Applications of FSI for Cardiovascular Haemodynamics - Computational Hemodynamics: Theory, Modelling and Applications - page 285

Fig. 8.50 First principal stresses are presented in the surrounding tissues along with blood veloci-
ties. The fibrous cap is seen to exhibit severe stresses, maximal in the inflow region ( white arrow ).
A pressure zone with negative first principal stresses ( red arrow ) was visible adjacent to the
area exposed to maximal stresses. The severe luminal narrowing resulted in a marked velocity
jet ( arrowheads ) and area of recirculating blood ( asterisk ). In contrast to findings at the inflow
region, stresses at the position depicted in the left inset were maximal at the interfacial region
between lipid core and fibrous cap. (Image from Kock et al. 2008)

as an incompressible, homogeneous, Newtonian, however Kock et al. (2008) used
a turbulent model to predict the fluid flow citing that carotid bifurcations with large
degrees of stenosis are more accurately depicted using k-ω models than both lami-
nar flow and k-ε models. Tissues were simulated as isotropic homogenous entities
with non-linear stress/strain dependency of human tissues based on a Neo-Hookean
hyper-elastic model. Their results showed first-principal stress distribution (max.
254.1 kPa, mean 181.4 kPa) and flow velocities for a patient with a systolic blood
pressure of 160 mmHg, severe carotid stenosis, and a large lipid core located imme-
diately below the carotid bifurcation beneath the internal carotid artery (Fig. 8.49 ).
The severe stenosis reduces the cross-sectional area, which produces a flow ac-
celeration characterized by a marked velocity jet (max. velocity 0.784 m/s). Fol-
lowing the minimum cross-sectional area, the flow separates and large areas of
recirculating blood flow are produced. The soft lipid core deformed significantly
generating severe stresses in the overlaying fibrous cap, most prominent in the up-
stream and downstream shoulder regions of the wall-adjacent fibrous cap region.
These regions experienced the highest principal stresses of 175.4 (upstream shoul-
der) and 254.1 kPa (downstream shoulder). Kock et al. (2008) suggests that maxi-
mal first-principal stress level, approaching established criteria for plaque rupture,
are located in the upstream and downstream shoulder regions of the fibrous cap
(Fig. 8.50 ).

8.5.7 Closure

Medical imaging modalities are able to characterize the atherosclerotic plaque in
terms of their morphological and mechanical properties. Non-invasive imaging
techniques not only identify flow-limiting vascular stenosis, but also detect calcified