title: Wall shear stress in the human common carotid artery as function of age and gender.
abstract: OBJECTIVE
  It has been postulated that in the arterial system mean wall shear stress is maintained at a constant value. The present study was performed to investigate the level of wall shear stress in the common carotid artery (CCA) as function of age and possible interactions between diameter and storage capacity, defined as the absolute area change per heart beat, with mean wall shear stress.
  
  
  METHODS
  Wall shear stress (wall shear rate multiplied by whole blood viscosity) was assessed in the right CCA of 111 presumed healthy male (n = 56) and female (n = 55) volunteers, varying in age between 10 and 60 years. Wall shear rate was measured with a high resolution ultrasound system. Simultaneously, arterial diameter and storage capacity were determined. Whole blood viscosity was calculated from haematocrit, plasma viscosity and shear rate.
  
  
  RESULTS
  From the second to the sixth age decade peak wall shear stress was significantly higher in males than in females and decreased from 4.3 Pa to 2.6 Pa (r = -0.56, p < 0.001) in males and from 3.3 Pa to 2.5 Pa (r = -0.54, p < 0.001) in females. Mean wall shear stress tended to decrease from 1.5 Pa to 1.2 Pa (r = -0.26, p = 0.057) in males and decreased significantly from 1.3 Pa to 1.1 Pa (r = -0.30, p = 0.021) in females. No significant difference in mean wall shear stress was found between males and females in any age decade. The diameter of the CCA increased significantly in both males (r = 0.26, p < 0.05) and females (r = 0.40, p < 0.003). Storage capacity decreased significantly in both sexes (males: r = -0.63, p < 0.001; females: r = -0.68, p < 0.001).
  
  
  CONCLUSIONS
  These observations suggest that the reduction in mean wall shear stress with age results from the concomitant increase in diameter in an attempt of the arterial system to limit the reduction in storage capacity of the arterial system with increasing age.
authors.affiliation: Department of Biophysics, Maastricht University, The Netherlands.
authors.forename: S K
authors.initials: SK
authors.lastname: Samijo
authors.forename: J M
authors.initials: JM
authors.lastname: Willigers
authors.forename: R
authors.initials: R
authors.lastname: Barkhuysen
authors.forename: P J
authors.initials: PJ
authors.lastname: Kitslaar
authors.forename: R S
authors.initials: RS
authors.lastname: Reneman
authors.forename: P J
authors.initials: PJ
authors.lastname: Brands
authors.forename: A P
authors.initials: AP
authors.lastname: Hoeks
mesh_terms: D000293:Adolescent; D000328:Adult; D000375:Aging / Q000502:physiology*; D001696:Biomechanical Phenomena; D001783:Blood Flow Velocity; D001794:Blood Pressure / Q000502:physiology; D017536:Carotid Artery, Common / Q000502:physiology*; D002648:Child; D005260:Female; D006400:Hematocrit; D006801:Humans; D008297:Male; D008875:Middle Aged; D012044:Regression Analysis; D012737:Sex Factors; D018709:Statistics, Nonparametric; D013314:Stress, Mechanical