title: Effects of smoking and hypertension on wall shear stress and oscillatory shear index at the site of intracranial aneurysm formation.
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.
authors.affiliation: Department of Medical Physics, Royal Hallamshire Hospital, Sheffield, UK. neurosurgery2007@gmail.com
authors.forename: Pankaj K
authors.initials: PK
authors.lastname: Singh
authors.forename: Alberto
authors.initials: A
authors.lastname: Marzo
authors.forename: Bethany
authors.initials: B
authors.lastname: Howard
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Rufenacht
authors.forename: Philippe
authors.initials: P
authors.lastname: Bijlenga
authors.forename: Alejandro F
authors.initials: AF
authors.lastname: Frangi
authors.forename: Patricia V
authors.initials: PV
authors.lastname: Lawford
authors.forename: Stuart C
authors.initials: SC
authors.lastname: Coley
authors.forename: D Rodney
authors.initials: DR
authors.lastname: Hose
authors.forename: Umang J
authors.initials: UJ
authors.lastname: Patel
mesh_terms: D000328:Adult; D000465:Algorithms; D001696:Biomechanical Phenomena; D001808:Blood Vessels / Q000473:pathology; D001809:Blood Viscosity; D002560:Cerebrovascular Circulation; D005260:Female; D006801:Humans; D006973:Hypertension / Q000473:pathology*; D007091:Image Processing, Computer-Assisted; D002532:Intracranial Aneurysm / Q000473:pathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D033081:Shear Strength; D012907:Smoking / Q000473:pathology*