title: The Concave Shape of the Forced Expiratory Flow-Volume Curve in 3 Seconds Is a Practical Surrogate of FEV1/FVC for the Diagnosis of Airway Limitation in Inadequate Spirometry.
abstract: BACKGROUND
  Spirometry is important for the differential diagnosis of dyspnea. However, some patients cannot exhale for ≥6 s to achieve the American Thoracic Society/European Respiratory Society criteria. The aim of this study was to demonstrate the reliability of a new parameter that quantifies the degree of concavity in the first 3 s to define airway limitation as a surrogate for the FEV1/FVC.
  
  
  METHODS
  Four hundred spirometry test results were selected through complete random sampling. The new parameter, termed the AUC3/AT3, was calculated as the area under the descending limb of the expiratory flow-volume curve before the end of the first 3 s (AUC3) divided by the area of the triangle before the end of the first 3 s (AT3). The AUC3/AT3was compared with the FEV1/FVC using Pearson's correlation analysis. The level of agreement between the AUC3/AT3and the FEV1/FVC in the detection of airway obstruction was analyzed using the kappa statistic. We also compared the diagnostic accuracy of the new index with that of the FEV1/forced expiratory volume in the first 3 s (FEV3).
  
  
  RESULTS
  There was a strong correlation (r = 0.88,P< .001) between the AUC3/AT3and the FEV1/FVC. There was also strong agreement between the AUC3/AT3and the FEV1/FVC in the detection of obstruction with kappa indices of 0.72 (Global Initiative for Chronic Obstructive Lung Disease [GOLD] criterion) and 0.67 (lower limit of normal criterion), and these values were greater than those obtained for the FEV1/FEV3. The AUC3/AT3also exhibited acceptable sensitivity, specificity, positive predictive value, and negative predictive value. The diagnostic accuracies of the AUC3/AT3were 86.3% (GOLD criterion) and 83.8% (lower limit of normal criterion), which were greater than the 76.0 and 74.0% obtained for the FEV1/FEV3, respectively.
  
  
  CONCLUSIONS
  The AUC3/AT3can be utilized as a surrogate parameter for the FEV1/FVC when patients cannot complete a 6-s expiratory effort. Additionally, the performance of this index is better than that of the FEV1/FEV3in the identification of airway limitations.
authors.affiliation: Department of Respiratory Medicine, Qilu Hospital, Shandong University, Jinan, Shandong, China.
authors.forename: Hao
authors.initials: H
authors.lastname: Li
authors.affiliation: Department of Respiratory Medicine, Qilu Hospital, Shandong University, Jinan, Shandong, China.
authors.forename: Chunhong
authors.initials: C
authors.lastname: Liu
authors.affiliation: Department of Respiratory Medicine, Qilu Hospital, Shandong University, Jinan, Shandong, China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Respiratory Medicine, Qilu Hospital, Shandong University, Jinan, Shandong, China. xiaowei4226@163.com.
authors.forename: Wei
authors.initials: W
authors.lastname: Xiao
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000402:Airway Obstruction / Q000175:diagnosis*; D019540:Area Under Curve; D004417:Dyspnea / Q000175:diagnosis*; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D013147:Spirometry / Q000706:statistics & numerical data*; D018709:Statistics, Nonparametric; D014797:Vital Capacity; D055815:Young Adult
keywords: airway obstruction; area under the curve; diagnosis; maximal expiratory flow-volume curves; respiratory function tests; spirometry