Metabolic responses to graded exercise in chronic heart failure

To determine if exercise intolerance and fatigue in chronic heart failure could be exacerbated by an abnormal metabolic response to exercise, we studied 12 patients with stable chronic heart failure and 12 normal volunteers during symptom-limited maximal treadmill exercise. Peak VO2 was 17.2 (15.1-19.2) ml.kg-1 x min-1 in patients and 29.9 (26.3-33.5) in controls (mean and 95% confidence intervals; P < 0.0001, t-test). Overall, levels in peripheral venous blood of glucose, glycerol and free fatty acids were greater in patients, although the differences became less marked with increasing exercise intensity. Noradrenaline was elevated in patients at rest, but the peak exercise response was similar to controls. Responses of adrenaline, insulin and glucagon were similar in both groups. We conclude that depletion of the levels of circulating substrates is not contributory to exercise intolerance and fatigue in chronic heart failure. Greater levels of glycerol and free fatty acids may be mediated by excess sympathetic nervous system activity, reflected in elevated noradrenaline levels.