Assessment of hyperinflation: comparison of GLI and ECSC lung volume reference equations

Abstract

BackgroundAssessment of static hyperinflation severity is crucial to identify COPD patients eligible for lung volume reduction. The current recommendation of residual volume (RV)≥175% predicted may need reconsideration due to potential differences between the Global Lung Function Initiative (GLI) and the European Community for Steel and Coal (ECSC) reference equations for RV and concerns about using %predicted.MethodsWe compared the RV reference values derived from the GLI and ECSC using mathematical simulated data and used a receiver operating characteristic curve to establish a new GLI-derived z-score cut-off for RV using body plethysmography data of severe COPD patients.ResultsThe GLI reference equation for RV consistently yields a lower predicted RV for individuals with an average or below average height (females ≤163 cm and males ≤177 cm). Our clinical cohort consisted of 1011 patients with COPD (38% GOLD stage III and 59% stage IV). In this cohort, a GLI-derived RV z-score of ≥2.9 could accurately replace the ECSC-derived 175% predicted cut-off and for 200% predicted, a z-score of ≥3.5 was established.ConclusionThere are substantial differences in predicted RV values between the GLI and ECSC, with the GLI generally yielding a lower predicted RV in the majority of individuals. A GLI-derived RV z-score of ≥2.9 could be used to replace the currently used cut-off of ≥175% predicted to identify potential lung volume reduction candidates.