Motivation: Challenges: Project GYRO LVAD: Project DeBakey

Modeling and Simulation of Blood Flow and Hemolysis in LVADs
Motivation:
Mathematical Modeling and Numerical Solution:
• heart disease as most frequent death cause for adults worldwide
• 50,000 persons could benefit from heart transplant (US)
• flow in the blood pump governed by incompressible Navier-Stokes
equations of mass and momentum conservation
• donor hearts available for only 2,500 patients each year (US)
• blood modeled as Newtonian fluid
• artificial hearts in use since 40 years
• in-house finite element solver XNS
• total (TAH) or partial (LVAD) replacement of heart function
• use of mesh-update techniques
• stabilized space-time Galerkin/Least-Squares (GLS) formulation
Simulation of the Flow Field:
• each revolution of the impeller divided in 200 time steps
• velocity and pressure data storage up to 30 GB for a revolution
• good correlation with experimental data, especially at low rpm
cardiovascular system: left
ventricle and aorta (red)
and right ventricle and
pulmonary artery (blue)
non-implantable blood
pump
implantable pulsatile
TAH by Abiomed
implantable pulsatile LVAD
by DLR
implantable rotary
LVAD by MicroMed
mm Hg
120
24.00
100
mm Hg
80
7.00
Challenges:
60
40
• required flow performance: 5 liters per minute
20
-10.00
0
0
• pump size should be as compact as possible
7500 exp
8500 exp
9500 exp
7500 cfd
9500 cfd
1
2
3
4
5
6
7
8
l per min
• risk: damage of blood cells due to high shear in mechanical pumps
• risk: thrombosis due to recirculation areas in the flow field
• LVAD pumps oxygen-rich blood from left ventricle into aorta
computed velocity vectors and pressure
distribution shown for a section of the
impeller of DeBakey LVAD
hydraulic performance: experimentally
obtained curves for different rotational
speeds and numerical results (red points)
Quantitative Blood Damage Prediction:
• red blood cell undergoes deformation under shear
Project GYRO LVAD:
• centrifugal blood pump, diameter ~6 cm, 2000–3000 rpm
• development at Baylor College of Medicine in Houston, Texas
• sublethal hemolysis: hemoglobin release through pores of
stretched red blood cell membrane
• at constant shear hemolysis is a function of time and shear
• numerical analysis of the flow field and cumulative damage in
0.25
terms of hemolysis at CATS
0.2
ellipsoidal
- oriented
- tank-treading
hemolyzing
- pores
- tank-treading
0.15
z
bi-concave
- monodispersed
- tumbling
same area
rouleaux
∆Hb/Hb
0.1
0.05
0
1
0.8
0.6
0.4
spherical droplet
ellipsoidal
- oriented
- tank-treading
0.2
highly-streched ellipsoidal
y
∆t (s)
0
0
50
100
x
150
200
250
σ (Pa)
shear rate
behavior of red blood cells undergoing
shear in analogy to the deformation of
a deforming droplet
red blood cells
grid with 1 million finite
elemens
pressure distribution
and pathlines
high shear regions
hemoglobin release as a function
of stress and time according to
Giersiepen equation
• morphology tensor represents red blood cell shape
• deformation tracked and hemolysis integrated along pathlines
• conversion to clinical measure (NIH) possible
Project DeBakey LVAD:
• axial blood pump, diameter ~1 cm, 7500–11500 rpm
strain-based
stress-based
• development at MicroMed Cardiovascular in Houston, Texas
• numerical analysis of the flow field at CATS
steady-shear experiments
• typical mesh composed of 5 million elements
shear stress
hemolysis
• 6 million unknowns per time step
strain-based versus stress-based
modeling approach
blood damage along pathlines
interactive exploration of the blood pump
at the Virtual Reality Center, Aachen
Contact:
original design of the DeBakey LVAD
grid with 5 million finite elements
pressure distribution at 10,000
rpm
Dipl.-Ing. Mehdi Behbahani (e-mail: [email protected])
Chair for Computational Analysis of Technical Systems (CATS)
RWTH Aachen University, Steinbachstr. 53B, D-52074 Aachen
http://www.cats.rwth-aachen.de