Reduced exercise tolerance in CHF may be related to factors other than impaired skeletal muscle oxidative capacity.
BACKGROUND
We sought to determine whether skeletal muscle oxidative capacity, fiber type proportions, and fiber size, capillary density or muscle mass might explain the impaired exercise tolerance in chronic heart failure (CHF). Previous studies are equivocal regarding the maladaptations that occur in the skeletal muscle of patients with CHF and their role in the observed exercise intolerance. Methods and results Total body O(2) uptake (VO(2peak)) was determined in 14 CHF patients and 8 healthy sedentary similar-age controls. Muscle samples were analyzed for mitochondrial adenosine triphosphate (ATP) production rate (MAPR), oxidative and glycolytic enzyme activity, fiber size and type, and capillary density. CHF patients demonstrated a lower VO(2peak) (15.1+/-1.1 versus 28.1+/-2.3 mL.kg(-1).min(-1), P<.001) and capillary to fiber ratio (1.09+/-0.05 versus 1.40+/-0.04; P<.001) when compared with controls. However, there was no difference in capillary density (capillaries per square millimeter) across any of the fiber types. Measurements of MAPR and oxidative enzyme activity suggested no difference in muscle oxidative capacity between the groups.


CONCLUSIONS
Neither reductions in muscle oxidative capacity nor capillary density appear to be the cause of exercise limitation in this cohort of patients. Therefore, we hypothesize that the low VO(2peak) observed in CHF patients may be the result of fiber atrophy and possibly impaired activation of oxidative phosphorylation.
Williams
Andrew D
AD
Centre for Rehabilitation, Exercise and Sport Science, Victoria University of Technology, Melbourne, Australia.
Selig
Steve
S
Hare
David L
DL
Hayes
Alan
A
Krum
Henry
H
Patterson
Jeremy
J
Geerling
Ralph H
RH
Toia
Deidre
D
Carey
Michael F
MF
D000255:Adenosine Triphosphate / Q000378:metabolism; D000368:Aged; D015992:Body Mass Index; D002196:Capillaries / Q000378:metabolism; D016022:Case-Control Studies; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D006333:Heart Failure / Q000378:metabolism / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008931:Mitochondria, Muscle / Q000378:metabolism; D018485:Muscle Fibers, Skeletal / Q000473:pathology; D018482:Muscle, Skeletal / Q000098:blood supply / Q000378:metabolism*; D010085:Oxidative Phosphorylation; D010101:Oxygen Consumption / Q000502:physiology
D000255:Adenosine Triphosphate