In COPD, skeletal muscle ATP resynthesis may be insufficient to meet demand during exercise due to excessive anaerobic and reduced oxidative (mitochondrial) energy production, leading to metabolic stress. We investigated the effect of outpatient pulmonary rehabilitation (PR) on the metabolic response (measured by exercise-induced accumulation of plasma ammonia) and determined whether this response predicted functional improvement following PR. 25 subjects with stable COPD [mean (SD) age 67 (8)years and FEV(1) 47 (18)% predicted] performed maximal cycling ergometry before and after PR. Plasma ammonia was measured at rest, during exercise and 2 min post-exercise. Following PR, there were significant increases in peak cycle WR and ISWT performance (Mean (SEM) changes 13.1 (2.0) W and 93 (15) m respectively, p < 0.001). Mean (SEM) rise in plasma ammonia was reduced at peak (Pre vs Post-PR: 29.0 (4.5) vs 20.2 (2.5) μmol/l, p < 0.05) and isotime (Pre vs Post-PR: 29.0 (4.5) vs 10.6 (1.7) μmol/l, p < 0.001) exercise. Improvements in exercise performance after PR were similar among subgroups who did versus those who did not show a rise in ammonia at baseline. The results suggest that muscle cellular energy production was better matched to the demands of exercise following PR. We conclude that a pragmatic outpatient PR programme involving high intensity walking exercise results in significant adaptation of the skeletal muscle metabolic response with a reduction in exercise-related metabolic stress. However, the outcome of PR could not be predicted from baseline metabolic response.
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