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

mean value of 0.0310 m s -1 . The outlet pressure (Fig. 2b) is set to be 122/82 mmHg (1
mmHg = 133.322 Pa), which corresponds to a normal pattern in a healthy person. The
cardiac cycle in Fig. 2 is assumed to be one second, modeling a patient with 60 bpm.
The Reynolds number ranges from 280 to 1690. In addition, the no-slip boundary
condition is applied at all vessel walls. Since the first two cycles of computations can
already generate a periodic output, data for the third cycle will be collected and
analyzed. The properties reported here are obtained at the systolic phase of a cardiac
cycle unless otherwise specified.
4. RESULTS
Fig. 2 Pulsatile blood flow waveform: (a) velocity inlet; (b) pressure outlet
In this section, various sizes of the dissected aorta are investigated. As the false lumen
changes from 40 mm to 80 mm, the spatial grids used in these five models are 40mm
(386,793 grids), 50mm (502,459 grids), 60mm (603,618 grids), 70mm (728,385 grids),
and 80mm (798,974 grids). In order to validate the simulation results, both mesh and
time step size independence tests are performed. These tests show that the results will
not be altered by either increasing the number of grids or reducing the time step size.
4.1 Effect of dissecting aneurysm sizes
Making use of the CFD software, the hemodynamic force can be calculated by
integrating the pressure over the surface area of the false lumen wall. This force is
computed for various dissecting aneurysm sizes at peak systole (time = 0.25s in the
cardiac cycle). As the dissected aorta swells from 40 mm to 80 mm, the resultant force
acting on the false lumen wall goes up from 54.5 N to 94.2 N, a 73% increase in force
magnitude (see Fig. 3).
Fig. 3 Relationship between the hemodynamic forces (horizontal, vertical and resultant
components) acting on the false lumen wall and the size of the aorta dissection