These results suggest that the blood pressure response during metaboreflex activation after mild rhythmic exercise is strongly dependent on the capacity to increase cardiac output rather than due to increased vascular resistance.

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.

Background-An important role of the increased stimulation of skeletal muscle ergoreceptors (intramuscular afferents sensitive to products of muscle work) in the genesis of symptoms of exertion intolerance in chronic heart failure (CHF) has been proposed. With the use of selective infusions and dietary manipulation methods, we sought to identify the role of H ϩ , K ϩ , lactate, and peripheral hemodynamics on ergoreflex overactivation. Methods and Results-Ten stable CHF patients (aged 67.9Ϯ2.5 years, peak oxygen uptake 16.3Ϯ1.2 mL · kg Ϫ1 · min Ϫ1 ) and 10 age-matched and sex-matched healthy subjects were studied. The ergoreflex contribution to ventilation was assessed by post-handgrip regional circulatory occlusion (PH-RCO) and computed as the difference in ventilation between PH-RCO and a control run without PH-RCO. This test was performed on 6 separate occasions. On each occasion a different chemical was infused (insulin, sodium nitroprusside, sodium bicarbonate, dopamine, or saline) or a 36-hour glucose-free diet was undertaken before the test. During all stages of the protocol, the local muscular blood effluent concentrations of H ϩ , K ϩ , glucose, and lactate were assessed. An ergoreflex effect on the ventilatory response was seen in patients (versus control subjects) during the saline infusions (6.7Ϯ2.3 L/min versus Ϫ0.1Ϯ0. Key Words: heart failure Ⅲ muscles Ⅲ nervous system, autonomic Ⅲ reflex Ⅲ ventilation T he ergoreflex consists of a brain stem autonomic and ventilatory response activated by signals from the periphery, such as free nerve ending group III and IV muscle afferents. 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. 4 The triggering mediators responsible for the ergoreflex stimulation and their involvement in the abnormal exercise responses in CHF remain to be established. Different metabolic and humoral products have been studied in animals [7][8][9][10][11][12] and in humans, 13-15 but few investigators have investigated factors specifically involved in the ergoreflex overactivation of CHF patients. 16,17 One (or more) of these mediators may be involved as a link between alterations in muscle metabolism and/or hemodynamics present in CHF and the ventilatory response to exercise, via activation of muscle reflex.We have investigated the role of the putative triggers in muscle ergoreflex activation. The id...

No abstract