**4. Physiology of a fistula access**

The creation of a fistula results in blood flow from an artery to a vein that is inherently nonphysiologic in many ways. The initial flow rate in the radial artery of 20-30 mL/min increases to 200-300 mL/min immediately after creation of an AV fistula, reaching flow rates of 600-1200 mL/min after maturation (Wedgewood, 1984). In addition, the blood flow in the vein is not pulsatile prior to fistula insertion, whereas it is after the fistula is created. High fistula blood flow, a prerequisite for venous dilation and a requirement for easy cannulation and adequate dialysis, is accompanied by high arterial pressure being transmitted to the vein. This intense increase in flow rate and pressure has a profound effect on the hemodynamics in the downstream vein (Albayrak, 2006). The dramatically increased arterial blood flow at the time of fistula creation ultimately leads to an overall increase in shear stress, early on an observed low shear stress is evident which is thought to contribute to intimal hyperplasia and resultant venous stenosis and ultimate thrombosis.
