Skeletal muscle function at low work level as a model for daily activities in patients with chronic heart failure

Aim. Metabolic exercise abnormalities have been reported in chronic heart failure patients. This study sought to evaluate whether these abnormalities affected daily activity. Methods and results. In 16 patients with moderate-to-severe chronic heart failure and in eight controls we measured femoral flow (thermodilution) and metabolism (glucose, lactate, free fatty acids, blood gas values) at rest and during a constant load of 20 W, which may mimic a daily activity. At rest, chronic heart failure patients had a leg flow similar to controls, but showed a higher leg oxygen consumption (4.6 ± 0.6 vs 2.6 ± 0.4 ml.min^-1; P <0.05), a higher arteriovenous oxygen difference (7.2 ± 0.5 vs 5.4 ± 0.7 ml.dl^-1; P <0.05), and a lower femoral vein pH (7.37 ± 5.-03 vs 7.42 ± 0.01; P = 0.01). At 20 W, chronic heart failure patients had a leg flow similar to controls, but showed increased lactate release (from resting 11.7 ± 33 to 142 ± 125 μg.min^-1 P <0.0001 vs controls, from resting 5.7 ± 15.4 to 50 ± 149 μg.min^-1 ns), higher arterial concentration of free fatty acids (781 ± 69 vs 481 ± 85 μmol.l^-1; P <0.01), lower femoral vein HCO₃ (24.1 ± 2.6 vs 26.3 ± 1.7 mmol.l^-1; P <0.05) and base excess (-2.3 ± 2.3 vs -0.24 ± 1.7 mmol.l^-1; P = 0.01). Conclusion. In chronic heart failure patients, the important cellular metabolic alterations already present at rest partially affect daily activities, owing to a further decrease in the efficiency of muscle metabolic processes, and may preclude tolerance of heavier activities. Such alterations appear, at least in part, independent of peripheral haemodynamic responses to exercise.