Aortic coarctation and arterial stenosis are a localized narrowing of the arterial lumen. The pressure-flow relation contains a linear term and a quadratic term the latter accounting for losses due to turbulence, and dominating in severe stenoses (area occlusion more than 85%) thereby limiting blood supply to the tissue. The Flow Reserve is defined as the ratio of flow during maximal dilatation and flow during control conditions, and is determined by the stenosis and also by the dilatory capacity of the periphery. Fractional Flow Reserve, FFR, is the ratio of the maximal flow with the stenosis present and maximal flow in a normal bed. During maximal dilation FFR ≈ Pdistal.minimal/Pao, with Pdistal.minimal the pressure distal of the stenosis during dilatation and Pao aortic pressure. The, nonlinear, relation between pressure drop over the stenosis and flow through it depends on the stenosis severity only.
Stenosis severity Flow reserve Fractional flow reserve Area ratio Vasodilation
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