Computer quantification of airway collapse on forced expiration to predict the presence of emphysema

Abstract

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 (R2 = 0.505, p < 0.0001) with little significant contribution of KCO, %predicted and FEV1, %predicted to the total model (total R2 = 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.

Automated Interpretation of Pulmonary Function Tests in Adults with Respiratory Complaints

“…How this disturbance should be defined is still unclear, but it is obvious that we should be less restrictive than what the current ATS/ERS rules are suggesting. One challenging approach may be the inclusion of new more selective parameters of PFTs to improve the differentiation between these diseases [29,30] . Another problem for the development of automated interpretation of lung function is its inherent dependency on the prevalence of the diseases comprised in the dataset.…”

The Aging Lung: Clinical and Imaging Findings and the Fringe of Physiological State

“…For low and medium grade emphysematous changes, HRCT is clearly superior to conventional X-ray imaging [18]. In addition to visual emphysema grading as described by Bankier et al [19], quantitative methods particularly demonstrate high correlation with pulmonary parameters [20]. These offer measurement during inspiration (extent of emphysema) as well as expiration (air trapping as correlate of the extent of air passage obstruction).…”

Computer quantification of &ldquo;angle of collapse&rdquo; on maximum expiratory flow volume curve for diagnosing asthma-COPD overlap syndrome

“…However, due to the loss of supporting structure and airway collapse during forced expiration, emphysema is featured by an abrupt decrease in flow following PEF and, thereafter, a more gradual decrease in flow, which results in a sharp angle in the MEFV curve 11–14. This angle in the MEFV curve was called the “angle of collapse (AC)” 12,14…”

“…Previous studies have demonstrated that a sharp AC in the MEFV curve was an indicator of emphysema 12–14. In clinical practice, the shape of the MEFV curve is usually evaluated by visual assessment, as only a few studies have used computer quantification methods to evaluate the shape of this curve 12,14.…”

“…In clinical practice, the shape of the MEFV curve is usually evaluated by visual assessment, as only a few studies have used computer quantification methods to evaluate the shape of this curve 12,14. In this study, we try to investigate the relationship between computer quantification of the AC and emphysema and investigate the value of the AC in the diagnosis of ACOS.…”