Clinical features of subjects with an isolated FEV 1 reduction

BACKGROUND: The clinical significance of an isolated reduction in forced expiratory volume in 1 second (FEV(1); i.e., low FEV(1), but normal forced vital capacity [FVC] and FEV(1)/FVC) has not been established. OBJECTIVE: To examine the clinical features of subjects with an isolated FEV(1) reduction. METHODS: Clinical, spirometry and radiological data were retrospectively collected from 15,192 subjects attending a medical check-up at the Health Promotion Center of the Asan Medical Center, Korea. Predicted spirometry values were calculated from the Korean reference equations, and the lower limit of normal was set at the 5th percentile. Subjects were divided into four groups: isolated FEV(1) reduction, normal (normal FVC, FEV(1) and FEV(1)/FVC), obstructive (low FEV(1)/FVC) and restrictive (low FVC and normal FEV(1)/FVC). The groups were compared in terms of clinical characteristics. RESULTS: Of the 15,192 subjects, 323 (2.1%) had an isolated FEV(1) reduction, 10,591 (69.7%) were normal, 951 obstructive (6.3%) and 3327 (22.0%) restrictive. The isolated FEV(1) reduction group had a higher proportion of subjects with smoking history (63.2% vs. 45.7%), radiology abnormalities (15.5% vs. 4.3%) and history of respiratory disease (8.4% vs. 3.0%) than the normal group (all P < 0.001). CONCLUSION: An isolated FEV(1) reduction suggests abnormal spirometry, and further study is needed to evaluate whether these cases belong to the obstructive or restrictive group.