Background: Forced expiratory volume in one second (FEV1) is widely used in grading the severity of the airflow limitation observed in chronic obstructive pulmonary disease (COPD). However, the characteristics of COPD classified by forced vital capacity (FVC) remain unknown. Hence, the characteristics of pulmonary function test (PFT) and clinical features of COPD patients classified by FVC were investigated.
Methods: COPD patients were classified into three groups by FVC: (I) large consistent FVC (LC-FVC): before bronchodilator (BBD) and after bronchodilator (ABD) FVC ≥80%pred; (II) inconsistent FVC (I-FVC): BBD FVC <80%pred, while ABD FVC ≥80%pred; (III) small consistent FVC (SC-FVC): BBD and ABD FVC <80%pred. The characteristics of pulmonary function and clinical features of 1,329 retrospective patients and 403 prospective patients were analyzed in different FVC subgroups.
Results: The percentages of LC-FVC, I-FVC and SC-FVC were 25.4%, 13.8% and 60.9%, respectively in the retrospective cohort, and were 34.0%, 15.6%, 50.4%, respectively in the prospective cohort. For the 1,329 retrospective patients, I-FVC showed the best responsiveness to bronchodilator when compared with those of LC-FVC and SC-FVC, no matter evaluated by FEV1 (0.21 vs. 0.14 vs. 0.10 L, P<0.001) or FVC (0.47 vs. 0.15 vs. 0.23 L, P<0.001), and similar results were found in the 403 prospective patients. Of the 405 retrospective patients who finished lung volume tests, I-FVC and SC-FVC demonstrated higher residual volume than that of LC-FVC (3.43 vs. 3.15 vs. 2.89 L, P<0.05), while I-FVC and LC-FVC showed higher total lung capacity than that of SC-FVC (5.92 vs. 6.06 vs. 5.18 L, P<0.05). In the prospective cohort, LC-FVC and I-FVC experienced more asthma comorbidity than that of SC-FVC (30.7% vs. 30.2% vs. 16.7%, P=0.005); I-FVC group tended to experience more exacerbation events than the other two groups (1.7 vs. 1.2 vs. 1.5, P=0.114).
Conclusions: COPD patients classified by BBD and ABD FVC showed obviously different clinical characteristics, which could assist in distinguishing I-FVC patients who may benefit most from bronchodilators.
Keywords: Global initiative for chronic obstructive lung disease (GOLD); bronchodilator responsiveness; lung volumes; treatment.