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The Coronary Microcirculation in Health and Disease

DOI: 10.1155/2013/238979

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Abstract:

Coronary blood flow is closely regulated to meet the changing metabolic demands of the working myocardium. Resistance of the coronary vasculature is determined by metabolic, myogenic, endothelial, and neural mechanisms. The influence of these control mechanisms varies throughout the coronary circulation, as they have dominant sites of action in vessels of different caliber. Coronary vascular resistance depends upon the coordinated response to these influences. Within a segment of the coronary circulation, resistance may be determined, for example, by competitive interaction between neural vasoconstriction and metabolic vasodilation. Such a system in which control occurs through multiple mechanisms with varying effects allows for precise control of coronary blood flow. This system also provides protection against dysfunction of a single control mechanism. If one fails, other control mechanisms can compensate for that loss of function. Thus, adequate delivery of oxygen and nutrients can be maintained despite potential dysfunction and large fluctuations in metabolic demands of the myocardium. In disease states, these regulatory mechanisms may also fail, and endothelial dysfunction is commonly seen in the setting of cardiac disease. Optimal cardioprotective therapies must target the coronary microcirculation and cardiac myocytes in tandem. Similarly, reversal of cardiac dysfunction requires concomitant amelioration of coronary microvascular dysfunction. 1. Introduction Coronary vascular resistance is determined by a variety of mechanisms including coronary vascular anatomy, extravascular cardiac compressive forces, and vascular smooth muscle contraction. The roles of coronary vascular anatomy and cardiac compressive forces in determining coronary blood flow have been the focus of numerous studies and various models describe the contribution of these factors to distribution of blood flow throughout the myocardium [1]; however, coronary vascular resistance is primarily determined by arteriolar tone. This review discusses (1) the factors influencing coronary vascular tone and their effects on coronary blood flow and (2) the impact of imbalance in factors that regulate coronary vascular tone on regulation of myocardial blood flow in disease states. Vascular tone is governed by metabolic, myogenic, endothelial, and neural influences. These control mechanisms act in concert to vary coronary vascular resistance according to the demands of the working myocardium. Fine-tuning of vascular tone within the coronary circulation depends on the balance of these controls.

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