Overview :

It is often possible to recognize patterns associated with obstructive or restrictive lung disease based on the results of pulmonary function testing.

With obstruction:

• Patients may have a normal or modestly reduced vital capacity, but the volume time tracing of the forced vital capacity will be abnormal.

• There is flattening of the slope of the curve at any given lung volume, reflecting reduced rate of airflow.

• The duration of the forced expiratory maneuver is prolonged; the changes in the rate of expiratory airflow reduce the FEV1, FEV3, FEV1-to-FVC, FEV3-to-FVC, and FEF(25-75%).

• In small airway disease: FVC is >= 81% of predicted, but FEF(25-75%) < 65%.

With restriction:

• The configuration of the volume-time tracing may not be abnormal.

• The FEV1 and FEV(3) are low because of the reduced vital capacity.

• The FEV1-to-FVC and FEV(3)-to-FVC are normal or even increased.

• The FEF(25-75%) is lower than predicted.

By examining the ratio of measured-to-predicted lung capacities it is possible to assess the severity of restrictive lung disease.

where:

• The forced vital capacity (FVC) is reported by some to be equivalent to vital capacity (VC).

Fishman A (editor). Pulmonary Diseases and Disorders, Second Edition. McGraw-Hill Book Company. 1988. pages 2483 and 2510

Murray J, Nadel J. Textbook of Respiratory Medicine, 2nd edition. W.B. Saunders Company. 1994. page 871