A Simplified Arithmetic Proof Of The Functionality Of The Distal Arteriovenous Fistula For Select Crural Revascularization
Nakul Rao, MD, Thomas Bernik, MD, Rama Bikkina, Herbert Dardik, MD.
Englewood Hospital & Med. Center, Englewood, NJ, USA.
OBJECTIVES:
To consider means to improve patency rates for femoral-crural bypasses. Simple arithmetic analysis of the components of Poiseuille’s Law can provide information on the relative resistances to flow at various levels following femoral-crural bypass. The deployment of a distal arteriovenous fistula (dAVF) may counter the negative impact of high resistance.
METHODS: Arbitrary dimensions for lower limb vessels were used to calculate the inverse of the radius to the fourth power and thereby obtain a value for “resistance” which in turn can be used to compare to other resistances at various sites based on radius. Methods to counter high runoff resistance include creation of a fistula at the distal anastomosis which reduces the overload from the bypass to a limited runoff.
RESULTS: Resistance at the distal anastomosis increases with decreasing radius. Comparison to the resistance at the proximal anastomosis also shows significant increases as the distance between anastomosis increases. An arteriovenous fistula constructed at the distal anastomosis modulates flow volume and velocity which are otherwise compromised particularly for long bypasses terminating at the mid or distal crural levels.
CONCLUSIONS:
Using simple arithmetic in Poisseuille’s Law, the relationships of resistances at specific sites along the bypass and runoff circulation can be shown to be functions of conduit length and runoff radius. Adding a dAVF at distal crural sites can improve patency of a bypass by diverting the overflow to the runoff into the high capacitant and low resistant venous system.
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