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This paper aims at evaluating the changes that head rotation poses on morphological and flow characteristics of the carotid bifurcation (CB) and on the distribution of parameters that are regarded as important in atherosclerosis development, such as relative particle residence time (RRT), normalized oscillatory shear index (nOSI), and helicity (HL). Using a subject-specific approach, six healthy volunteers were MR-scanned in two head postures: supine neutral and prone with rightward head rotation. Cross-sectional flow velocity distribution was obtained using phase-contrast MRI at the common carotid artery (CCA). Our results indicate that peak systolic flow rate is reduced at the prone position in most cases for both CCAs. Morphological MR images are used to segment and construct the CB models. Numerical simulations are performed and areas exposed to high helicity or unfavorable hemodynamics are calculated. Head rotation affects the instantaneous spatial extent of high helicity regions. Posture-related observed differences in the distribution of nOSI and RRT suggest that inlet flow waveform tends to moderate geometry-induced changes in the qualitative and quantitative distribution of atherosclerosis-susceptible wall regions. Overall, presented results indicate that an individualized approach is required to fully assess the postural role in atherosclerosis development and in complications arising in stenotic and stented vessels. © 2013 IEEE. 18 3 783 789 Cited By :6

Stimulated by a recent controversy regarding pressure drops predicted in a giant aneurysm with a proximal stenosis, the present study sought to assess variability in the prediction of pressures and flow by a wide variety of research groups. In phase I, lumen geometry, flow rates, and fluid properties were specified, leaving each research group to choose their solver, discretization, and solution strategies. Variability was assessed by having each group interpolate their results onto a standardized mesh and centerline. For phase II, a physical model of the geometry was constructed, from which pressure and flow rates were measured. Groups repeated their simulations using a geometry reconstructed from a micro-computed tomography (CT) scan of the physical model with the measured flow rates and fluid properties. Phase I results from 25 groups demonstrated remarkable consistency in the pressure patterns, with the majority predicting peak systolic pressure drops within 8% of each other. Aneurysm sac flow patterns were more variable with only a few groups reporting peak systolic flow instabilities owing to their use of high temporal resolutions. Variability for phase II was comparable, and the median predicted pressure drops were within a few millimeters of mercury of the measured values but only after accounting for submillimeter errors in the reconstruction of the life-sized flow model from micro-CT. In summary, pressure can be predicted with consistency by CFD across a wide range of solvers and solution strategies, but this may not hold true for specific flow patterns or derived quantities. Future challenges are needed and should focus on hemodynamic quantities thought to be of clinical interest.

Variations in blood oxygen concentrations are not only part of the normal physiology but they may also indicate various pathological conditions. In the present work, we examined the influence of oxygen concentration on the rheological properties of whole human blood. Blood samples were taken from two healthy donors, a male and a female, with hematocrits 0.47 and 0.42, respectively. In addition to the original samples of normal oxygen concentration (normoxemia), samples of different blood oxygen level were also prepared by using the perfusion cell equipped with a gas supply to induce either hypoxemia by driving out the oxygen saturating blood by nitrogen or hyperoxemia by saturating blood with oxygen. The rheology of the samples was measured using a Physica MCR 301 rheometer equipped with a sensor designed for hemorheology. The rheological results showed that oxygen-depleted blood exhibited lower viscosity and a lower yield stress when fitted to the Herschel-Bulkley constitutive model. Blood flow simulations of the effect of oxygen concentration on the local hemodynamics were also carried out in an idealized axisymmetric 75 % stenosis and in a realistic carotid bifurcation geometry constructed from MRI images obtained from a healthy male volunteer. The modified Herschel-Bulkley model with the Papanastasiou regularization was used to account for both the shear thinning and finite yield stress properties of blood. The results of this work showed that oxygen concentration affects the rheology and flow behavior of blood, suggesting compensatory responses under hypoxic conditions leading to a lower blood viscosity. © 2016, Springer-Verlag Berlin Heidelberg. 55 11-12 921 933

Head and neck postures may cause morphology changes to the geometry of the carotid bifurcation (CB) that alter the low and oscillating wall shear stress (WSS) regions previously reported as important in the development of atherosclerosis. Here the right and left CB were imaged by MRI in two healthy subjects in the neutral head posture with the subject in the supine position and in two other head postures with the subject in the prone position: (1) rightward rotation up to 80, and (2) leftward rotation up to 80. Image-based computational models were constructed to investigate the effect of posture on arterial geometry and local hemodynamics. The area exposure to unfavorable hemodynamics, based on thresholds set for oscillatory shear index (OSI), WSS and relative residence time, was used to quantify the hemodynamic impact on the wall. Torsion of the head was found to: (1) cause notable changes in the bifurcation and internal carotid artery angles and, in most cases, on cross-sectional area ratios for common, internal and external carotid artery, (2) change the spatial distribution of wall regions exposed to unfavorable hemodynamics, and (3) cause a marked change in the hemodynamic burden on the wall when the OSI was considered. These findings suggest that head posture may be associated with the genesis and development of atherosclerotic disease as well as complications in stenotic and stented vessels. © 2012 International Federation for Medical and Biological Engineering. 51 1-2 207 218 Cited By :7

The use of realistic anatomic human carotid artery bifurcation (CB) models with a realistic blood waveform leads to physiologically relevant numerical simulations. To study the effects of head posture on the geometry and hemodynamics of the CB, Magnetic resonance imaging (MRI) was used on six healthy volunteers in two different head postures: 1) the supine neutral (N) and 2) the prone with rightward head rotation (P) up to 80°. Geometric differences with posture change in both the left (LCA) and right (RCA) carotid arteries were reported before [1]. The blood velocity waveform for each individual was obtained using phase-contrast MRI (PCMRI) at five diameters upstream of CB. Results have shown that peak systolic blood flow rate is reduced, in the prone position for both RCA and LCA in all six volunteers. To investigate the effects of the reduced peak systolic flow on the hemodynamics of the CB, numerical simulations were performed for a volunteer that exhibited the most geometric changes for the prone position in comparison to the other five based on specific geometric parameters [1, 2]. For the two investigated head postures the observed measured input waveforms were used.Copyright © 2013 by ASME

Atherosclerosis is the third leading cause of morbidity and mortality in the Western world. Low and oscillating wall shear stress (WSS) regions have been previously reported as parameters that correlate with the development of atherosclerosis. In this study we investigated geometric and hemodynamic changes in the carotid bifurcation as a result of posture change. Data from magnetic resonance imaging (MRI) were used to construct three dimensional (3D) surface models and computational fluid dynamic (CFD) fields. Two healthy volunteers were imaged by MRI in three different head postures: a) the supine neutral (N) head position, b) the prone position with leftward head rotation (LR) up to 80° and c) the prone position with rightward head rotation (RR) up to 80°. The area exposure to unfavorable hemodynamics, based on thresholds set for oscillatory shear index (OSI), WSS and relative residence times (RRT), was used to quantify the hemodynamic impact on the wall. Significant change in the hemodynamic burden on the wall was found for the OSI. The velocity profile at the common carotid artery (CCA) upstream of the carotid bifurcation (CB) was investigated at the supine and RR prone position for six healthy volunteers. The results indicated that blood flow rate decreased at peak systole, for the prone position for both the right and left CCAs. © 2012 IEEE. 727 731 Sponsors: IEEE IEEE Computer Society University of Cyprus Biological and AI Foundation (BAIF) Frederick University Conference code: 95206

Previous investigators have reported that posture changes may influence the geometry and hemodynamics of the carotid bifurcation [1,2]. As a result, head rotation may cause geometric changes that alter the hemodynamic variables previously cited to correlate with the development of atherosclerosis. Glor et al. [1] had reported changes in the right carotid bifurcation geometry with leftward rotation of the head. Aristokleous et al. [2] have reported that geometric differences in the right and left carotid bifurcation occur with a rightward rotation of the head in 10 healthy volunteers [2]. Also, a similar study on bilateral head rotation on the left and right carotid bifurcation of two volunteers has shown similar results [3]. In this study a group of four patients with atherosclerotic disease in the carotid arteries was investigated at two head postures, a) the supine neutral and b) the prone sleeping with head rotation leftwards up to 80° to investigate the level of stenosis and the changes in geometric parameters with head rotation.

This work is a collaborative effort between the Biomechanics and Living System Analysis Laboratory (BIOLISYS) in Cyprus and the Biomechanics Laboratory of IACM/FORTH in Greece. Both labs combine interdisciplinary skills from engineering, medicine and biology to provide solutions to clinical problems associated with cardiovascular and other diseases. For this study, numerical flow simulations were performed using: a) open source software VMTK and commercial software ICEM CFD as pre-processors, b) the finite volume based solver Fluent and c) Tecplot 360 (Amtec Inc.) for post-processing.Copyright © 2012 by ASME

Posture changes may influence the geometry and hemodynamics of the carotid bifurcation [1]. As a result, head rotation may cause geometric changes that alter the hemodynamic variables previously cited to correlate with the development of atherosclerosis. Such variables include oscillating wall shear stress (WSS) and particle residence times. Glor et al. [1] had reported changes in the right carotid bifurcation geometry with leftward rotation of the head. We have previously reported that geometric differences in the right and left carotid bifurcation occur with a rightward rotation of the head [2]. To investigate the geometric changes in the carotid geometry that occur in the prone sleeping position with rightward and leftward head rotation, we have performed studies in two healthy young volunteers. We defined specific geometric parameters of the carotid bifurcation, such as bifurcation angle, internal carotid artery (ICA) angle, ICA planarity angle, in-plane asymmetry angle, tortuosity, curvature, area and diameter ratios, and compared their corresponding values in three head postures: 1) the supine neutral position, 2) the prone sleeping position with head rotation to the right (∼80 degrees), and 3) the prone sleeping position with head rotation to the left (∼80 degrees).

During the complicated cardiac surgery on a non-beating heart with cardiopulmonary bypass, protection of the heart is accomplished by injecting cold cardioplegic solutions. In most forms of circulatory shock, it is necessary to immediately restore the circulating volume. Intravenous solutions of volume expanders, such as hydroxyethyl starch and dextrans, are used to increase the volume of fluid in the circulating blood. In this work, blood samples of six donors were obtained and used to prepare mixtures with different volume expanders in concentrations ranging from 10 to 50 vol./vol.%. The flow curves of all mixtures in the temperature range from 4°C to 37°C were constructed and fitted to the Herschel-Bulkley model, in order to extract the shear thinning and yield stress parameters. To assess the influence of the observed changes in the rheological properties of blood on the hemodynamics in arterial vasculature, a realistic three-dimensional rigid-wall computational model was constructed from MRI images of the right carotid bifurcation obtained in vivo from a healthy male volunteer. The time-varying flow field was numerically computed using the Newtonian model as well as the Herschel-Bulkley model with the Papanastasiou regularization. The numerical simulations indicate only moderate changes in the time-averaged flow field that become accentuated when the instantaneous flow field is considered. We also found that although the influence of temperature, hematocrit, and volume expanders on hemodynamics is significant, this can primarily be attributed to the changes in the nominal viscosity of the flow medium. © 2011 Springer-Verlag. 50 4 389 402 Cited By :19

Segmented cross-sectional MRI images were used to construct 3-D virtual models of the carotid bifurcation in ten healthy volunteers. Geometric features, such as bifurcation angle, internal carotid artery (ICA) angle, planarity angle, asymmetry angle, tortuosity, curvature, bifurcation area ratio, ICA/common carotid artery (CCA), external carotid artery (ECA)/CCA, and ECA/ICA diameter ratios, were calculated for both carotids in two head postures: 1) the supine neutral position and 2) the prone sleeping position with head rotation to the right (∼80°). The results obtained have shown that head rotation causes 1) significant variations in bifurcation angle [32% mean increase for the right carotid (RC) and 21% mean decrease for the left carotid (LC)] and internal carotid artery angle (97% mean increase for the RC, 43% mean decrease for the LC) 2) a slight increase in planarity and asymmetry angles for both RC and LC 3) minor and variable curvature changes for the CCA and for the branches 4) slight tortuosity changes for the braches but not for the CCA and 5) unsubstantial alterations in area and diameter ratios (percentage changes < 10). The significant geometric changes observed in most subjects with head posture may also cause significant changes in bifurcation hemodynamics and warrant future investigation of the hemodynamic parameters related to the development of atherosclerotic disease such as low oscillating wall shear stress and particle residence times. © 2006 IEEE. 15 1 148 154 Cited By :16

The influence of posture change on the geometry and hemodynamics of the carotid bifurcation has not been thoroughly studied [1,2,3]. Such changes may alter the hemodynamic variables that are generally associated with the development of atherosclerosis, such as low oscillating wall shear stress (WSS) and particle residence times. Glor et al. (2004) had reported changes in the right carotid bifurcation geometry with leftward rotation of the head. We have previously reported that geometric differences in the right and left carotid bifurcation occur with a rightward rotation of the head [3].Copyright © 2010 by ASME

Segmented cross sectional MRI images were used to construct 3D virtual models of the carotid bifurcation in 5 healthy volunteers. Geometric features such as bifurcation angle, planarity angle, asymmetry angle tortuosity and curvature were calculated for the normal head posture and were compared to the equivalent values acquired with the head rotated clockwise by up to 80 degrees. The results obtained have shown that head rotation causes: 1) significant variations in bifurcation angle, planarity angle, asymmetry angle and internal carotid artery angle 2) tortuosity changes for the braches but not for the common carotid and 3) significant curvature changes for the common carotid artery (CCA) but not for the branches. The significant geometric changes observed in most subjects with head posture, may cause significant changes in hemodynamics and warrants future investigation of the hemodynamic parameters related to the development of atherosclerotic disease such as low oscillating wall shear stress and particle residence times. ©2009 IEEE. Sponsors: IBM Italia S.p.A. Datamed SA, Healthcare Integrator LinkSCEEM: Link. Sci. Comput. Eur. East. Mediterr. AGIOS THERISSOS M.R.1. Medical Diagnostic Center University of Cyprus Conference code: 79527 Cited By :1

39 40 Sponsors: 10th ASME Summer Bioengineering Conference, SBC2008 Conference code: 80362

385 386 Sponsors: ASME Bioengineering Division Conference code: 71512 Cited By :4

Previous investigators have reported that posture changes may influence the geometry and hemodynamics of the carotid bifurcation [1,2]. As a result, head rotation may cause geometric changes that alter the hemodynamic variables previously cited to correlate with the development of atherosclerosis. Glor et al. [1] had reported changes in the right carotid bifurcation geometry with leftward rotation of the head. Aristokleous et al. [2] have reported that geometric differences in the right and left carotid bifurcation occur with a rightward rotation of the head in 10 healthy volunteers [2]. Also, a similar study on bilateral head rotation on the left and right carotid bifurcation of two volunteers has shown similar results [3]. In this study a group of four patients with atherosclerotic disease in the carotid arteries was investigated at two head postures, a) the supine neutral and b) the prone sleeping with head rotation leftwards up to 80° to investigate the level of stenosis and the changes in geometric parameters with head rotation.