Bioenergetics and intermuscular fat in chronic obstructive pulmonary disease-associated quadriceps weakness.

INTRODUCTION

Chronic obstructive pulmonary disease (COPD) is associated with metabolic abnormalities in muscles of the lower limbs, but it is not known whether these abnormalities are generalized or limited to specific muscle groups, nor is there an easy way of predicting their presence.

METHODS

Metabolism in the quadriceps and biceps of 14 COPD patients and controls was assessed during sustained contraction using 31-phosphorus magnetic resonance spectroscopy ((31) P MRS). T1 MRI was used to measure quadriceps intermuscular adipose tissue (IMAT).

RESULTS

COPD patients had prolonged quadriceps phosphocreatine time (patients: 38.8 ± 12.7 s; controls: 25.2 ± 10.6 s; P = 0.006) and a lower pH (patents: 6.88 ± 0.1; controls: 6.99 ± 0.06; P = 0.002). Biceps measures were not significantly different. IMAT was associated with a nadir pH <7.0 (area under the curve = 0.84).

CONCLUSIONS

Anaerobic metabolism during contraction was characteristic of quadriceps, but not biceps, muscles of patients with COPD and was associated with increased IMAT. Because IMAT can be assessed quickly by conventional MRI, it may be a useful approach for identifying patients with abnormal muscle bioenergetics.