| FEF | Forced Expiratory Flow |
|---|---|
| FEF | forced expiratory flow |
| FEF25-75% | Forced Expiratory Flow from 25 to 75 % of the vital capacity |
| FEF50 | forced expiratory flow at 50% of forced vital capacity |
| FEF50/FIF50 | ratio of expiratory flow to inspiratory flow at 50% of forced vital capacity |
| FEFV | forced expiratory flow volume |