Abstract
Fick’s principle states that oxygen consumption of an organ or organism is equal to the product of blood flow and oxygen extraction from the blood. Among all organs, the heart is unique in that oxygen extraction is constantly close to maximal. Thus, the only way that this metabolically demanding organ can increase oxygen consumption is by increasing coronary blood flow. In this aspect of oxygen delivery, the heart also is unique because most flow occurs in diastole instead of in systole. In other organs, blood flows down a pressure gradient from its arterial source through the resistance of the arterioles into the capillary bed and thence venous return. In the heart, the compression of the vasculature by its surrounding muscle during systole impedes flow so that while the pressure head for flow is maximum in systole, flow is maximum in diastole. Thus, a simple “vascular waterfall” model in which flow moves from highest to lowest pressure does not fully explain observed myocardial flow phenomena. Article p 1768 In this week’s Circulation , Davies et al1 used computer analysis of recordings of blood flow and pressure to detect and quantify intracoronary …
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