Effect of Metaboreflex on Cardiovascular System in Subjects of Metabolic Syndrome

Abstract

INTRODUCTIONPhysical activity is any bodily movement produced by skeletal muscles that results in energy expenditure [1]. An emphasis has been placed on understanding the role of physical activity in the prevention and management of obesity which is responsible for the increasing prevalence of metabolic syndrome in the U.S. and worldwide due to sedentary lifestyles [2][3][4].When physical activity is planned, structured, and repetitive with an objective to improve or maintain the physical fitness, then it is known as exercise [1]. Exercise can be of three types: isometric, isotonic or rhythmic and isokinetic [1]. The cardiovascular and haemodynamic changes during exercise are regulated by autonomic activity which itself is under control of several neural mechanisms [5]. These neural mechanisms are central command, exercise pressor reflex and baroreflex. Central command is a feed-forward mechanism from the cortical centres in brain. The metaboreflex or exercise pressor reflex is feedback mechanism from the exercising skeletal muscle. The baroreflex is a negative feedback mechanism that can either be arterial, originating from the carotid sinus and aortic arch, or cardiopulmonary, originating from the heart and pulmonary vasculature [5].In healthy individuals, exercise causes the sympathetic tone to dominate over parasympathetic tone thereby augmenting the heartrate, myocardial contractility and peripheral vasoconstriction in the vascular beds of organs and tissues not involved in exercise [6].Some dysregulation in these mechanisms has been demonstrated in various diseases, mainly circulatory and metabolic diseases [6]. Further investigation in this field is warranted on the correction of the dysregulation of these reflexes [6].In metaboreflex, during exercise, metabolites like lactate, potassium, phosphate, adenosine, bradykinin and arachidonic acid products start accumulating in the skeletal muscle [7,8]. These metabolites are sensed by the receptors present within the muscles, which relay this information to the dorsal horn of spinal cord via Group III and IV muscle afferents [7,8]. Finally the information reaches to the nucleus tractus solitarius and other cardiovascular controlling areas in the brain stem that regulate the blood flow in contracting skeletal muscles by several haemodynamic adjustments [7,8].In metabolic syndrome, drug therapies directed towards the individual risk factors (i.e., hypertension, obesity, dyslipidemia) might be required [9]. In order to know the effect of individual components of metabolic syndrome on EPR, many studies were conducted [10][11][12][13]

Altered Autonomic Function in Metabolic Syndrome: Interactive Effects of Multiple Components

“…Similar effects during exercise are observed regarding the impact of MetS on muscle metaboreflex activation, in which an enhanced vasoconstrictor response is observed similar to what has been seen in hypertension [22,23,53,82]. Furthermore, studies assessing the impact of obesity have shown that obesity alone does not significantly alter hemodynamics [23].…”

“…Both hypertension and MetS have been linked to autonomic dysfunction and exercise intolerance, [14][15][16][17][18][19]22,23,32,53]. Hypertension has been studied extensively in the context of exercise; hypertension modifies the muscle metaboreflex and the arterial baroreflex as well as their interactions [15,[17][18][19]32,54,55].…”

Blood Pressure Response to Muscle Metaboreflex Activation is Impaired in Men Living with HIV

“…It has long been known that during acute circulatory stresses, such as exercise, arterial pressure is controlled almost entirely by nervous reflex mechanisms [37]. Moreover, SBP has been reported to be more sensitive to metaboreflex than DBP in individuals with autonomic impairment [38,39]. It is therefore possible that a greater sympathetic outflow resulting from metaboreflex within the short periods of PEMI and CER protocols had more effect on SBP than DBP.…”

Inspiratory Muscle Training Intensity in Patients Living with Cardiovascular Diseases: A Systematic Review

“…This accumulation triggers the metaboreflex that redirects the blood flow via sympathetic activation from the periphery muscles to the diaphragmatic area, thus avoiding dyspnoea due to reduction in blood supply to respiratory muscles. However, this peripheral blood flow redistribution may be responsible for the interruption of exercise as well as activities of daily living due to peripheral muscle fatigue [9,10]. Therefore, delaying the onset of this reflex might predispose individuals to a more active lifestyle and improved exercise tolerance.…”