Hemodynamics of infrapopliteal PTFE bypasses and adjunctive arteriovenous fistulas

Abstract

Purpose. Blood flow, pressure and peripheral resistance in patients with established polytetrafluoroethylene (PTFE) grafts and adjunctive arteriovenous fistulas (AVF) have rarely been investigated. To better elucidate the effects of this AVF, we obtained noninvasive measurements of hemodynamic variables in patients with infrapopliteal PTFE grafts and an AVF. Methods. Systolic, mean and diastolic arm and toe pressures were measured with an oscillometric technique employed in automatic blood pressure monitors. Peak-systolic velocity, end-diastolic velocity and flow rates at the graft and recipient distal artery were measured with duplex ultrasound. Resistance for the leg and foot in peripheral resistance units ( PRU ) was estimated as mean arm pressure divided by graft flow rate and as mean toe pressure divided by distal artery flow rate respectively. We analyzed data from 21 patients. Toe pressures were measurable in 13 patients. Bypass graft inflow was at the external iliac artery in 11 patients, common femoral in six, common iliac in two and superficial femoral in two. The distal anastomosis was at the anterior tibial artery in 10 patients, peroneal in seven and posterior tibial in four patients. Results. Graft systolic and diastolic velocities were 91±46 (mean±sd) and 38±31 (mean±sd) cm/s respectively. Toe systolic pressure averaged 81±28 (mean±SD) mmHg with a corresponding toe/brachial index (TBI) of 0.53±0.18 (mean±SD). The ratio between arm mean pressure, 104±20 (mean±SD) mmHg, and graft flow rate, 413±290 (mean±sd) ml/min, yielded an estimated leg resistance of 0.32±0.20 peripheral resistance units (PRU) (mean±sd). The ratio between mean toe pressure, 51±21 (mean±SD) mmHg, and distal artery flow rate, 37±26 (mean±SD) ml/min, produced an estimated foot resistance averaging 1.66±1.18 PRU (mean±sd). Conclusions. Average graft flow rate was five times greater than flow reported for standard tibial bypasses. Although distal artery flow rate and graft peak systolic velocity were within reported normal ranges, mean toe pressure and toe-brachial index were below normal. Leg and foot resistances were decreased. These data suggest that bypasses with arteriovenous fistulas have increased flow, desirable for graft patency, but may affect distal perfusion pressure.