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Figure 3 This figure shows illustrative examples of two types of stenosis with respective hyperemic pressure traces. These examples were not cases from the primary data set but are chosen to illustrate this concept. In the case of stenosis A, a discrete stenosis in a right coronary artery (RCA), friction is less important, the resting pressure gradient is low but increases markedly on induction of hyperemia as the quadratic relationship of the fluid dynamic equation is dominant. Pressure-derived coronary flow reserve (CFR) is overestimated in this situation. With the longer, more diffuse but less severe stenosis B, the resting pressure gradient is greater, but the increase on induction of hyperemia is less, as the linear component of the fluid dynamic equation (f) is more important. In this latter stenosis, pressure-derived CFR is underestimated. FFR = fractional flow reserve; Pa = aortic pressure; Pd = distal coronary pressure.
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