Skeletal Muscle Reflex in Heart Failure Patients

Abstract

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...

Recommendations on the use of exercise testing in clinical practice

“…V9E at any given V9CO 2 is typically increased. Contributory factors include: premature metabolic acidaemia (reflecting reduced O 2 delivery and/or utilisation) [146,147]; increased physiological dead space [4]; increased sympathetic system activation via mechano-or pressor-receptor stimulation in the exercising muscles [148][149][150][151][152] and, possibly, contributions from cardiopulmonary vagal and sympathetic reflexes [132,153,154]. Several studies have shown that breathing pattern in CHF is more rapid and shallow than in healthy controls at any given V9E [4,155,156].…”

Role of the Exercise Pressor Reflex in Rats With Dilated Cardiomyopathy

“…As discussed, the mechanisms by which the mechanoreflex becomes exaggerated are presently unclear. Furthermore, a great deal of controversy exists regarding the contribution of the metabolic component of the EPR, because its activity has been reported to be both enhanced 14,15,21,34 and reduced 10,22 in response to exercise in CHF patients. As stated, it is plausible that initial reductions in peripheral blood flow result in an abnormal accumulation of exercise-induced metabolites in the muscle interstitium.…”

Comportamento do ergorreflexo na insuficiência cardíaca

“…Therefore, even in terms of anatomical differentiation and regarding the physiological triggers, there is a degree of overlapping between mechano and metaboreceptors and more recent observations have challenged the classic description of these receptors as distinct structures 19,20 . Hence, we use the terms "ergoreceptors", which contemplate both types of afferences and "ergoreflex", which is the reflex triggered by both types of receptors 16,[21][22][23] .…”

“…Thus, early acidosis occurs, as well as depletion of the high-energy compounds developed during the exercise, which, in turn, trigger other compensatory mechanisms. In normal individuals, these compensatory mechanisms would keep the skeletal muscle performance and cause the stimulation of several afferents, such as muscle ergoreceptors, which communicate with the brainstem on the level of muscle work -which triggers the ergoreflex 16,[21][22][23] .…”