Artículos de revistas: "Velocimetry of blood flows"

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Bitsch, L., L. H. Olesen, C. H. Westergaard, H. Bruus, H. Klank y J. P. Kutter. "Micro particle-image velocimetry of bead suspensions and blood flows". Experiments in Fluids 39, n.º 3 (29 de junio de 2005): 507–13. http://dx.doi.org/10.1007/s00348-005-0967-7.

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Kiel, J. W., G. L. Riedel, G. R. DiResta y A. P. Shepherd. "Gastric mucosal blood flow measured by laser-Doppler velocimetry". American Journal of Physiology-Gastrointestinal and Liver Physiology 249, n.º 4 (1 de octubre de 1985): G539—G545. http://dx.doi.org/10.1152/ajpgi.1985.249.4.g539.

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To determine the feasibility of measuring gastric mucosal blood flow by laser-Doppler velocimetry (LDV), we utilized two LDV flowmeters to monitor blood flow in mucosa and serosa of chambered canine stomach. In isolated, nonautoregulating gastric segments vasodilated with isoproterenol, LDV mucosal and muscularis blood flows were both linearly related to total electromagnetic blood flow during step increases in perfusion pressure. To assess the depth of the LDV measurement, we recorded reactive hyperemia following arterial occlusion. Reactive hyperemia was frequently registered in the mucosa but rarely in muscularis. Placing a layer of nonperfused mucosa-submucosa between the probe and the perfused mucosa abolished the resting LDV mucosal flow signal and attenuated the recording of peak hyperemia by 85%. Furthermore, intra-arterial infusions of both adenosine and isoproterenol frequently increased LDV mucosal flow and decreased LDV muscularis flow, although total flow was consistently increased. These findings indicate that our LDV instruments yield linear, superficial measurements of gastric blood flow in either mucosa or muscularis. Although calibration in absolute units remains to be achieved, our results demonstrate that LDV is a practical means of studying the gastric mucosal microcirculation.

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Raghav, Vrishank, Chris Clifford, Prem Midha, Ikechukwu Okafor, Brian Thurow y Ajit Yoganathan. "Three-dimensional extent of flow stagnation in transcatheter heart valves". Journal of The Royal Society Interface 16, n.º 154 (mayo de 2019): 20190063. http://dx.doi.org/10.1098/rsif.2019.0063.

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The recent unexpected discovery of thrombosis in transcatheter heart valves (THVs) has led to increased concerns of long-term valve durability. Based on the clinical evidence combined with Virchow's triad, the primary hypothesis is that low-velocity blood flow around the valve could be a primary cause for thrombosis. However, due to limited optical access in such unsteady three-dimensional biomedical flows, measurements are challenging. In this study, for the first time, we employ a novel single camera volumetric velocimetry technique to investigate unsteady three-dimensional cardiovascular flows. Validation of the novel volumetric velocimetry technique with standard planar particle image velocimetry (PIV) technique demonstrated the feasibility of adopting this new technique to investigate biomedical flows. This technique was used to quantify the three-dimensional velocity field in the vicinity of a validated, custom developed, transparent THV in a bench-top pulsatile flow loop. Large volumetric regions of flow stagnation were observed in the neo-sinus throughout the cardiac cycle, with stagnation defined as a velocity magnitude lower than 0.05 m s −1 . The volumetric scalar viscous shear stress quantified via the three-dimensional shear stress tensor was within the range of low shear-inducing thrombosis observed in the literature. Such high-fidelity volumetric quantitative data and novel imaging techniques used to obtain it will enable fundamental investigation of heart valve thrombosis in addition to providing a reliable and robust database for validation of computational tools.

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Lee, Sang Joon, Han Wook Park y Sung Yong Jung. "Usage of CO2microbubbles as flow-tracing contrast media in X-ray dynamic imaging of blood flows". Journal of Synchrotron Radiation 21, n.º 5 (31 de julio de 2014): 1160–66. http://dx.doi.org/10.1107/s1600577514013423.

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X-ray imaging techniques have been employed to visualize various biofluid flow phenomena in a non-destructive manner. X-ray particle image velocimetry (PIV) was developed to measure velocity fields of blood flows to obtain hemodynamic information. A time-resolved X-ray PIV technique that is capable of measuring the velocity fields of blood flows under real physiological conditions was recently developed. However, technical limitations still remained in the measurement of blood flows with high image contrast and sufficient biocapability. In this study, CO2microbubbles as flow-tracing contrast media for X-ray PIV measurements of biofluid flows was developed. Human serum albumin and CO2gas were mechanically agitated to fabricate CO2microbubbles. The optimal fabricating conditions of CO2microbubbles were found by comparing the size and amount of microbubbles fabricated under various operating conditions. The average size and quantity of CO2microbubbles were measured by using a synchrotron X-ray imaging technique with a high spatial resolution. The quantity and size of the fabricated microbubbles decrease with increasing speed and operation time of the mechanical agitation. The feasibility of CO2microbubbles as a flow-tracing contrast media was checked for a 40% hematocrit blood flow. Particle images of the blood flow were consecutively captured by the time-resolved X-ray PIV system to obtain velocity field information of the flow. The experimental results were compared with a theoretically amassed velocity profile. Results show that the CO2microbubbles can be used as effective flow-tracing contrast media in X-ray PIV experiments.

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Starodumov, Ilya, Sergey Sokolov, Ksenia Makhaeva, Pavel Mikushin, Olga Dinislamova y Felix Blyakhman. "Obtaining Vortex Formation in Blood Flow by Particle Tracking: Echo-PV Methods and Computer Simulation". Inventions 8, n.º 5 (9 de octubre de 2023): 124. http://dx.doi.org/10.3390/inventions8050124.

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Micrometer-sized particles are widely introduced as fluid flow markers in experimental studies of convective flows. The tracks of such particles demonstrate a high contrast in the optical range and well illustrate the direction of fluid flow at local vortices. This study addresses the theoretical justification on the use of large particles for obtaining vortex phenomena and its characterization in stenotic arteries by the Echo Particle Velocimetry method. Calcite particles with an average diameter of 0.15 mm were chosen as a marker of streamlines using a medical ultrasound device. The Euler–Euler model of particle motion was applied to simulate the mechanical behavior of calcite particles and 20 µm aluminum particles. The accuracy of flow measurement at vortex regions was evaluated by computational fluid dynamics methods. The simulation results of vortex zone formation obtained by Azuma and Fukushima (1976) for aluminum particles with the use of the optical velocimetry method and calcite particles were compared. An error in determining the size of the vortex zone behind of stenosis does not exceed 5%. We concluded that the application of large-size particles for the needs of in vitro studies of local hemodynamics is possible.

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Park, Cheol Woo, Se Hyun Shin, Gyu Man Kim, Jin Hong Jang y Yoon Hee Gu. "A Hemodynamic Study on a Marginal Cell Depletion Layer of Blood Flow Inside a Microchannel". Key Engineering Materials 326-328 (diciembre de 2006): 863–66. http://dx.doi.org/10.4028/www.scientific.net/kem.326-328.863.

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Biological flows, especially blood flow, have attracted a great deal of attention from fluid engineering and hemodynamic investigation fields with advances in bio-technology. The flow of blood carries dissolved gases, nutrients, hormones, and metabolic waste through the circulatory system in the human body. In the present study, the characteristics of blood flow inside a microchannel are investigated by using a micro-particle image velocimetry (micro-PIV) and an optical image processing technique. The motion of red blood cells (RBCs) was visualized with a high-speed CCD camera. The microchannel is made of polydimethylsiloxane (PDMS) material and a slide-glass is attached to the top. The thickness of the margin cell depletion layer is calculated from an acquired raw image through the image processing method, with variations in microchannel width.

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7

Weng, Yiming. "The influence of vortices on hemodynamics in blood vessels". Theoretical and Natural Science 6, n.º 1 (3 de agosto de 2023): 172–80. http://dx.doi.org/10.54254/2753-8818/6/20230216.

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Blood flow in vessels is affected by several factors like vessel shape, blood thickness, and heart function. Swirling patterns of flow, called vortices, are often seen in blood vessels and can affect how blood flows. This study aims to understand how vortices affect blood flow and the reasons behind these changes. Different instruments, like particle image velocimetry (PIV), computational fluid dynamics (CFD), and magnetic resonance imaging (MRI), were used to measure and analyze blood flow. CFD simulations were done using realistic blood vessel models to study how vortices form and how they affect blood velocity and pressure. The results show that vortices can cause significant changes in blood velocity and pressure, which can lead to changes in blood flow. The increased wall shear stress may contribute to the development of heart disease. This research highlights the importance of considering the impact of vortices on blood flow dynamics when designing and assessing cardiovascular devices and treatments.

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Kvietys, P. R., A. P. Shepherd y D. N. Granger. "Laser-Doppler, H2 clearance, and microsphere estimates of mucosal blood flow". American Journal of Physiology-Gastrointestinal and Liver Physiology 249, n.º 2 (1 de agosto de 1985): G221—G227. http://dx.doi.org/10.1152/ajpgi.1985.249.2.g221.

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In autoperfused preparations of feline jejunum, blood flow was measured from the mucosal surface with laser-Doppler velocimetry (LDV) and hydrogen gas (H2) clearance techniques while blood flow was altered by intra-arterial infusions of isoproterenol. LDV and H2 clearance estimates of blood flow were compared with total-wall and mucosal-submucosal blood flows measured with the radiolabeled microsphere technique. Over the range (26.3–73.6 ml X min-1 X 100 g-1) of blood flows attained, a series of direct linear relationships were obtained among LDV, H2 clearance, and microsphere estimates of jejunal blood flow. The slopes of these relationships indicated that the H2 clearance technique over-estimates total intestinal blood flow but reflects mucosal-submucosal flow as measured with microspheres. LDV measurements of blood flow from the mucosal surface were equally well correlated with total and mucosal-submucosal blood flow measured by microspheres, thereby not allowing for a definitive conclusion on the measurement depth of the LDV method. However, the ability of the LDV method to detect changes in blood flow in the perfused gut, even through 3 mm of unperfused tissue, casts a doubt on the assumption that the LDV method has a spatial resolution of less than 0.5–1.0 mm. The results of this study indicate that the H2 clearance technique can be used to measure mucosal blood flow in the small intestine. By contrast, the precise measurement depth of the LDV method is still uncertain and requires further evaluation.

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9

Coutinho, G., M. Rossi, A. Moita y A. L. N. Moreira. "3D Particle Tracking Velocimetry Applied To Platelet-Size Particles In Red Blood Cells Suspensions Flows Through Squared Microchannels". Proceedings of the International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics 20 (11 de julio de 2022): 1–12. http://dx.doi.org/10.55037/lxlaser.20th.44.

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General defocusing particle tracking (GDPT) method is used to characterize the motion of platelet-size particles within red blood cell (RBC) suspension flows through straight-square microchannels. The method is able to characterize the three-dimensional (3D) nature of particle-RBC interactions, however the measurement depth is limited by the height of the microchannel and hematocrit level (Hct). The RBC mask the particle images and detection becomes impossible above a limit depth. The pressure-driven flow is characterized by velocity distributions and 3D trajectories of platelet-size particles within the RBC suspensions. At large hematocrit levels (Hct=30 %), the velocity distribution exhibits a blunter profile typical of blood flow in capillary-size microchannels. In addition, the interplay between blood viscosity and pressure-driven flow causes the velocity magnitude to decrease, in the center region, with increasing hematocrit. The platelet-size particles exhibit larger velocity fluctuations along the spanwise and vertical directions as Hct is increased, both inside the RBC-rich region and cell-free layer (CFL). On one hand, inside the RBC-rich zone the increasing number of flowing RBC leads to more frequent particle-RBC collisions. On the other hand, even though the particle movement inside the CFL is confined between the boundary of the RBC and the wall of the microchannel, as the thickness of the CFL decreases (i.e. increasing Hct) the collisions with RBC become more frequent. To the authors knowledge, these results represent the first experimental characterization of 3D platelet-size particle behaviour and near-wall dynamics within RBC-suspensions, and it paves the way for more detailed particle-cell flows characterization.

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10

Jung, Sung Yong, Han Wook Park, Bo Heum Kim y Sang Joon Lee. "Time-resolved X-ray PIV technique for diagnosing opaque biofluid flow with insufficient X-ray fluxes". Journal of Synchrotron Radiation 20, n.º 3 (1 de marzo de 2013): 498–503. http://dx.doi.org/10.1107/s0909049513001933.

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X-ray imaging is used to visualize the biofluid flow phenomena in a nondestructive manner. A technique currently used for quantitative visualization is X-ray particle image velocimetry (PIV). Although this technique provides a high spatial resolution (less than 10 µm), significant hemodynamic parameters are difficult to obtain under actual physiological conditions because of the limited temporal resolution of the technique, which in turn is due to the relatively long exposure time (∼10 ms) involved in X-ray imaging. This study combines an image intensifier with a high-speed camera to reduce exposure time, thereby improving temporal resolution. The image intensifier amplifies light flux by emitting secondary electrons in the micro-channel plate. The increased incident light flux greatly reduces the exposure time (below 200 µs). The proposed X-ray PIV system was applied to high-speed blood flows in a tube, and the velocity field information was successfully obtained. The time-resolved X-ray PIV system can be employed to investigate blood flows at beamlines with insufficient X-ray fluxes under specific physiological conditions. This method facilitates understanding of the basic hemodynamic characteristics and pathological mechanism of cardiovascular diseases.

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Sanchez, Zyrina Alura C., Vignesha Vijayananda, Devin M. Virassammy, Liat Rosenfeld y Anand K. Ramasubramanian. "The interaction of vortical flows with red cells in venous valve mimics". Biomicrofluidics 16, n.º 2 (marzo de 2022): 024103. http://dx.doi.org/10.1063/5.0078337.

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The motion of cells orthogonal to the direction of main flow is of importance in natural and engineered systems. The lateral movement of red blood cells (RBCs) distal to sudden expansion is considered to influence the formation and progression of thrombosis in venous valves, aortic aneurysms, and blood-circulating devices and is also a determining parameter for cell separation applications in flow-focusing microfluidic devices. Although it is known that the unique geometry of venous valves alters the blood flow patterns and cell distribution in venous valve sinuses, the interactions between fluid flow and RBCs have not been elucidated. Here, using a dilute cell suspension in an in vitro microfluidic model of a venous valve, we quantified the spatial distribution of RBCs by microscopy and image analysis, and using micro-particle image velocimetry and 3D computational fluid dynamics simulations, we analyzed the complex flow patterns. The results show that the local hematocrit in the valve pockets is spatially heterogeneous and is significantly different from the feed hematocrit. Above a threshold shear rate, the inertial separation of streamlines and lift forces contribute to an uneven distribution of RBCs in the vortices, the entrapment of RBCs in the vortices, and non-monotonic wall shear stresses in the valve pockets. Our experimental and computational characterization provides insights into the complex interactions between fluid flow, RBC distribution, and wall shear rates in venous valve mimics, which is of relevance to understanding the pathophysiology of thrombosis and improving cell separation efficiency.

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12

Borazjani, Iman, John Westerdale, Eileen M. McMahon, Prathish K. Rajaraman, Jeffrey J. Heys y Marek Belohlavek. "Left Ventricular Flow Analysis: Recent Advances in Numerical Methods and Applications in Cardiac Ultrasound". Computational and Mathematical Methods in Medicine 2013 (2013): 1–11. http://dx.doi.org/10.1155/2013/395081.

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The left ventricle (LV) pumps oxygenated blood from the lungs to the rest of the body through systemic circulation. The efficiency of such a pumping function is dependent on blood flow within the LV chamber. It is therefore crucial to accurately characterize LV hemodynamics. Improved understanding of LV hemodynamics is expected to provide important clinical diagnostic and prognostic information. We review the recent advances in numerical and experimental methods for characterizing LV flows and focus on analysis of intraventricular flow fields by echocardiographic particle image velocimetry (echo-PIV), due to its potential for broad and practical utility. Future research directions to advance patient-specific LV simulations include development of methods capable of resolving heart valves, higher temporal resolution, automated generation of three-dimensional (3D) geometry, and incorporating actual flow measurements into the numerical solution of the 3D cardiovascular fluid dynamics.

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Tajikawa, Tsutomu, Wataru Ishihara, Shimpei Kohri y Kenkichi Ohba. "Development of Miniaturized Fiber-Optic Laser Doppler Velocimetry Sensor for Measuring Local Blood Velocity: Measurement of Whole Blood Velocity in Model Blood Vessel Using a Fiber-Optic Sensor with a Convex Lens-Like Tip". Journal of Sensors 2012 (2012): 1–11. http://dx.doi.org/10.1155/2012/426476.

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A miniaturized fiber-optic laser Doppler velocimetry sensor has been developed to measure the local blood velocity in vivo. The laser beam emitted from the sensor tip can be focused at any distance between 0.1 and 0.5 mm from the tip. Consequently, the sensor has a sufficiently high signal-to-noise ratio to measure the local velocity in almost any opaque fluid, including blood. The sensor head is inserted in an injection needle or a catheter tube. In the former case, it is inserted at an angle to the wall of a vessel and is scanned across the vessel to measure the velocity distribution. In the latter case, it is aligned parallel with the flow in a vessel. For all flows of whole human blood, whole caprine blood, and 69% hematocrit of bovine blood, the velocity distribution across the vessel could be measured very accurately. The insertion angle of the fiber into the flow significantly affects the measurement accuracy; an angle of about 50° is suitable when an injection needle is used. When a catheter is employed, an insertion direction opposite to the flow direction is better than parallel to the flow due to the generation of a wake behind the fiber.

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14

Jones, C. J., M. J. Lever, Y. Ogasawara, K. H. Parker, K. Tsujioka, O. Hiramatsu, K. Mito, C. G. Caro y F. Kajiya. "Blood velocity distributions within intact canine arterial bifurcations". American Journal of Physiology-Heart and Circulatory Physiology 262, n.º 5 (1 de mayo de 1992): H1592—H1599. http://dx.doi.org/10.1152/ajpheart.1992.262.5.h1592.

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As local variations in blood flow are implicated in atherogenesis at bifurcations, we measured in vivo blood velocities in different planes within exposed iliofemoral arterial bifurcations in 8 dogs using 20-MHz, 80-channel Doppler ultrasound velocimetry. Cardiac frequency was fixed at 2 Hz by pacing. Local geometry was characterized using 25-MHz, B-mode ultrasound images, photographs, and methacrylate casts. The bifurcations were asymmetrical and planar to within 5 degrees, the diameter ratios of the daughter vessels ranged from 1.47 to 2.00, and the angles between them ranged from 40 to 76 degrees. Measured velocities indicated that just upstream of the bifurcation mean peak Reynolds numbers ranged from 196 to 564 and Womersley (frequency) parameters ranged from 2.00 to 4.1. At the level of the bifurcation, secondary flows were insignificant in the normal plane but strong in the plane of the bifurcation. As a result, two-dimensional velocity fields, reconstructed by vector addition of velocities measured in the plane of the bifurcation, differed markedly from the one-dimensional profiles calculated assuming flow parallel to the vessel axis. In the two-dimensional velocity fields, forward flow was directed toward the flow divider and reversal occurred earliest near the outer wall. Wide spatial and temporal variations in the shear stress at the endothelium are implied by these detailed, in vivo measurements of the bifurcation velocity fields.

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15

Yu, Paulo y Vibhav Durgesh. "Modal Decomposition Techniques: Application in Coherent Structures for a Saccular Aneurysm Model". Fluids 7, n.º 5 (9 de mayo de 2022): 165. http://dx.doi.org/10.3390/fluids7050165.

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Aneurysms are localized expansions of blood vessels which can be fatal upon rupture. Studies have shown that aneurysm flows exhibit complex flow phenomena which consist of single or multiple vortical structures that move within the flow cycle. Understanding the complex flow behaviors of aneurysms remain challenging. Thus, the goal of this study is to quantify the flow behavior and extract physical insights into aneurysm flows using advance data decomposition methods, Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD). The velocity field data were obtained by performing 2D Particle Image Velocimetry (2D PIV) on the mid-plane of an idealized, rigid, saccular aneurysm model. The input flow conditions were set to Rep=50 and 150 for a fixed α=2 using a precisely controlled piston pump system. POD was used to quantify the spatial features of the flows, while DMD was used to obtain insight on the dynamics. The results obtained from POD and DMD showed the capability of both methods to quantify the flow field, with the modes obtained providing different insights into the flow evolution in the aneurysm. The curve-fitting step of the POD time-varying coefficients, and the appropriate selection of DMD modes based on their energy contribution, allowed the mathematical flow models from POD and DMD to reconstruct flow fields at any given time step. This can be used for validation of numerical or computational data.

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Rodgers, G. P., A. N. Schechter, C. T. Noguchi, H. G. Klein, A. W. Nienhuis y R. F. Bonner. "Microcirculatory adaptations in sickle cell anemia: reactive hyperemia response". American Journal of Physiology-Heart and Circulatory Physiology 258, n.º 1 (1 de enero de 1990): H113—H120. http://dx.doi.org/10.1152/ajpheart.1990.258.1.h113.

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With the technique of laser-Doppler velocimetry, cutaneous blood flows in the forearm of patients with stable sickle cell disease after graded periods of proximal ischemia were compared with normal subjects matched for age, race, and sex, and with patients with anemia caused by beta(+)-thalassemia. In the sickle cell patients the reactive hyperemia was characterized by an increased time interval between the release of the occlusion and the peak amplitude response (time-to-peak) and by a greater period of blood flow above the base-line value (payback ratio) compared with controls. In addition, prolongation of the occlusion period led to an augmentation in the magnitude of the characteristic basal flow oscillations or an induction of this phenomenon at sites not exhibiting it before ischemia. Base-line or ischemia-provoked flow oscillations of either this magnitude or frequency were only observed in normal or thalassemic controls during brief intervals in the rapidly decaying portion of the hyperemic response and in one subject with homozygous hemoglobin C disease. These results would support a model of a local integrative control of microcirculatory blood flow, which appears to become augmented, synchronized, and sustained in sickle cell subjects.

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Molochnikov, Valeriy, Gennadiy Khubulava, Evgeniy Kalinin, Natalya Pashkova y Ilya Nikiforov. "Experimental and numerical study of flow structure in a model of distal anastomosis of femoral artery". Russian journal of biomechanics. 27, n.º 3 (30 de septiembre de 2023): 27–40. http://dx.doi.org/10.15593/rjbiomech/2023.3.03.

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Physical and numerical simulation of the steady blood flow was carried out focusing on the distal end-to-side anastomosis of a graft to the femoral artery. The angle between the graft and the artery was 60°. Two Reynolds numbers were considered that corresponded to the physiological range when estimated using the average (Re = 240) and maximum (Re = 1640) blood flow through the human femoral artery over a single cardiac cycle. The experiment included flow visualization and measurements of instantaneous vector fields of velocity using an optical SIV (Smoke Image Velocimetry) technique. Direct numerical simulation (DNS) was employed for numerical study. The distribution of blood flows through the branches of the main artery was 80 % in the antegrade and 20 % in the retrograde direction. Main patterns in the distribution of velocity and its root-mean-square fluctuations in both branches of the main artery were revealed. Flow separation regions were observed in the branching area. Additionally, secondary flows (Prandtl’s vortices of the first kind) were revealed. The flow in the branching area was still laminar Re = 240, while the signs of transition to turbulence were documented within separation regions at Re = 1640. Distributions of streamwise and circumferential components of skin friction vector were estimated. In some regions of flow, these components were shown to be comparable in size. The location of regions was revealed in which the friction magnitude in the considered flow regimes was lower than the one in an unimpaired artery (developed laminar flow in a circular pipe) at appropriate Reynolds numbers.

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Friedman, M. H. "Arterial Fluid Mechanics and Biological Response". Applied Mechanics Reviews 43, n.º 5S (1 de mayo de 1990): S103—S108. http://dx.doi.org/10.1115/1.3120788.

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To better understand the response of the arterial wall to the adjacent blood flow, corresponding hemodynamic and histomorphometric data are obtained at multiple sites in human arteries. The hemodynamic data are obtained by perfusing realistically compliant flow-through casts of vascular segments with physiologically realistic pulsatile flows and measuring near-wall velocities by laser Doppler velocimetry. The hemodynamic and histologic data in combination suggest that the thickening response of the innermost layer of the vessel wall, which may precede atherosclerosis at the site, varies with time and wall shear: at early times, sites exposed to relatively high and unidirectional shears are thicker, while at later times, their thickness is exceeded by that at sites exposed to relatively low or oscillatory shear forces. A biologically plausible mathematical model of the thickening process supports the hypothesis that this behavior can be the consequence of multiple shear-dependent processes in the vessel wall.

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Fraser, Katharine H., Christian Poelma, Bin Zhou, Eleni Bazigou, Meng-Xing Tang y Peter D. Weinberg. "Ultrasound imaging velocimetry with interleaved images for improved pulsatile arterial flow measurements: a new correction method, experimental and in vivo validation". Journal of The Royal Society Interface 14, n.º 127 (febrero de 2017): 20160761. http://dx.doi.org/10.1098/rsif.2016.0761.

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Blood velocity measurements are important in physiological science and clinical diagnosis. Doppler ultrasound is the most commonly used method but can only measure one velocity component. Ultrasound imaging velocimetry (UIV) is a promising technique capable of measuring two velocity components; however, there is a limit on the maximum velocity that can be measured with conventional hardware which results from the way images are acquired by sweeping the ultrasound beam across the field of view. Interleaved UIV is an extension of UIV in which two image frames are acquired concurrently, allowing the effective interframe separation time to be reduced and therefore increasing the maximum velocity that can be measured. The sweeping of the ultrasound beam across the image results in a systematic error which must be corrected: in this work, we derived and implemented a new velocity correction method which accounts for acceleration of the scatterers. We then, for the first time, assessed the performance of interleaved UIV for measuring pulsatile arterial velocities by measuring flows in phantoms and in vivo and comparing the results with spectral Doppler ultrasound and transit-time flow probe data. The velocity and flow rate in the phantom agreed within 5–10% of peak velocity, and 2–9% of peak flow, respectively, and in vivo the velocity difference was 9% of peak velocity. The maximum velocity measured was 1.8 m s −1 , the highest velocity reported with UIV. This will allow flows in diseased arteries to be investigated and so has the potential to increase diagnostic accuracy and enable new vascular research.

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Ravensbergen, J., J. K. B. Krijger, B. Hillen y H. W. Hoogstraten. "Merging flows in an arterial confluence: the vertebro-basilar junction". Journal of Fluid Mechanics 304 (10 de diciembre de 1995): 119–41. http://dx.doi.org/10.1017/s0022112095004368.

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The basilar artery is one of the three vessels providing the blood supply to the human brain. It arises from the confluence of the two vertebral arteries. In fact, it is the only artery of this size in the human body arising from a confluence instead of a bifurcation. Earlier work, concerning flow computations in simplified models of the basilar artery, has demonstrated that a junction causes distinctive flow phenomena. This paper presents three-dimensional finite-element computations of steady viscous flow in a rigid symmetrical junction geometry representing the anatomical situation in a more realistic way. The geometry consists of two round tubes merging into a single round outlet tube. The Reynolds number for the basilar artery ranges from 200 to 600, and both symmetrical and asymmetrical inflow from the two inlet tubes has been considered.Just downstream of the confluence a ‘double hump’ axial velocity profile is found. In the transition zone the flow pattern appears to have a complicated structure. In the symmetrical case the axial velocity profile shows a sharp central ridge, whereas in the asymmetrical case the highest ‘hump’ crosses the centreline of the tube. The flow has a highly three-dimensional character with secondary velocities easily exceeding 25% of the mean axial flow velocity. The secondary flow pattern consists of four vortices. Under all simulated flow conditions, the inlet length turns out to be much larger than the average length of the human basilar artery.To validate the computational model, a comparison is made between numerical and experimental results for a junction geometry consisting of tubes with a rectangular cross-section. The experiments have been performed in a Perspex model with laser Doppler velocimetry and dye injection techniques. Good agreement between experimental and computational results is found. Moreover, all essential flow phenomena turn out to be quite similar to those obtained for the circular tube geometry.

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Yousif, Majid Y., David W. Holdsworth y Tamie L. Poepping. "A blood-mimicking fluid for particle image velocimetry with silicone vascular models". Experiments in Fluids 50, n.º 3 (29 de agosto de 2010): 769–74. http://dx.doi.org/10.1007/s00348-010-0958-1.

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Bluestein, Danny, Edmond Rambod y Morteza Gharib. "Vortex Shedding as a Mechanism for Free Emboli Formation in Mechanical Heart Valves". Journal of Biomechanical Engineering 122, n.º 2 (3 de noviembre de 1999): 125–34. http://dx.doi.org/10.1115/1.429634.

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The high incidence of thromboembolic complications of mechanical heart valves (MHV) limits their success as permanent implants. The thrombogenicity of all MHV is primarily due to platelet activation by contact with foreign surfaces and by nonphysiological flow patterns. The latter include elevated flow stresses and regions of recirculation of blood that are induced by valve design characteristics. A numerical simulation of unsteady turbulent flow through a bileaflet MHV was conducted, using the Wilcox k–ω turbulence model for internal low-Reynolds-number flows, and compared to quantitative flow visualization performed in a pulse duplicator system using Digital Particle Image Velocimetry (DPIV). The wake of the valve leaflet during the deceleration phase revealed an intricate pattern of interacting shed vortices. Particle paths showed that platelets that were exposed to the highest flow stresses around the leaflets were entrapped within the shed vortices. Potentially activated, such platelets may tend to aggregate and form free emboli. Once formed, such free emboli would be convected downstream by the shed vortices, increasing the risk of systemic emboli. [S0148-0731(00)01202-4]

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23

Barrere, Nicasio, Javier Brum, Alexandre L'her, Gustavo L. Sarasúa y Cecilia Cabeza. "Vortex dynamics under pulsatile flow in axisymmetric constricted tubes". Papers in Physics 12 (16 de junio de 2020): 120002. http://dx.doi.org/10.4279/pip.120002.

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Improved understanding of how vortices develop and propagate under pulsatile flow can shed important light on the mixing and transport processes occurring in such systems, including the transition to turbulent regime. For example, the characterization of pulsatile flows in obstructed artery models serves to encourage research into flow-induced phenomena associated with changes in morphology, blood viscosity, wall elasticity and flow rate. In this work, an axisymmetric rigid model was used to study the behaviour of the flow pattern with varying degrees constriction ($d_0$) and mean Reynolds ($\bar{Re}$) and Womersley numbers ($\alpha$). Velocity fields were obtained experimentally using Digital Particle Image Velocimetry and generated numerically. For the acquisition of data, $\bar{Re}$ was varied from 385 to 2044, $d_0$ was 1.0 cm and 1.6 cm, and $\alpha$ was varied from 17 to 33 in the experiments and from 24 to 50 in the numerical simulations. Results for the Reynolds number considered showed that the flow pattern consisted of two main structures: a central jet around the tube axis and a recirculation zone adjacent to the inner wall of the tube, where vortices shed. Using the vorticity fields, the trajectory of vortices was tracked and their displacement over their lifetime calculated. The analysis led to a scaling law equation for maximum vortex displacement as a function of a dimensionless variable dependent on the system parameters Re and $\alpha$.

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24

Tiederman, W. G., M. J. Steinle y W. M. Phillips. "Two-Component Laser Velocimeter Measurements Downstream of Heart Valve Prostheses in Pulsatile Flow". Journal of Biomechanical Engineering 108, n.º 1 (1 de febrero de 1986): 59–64. http://dx.doi.org/10.1115/1.3138581.

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Elevated turbulent shear stresses resulting from disturbed blood flow through prosthetic heart valves can cause damage to red blood cells and platelets. The purpose of this study was to measure the turbulent shear stresses occurring downstream of aortic prosthetic valves during in-vitro pulsatile flow. By matching the indices of refraction of the blood analog fluid and model aorta, correlated, simultaneous two-component laser velocimeter measurements of the axial and radial velocity components were made immediately downstream of two aortic prosthetic valves. Velocity data were ensemble averaged over 200 or more cycles for a 15-ms window opened at peak systolic flow. The systolic duration for cardiac flows of 8.4 L/min was 200 ms. Ensemble-averaged total shear stress levels of 2820 dynes/cm2 and 2070 dynes/cm2 were found downstream of a trileaflet valve and a tilting disk valve, respectively. These shear stress levels decreased with axial distance downstream much faster for the tilting disk valve than for the trileaflet valve.

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25

Song, Zhiyong, Pengrui Zhu, Lianzhi Yang, Zhaohui Liu, Hua Li y Weiyao Zhu. "Study on the radial sectional velocity distribution and wall shear stress associated with carotid artery stenosis". Physics of Fluids 34, n.º 5 (mayo de 2022): 051904. http://dx.doi.org/10.1063/5.0085796.

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Atherosclerosis is an important cause of cardiovascular disease. The wall shear stress (WSS) is one of the key factors of plaque formation and dislodgement. Currently, WSS estimation is based on the measurement of the blood velocity gradient. However, due to the lack of flow field measurements in carotid stenosis vessels, the two distribution forms (parabolic and non-parabolic) commonly considered in numerical simulations could cause WSS estimates to differ by more than 40%, which could seriously affect the accuracy of mechanical analysis. This study applied three-dimensional (3D) printing technology to create an experimental model of real-structure carotid arteries. Microparticle image velocimetry was adopted to comprehensively measure blood velocity field data at the stenosis location, providing experimental validation of numerical simulation (Fluent; finite volume method) results. Then, the flow field was simulated at a normal human heart rate (45–120 beats per minute). The radial sectional velocity exhibited a plateau-like distribution with a similar velocity in the central region (more than 65% of the total channel width). This study provides an accurate understanding of the WSS at the carotid stenosis location and proposes a reliable method for the study of flow fields under various blood flow conditions.

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26

Koelink, M. H., F. F. M. de Mul, A. L. Weijers, J. Greve, R. Graaff, A. C. M. Dassel y J. G. Aarnoudse. "Fiber-coupled self-mixing diode-laser Doppler velocimeter: technical aspects and flow velocity profile disturbances in water and blood flows". Applied Optics 33, n.º 24 (20 de agosto de 1994): 5628. http://dx.doi.org/10.1364/ao.33.005628.

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27

Fujinami, Kotaro y Katsuaki Shirai. "Performance Evaluation of Cross-Correlation Based Photoacoustic Measurement of a Single Object with Sinusoidal Linear Motion". Applied Sciences 13, n.º 24 (12 de diciembre de 2023): 13202. http://dx.doi.org/10.3390/app132413202.

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Photoacoustic (PA) velocimetry holds the advantage of detecting ultrasound signals from selective targets sensitive to specific wavelengths of light irradiation. In particular, it is expected to be applied for measuring blood flow in microvasculature. However, PA velocimetry has not been sufficiently investigated for small velocity ranges down to several tens of millimeters per second. This study evaluates the performance and uncertainty of PA velocity measurements using a single graphite cylinder (GC) as a moving object. A pair of short laser pulses irradiated the object within a brief time interval. The velocity was measured based on the cross-correlation peak of successive PA signal pairs in the time domain. The limiting measurement uncertainty was 3.4 mm/s, determined by the sampling rate of the digitizer. The object motion was controlled in a sinusoidal linear motion, realized using a loudspeaker. With the PA measurement, the velocity of the object was obtained with a time resolution in milliseconds and with directional discrimination. Notably, the PA velocity measurements successfully provided the local velocities of the object across a wide range, with the reference velocity obtained as the time derivative of the displacement data acquired using a laser displacement sensor (LDS). The PA measurement exhibited uncertainties ranging from 0.86 to 2.1 mm/s for the maximum and minimum velocities during the experiment. The uncertainties are consistent with those in stationary cases, and nearly constant in the investigated velocity range. Furthermore, the PA measurements revealed local fine velocities of the object, which were not resolved by the reference velocities of the LDS measurements. The capability of the PA velocity measurement was found to be advantageous for measurements of objects with dynamic variations in magnitude and direction.

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28

Discetti, Stefano y Filippo Coletti. "Volumetric velocimetry for fluid flows". Measurement Science and Technology 29, n.º 4 (6 de marzo de 2018): 042001. http://dx.doi.org/10.1088/1361-6501/aaa571.

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29

Ilic, Jelena, Slavica Ristic y Milesa Sreckovic. "Laser doppler velocimetry and confined flows". Thermal Science 21, suppl. 3 (2017): 825–36. http://dx.doi.org/10.2298/tsci160720278i.

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Finding the mode, in which two component laser Doppler velocimetry can be applied to flows confined in cylindrical tubes or vessels, was the aim of this study. We have identified principle issues that influence the propagation of laser beams in laser Doppler velocimetry system, applied to flow confined in cylindrical tube. Among them, the most important are influences of fluid and wall refractive indices, wall thickness and internal radius ratio and beam intersection angle. In analysis of the degrees of these influences, we have applied mathematical model, based on geometrical optics. The separation of measurement volumes, that measure different velocity components, has been recognized as the main drawback. To overcome this, we propose a lens with dual focal length ? primary focal length for the measurement of one velocity component and secondary focal length for the measurement of the other velocity component. We present here the procedure for calculating the optimal value of secondary focal length, depending on experimental set-up parameters. The mathematical simulation of the application of the dual focal length lens, for chosen cases presented here, confirmed the accuracy of the proposed procedure.

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30

Yang, Yao-Yu y Shih-Chung Kang. "Crowd-based velocimetry for surface flows". Advanced Engineering Informatics 32 (abril de 2017): 275–86. http://dx.doi.org/10.1016/j.aei.2017.03.007.

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31

Yu, Paulo y Vibhav Durgesh. "Comparison of Flow Behavior in Saccular Aneurysm Models Using Proper Orthogonal Decomposition". Fluids 7, n.º 4 (23 de marzo de 2022): 123. http://dx.doi.org/10.3390/fluids7040123.

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Aneurysms are abnormal ballooning of a blood vessel. Previous studies have shown presence of complex flow structures in aneurysms. The objective of this study was to quantify the flow features observed in two selected saccular aneurysm geometries over a range of inflow conditions using Proper Orthogonal Decomposition (POD). For this purpose, two rigid-wall saccular aneurysm models geometries were used (i.e., the bottleneck factor of 1 and 1.6), and the inflow conditions were varied using a peak Reynolds number (Rep) from 50 and 270 and Womersley number (α) from 2 and 5. The velocity flow field data for the studied aneurysm geometries were acquired using Particle Image Velocimetry (PIV). The average flow field from the PIV measurement showed that the model geometry and Rep have more significant impact on the average flow field than the variations in α. The POD results showed that the method was able to quantify the flow field characteristics between the two model geometries. The mode shapes obtained showed different spatial structures for each inflow scenarios and models. The POD energy results showed that more than 80% of the fluctuating kinetic energy were captured within five POD modes for BF=1.0 flow scenarios, while they were captured within ten modes for BF=1.6. The time varying coefficient results showed the complex interplay of POD modes at different inflow scenarios, highlighting important modes at different phases of the flow cycle. The low-order reconstruction results showed that the vortical structure either proceeded outward or stayed within the aneurysm, and this behavior was highly dependent on α, Rep, and model geometry that were not evident in average PIV results.

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32

Danehy, Paul M., Ross A. Burns, Daniel T. Reese, Jonathan E. Retter y Sean P. Kearney. "FLEET Velocimetry for Aerodynamics". Annual Review of Fluid Mechanics 54, n.º 1 (5 de enero de 2022): 525–53. http://dx.doi.org/10.1146/annurev-fluid-032321-025544.

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Long-lasting emission from femtosecond excitation of nitrogen-based flows shows promise as a useful mechanism for a molecular tagging velocimetry instrument. The technique, known as femtosecond laser electronic excitation tagging (FLEET), was invented at Princeton a decade ago and has quickly been adopted and used in a variety of high-speed ground test flow facilities. The short temporal scales offered by femtosecond amplifiers permit nonresonant multiphoton excitation, dissociation, and weak ionization of a gaseous medium near the beam's focus without the generation of a laser spark observed with nanosecond systems. Gated, intensified imaging of the resulting emission enables the tracking of tagged molecules, thereby measuring one to three components of velocity. Effects of local heating and acoustic disturbances can be mitigated with the selection of a shorter-wavelength excitation source. This review surveys the development of FLEET over the decade since its inception, as it has been implemented in several test facilities to make accurate, precise, and seedless velocimetry measurements for studying complex high-speed flows.

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33

Maicke, Brian A. y Joseph Majdalani. "Particle Image Velocimetry in Confined Vortex Flows". Journal of Physics: Conference Series 548 (24 de noviembre de 2014): 012060. http://dx.doi.org/10.1088/1742-6596/548/1/012060.

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34

Brandner, Markus y Gert Holler. "Optical velocimetry in cryogenic two-phase flows". Procedia Engineering 5 (2010): 1474–77. http://dx.doi.org/10.1016/j.proeng.2010.09.395.

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35

Maas, H. G., A. Gruen y D. Papantoniou. "Particle tracking velocimetry in three-dimensional flows". Experiments in Fluids 15, n.º 2 (julio de 1993): 133–46. http://dx.doi.org/10.1007/bf00190953.

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36

Hessenkemper, H. y T. Ziegenhein. "Particle Shadow Velocimetry (PSV) in bubbly flows". International Journal of Multiphase Flow 106 (septiembre de 2018): 268–79. http://dx.doi.org/10.1016/j.ijmultiphaseflow.2018.04.015.

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37

Malik, N. A., Th Dracos y D. A. Papantoniou. "Particle tracking velocimetry in three-dimensional flows". Experiments in Fluids 15-15, n.º 4-5 (septiembre de 1993): 279–94. http://dx.doi.org/10.1007/bf00223406.

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38

Dracos, Th y A. Gruen. "Videogrammetric Methods in Velocimetry". Applied Mechanics Reviews 51, n.º 6 (1 de junio de 1998): 387–413. http://dx.doi.org/10.1115/1.3099011.

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Photogrammetry has been successfully applied in surveying and mapping for a long time. New imaging techniques, digital data acquisition and storage and powerful computing facilities transformed photogrammetry into videogrammetry, a technique applied in many fields for precise and reliable position measurements. Two applications of videogrammetry in fluid mechanics are presented in this article. Both are at their present stage of development suited for three-dimensional velocity measurements in liquids. One is based on tracking particles seeded in the liquid by using three to four synchronized video-cameras (PTV). It allows one to determine accurately the velocity vectors at a large number of points inside a thick observation volume and also to follow the trajectories of these particles for sufficiently long time periods. It is especially well suited for Lagrangian measurements in flows. The other tracks small three-dimensional patterns in flows of liquids tagged by fluorescent dye (LIFV). The three-dimensional Laser Induced Fluorescence images needed are obtained by sweeping rapidly a thin laser-light sheet with simultaneous imaging using a high speed solid-state camera. The method yields the shift and deformations of the liquid volumes associated with these patterns and allows one to determine velocity vectors and their derivatives simultaneously and accurately at a large number of points inside the observation volume. This review article includes 100 references.

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39

Thompson, B. E., O. Bouchery y K. D. Lowney. "Refractive-Index-Matching Laser Velocimetry for Complex, Isothermal Flows". Journal of Fluids Engineering 120, n.º 1 (1 de marzo de 1998): 204–7. http://dx.doi.org/10.1115/1.2819650.

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Refractive-Index-Matching Laser Velocimetry (RIMLV) obtains velocity distributions inflow through complex geometries. Laser velocimetry is used to measure the flow of a constant-temperature mixture that has the refractive index of acrylic models. This mixture can be used to obtain duct Reynolds numbers in the turbulent regime at moderate expense. Measurements can be obtained at desired locations, specifically inside complex models even if laser beams pass through multiple curved surfaces, which is advantageous when comparing measured and calculated results.

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40

Wills, Angus O., Manuj Awasthi, Danielle J. Moreau y Con J. Doolan. "Schlieren Image Velocimetry for Wall-Bounded Supersonic Flows". AIAA Journal 58, n.º 9 (septiembre de 2020): 4174–77. http://dx.doi.org/10.2514/1.j059586.

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41

Maurice, Mark S. "Laser velocimetry seed particles within compressible, vortical flows". AIAA Journal 30, n.º 2 (febrero de 1992): 376–83. http://dx.doi.org/10.2514/3.10928.

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42

Roehle, I. y C. E. Willert. "Extension of Doppler global velocimetry to periodic flows". Measurement Science and Technology 12, n.º 4 (19 de marzo de 2001): 420–31. http://dx.doi.org/10.1088/0957-0233/12/4/306.

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43

Westerweel, Jerry, Gerrit E. Elsinga y Ronald J. Adrian. "Particle Image Velocimetry for Complex and Turbulent Flows". Annual Review of Fluid Mechanics 45, n.º 1 (3 de enero de 2013): 409–36. http://dx.doi.org/10.1146/annurev-fluid-120710-101204.

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44

Prasad, A. K. y R. J. Adrian. "Stereoscopic particle image velocimetry applied to liquid flows". Experiments in Fluids 15, n.º 1 (junio de 1993): 49–60. http://dx.doi.org/10.1007/bf00195595.

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45

Bergthorson, J. M. y P. E. Dimotakis. "Particle velocimetry in high-gradient/high-curvature flows". Experiments in Fluids 41, n.º 2 (5 de mayo de 2006): 255–63. http://dx.doi.org/10.1007/s00348-006-0137-6.

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46

Ribarov, L. A., J. A. Wehrmeyer, R. W. Pitz y R. A. Yetter. "Hydroxyl tagging velocimetry (HTV) in experimental air flows". Applied Physics B: Lasers and Optics 74, n.º 2 (1 de febrero de 2002): 175–83. http://dx.doi.org/10.1007/s003400100777.

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47

Lee, Sang Joon y Seok Kim. "Advanced particle-based velocimetry techniques for microscale flows". Microfluidics and Nanofluidics 6, n.º 5 (29 de enero de 2009): 577–88. http://dx.doi.org/10.1007/s10404-009-0409-6.

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48

Ziegenhein, T. y D. Lucas. "On sampling bias in multiphase flows: Particle image velocimetry in bubbly flows". Flow Measurement and Instrumentation 48 (abril de 2016): 36–41. http://dx.doi.org/10.1016/j.flowmeasinst.2016.02.003.

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49

Matulka, A. M., Y. Zhang y Y. D. Afanasyev. "Complex environmental beta-plane turbulence: laboratory experiments with altimetric imaging velocimetry". Nonlinear Processes in Geophysics Discussions 2, n.º 6 (9 de noviembre de 2015): 1507–29. http://dx.doi.org/10.5194/npgd-2-1507-2015.

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Abstract. Results from the spectral analyses of the flows in two experiments where turbulent flows were generated in a rotating tank with topographic β-effect, are presented. The flows were forced either by heating water from below or supplying fresh water at the top of saline layer. The flow was essentially barotropic in the first experiment and baroclinic in the second experiment. The gradient of the surface elevation was measured using optical altimetry (Altimetric Imaging Velocimetry). Multiple zonal jets of alternating direction were observed in both experiments. Turbulent cascades of energy exhibit certain universal properties in spite of the different nature of flows in the experiments.

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50

Ortiz-Villafuerte, Javier, D. R. Todd y Yassin A. Hassan. "VELOCITY MEASUREMENTS IN BUBBLY FLOWS WITH PARTICLE TRACKING VELOCIMETRY". Journal of Flow Visualization and Image Processing 8, n.º 2-3 (2001): 10. http://dx.doi.org/10.1615/jflowvisimageproc.v8.i2-3.120.

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