Association between respiratory variables and exercise capacity in COPD patients

Background and Objective: Chronic Obstructive Pulmonary Disease (COPD) is characterized by progressive airflow limitation associated with an inflammatory response. The aim of the study was to evaluate the influence and the association of respiratory variables on exercise capacity in COPD patients. Methods: A cross-sectional study evaluated 39 COPD patients to obtain forced expiratory volume in one second (FEV1) and forced vital capacity (FVC). Respiratory muscle strength (RMS) was evaluated at its maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) components. Exercise capacity was assessed by Six-Minute Walk Test (6MWT) and Incremental Shuttle Walking Test (ISWT). Results: FEV1 (39.8 +/- 15.3%predicted) and FVC (60.2 +/- 17.1%predicted) were reduced, which classified them in stages 11 (21%), III (51%) and IV (28%). MIP (92.7 +/- 14.6% predicted) and MEP (97.6 +/- 19.0% predicted) were within the expected values. A moderate correlation was observed between the ISWT vs FEV1 (r=0.35;p=0.02) and ISWT vs FVC (r=0.42;p<0.001), 6MWT vs FEV1 (r=0.38;p=0.01) and 6MWT vs FVC (r=0.52;p<0.001). RMS showed a moderate correlation with the ISWT [MIP (r=0.44;p=0.005); MEP (r=0.57;p<0.001)] and 6MWT [MIP (r=0.43;p=0.006); MEP (r=0.59;p<0.001)]. MEP and FEV1 influenced 37% of performance at the 6MWT and MEP alone influenced 58% of distance walked at the ISWT. Conclusion: Reducing both respiratory muscle strength and lung volumes were associated with changes in exercise and they adversely affected the maximum and submaximal exercise capacity in COPD patients.