CFD final Project Modeling the Access Point on the Brachial Artery

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CFD final Project Modeling the Access Point on the Brachial Artery. Novemer 16, 2010 Nicole Varble. Problem Definition- Overview. Problem- Patients on hemodialysis need an access point Native vessels become overstressed - PowerPoint PPT Presentation


CFD Project Proposal Modeling the Access Point on the Brachial Artery

CFD final Project Modeling the Access Point on the Brachial ArteryNovemer 16, 2010Nicole VarbleProblem Definition- OverviewProblem- Patients on hemodialysis need an access pointNative vessels become overstressedSolution- Create an access vessel between an artery and vein in the armHigh flowLow PressureCan be punctured repeatedlyResulting Problem- Adequate flow does not reach the hand Blood flow is redirected through access vesselHand is deprived of nutrientsArteryFigure 1: Native CirculationVeinHand Artery VeinHandFigure 2: Native Circulation w/ AVFAVFArea of InterestProblem Definition- Overview Brachial ArteryProximal Distal VeinHandAVF Hand Hand1. Proximal Brachial Artery2. Distal Brachial Artery4. Antegrade Flow- Forward5. Retrograde Flow- BackwardsFigure 3Figure 4Figure 5Project Definition- OverviewGoal: Gain insight to the flow patterns at the intersection of native artery and access vesselInterests comes from my thesis workModel of the entire arms vasculatureNative circulation (NC), NC with access, NC with access and DRIL (a corrective procedure)For this project only interested in what happens at the intersection pointLittle research on the topic

Area of InterestD.J. Minion, E. Moore, E. Endean, and K. (Lexington, "Revision Using Distal Inflow: A Novel Approach to Dialysis- associated Steal Syndrome," Annals of Vascular Surgery, vol. 19, 2005, pp. 625- 628.Figure 6: Brachialcephalic ateriovenous fistulaBrachial ArteryAccess VesselProject Definition- AimsAim 1: Create the geometry based on the average blood vessel diameter, length and boundary conditions. Analyze the entrance to the access vessel and the magnitude and direction of flow to the hand.

Aim 2: Change the boundary conditions to that of a hypertensive patient (elevated blood pressure). Determine flow conditions at the access changed. Aim 3: If backwards flow does not occur in Aim 1, determine the boundary conditions at the outlet for which backwards flow occurs. If backwards flow does occur, determine a threshold at which this does occur and quantify in terms of differential pressure between the two outlets.

Project Definition- AssumptionsAssumptions: Non- puslitile flow Blood vessels are idealized a perfect cylinders with sections of constant diameterDiameters are based on the average size of blood vessels complied from current literatureInlet and outlet pressures and flows are based on average pressures and flows in the vessels and bloodThe working fluid, is considered a non-Newtonian fluid with an average density and dynamic viscosity.

Figure 7: 2D schematic of brachial artery and access vessel

Project Definition- Boundary ConditionsNameParameterValueUnitsConditionCitationBrachial DiameterDb4.4mm1,2[1]0.0044mAccess DiameterDa5.5mm1,2[2]0.0055mBrachial Length InL113cm1,2[3]0.13mBrachial Length OutL213cm1,2[3]0.13mAccess LengthL310cm1,2[4]0.1mInlet VelocityVo570mL/min1,2[5]9.50E-06m3/sBrachial Pressure OutP167mmHg1[5]8,930PaBrachial Pressure OutP187mmHg211,600PaAccess Pressure OutP247mmHg1[5]6,270PaAccess Pressure OutP267mmHg28,930PaTable 1: Geometry and Boundary ConditionsProject Definition- Geometry and Boundary ConditionsOne velocity inlet (constant)Proximal brachial artery Two pressure outletsDistal brachial arteryAccess vessel

Pressure DifferencedP = P1- P2Velocity inlet fixedOnly P2 changed

Figure 8: 3D geometry created in Gambit

Figure 9: Specified Boundary Condition, one inlet velocity and two outlet pressuresMeshEdge meshedSuccessive ratio = 1.016Interval count = 10Faces meshedQuad/paveInterval count = 10Volume meshedDefault Tet/hybridInterval size = 1

Figures 9 and 10: Close up image on bifurcation and mesh geometry, the originally meshed (yellow) and originally meshed faces (green) labeled

Mesh- Grid Independent SolutionPercentage of Total Inflow in Distal Brachial ArteryNumber of ElementMesh 2Mesh 3Mesh 4Ideal MeshFigure 11: Analysis of grid independent solution. Knee of the curve (ideal mesh) is identified.Numerical ProceduresConvergence Set to 1e-6, converged in every casePressure- Velocity CouplingSchemeSIMPLESIMPLECPISOCoupledGradientGreen- Gause Cell BasedGreen- Gause Node BasedLeast Squares Cell BasedPressureStandardPRESTO!LinearSecond OrderBody Force WeightedMomentumFirst Order UpwindSecond Order UpwindPower LawQUICKThird Order MUSCLTable 2: Numerical Procedures (choices highlighted in orange)ResultsAnalyzedAim 1 and 2 Nature of flow in normal and hypertensive casesAim 1, 2 and 3Point of maximum flowPressure throughout control volume to identify the low pressure vesselDirection and Magnitude of flow in the distal brachial artery

OutcomeIdentify what at what pressure difference retrograde (backwards) flow occurs

Results- Normal and Hypertensive CasePossible turbulent regions found at bifurcationFlow reversal immediately presentWhen changed to the hypertensive case, only a slight increase in in velocity magnitude, no other change (pressure difference??)

Turbulent RegionFlow ReversalTurbulent RegionFigure 12: Velocity vector plot at normal flow conditions. Note flow reversal in the distal portion of the brachial artery and turbulent regions at the bifurcationConditiondP [mmHg]% of Flow in Distal BrachRetrograde?Location of VmaxAimNormal20-33.30%yesinlet of access1Hypertensive20-33.49%yesinlet of access2Results- Velocity Magnitude

Figures 13 and 14: Velocity Magnitude contour plot. Iso-surface was created along constant z-axis. Maximum velocity occurring just beyond bifurcation in the access vessel and in the proximal brachial artery for dP = to 20 and 5 mmHg respectivelyResults- Static PressureContour plot of static pressure on a constant z- surface. Low pressure vessels are where flow will preferentially travel

Figures 15, 16 and 17: Contour plot of static pressure on a constant z- surface. The low pressure vessels where flow will preferentially flow are label. Results- Direction of FlowFigures 18- 21: Velocity vector plots on a constant z- surface. Flow reversal occurs at dP of 20 mmHg and 8 mmHg and forward flow occurs at 5 mmHg and 0 mmHg.

dP = 20 mmHg

dP = 8 mmHg

dP = 5 mmHg

dP = 0 mmHgRetrograde FlowRetrograde FlowAntegrade FlowAntegrade FlowResults- Prediction of FlowRetrograde

Antegrade Figure 22: Relationship between differential pressure between distal brachial artery and access vessel and percent of total inflow in distal brachial arteryResults- SummaryConditiondP [mmHg]% of Flow in Distal BrachRetrograde?Location of VmaxAimNormal20-33.30%yesinlet of access1Hypertensive20-33.49%yesinlet of access210-2.20%yesinlet of access392.29%noinlet of access386.38%noinlet of access3710.13%noinlet of access3516.98%noprox brach3031.74%noprox brach3

Figure 23: 2D schematic of modeled blood vessel geometry and boundary conditions Table 3: Summary of Results ConclusionsMaximum velocity occurs just beyond bifurcation or in proximal brachial arteryAll cases, access vessel acts as a low pressure vessel (flow preferentially travels through it)When differential pressure between outlets is limited to 10 mmHg flow is antegrade

CFD model predicts when retrograde flow in distal brachial artery will occur based on differential pressureExperimental verification neededPotentially physicians can use this relationship or something similar to eliminate need for corrective procedures (DRIL)Questions?References[1] A. Peretz, D.F. Leotta, J.H. Sullivan, C.a. Trenga, F.N. Sands, M.R. Aulet, M. Paun, E.a. Gill, and J.D. Kaufman, "Flow mediated dilation of the brachial artery: an investigation of methods requiring further standardization.," BMC cardiovascular disorders, vol. 7, 2007, p. 11.

[2] J. Zanow, U. Krueger, P. Reddemann, and H. Scholz, "Experimental study of hemodynamics in procedures to treat access-related ischemia," Journal of Vascular Surgery, 2008, pp. 1559-1565.

[3] V. Patnaik, G. Kalsey, and S. Rajan, "Branching Pattern of Brachial Artery-A Morphological Study," J. Anat. Soc. India, vol. 51, 2002, pp. 176-186.

[4] W.S. Gradman, C. Pozrikidis, L. Angeles, and S. Diego, "Analysis of Options for Mitigating Hemodialysis Access-Related Ischemic Steal Phenomena," Annals of Vascular Surgery, vol. 18, 2004, pp. 59-65.

[5] K.A. Illig, S. Surowiec, C.K. Shortell, M.G. Davies, J.M. Rhodes, R.M. Green, and N. York, "Hemodynamics of Distal Revascularization- Interval Ligation," Annals of Vascular Surgery, vol. 19, 2005, pp. 199-207.[6] C.L. Wixon, J.D. Hughes, and J.L. Mills, "Understanding Strategies for the Treatment of Ischemic Steal Syndrome after Hemodialysis Access," Elsevier Science, 2000, pp. 301-310.


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