Peripheral Muscle Weakness Contributes to Exercise Limitation in COPD

摘要

Recently, it was suggested that fatigue of peripheral muscles could contribute to exercise limitation in patients with chronic obstructive pulmonary disease (COPD). In order to quantify the role of peripheral muscle force, we restudied potential determinants of exercise capacity (6-min walking distance [6 MWD] and maximal oxygen consumption [VO_2max]) in 41 consecutive COPD patients (FEV_1, 43 ± 19% of predicted, TL_(CO), 56 ± 25% of predicted) admitted to our pulmonary rehabilitation program. VO_2max (incremental cycle ergometer test), 6 MWD (best of three), lung function (FEV_1, FVC, TLC, FRC), diffusing capacity (TL_(CO)), isometric quadriceps force (QF), hand grip force (HF), and maximal inspiratory (PI_(max)) and expiratory (PE_(max)) pressures were measured. Patients had a poor 6 MWD (372 ± 136 m) and VO_2max (1.35 ± 0.60 L, 71%), reduced respiratory (PI_(max) 65 ± 27%) and peripheral muscle force (QF 74 ± 27%, HF 82 ± 23%). In single regression analysis, significant correlations (r) were found for VO_2 max and TL_(CO) (0.68), FEV_1 (0.64), QF (0.55), HF (0.53), and body weight (0.49). Walking distance was significantly correlated with QF (0.63), HF (0.61), PI_(max) (0.49), and TL_(CO) (0.38). In stepwise multiple regression analysis, the variables significantly contributing to 6 MWD were QF and PI_(max). For VO_2max, variables significantly contributing were TL_(CO), QF, and FEV_1. We conclude that lung function and peripheral muscle force are important determinants of exercise capacity in COPD.