Factors Associated with the Discrepancy between Exercise Capacity and Airflow Limitation in Patients with Chronic Obstructive Pulmonary Disease

Background: Exercise capacity is associated with lung function decline in chronic obstructive pulmonary disease (COPD) patients, but a discrepancy between exercise capacity and airflow limitation exists. This study aimed to explore factors contributing to this discrepancy in COPD patients. Methods: Data for this prospective study were obtained from the Korean COPD Subgroup Study. The exercise capacity and airflow limitation were assessed using the 6 -minute walk distance (6-MWD; m) and forced expiratory volume in 1 second (FEV1). Participants were divided into four groups: FEV1 >50%+6-MWD >350, FEV1 >50%+6MWD <= 350, FEV1 <= 50%+6-MWD >350, and FEV1 <= 50%+6-MWD <= 350 and their clinical characteristics were compared. Results: A total of 883 patients (male:female, 822:61; mean age, 68.3 +/- 7.97 years) were enrolled. Among 591 patients with FEV1 >50%, 242 were in the 6-MWD <= 350 group, and among 292 patients with FEV1 <= 50%, 185 were in the 6-MWD >350 group. The multiple regression analyses revealed that male sex (odds ratio [OR], 8.779; 95% confidence in- terval [CI], 1.539 to 50.087; p=0.014), current smoking status (OR, 0.355; 95% CI, 0.178 to 0.709; p=0.003), and hemoglobin levels (OR, 1.332; 95% CI, 1.077 to 1.648; p=0.008) were significantly associated with discrepancies in exercise capacity and airflow lim- itation in patients with FEV1 >50%. Meanwhile, in patients with FEV1 <= 50%, diffusion capacity of carbon monoxide (OR, 0.945; 95% CI, 0.912 to 0.979; p=0.002) was signifi- cantly associated with discrepancies between exercise capacity and airflow limitation. Conclusion: The exercise capacity of COPD patients may be influenced by factors oth- er than airflow limitation, so these aspects should be considered when assessing and treating patients.