19%

1. artery vein 19% 4% 11% 49% PTFE

2. Experimental Characterization of Transitional Unsteady Flow Inside a Graft-to-Vein Junction Nurullah Arslan Mechanical Engineering Department The University of Illinois at Chicago

3. Argon-Ion laser 750mW Downstream tank Upstream Tank LDA probe Radiator Heater 10% 90% Test section Ball valve Pump Ball valve

4. Color Doppler Ultrasound QMAX  2.5 l/min QMEAN  1.5 l/min QMIN 1 l/min 10%

5. Color Doppler Ultrasound QMAX  2.5 l/min QMEAN  1.5 l/min QMIN 1 l/min 10%

6. AV Graft Image Taken by Color Duplex Ultrasound

7. Arterio-Venous (A-V) Grafts Hemodialysis Patients Schmidt et al., Vascular Access for Hemodialysis, 1985

8. PTFE Graft just after Implantation(Reference: Access Surgery, 1982)

9. Arterial Bypass Graft Failure Hemodynamics low and oscillating WSS Tissue growth Thickening of the vessel wall Intimal Hyperplasia Stenosis (narrowing of the vessel) Failure Blockage stops blood flow Thrombosis (blood clot)

10. Arterial PTFE Graft Model(Loth et al.) Similar Geometry but different flow conditions Re=222

11. IH Distribution for Arterial Grafts

12. LDA Results for Arterial Graft

13. Results Under Arterial Flow ConditionsRemean=222(Loth et al.) Summary: 1) No Turbulence 2) No separation was observed 3) Flow was complex with strong secondary flow patterns 4) Pulsatility affected the flow field greatly (velocity profiles were more blunt) 5) WSS values were generally low in the anastomosis

14. Events Leading to AV Graft Failure Hemodynamics Turbulence & WSS Energy Transfer to the wall Tissue Vibration Enthothelial Cell Damage Tissue growth Thickening of the vessel wall Intimal Hyperplasia Stenosis (narrowing of the vessel) Increased turbulence Platelet activation Failure Blockage stops blood flow Thrombosis (blood clot)

15. Graft to Vein Junction

16. Canine AV Graft Study (A) 3-D schematic representation of perianastomotic tissue vibration. (B) Schematic representations of longitudinal (C) Transverse views of perianastomotic tissue vibration Fillinger et al., Hemodynamics and Intimal Hyperplasia, 1991

17. Stenosis Location inside the A-V graft Thickness (mm) Re10-3

18. Fillinger Concluded 1) Tissue vibration 2) Reynolds Number intimal hyperplasia at the venous anastomosis

19. Other AV Graft Model Studies(No turbulent measurements) • Velocity measurements and WSS estimation (Shu et al.) • Velocity patterns by flow visualization (Krueger et al. ) • Flow patterns using flow visualization (Bakran et al.)

20. Turbulence Studies • Turbulence measurements in constricted tubes (Deshpande et al., 1980, Jones et al., 1985, Kehoe et al., 1990) • High Reynolds stresses may cause red blood cell damage and platelet activation (Sutera, S.P. and Mehrjardi, M.H., 1975) Stenosis

21. Objective To determine the distribution of turbulence and Reynolds stresses within the an AV graft using in vitro modeling techniques

22. Summary of In Vivo Measurements Patient II Patient I Graft Diameter(mm) 6 6.7 Umax(m/s) 1.5 1.2 Umin(m/s) 1 0.8 Remax 27002400 Remin 18001600 Qmax(ml/min)2544 2525 Qmin(ml/min)1696 1683 Womersley number() 4.8 5.3 Re = VD/, Q = VA, A = R2  = R(2 f/µ)1/2 µ=3.5 mPa/s, =1.05 g/cm3

23. Methods

24. In Vitro MeasurementsBifurcation plane and  planeFlow Division: DVS:Graft = 10:90 Steady Flow Re = 1060, 1820, 2530, 2720 umean, vmean, urms, vrms, u´v ´ Pulsatile Flow Repeak= 2470, Remean= 1762 uens, vens, urms, vrms, u´v´ as ƒ(t)

25. Measurement Locations in A-V Graft x indicates measurements lines perpendicular to the plane of bifurcation

26. Velocity Profiles at Graft Inlet and DVS Re=1060 GRAFT inlet DVS

27. Velocity Profiles at Graft Inlet and DVS Re=2530 DVS GRAFT inlet

28. In Vitro Flow Wave Form at Graft inlet and DVS (Graft:DVS = 85:15)

29. Velocity Profiles at Systolic Acceleration and Peak

30. Velocity Profiles at Systolic Deceleration and Diastole

31. Results Under AV Flow Conditions 1) Separation 2) Turbulence 3) Secondary Flow 4) Pulsatility 5) WSS

32. Midplane Velocity Vectors Re = 1060

33. Midplane Velocity Vectors Re = 1060 and 2530

34. ~0.1 Dv Toe <1.0 Dv PVS Separation Bubble

35. Mean Velocity in the Plane  to the Bifurcation Plane Re=1060 and 2530

36. Results Under AV Flow Conditions 1) Separation small region near the toe creating a low WSS region 2) Turbulence (Urms, Vrms, and RS) 3) Secondary Flow 4) Pulsatility 5) WSS

37. Turbulent Fluctuations (Urms)Re = 1060

38. Turbulent Fluctuations (Urms)Re = 1060 and 2530

39. Urms at the Perpendicular Plane Re=1060 and 2530

40. Turbulent Fluctuations (Vrms)Re = 1060 and 2530

41. Vrms at the Perpendicular Plane Re=1060 and 2530

42. Reynolds Stress( )Re = 1060 and 2530

43. Reynolds Stress( )at the Perpendicular Plane Re = 1060 and 2530

44. Results Under AV Flow Conditions 1) Separation small region near the toe creating a low WSS region 2) Turbulence high Urms,Vrms, RS at these Re #s and localized near the toe 3) Secondary Flow 4) Pulsatility 5) WSS

45. Secondary Flow Field Inside AV Graft

46. V component of the Velocity, Perpendicular to Bifurcation Re=1060

47. Results Under AV Flow Conditions 1) Separation small region near the toe creating a low WSS region 2) Turbulence high Urms,Vrms, RS at these Re #s and localized near the toe 3) Secondary Flow strong and complicated 4) Pulsatility 5) WSS

48. Velocity Profiles at Systolic Peak and Diastole Systolic Peak Diastole

49. Turbulent Fluctuations (Urms)Phase Angles 60 and 300

50. Turbulence Intensity for Pulsatile Flow Repeak = 2470 x/D=+1.2 Toe side Floor side