Measure of the maximum amount of air that can be expelled in a given number of seconds during aÂ FORCED VITAL CAPACITYÂ determination . It is usually given asÂ FEVÂ followed by a subscript indicating the number of seconds over which the measurement is made, although it is sometimes given as a percentage of forced vital capacity. The trait is Experimental Factor Ontology identifier EFO_0004314 (forced expiratory volume). Also known as: FEV1, FEVt, timed vital capacity.