Biomedical Engineering Reference
In-Depth Information
Fig. 1.6.
Demonstration that shearthinning has a minor effect on carotid bifurcation shear patterns
relative to the effects of geometric uncertainty, and can be approximated well by choosing an ap-
propriate characteristic (Newtonian) viscosity. Adapted from [30]
of patient-specific CFD models by incorporating non-Newtonian rheologies may be
wasted if interindividual differences in hematocrit or plasma viscosity are not simi-
larly accounted for [35].
For aneurysms the story may be different, because there is a greater likelihood of
large and persistent recirculation zones, and hence persistent low shear rates, within
the aneurysm sac. Although our own unpublished studies of shear-thinning effects
for the giant saccular aneurysm CFD model of [36] suggested only a minor influence,
Rayz et al. [37] have convincingly demonstrated that regions of stagnant flow pre-
dicted by a non-Newtonian CFD model of a fusiform basilar aneurysm matched the
subsequently observed distribution of thrombus better than that predicted by a New-
tonian CFD model. The author has also been told by neurosurgeons that differently-
shaded streams of blood are often visible through the thin, near-transparent walls
of cerebral aneurysms during surgery, suggesting spatiotemporal variations in the
properties of blood that have also been observed by ultrasound imaging of the carotid
arteries [38].
As noted earlier, implicit in most studies on the effect of rheology for large
artery flows is the assumption that shear thinning dominates over other possible
non-Newtonian properties of blood. For example, all shear-thinning models presume
