Diagnostic Value of the Maximal Expiratory Flow-Volume Curve for Central Airway Obstruction

To investigate the factors associated with plateau-like changes during the expiratory phase of maximal expiratory flow-volume (MEFV) curves and their diagnostic value in identifying central airway obstruction (CAO).

Totally 59 patients with expiratory phase plateau-like changes in the MEFV curves who were treated in Henan Provincial People's Hospital from January 2019 to November 2020 were included in this retrospective analysis. Patients with CAO were recruited into the experimental group, and those without CAO were recruited into the control group. Peak expiratory flow (PEF), forced expiratory flow (FEF) 25% (FEF25), 50% (FEF50), 75% (FEF75), forced expiratory volume in 1 second (FEV1), and vital capacity (VC MAX) were compared between two groups. The receiver operating characteristic (ROC) curve was conducted for diagnostic value.

There were 12 cases in the experimental group (8 males and 4 females) and 47 cases in the control group (15 males and 32 females). Analyses using a Chi-squared test and a normal test showed that CAO was correlated with PEF, FEF25, FEF50, FEF75, FEV1, VC MAX, and their actual/predicted values (P < 0.05). The area under-curve (AUC) of PEF was 0.966 (95% confidence interval [CI]: 0.912-1.000), and the AUC of actual PEF/predicted PEF (%) was 0.966 (95% CI: 0.918-1.000). The AUC of FEF25 was 0.915 (95% CI: 0.805-1.000), and 0.908 (95% CI: 0.782-1.000) of actual FEF25/predicted FEF25 (%). The ROC curves suggested that PEF, FEF25, and their actual/predicted values had a high diagnostic value for CAO.

This study showed that MEFV curves with expiratory phase plateau-like changes were not specific to patients with CAO; they could also be seen in patients without CAO, and they were highly indicative of CAO when combined with a significant decrease in PEF, FEF25, and their actual/predicted values. In subjects without CAO, the MEFV curve can form an expiratory phase plateau when the driving pressure is high enough and the equal pressure point and/or the choke point remains in the large airway.