ABSTRACT
This chapter reviews the major factors governing energy losses and therefore pressure drop across a stenotic lesion. Energy losses are influenced by viscous effects, flow separation, and possibly turbulence. Viscous losses are due to ordinary wall friction; in the stenotic area, viscous losses are accentuated because of increased blood velocity. Separation losses are due to the facts that flow downstream to the stenosis separates from the vessel wall, forming eddies which dissipate additional energy. Effects of coronary stenoses on coronary flow depend importantly on vasodilator reserve at the arteriolar level, that is, effects of epicardial stenoses are potentially counteracted by vasodilation at the arteriolar level. To illustrate this more specifically, the chapter uses the so-called steady-state pressure-flow diagram. Coronary flow is plotted against coronary artery pressure. The coronary circulation has the ability to adjust between the bounds of maximum vasoconstriction and maximum vasodilation. Different degrees of stenosis, ranging from 50 to 90% diameter narrowing, are illustrated by small solid circles.
