Computer quantification of airway collapse on forced expiration to predict the presence of emphysemaReport as inadecuate

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Respiratory Research

, 14:131

First Online: 19 November 2013Received: 17 June 2013Accepted: 18 November 2013


BackgroundSpirometric parameters are the mainstay for diagnosis of COPD, but cannot distinguish airway obstruction from emphysema. We aimed to develop a computer model that quantifies airway collapse on forced expiratory flow–volume loops. We then explored and validated the relationship of airway collapse with computed tomography CT diagnosed emphysema in two large independent cohorts.

MethodsA computer model was developed in 513 Caucasian individuals with ≥15 pack-years who performed spirometry, diffusion capacity and CT scans to quantify emphysema presence. The model computed the two best fitting regression lines on the expiratory phase of the flow-volume loop and calculated the angle between them. The collapse was expressed as an Angle of collapse AC which was then correlated with the presence of emphysema. Findings were validated in an independent group of 340 individuals.

ResultsAC in emphysema subjects N = 251 was significantly lower 131° ± 14° compared to AC in subjects without emphysema N = 223, 152° ± 10° p < 0.0001. Multivariate regression analysis revealed AC as best indicator of visually scored emphysema R = 0.505, p < 0.0001 with little significant contribution of KCO, %predicted and FEV1, %predicted to the total model total R = 0.626, p < 0.0001. Similar associations were obtained when using CT-automated density scores for emphysema assessment. Receiver operating characteristic ROC curves pointed to 131° as the best cut-off for emphysema 95.5% positive predictive value, 97% specificity and 51% sensitivity. Validation in a second group confirmed the significant difference in mean AC between emphysema and non-emphysema subjects. When applying the 131° cut-off, a positive predictive value of 95.6%, a specificity of 96% and a sensitivity of 59% were demonstrated.

ConclusionsAirway collapse on forced expiration quantified by a computer model correlates with emphysema. An AC below 131° can be considered as a specific cut-off for predicting the presence of emphysema in heavy smokers.

KeywordsSpirometry Pulmonary emphysema Flow-volume loops Chronic obstructive pulmonary disease Lung collapse AbbreviationsACAngle of collapse

BMIBody mass index

COPDChronic obstructive pulmonary disease

DLCO: Carbon monoxide diffusing capacity

FEV1Forced expiratory volume in one second

FVCForced vital capacity

HUHounsfield units

I CCIntraclass correlation coefficient

KCOCarbon monoxide transfer coefficient

MSEMean square error

MTTMean transit time

ROCReceiver operating characteristic.

Electronic supplementary materialThe online version of this article doi:10.1186-1465-9921-14-131 contains supplementary material, which is available to authorized users.

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Author: Marko Topalovic - Vasileios Exadaktylos - Anneleen Peeters - Johan Coolen - Walter Dewever - Martijn Hemeryck - Pieter Slag


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