Systolic flow limitation in stenotic lower-extremity vein grafts

Our purpose was to investigate the hemodynamic theory that the blood flow rate through a stenotic arterial graft is limited by the onset of turbulence, which acts as a barrier at peak systole against further increases in systolic flow.

We used duplex ultrasonography to examine 25 stenotic infrainguinal vein grafts. Theory predicts that the flow limitation occurs at peak systole at a stenotic velocity greater than 250 cm/sec, which corresponds to a residual stenotic lumenal diameter of 0.36 cm (Reynolds No. 2000). These numbers are based on the assumption that the 68 ml/min blood flow is supplied by the femoropopliteal graft to the resting lower leg only during systole. When the lumen is smaller than 0.36, peak systolic velocity (PSV) must exceed 250 cm/sec. The increased velocity results in poststenotic turbulence. This turbulent condition restricts the average graft systolic flow to less than the 68 ml/min required by the lower leg, so diastolic flow is needed to make up the deficit.

Twenty vein grafts with PSVs of 250 cm/sec or greater had end-diastolic velocities of 50 cm/sec or greater as predicted; three grafts with PSVs of 256 to 300 cm/sec and two grafts with PSVs of less than 250 cm/sec had no forward diastolic flow.

The onset of turbulence in a stenotic vein graft supplying the lower leg occurs at a PSV of 250 cm/sec or greater. The appearance of diastolic flow maintains the average graft volume flow.