1. Project #2: Hemodynamic Evaluation of Arteriovenous Fistula
Sponsored by: the National Science Foundation Grant ID No: DUE
Research by: Briana Conners, Junior, Chemical Engineering and Ken Okoye, Junior, Biomedical Engineering
Support by: Dr. Rupak Banerjee and Ehsan Rajabi Jaghargh, School of Mechanical Engineering
College of Engineering and Applied Science; University of Cincinnati; Cincinnati, Ohio

2. Arteriovenous Fistula (AVF)
AV Fistula – a surgically created connection between an artery and a vein
Used to increase blood flow for dialysis
In 20 – 50% of patients, the created fistulas failed to fully dilate to accommodate the increased flow.

3. Blood Flow
Blood exerts a shear stress on the walls of the blood vessels as it flows through the vessel lumen.
Blood vessels remodel to maintain constant wall shear stresses (WSS).
If the WSS is low, smooth muscle cells are signaled to migrate to center of vessel wall.
The blood vessel thickening reduces flow, inhibiting vascular access for dialysis.

4. Project Goals and Objectives
Establish a correlation between the configuration of entry of a arteriovenus fistula and the vessel wall shear stresses.
Objective
Model blood flow in four angle cases using computational fluid dynamics using data.
Derive the WSS profiles for the different AV fistula configuration
Establish the impact of difference on the intima-media thickening

5. Project Research Tasks
Conduct literature review about topic including clinical, in vitro, in vivo, and computational research.
Create models using in vivo ateriovenus fistula data.
Through computational fluid dynamics, analyze blood flow in fistula with 4 varying angles of vein-artery attachment.
Recommend most effective fistula configuration.

6. Project Timeline Task Week 1 2 3 4 5 6 7 8 9 10 11 12 Complete Roadmap
Identify Goals and Objectives
Conduct Literature Survey
Lab Orientation
Create Models Using CFD
Prepare Final Deliverables:
Final Technical Paper
Final PowerPoint
Final Display Poster
NSF Summary Report
Final Report and Presentation

7. Final Deliverable Completion
Final Deliverables
Week 1 2 3 4 5 6 7 8 9 10 11 12
Technical Paper 0% 2%
PowerPoint 3%
10%
Display Poster
NSF Summary

8. Phase 1: Literature review

9. End Stage Renal Disease (ESRD) Patients

10. Vascular Access
PTFE (polytetrafluroethylene) Graft: Bridge between an artery and vein.
Arteriovenous Fistula (AVF): Surgical connection of the end of a vein to the side of an artery

11. Fistula versus graft survival in patients starting hemodialysis with a permanent vascular access comparing DOPPS results from Europe and United States.
Konner K et al. JASN 2003;14:
©2003 by American Society of Nephrology

12. Mature AVF Characteristics
Blood flow rate: ml/min (normal blood flow rate is 25 ml/min in radial artery at rest)
Diameter: at least 4 mm are needed for an AVF adequately support the dialysis (3-5hr) therapy3.
Time: These parameters should be met within 4 to 6 week or they will be deemed an early failure3. 

13. Vein remodeling
Arterial endothelial cells sense the sudden increase in flow try to maintain the baseline physiological level by dilating.
Mechanism:
Acute: Release of nitric oxide, the strongest endogenous arterio-dilating agent, by the endothelium cells28. The NO causes smooth muscle relaxation2.
Chronic: Fragmentation of the elastic lamina by matrix metalloproteinases which are activated by NO.

14. AVF failure (20 to 50%) fail to successfully support dialysis
veins or arteries do not dilate, possibly due to the severe vascular disease of the patient.
venous neointimal hyperplasia, thickening of the vessel wall, which leads to common juxta-anastomotic stenosis, is currently the single most important reason for an AVF to fail to mature3.

15. Configuration effects
Walls shear stresses are abnormal
Low areas
High areas
Oscillatory pattern
Endothelium layer confused

16. Data collection Studies performed by Dr. Banerjee and his group.
Flow – flow probes and flow wires
Pressure – intravascular ultrasound, CT angiography

17. Using models as predictors
Determined that porcine models are viable.
AVF configuration significantly affects the hemodynamics
Hemodynamics, in turn, affect the likelihood of fistula maturation
Initial WSS + following trend

18. Questions?