Abstract
Peripheral muscle dysfunction in COPD patients has been related to a muscle/fiber atrophy and oxidative metabolism reduction, which mimicks a severe disuse. Thus, we investigated the structure and mitochondrial function in skeletal muscle biopsies from patients with COPD and sedentary healthy subjects (SHS).
24 stage I-III (according to the GOLD classification) COPD patients and 21 age-matched SHS (<150m/W of moderate-vigorous PA) had accelerometry recording, quadriceps function and muscle mass (impedancemetry) assessment. All subjects had a biopsy of the quadriceps, allowing assessment of the respiratory parameters and mitochondrial ATP synthesis, and of the muscle morphology (immunohistochemistry). Results are presented in mean ± SD or median [inter-quartile range].
COPD patient and PA level-matched SHS (activity counts/day: 133±70 vs 135±48; p=0,9), had the same muscle mass and fiber cross-sectional areas. However, there was a reduction of the quadriceps endurance and of the type I fiber proportion (35% [28-49] vs 41% [38-53]; p<0,05). While the maximal ADP-stimulated respiration (state 3) with pyruvate substrate was comparable in COPD and SHS, the ATP/O value (ratio between ATP synthesis and oxygen consumption) was significantly reduced in COPD (0,96±0,4 vs 2,6±0,8; p<0,001), and observed in early stages.
This study showed an early impairment of the muscle oxidative metabolism (type I fibers and mitochondrial efficiency), unexplained by the PA reduction in COPD patients and suggest that the oxidative phosphorylation alteration (OXPHOS pathway) occurs in the PHOS part, i.e. the ATP synthesis rate.
- © 2011 ERS