Background: Spirometric parameters are the mainstay for diagnosis of COPD, but cannot distinguish airway\r\nobstruction from emphysema. We aimed to develop a computer model that quantifies airway collapse on forced\r\nexpiratory flowââ?¬â??volume loops. We then explored and validated the relationship of airway collapse with computed\r\ntomography (CT) diagnosed emphysema in two large independent cohorts.\r\nMethods: A computer model was developed in 513 Caucasian individuals with =15 pack-years who performed\r\nspirometry, diffusion capacity and CT scans to quantify emphysema presence. The model computed the two best\r\nfitting regression lines on the expiratory phase of the flow-volume loop and calculated the angle between them.\r\nThe collapse was expressed as an Angle of collapse (AC) which was then correlated with the presence of emphysema.\r\nFindings were validated in an independent group of 340 individuals.\r\nResults: AC in emphysema subjects (N = 251) was significantly lower (131Ã?° Ã?± 14Ã?°) compared to AC in subjects without\r\nemphysema (N = 223), (152Ã?° Ã?± 10Ã?°) (p < 0.0001). Multivariate regression analysis revealed AC as best indicator of visually\r\nscored emphysema (R2 = 0.505, p < 0.0001) with little significant contribution of KCO, %predicted and FEV1, %predicted\r\nto the total model (total R2 = 0.626, p < 0.0001). Similar associations were obtained when using CT-automated density\r\nscores for emphysema assessment. Receiver operating characteristic (ROC) curves pointed to 131Ã?° as the best cut-off\r\nfor emphysema (95.5% positive predictive value, 97% specificity and 51% sensitivity). Validation in a second group\r\nconfirmed the significant difference in mean AC between emphysema and non-emphysema subjects. When applying\r\nthe 131Ã?° cut-off, a positive predictive value of 95.6%, a specificity of 96% and a sensitivity of 59% were demonstrated.\r\nConclusions: Airway collapse on forced expiration quantified by a computer model correlates with emphysema. An\r\nAC below 131Ã?° can be considered as a specific cut-off for predicting the presence of emphysema in heavy smokers
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