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/AT3 was compared with the FEV1/FVC using Pearson's correlation analysis. The level of agreement between the AUC3/AT3 and 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/AT3 and the FEV1/FVC. There was also strong agreement between the AUC3/AT3 and 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/AT3 also exhibited acceptable sensitivity, specificity, positive predictive value, and negative predictive value. The diagnostic accuracies of the AUC3/AT3 were 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/AT3 can 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/FEV3 in the identification of airway limitations.
- respiratory function tests
- airway obstruction
- maximal expiratory flow-volume curves
- area under the curve
- Correspondence: Wei Xiao MD, Department of Respiratory Medicine, Qilu Hospital, Shandong University, No. 107, Wenhua Xi Road, Jinan, Shandong 250012, China. E-mail: .
This work was supported by Key Research and Development Program of Shandong Province Grant 2015GSF118064. The authors have disclosed no conflicts of interest.
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