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

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 Test section LDA probe Radiator Heater Pump Ball valve 90% 10% Ball valve

4. Color Doppler Ultrasound Q MAX  2.5 l/min Q MEAN  1.5 l/min Q MIN  1 l/min 10%

5. Color Doppler Ultrasound Q MAX  2.5 l/min Q MEAN  1.5 l/min Q MIN  1 l/min 10%

6. AV Graft Image Taken by Color Duplex Ultrasound

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

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

9. Hemodynamics low and oscillating WSS Arterial Bypass Graft Failure 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 Conditions Re mean =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. Hemodynamics Turbulence & WSS Events Leading to AV Graft Failure 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. Fillinger et al., Hemodynamics and Intimal Hyperplasia, 1991 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

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

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 äTurbulence measurements in constricted tubes (Deshpande et al., 1980, Jones et al., 1985, Kehoe et al., 1990) äHigh 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 I Patient II Graft Diameter(mm)6 6.7 U max (m/s)1.5 1.2 U min (m/s)10.8 Re max 27002400 Re min 18001600 Q max (ml/min)25442525 Q min (ml/min)16961683 Womersley number(  )4.85.3 Re =  VD/ , Q = VA, A =  R 2  = R(2  f  /µ) 1/2 µ=3.5 mPa/s,  =1.05 g/cm 3

23. Methods

24. In Vitro Measurements Bifurcation plane and  plane Flow Division: DVS:Graft = 10:90 Steady Flow Re = 1060, 1820, 2530, 2720 u mean, v mean, u rms, v rms, u´v ´ Pulsatile Flow Re peak = 2470, Re mean = 1762 u ens, v ens, u rms, v rms, u´v´ as ƒ(t)

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

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

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

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. Separation Bubble ~0.1 D v PVS Toe <1.0 D v

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 (U rms, V rms, and RS) 3) Secondary Flow 4) Pulsatility 5) WSS

37. Turbulent Fluctuations (U rms ) Re = 1060

38. Turbulent Fluctuations (U rms ) Re = 1060 and 2530

39. U rms at the Perpendicular Plane Re=1060 and 2530

40. Turbulent Fluctuations (V rms ) Re = 1060 and 2530

41. V rms 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 U rms,V rms, 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. Re=1060 V component of the Velocity, Perpendicular to Bifurcation

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

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

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

50. Turbulence Intensity for Pulsatile Flow Re peak = 2470 x/D=+1.2 Toe sideFloor side

51. Reynolds Stress for Pulsatile Flow Re peak = 2470 x/D=+1.2 Toe sideFloor side

52. Animation

53. Results Under AV Flow Conditions 1) Separation small region near the toe creating a low WSS region 2) Turbulence high U rms,V rms, RS at these Re #s and localized near the toe 3) Secondary Flow strong and complicated 4) Pulsatility similar to steady flow results in general with slightly lower turbulence levels 5) WSS

54. WSS in the Present Study and Low Re# Study (Loth 1993)

55. Results Under AV Flow Conditions 1) Separation small region near the toe creating a low WSS region 2) Turbulence high U rms,V rms, RS at these Re #s and localized near the toe 3) Secondary Flow strong and complicated 4) Pulsatility similar to steady flow results in general with slightly lower turbulence levels 5) WSS generally high in graft and PVS

56. Discussion

57. Separation Regions Phase=300  Phase=60  Shu et al., 1987Present Study

58. Mean Velocity Profiles at Graft Inlet and Upstream of a Constricted Tube Deshpande(1980) Present study

59. Turbulent Measurements in a Straight Tube U rms /U c r/R

60. Conclusions  Reynolds stress can be high between 1000-2000 dynes/cm 2  Turbulent intensity can be high 10-20%  Both are focal in our model at the toe inside PVS  Secondary flow are significantly altered due to Re number (as I described before)  Pulsatility does not have a dramatic effect due to large steady component in our mode  Pulsatility reduces U rms by greater amount 30% U rms and 15% RS  Less turbulent under pulsatile flow  Low WSS present, however focal at the toe

61. FUTURE STUDIES  Clinical Studies  Different models (geometry, elastic, Q)  Vibration experiments (coherent structures)  WSS calculations  Cellular studies (mechanistic approach) Venaflo

62. Nomenclature-AV Loop Graft Arterial Anastomosis PTFE Graft (Polytetrafluoroethylene ) Venous Anastomosis PVS (Proximal vein Segment) DVS (Distal vein Segment)

63. +v’ U(y) +v ´ -v ´ y x Reynolds Stress(  u´v´) BL Theory, Schlichting, 7th Ed., page 560 Fluid particles with v´ > 0 arrive at a layer from a region where a smaller u prevails which gives rise to a u´ > 0 Hence  u´v´ < 0

64. Main frame Slygard model Shaker Schematic for the Vibration Experiments (Top view) Function generator Power amplifier

65. Velocity Power Spectra 1.2 D from toe, 0.16 D from wall

66. Mean Velocities at the Plane Perpendicular to Midplane (0.8D from hood and 0.5D from floor Re = 1060)

67. Turbulent fluctuation (V rms ) Re = 1060

68. Reynolds Stress(  ) Re = 1060