Predict Question Lung diseases are often classified as obstructive or restrictive. An obstructive disease affects airflow, and a restrictive disease usually reduces volumes and capacities. Although they are not diagnostic, pulmonary function tests such as forced expiratory volume (FEV) can help a clinician determine the difference between obstructive and restrictive diseases. Specifically, an FEV is the forced volume expired in 1 second. In obstructive diseases such as chronic bronchitis and asthma, airway radius is decreased. Thus, FEV will decrease proportionately. increase proportionately. not change significantly. Submit