What is a 'restrictive' defect?

We studied 211 sets of pulmonary function data to evaluate spirographic findings in patients with restrictive defects, and to determine the significance of the spirographic interpretation of restriction. A combination of clinical and body plethysmographic data was used as the standard for the diagnosis of restriction. Restriction was diagnosed spirographically when forced vital capacity (FVC) was low and the ratio of one-second forced expiratory volume (FEV1) to FVC (FEV1/FVC%) was normal. With these criteria, using 70% as the lower limit of normal for FEV1/FVC%, the spirogram had a 93% sensitivity and an 82% specificity for the detection or exclusion of a restrictive defect. Ten percent of patients with pure obstructive defects by clinical and plethysmographic criteria showed a restrictive defect on the spirogram. Combined obstructive and restrictive defects were rare; in these cases the spirogram showed a restrictive defect but missed the obstructive component.