Quantitative CT measures of emphysema and airway wall thickness are related to DLCO

SummaryThere is limited knowledge on the relationship between diffusing capacity of the lung for carbon monoxide (DLCO) and quantitative computed tomography (CT) measures of emphysema and airway wall thickness.Study questionWhat is the relationship between DLCO and the quantitative CT measures of emphysema and airway wall thickness in subjects with and without COPD?MethodsWe included 288 COPD subjects (70% men) and 425 non-COPD subjects (54% men). All subjects were current or ex-smokers older than 40 years and all subjects underwent spirometry, diffusing capacity tests and CT examination. Quantitative CT measures included % low attenuation areas <−950 HU (%LAA) and standardized airway wall thickness (AWT-Pi10).ResultsMultiple linear regression analyses showed significant associations between DLCO and both %LAA and AWT-Pi10 in the COPD group. The adjusted regression coefficients (SE) for DLCO (mmol min−1 kPa−1) were −1.15 (0.11) per 10% increase in %LAA and 0.08 (0.03) per 0.1 mm increase in AWT-Pi10, and the models’ adjusted R2 was 0.65 and 0.49, respectively.ConclusionsCT measured emphysema explains a large fraction of the variation of DLCO among COPD subjects, and more so in men. Airway wall thickness is also significantly associated with DLCO, but explains a much smaller fraction of the variation.