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Original research
Newtonian viscosity model could overestimate wall shear stress in intracranial aneurysm domes and underestimate rupture risk
  1. Jianping Xiang1,2,
  2. Markus Tremmel1,3,
  3. John Kolega1,5,
  4. Elad I Levy1,3,4,
  5. Sabareesh K Natarajan1,3,
  6. Hui Meng1,2,3
  1. 1Toshiba Stroke Research Center, University at Buffalo, State University of New York, Buffalo, New York, USA
  2. 2Department of Mechanical and Aerospace Engineering, University at Buffalo, State University of New York, Buffalo, New York, USA
  3. 3Department of Neurosurgery University at Buffalo, State University of New York and Millard Fillmore Gates Hospital, Kaleida Health, Buffalo, New York, USA
  4. 4Department of Radiology University at Buffalo, State University of New York, Buffalo, New York, USA
  5. 5Department of Pathology & Anatomical Sciences University at Buffalo, State University of New York, Buffalo, New York, USA
  1. Correspondence toDr Hui Meng, Toshiba Stroke Research Center, University at Buffalo, State University of New York, 447 Biomedical Research Building, 3435 Main Street, Buffalo, NY 14214, USA; huimeng{at}buffalo.edu

Abstract

Objective Computational fluid dynamics (CFD) simulations of intracranial aneurysm hemodynamics usually adopt the simplification of the Newtonian blood rheology model. A study was undertaken to examine whether such a model affects the predicted hemodynamics in realistic intracranial aneurysm geometries.

Methods Pulsatile CFD simulations were carried out using the Newtonian viscosity model and two non-Newtonian models (Casson and Herschel-Bulkley) in three typical internal carotid artery saccular aneurysms (A, sidewall, oblong-shaped with a daughter sac; B, sidewall, quasi-spherical; C, near-spherical bifurcation). For each aneurysm model the surface distributions of shear rate, blood viscosity and wall shear stress (WSS) predicted by the three rheology models were compared.

Results All three rheology models produced similar intra-aneurysmal flow patterns: aneurysm A had a slowly recirculating secondary vortex near the dome whereas aneurysms B and C contained only a large single vortex. All models predicted similar shear rate, blood viscosity and WSS in parent vessels of all aneurysms and in the sacs of B and C. However, large discrepancies in shear rate, viscosity and WSS among predictions by the various rheology models were found in the dome area of A where the flow was relatively stagnant. Here the Newtonian model predicted higher shear rate and WSS values and lower blood viscosity than the two non-Newtonian models.

Conclusions The Newtonian fluid assumption can underestimate viscosity and overestimate shear rate and WSS in regions of stasis or slowly recirculating secondary vortices, typically found at the dome in elongated or complex-shaped saccular aneurysms as well as in aneurysms following endovascular treatment. Because low shear rates and low WSS in such flow conditions indicate a high propensity for thrombus formation and rupture, CFD based on the Newtonian assumption may underestimate the propensity of these events.

  • Casson model
  • Herschel-Bulkley model
  • non-Newtonian
  • wall shear stress
  • shear rate
  • viscosity
  • blood rheology
  • thrombosis
  • aneurysm
  • artery
  • blood flow
  • vessel wall
  • brain
  • tumor
  • spine
  • thrombectomy
  • catheter

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Footnotes

  • Disclosures Dr. Kolega, Dr. Natarajan, Dr. Tremmel, and Mr. Xiang have no final relationships to disclose. Dr. Meng is the principal investigator of the aforementioned NIH grant. Dr. Levy receives research grant support (principal investigator: Stent-Assisted Recanalization in acute Ischemic Stroke, SARIS), other research support (devices), and honoraria from Boston Scientific* and research support from Codman & Shurtleff, Inc. and ev3/Covidien Vascular Therapies; has ownership interests in Intratech Medical Ltd. and Mynx/Access Closure; serves as a consultant on the board of Scientific Advisors to Codman & Shurtleff, Inc.; serves as a consultant per project and/or per hour for Codman & Shurtleff, Inc., ev3/Covidien Vascular Therapies, and TheraSyn Sensors, Inc.; and receives fees for carotid stent training from Abbott Vascular and ev3/Covidien Vascular Therapies. Dr. Levy receives no consulting salary arrangements. All consulting is per project and/or per hour. (*Boston Scientific's neurovascular business has been acquired by Stryker.)

  • Funding This work was partially supported by NIH grant R01NS064592 and a grant from Toshiba Medical Systems.

  • Competing interests None.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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