The Ergoreflex in patients with chronic stable heart failure
Introduction
The symptoms of breathlessness, fatigue and reduced exercise capacity are causes of much morbidity in patients with chronic heart failure. The pathophysiological basis of such symptoms remains unclear.
Patients with chronic heart failure have impaired exercise responses, [1]with a reduced peak oxygen consumption, [2]and an increased ventilatory response to a given workload, characterised by an increase in the slope relating ventilation to carbon dioxide production 3, 4.
Exercise capacity correlates poorly with indicators of central haemodynamic function such as pulmonary wedge pressure, and also with New York Heart Association class and rate of perceived exertion 2, 5, 6, 7, 8. Pharmacological intervention to improve haemodynamics with drugs such as nitrates and dobutamine does not improve exercise capacity 9, 10, and cardiac transplantation, although improving central haemodynamic function, does not improve the increased ventilatory equivalent seen in chronic heart failure 11, 12. This, along with the fact that an exercise training programme improves ventilatory responses without any improvement in central haemodynamic function [13], implies that some peripheral mechanism may be responsible for exercise limitation in chronic heart failure.
Changes in skeletal muscle are well documented in chronic heart failure. Decreased size and strength of the major muscles has been shown, [14]along with a shift from type I (aerobic) to type II (anaerobic) muscle fibres [15]. There is also reduced enzymatic capacity of muscle with rapid development of acidosis on exercise 16, 17, 18.
Nerve endings that are sensitive to metabolites exist in skeletal muscle: these have been termed ergoreceptors [19]. Stimulation of these receptors by metabolites of exercise causes an increase in blood pressure and ventilation: this reflex is enhanced in chronic heart failure [20]. Early metabolic distress on exertion due to skeletal muscle abnormalities may lead to build-up of the metabolites of exercise, causing excessive ergoreceptor stimulation, manifesting as dyspnoea and exercise limitation.
An exaggerated ergoreflex response in chronic heart failure has only been documented in the arm muscles [20]. Clearly in terms of day to day activity, the legs are more important than the arms: they are bigger (and presumably more dominant in the generation of dyspnoea and fatigue), and necessary for mobility. This study therefore investigates the ergoreflex in the leg of patients with chronic heart failure.
Section snippets
Methods
The Greater Glasgow Health Board West ethics committee approved this study. All participants gave witnessed written informed consent.
Ten patients with chronic stable heart failure were recruited from a cardiology clinic at the Western Infirmary, Glasgow (Table 1). Heart failure was defined as exercise intolerance through breathlessness or fatigue, and evidence of left ventricular systolic dysfunction as defined by echocardiography or radionucleotide ventriculography. The aetiology of heart
Results
All 10 chronic heart failure patients and nine controls completed the three parts of the protocol.
There were no significant differences in any of the measured resting variables between chronic heart failure patients and control subjects (Table 2). Peak exercise variables did not differ between patients and controls, therefore a similar metabolic load was applied to each group. Leg exercise significantly increased blood pressure, ventilation, oxygen consumption, carbon dioxide production,
Discussion
A peripheral mechanism arising from skeletal muscle may contribute to exertional dyspnoea in chronic heart failure patients. Early metabolic distress of skeletal muscle on exertion, perhaps due to the abnormal muscle in patients with chronic heart failure, may lead to build-up of the metabolites of exercise. This causes overstimulation of ergoreceptors in the skeletal muscle that increase ventilation, manifesting as dyspnoea.
There is a reflex arising in skeletal muscle that increases
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