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

Point P7, located at the toe of the ETS anastomosis, shows the minimum disparity
between the WSS time-history of the rigid and compliant models where the two graphs
are almost identical (Fig.2a). On the other hand, P6, located on the graft outer wall
proximal to the ETS anastomosis, demonstrates the most discrepancy with up to 21%
increase in the WSS magnitude in the rigid model compared to that of the distensible
model (Fig.2b), which can be attributable to the higher DV in the graft than in the
coronary artery. The profile of the WSS curves at proximal locations such as P1 is more
analogous to the calculated pressure waveform (see Fig.2c), than those at distal
locations. The overall shape of the WSS time-history curves is similar between the rigid
and distensible models, with the WSS magnitude being generally higher in the rigidwall
model due to its smaller vessel diameter and the consequent higher velocity.
However, at point P8, located on the ceiling wall of the coronary artery just distal to the
toe of the ETS anastomosis, the magnitude of the WSS in the compliant model is higher
than that in the rigid model (Fig.2d), unlike the other points. This is due to the higher
flow separation at this point in the rigid-wall model compared to the distensible model,
which results in a significant reduction of WSS magnitude, and is in agreement with the
aforementioned observations.
Comparison of the TAWSS between the rigid and compliant models (both for the
Newtonian and non-Newtonian fluid models) demonstrates a decrease in the TAWSS at
all critical locations in the compliant model, which ranges between 3% (on the suture
line) and 32% (on the heel) in the conventional ETS model, and from 4% (at the toe of
the STS anastomosis) to 27% (on the suture line of the STS anastomosis) in the SQA
model. Also, the wall compliance has somewhat increased the oscillatory nature of the
flow.
Comparison of the TAWSS gradient (TAWSSG) between the rigid and compliant
models (both for the Newtonian and non-Newtonian fluid models) indicates that the
TAWSSG is generally decreased in compliant models at the ETS anastomosis of both
the conventional and SQA models (except on the artery bed of ETS anastomosis of
SQA model in the case of Newtonian fluid). The TAWSSG is decreased at all the
critical locations of the ETS anastomosis in the SQA configuration as compared to the
conventional ETS anastomosis in the case of compliant model with non-Newtonian
fluid, while this advantage can be observed only at the heel and on the artery bed in the
case of the rigid-wall model with Newtonian fluid. This manifests a more uniform
distribution of WSS at the ETS anastomosis of the SQA configuration, which can lessen
the vessel wall permeability and atherosclerotic lesion development, and further unveils
the advantages of the SQA design over the conventional ETS anastomosis.
The effect of non-Newtonian rheology on the HPs is heterogeneous. The ETS
anastomoses (of both the conventional and SQA models) experience mostly a decrease
in the TAWSS (except at the heel), while the STS anastomosis of the SQA model
undergoes an increase in this HP. The flow oscillation is increased at the toe of the
anastomosis, whereas it is decreased at the heel and on the artery bed, due to the shear
thinning behavior of the blood.
Although vessel wall compliance and non-Newtonian rheology have shown modest
influence on the HPs in each model, they have unveiled further advantages of the
coupled SQA model over the conventional ETS anastomosis which had not been
revealed in our previous study with the rigid-wall and Newtonian fluid models [6].