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Research Papers

Computational Fluid Dynamics Simulations of Intracranial Aneurysms at Varying Heart Rates: A “Patient-Specific” Study

[+] Author and Article Information
Jingfeng Jiang1

Department of Medical Physics, University of Wisconsin-Madison, Madison, WI 53705jjiang2@wisc.edu

Charles Strother

Department of Radiology, University of Wisconsin-Madison, Madison, WI 53705

1

Corresponding author.

J Biomech Eng 131(9), 091001 (Aug 04, 2009) (11 pages) doi:10.1115/1.3127251 History: Received July 21, 2008; Revised March 23, 2009; Published August 04, 2009

Rupture of an intracranial aneurysm (IA) is frequently associated with intense physical exertion and/or emotional excitement, events that are typically also accompanied by sudden significant changes in both heart rate and blood pressure. Very few experimental studies of aneurysm hemodynamics have examined the impact on hemodynamic parameters in and around an aneurysm resulting from changes in heart rate. In order to further understanding these changes, as they relate to hemodynamic features that may contribute to rupture of an IA, we examined the characteristics of pulsatile flow in and around two “patient-specific” intracranial aneurysms at three different cardiac frequencies. Three dimensional X-ray angiographic data (3D-DSA) were used to reconstruct accurate and patient-specific aneurysm geometries. Then, computational fluid dynamics techniques were utilized to analyze the characteristics of blood flow in and around the two aneurysms. Physiologically realistic flow conditions, as measured by transcranial Doppler ultrasound, were used in the simulations. Our results showed that there were significant changes in the overall flow patterns (e.g., vortex formation and translation) associated with the changes of heart rates. In both aneurysms, the calculated wall shear stress exhibited substantial increases with an increase in heart rate. Our results suggest that the changes in local hemodynamic forces associated with variations in heart rate are dependent not only on the heart rate but also on the aneurysm geometry. This thus precludes applying our observations about the impact of variations in cardiac rate to aneurysms in general.

Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 5

Gross patterns of aneurismal flow for Aneurysm A, illustrated using a velocity isosurface (0.2 m/s) at early diastole for three different heart rates: (a) 60 bpm, (b) 100 bpm, and 150 bpm

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Figure 4

Velocity profiles on two planes through Aneurysm A (a) axial to the ostium (b) perpendicular to the ostium for three different mesh resolutions: ((c) and (f) 800,000 cells, ((d) and (g)0 1,500,000 cells, and ((e) and (f)) 3,000,000 cells. The unit for velocity values is m/s and were obtained under a steady flow simulation assuming a 250 ml/min flow with parabolic velocity profile at the inlet.

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Figure 3

Inlet velocity waveforms adopted from transcranial Doppler ultrasound (14-15). The solid, dotted, and dash-dotted lines represents nominally 60 bpm, 100 bpm and 150 bpm heart rates, respectively.

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Figure 7

Three-dimensional streamlines of aneurysm flow overlaid with velocity amplitude (unit: m/s) in and around Aneurysm A at three different stages of the cardiac cycle: (a) initial systole, (b) peak systole, and (c) initial diastole. The flow was simulated with 150 bpm waveform. The arrows point to the velocity vortices.

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Figure 8

Three-dimensional streamlines of aneurysm flow overlaid with velocity amplitude (unit: m/s) in and around Aneurysm B at three different stages of the cardiac cycle: (a) initial systole, (b) peak systole, and (c) initial diastole. The flow was simulated with 150 bpm waveform. The arrows point to the velocity vortices.

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Figure 9

Spatially averaged flow-inducing aneurysm pressures of (a) Aneurysm A and (b) Aneurysm B. The “error” bars on both plots represent one standard deviation of the flow-induced aneurysm pressure.

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Figure 2

Streamlines (i.e., lines of tangent to instantaneous velocity vectors) of CFD simulated velocity vectors at peak systole (ENSIGHT Software (Computational Engineering International, Apex, NC). The results shown were obtained using the 150 bpm waveform: (a) Aneurysm A and (b) Aneurysm B. In this figure, MCA, ACA, ICA, and PCA stand for middle cerebral artery, anterior cerebral artery, internal carotid artery, and posterior cerebral artery, respectively.

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Figure 1

A flowchart of computational fluid dynamics simulations presented in this paper

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Figure 6

Gross patterns of aneurismal flow for Aneurysm B, illustrated using a velocity isosurface (0.2 m/s) at the early diastole for three different heart rates: (a) 60 bpm, (b) 100 bpm, and (c) 150 bpm

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Figure 10

The calculated sizes of the impingement zone for (a) Aneurysms A and (b) Aneurysm B. The peak systole is around 0.3 at the normalized cardiac cycle (X-axis).

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Figure 11

(a) Comparison of the calculated spatially registered wall shear stresses for initial diastole phase of the cardiac cycle in Aneurysm A. The X-axis displays the calculated wall shear stresses (Pa) of 60 bpm frequency (base line) and Y-axis displays the corresponding wall shear stresses (Pa) of 100 bpm or 150 bpm frequency for the same spatial locations. The locations (see arrows in (b)) where the wall shear stresses are significantly elevated (increase more than a factor of 2 and the wall shear stress is greater than 4 Pa under 150 bpm frequency) at the initial diastole phase are shown in (b). (c) Wall shear stresses of an arbitrary point within the substantial impingement zone as marked by the dot in (b) for three different heart rates are plotted out for the entire normalized cardiac cycle where the peak systole is at 0.3.

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Figure 12

(a) Comparison of the calculated spatially-registered wall shear stresses for initial diastole phase of the cardiac cycle in Aneurysm B. The X-axis displays the calculated wall shear stresses (Pa) of 60 bpm frequency (base line) and Y-axis displays the corresponding wall shear stresses (Pa) of 100 or 150 bpm frequency for the same spatial locations. The locations (see arrows in (b)) where the wall shear stresses are significantly elevated (increase more than a factor of 2 and the wall shear stress is greater than 4 Pa under the 150 bpm frequency) at the initial diastole phase are shown in (b). (c) Wall shear stress of an arbitrary point within the substantial impingement zone as marked by the dot in (b) for three different heart rates are plotted out for the entire normalized cardiac cycle where the peak systole is at 0.3.

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Figure 13

Relative spectral power of the wall shear stresses displayed in Fig. 1: (a) 60 bpm, (b) 100 bpm, and (c) 150 bpm

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Figure 14

Frequencies (Hz) of the wall shear stress corresponding to the peak power in the relative power spectra for Aneurysm A: (a) 60 bpm, (b) 100 bpm, and (c) 150 bpm. The time-averaged wall shear stress distribution of Aneurysm A over a cardiac cycle (a heart rate of 150 bpm) is shown in (d).

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Figure 15

Frequencies (Hz) of the wall shear stress corresponding to the peak power in the relative power spectra for Aneurysm B: (a) 60 bpm, (b) 100 bpm, and (c) 150 bpm

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