Assessing Obstructive and Restrictive Patterns

With obstruction:

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

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

(3) 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%).

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

With restriction:

(1) The configuration of the volume-time tracing may not be abnormal.

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

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

(4) 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).