Muscle glucose metabolism in chronic obstructive pulmonary disease patients

Muscle dysfunction is one of the most extensively studied manifestations of COPD. Metabolic changes in muscle are difficult to study in vivo, due to the lack of non-invasive techniques. Our aim was to evaluate metabolic activity simultaneously in various muscle groups in COPD patients.

Thirty-nine COPD patients and 21 controls with normal lung function, due to undergo computed axial and positron emission tomography for staging of localized lung lesions were included. After administration of 18-fluordeoxyglucose, images of 2 respiratory muscles (costal and crural diaphragm, and rectus abdominus) and 2 peripheral muscles (brachial biceps and quadriceps) were obtained, using the standard uptake value as the glucose metabolism index.

Standard uptake value was higher in both portions of the diaphragm than in the other muscles of all subjects. Moreover, the crural diaphragm and rectus abdominus showed greater activity in COPD patients than in the controls (1.8±0.7 vs 1.4±0.8; and 0.78±0.2 vs 0.58±0.1; respectively, P<.05). A similar trend was observed with the quadriceps. In COPD patients, uptake in the two respiratory muscles and the quadriceps correlated directly with air trapping (r=0.388, 0.427 and 0.361, respectively, P<.05).

There is greater glucose uptake and metabolism in the human diaphragm compared to other muscles when the subject is at rest. Increased glucose metabolism in the respiratory muscles (with a similar trend in their quadriceps) of COPD patients is confirmed quantitatively, and is directly related to the mechanical loads confronted.