Fig. 4. Comparison of pulmonary function between patients with and without mucus plugs in asthmatic, ACO, and COPD patients. (A) Spirometry. (B) Respiratory resistance. (C) Respiratory reactance.

ACO, asthma-chronic obstructive pulmonary disease overlap; COPD, chronic obstructive pulmonary disease; FEV1, forced expiratory volume in 1 second; FVC, forced vital capacity; FEF 25–75, forced expiratory flow at 25%–75% of forced vital capacity; R5 and R20, respiratory resistance at 5 and 20 Hz; R5–R20, the difference between R5 and R20; X5, respiratory reactance at 5 Hz; Fres, resonant frequency; ALX, low-frequency reactance area.