title: Large variations in absolute wall shear stress levels within one species and between species.
abstract: Wall shear stress (WSS), the frictional force between blood and endothelium, is an important determinant of vascular function. It is generally assumed that WSS remains constant at a reference value of 15 dyn/cm(2). In a study of small rodents, we realized that this assumption could not be valid. This review presents an overview of recent studies in large and small animals where shear stress was measured, derived from velocity measurements or otherwise, in large vessels. The data show that large variations exist within a single species (human: variation of 2-16 N/m(2)). Moreover, when we compared different species at the same location within the arterial tree, an inverse relationship between animal size and wall shear stress was noted. When we related WSS to diameter, a unique relationship was derived for all species studied. This relationship could not be described by the well-known r(3) law of Murray, but by the r(2) law introduced by Zamir et al. in 1972. In summary, by comparing data from the literature, we have shown that: (i) the assumption of a physiological WSS level of approximately 15 dyn/cm(2) for all straight vessels in the arterial tree is incorrect; (ii) WSS is not constant throughout the vascular tree; (iii) WSS varies between species; (iv) WSS is inversely related to the vessel diameter. These data support an "r(2) law" rather than Murray's r(3) law for the larger vessels in the arterial tree.
authors.affiliation: Department of Cardiology, Thoraxcenter, Erasmus MC, Rotterdam, The Netherlands. c.cheng@erasmusmc.nl
authors.forename: Caroline
authors.initials: C
authors.lastname: Cheng
authors.forename: Frank
authors.initials: F
authors.lastname: Helderman
authors.forename: Dennie
authors.initials: D
authors.lastname: Tempel
authors.forename: Dolf
authors.initials: D
authors.lastname: Segers
authors.forename: Beerend
authors.initials: B
authors.lastname: Hierck
authors.forename: Rob
authors.initials: R
authors.lastname: Poelmann
authors.forename: Arie
authors.initials: A
authors.lastname: van Tol
authors.forename: Dirk J
authors.initials: DJ
authors.lastname: Duncker
authors.forename: Danielle
authors.initials: D
authors.lastname: Robbers-Visser
authors.forename: Nicolette T C
authors.initials: NT
authors.lastname: Ursem
authors.forename: Rien
authors.initials: R
authors.lastname: van Haperen
authors.forename: Jolanda J
authors.initials: JJ
authors.lastname: Wentzel
authors.forename: Frank
authors.initials: F
authors.lastname: Gijsen
authors.forename: Anton F W
authors.initials: AF
authors.lastname: van der Steen
authors.forename: Rini
authors.initials: R
authors.lastname: de Crom
authors.forename: Rob
authors.initials: R
authors.lastname: Krams
mesh_terms: D000818:Animals; D001158:Arteries / Q000000981:diagnostic imaging / Q000502:physiology; D001696:Biomechanical Phenomena; D001783:Blood Flow Velocity / Q000502:physiology*; D004285:Dogs; D004730:Endothelium, Vascular / Q000033:anatomy & histology / Q000502:physiology*; D006801:Humans; D051379:Mice; D011673:Pulsatile Flow / Q000502:physiology*; D011817:Rabbits; D051381:Rats; D013045:Species Specificity; D018615:Ultrasonography, Doppler, Color