Effects of Pulsatile Flow Rate and Shunt Ratio in Bifurcated Distal Arteries on Hemodynamic Characteristics Involved in Two Patient-Specific Internal Carotid Artery Sidewall Aneurysms: A Numerical Study

Abstract

The pulsatile flow rate (PFR) in the cerebral artery system and shunt ratios in bifurcated arteries are two patient-specific parameters that may affect the hemodynamic characteristics in the pathobiology of cerebral aneurysms, which needs to be identified comprehensively. Accordingly, a systematic study was employed to study the effects of pulsatile flow rate (i.e., PFR-I, PFR-II, and PFR-III) and shunt ratio (i.e., 75:25 and 64:36) in bifurcated distal arteries, and transient cardiac pulsatile waveform on hemodynamic patterns in two internal carotid artery sidewall aneurysm models using computational fluid dynamics (CFD) modeling. Numerical results indicate that larger PFRs can cause higher wall shear stress (WSS) in some local regions of the aneurysmal dome that may increase the probability of small/secondary aneurysm generation than under smaller PFRs. The low WSS and relatively high oscillatory shear index (OSI) could appear under a smaller PFR, increasing the potential risk of aneurysmal sac growth and rupture. However, the variances in PFRs and bifurcated shunt ratios have rare impacts on the time-average pressure (TAP) distributions on the aneurysmal sac, although a higher PFR can contribute more to the pressure increase in the ICASA-1 dome due to the relatively stronger impingement by the redirected bloodstream than in ICASA-2. CFD simulations also show that the variances of shunt ratios in bifurcated distal arteries have rare impacts on the hemodynamic characteristics in the sacs, mainly because the bifurcated location is not close enough to the sac in present models. Furthermore, it has been found that the vortex location plays a major role in the temporal and spatial distribution of the WSS on the luminal wall, varying significantly with the cardiac period.

Keywords: bifurcated shunt ratio; computational fluid dynamics (CFD); hemodynamic behaviors; internal carotid artery sidewall aneurysm (ICASA); oscillatory shear index (OSI); pulsatile flow rate (PFR); time-averaged pressure (TAP); wall shear stress (WSS).

Figure 1

Schematic of the computational domain with hybrid mesh details in ICASA models: (a) ICASA−1 and (b) ICASA−2.

Figure 2

Mesh independence tests for the two CA models: (a) ICASA−1 and (b) ICASA−2.

Figure 3

Transient pulsatile flow rate boundary conditions at the internal carotid artery (ICA) inlet.

Figure 4

Visualized instantaneous $WSS$ distributions on selected region (R1) of ICASA−1 model at selected instants and shunt ratio of q_A1:q_A2 = 75:25 under corresponded PFRs: (a) PFR−I, (b) PFR−II, and (c) PFR−III.

Figure 5

Visualized instantaneous $WSS$ distributions on selected region (R2) of ICASA−2 model at selected instants and shunt ratio of q_A1:q_A2 = 75:25 under corresponded PFRs: (a) PFR−I, (b) PFR−II, and (c) PFR−III.

Figure 6

Visualized instantaneous $WSS$ distributions on selected region (R2) of ICASA−2 model at selected instants and shunt ratio of q_A1:q_A2 = 64:36 under corresponded PFRs: (a) PFR−I, (b) PFR−II, and (c) PFR−III.

Figure 7

Visualized flow streamlines in ICASA−1 (S1) and ICASA−2 (S2) models under different conditions at t₂ = 0.13 s: (a) ICASA−1, q_A1:q_A2 = 75:25, and PFR−I, (b) ICASA−1, q_A1:q_A2 = 75:25, and PFR−II, (c) ICASA−1, q_A1:q_A2 = 75:25, and PFR−III, (d) ICASA−2, q_A1:q_A2 = 75:25, and PFR−I, (e) ICASA−2, q_A1:q_A2 = 75:25, and PFR−II, (f) ICASA−2, q_A1:q_A2 = 75:25, and PFR−III, (g) ICASA−2, q_A1:q_A2 = 64:36, and PFR−I, (h) ICASA−2, q_A1:q_A2 = 64:36, and PFR−II, and (i) ICASA−2, q_A1:q_A2 = 64:36, and PFR−III.

Figure 8

$OSI$ distributions in ICASA−1 and ICASA−2 models under different conditions: (a) ICASA−1, q_A1:q_A2 = 75:25, and PFR−I, (b) ICASA−1, q_A1:q_A2 = 75:25, and PFR−II, (c) ICASA−1, q_A1:q_A2 = 75:25, and PFR−III, (d) ICASA−2, q_A1:q_A2 = 75:25, and PFR−I, (e) ICASA−2, q_A1:q_A2 = 75:25, and PFR−II, (f) ICASA−2, q_A1:q_A2 = 75:25, and PFR−III, (g) ICASA−2, q_A1:q_A2 = 64:36, and PFR−I, (h) ICASA−2, q_A1:q_A2 = 64:36, and PFR−II, and (i) ICASA−2, q_A1:q_A2 = 64:36, and PFR−III.

Figure 9

Nondimensionalized velocity profiles V* at the designated cross lines across the aneurysmal sac at t₂ = 0.22 s in ICASA models: (a) ICASA−1 and (b) ICASA−2.

Figure 10

Visualized velocity profiles at t₂ = 0.22 s in extracted planes of ICASA models: (a) ICASA−1, q_A1:q_A2 = 75:25, and PFR−I, (b) ICASA−1, q_A1:q_A2 = 75:25, and PFR−II, (c) ICASA−1, q_A1:q_A2 = 75:25, and PFR−III, (d) ICASA−2, q_A1:q_A2 = 75:25, and PFR−I, (e) ICASA−2, q_A1:q_A2 = 75:25, and PFR−II, (f) ICASA−2, q_A1:q_A2 = 75:25, and PFR−III, (g) ICASA−2, q_A1:q_A2 = 64:36, and PFR−I, (h) ICASA−2, q_A1:q_A2 = 64:36, and PFR−II, and (i) ICASA−2, q_A1:q_A2 = 64:36, and PFR−III.

Figure 11

$TAP$ distributions on the arterial walls of ICASA models: (a) ICASA−1, q_A1:q_A2 = 75:25, and PFR−I, (b) ICASA−1, q_A1:q_A2 = 75:25, and PFR−II, (c) ICASA−1, q_A1:q_A2 = 75:25, and PFR−III, (d) ICASA−2, q_A1:q_A2 = 75:25, and PFR−I, (e) ICASA−2, q_A1:q_A2 = 75:25, and PFR−II, (f) ICASA−2, q_A1:q_A2 = 75:25, and PFR−III, (g) ICASA−2, q_A1:q_A2 = 64:36, and PFR−I, (h) ICASA−2, q_A1:q_A2 = 64:36, and PFR−II, and (i) ICASA−2, q_A1:q_A2 = 64:36, and PFR−III.

Figure 12

Comparisons of velocity profiles in the extracted plane C−C′ and velocity distributions in selected lines f and g in ICASA−2 model under different bifurcated shunt ratios: (a) velocity profiles at plane C−C′ under q_A1:q_A2 = 75:25, (b) velocity profiles at plane C−C′ under q_A1:q_A2 = 64:36, and (c) nondimensionalized velocity profiles at lines g and f.

Figure 13

Velocity profiles and flow streamlines in selected planes and $WSS$ distributions on the edges of selected planes in ICASA−1 and ICASA−2 models at selected instants: (a) velocity profiles and streamlines in plane Y = −0.180 m of ICASA−1 model, (b) velocity profiles and streamlines in plane X = 0.0073 m of ICASA−2 model, (c) $WSS$ distributions at the edges of plane Y = −0.180 m of ICASA−1 model, and (d) $WSS$ distributions at the edges of plane X = 0.0205 m of ICASA−2.