Muscle fatigue and dyspnoea in chronic heart failure: two sides of the same coin?

The pathogenesis of the limiting symptoms in patients with chronic heart failure, shortness of breath and fatigue on exercise, are poorly understood. We analysed data from 222 incremental symptom limited exercise tests to determine whether there were differences between patients stopped by breathlessness or fatigue. One hundred and sixty patients were stopped by breathlessness and 62 by fatigue. There was no differences between the two groups in underlying diagnosis or in exercise performance (peak oxygen consumption 15.66 (+/- 5.62) ml.kg-1.min-1 in the fatigue group, 15.13 (+/- 4.64) in the breathless group). The ventilatory response as assessed by ventilatory response to carbon dioxide production (VE/VCO2 slope) was not different between the two groups (2.61 (+/- 0.96) in the fatigue group, 3.03 (+/- 1.23) in the breathless group: P = ns). There were no differences between the two groups in left ventricular dimensions, left ventricular ejection fraction or left ventricular end-diastolic pressure. The limiting symptoms of breathlessness and fatigue in chronic heart failure are two sides of the same coin. Any pathophysiological explanation of exercise limitation in chronic heart failure must unify these two symptoms.