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Figure 1 Simultaneous determination of intracoronary flow velocity (cm/s) and pressure (mm Hg) measurements. The flow velocity trend over 90 s is shown during vessel occlusion (V_occl) and during vessel patency (V_ø-occl) in the left upper panel of the figure. In the upper part, the instantaneous flow velocity signal (cm/s) during vessel occlusion is represented. On the right, simultaneous aortic (P_ao) and distal occlusive (P_occl) pressure is shown. The pressure-derived collateral flow index (CFI_P) was calculated as follows: (P_occl – 5)/(P_ao – 5). Doppler-derived CFI_V: V_occl/V_ø-occl. CFIv = velocity-derived index of collateral flow.