A Forced expiratory volume (FEV) is Denotes the volume of gas that is exhaled in a given time interval during the execution of a forced vital capacity. Conventionally, the times used are 0.5, 0.75, or 1 sec, symbolized FEV0.5, FEV0.75, FEV1. These values are often expressed as a percent of the forced vital capacity, e.g. (FEV1 /VC) x 100.