ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

the different virtual surgical designs of these patients, with the “Y” shape often less
sensitive to this parameter [14]. Sensitivities of the results to rest versus exercise
conditions, or with respiration effects are other examples of robustness tests [6, 14, 17].
5.2 Predictability enhanced by 3D-closed loop model of the entire circulation
The results section featured virtual surgical designs simulations with hypotheses on the
boundary conditions [14]. Outlet boundary conditions were kept unchanged compared
to preoperatively, state for which they were designed based on patient-specific clinical
measurements as described in the methods section [12]. At the outlets, a relationship
between pressure and flow was prescribed, so both could adapt to the virtual surgery
where a graft was connected in different ways to the preoperative geometry and thus
bringing additional flow. By contrast, flow rates were prescribed at the inlets based on
preoperative PC-MRI measurements boundary conditions and hypotheses on how they
might have changed from preoperatively to postoperatively. To rather predict these
inflow changes, a closed-loop lumped-parameter model of the entire circulation was
thus tuned for one patient to its MRI, ultrasound and catheterization pressure
measurements and coupled to the 3D model [6]. Results showed that flow rates at both
inlets (SVC, IVC) changed from the preoperative to the postoperative states, in
coherence with physiological knowledge. Of course, the closed-loop model presents
many parameters that are not easy to tune based on clinical measurements, and it
remains to be validated that the parameters do not change significantly due to the
surgery, but such an approach enhances the predictability potential of virtual surgeries.
6. CONCLUSION
In conclusion, we have presented a summary of numerical methods that we have
developed for patient-specific 3D-0D simulations and shown different ways of
translating patient-specific measurements into boundary conditions specification.
Applications to single ventricle palliation included a 5-patient study before their Fontan
surgery and, based on these preoperative data, a performance evaluation and
optimization of different virtual surgical designs in which the non-conventional “Y”
shape seems the most promising. Sensitivity of the results to hemodynamics input data
shows that it needs to be evaluated to enhance the significance of the results. Finally,
patient-specific 3D-0D closed loop lumped models present an increased predictability
potential. However, boundary conditions parameter estimation remains a challenge and
for which new methods are actively sought for [18].
7. REFERENCES
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computational simulation in congenital heart disease for the clinician. Progress in
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2. Vignon-Clementel IE, Figueroa CA, Jansen KE and Taylor CA (2006) Outflow
boundary conditions for three-dimensional finite element modeling of blood flow and
pressure in arteries. Comp Methods in Applied Mech and Eng 195: 3776-3796
3. Moghadam ME, Bazilevs Y, Hsia T-Y, Vignon-Clementel IE, Marsden AL and
Modeling Congenital Hearts A (2011) A comparison of outlet boundary treatments for
prevention of backflow divergence with relevance to blood flow simulations.