Nicole Varble

Abstract

One of the largest problems facing vascular surgeons today is malfunctioning arteriovenous fistulas (AVF) in patients on hemodialysis. A radial- cephalic AVF is a vessel in the arm that directs blood flow from the high pressure arteries to the low pressure veins and is put in place so blood can be withdrawn from a patient at a point where high volume blood flow occurs. After a period of maturation, the fistula often expands to adapt for the increase flow and can therefore be accessed repeatedly for hemodialysis. However, in a small percentage of cases, access related steal can lead to ischemia of the hand and threaten the patient with gangrene and amputation. This is a recognizable problem and is currently being treated with a method called Distal Revascularization and Interval Ligation (DRIL) in which a vast majority of cases see improved blood flow and pressure to the digits all while maintaining the AVF. The DRIL procedure has been widely accepted as an effective method to prevent the onset of steal, however the flow mechanisms and reasoning behind its success is not well understood. Thus far, attempts of explaining the procedure have been sparse and incomplete, often disregarding factors such as the compliance of the vessels and the pressures and flows on the venous side of the vasculature. To study this problem, a physical model was built using tubing with comparable resistances and compliances to that of native vessels. The native circulation was first built, including the venous side, which will provide a unique baseline for the study. An emphasis was placed on creating a system with physiologic pressures on both the arterial side and venous side. Once the model successfully represented the native blood flow, it was adapted for an AVF. Upon this adaptation, variations of radius, length, and position were tested. Furthermore, this model can easily be adapted to model hypertensive patients, much like those on hemodialysis and can offer additional insight as to if those patients are more susceptible to access related ischemia. Observations of pressures and flows led to a comprehensive study of the hemodynamics of the native arm circulation, an AVF and the DRIL procedure. When the model is integrated into the hemodynamic simulator loop, physiologic pressures have been produced in the arterial side of 125/55 mmHg and a damped waveform with a mean pressure of 18 mmHg was found on the venous side. Mean aortic flow was 4.7 L/min.

Library of Congress Subject Headings

Hemodynamics; Fistula, Arteriovenous--Prevention; Blood vessels--Models

Publication Date

6-29-2011

Document Type

Thesis

Department, Program, or Center

Mechanical Engineering (KGCOE)

Advisor

Day, Steven

Comments

Note: imported from RIT’s Digital Media Library running on DSpace to RIT Scholar Works. Physical copy available through RIT's The Wallace Library at: QP105 .V37 2011

Campus

RIT – Main Campus

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