Exercise capacity in heart failure patients: relative importance of heart and skeletal muscle.
The knee extensor and the whole-body exercise capacities were measured in 11 chronic heart failure (CHF) patients and 11 healthy age- and sex-matched controls, and were related to ejection fraction and to biochemical and histochemical markers of the musculature. The CHF patients had a 39% lower maximal oxygen uptake measured on an ergometer cycle than the healthy controls (1.54 +/- 0.57 vs. 2.51 +/- 0.70 1 min-1, P < 0.001). The low exercise capacity was markedly related to the ejection fraction (r = 0.77, P < 0.001). The maximal strength of m. quadriceps femoris was 15% lower in the CHF patients than in the controls (P < 0.05). The cross-sectional area (CSA) of m. quadriceps femoris explained 55% (r = 0.74, P < 0.001) of the difference in strength between both groups. The endurance capacity of m. quadriceps femoris was 30% lower in CHF patients than in controls, partly as a result of the 25% lower capillary density (P < 0.05) and the 27% lower aerobic enzyme capacity (P < 0.05), as estimated by the citrate synthase activity, in the CHF patients. The citrate synthase activity correlated with the maximal oxygen uptake (r = 0.61, P < 0.05). Moreover, the ejection fraction, together with the CSA of m. quadriceps femoris, explained 75% (r = 0.86%, P < 0.01) of the difference in maximal oxygen uptake between CHF patients and controls. These results demonstrate that CHF patients have both a lower local and a lower whole-body work capacity than healthy controls. This is a function of a smaller leg muscle mass and a lower capillary density and mitochondrial enzyme capacity in the CHF patients; however, a lowered pump capacity of the heart is the factor which limits the exercise capacity the most.
Magnusson
G
G
Department of Physiology and Pharmacology, Karolinska Institute, Huddinge Hospital, Sweden.
Kaijser
L
L
Rong
H
H
Isberg
B
B
Sylvén
C
C
Saltin
B
B
D000368:Aged; D002196:Capillaries / Q000473:pathology; D004798:Enzymes / Q000378:metabolism; D005080:Exercise Test; D005260:Female; D006321:Heart / Q000503:physiopathology*; D006333:Heart Failure / Q000473:pathology / Q000503:physiopathology*; D006801:Humans; D007537:Isometric Contraction; D007866:Leg; D008297:Male; D008875:Middle Aged; D018763:Muscle Fatigue; D018482:Muscle, Skeletal / Q000098:blood supply / Q000473:pathology / Q000503:physiopathology*; D010807:Physical Endurance
D004798:Enzymes