In fact, the left ventricular subendocardial blood flow ceases during systole and there may actually be a reversal of flow in intramural coronary vessels. This effect is masked by the capacitance properties of epicardial coronary vessels. Therefore, the duration of diastolic phase is crucial to subendocardial perfusion (see below).
Estimation of contribution of these mechanical forces to the total coronary resistance is confounded by many technical errors. However, approximately 3050 percent of total coronary vasculature resistance can be attributed to these forces. At maximal coronary dilation, removal of extravascular compressive forces increases coronary blood flow by approximately 50 percent. In the presence of coronary artery disease, when distal coronary vascular beds are maximally dilated, the effects of compressive forces become most pronounced. buy ortho tri-cyclen
Diastolic phase: This factor is very closely related to the compressive forces in influencing coronary blood flow. However, it is reviewed separately to emphasize its importance. During the diastolic phase, the compressive forces are at their minimum and coronary resistance is at its nadir. Coronary blood flow reaches its peak during this phase. As noted above, the subendocardium receives blood only during this period.