Skeletal muscle dysfunction in people with COPD and recipients of lung transplants.

摘要

Chronic obstructive pulmonary disease (COPD) is a respiratory condition with multisystemic effects resulting in skeletal muscle dysfunction. Lung transplantation is a treatment option for people with COPD resulting in improved lung function, however, skeletal muscle dysfunction persists and may be worsened following transplantation due to a period of bedrest and the myopathic effects of immunosuppressant medications. We hypothesized that impairments in skeletal muscle function of the quadriceps and hamstrings in people with COPD would be related to changes in skeletal muscle structure and these impairments would be accentuated in lung transplant recipients. Two pilot studies (Studies 1 and 2) were performed to establish methodology. In Study 3 , magnetic resonance imaging showed uniform atrophy of the thigh muscles and intramuscular fat infiltration in the quadriceps and hamstrings of people with COPD compared to age-, sex-, and body mass index (BMI)-matched controls. Notably, eccentric torque normalized to muscle volume was greater in people with COPD compared to controls. Study 4 showed that despite shorter times to task failure for sustained isometric quadriceps contractions, people with COPD showed similar changes in EMG median frequency and amplitude compared to controls. Quantification of cellular features of the vastus lateralis (VL) in Study 5 showed a greater proportion of abnormal muscle and small, angular fibers in people with COPD compared to controls. A larger proportion of people with COPD showed increased connective tissue in the VL compared to controls. Comparison of people with COPD to lung transplant recipients in Study 6 showed a similar amount of muscle atrophy, a wide variation in intramuscular fat infiltration, shorter times to task failure for the quadriceps and small, abnormal histological features of the VL. In summary, these findings suggest that although people with COPD demonstrate impairments in skeletal muscle structure and function (e.g. atrophy, fat infiltration, reduced endurance), they have a preservation of eccentric torque and motor unit firing properties. The variation of findings in transplant recipients, partly attributable to a small and diverse sample, limited our ability to test our hypothesis of whether changes in skeletal muscle structure and function would be accentuated in this group of individuals.