simulations of hypertrophic obstructive cardiomyopathy (hocm) in a human heart left ventricle using...

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)


Considerable Interest Lately: LV, HOCM, Heart Fluid Structure Interactions


Human Heart Model

Model courtesy of Dr. Jingwen Hu, PhDUniversity of Michigan Transportation Research Institute

Real Geometry of LV

mm

MITRALAORTIC

LV-left ventricle


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 thickeningSeptal subaortic bulge, Flow obstruction

Mechanism of dynamic outflow tract obstruction. The upper schematic shows a representation of the mitral leaflets. The elongated mitral leaflets that are drawn into the Left Ventricular Outflow Tract during early systole with midsystolic prolonged systolic anterior motion- septal contact, malcoaptation of the mitral leaflets, and the resultant posteriorly directed jet of mitral regurgitation.


Simulated 3D LV Geometry – fully parametric

in Design Modeler

Imposed wall motion

Parametric Geometry Definition


http://www.echopedia.org/wiki/Normal_Values_of_TTE#Left_Ventricle

Typical Heart Left Ventricle LV Dimensions


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


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”


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


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


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


Mass Flow – Mitral and AorticRe=5281

Aortic Outflow

Positive—Mitral inflow

Negative-Aortic outflow

Mitral inflow

Zero—Mitral inflow during systolic contraction

Close to zero during diastolic expansion.


Diastolic Phase

CFX14CFX4


CFX22

Beginning of Systolic Contraction

CFX18

End of Diastolic

Wall motion


Systolic –flow squeeze action

CFX23 CFX29

Wall motion

Recirculations are getting suppressed

No mitral outflow

No mitral outflow


End of Systolic Phase

CFX34CFX31

No recirculations are left due to flow squeeze action

No mitral outflowAortic outflow Aortic outflow


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


Transient 2-way FSI Valve Motion Obstruction Mechanism

Septum Hump

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 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


Transient 2-way FSI Valve Motion Obstruction Mechanism



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



Moving Wall and Systolic EngagementValve: E= 2.5MPa, v=0.33 Inlet 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


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


Transient 2-way FSI Valve Motion Obstruction Mechanism -2

Towards the end of systole, insteadof 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.


Septum Hump


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


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;


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)

simulations of hypertrophic obstructive cardiomyopathy (hocm) in a human heart left ventricle using...

Healthcare

santa clara

oscillating cfxansys

mass flow mitral

way fsi valve motionsimulation

flow effect of valves

cfx outflow boundarycondition

left ventricle cfxmoving

way fsitutorial cfx