COPD: Pulmonary damage beyond FEV1

Background: Chronic Obstructive Pulmonary Disease (COPD) is a heterogeneous disease: Forced Expiratory Volume in 1 second (FEV1) does not adequately reflect disease severity. In addition, parenchymal damage can be present even in mild obstruction. We hypothesize that patients with COPD referred to a pulmonologist can have hyperinflation and lowered diffusion capacity even in the presence of mild obstruction. Methods: A retrospective lung function database search was performed, covering all new COPD patients (N=4278) in a Dutch hospital between 1998-2012. Besides spirometry, Total Lung Capacity (TLC), Residual Volume (RV), and Diffusion Capacity (DLCO) were measured. FEV1 was categorised according to the Global initiative for Chronic Obstructive Lung Disease (GOLD). Only patients with a FEV1/VC < 0.70, a confirmed COPD diagnosis by a pulmonologist, and a complete dataset were included. Results: As GOLD stage increases, RV/TLC ratio (normal<40%) increases and DLCO decreases (both p<0.01, ANOVA). A relevant proportion of patients with mild obstruction show severe hyperinflation and/or impaired diffusion capacity ![Figure][1] . Conclusion: Pulmonary damage measured by RV/TLC and DLCO increases with airflow obstruction. However, a relevant proportion of COPD patients have mild obstruction with hyperinflation and/or lowered diffusion capacity. Hence, COPD patients with persistent symptoms, even in GOLD I obstruction, might also require assessment of RV/TLC and DLCO analysis. [1]: pending:yes