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  • Journal article
    Chooi KY, Comerford A, Sherwin SJ, Weinberg PDet al., 2016,

    Intimal and medial contributions to the hydraulic resistance of the arterial wall at different pressures: a combined computational and experimental study

    , Journal of the Royal Society Interface, Vol: 11, ISSN: 1742-5689

    The hydraulic resistances of the intima and media determine water flux and the advection of macromolecules into and across the arterial wall. Despite several experimental and computational studies, however, these trans- port processes and their dependence on transmural pressure remain incompletely understood. Here we use a combination of experimental and computational methods to ascertain how the hydraulic permeability of the rat abdominal aorta depends on these two layers and how it is affected by structural rearrangement of the media under pressure. Ex vivo experiments determined the conductance of the whole wall, the thickness of the media, and the geometry of medial smooth muscle cells and extracellular matrix. Numerical methods were used to compute water flux through the media. Intimal values were obtained by subtraction. A mechanism was iden- tified that modulates pressure-induced changes in medial transport properties: compaction of the extracellular matrix leading to spatial reorganisation of smooth muscle cells. This is summarised in an empirical constitutive law for permeability and volumetric strain. This led to the physiologically interesting observation that, as a consequence of the changes in medial microstructure, the relative contributions of the intima and media to the hydraulic resistance of the wall depend on the applied pressure; medial resistance dominated at pressures above ∼93mmHg in this vessel.

  • Conference paper
    Tzortzis KN, Roney CH, Qureshi NA, Ng FU, Lim PHANGBOON, Sherwin S, Peters NS, Cantwell Cet al., 2015,

    Influence of left atrial geometry on rotor core trajectories in a model of atrial fibrillation

    , Computing in Cardiology, Publisher: IEEE, Pages: 481-484, ISSN: 2325-8861

    Left atrial anatomy and myocardial architecture areknown to influence rotor initiation and maintenance.However, identifying their relative contribution clinicallyis challenging. The present study aims to investigate insilico the effect of left atrial geometry in isolation onrotor generation and evolution through thespatiotemporal tracking of phase singularities. Aftermeandering for a short period of time, rotors areattracted to specific areas of the chamber where there ishigh curvature, primarily near the base of the left atrialappendage and the junctions of the pulmonary veins. Thissuggests that the left atrial anatomy could play a key rolein the perpetuation of fibrillatory activity.

  • Journal article
    Cantwell CD, Moxey D, Comerford A, Bolis A, Rocco G, Mengaldo G, de Grazia D, Yakovlev S, Lombard J-E, Ekelschot D, Jordi B, Xu H, Mohamied Y, Eskilsson C, Nelson B, Vos P, Biotto C, Kirby RM, Sherwin SJet al., 2015,

    Nektar++: An open-source spectral/hp element framework

    , Computer Physics Communications, Vol: 192, Pages: 205-219, ISSN: 1879-2944

    Nektar++ is an open-source software framework designed to support the development of high-performance scalable solvers for partial differential equations using the spectral/hphp element method. High-order methods are gaining prominence in several engineering and biomedical applications due to their improved accuracy over low-order techniques at reduced computational cost for a given number of degrees of freedom. However, their proliferation is often limited by their complexity, which makes these methods challenging to implement and use. Nektar++ is an initiative to overcome this limitation by encapsulating the mathematical complexities of the underlying method within an efficient C++ framework, making the techniques more accessible to the broader scientific and industrial communities. The software supports a variety of discretisation techniques and implementation strategies, supporting methods research as well as application-focused computation, and the multi-layered structure of the framework allows the user to embrace as much or as little of the complexity as they need. The libraries capture the mathematical constructs of spectral/hphp element methods, while the associated collection of pre-written PDE solvers provides out-of-the-box application-level functionality and a template for users who wish to develop solutions for addressing questions in their own scientific domains.

  • Journal article
    Mohamied Y, Rowland EM, Bailey EL, Sherwin SJ, Schwartz MA, Weinberg PDet al., 2015,

    Change of Direction in the Biomechanics of Atherosclerosis

    , ANNALS OF BIOMEDICAL ENGINEERING, Vol: 43, Pages: 16-25, ISSN: 0090-6964
  • Journal article
    Mohri Z, Rowland EM, Clarke LA, De Luca A, Peiffer V, Krams R, Sherwin SJ, Weinberg PDet al., 2014,

    Elevated Uptake of Plasma Macromolecules by Regions of Arterial Wall Predisposed to Plaque Instability in a Mouse Model

    , PLoS One, Vol: 9, ISSN: 1932-6203

    Atherosclerosis may be triggered by an elevated net transport of lipid-carryingmacromolecules from plasma into the arterial wall. We hypothesised that whetherlesions are of the thin-cap fibroatheroma (TCFA) type or are less fatty and morefibrous depends on the degree of elevation of transport, with greater uptake leadingto the former. We further hypothesised that the degree of elevation can depend onhaemodynamic wall shear stress characteristics and nitric oxide synthesis. Placinga tapered cuff around the carotid artery of apolipoprotein E -/- mice modifiespatterns of shear stress and eNOS expression, and triggers lesion development atthe upstream and downstream cuff margins; upstream but not downstream lesionsresemble the TCFA. We measured wall uptake of a macromolecular tracer in thecarotid artery of C57bl/6 mice after cuff placement. Uptake was elevated in theregions that develop lesions in hyperlipidaemic mice and was significantly moreelevated where plaques of the TCFA type develop. Computational simulations andeffects of reversing the cuff orientation indicated a role for solid as well as fluidmechanical stresses. Inhibiting NO synthesis abolished the difference in uptakebetween the upstream and downstream sites. The data support the hypothesis thatexcessively elevated wall uptake of plasma macromolecules initiates thedevelopment of the TCFA, suggest that such uptake can result from solid and fluidmechanical stresses, and are consistent with a role for NO synthesis. Modificationof wall transport properties might form the basis of novel methods for reducingplaque rupture.

  • Conference paper
    Roney CH, Cantwell C, Qureshi NA, Ali RL, Chang ETY, Lim PB, Sherwin SJ, Peters NS, Siggers JH, Ng FSet al., 2014,

    An Automated Algorithm for Determining Conduction Velocity, Wavefront Direction and Focal Source Location using a Multipolar Catheter

    , IEEE Engineering in Medicine and Biology Conference

    Determining locations of focal arrhythmia sources and quantifying myocardial conduction velocity (CV) are two major challenges in clinical catheter ablation cases. CV, wavefront direction and focal source location can be estimated from multipolar catheter data, but currently available methods are time-consuming, limited to specific electrode configurations, and can be inaccurate. We developed automated algorithms to rapidly identify CV from multipolar catheter data with any arrangement of electrodes, whilst providing estimates of wavefront direction and focal source position, which can guide the catheter towards a focal arrhythmic source. We validated our methods using simulations on realistic human left atrial geometry. We subsequently applied them to clinically-acquired intracardiac electrogram data, where CV and wavefront direction were accurately determined in all cases, whilst focal source locations were correctly identified in 2/3 cases. Our novel automated algorithms can potentially be used to guide ablation of focal arrhythmias in real-time in cardiac catheter laboratories.

  • Conference paper
    Ali RL, Cantwell CD, Roney CH, Qureshi NA, Lim PB, Siggers JH, Sherwin SJ, Peters NSet al., 2014,

    A novel method for quantifying localised correlation of late-gadolinium intensity with conduction velocity

    , Computing in Cardiology (CinC) 2014, Pages: 193-196

    Patient-specific computer models of the human atria have the potential to aid clinical intervention in the treatment of cardiac arrhythmias. However, quantifying and integrating the heterogeneous qualities of the myocardium through imaging is particularly challenging due to the unknown relationship between voxel intensity and tissue conductivities. We establish a method to determine the relationship between local conduction velocity and scar density, extracted through the analysis of late-gadolinium enhanced magnetic resonance imaging data.

  • Journal article
    Peiffer V, Sherwin SJ, Weinberg PD, 2013,

    Does low and oscillatory wall shear stress correlate spatially with early atherosclerosis? A systematic review

    , CARDIOVASCULAR RESEARCH, Vol: 99, Pages: 242-250, ISSN: 0008-6363
  • Journal article
    Peiffer V, Bharath AA, Sherwin SJ, Weinberg PDet al., 2013,

    A Novel Method for Quantifying Spatial Correlations Between Patterns of Atherosclerosis and Hemodynamic Factors

  • Conference paper
    Alastruey J, Parker KH, Sherwin SJ, 2012,

    Arterial pulse wave haemodynamics

    , Pages: 401-442

    The shape of the arterial pulse wave is intimately related to the physical properties of the cardiovascular system. Understanding the mechanisms underlying this relation is clinically relevant, since pulse waveforms carry valuable information for the diagnosis and treatment of disease. We overview some numerical, theoretical and experimental efforts (using in vivo and in vitro data) made in this field of research, focusing on the physical aspects of arterial pulse wave propagation in the systemic circulation. The mathematical and numerical tools that we describe are based on the one-dimensional formulation in the time-domain. © BHR Group 2012 Pressure Surges 11.

  • Conference paper
    Peiffer V, Rowland M, Weinberg PD, Sherwin SJet al., 2011,

    Database of rabbit aortic geometries for use in computational flow studies

    , Pages: 19-20
  • Conference paper
    Clavica F, Alastruey J, Borlotti A, Sherwin SJ, Khir AWet al., 2010,

    One-dimensional computational model of pulse wave propagation in the human bronchial tree

    , 32nd Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Buenos Aires, Argentina
  • Journal article
    Alastruey J, Parker KH, Peiro J, Sherwin SJet al., 2009,

    Analysing the pattern of pulse waves in arterial networks: a time-domain study

    , JOURNAL OF ENGINEERING MATHEMATICS, Vol: 64, Pages: 331-351, ISSN: 0022-0833
  • Journal article
    Alastruey J, Sherwin SJ, Parker KH, Rubens DDet al., 2009,

    Placental transfusion insult in the predisposition for SIDS: A mathematical study

    , EARLY HUMAN DEVELOPMENT, Vol: 85, Pages: 455-459, ISSN: 0378-3782
  • Journal article
    Moore P, Barlis P, Spiro J, Ghimire G, Roughton M, Di Mario C, Wallis W, Ilsley C, Mitchell A, Mason M, Kharbanda R, Vincent P, Sherwin S, Dalby Met al., 2009,

    A Randomized Optical Coherence Tomography Study of Coronary Stent Strut Coverage and Luminal Protrusion With Rapamycin-Eluting Stents

    , Journal of the American College of Cardiology Cardiovascular Interventions, Vol: 2, Pages: 437-444, ISSN: 1936-8798

    Objectives We used optical coherence tomography, which has a resolution of <20 mu m, to analyze thin layers of neointima in rapamycin-eluting coronary stents.Background Lack of neointimal coverage has been implicated in the pathogenesis of drug-eluting coronary stent thrombosis. Angiography and intracoronary ultrasound lack the resolution to examine this.Methods We conducted a randomized trial in patients receiving polymer-coated rapamycin-eluting stents (Cypher, Cordis, Johnson & Johnson, Miami, Florida) and nonpolymer rapamycin-eluting stents (Yukon, Translumina, Hechingen, Germany) to examine neointimal thickness, stent strut coverage, and protrusion at 90 days. Twenty-four patients (n = 12 for each group) underwent stent deployment and invasive follow-up at 90 days with optical coherence tomography. The primary end point was binary stent strut coverage. Coprimary end points were neointimal thickness and stent strut luminal protrusion.Results No patient had angiographic restenosis. For polymer-coated and nonpolymer rapamycin-eluting stents, respectively, mean (SD), neointimal thickness was 77.2 (25.6) mu m versus 191.2 (86.7) mu m (p < 0.001). Binary stent strut coverage was 88.3% (11.8) versus 97.2% (6.1) (p = 0.030). Binary stent strut protrusion was 26.5% (17.5) versus 4.8% (8.6) (p = 0.001).Conclusions Mean neointimal thickness for the polymer-coated rapamycin-eluting stent was significantly less than the nonpolymer rapamycin-eluting stent but as a result coverage was not homogenous, with >10% of struts being uncovered. High-resolution imaging allowed development of the concept of the protrusion index, and >25% of struts protruded into the vessel lumen with the polymer-coated rapamycin-eluting stent compared with <5% with the nonpolymer rapamycin-eluting stent. These findings may have important implications for the risk of stent thrombosis and, therefore, future stent design. (An optical coherence tomography study to determine stent coverag

  • Journal article
    Vincent PE, Sherwin SJ, Weinberg PD, 2009,

    The Effect of a Spatially Heterogeneous Transmural Water Flux on Concentration Polarization of Low Density Lipoprotein in Arteries

    , Biophysical Journal, Vol: 96, Pages: 3102-3115, ISSN: 0006-3495

    Uptake of low density lipoprotein (LDL) by the arterial wall is likely to play a key role in atherogenesis. A particular process that may cause vascular scale heterogeneity in the rate of transendothelial LDL transport is the formation of a flow-dependent LDL concentration polarization layer on the luminal surface of the arterial endothelium. In this study, the effect of a spatially heterogeneous transmural water flux (that traverses the endothelium only via interendothelial cell clefts) on such concentration polarization is investigated numerically. Unlike in previous investigations, realistic intercellular cleft dimensions are used here and several values of LDL diffusivity are considered. Particular attention is paid to the spatially averaged LDL concentration adjacent to different regions of the endothelial surface, as such measures may be relevant to the rate of transendothelial LDL transport. It is demonstrated in principle that a heterogeneous transmural water flux can act to enhance such measures, and cause them to develop a shear dependence (in addition to that caused by vascular scale flow features, affecting the overall degree of LDL concentration polarization). However, it is shown that this enhancement and additional shear dependence are likely to be negligible for a physiologically realistic transmural flux velocity of 0.0439 mu m s(-1) and an LDL diffusivity (in blood plasma) of 28.67 mu m(2) s(-1). Hence, the results imply that vascular scale studies of LDL concentration polarization are justified in ignoring the effect of a spatially heterogeneous transmural water flux.

  • Journal article
    Peiro J, Sherwin SJ, Giordana S, 2008,

    Automatic reconstruction of a patient-specific high-order surface representation and its application to mesh generation for CFD calculations

    , MEDICAL & BIOLOGICAL ENGINEERING & COMPUTING, Vol: 46, Pages: 1069-1083, ISSN: 0140-0118
  • Journal article
    Cookson AN, Doorly DJ, Sherwin SJ, 2008,

    Mixing through stirring of steady flow in small amplitude helical pipes

    , Ann. Biomed. Engrg., Vol: 37, Pages: 710-721

    In this paper we numerically simulate flow in a helical tube for physiological conditions using a co-ordinate mapping of the Navier–Stokes equations. Helical geometries have been proposed for use as bypass grafts, arterial stents and as an idealized model for the out-of-plane curvature of arteries. Small amplitude helical tubes are also currently being investigated for possible application as A–V shunts, where preliminary in vivo tests suggest a possibly lower risk of thrombotic occlusion. In-plane mixing induced by the geometry is hypothesized to be an important mechanism. In this work, we focus mainly on a Reynolds number of 250 and investigate both the flow structure and the in-plane mixing in helical geometries with fixed pitch of 6 tube diameters (D), and centerline helical radius ranging from 0.1D to 0.5D. High-order particle tracking, and an information entropy measure is used to analyze the in-plane mixing. A combination of translational and rotational reference frames are shown to explain the apparent discrepancy between flow field and particle trajectories, whereby particle paths display a pattern characteristic of a double vortex, though the flow field reveals only a single dominant vortex. A radius of 0.25D is found to provide the best trade-off between mixing and pressure loss, with little increase in mixing above R = 0.25D, whereas pressure continues to increase linearly.

  • Conference paper
    Kazakidi A, Sherwin SJ, Weinberg PD, 2007,

    Reverse flow in arterial branches influences wall shear stress patterns around branch ostia

    , Joint Autumn Meeting of the British-Society-for-Cardiovascular-Research/British-Atherosclerosis-Society, Publisher: B M J PUBLISHING GROUP, ISSN: 1355-6037
  • Conference paper
    Vincent PE, Sherwin SJ, Weinberg PD, 2007,

    Computational investigation of a mechanism by which blood flow could control lipoprotein uptake by the arterial

    , Joint Autumn Meeting of the British-Society-for-Cardiovascular-Research/British-Atherosclerosis-Society, Publisher: B M J PUBLISHING GROUP, ISSN: 1355-6037
  • Journal article
    Alastruey J, Parker KH, Peiro J, Byrd SM, Sherwin SJet al., 2007,

    Modelling the circle of Willis to assess the effects of anatomical variations and occlusions on cerebral flows

    , JOURNAL OF BIOMECHANICS, Vol: 40, Pages: 1794-1805, ISSN: 0021-9290
  • Conference paper
    Lee KE, Parker KH, Sherwin SJ, Car CGet al., 2007,

    The effects of geometrical configurations on steady flow in non-planar double bends

    , World Congress on Medical Physics and Biomedical Engineering, Publisher: SPRINGER-VERLAG BERLIN, Pages: 3461-+, ISSN: 1680-0737
  • Journal article
    Dongbin Xiu, Spencer Sherwin, 2007,

    Parametric uncertainty analysis of pulse wave propagation in a model of a human arterial network

    , J. Computational Physics, Vol: 226, Pages: 1385-1407
  • Journal article
    Alastruey J, Parker KH, Peiró J, Sherwin SJet al., 2006,

    Can the modified Allen's test always detect sufficient collateral flow in the hand? A computational study.

    , Comput Methods Biomech Biomed Engin, Vol: 9, Pages: 353-361, ISSN: 1025-5842

    Blood flow in the largest arteries of the arm up to the digital arteries is numerically modelled using the one-dimensional equations of pressure and flow wave propagation in compliant vessels. The model can be applied to different anatomies of arterial networks and can simulate compression of arteries, these allowing us to simulate the modified Allen's test (MAT) and to assess its suitability for the detection of sufficient collateral flow in the hand if radial blood supply is interrupted. The test measures blood flow in the superficial palmar arch before and during compression of the radial artery. The absence of reversal flow in the palmar arch with the compression indicates insufficient collateral flow and is referred to as a positive MAT. This study shows that small calibres of the superficial palmar arch and insufficient compression of the radial artery can lead to false-positive results. Measurement of the drop in digital systolic pressures with compression of the radial artery has proved to be a more sensitive test to predict the presence of sufficient ulnar collateral flow in networks with small calibres of the superficial palmar arch. However, this study also shows that digital pressure measurements can fail in detecting enough collateral flow if the radial artery is insufficiently compressed.

  • Journal article
    Giordana S, Sherwin SJ, Peiro J, Doorly DJ, Crane JS, Lee KE, Cheshire NJW, Carco CGet al., 2005,

    Local and global geometric influence on steady flow in distal anastomoses of peripheral bypass grafts

  • Conference paper
    Gambaruto AM, Radaelli A, Doorly DJ, Sherwin SJ, Peiro Jet al., 2005,

    Sensitivity study on by-pass graft reconstruction with emphasis on flow solutions

    , Pages: 832-833
  • Journal article
    Sherwin SJ, Blackburn HM, 2005,

    Three-dimensional instabilities and transition of steady and pulsatile axisymmetric stenotic flows

    , JOURNAL OF FLUID MECHANICS, Vol: 533, Pages: 297-327, ISSN: 0022-1120
  • Conference paper
    Pitt RE, Sherwin SJ, Theofilis V, 2005,

    BiGlobal stability analysis of steady flow in constricted channel geometries

    , 8th ICFD Conference on Numerical Methods for Fluid Dynamics, Publisher: JOHN WILEY & SONS LTD, Pages: 1229-1235, ISSN: 0271-2091
  • Journal article
    Giordana S, Sherwin SJ, Peiro J, Doorly DJ, Papaharilaou Y, Caro CG, Watkins N, Cheshire N, Jackson M, Bicknall C, Zervas Vet al., 2005,

    Automated classification of peripheral distal by-pass geometries reconstructed from medical data

    , JOURNAL OF BIOMECHANICS, Vol: 38, Pages: 47-62, ISSN: 0021-9290
  • Conference paper
    varghese S, Frankel S, Pitt R, Sherwin SJet al., 2004,

    Numerical simulation of pulsatile flow through stenotic vessels

    , Turbulence and shear flow phenomena, Sendai, Japan, 25 - 27 June 2003

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