Prediction of lung hyperinflation by forced spirometry: Results from COSYCONET

Abstract

Background: Lung hyperinflation is major determinant of prognosis and response to therapy in COPD. It is linked to air trapping and usually determined by body plethysmography or gas dilution. As the availability of these methods is limited, the question arises to which extent hyperinflation can be estimated from spirometry.

Methods: We used data from patients of GOLD grades 1–4 obtained in Visits 1–5 of the COPD cohort COSYCONET. Predictive parameters were derived from Visit 1 data, while Visit 2–5 data were used to assess reproducibility. Data from all visits were pooled to determine prediction models for males and females, including age, height and BMI as covariates. Hyperinflation was defined as residual volume to total lung capacity ratio (RV/TLC) above the ULN.

Results: Visit 1 data from 1988 patients were available for analysis (FEV1 53.1±18.4 %pred; FVC 78.8±18.8 %pred; RV/TLC 0.547±0.107). In total, 7157 data sets were analyzed. Among measures of hyperinflation, RV/TLC turned out to be most reliable, with FEV1 %pred and FVC %pred being sufficient for prediction. Their relationship to RV/TLC could be depicted in nomograms. Even when neglecting the effects of covariates, RV/TLC above ULN could be predicted by FEV1 %pred, FVC %pred or their combination with an AUC of 0.882, 0.869 and 0.899. Other parameters, i.p. slow inspiratory vital capacity, did not play a role.

Conclusions: The degree of hyperinflation in terms of RV/TLC can be estimated from forced spirometry, with an accuracy sufficient for inferring the presence of significant hyperinflation defined by RV/TLC above the upper limit of normal. This may be useful for clinical settings, where body plethysmography is not available.