Maximum expiratory flow volume curve

The maximum expiratory flow-volume curve (MEFV) is the rapid expiratory to the residual level after inhaling deeply to the total lung volume. Correlation curves of lung volume and corresponding air velocity were plotted by XY recorder. Commonly used indicators are: 1. Maximum expiratory flow (PEF): refers to the expiratory flow indicated by the highest point of the MEFV curve. 2.50% vital capacity maximum expiratory flow (V ↓ 50): refers to the expiratory flow when the vital capacity is 50%. 3.25% lung capacity maximum expiratory flow (V ↓ 25): refers to the expiratory flow when the vital capacity is 25%. Decreased values ​​of V ↓ 50 and V ↓ 25 indicate small airway obstruction. Obstructive ventilation disorder, MEFV flow reduction in each stage, the descending branch is concave. Restricted ventilation disorder has high MEFV flow, small vital capacity, high curves, and large inclination.