Forced Expiratory Flow - Forced expiratory Flow is a measure
of how much air can be expired from the lungs. It is a flow rate
measurement. It is measured as liters/second or liters/minute. The
FVC expiratory curve is divided into quartiles and therefore there is
a FEF that exists for each quartile. The quartiles are expressed as
FEF25%, FEF50%, and FEF75% of FVC.