simulations of hypertrophic obstructive cardiomyopathy (hocm) in a human heart left ventricle using...
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1 © 2014 ANSYS, Inc. ANSYS Users Regional Conference, Santa Clara 2014
Simulations of Hypertrophic Obstructive Cardiomyopathy (HOCM) in a Human Heart Left Ventricle using ANSYS/CFX/Fluent
Vladimir Kudriavtsev (Intevac), Metin Ozen, Can Ozcan (Ozen Engineering)
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Considerable Interest Lately: LV, HOCM, Heart Fluid Structure Interactions
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Human Heart Model
Model courtesy of Dr. Jingwen Hu, PhDUniversity of Michigan Transportation Research Institute
Real Geometry of LV
mm
MITRALAORTIC
LV-left ventricle
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Schematic diagram of a patient with a normal heart (left) and
a patient with hypertrophic cardiomyopathy (right).
Nishimura R A et al. Circulation. 2003;108:e133-e135
Copyright © American Heart Association, Inc. All rights reserved.
Wall thickening
Septal subaortic
bulge, Flow
obstruction
Mechanism of dynamic outflow tractobstruction. The upper schematic shows arepresentation of the mitral leaflets. Theelongated mitral leaflets that are drawn into theLeft Ventricular Outflow Tract during earlysystole with midsystolic prolonged systolicanterior motion- septal contact, malcoaptationof the mitral leaflets, and the resultantposteriorly directed jet of mitral regurgitation.
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Simulated 3D LV Geometry –fully parametric
in Design Modeler
Imposed wall motion
Parametric Geometry Definition
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http://www.echopedia.org/wiki/Normal_Values_of_TTE#Left_Ventricle
Typical Heart Left Ventricle LV Dimensions
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CFX Model Definition
Wall Motion is Prescribed as sin time dependent in
Radial and Axial
Inlet pressure is prescribed as sin or cos time dependent
wave, which is always positive
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Oscillating CFX-ANSYS 2-way FSITutorial CFX, P=600Pa
We increase boundary pressure up to 600Pa. Tutorial Fails, negative mesh volume P>680Pa
Fails, when “angle” <90 deg
“angle”
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Valve Hyper-elastic Transient Simulations
Valve Initial Position
Moonley-Rivlin Model;Pressure extrapolation from Transient Simulation. Requires multiple and small time steps
Valve fully open
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First CFX-ANSYS 2Way FSI Results: Flow Valve Interactions
Coupled flow simulation fails due to negative mesh when valve deformation significant
Hyper-elastic valve model (stand alone) with external pressure allows significant deformation, when not coupled with CFX
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No Valves, blocking flow effect of valves is simulated using transient (sin or cos) pressure pulse at Mitral Inlet and CFX Outflow Boundary condition (does not allow backflow) for Aortic Valve
Moving Wall to simulate displacement and ejection effect during systole and volume filling effect during diastole
Stroke Volume, displacement volume and pressure magnitude , heart rate are matched
Example of Systolic-Diastolic Transient Flow in Left Ventricle (CFX)
Example of Steady State Simulation,Clearly grossly inadequate for the mechanics
involved
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Mass Flow – Mitral and Aortic
Re=5281
Aortic Outflow
Positive—Mitral inflow
Negative-Aortic outflow
Mitral inflow
Zero—Mitral inflow during systolic contraction
Close to zero during diastolic expansion.
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Diastolic Phase
CFX14CFX4
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CFX22
Beginning of Systolic Contraction
CFX18
End of Diastolic
Wall motion
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Systolic –flow squeeze action
CFX23 CFX29
Wall motion
Recirculations are getting suppressed
No mitral outflow
No mitral outflow
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End of Systolic Phase
CFX34CFX31
No recirculations are left due to flow squeeze action
No mitral outflowAortic outflow Aortic outflow
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Transient 2-way FSI Valve Motion Simulation with Remeshing (FLUENT, 2D)
Small Septum HumpLarger Septum Hump, valve is entrained closer to septum wall
NO WALL MOTIONNo Aortic Valve/No aortic outflow blockage
diastolic
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Transient 2-way FSI Valve Motion Obstruction Mechanism
Septum Hump
Systolic wall motion direction
Systolic wall motion direction
From this moment and on as LV wall and septum move towards each other during systole (creating ejection into aortic valve) MITRAL leaflet that is already deflected and obstructing diastolic flow with Venturieffect of lower pressure behind it only gets pushed further by mechanical forces and fluid forces to do more obstruction as lower pressure zone behind it fails to create enough lateral push
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Transient 2-way FSI Valve Motion Obstruction Mechanism
Systolic wall motion direction
Systolic wall motion direction
Venturi effect of lower pressure behind it only gets pushed further by mechanical forces and fluid forces to do more obstruction as lower pressure zone behind it fails to create enough lateral push
Systolic wall motion direction
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Moving Wall and Systolic EngagementValve: E= 2.5MPa, v=0.33Inlet and wall conditions are copy/paste from your simulation setup.Inlet condition: 2000 Pa * abs(sin(t*3.85))Wall Movement: 0.005*abs(sin(t*3.85)) or 0.015*abs(sin(t*3.85))
End of diastolic flow obstruction (valve laterally deflected)
Recirculation formed
Recirculation pushed toward hump and aorta
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Systolic Obstruction and Lateral Entrainment of Mitral Leaflet Systolic flow obstruction
Recirculation blocks aortic outflow,Creates low pressure zone
Entrains valve laterally intoObstructive position as wall is moving inward
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Transient 2-way FSI Valve Motion Obstruction Mechanism -2
Towards the end of systole, instead of being pushed away into normal position, leaflet is entrained laterally right into the aortic exit path – thus blocking outflow and this positioning is stable. No forces at play to return it back to normal.
Systolic wall motion direction
Septum Hump
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Obstruction Mechanism -3 (Large Hump & Long Valve Leaflet)
Towards the end of diastolic periodMitral valve leaflet deflected
Septum Hump
End Diastolic,Valve Leaflet Flip Flapped
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Obstruction Mechanism -4 (Large Hump & Long Valve Leaflet)
xxxxxx
Septum Hump
Flow Through Mitral Valve Stopped.Complete Flow Obstruction – Full contact of hump and mitral valve.Computation failed, flow stopped!!!!
Heart Stopped as Well!Early Systolic
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Echocardiographic results - HOCM
Flapping and flow obstructionduring ejection (systole)
Hump Touchdown duringexpansion (diastole)
Both valves closed
End of diastole and Aortic valve closed
Aortic opened, mitral closed
Mitral opened, aortic closed
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Left Ventricular Outflow
Diastolic
Aortic
Mitral
Septum Hump(bulge)
Systolic
Large Outflow Small Outflow
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Summary of Work -1
-Studied LV geometries and more detailed models, developed simplified parametric transient 3D model with moving wallsusing CFX;-Studied “2 way FSI” Capabilities of ANSYS/CFX for moving elastic valve of fixed thickness [oscillating.* Tutorial]. Found limitations of method when large deformation are involved due to negative grid and deficiencies of grid interpolation in CFX;-Studied separate valve motion transient analysis with hyper-elastic valve material model and extrapolated pressure loads from transient CFX flow model. Demonstrated capability to simulate transient valve motion in the solid ANSYS module;
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Summary of Work -2
-Coupled valve motion with transient flow in moving ANSYS/CFX, failed interpolated meshes due to inability to re-mesh;-Used Fluent/ANSYS 2-way FSI with re-meshing to study deforming valve problem in 2D;-demonstrated interaction of 2D moving valve with moving mesh for simulations with hump and without hump on wall septum.-demonstrated mechanism of mitral valve flow obstruction for HOCM.
Next steps: conduct similar analysis in 3D or find way to solve in ANSYS /CFX environment (try shell models with no thickness for valve to ease mesh interpolation)
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Left Ventricular Outflow
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