THE QUANTIFICATION OF TURBULENCE INSIDE AN ARTERIOVENOUS GRAFT UNDER STEADY AND PULSATILE FLOW CONDI

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THE QUANTIFICATION OF TURBULENCE INSIDE AN
ARTERIO-VENOUS GRAFT UNDER STEADY AND PULSATILE
FLOW CONDITIONS
Biofluids Cell Mechanics Laboratory
Nurullah Arslan Industrial Engineering Graduate
Institute of Sciences and Engineering
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Arteriovenous Grafts Hemodialysis Patients
PTFE graft
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Distribution of Stenosis Kanterman et al., (1995)
67Patients
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FINANCIAL REPORT END STAGE RENAL DISEASE
(ESRD) HEALTH SUBCOMMITTE HEARING (APRIL 3, 1995
Washington, DC.)
IN 1995, MEDICARE IS EXPECTED TO SPEND NEARLY 8
BILLION, OR OVER 4 OF ALL TOTAL SPENDING ON
OVER 200,000 ESRD PATIENTS. THAT IS ABOUT
40,000 PER BENEFICIARY
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MOTIVATIONImprove Patency rate

• Repeated reconstruction of the AV graft is
  expensive and uncomfortable for the patient

• A better understanding of the fluid dynamic
  environment may help understand the causes of
  graft failure

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NOMENCLATURE
PVS
Arterial Anastomosis
Venous Anastomosis
DVS
PTFE Graft

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PICTURE OF A REAL CONNECTION FROM A SURGERY
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LITERATURE REVIEW
COLOR DOPPLER ULTRASOUND MEASUREMENTS Fillinger
et al. (1991)

• replace or revise the vascular access every three
  years in over half of their of patients
• indicated turbulence (tissue vibration) and
  Reynolds number to be well correlated with
  intimal-thickening at the venous anastomosis

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LASER DOPPLER ANEMOMETER MEASUREMENTS AND FLOW
VISUALIZATION STUDIES (SHU ET AL. 1991)

• A realistic model geometry of A-V graft
• Velocity profiles
• Implicate the stagnation point and separation
  region
• Poor wall shear stress measurements
• No turbulent measurements

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TURBULENCE STUDIES

• Turbulent measurements in straight pipes(Laufer
  et al. 1954)
• The effects of turbulence on blood flow in
  constricted tubes(Deshpande et al., 1980, Jones
  et al., 1985, Kehoe et al., 1990)
• Red blood cell damage caused by high Reynolds
  stresses

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OBJECTIVE

• To determine the distribution of turbulence and
  Reynolds stresses
• To define the critical regions such as separation
  region, stagnation point, and high turbulent
  region

within the venous anastomosis of an A-V graft
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METHODS

• Laser Doppler anemometry measurements inside an
  in vitro upscaled model of the venous anastomosis
  
• Steady flow experiments representative of mean
  flow conditions (Reynolds number)
• Newtonian fluid, rigid model

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COLOR DOPPLER ULTRASOUND MEASUREMENTS TAKEN FROM
AN A-V GRAFT INSIDE A HUMAN PATIENT
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Graft
DVS
PVS
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IN VIVO MEASUREMENTS Doppler Ultrasound
PVS
PTFE graft
0.50
0.67
Diameter (cm)
Mean Velocity (cm/s)
110
94
Peak Velocity (cm/s)
390
170
Mean Flowrate (ml/sec)
33 (2 l/min)
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Peak Flowrate (ml/sec)
76
59 (3.5 l/min)
Flowrate were computed assuming flat velocity
profile
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IN VIVO MEASUREMENTS
PVS
PTFE graft
Re (mean)
1900
1700
Re (peak)
3400
5800
4.0
Womersley
5.3
Mean WSS (dynes/cm2)
39
63
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EQUATIONS
Reynolds number Womersley number Wall shear
stress
QAV
Flow Rate
Properties of blood
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EXPERIMENTAL SETUP
Argon-Ion laser 750mW
Downstream tank
Upstream Tank
LDA probe
Radiator
Heater
Test section
Fluid 42 Water 58 Glycerin
Pump
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LASER DOPPLER ANEMOMETER OPTIMUM PARAMETER
SELECTION FOR TURBULENT MEASUREMENTS
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The measurement locations in the bifurcation
plane and the plane which is perpendicular to
bifurcation plane (x sign shows the measurement
points in the vertical direction)
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RESULTS EXERCISE CONDITION FOR
GRAFT(PVSDVS1000)
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VECTOR PLOTS FOR Re650 and 1000
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VECTOR PLOTS FOR Re2000 and 2300
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URMS VALUES FOR Re650 and 1000
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URMS VALUES FOR Re2000 and 2300
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VRMS VALUES FOR Re650 and 1000
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VRMS VALUES FOR Re2000 and 2300
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Reynolds stress(uv) VALUES FOR Re650 and 1000
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Reynolds stress(uv) VALUES FOR Re2000 and
2300
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RESULTSHEMODIALYSIS CONDITION(PVSDVS9010)
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VECTOR PLOTS FOR Re1000 and 1500
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VECTOR PLOTS FOR Re2000 and 2300
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URMS VALUES FOR Re1000 and 1500
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URMS VALUES FOR Re2000 and 2300
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Reynolds stress(uv) VALUES FOR Re1000 and 1500
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Reynolds stress(uv) VALUES FOR Re2000 and
2300
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NEAR WALL VELOCITY MEASUREMENTS FOR
Re2300 (Separation region)
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CONCLUSIONS

• Toe side of the PVS
• high turbulence (29) , high Reynolds stresses
  (1263 dyne/cm2), strong secondary flow, and a
  large separation region
• is often sited as the location of stenosis
  formation in A-V grafts

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FUTURE WORK

• use a more physiological geometry
• repeat measurements under pulsatile flow
  conditions
• track the condition of patients graft

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Midplane Velocity Vectors at Re650
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Midplane Velocity Vectors at Re1000
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Turbulence Intensity RMS of Axial Velocity
Component at Re650
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In Vivo flow wave form at Graft and DVS
(GraftDVS9010)
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Turbulent Fluctuation at P12 for Pulsatile
flow Re2000 for steady flow and Remax2021 for
pulsatile flow
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Power spectrum analysis at high turbulent region
(p12) for pulsatile flow