Applications of FSI for Cardiovascular Haemodynamics - Computational Hemodynamics: Theory, Modelling and Applications - page 259

Fig. 8.26 First principal stress at the LCx side bifurcation shoulder denoted by a red dot on the
bifurcation

occurs at the LCx side bifurcation shoulder ( σ max = 0.27 MPa) rather than the bifur-
cation apex ( σ max = 0.24 MPa).
The image-based model also displays a similar stress variation profile with the
idealized model ( θ = 90°) both on the bifurcation apex and the LCx side bifurcation
shoulder. Along with the results shown in Fig. 8.24 , it can be demonstrated that the
idealized models are capable of representing key FSI results for further analysis.

8.4.4 Haemodynamic Results Analysis

The WSS-based oscillatory shear index (OSI) is a flow indicator used to evaluate the
total shear stress exerted on the arterial wall (Fig. 8.27 ). It can be regarded as the frac-
tion of angle and magnitude change between the instantaneous WSS and the time-
averaged WSS ranging from 0 to 0.5. High OSI indicates unsteady and oscillatory
flow with low WSS which leads to a predisposition of endothelial dysfunction and
atherogenesis (Dong et al. 2013b; Ku et al. 1985b). Generally, high OSI regions are
concentrated at the origins and proximal LCx branches with no significant differences
among idealized models. This indicates the affected regions are susceptible to prog-
ress atherosclerotic changes due to the presence of disturbed flow. As a reference, the
image-based model shows a similar OSI distribution except in the distal LAD branch,
where a locally high OSI is found caused by a moderate bulge section. Due to this
luminal expansion, local flow separation and disturbance appear as a result.
Wall shear stress predicted by FSI and rigid model are compared in Fig. 8.28a .
The rigid model predicts a greater distribution of higher WSS values at peak diastole