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 (FEV1) can help a clinician determine the difference between obstructive and
restrictive diseases. Specifically, an FEV1 is the forced volume expired in 1 second.
In obstructive diseases such as chronic bronchitis and asthma, airway radius is decreased. Thus, FEV1 will:.