Clinical Neurology and Neurosurgery 112 (2010) 306–313 Contents lists available at ScienceDirect Clinical Neurology and Neurosurgery journal homepage: www.elsevier.com/locate/clineuro Effects of smoking and hypertension on wall shear stress and oscillatory shear index at the site of intracranial aneurysm formation Pankaj K. Singh a,b,∗ , Alberto Marzo c , Bethany Howard d , Daniel A. Rufenacht e , Philippe Bijlenga f , Alejandro F. Frangi g,h,i , Patricia V. Lawford c , Stuart C. Coley j , D. Rodney Hose c , Umang J. Patel b a Department of Medical Physics, Royal Hallamshire Hospital, Sheffield, UK b Department of Neurosurgery, Royal Hallamshire Hospital, Sheffield, UK c Academic Unit of Medical Physics, School of Medicine and Biomedical Sciences, University of Sheffield, Sheffield, UK d Academic Unit of Medical Physics, School of Biomedical Sciences, University of Sheffield, Sheffield, UK e Department of Neuroradiology, Institute of Radiology, University Hospital Basel, Petersgraben, Basel, Switzerland f Clinic of Neurosurgery, Department of Clinical Neurosciences, Geneva University Hospital, Switzerland g Center for Computational Imaging & Simulation Technologies in Biomedicine, Universitat Pompeu Fabra (UPF), Barcelona, Spain h Center for Networked Biomedical Research on Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), Spain i Institució Catalana de Recerca i Estudis Avac ¸ ats (ICREA), Barcelona, Spain j Department of Neuroradiology, Royal Hallamshire Hospital, Sheffield, UK article info Article history: Received 5 August 2009 Received in revised form 6 November 2009 Accepted 28 December 2009 Available online 21 January 2010 Keywords: Blood viscosity Computational fluid dynamics (CFD) Hemodynamics Hypertension Initiation Intracranial aneurysm Smoking Wall shear stress (WSS) Oscillatory shear index (OSI) abstract Objective: The mechanisms by which smoking and hypertension lead to increased incidence of intracranial aneurysm (IA) formation remain poorly understood. The current study investigates the effects of these risk factors on wall shear stress (WSS) and oscillatory shear index (OSI) at the site of IA initiation. Methods: Two (n = 2) IAs from two patients with history of smoking and hypertension were artificially removed with the help of software @neuFuse (Supercomputing Solutions ® , Bologna, Italy) and the vessel geometry reconstructed to mimic the condition prior to IA formation. Two computational fluid dynamics (CFD) analyses were performed on each data-set by using in turn the normal physiological values of blood viscosity (BV), and high BV values specific to smoking and hypertension, obtained from literature. Results: At normal BV, high WSS (>15 Pa) was observed at the site of IA initiation in both patients. When BV values specific to smoking and hypertension were used, both the areas affected by high WSS (>15 Pa) and the maximum WSS were increased whilst the magnitude and distribution of OSI showed no significant change. Conclusions: Long-term exposure to high WSS may result in an increased risk of IA development. An incremental increase in areas of high WSS observed secondary to smoking and hypertension may indicate a further increase in the risk of IA initiation. Interestingly, the relationship between BV and the area of increased WSS was not linear, reflecting the need for patient-specific CFD analysis. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved. 1. Introduction Aneurysmal subarachnoid hemorrhage (SAH) remains a major cause of morbidity and mortality in neurosurgical patients [34,51]. Smoking and hypertension are well-established risk factors in IA formation [6,16,35,38,40]. However, their roles in the mechanisms that regulate aneurysm formation are poorly understood and are essentially limited to their statistical associations. ∗ Corresponding author at: Department of Neurosurgery, Royal Hallamshire Hos- pital, Glossop Road, Sheffield S10 2JF, UK. Tel.: +44 114 2712180; fax: +44 114 2713314. E-mail address: neurosurgery2007@gmail.com (P.K. Singh). Recent evidence indicates WSS and OSI as important underly- ing hemodynamic factors in IA formation [9,11,24,49]. One of the important parameters influencing WSS is blood viscosity, which in turn is influenced by smoking and hypertension [17,41]. The current study employs CFD to predict the effect of smoking and hypertension on the WSS patterns at the site of IA initiation with aim to explore the possible underlying mechanisms leading to their formation. 2. Materials and methods 2.1.1. Study design and patients’ recruitment The study was conducted jointly in the Departments of Neu- rosurgery and Neuroradiology, Royal Hallamshire Hospital, and 0303-8467/$ – see front matter. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.clineuro.2009.12.018