Bioenergetics and intermuscular fat in chronic obstructive pulmonary disease-associated quadriceps weakness.
BACKGROUND
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.
Clinical Imaging Centre, GlaxoSmithKline Research and Development, Hammersmith Hospital, London, UK.
Gregory Samuel
GS
Shields
Graziele S
GS
Coissi
Pilar
P
Jimenez-Royo
Giulio
G
Gambarota
Rahul
R
Dimber
Nicholas S
NS
Hopkinson
Paul M
PM
Matthews
Andrew P
AP
Brown
Michael I
MI
Polkey
D000368:Aged; D004734:Energy Metabolism; D015444:Exercise; D005223:Fats / Q000378:metabolism*; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology; D010725:Phosphocreatine / Q000378:metabolism; D010759:Phosphorus Isotopes; D029424:Pulmonary Disease, Chronic Obstructive / Q000473:pathology* / Q000503:physiopathology; D052097:Quadriceps Muscle / Q000503:physiopathology*; D012372:ROC Curve; D012720:Severity of Illness Index
D005223:Fats; D010759:Phosphorus Isotopes; D010725:Phosphocreatine
31P-MRS; adipose tissue; anaerobic metabolism; intermuscular fat; skeletal muscle