Contribution of skeletal muscle ‘ergoreceptors’ in the human leg to respiratory control in chronic heart failure

The role of skeletal muscle ergoreceptors (afferents sensitive to muscle contraction, differentiated into metaboreceptors, sensitive to metabolic changes, and mechanoreceptors, sensitive to mechanical changes) in the genesis of the increased ventilatory drive in chronic heart failure is controversial. We have aimed to clarify the contribution of muscle metaboreceptors in the leg to ventilation and to compare this with the contribution of mechanoreceptors. Eighteen heart failure patients and 12 controls were studied. Metaboreceptor and mechanoreceptor responses were measured in the leg by bicycle exercise with and without regional circulatory occlusion during recovery, and by active and equivalent passive limb movement, respectively.Patients, in comparison with controls, had a lower peak VO2 (Oxygen uptake) (18.1+/-1.6 vs. 24.5+/-2.5 ml min(-1) kg(-1), P< 0.05), and an evident metaboreceptor contribution to the ventilatory response (3.5+/-1.6 vs. -4.0+/-1.3 l min(-1), P<0.001). Passive limb movement increased ventilation in both patients and controls (+3.7+/-0.4 and +2.9+/-0.5 l min(-1) from baseline, P<0.003), but this was associated with an increase in VO2 (+0.1+/-0.01 and +0.1+/-0.02 l min(-1) from baseline, P<0.001). The ratio of the increase in ventilation to the increase in VO2 during passive movement was not significantly higher than that during active exercise for either patients or controls, suggesting a limited contribution from the mechanoreceptors. In chronic heart failure the presence of a muscle metaboreceptor reflex is also demonstrated in the leg, while mechanoreceptors exhibited a non-significant contribution in both patients and controls. The hypothesis of a peripheral origin of symptoms of exertional intolerance in this syndrome is confirmed as being mainly due to metabolic stimulation of the muscle metaboreceptors.