These maneuvers provide several measures: FVC: Maximal amount of air that the patient can forcibly exhale after taking a maximal inhalation FEV1: Volume exhaled in the first second Peak expiratory flow (PEF): Maximal speed of airflow as the patient exhales FEV1 is the most reproducible flow parameter and is especially useful in diagnosing and monitoring patients with obstructive pulmonary disorders (eg, asthma, COPD [chronic obstructive pulmonary disease]).