SYSTOLIC FLOW LIMITATION IN STENOTIC LOWER-EXTREMITY VEIN GRAFTS

Purpose: Our purpose was to investigate the hemodynamic theory that th e blood flow rate through a stenotic arterial graft is limited by the onset of turbulence, which acts as a barrier at peak systole against f urther increases in systolic flow. Methods: We used duplex ultrasonogr aphy to examine 25 stenotic infrainguinal vein grafts. Theory predicts that the flow limitation occurs at peak systole at a stenotic velocit y greater than 250 cm/sec, which corresponds to a residual stenotic lu menal 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 fe moropopliteal graft to the resting lower leg only during systole. When the lumen is smaller than 0.36 cm, peak systolic velocity (PSV) must exceed 250 cm/sec. The increased velocity results in poststenotic turb ulence. This turbulent condition restricts the averaged graft systolic flow to less than the 68 ml/min required by the lower leg, so diastol ic flow is needed to make up the deficit. Results: 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 c m/sec and two grafts with PSVs of less than 250 cm/sec had no forward diastolic flow (p = 0.03). None of 10 normal grafts had forward diasto lic flow. Conclusion: 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 Bow maintains the average graft volume flow.