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

data using commercial software (Mimics ® , Materialise NV, Leuven, Belgium) and the
same methodology as that described in Biglino et al. [5]. The 3D volume (Fig. 1, in red)
was suitably modified for connection and pressure measurements in a mock circuit,
including fanning outlets and three small openings (Fig. 1, green arrows) on the wall at
the level of the arch a) right upstream the AC, b) right downstream the AC and c) about
10 isthmus diameters downstream the AC allowing for pressure recovery. The model
was either rapid prototyped using a robust transparent resin (Watershed ® 11122, DSM
Somos, Elgin, IL) for use in the experimental test, or finite volume meshed with Gambit
2.3.16 (Fluent, ANSYS Inc., Canonsburg, PA, USA), after removing the pressure ports,
for use in-silico. In both cases, the 3D model was rigid-walled, with one inlet
(ascending aorta) and five outlets (three main brachiocephalic vessels, descending aorta
and mBT shunt).
3.2 Experimental study
Fig. 1 Schematic of the multiscale system. Qin: inlet
flow; Ri: resistance, Ci: compliance; UB (LB): upper
(lower) body, P: pulmonary; VAD: ventricular assist
device; RES: reservoir. Green arrows: pressure ports.
The phantom was inserted into a mock circulatory
system (Fig. 1), with the inlet attached to a
ventricular assist device (VAD) (Excor ® 25 ml,
Berlin Heart, Berlin, Germany) simulating the
single ventricle, and the outlets to three
downstream lumped impedances, namely
resistive-compliant (RC) elements representing the
peripheral upper body (UB), lower body (LB) and
pulmonary (P) circulations. The brachiocephalic
outlets were merged into a manifold and linked to
the UB impedance. An additional compliance was
interposed between the VAD and the 3D inlet in
order to simulate aortic arch compliance. This
mock loop configuration, combining a 3D structure and a LPN, can be considered as an
in-vitro multiscale system. The C elements were Windkessel chambers of adjustable air
volume, equal to 1.0·10 -4 , 5.7·10 -4 and 5.4·10 -4 L/mmHg for UB, LB and P, respectively,
while needle-pinch valves with different closure extents were used to replicate
resistances. Preliminary steady flow measurements were performed on the valves at
different flow rates in order to extrapolate the associated resistance, expected to be nonlinear,
for in-silico implementation. Resistances of the lumped impedances were
connected to an open reservoir providing a constant pressure of 16 mmHg to feed back
to the ventricle.
An experimental test was performed during pulsatile flow with heart rate set at 125
bpm, stroke volume at 16.3e -3 L and diastolic time fraction at 50%, being these values
representative for a Norwood patient [11]. A solution of 33.5% glycerine in water by
weight, accepted in the literature as a suitable blood analogue for pediatric patients [5],
was used. Pressure was measured using a factory-precalibrated fiber-optic sensor
(Preclin 420, Samba Sensors, Västra Frölunda, Sweden) inserted via the three pressure
ports of the 3D model. Flow was measured with ultrasonic flow probes (9PXL,
Transonic Inc, Ithaca, NY, USA) placed at the UB, LB and P outlets upstream of the
compliances.