Strengthening Our Understanding of Muscle Metaboreflex Control in Patients with Coronary Artery Disease: (Dis)association Between Physical Fitness and Hemodynamic Responses

Ischemic Heart Disease remains a leading cause of mortality worldwide. In addition to pharmacologic therapy and coronary revascularization, healthy lifestyle interventions such as diet and exercise are essential components of disease management. Although exercise training is a Class I recommendation for patients with ischemic heart disease, physical exertion is not without risk in this population. Indeed, an exercise stress test is a well-established method for inducing myocardial ischemia. Furthermore, patients with ischemic heart disease often exhibit abnormal cardiovascular responses during exercise, which makes exercise prescription both challenging and potentially risky in this clinical population. Therefore, understanding the physiological mechanisms underlying the altered cardiovascular control at rest and during exercise, as well as the cardioprotective effects of exercise training in patients with ischemic heart disease, is critical for improving treatment strategies and optimizing disease management.

The cardiovascular responses to exercise are orchestrated by several integrative neural control mechanisms, including central command, the exercise pressor reflex, the arterial and cardiopulmonary baroreflexes, and the central and peripheral chemoreflexes. The exercise pressor reflex comprises group III and IV skeletal muscle afferents that discharge in response to mechanical deformation (i.e., muscle mechanoreflex) and the accumulation of metabolic by-products of muscle contraction (i.e., muscle metaboreflex).^, Inputs from group III/IV afferent fibers synapse within cardiovascular control areas in the brainstem that reflexively decrease parasympathetic and increase sympathetic nerve activity, leading to increased Heart Rate (HR), cardiac output, total peripheral resistance, and arterial blood pressure during exercise.^, It has been shown that the blood pressure responses to exercise and metaboreflex activation are directly associated with absolute muscle strength in young, healthy adults.^, Moreover, exercise training-induced improvements in cardiorespiratory fitness can modulate metaboreflex control. Nevertheless, the extent to which the cardiovascular responses to muscle metaboreflex activation are related to markers of physical fitness in patients with Coronary Artery Disease (CAD) is currently unknown.

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