Biorheology - Volume 39, issue 3-4

Authors: Caro, Colin | Jeremy, Jamie | Watkins, Nick | Bulbulia, Richard | Angelini, Gianni | Smith, Frank | Wan, Song | Yim, Anthony | Sherwin, Spencer | Peiró, Joaquim | Papaharilaou, Yannis | Falzon, Brian | Giordana, Sergio | Griffiths, Clydd

Article Type: Research Article

Abstract: The long‐term success of arterial bypass grafting with autologous saphenous veins is limited by neointimal hyperplasia (NIH), which seemingly develops preferentially at sites where hydrodynamic wall shear is low. Placement of a loose‐fitting, porous stent around end‐to‐end, or end‐to‐side, autologous saphenous vein grafts on the porcine common carotid artery has been found significantly to reduce NIH, but the mechanism is unclear. In a preliminary study, we implanted autologous saphenous vein grafts bilaterally on the common carotid arteries of pigs, placing a stent around one graft and leaving the contralateral graft unstented. At sacrifice 1 month post implantation, the grafts were …pressure fixed in situ and resin casts were made. Unstented graft geometry was highly irregular, with non‐uniform dilatation, substantial axial lengthening, curvature, kinking, and possible long‐pitch helical distortion. In contrast, stented grafts showed no major dilatation, lengthening or curvature, but there was commonly fine corrugation, occasional slight kinking or narrowing of segments, and possible long‐pitch helical distortion. Axial growth of grafts against effectively tethered anastomoses could account for these changes. CFD studies are planned, using 3D MR reconstructions, on the effects of graft geometry on the flow. Abnormality of the flow could favour the development of vascular pathology, including NIH. Show more

Keywords: Graft geometry, graft casts, graft elongation, graft buckling

Citation: Biorheology, vol. 39, no. 3-4, pp. 507-512, 2002

Authors: Friedman, Morton H.

Article Type: Research Article

Abstract: Geometric parameters and features vary within the vasculature. Furthermore, at any given anatomic site, there are substantial variations in geometry among individuals. These variations can contribute to a corresponding variability in the hemodynamic environment and, to the extent that hemodynamics affects the atherosclerotic process, the progress of vascular disease. Measurements of the geometry and wall morphometry of post‐mortem human coronary arteries demonstrate a relationship between these variables that supports the notion that geometric variations can contribute to a corresponding variability in the local rate of progression of arterial disease. The dynamic geometry of the coronary arteries also varies from site …to site and among individuals, and this variability too may play a role in the epidemiology of coronary artery disease. Show more

Citation: Biorheology, vol. 39, no. 3-4, pp. 513-517, 2002

Authors: Goubergrits, L. | Affeld, K. | Fernandez‐Britto, J. | Falcon, L.

Article Type: Research Article

Abstract: The influence of blood flow on the depositions and development of atherosclerotic lesions have been observed and described since the 19th century. Observations have shown that depositions correlate with regions of low wall shear stress. However, the exact correlations between depositions, vessel geometry and flow parameters are not yet known. The purpose of this study was the quantification of atherosclerosis risk factors in carotid bifurcation. This artery has attracted particular interest because lesions are often found in this bifurcation. Post mortem, the arteries are excised and vessel casts are produced. Afterwards, the arteries are analyzed morphometrically. The vessel casts are …used for the assessment of some geometrical parameters. 31 carotid bifurcations were analyzed in this study. Eight vessel casts were digitized and rendered three‐dimensional mathematical models of the arteries. These data were imported by the computational fluid dynamics program FLUENT. Further, the blood flow was reconstructed in a computer model based on the individual vessel geometry. The flow parameters, such as velocity, pressure and wall shear stress were computed. At the same time the geometrical parameters and wall alterations are known. This permits the comparison of the anatomical shape and its flow with the distribution and level of the wall alterations. Show more

Keywords: Carotid bifurcation, wall shear stress, computational fluid dynamics

Citation: Biorheology, vol. 39, no. 3-4, pp. 519-524, 2002

Authors: Papaharilaou, Y. | Doorly, D.J. | Sherwin, S.J. | Peiro, J. | Griffith, C. | Cheshire, N. | Zervas, V. | Anderson, J. | Sanghera, B. | Watkins, N. | Caro, C.G.

Article Type: Research Article

Abstract: We report methods for (a) transforming a three‐dimensional geometry acquired by magnetic resonance angiography (MRA) in vivo, or by imaging a model cast, into a computational surface representation, (b) use of this to construct a three dimensional numerical grid for computational fluid dynamic (CFD) studies, and (c) use of the surface representation to produce a stereo‐lithographic replica of the real detailed geometry, at a scale convenient for detailed magnetic resonance imaging (MRI) flow studies. This is applied to assess the local flow field in realistic geometry arterial bypass grafts. Results from a parallel numerical simulation and MRI measurement of flow …in an aorto‐coronary bypass graft with various inlet flow conditions demonstrate the strong influence of the graft inlet waveform on the perianastomotic flow field. A sinusoidal and a multi harmonic coronary flow waveform both with a mean Reynolds number (Re) of 100 and a Womersley parameter of 2.7 were applied at the graft inlet. A weak axial flow separation region just distal to the toe was found in sinusoidal flow near end deceleration (Re = 25). At the same location and approximately the same point in the cycle (Re = 30) but in coronary flow, the axial flow separation was stronger and more spatially pronounced. No axial flow separation occurred in steady flow for Re = 100. Numerical predictions indicate a region in the vicinity of the suture line (where there is a local narrowing of the graft) with a wall shear magnitude in excess of five times that associated with fully developed flow at the graft inlet. Show more

Keywords: Coronary arteries, hemodynamics, shear stress, distal anastomosis, unsteady flow

Citation: Biorheology, vol. 39, no. 3-4, pp. 525-531, 2002

Authors: Weinberg, Peter D.

Article Type: Research Article

Abstract: The distribution of lesions around arterial branch points is complex and changes with age. Four distinct patterns – here termed the arrowhead pattern, the lateral pattern, the upstream streak and the volcano – have been reported around the origins of intercostal arteries in the human aorta at different ages. The first two patterns also occur in young and old rabbits, the third in minipigs, and the fourth in apolipoprotein E/LDL receptor knockout mice. It is unclear how all four patterns can depend solely on flow; a particular problem is that the prevalence of lipid deposition remains highly nonuniform for several …branch diameters upstream of the ostium. Variations in the prevalence of fatty streaks may originate near the branch and then spread by the migration of activated endothelial cells towards the heart. The pattern of raised lesions may reflect a different aetiology. Show more

Keywords: Atherosclerosis, distribution, haemodynamics, endothelial migration

Citation: Biorheology, vol. 39, no. 3-4, pp. 533-537, 2002

Authors: Dewey, Jr., C. Forbes

Article Type: Research Article

Abstract: This paper is presented as a summary and synthesis of the presentations at the conference entitled “Breaking Symmetry in Haemodynamics”. As the accompanying papers will attest, there has been enormous progress in understanding the effects of fluid flow on the arterial endothelium and the consequential effects on the vessel wall. It is now clearly understood that the focal lesions found in atherosclerotic arteries are the product of asymmetrical flow and the resulting disturbed flow that occurs near arterial bifurcations and other selected points around the human vasculature. The flow in large vessels can now be determined accurately with MR and …in vitro cast models. Although theory allows arterial flow to be characterized by asymmetry in time and space, our understanding of the processes that act to translate this asymmetry into pathology is becoming much more symmetric, or complete. The new frontiers of research in arterial flow are now translating to smaller scales, at the cellular level and below. Show more

Keywords: Fluid shear stress, arterial bifurcations, endothelial cells, cell cytoskeleton, actin polymerization, atherosclerosis, haemodynamics

Citation: Biorheology, vol. 39, no. 3-4, pp. 541-549, 2002

Article Type: Abstract

Citation: Biorheology, vol. 39, no. 3-4, pp. 553-575, 2002