title: Computer quantification of "angle of collapse" on maximum expiratory flow volume curve for diagnosing asthma-COPD overlap syndrome.
abstract: BACKGROUND
  In a previous study, we demonstrated that asthma patients with signs of emphysema on quantitative computed tomography (CT) fulfill the diagnosis of asthma-COPD overlap syndrome (ACOS). However, quantitative CT measurements of emphysema are not routinely available for patients with chronic airway disease, which limits their application. Spirometry was a widely used examination tool in clinical settings and shows emphysema as a sharp angle in the maximum expiratory flow volume (MEFV) curve, called the "angle of collapse (AC)". The aim of this study was to investigate the value of the AC in the diagnosis of emphysema and ACOS.
  
  
  METHODS
  This study included 716 participants: 151 asthma patients, 173 COPD patients, and 392 normal control subjects. All the participants underwent pulmonary function tests. COPD and asthma patients also underwent quantitative CT measurements of emphysema. The AC was measured using computer models based on Matlab software. The value of the AC in the diagnosis of emphysema and ACOS was evaluated using receiver-operating characteristic (ROC) curve analysis.
  
  
  RESULTS
  The AC of COPD patients was significantly lower than that of asthma patients and control subjects. The AC was significantly negatively correlated with emphysema index (EI;r=-0.666,P<0.001), and patients with high EI had a lower AC than those with low EI. The ROC curve analysis showed that the AC had higher diagnostic efficiency for high EI (area under the curve =0.876) than did other spirometry parameters. In asthma patients, using the AC ≤137° as a surrogate criterion for the diagnosis of ACOS, the sensitivity and specificity were 62.5% and 89.1%, respectively.
  
  
  CONCLUSIONS
  The AC on the MEFV curve quantified by computer models correlates with the extent of emphysema. The AC may become a surrogate marker for the diagnosis of emphysema and help to diagnose ACOS.
authors.affiliation: Department of Pulmonary Medicine, Qilu Hospital, Shandong University, Jinan, People's Republic of China.
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.affiliation: Department of Pulmonary Medicine, Qilu Hospital, Shandong University, Jinan, People's Republic of China.
authors.forename: Mengshuang
authors.initials: M
authors.lastname: Xie
authors.affiliation: Department of Pulmonary Medicine, Qilu Hospital, Shandong University, Jinan, People's Republic of China.
authors.forename: Shuang
authors.initials: S
authors.lastname: Dou
authors.affiliation: Department of Pulmonary Medicine, Qilu Hospital, Shandong University, Jinan, People's Republic of China.
authors.forename: Liwei
authors.initials: L
authors.lastname: Cui
authors.affiliation: Department of Pulmonary Medicine, Qilu Hospital, Shandong University, Jinan, People's Republic of China.
authors.forename: Wei
authors.initials: W
authors.lastname: Xiao
mesh_terms: D000368:Aged; D019540:Area Under Curve; D001249:Asthma / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000503:physiopathology; D016022:Case-Control Studies; D003198:Computer Simulation; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008297:Male; D008449:Maximal Expiratory Flow-Volume Curves; D008875:Middle Aged; D061330:Multidetector Computed Tomography; D011237:Predictive Value of Tests; D029424:Pulmonary Disease, Chronic Obstructive / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000503:physiopathology; D011656:Pulmonary Emphysema / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000503:physiopathology; D012123:Pulmonary Ventilation; D012372:ROC Curve; D013147:Spirometry; D013577:Syndrome
keywords: COPD; MEFV; airway collapse; asthma; emphysema; overlap