Chronic Obstructive Pulmonary Disease And Skeletal Muscle Energetics During Exercise: A 31p-mrs Study

Abstract

PURPOSE: Biochemical and histochemical changes observed in the peripheral skeletal muscle of patients with COPD likely alter muscle energy production during exercise and recovery which may in turn affect exercise capacity. METHODS: We used 31P-magnetic resonance spectroscopy (31P-MRS) to examine the energy cost and skeletal muscle energetics in patients with COPD during dynamic plantar flexion exercise in comparison to well-matched healthy control subjects. RESULTS: At the onset of exercise, the PCr time constant was shorter in the patients with COPD compared to the controls (controls: 34 ± 10 s, COPD: 21 ± 4 s, P < 0.05). Patients with COPD displayed a higher energy cost of contraction compared to the controls (control: 6.1 ± 3.1 % of rest·min-1·W-1, COPD: 13.6 ± 8.3 % of rest·min-1·W-1, P < 0.05). The initial PCr resynthesis rate was also significantly attenuated in patients with COPD compared to controls (control: 74 ± 17 % of rest·min-1, COPD: 52 ± 13 % of rest·min-1, P < 0.05) and the patients tended to display a greater acidosis for a given PCr consumption as illustrated by the lower Y-intercept of the regression line for end-of-exercise pH and PCr values. CONCLUSION: Our results reveal, for the first time, that a higher ATP cost of contraction may substantially contribute to the lower mechanical efficiency previously reported in patients with COPD. In addition, this study suggests that patients with COPD rely more heavily on anaerobic rather than aerobic metabolism during exercise, which is likely related to the recognized predominance of fast-twitch skeletal muscle fibers in this population or due to a disturbance in metabolic control.