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

Abstract

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.

Skeletal Muscle Reflex in Heart Failure Patients

“…1 It has been hypothesized that muscle metabolic abnormalities and/or circulatory insufficiencies of chronic heart failure (CHF) cause local overproduction and accumulation of muscle metabolic products, which trigger the ergoreceptors. 2,3 Our lab and others have confirmed this hypothesis by demonstrating that the muscle ergoreflexes of the forearm muscles, 4 the small muscles used in dorsiflexing the foot, 5 and the muscles of the quadriceps 6 cause an enhanced ventilatory response in CHF. An overactivation of the muscle ergoreflex during exercise has been shown to be closely related to patient symptoms and to the ventilatory response to exercise, and a role of this reflex in contributing to exercise intolerance in CHF has been proposed.…”

“…The difference between these two changes was computed as a measure of the reflex activity. 6 Figure 1 is a schematic representation of the methodology of the ergoreflex measurement.…”

“…On the basis of our own 4,6 and others' experiences, 15,19 we have chosen the first approach to assess the role of extracellular hydrogen ion (H ϩ ), potassium (K ϩ ) (by sodium-bicarbonate and insulindextrose infusions), glucose metabolism (ie, glycogen-free diet), and peripheral vasoconstriction (dopamine infusion). The second method has been selected to address the issue of role of vasodilatation on the reflex by infusing sodium nitroprusside.…”

“…This protocol has been shown to isolate the activity of the ergoreflex after exercise by "freezing" the chemical status of the muscle at peak exercise. 4,6 For the calculation of the ergoreceptor activity, the changes in ventilation (L/min) between the second and third minute of PH-RCO recovery and the second-and third-minute control recovery without PH-RCO with regard to the corresponding mean baseline values were measured. The difference between these two changes was computed as a measure of the reflex activity.…”

Fluido torácico total – Um possível determinante da eficácia ventilatória em doentes com insuficiência cardíaca

“…Tem sido discutido o papel do aumento da sensibilidade dos quimioreceptores musculares na hiperventilação ao esforço em doentes com ICC [13][14][15] . O «ergoreflexo», que estará aumentado nestes doentes, é um complexo refl exo metabólico pelo qual quimioreceptores dos músculos periféricos, sensíveis a bioprodutos metabólicos locais produzidos durante o exercício, iniciam um refl exo neuronal que leva à hiperventilação 5 .…”