LAUSR

BACKGROUND Most pulmonary conditions reduce forced vital capacity (FVC), but studies of patients with combined pulmonary fibrosis and emphysema demonstrate that reductions in FVC are less than expected when these two conditions coexist clinically. RESEARCH QUESTION Do interstitial lung abnormalities (ILA), chest computed tomography (CT) imaging findings that may suggest an early stage of pulmonary fibrosis in undiagnosed individuals, affect the association between emphysema and FVC? STUDY DESIGN AND METHODS Measures of ILA and emphysema were available in 9579 and 5277 participants from phases 1 (2007-2011) and 2 (2012-2016) of COPDGene, respectively. ILA were defined by Fleischner Society guidelines. Adjusted linear regression models were used to assess the associations and interactions between ILA, emphysema, measures of spirometry and lung function. RESULTS ILA were present in 528 (6%), and 580 (11%), of participants in phases 1 and 2 of COPDGene, respectively. ILA modified the association between emphysema and FVC (P<0.0001 for interaction) in both phases. In phase 1, in those without ILA, a 5% increase in emphysema was associated with a reduction in FVC (-110 cc, 95% confidence interval [CI] -121, -100; P<0.0001) however, in those with ILA it was not (-11cc, 95% CI -53,31; P=0.59). In contrast, there was no interaction between ILA and emphysema on total lung capacity (TLC) nor on diffusing capacity of carbon monoxide (DLCO). INTERPRETATION The presence of ILA attenuates the reduction in FVC associated with emphysema.