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A fluid-structure approach to optimize the thrombogenic potential of artificial heart valves

Authors:

Abstract

Boundary conditions The Inlet and Outlet reservoirs were characterized by physiological pressure waveforms extracted from experimental testing, thus obtaining comparable working conditions between the computational model and the ViVitro benchmark. Figure 2 – Schematic visualization of the ideal optimization process implemented with the FSI numerical approach FSI Exp. [2] v max 3.37 3.42 ms -1 Effective Orifice Area 1.54 1.47 cm 2 trans-valvular ∆íµí±ƒ 18.60 20.91 mmHg Ejection time 320 304 ms Figure 3 – Visualization of the velocity field contours on a cross-sectional plane (upper panels) and of the FSI and experimental kinematic of the device (lower panels), at four different time-points: (A) early systole, (B) systolic peak, (C) closing phase, (D) stable diastole. Acknowledgments The research leading to these results has received fundings from the Cariplo Foundation Project, Grant Agreement N° 2011-2241.
A fluid-structure approach to optimize
the thrombogenic potential of
artificial heart valves
Filippo Piatti1, Francesco Sturla1,2,
Thomas E. Claiborne3, Danny Bluestein3, Alberto Redaelli1
1Dept. of Electronics, Information and Bioengineering, Politecnico di Milano, Milan, Italy
2Division of Cardiac Surgery, Università degli Studi di Verona, Verona, Italy
3Dept. of Biomedical Engineering, Stony Brook University, New York, USA
Materials and Methods
filippo.piatti@polimi.it CAE Conference 2014
Results and Discussion
Introduction
Figure 1 (A) Prototype of the polymeric aortic valve (Innovia LLC, Miami, USA). (B)
ViVitro gold standard testing benchmark (ViVitro Labs, BC, Canada)
Boundary conditions
The Inlet and Outlet reservoirs were characterized by physiological
pressure waveforms extracted from experimental testing, thus
obtaining comparable working conditions between the computational
model and the ViVitro benchmark.
Figure 2 Schematic visualization of the ideal
optimization process implemented with the FSI
numerical approach
FSI
Exp. [1]
v
max
3.37
3.42
ms
-1
Effective
Orifice Area
1.54
1.47
cm
2
trans
-
valvular
𝑃
18.60
20.91
mmHg
Ejection
time 320 304
ms
Figure 3 Visualization of the velocity field contours on a cross-sectional plane
(upper panels) and of the FSI and experimental kinematic of the device (lower
panels), at four different time-points: (A) early systole, (B) systolic peak, (C) closing
phase, (D) stable diastole.
Acknowledgments
The research leading to these results has received fundings from the Cariplo Foundation Project,
Grant Agreement N°2011-2241.
Table 1 Numerical verification variables
References
1. T. E. Claiborne et al. (2013) Journal of Biomechanical Engineering
2. D. Bluestein et al. (2010) Annals of Biomedical Engineering
(B) (C) (D)
(A)
(B)
(A)
Moreover, a quantitative
validation of the numerical
results was accomplished
through the evaluation of fluid
dynamic variables and the
comparison with device
performances, as highlighted
in Table 1.
Outlet
reservoir
Inlet
reservoir
Fluid
duct
ViVitro
wall
Aortic
valve
Computational optimization process
FSI approach
Detailed numerical results
Kinematic analysis
Fluid dynamic performances
Thrombogenic analysis
Micro-scale particle tracking analysis
Stress-time evaluation
High-risk spots
Revision of the design
Post-processing
High velocity hotspots
Vortex propagation
Particle tracking (blood
components emulation)
Thrombogenic analysis
A particle tracking methodology was adopted to obtain the trajectories of
numerical ideal platelets. Numerical models were used to combine
stress and time (τ(t))so as to perform a quantification of the
thrombogenic potential of the device as well as of critical hot-spots.
Experimental procedures are commonly used to obtain an overall
quantification of the fluid dynamic and thrombogenic performances of
cardiovascular devices [2].
Meanwhile, the implementation of acomputational approach could
mimic the realistic operative conditions of a testing benchmark and
provide extremely localized and detailed information.
Experimental testing
Long lasting and high
cost procedures
Physical prototypal device
Kinematic and fluid
dynamic performances:
overall evaluation
The computational models (Figure 2, left) and their finite element
discretization were implemented on ANSYS Gambit 2.4.6 (ANSYS,
Canonsburg, USA). The FSI simulation was performed with the explicit
solver LS-DYNA R6 (LSTC, Livermore, USA), coupling eulerian fluid
elements and lagrangian solid ones.
At this aim, this work presents an innovative tool that emulates a gold
standard testing benchmark (Figure 1-A) to perform a micro-scale
analysis of the performances of a prototypal polymeric heart valve
(Figure 1-B) in order to identify thrombogenic localized hot-spots for
further possible design optimizations.
In first instance, the numerical solution was compared with experimental
results and its reliability was verified: as reported in Figure 3, valvular
kinematics was qualitatively compared with the in-vitro mechanical
response.
The thrombogenic evaluation was able to
highlight the commissural zones as high-risk
locations, due to vortexes propagation (figure 4-
A). Micro-scale analysis was used to extract the
stress-time history of selected dangerous
trajectories.
Core Commissure
τ(t)
Conclusions
The proposed tool was able to accurately replicate realistic experimental
working conditions. Moreover, a micro-scale analysis provided detailed
information regarding the thrombogenic potential of particular zones,
potentially allowing for further design optimization of the device.
Figure 4 (A) Trajectories of the Core and Commissural zones. (B) Stress-time
waveforms extracted from the domain
(A) (B)
0
10
20
30
40
50
0 0,1 0,2 0,3 0,4 0,5
Stress (dyne/cm2)
Time (s)
Core
Commissure
Article
Thromboembolism and the attendant risk of cardioembolic stroke remains an impediment to the development of prosthetic cardiovascular devices. In particular, altered haemodynamics are implicated in the acute blood cell damage that leads to thromboembolic complications, with platelet activation being the underlying mechanism for cardioemboli formation in blood flow past mechanical heart valves (MHVs) and other blood re-circulating devices. In this work, a new modeling paradigm for evaluating the cardioembolic risk of MHVs is described. In silico fluid-structure interaction (FSI) approach is used for providing a realistic representation of the flow through a bileaflet MHV model, and a Lagrangian analysis is adopted for characterizing the mechanism of mechanically induced activation of platelets by means of a mathematical model for platelet activation state prediction. Additionally, the relationship between the thromboembolic potency of the device and the local flow dynamics is quantified by giving a measure of the role played by the local streamwise and spanwise vorticity components. Our methodology indicates that (i) mechanically induced activation of platelets when passing through the valve is dependent on the phase of the cardiac cycle, where the platelet rate of activation is lower at early systole than late systole; (ii) local spanwise vorticity has greater influence on the activation of platelets (R>or=0.94) than streamwise vorticity (R>or=0.78). In conclusion, an integrated Lagrangian description of key flow characteristics could provide a more complete and quantitative picture of blood flow through MHVs and its potential to activate platelets: the proposed "comprehensive scale" approach could represent an efficient and novel assessment tool for MHV performance and may possibly lead to improved valve designs.
  • T E Claiborne
T. E. Claiborne et al. (2013) Journal of Biomechanical Engineering
  • D Bluestein
D. Bluestein et al. (2010) Annals of Biomedical Engineering