Study objective: This study was designed to investigate the extent of clinical muscle dysfunction in stable patients with COPD who were attending an out-patient pulmonary clinic compared with that of age-matched control subjects without COPD.
Design and subjects: Respiratory muscle and hand grip strength, steady-state O2 kinetics, and body composition were measured in 32 patients with COPD (19 women) [mean (± SD) FEV1, 38 ± 11% predicted] and 36 age-matched control subjects (13 women).
Results: Measurements of handgrip force (mean, 97 ± 32% vs 106 ± 26% predicted, respectively), maximal expiratory pressure (mean, 57 ± 33% vs 61 ± 22% predicted, respectively), steady-state O2 kinetics (mean τ, 72 ± 34 s vs 78 ± 37 s, respectively) and steady-state CO2 kinetics (mean τ, 77 ± 38 s vs 65 ± 32 s, respectively) at submaximal exercise were similar in patients and control subjects. All the subjects, except for one female COPD patient, had a normal fat-free mass index (FFMI), although on average the FFMI was lower in male patients (19.8 ± 2.8) than in male control subjects (23.0 ± 2.8; p < 0.01).
Conclusions: In patients with COPD who were attending a regular outpatient pulmonary clinic, there was no evidence of reduced upper extremity and expiratory muscle strength or prolonged O2 and CO2 kinetics during isowork submaximal cardiopulmonary exercise compared to healthy, age-matched control subjects. Also, a normal body composition was found in nearly all COPD patients. This argues against the existence of a clinically significant systemic myopathy in most stable patients with severe COPD and normal FFMI.