Dissertations / Theses on the topic 'Cardiovascular fluid mechanic'

Thesis (Ph. D.)--University of Glasgow, 1998.
Thesis submitted to the Department of Cardiac Surgery, Faculty of Medicine, University of Glasgow, in fulfilment of the degree of Doctor of Philosophy. Print version also available.

Thesis (Ph. D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2005.
Yoganathan, Ajit, Committee Member ; Sturm, Terry, Committee Member ; Webster, Donald, Committee Member ; Roberts, Philip, Committee Member ; Sotiropoulos, Fotis, Committee Chair ; Fritz, Hermann, Committee Member. Includes bibliographical references.

Atherosclerosis is a disease of the cardiovascular system where a stenosis may develop in an artery which is an abnormal narrowing in the blood vessel that adversely affects the blood flow. Due to the constriction of the blood vessel, the flow is disturbed, forming a jet and recirculation downstream of the stenosis. Dynamic pressure fluctuations on the inner wall of the blood vessel leads to the vibration of the vessel structure and acoustic energy is propagated through the surrounding tissue that can be detected on the skin surface. Acoustic energy radiating from the interaction of blood flow and stenotic blood vessel carries valuable information from a diagnostic perspective. In this study, a constricted blood flow is modeled by using ADINA finite element analysis software together with the blood vessel in the form of a thin cylindrical shell with an idealized blunt constriction. The flow is considered as incompressible and Newtonian. Water properties at indoor temperature are used for the fluid model. The diameter of the modeled vessel is 6.4 mm with 87% area reduction at the throat of the stenosis. The flow is investigated for Reynolds numbers 1000 and 2000. The problem is handled in three parts which are rigid wall Computational Fluid Dynamics (CFD) solution, structural analysis of fluid filled cylindrical shell, and Fluid Structure Interaction (FSI) solutions of fluid flow and vessel structure. The pressure fluctuations and consequential vessel wall vibrations display broadband spectral content over a range of several hundred Hz with strong fluid-structural coupling. Maximum dynamic pressure and vibration amplitudes are observed around the reattachment point of the flow near the exit of the stenosis and this effect gradually decreases along downstream of flow. Results obtained by the numerical simulations are compared with relevant studies in the literature and it is concluded that ADINA can be used to investigate these types of problems involving high frequency pressure fluctuations of the fluid and the resulting vibratory motion of the surrounding blood vessel structure.

The diseases of cardiovascular system and the respiratory system have been the second and third killers causing deaths in Hong Kong. In this stressful civilized world, the prevalence and incidence of these diseases increased prominently which arouse our concern on the theories behind the pathological conditions. This report will focus on the biofluid mechanics in the large artery and in the upper airway. Thoracic aortic dissection, characterized by the tearing in the middle layer of vessel wall, is a catastrophic vascular disorder. The wall of the newly formed channel, the false lumen, is weakened and prone to aortic events. Endovascular repair is a minimally invasive technique for treating dissection patients. The biomechanical factors and the length of endograft were studied by computational fluid dynamics. Two geometrical factors showed a significant impact on the backflow in the false lumen. A larger false lumen and a larger distal tear size greatly affected the extent of thrombosis in the false lumen. It made the false lumen under a higher risk of vessel rupture. The computational prediction also demonstrated a more stable hemodynamic condition in the model with a longer endograft. These results provide important information for the clinicians to propose the surgical procedures and to improve the design of endografts. Airway obstruction is a common breathing disorder but it is always underdiagnosed. Obstructive sleep apnea (OSA) and different dentofacial deformities are two pathological conditions in which the patients have the abnormal sizes of airways. Computational fluid dynamic was employed in both conditions with patient–specific models. In the part of OSA, pre– and post–operative models were studied. The dimensions and flow resistance of the upper airway showed a significant improvement after mandibular distraction. The percentage of stenosis and the flow resistance was reduced by 27.3% and 40.7% respectively. For the patients in three facial skeletal deformity groups, the cross–sectional area and the flow resistance were compared. The patients with Class II deformity had the smallest retroglossal and retroplatal dimensions as well as the greatest flow resistance. The results confirmed the effectiveness of mandibular distraction and also provide valuable implications for the clinicians on the treatment planning, particularly for the Class II subjects.
published_or_final_version
Mechanical Engineering
Master
Master of Philosophy

The heart is a complex organ and much is still unknown about its mechanical function. In order to use simulations to study heart mechanics, fluid and solid components and their interaction should be incorporated into any numerical model. Many previous studies have focused on myocardium motion or blood flow separately, while neglecting their interaction. Previous fluid-structure interaction (FSI) simulations of heart mechanics have made simplifying assumptions about their solid models, which prevented them from accurately predicting the stress-stain behaviour of the myocardium. In this work, a numerical model of the canine left ventricle (LV) is presented, which serves to address the limitations of previous studies. A canine LV myocardium material model was developed for use in conjunction with a commercial finite element code. The material model was modified from its original form to make it suitable for use in simulations. Further, numerical constraints were imposed when calculating the material parameter values, to ensure that the model would be strictly convex. An initial geometry and non-zero stress state are required to start cardiac cycle simulations. These were generated by the static inflation of a passive LV model to an end-diastolic pressure. Comparisons with previous measurements verified that the calculated geometry was representative of end diastole. Stresses calculated at the specified end diastolic pressure showed complex spatial variations, illustrating the superiority of the present approach over a specification of an arbitrary stress distribution to an end-diastolic geometry. In the third part of this study, FSI simulations of the mechanics of the LV were performed over the cardiac cycle. Calculated LV cavity pressures agreed well with previous measurements during most of the cardiac cycle, but deviated from them during rapid filling, which resulted in non-physiological backflow. This study is the first one to present a detailed analysis of the temporal and spatial variations of the properties of both the solid and the fluid components of the canine LV. The observed development of non-uniform pressure distributions in the LV cavity confirms the advantage of performing FSI simulations rather than imposing a uniform fluid pressure on the inner surface of the myocardium during solid-only simulations.

Single ventricle heart defects are present in two of every 1000 live births in the US. In this condition the systemic and pulmonary blood flow mix in the functioning ventricle, resulting in insufficient blood oxygenation to sustain life. As part of the palliation of these defects, the staged surgical procedure, known as the Fontan procedure, is performed. Here, the venous returns are directed to the pulmonary arteries, bypassing the right heart and forming the Total Cavopulmonary Connection (TCPC). Even though the palliation improves life expectancy, there are numerous long-term complications that become more prevalent as patients reach adulthood. Many of these complications have been related to the function of the single ventricle circulation, especially to the abnormal TCPC hemodynamics, for which this has been the focus of research throughout the years. Recent progress has been made with the availability of improved medical imaging techniques and computational modeling tools; however, there is limited information on how these evolve in time. In order to improve the Fontan palliation, image-based surgical planning has been used in the most complex cases to prospectively design the TCPC, aiming to improve the hemodynamics. Even though this paradigm has shown promising results, improvement is needed to provide more realistic predictions of the post-operative outcomes. To address this, in this thesis we have developed a novel surgical planning framework that allows us to: (i) model the interaction of the TCPC and global circulation hemodynamics, and (ii) assess the robustness of the surgical option proposed. Here, the single ventricle circulation is modeled using a lumped parameter model, coupled to a computational fluid solver to describe the local TCPC hemodynamics. With this framework, we can predict the immediate post-operative state, model various physiological scenarios, and assess the impact on the local hemodynamics and global circulation. This will allow us to provide information on the effect on the global hemodynamics to the clinical team. In addition to the surgical planning advancements obtained in this thesis, we have performed the largest longitudinal Fontan study to date in which we have evaluated the evolution of the Fontan physiology in time and the effect it has on the energy efficiency of the TCPC. In this thesis, we have studied the short and long-term effects that geometrical and physiological changes have on the Fontan hemodynamics. With this, we have improved the understanding of the Fontan physiology in terms of the short-term effects of Fontan palliation and the long-term deterioration of the changing single ventricle physiology.

La progressió de l'aterosclerosi i la trombosi en pacients amb risc de malaltia cardiovascular depèn en gran mesura de l'entorn únic a nivell físic i bioquímic cada individu. Característiques tals com l'arquitectura de la vasculatura, la composició bioquímica de la sang o el tipus de tractament defineixen el resultat de les intervencions cardiovasculars. La col•locació d'un stent o d'un bypass busca recuperar la permeabilitat del vas, però es veu limitada per la restenosis i la trombosi. El disseny de models multi-escala específics per a cada pacient pot ajudar a entendre la progressió d'aquests esdeveniments en tenir la capacitat per integrar les respostes cel•lulars microscòpiques en el context del flux macroscòpic i de les condicions estructurals. Aquests models poden proporcionar informació sobre com mitigar respostes adverses en funció de cada individu. Emprant mètodes in silico i in vitro prèviament validats, s'ha desenvolupat una plataforma de replicació arterial per reproduir bifurcacions vasculars coronàries i caròtides derivades d'imatges clíniques que s'han fet servir per generar arxius computacionals per a anàlisi in silico per una banda i per fabricar models arterials polimèrics biocompatibles per a anàlisis in vitro de l’altra. En paral•lel amb les simulacions de flux, els models físics van ser sembrats amb cèl•lules vasculars centrals en l'hemostàsia i la resposta a les lesions. Els models vasculars van ser exposats a fluxos fisiològics rellevants i a entorns urèmics, inflamatoris o anti-proliferatius. Després de la caracterització funcional dels models, el progrés de l'aterosclerosi i la trombosi es va quantificar a nivell local i es va correlacionar amb les característiques biològiques, químiques i físiques de l'entorn cel•lular. La quantitat de recirculació i la presència d'agents inflamatoris, productes químics anti proliferatius i de sèrum i soluts urèmics van ser crítics per a l'activació dels biomarcadors d'evolució d'aterosclerosi i trombosi . Plataformes integrades tals com la descrita en aquesta tesi podrien ser molt útils en una varietat de camps de la biomedicina. La plataforma pot ajudar els investigadors a respondre una sèrie de qüestions biològiques clínicament rellevants i té la capacitat de produir empelts vasculars bioimplantables en un futur pròxim.
La progresión de la aterosclerosis y la trombosis en pacientes con riesgo de enfermedad cardiovascular depende en gran medida del entorno único a nivel físico y bioquímico de cada individuo. Características tales como la arquitectura de la vasculatura, composición bioquímica de la sangre o el tipo de tratamiento definen el resultado de las intervenciones cardiovasculares. La colocación de un stent o de un bypass busca recuperar la permeabilidad del vaso, pero se ve limitada por la restenosis y la trombosis. El diseño de modelos multi-escala específicos para cada paciente puede ayudar a entender la progresión de estos eventos al tener capacidad para integrar las respuestas celulares microscópicas en el contexto del flujo macroscópico y de las condiciones estructurales. Dichos modelos pueden proporcionar información sobre cómo mitigar respuestas adversas en función de cada individuo. Usando métodos in silico e in vitro previamente validados se ha desarrollado una plataforma de replicación arterial para reproducir bifurcaciones vasculares coronarias y carótidas derivadas de imágenes clínicas, que se han usado para generar archivos computacionales para análisis in silico por un lado y para fabricar modelos arteriales poliméricos biocompatibles para análisis in vitro por otro. En paralelo con las simulaciones de flujo, los modelos físicos fueron sembrados con células vasculares centrales en la hemostasia y la respuesta a las lesiones. Los modelos vasculares fueron expuestos a flujos fisiológicos relevantes y a entornos urémicos, inflamatorios o anti proliferativos. Tras la caracterización funcional de los modelos, el progreso de la aterosclerosis y la trombosis se cuantificó a nivel local y se correlacionó con las características biológicas, químicas y físicas del entorno celular. La cantidad de recirculación y la presencia de agentes inflamatorios, productos químicos anti proliferativos y de suero y solutos urémicos fueron críticos para la activación de los biomarcadores de evolución de aterosclerosis y trombosis. Plataformas integradas tales como la descrita en esta tesis podrían ser muy útiles en una variedad de campos de la biomedicina. La plataforma puede ayudar a los investigadores a responder una serie de cuestiones biológicas clínicamente relevantes y tiene la capacidad de producir injertos vasculares bioimplantables en un futuro próximo.
Progression of atherosclerosis and thrombosis in patients at risk of cardiovascular disease depend heavily upon the unique physical and biochemical environment of each individual. Characteristics such as vessel architecture, biochemical composition of blood or type of treatment define the outcome of cardiovascular interventions. Stent placement and graft positioning seek to recover vessel patency, yet are limited by restenosis and thrombosis. Composite, patient-specific, multi-scale models able to integrate microscopic cellular responses in the context of relevant macroscopic flow and structural conditions may help understand the progression of these events, providing insight into how to mitigate adverse responses in specific settings and individuals. Based on previously validated in silico and in vitro methods, an arterial replication platform was developed. Vascular architectures from coronary and carotid bifurcations were derived from clinical imaging and used to generate conjoint computational meshing for in silico analysis and polymeric, biocompatible scaffolds for in vitro models. In parallel with three dimensional flow simulations, the geometrically-realistic constructs were seeded with vascular cells critical to vessel hemostasis and response to injury and exposed to relevant, physiologic flows and uremic, inflammatory or anti-proliferative conditions. Following functional characterization, in vitro surrogates of atherosclerotic and thrombogenic progression were locally quantified and correlated with the biological, chemical and physical characteristics of the cellular environment. The extent of recirculation and the presence of inflammatory agents, anti-proliferative chemicals and uremic serum and solutes were critical to the activation of atherosclerosis and thrombosis progression biomarkers. Integrated frameworks such as the one described in this thesis could be very useful in a range of biomedical fields. The platform may help researchers to answer an array of biological and clinically relevant questions and holds the capacity to cast bioimplantable vascular grafts in a close future.

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O objetivo deste trabalho é estudar a modelagem do escoamento de fluidos incompressíveis, visando modelar a hemodinâmica presente no sistema cardiovascular humano. Para tanto, vamos usar método de lattice Boltzmann (LBM), baseado na cinética mesoscópica, que permite simular o comportamento macro-contínuo da dinâmica de fluidos. Acoplado a este método, será usado um método de fronteira imersa para modelar as interações entre fluido e estrutura (como ocorre entre o sangue e a parede arterial). Ainda, visando a modelagem de condições fisiológicas realistas, será empregada uma abordagem de acoplamento de modelos dimensionalmente heterogêneos. Para isto serão desenvolvidos algoritmos para acoplar o LBM com um método de diferenças finitas, para a modelagem unidimensional do escoamento de sangue em vasos deformáveis. Serão detalhados diversos aspectos e desenvolvimentos teóricos dos métodos introduzidos e faremos estudos de caráter numérico, através de simulações de problemas estacionários e transientes, cujas características são similares às encontradas na modelagem do escoamento sanguíneo em artérias. Visando prover técnicas e orientações para a modelagem do escoamento sanguíneo no sistema arterial em regime fisiológico de forma acurada e computacionalmente eficiente por meio do uso do LBM.

L'utilisation d'Assistance Circulatoire Mécanique (ACM) augmente dans le cas d'insuffisance cardiaque terminale ne répondant pas aux traitements médicaux. Dans ce contexte nous avons: 1) présenté une vue d'ensemble des problématiques cliniques, 2) élaboré une nouvelle approche de planification assistée par ordinateur pour l'implantation d'ACM, 3) implémenté un modèle CFD pour comprendre l'hémodynamique ventriculaire induite par la canule apicale. Afin de diminuer les complications, des critères quantitatifs optimisant la décharge ventriculaire pourraient être déterminés par CFD. La planification fournirait des informations permettant de choisir le dispositif et adapter la stratégie clinique
Mechanical Circulatory Support (MCS) therapy is increasingly considered for patients with advanced heart failure unresponsive to optimal medical treatments. In this context, we: 1) presented an overview of clinical issues raised by MCS implantation, 2) designed a novel computer-assisted approach for planning the implantation, 3) implemented a CFD model to understand the ventricle hemodynamics induced by the inflow cannula pose. With the aim of decreasing complications and morbidity, quantitative criteria for optimizing ventricle unloading could be determined through CFD, and the planning approach may provide valuable information for choosing the device and adapting the clinical strategy

Defective or diseased native valves have been replaced by bileaflet mechanical heart valves (BMHVs) for many years. However, severe complications still exist, and thus blood damage that occurs in BMHV flows must be well understood. The aim of this research is to numerically study platelet damage that occurs in BMHV flows. The numerical suspension flow method combines lattice-Boltzmann fluid modeling with the external boundary force method. This method is validated as a general suspension flow solver, and then validated against experimental BMHV flow data. Blood damage is evaluated for a physiologic adult case of BMHV flow and then for BMHVs with pediatric sizing and flow conditions. Simulations reveal intricate, small-scale BMHV flow features, and the presence of turbulence in BMHV flow. The results suggest a shift from previous evaluations of instantaneous flow to the determination of long-term flow recirculation regions when assessing thromboembolic potential. Sharp geometries that may induce these recirculation regions should be avoided in device design. Simulations for predictive assessment of pediatric sized valves show increased platelet damage values for potential pediatric valves. However, damage values do not exceed platelet activation thresholds, and highly damaged platelets are found far from the valve. Thus, the increased damage associated with resized valves is not such that pediatric valve development should be hindered. This method can also be used as a generic tool for future evaluation of novel prosthetic devices or cardiovascular flow problems.

In cardiovascular medicine, the assessment of blood flow is fundamental to the understanding and detection of disease. Many pharmaceutical, interventional, and surgical treatments impact the flow. The primary purpose of the cardiovascular system is to drive, control and maintain blood flow to all parts of the body. In the normal cardiovascular system, fluid transport is maintained at high efficiency and the blood flow is essentially laminar. Disturbed and turbulent blood flow, on the other hand, appears to be present in many cardiovascular diseases and may contribute to their initiation and progression. Despite strong indications of an important interrelationship between flow and cardiovascular disease, medical imaging has lacked a non-invasive tool for the in vivo assessment of disturbed and turbulent flow. As a result, the extent and role of turbulence in the blood flow of humans have not yet been fully investigated. Magnetic resonance imaging (MRI) is a versatile tool for the non-invasive assessment of flow and has several important clinical and research applications, but might not yet have reached its full potential. Conventional MRI techniques for the assessment of flow are based on measurements of the mean velocity within an image voxel. The mean velocity corresponds to the first raw moment of the distribution of velocities within a voxel. An MRI framework for the quantification of any moment (mean, standard deviation, skew, etc.) of arbitrary velocity distributions is presented in this thesis. Disturbed and turbulent flows are characterized by velocity fluctuations that are superimposed on the mean velocity. The intensity of these velocity fluctuations can be quantified by their standard deviation, which is a commonly used measure of turbulence intensity. This thesis focuses on the development of a novel MRI method for the quantification of turbulence intensity. This method is mathematically derived and experimentally validated. Limitations and sources of error are investigated and guidelines for adequate application of MRI measurements of turbulence intensity are outlined. Furthermore, the method is adapted to the quantification of turbulence intensity in the pulsatile blood flow of humans and applied to a wide range of cardiovascular diseases. In these applications, elevated turbulence intensity was consistently detected in regions where highly disturbed flow was anticipated, and the effects of potential sources of errors were small. Diseased heart valves are often replaced with prosthetic heart valves, which, in spite of improved benefits and durability, continue to fall short of matching native flow patterns. In an in vitro setting, MRI was used to visualize and quantify turbulence intensity in the flow downstream from four common designs of prosthetic heart valves. Marked differences in the extent and degree of turbulence intensity were detected between the different valves. Mitral valve regurgitation is a common valve lesion associated with progressive left atrial and left ventricular remodelling, which may often require surgical correction to avoid irreversible ventricular dysfunction. The spatiotemporal dynamics of flow disturbances in mitral regurgitation were assessed based on measurements of flow patterns and turbulence intensity in a group of patients with significant regurgitation arising from similar valve lesions. Peak turbulence intensity occurred at the same time in all patients and the total turbulence intensity in the left atrium appeared closely related to the severity of regurgitation. MRI quantification of turbulence intensity has the potential to become a valuable tool in investigating the extent, timing and role of disturbed blood flow in the human cardiovascular system, as well as in the assessment of the effects of different therapeutic options in patients with vascular or valvular disorders.

L'utilisation de stents actifs (DES) a révolutionné le traitement de l'athérosclérose. Le relargage contrôlé de médicaments anti-prolifératifs dans la paroi artérielle (PA) a permis de réduire fortement le taux de resténose intra-stent. Mais le risque de thromboses intra-stents tardives demeure un enjeu majeur des DES en partie lié au retard de cicatrisation de la PA endommagée lors de l'implantation. Cette thèse présente une méthode d'optimisation du design des DES afin d'inhiber la resténose sans affecter la cicatrisation. Pour quantifier la performance des différents designs, un modèle numérique décrivant l'écoulement sanguin et le transport de médicaments dans les artères stentées a été développé. Il prend en compte la structure multi-couches de la PA et les interactions du médicament avec les cellules. Un algorithme d'optimisation est couplé au modèle afin d'identifier les DES optimaux. L'optimisation du temps de relargage ainsi que de la concentration initiale du médicament dans le revêtement du DES ont un effet significatif sur la performance. Lorsque le médicament utilisé est le paclitaxel, les solutions optimales consistent à relarguer le produit à des concentrations nettement inférieures à celles des DES actuels soit pendant quelques heures, soit pendant une durée d'un an. Pour le sirolimus, un relargage lent est nécessaire. Les formes optimales des spires du DES sont toujours allongées mais profilées seulement lorsque le relargage est rapide. Ces résultats permettent d'expliquer en partie les performances des différents DES récents et révèlent un fort potentiel d'amélioration dans la conception des DES par rapport aux dispositifs commerciaux actuels.

This thesis focuses on special arterial fluid mechanics techniques developed for patient-specific computer modeling of blood flow in cerebral arteries with aneurysm and stent. These techniques are used in conjunction with the core computational technique, which is the space–time version of the variational multiscale (VMS) method and is called “DST/SST-VMST.” The special techniques include using NURBS for the spatial representation of the surface over which the stent mesh is built, mesh generation techniques for both the finite- and zero-thickness representations of the stent, techniques for generating refined layers of mesh near the arterial and stent surfaces, and models for representing double stent. We compute the unsteady flow patterns in the aneurysm and investigate how those patterns are influenced by the presence of single and double stents. We also compare the flow patterns obtained with the finite- and zero-thickness representations of the stent.

The mechanisms behind cardiovascular disease (CVD) initiation and progression are not fully elucidated. It is hypothesized that blood flow patterns regulate endothelial cell (EC) function to affect the progression of CVDs. A system that subjects ECs to physiologically-relevant shear stress waveforms within microfluidic devices has not yet been demonstrated, despite the advantages associated with the use of these devices. In this work, a bioreactor was designed to fulfill this need. Waveforms from regions commonly affected by CVDs including were derived. Pump motion and fluid flow profiles were validated by actuator motion tracking, particle image velocimetry, and flowmeters. While several relevant waveforms were successfully replicated, physiological waveforms could not be produced at physiological frequencies owing to actuator velocity and accuracy limitations, as well as dampening effects in the system. Overall, this work lays the foundation for designing a system that provides insight into the role of shear stress in CVD pathogenesis.

Author's name: Bc. Irena Malá School: Charles university, Prague 1st Faculty of Medicine Institut of Theory and Practice of Nursing Vídeňská 800, 140 59 Prague 4 - Krč Program: Health Care Administration Title: Early postoperative care of the patient with the left ventricular assist device HeartMate II Diploma thesis supervisor: PhDr. Hocková Jana, PhD. Number of pages: 170 Number of attachments: 41 Year: 2013 Key words: early postoperative care, hypotermia, blood transfusion, fluid resuscitation, perioperative cardiovascular dysfunction, pharmacologic support, ventricular assist device HeartMateII, monitoration, device, cardiac arrhythmias, ventilation management, postoperative anticoagulation, glycemic kontrol, renal insufficiency, nutrition, nursing, complications, physiotherapy, psychological aspects The occurrence of the heart failure is similar to an epidemic with high mortality. This fact, together with stagnate or even decreasing number of suitable donors, led to a need of replacing the heart pump activity with an artificial one. Mechanical cardiac support systems are sophisticated devices that are able to support a certain period of time or completely replace the function of the heart as a pump. The indications implantation of mechanical cardiac support is significant symptomatic heart...