Fig. 2.

Pressure and flow across a stenosis. The pressure gradient across a stenosis is determined by the sum of viscous and separation losses. Flow separation and the formation of eddies prevent complete pressure recovery at the exit. Measurement of intracoronary hemodynamics includes proximal perfusion pressure (P_a), coronary pressure and flow velocity distal to the stenosis (P_d and V_d, respectively), and the venous pressure (P_v), which is usually assumed to be negligible. ΔP is the difference between Pd and Pa. Normal diameter (reproduced from van de Hoef TP et al., Nature Reviews Cardiology. 2013;10(8):439–52(64), with permission) [11]) (D_n), stenosis diameter (D_s), proximal velocity (V_n), and stenosis velocity (V_s) are indicated. Adapted from van de Hoef TP et al., Nature Reviews Cardiology. 2013;10(8):439–52(64), with permission [11]