K_CO, sometimes written as D_LCO/V_A) in the Japanese population. A generalised additive model for location size and shape (GAMLSS) was used to build each equation.

Methods: To collect pulmonary function data throughout a broad age range, we prospectively obtained pulmonary function data from healthy volunteers and retrospectively obtained data from patients with normal diffusing capacity aged 16-85 years.

Results: In total, 702 tests were conducted. The validation group z-scores, except for D_LCO in males, showed substantial discrepancies between the Global Lung Initiative (GLI) baseline prediction equations and the present study's prediction equations, indicating the need for a new reference value prediction approach. The root mean square errors of the D_LCO, V_A, and K_CO reference values obtained from the present study's prediction equations were lower than those derived from the GLI and previous linear regression equations.

Conclusions: Reference values obtained in this study were more appropriate for our sample than those derived from the existing baseline prediction equations. This research's contribution is the development of a more precise prediction equation that can be used to establish a reference value range for pulmonary diffusing capacity.

Ethics and dissemination: This research does not include any dissemination plan (publications, data deposition and curation).

Keywords: Pulmonary diffusing capacity; Pulmonary function test; Pulmonology; Reference values; Transfer coefficient of the lungs for carbon monoxide.