Abstract:
Aneurysms are localized blood-filled balloon-like bulges which can occur in any blood vessel.
The term coronary artery aneurysm refers to both diffuse, where arterial segments dilate more
than 1.5 times of the largest diameter of a coronary artery and spherical or saccular dilation.
Atherosclerosis is the main cause of these anomalies in adults and Kawasaki disease in children
and adolescents. In this study, the simulation has been done for S shaped coronary artery with
saccular aneurysm using physiological flow rate condition on the inlet boundary and a
corresponding physiological pressure condition on the outlet boundary to precisely describe the
cyclic nature of heart. In simulating blood flow, one important aspect is to accurately model
blood as a fluid. As instantaneous shear rate varies from 0 to 1000s-1 over a cardiac cycle
depending on circumstances, it is always beneficial to examine the non-Newtonian effect on
physiological blood flows. Both Newtonian and non-Newtonian models have been compared in
this study to justify the use of Non Newtonian model. Previous experimental investigations show
a transition to turbulent flow occurring during the deceleration phase of the cardiac cycle.
Moreover, Irregularities in flow geometry create flow separation, recirculation, reattachment and
turbulence. Laminar and k − ω turbulence model have been compared to choose the k − ω
turbulence model over Laminar model. Validation has been conducted using a simple 90o bend
channel with a pulsatile velocity inlet boundary condition. Flow has been considered as
Newtonian, Laminar, incompressible. This allows comparing the simulated results with the
experimental investigation. Axial velocity profiles and secondary flow patterns have been
compared and found in good agreement.
Though Patient-specific models are attractive for understanding the specific blood flow
dynamics in real human body, based on several studies, idealized model of S shaped curved
coronary artery of diameter 3.5 mm with time-averaged Reynolds number of 150 has been
analyzed in the present study for illustrating the relationship between geometric characteristics
and inflow features at four different time periods of cardiac cycle. Temporal and spatial
distribution of axial velocity profiles and secondary flow patterns have been analyzed. Wall
shear stress (WSS) and Time averaged wall shear stress (TAWSS) have been found to have
higher values in artery with aneurysm than healthy artery. At a fixed neck size the values of WSS
and TAWSS remain more or less constant during the growth of aneurysm. But these values have
been observed to change while changing the time periods of cardiac cycle. Maximum value of
WSS has been observed to increase with the decrease of time period at minimum velocities of
systolic and diastolic phase, but observed to decrease with the decrease of time period at
maximum velocities of systolic and diastolic phase. Oscillatory Shear Index (OSI) varies
between 0 and 0.5 depending on cyclic variation of WSS vector. But, OSI has been found to
decrease with the decrease of time period. Relative Residence Time (RRT) has been checked and
observed that spots of high RRT decrease with the decrease of time period.
