Dissertations / Theses on the topic 'Heart valve'
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1
Peacock, J. A. "Heart valve haemodynamics." Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371560.
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Tseng, Yuan-Tsan. "Heart valve tissue engineering." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:e67c780d-d60f-42e7-9311-dd523f9141b3.
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Since current prosthetic heart valve replacements are costly, cause medical complications, and lack the ability to regenerate, tissue-engineered heart valves are an attractive alternative. These could provide an unlimited supply of immunological-tolerated biological substitutes, which respond to patients' physiological condition and grow with them. Since collagen is a major extra cellular matrix component of the heart valve, it is ideal material for constructing scaffolds. Collagen sources have been shown to influence the manufacturing of collagen scaffolds, and two commercial sources of collagen were obtained from Sigma Aldrich and Devro PLC for comparison. Consistencies between the collagens were shown in the primary and secondary structures of the collagen, while inconsistencies were shown at the tertiary level, when a higher level of natural crosslinking in the Sigma collagen and longer polymer chains in the Devro collagen were observed. These variations were reduced and the consistency increased by introducing crosslinking via dehydrothermal treatment (DHT). Collagen scaffolds produced via freeze-drying (FD) and critical point-drying with cross-linking via DHT or 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide /N-hydroxysuccinimide (EDC/NHS) were investigated. All the scaffolds were compatible with mesenchymal stem cells (MSCs) according to the proliferation of the cells and their ability to produce ECM, without differentiating between osteogenic, chondrogenic or endothelial lineages. The FD EDC/NHS scaffold demonstrated the most suitable physical property of all. This result illustrates that FD EDC/NHS crosslinking is the most suitable scaffold investigated as a start for heart valve tissue engineering. To prepare a scaffold with a controlled local, spatial and temporal delivery of growth factor, a composite scaffold comprising poly (lactic-co-glycolic acid) (PLGA) microspheres was developed. This composite scaffold demonstrated the same compatibility to the MSCs as untreated scaffold. However, the PLGA microspheres showed an increase in the deterioration rate of Young's modulus because of the detachment of the microspheres from the scaffold via cellular degradation.
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Damen, Bas Stefaan, and bsdamen@hotmail com. "Design, Development, and Optimisation of a Culture Vessel System for Tissue Engineering Applications." Swinburne University of Technology. n/a, 2003. http://adt.lib.swin.edu.au./public/adt-VSWT20040512.125051.
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A Tissue Engineering (TE) approach to heart valve replacement has the aim of producing an implant that is identical to healthy tissue in morphology, function and immune recognition. The aim is to harvest tissue from a patient, establish cells in culture from this tissue and then use these cells to grow a new tissue in a desired shape for the implant. The scaffold material that supports the growth of cells into a desired shape may be composed of a biodegradable polymer that degrades over time, so that the final engineered implant is composed entirely of living tissue. The approach used at Swinburne University was to induce the desired mechanical and functional properties of tissue and is to be developed in an environment subjected to flow stresses that mimicked the haemodynamic forces that natural tissue experiences. The full attainment of natural biomechanical and morphological properties of a TE structure has not as yet been demonstrated.
In this thesis a review of Tissue Engineering of Heart Valves (TEHVs) is presented followed by an assessment of biocompatible materials currently used for TEHVs. The thrust of the work was the design and development of a Bioreactor (BR) system, capable of simulating the corresponding haemodynamic forces in vitro so that long-term cultivation of TEHVs and/or other structures can be mimicked. A full description of the developed BR and the verification of its functionality under various physiological conditions using Laser Doppler Anemometry (LDA) are given. An analysis of the fluid flow and shear stress forces in and around a heart valve scaffold is also provided.
Finally, preliminary results related to a fabricated aortic TEHV-scaffold and the developed cell culture systems are presented and discussed. Attempts to establish viable cell lines from ovine cardiac tissue are also reported.
4
Yap, Cheng-Hon. "Factors influencing cryopreserved allograft heart valve degeneration." Connect to thesis, 2006. http://repository.unimelb.edu.au/10187/2120.
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Heart valve replacement is becoming more commonplace in developed nations. Despite this the ideal valve prosthesis has not been found. The allograft valve has been used for over 40 years and remains an important prosthesis with many advantages. However, like other biological valve prosthesis, they have a finite durability. The causes of allograft valve degeneration are still unknown. The study aims to identify factors associated with cryopreserved allograft valve degeneration. Knowledge of such factors will improve our understanding of the potential causes and mechanisms of allograft heart valve degeneration. (For complete abstract open document)
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Anstine, Lindsey J. "Valve cell dynamics in developing, mature, and aging heart valves." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1478692972995079.
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Nordquist, Emily M. "Exploring Heart Valve Homeostasis and Repair." The Ohio State University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=osu1617621956339594.
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Lefebvre, Xavier. "Systolic anterior motion of the mitral valve in obstructive hypertrophic cardiomyopathy : an in-vitro study." Diss., Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/11712.
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Gieseking, Elizabeth Robinson. "Control mechanism for the papillary muscles of the mitral valve : an In Vitro study." Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/10912.
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Bishop, Winona F. "Hydrodynamic performance of mechanical and biological prosthetic heart valves." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/29461.
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One of the major achievements in cardiac surgery over the past 30 years has been the ability to replace severely diseased heart valves with prosthetic ones. The option of using prosthetic heart valves for the treatment of valvular diseases has improved and prolonged many lives. This is reflected in around 120,000 heart valve replacement operations carried out every year in North America alone to correct the cardiovascular problems of stenosis, insufficiency, regurgitation, etc.
The development of artificial heart valves depends on reliable knowledge of the hemodynamic performance and physiology of the cardiovascular system in addition to a sound understanding, at the fundamental level, of the associated fluid mechanics.
It is evident from the literature review that noninvasive measurements in a confined area of complex transient geometry, providing critical information relating to valve performance, are indeed scarce.
This thesis presents results of an extensive test program aimed at measuring turbulence
stresses, steady and transient velocity profiles and their decay downstream of the mitral valve. Three mechanical tilting disc-type heart valves (Björk-Shiley convexo- concave, Björk-Shiley monostrut, and Bicer-Val) and two biological tissue valves (Hancock II and Carpentier-Edwards supraannular) are studied. The investigation
was carried out using a sophisticated and versatile cardiac simulator in conjunction with a highly sensitive, noninvasive, two-component three-beam laser doppler anemometer system. The study covers both the steady (valve fully open) and pulsatile (resting heart rate) flow conditions. The continuous monitoring of the parametric time histories revealed useful details of the complex flow as well as helped establish location and timing of the peak parameter values. In addition,
orientation experiments are conducted on the mechanical valves in an attempt to reduce
stresses by altering the position of the major orifice. The experiments suggest correlation between high stresses and orientation.
Based on the the data, the following general conclusions can be made:
(i) Hemodynamic test results should be presented in nondimensional form to render them independent of test facilities, flow velocities, size of models, etc. This would facilitate comparison of results by different investigators, using different facilities and test conditions.
(ii) The valves tested showed very disturbed flow fields which generated high turbulent stresses presenting a possibility of thromboembolism and, perhaps,
haemolysis.
(iii) Implantation orientation of the valve significantly affect the mechanical prostheses
flow field. The single vortex formation in the posterior orientation results in a reduction in stresses compared to the anterior configuration.
(iv) The present results together with the earlier information on pressure drop and regurgitation provide a comprehensive and organized picture of the valve performance.
(v) The information is fundamental to the improvement in valve design, and development of guidelines for test methodology and acceptable performance criteria for marketing of the valves.Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate
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Jimenez-Mejia, Jorge Hernan. "The loading and function of the mitral valve under normal, pathological and repair conditions : an in vitro study /." Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-11102006-003456/.
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Thesis (Ph. D.)--Biomedical Engineering, Georgia Institute of Technology, 2007.Ajit Yoganathan, Committee Chair ; Thomas Vassiliades, Committee Member ; Joseph Gorman, Committee Member ; Marc Levenston, Committee Member ; John N. Oshinski, Committee Member.
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Bissessor, Naylin. "Complex Heart Valve Disease: Functional Capacity and Natriuretic Peptides Predict Outcomes in mixed and Multiple Heart Valve Disease." Thesis, Griffith University, 2013. http://hdl.handle.net/10072/367217.
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Chronic mixed and multiple heart valve disease constitutes a complex group of cardiac pathologies that are prevalent world wide causing significant mortality and morbidity. The American Heart Association and the European Society of Cardiology concede in their guidelines that little data exists in the international literature on this important subject. Patients tend to adopt a sedentary lifestyle in order to cope with this illness and avoid symptoms causing a steady decline in functional capacity. A physically active lifestyle
is imperative for a good quality of life and cardiovascular wellness. Significant functional impairment through disease portends an adverse prognosis.
Functional capacity impairment can be objectively measured through formal cardiopulmonary exercise testing through determining the peak oxygen consumption (peakVO2). Exercise intolerance may suggest significant underlying symptoms especially in asymptomatic or mildly symptomatic states with severe heart valve lesions. The onset of symptoms is central to the decision to operate and surgical valve replacement. The peakVO2
measurement is the international gold standard of functional aerobic capacity and is widely used in heart failure and cardiac transplant to predict prognosis and outcome. The role of peakVO2 has not been evaluated in complex heart valve disease.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Medical Science
Griffith Health
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Peacock, Jacqueline D. "The Role of Sox9 in Heart Valve Development and Disease." Scholarly Repository, 2011. http://scholarlyrepository.miami.edu/oa_dissertations/543.
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Heart valve structures open and close during the cardiac cycle to provide unidirectional blood flow through the heart, critical for efficient cardiovascular function. Valve dysfunction results in either incomplete opening or incomplete closure of the valve. Both types of valve dysfunction decrease efficiency of blood flow, increasing the load on the myocardium and leading to secondary heart disease such as pathological hypertrophy and heart failure. There are currently no effective treatments to prevent or slow the progression of valve disease, and there are no pharmacological treatments for advanced valve disease. Although most valve disease is associated with aging, increasing evidence suggests that valve disease often has origins in development. Congenital valvuloseptal defects affect many newborns, ranging from life-threatening malformations requiring immediate repair to more subtle, often undiagnosed defects that increase susceptibility to valve disease later in life. Therefore, an improved understanding of the mechanisms of heart valve formation and maintenance of adult valves may serve as an important step in improving valve disease treatment options. In this work, the mechanisms of normal valve development and the role of Sox9 in developing and mature valves are further studied. The temporal and spatial expression of extracellular matrix genes and proteins are examined throughout normal murine valve development. Sox9 function in the processes of valve development and valve maintenance is examined using mouse models of conditional Sox9 loss-of-function. Heart valve phenotypes in mice with reduced Sox9 function are examined throughout development and in adult mice with resultant calcific valve disease. The possible causative mechanisms of calcific valve disease in mice with reduced Sox9 function are further investigated by identification of novel possible targets of Sox9 transcriptional regulation. Together these studies improve our understanding of heart valve development, characterize a model of heart valve calcification with genetic etiology, and identify and characterize novel targets of Sox9.
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Akutsu, Toshinosuke. "Hydrodynamic performance of mechanical prosthetic heart valve." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/26638.
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Each year, more than 10,000 operations aimed at replacement of diseased heart valves by prosthetic devices are carried out in North America alone. Physiological compatibility, structural integrity and favorable hemodynamics represent three important criteria governing the design of a prosthetic heart valve. The thesis studies fundamental fluid characteristics of three widely used mechanical heart valve configurations, namely, the Starr-Edwards, Bjork-Shiley and St. Jude.
In the beginning, the pertinent available literature is reviewed which clearly points out limitations concerning the available information and their presentation.
This is followed by a detailed description of design, construction, calibration and Instrumentation of a steady flow glycerol-water solution tunnel and a pulsatile flow cardiac simulator. The former test facility is ideally suited for testing heart valves under fully open condition during which the maximum flow and pressure (energy) losses occur. The latter simulates the transient condition over a typical cardiac cycle rather precisely. Highly sensitive Barocel pressure transducing system, magnetic flowmeters, laser-doppler anemometer, and a microprocessor controlled waveform generator together with sophisticated data acquisition and processing system makes the facility ideal and unique for the purpose.
Finally, the results of three distinct series of experiments with prosthetic valves using:
(i) the steady flow glycerol-water solution tunnel;
(ii) the steady flow in the cardiac pulse duplicator; and
(iii) the pulsatile flow cardiac simulator; are presented and discussed.
The significant contribution of the project lies in the fundamental data on pressure drop and its partial recovery; velocity profile, turbulence intensity, shear stress and their decay downstream; both in steady and pulsatile flow conditions. The results provide a comprehensive picture, fundamental insight and physical appreciation as to the hydrodynamic performance of prosthetic heart valves which would serve as reference for future development.
Emphasis throughout is on the use of proper nondimensional parameters to make the information independent of test facilities, flow velocities, size of the models, etc., which should represent a welcome step forward. It would make comparison of results obtained by different investigators using different test-facilities possible.
Based on the results following general conclusions can be made:
(a) Nondimensional pressure drop and discharge coefficient results suggest the Starr-Edwards configuration to be fluid dynamically superior.
(b) There is a significant and rapid recovery of pressure in the wake which depends on the Reynolds number and size of the downstream section. In the present study it was found to be as large as 24%! Hence, considering pressure drop immediately across a heart valve as a measure of its performance, as widely reported in literature, can be misleading.
(c) The Starr-Edwards prosthesis has a relatively lower value for the maximum velocity and turbulence intensity and their rapid decay in the wake compared to the Bjork-Shiley and St. Jude valves.
(d) Adjustment of parameters characterizing the cardiac network affect details of the cardiac cycle.
(e) At the onset of systole all the valves show negative flow until the valve-closure is complete. The Starr-Edwards valve has the largest negative flow rate as well as the longest duration until its closure while the St. Jude valve shows the smallest amount of reversed flow over the shortest time. Negative flow is a significant parameter since the loss in volume must be compensated either by increasing the heart rate or the stroke volume.
(f) All the valves show a decrease in Cp with an Increase in the Reynolds number. Thus the valve performance improves at higher Reynolds numbers. The degree of improvement depends on the valve configuration and is relatively smaller for the ball and cage geometry.
(g) During the pulsatile flow study, the maximum velocity recorded for the Starr-Edwards valve, at a given downstream location, is essentially the same as that observed during steady flow case. On the other hand, the turbulence Intensity is distinctly lower. Similar trends were observed for the other two configurations. In general, the peak velocity and turbulence intensity for the St. Jude valve are smaller than those for the Bjork-Shiley case.
(h) For the Starr-Edwards prosthesis, the sticking character of the ball may substantially alter the pressure-flow rate relation. The thesis ends with several recommendations for future work which are likely to be rewarding.Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate
14
Hui, Andrew J. "Hydrogel-based artificial heart valve stent material." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0018/MQ58005.pdf.
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Duong, Tiffany. "Mechanisms of NR2Fs in Heart Valve Development." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1505149242216719.
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Williams, Franklin Pierce. "The numerical simulation of flow through an axisymmetric aortic heart valve." Diss., Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/9378.
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Siefert, Andrew William. "Mitral valve force balance: a quantitative assessment of annular and subvalvular forces." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53434.
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In vitro and in vivo models were proposed to evaluate the effects of ischemic mitral regurgitation and surgical repair on the function and mechanics of the heart’s mitral valve. In specific aim 1, a novel transducer was developed to measure the radially directed forces that may act on devices implanted to the mitral annulus. In an ovine model, radial forces were found to statistically increase with left ventricular pressure and were reduced in the setting of ischemic mitral regurgitation. In specific aim 2, the suture forces required to constrain true-sized and undersized annuloplasty rings to the mitral annulus of ovine animals was evaluated. Suture forces were observed to be larger on the anterior aspect of the rings and were elevated with annular undersizing. In specific aim 3, an in vitro simulator’s ability to mimic healthy and ischemic mitral regurgitation ovine mitral valve function was evaluated. After understanding the accuracy of the model, the in vitro ischemic mitral regurgitation model was used to evaluate the progressive effects of annuloplasty on strut and intermediary chordal tethering. The generated data and knowledge will contribute to the development of more durable devices and techniques to assess the significant clinical burden known as ischemic mitral regurgitation.
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Simon, Hélène A. "Influence of the implant location on the hinge and leakage flow fields through bileaflet mechanical heart valves." Available online, Georgia Institute of Technology, 2004:, 2003. http://etd.gatech.edu/theses/available/etd-04012004-192539/unrestricted/helene%5Fsimon%5Fa%5F200405%5Fmast.pdf.
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Thesis (M.S.)--Chemical Engineering, Georgia Institute of Technology, 2003.Sambanis Athanassios, Committee Member ; Sotiropoulos Fotis, Committee Member ; Yoganathan Ajit, Committee Chair. Includes bibliographical references (leaves 239-243).
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Wallby, Lars. "Signs of inflammation in different types of heart valve disease : The VOCIN study." Doctoral thesis, Linköping : Department of Medical and Health Sciences, Linköping University, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-11330.
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Spinner, Erin M. "Tricuspid valve mechanics: understanding the effect of annular dilatation and papillary muscle displacement." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/45754.
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Tricuspid regurgitation (TR), back flow of blood from the right ventricle to the right atrium, has been reported in approximately 85% of the population, with 16% having mild or severe TR. Patients with untreated moderate to severe TR are likely to experience decreased exercise capacity and have increased morbidity and mortality, thus affecting the patient's quality of life. Current methods of repair offer limited rates of success, and many patients require further operations to correct returning levels of TR. Incomplete repair may be due to incomplete understanding of the functional anatomy and mechanics of the TV and the underlying causes of TR.
It was hypothesized that alterations in the geometry of tricuspid valve annular and subvalvular apparatus induced by ventricular dilatation determine the severity of TR. In vivo measurements of papillary muscle (PM) position in patients with single or biventricular dilatation revealed PM displacement away from the center of the annulus as compared to control patients. Additionally, pulmonary arterial pressure, annulus area, ventricular size and apical displacement of the anterior PM were highly correlated with the severity of TR. An in vitro right-heart simulator was developed to investigate isolated mechanics of TR. Through these in vitro studies it was demonstrated that the tricuspid valve begins to leak at only 40% dilation, much lower than the mitral valve. Additionally, it was shown that isolated PM displacement resulted in significant TR. The highest levels of TR were achieved with a combination of annular dilatation and PM displacement. Alterations in leaflet coaptation, as quantified by measuring the amount of leaflet available for coaptation and leaflet mobility were observed with annular dilatation and PM displacement, both isolated and combined. The changes in leaflet coaptation resulted in redistribution of the forces on the chords originating from the anterior PM and inserting into the anterior and posterior leaflets.
The findings herein provide the clinical and scientific community with a mechanistic understanding of the tricuspid valve to further improve intervention and repair of TV disease.
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Simpson, Michael S. "An in vitro investigation of systolic anterior motion of the mitral valve." Thesis, Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/33615.
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Hellgren, Laila. "Heart Valve Surgery : Preoperative Assessment and Clinical Outcome." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5929.
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Mackay, Tom G. "Towards a tri-leaflet polyurethane heart valve prothesis." Thesis, University of Strathclyde, 1992. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=21350.
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Given the poor durability of bioprosthetic heart valves and thrombogenicity of mechanical valves, recent attention has been directed towards synthetic leaflet valves. The work of this thesis forms part of a project to develop a tri-leaflet polyurethane heart valve prosthesis. Two aspects have been addressed: in vitro valve function and durability test methods, and fabrication techniques for polyurethane valves. Existing in vitro valve testing facilities, comprising a hydrodynamic function tester (pulse duplicator) and accelerated fatigue testers, have been upgraded. An improved data acquisition system combined with a computerised control system has been developed for the pulse duplicator. The new system allows valve function to be more efficiently and reliably assessed, and also provides a means for characterising the pulse duplicator and its transducers. Accelerated fatigue testing facilities have been similarly enhanced by the introduction of a computerised data acquisition system. In order to exploit the design potential offered by the use of a synthetic material, an integrated CAD/CAM system has been developed for producing sculptured valve formers. Such formers have been incorporated into injection moulding tools for tri-leaflet polyurethane valves. Polyurethane valves have been moulded, but to date not with sufficiently thin leaflets: the required leaflet thickness (< 150 gm) results in a mould cavity which presents an enormous resistance to flow in the injection moulding process. However, a finite element-based mathematical model has been used to simulate the flow of molten polyurethane into the mould cavity and initial results suggest that it should indeed be possible to injection mould a polyurethane valve and a practicable means of achieving this has been identified. The sculptured formers incorporated into the injection moulding tools have also been used to create dip moulded tri-leaflet polyurethane valves. These dip moulded valves, though difficult to produce consistently, function reasonably well in the pulse duplicator and accelerated fatigue tests are in progress.
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Thornton, Miles. "Finite element analysis of pericardial heart valve prostheses." Thesis, University of Sheffield, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265608.
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Chen, Qi. "Collagen-based scaffolds for heart valve tissue engineering." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:5a03aee6-3672-4c29-8d43-64074bbcd467.
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Tissue engineered heart valve (TEHV) is believed to be a promising candidate for curative heart valve replacements. Collagen, elastin and chondroitin-4-sulfate (C4S) comprise the extra-cellular matrix (ECM) of native heart valves and therefore are suitable materials for TEHV scaffolds. Freeze-drying technique was able to produce scaffolds with relative densities of 0.3%-2.0% and pore sizes of 33.2µm-201.5µm, without having any major effects on the ultra-structures on the scaffold materials. Subsequent dehydrothermal (DHT) treatment and ultra-violet (UV) irradiation introduced inter- or intra-molecular crosslinks in the scaffolds in forms of ester and amide bonds, as well as the accompanying denaturation of the proteins (i.e. ultra-structure transition from helices to random coils). The collagen-based scaffolds had tensile, compressive and effective bending moduli ranging from 39.8kPa to 1082kPa, from 2.4kPa to 213.9kPa, and from 11.0kPa to 415.8kPa, respectively. The different behaviours of the wall stretching and the wall buckling in the individual pores of the scaffolds contributed to the different tensile, compressive and bending moduli. The mechanical properties could be tailored through controlling the freezing temperature, the relative density and the composition of the scaffolds. A lower freezing temperature might lead to lower mechanical properties because different pore structures were introduced. When the the relative density of the scaffold increased, the values of the moduli increased exponentially, with an exponential dependence factor larger for the compressive modulus than for the tensile modulus. Adding elastin or C4S into the collagen scaffolds lowered the mechanical properties due to the decrease in the collagen content. Layered structures that combined collagen-rich layers with elastin-rich and/or C4S -rich layers allowed the scaffolds to make use of the different mechanical properties of different layers, and hence to show anisotropic bending behaviour depending on the loading directions. The lower effective bending modulus (9.6 to 25.0kPa) in the with curvature (WC) direction than that (18.1kPa to 39.3kPa) in the against curvature (AC) direction mimicked the characteristic behaviour of the native heart valves and would be beneficial for a mechanically desirable TEHV. The DHT treatment and UV irradiation were able to increase the mechanical properties of the scaffolds to up to 2.5 times of the original values, by reinforcing the scaffold materials with more crosslinks. In the hydrated status, the hydrophilic C4S improved the water uptake ability of the scaffold and the hydrophobic elastin reduced it. The hydrated layered scaffolds still exhibited bending anisotropy despite much lower effective bending modulus. Finite element models of the scaffolds produced results that were in agreement with the experiments, and enabled us to perform distributed loading and internal stress analysis on the scaffolds. The collagen-based scaffolds were seeded with cardiosphere-derived cells (CDCs), and they attached to the scaffolds and showed visible cell division, proliferation and migration. The CDCs exhibited preferred proliferation behaviours on the collagen-C4S scaffolds to that on the collagen-elastin scaffolds because of the cell affinity to the C4S, as well as the elastin-induced contractile cell phenotype and scaffold volume shrinkage. This difference seemed to be less evident in the layered scaffolds due to the cell communication between the layers. The crosslinking process also had effects on the cell proliferation in the ways that it induced ultra-structure changes or volume shrinkage in the scaffolds. The layered scaffold-cell constructs designed and produced in this study served as a forwarding step towards a mechanically desirable and biologically active TEHV.
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Burleson, Armelle Cagniot. "Analysis of turbulent jets for the determination of heart valve leakage." Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/11307.
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Caldas, Guilherme Martins Marrelli. "Avaliação anatômica comparativa da valva mitral e da valva aórtica de corações normais e com cardiomiopatia dilatada isquêmica e idiopática." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/10/10137/tde-04072007-124422/.
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O objetivo deste trabalho foi estudar e comparar a valva mitral e a valva aórtica e em corações com cardiomiopatia dilatada (CMD) de etiologia isquêmica e idiopática, em relação aos corações humanos normais, buscando identificar variações que possam auxiliar em diagnósticos por imagem e para o tratamento cirúrgico das mesmas. Este estudo analisou 22 corações normais, 15 corações dilatados de etiologia isquêmica e 15 corações dilatados de etiologia idiopática, fixados em formaldeído a 10%. Foram obtidas medidas por meio de fotografias digitais dos corações e, posteriormente, utilizando-se software, foram analisados as distâncias e os perímetros da valva mitral e da valva aórtica, que foram comparadas por meio de testes estatísticos. Nos corações normais, a área da valva mitral foi de 5,44 ± 0,82 cm2 e o perímetro de 8,91 ± 0,57 cm, e nos corações com CMD de etiologia isquêmica e idiopática, a área foi de, respectivamente, 7,38 ± 1,76 cm2 e 7,03 ± 1,44 cm2, e o perímetro foi de, respectivamente, 10,41 ± 1,37 cm e 9,97 ± 1,23 cm. O perímetro de inserção da cúspide anterior da valva mitral, nos corações normais, foi de 3,68 ± 0,52 cm e nos corações com CMD de etiologia isquêmica e idiopática foi de, respectivamente, 3,99 ± 0,86 cm e 3,62 ± 0,78 cm. A menor distância perimetral entre os trígonos fibrosos (porção fibrosa), nos corações normais, foi de 2,06 ± 0,26 cm e nos corações com CMD de etiologia isquêmica e idiopática foi de, respectivamente, 2,64 ± 0,37 cm e 2,34 ± 0,37 cm. Nos corações normais, a área da valva aórtica foi de 3,46 ± 0,66 cm2 e o perímetro de 6,83 ± 0,66 cm. Nos corações com CMD de etiologia isquêmica e idiopática, a área da valva aórtica foi de, respectivamente, 5,22 ± 1,53 cm2 e 3,44 ± 1,33 cm2, e o perímetro de, respectivamente, 8,26 ± 1,24 cm e 6,82 ± 1,37 cm. Nos casos de CMD idiopática e isquêmica, a valva mitral apresentava-se aumentada, tanto na sua área e em seu perímetro, quanto na maior e na menor distância perimetral entre os trígonos fibrosos. Em relação à valva aórtica, apenas nos corações com CMD isquêmica houve aumento estatisticamente significante em sua área e em seu perímetro, enquanto que nos corações com CMD idiopática não houve diferença quando comparados aos corações normais. Há manutenção da proporcionalidade, dos corações normais para os com CMD idiopática e isquêmica, das distâncias entre os trígonos fibrosos. Há evidência de que o aumento da valva mitral e da valva aórtica, quando ocorrem na CMD, se dão de forma independente.The objective of this work was to study and to compare mitral valve as well as aortic valve in the ischemic and idiopathic dilated cardiomyopathy (CMD) in relation to the normal hearts, searching to identify variations that can assist in diagnostic for image and for the surgical treatment of the same ones. This study it analyzed 22 normal hearts, 15 dilated hearts of ischemic etiology and 15 dilated hearts of idiopathic etiology, fixed in formaldehyde 10%. They had been gotten measured through digitalized photographs of the hearts, and, through software, the distances and perimeters of the mitral valve and of the aortic valve had been analyzed, that later they had been compared through statistical tests. In the normal hearts, the area the mitral valve was 5.44 ± 0.82 cm2 and the perimeter of 8.91 ± 0.57 cm. In the hearts with ischemic and idiopathic CMD the area of the mitral valve were, respectively, 7.38 ± 1.76 cm2 and 7.03 ± 1.44 cm2, and to the perimeter it were, respectively, 10.41 ± 1.37 cm and 9.97 ± 1.23 cm. The perimeter of insertion of anterior cusp of mitral valve in the normal hearts was 3.68 ± 0.52 cm, in the hearts with ischemic and idiopathic CMD were, respectively, 3.99 ± 0.86 cm and 3.62 ± 0.78 cm. The lesser length enter the fibrous trigones (fibrous portion) in the normal hearts was 2.06 ± 0.26 cm and in the hearts with ischemic and idiopathic CMD were, respectively, 2.64 ± 0.37 cm and 2.34 ± 0.37 cm In the normal hearts the area of aortic valve was 3.46 ± 0.66 cm2 and the perimeter of 6.83 ± 0.66 cm. In the hearts with ischemic and idiopathic CMD the area of aortic valve were, respectively, 5.22 ± 1.53 cm2 and 3.44 ± 1.33 cm2, and the perimeter of, respectively, 8.26 ± 1.24 cm and 6.82 ± 1.37 cm. In the cases of idiopathic and ischemic CMD, mitral valve is presented increased, as much in its area and its perimeter, how much in the greater and the lesser perimetral distance between the fibrous trigones. In relation to aortic valve, only in the hearts with Ischemic CMD it had significant statistic increase in its area and its perimeter, whereas in the hearts with Idiopathic CMD it did not have difference when compared with the normal hearts. It has maintenance of the proportionality, the normal hearts for the ones with idiopathic and ischemic CMD, of the distances between the fibrous trigones. It has evidence of that the increase of mitral valve and aortic valve, when they occur in the CMD, occurs of independent form.
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Heinrich, Russell Shawn. "Assessment of the fluid mechanics of aortic valve stenosis with in vitro modeling and control volume analysis." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/16664.
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Einstein, Daniel Richard. "Nonlinear acoustic analysis of the mitral valve /." Thesis, Connect to this title online; UW restricted, 2002. http://hdl.handle.net/1773/8064.
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Vesier, Carol Cockerham. "The role of papillary muscle-mitral valve geometry in systolic anterior motion of the mitral valve." Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/10279.
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Sharma, Vishal. "Natriuretic peptides in valvular heart disease." Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/23463.
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Plasma natriuretic peptide concentrations rise in response to either atrial or ventricular wall stretch and have been found to be useful in the diagnosis and assessment of patients with congestive cardiac failure. Although previous studies have suggested that plasma natriuretic peptides may offer some prognostic information in patients with valvular heart disease, it is unclear whether concentrations reflect disease severity and how plasma concentrations vary across different valve lesions. The aim of this research was to identify the factors that affect natriuretic peptide releases in valvular heart disease (VHD) and to investigate whether natriuretic peptides can be used in clinical practice to identify those patients who may benefit from early intervention. Plasma brain natriuretic peptide (BNP) and atrial natriuretic peptide (ANP) concentrations were measured in patients with normal left ventricular (LV) systolic function and isolated VHD (mitral regurgitation, MR, n=33; aortic regurgitation, AR, n=39; aortic stenosis, AS, n=34; mitral stenosis, MS, n=30), and age and sex matched controls (n=39) immediately prior to exercise stress echocardiography. Peptide levels were compared against age and sex matched controls and against markers of severity for each valve lesions and across different valve lesions. Compared to controls, patients with all types of VHD had elevated plasma BNP concentrations [(MR median 35(inter quartile range 23-52), AR 34(22-45), AS 31(22-60), MS 58(34-90); controls 24(16-33) pg/mL; p < 0.01 for all]. LV end diastolic volume index varied by valve lesion; [MR (mean ± standard deviation 77±14), AR (91±28), AS (50±17), MS (43±11), controls (52±13) mL/m2; p < 0.0001]. There were no associations between LV volume and BNP. Left atrial (LA) area index varied [MR (18±4cm2/m2), AR (12±2), AS (11±3), MS (19±6), controls (11±2); p < 0.0001], but correlated with plasma BNP concentrations: MR (r=0.42,p=0.02), MS (r=0.86,p < 0.0001), AR (r=0.53,p=0.001), AS (r=0.52, p=0.002). Higher plasma BNP concentrations were associated with increased pulmonary artery pressure and reduced exercise capacity. Despite adverse cardiac remodelling, 81(60%) patients had a BNP concentration within the normal range. In patients with MS BNP was strongly associated with left atrial area index (r=0.86; p < 0.0001) and a BNP level of greater than 2 times the upper limit of normal identified patients who fulfilled guideline criteria for intervention (Area under the curve (AUC) 0.87 [0.74,0.99], p =0.006) and lower exercise capacity (AUC 0.82 [0.67,0.97]; p=0.004). In AR patients significant remodelling could occur whilst BNP remained within the normal range and in general BNP appeared less useful in assessing disease severity. However raised levels of BNP was associated with more severe AR as assessed by left ventricular outflow tract:AR Jet area ratio (r=0.43 p=0.0007). AR patients with an abnormal BNP had signs of early LV dysfunction on exercise with a lower LV longitudinal strain rate post exercise compared to AR patients with a normal BNP (0.68±0.31 vs. 1.06±0.45 1/sec; p=0.02). In MR patients, higher plasma BNP concentrations were associated with larger left atrial area index (r=0.42, p=0.02), higher pulmonary artery pressure (r=0.53, p=0.002) and a lower exercise time (r=-0.60, p=0.0002). BNP was not associated with any marker of left ventricular size or function in MR. These findings suggest that despite significant LV remodelling, plasma BNP concentrations are often normal in patients with VHD. Consequently, plasma BNP concentrations should be interpreted with caution when assessing patients with VHD. However natriuretic peptide levels offer complementary information to the standard assessment of patients with VHD and an unexplained finding of an elevated BNP in an otherwise asymptomatic patient should prompt further investigation.
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Dellgren, Göran. "Aortic valve replacement with stentless bioprostheses : prospective long-term studies of the Biocor and the Toronto SPV /." Stockholm : Karolinska institutet, 2002. http://diss.kib.ki.se/2002/91-7349-152-7.
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Toosisaidy, Navid. "From native valvular biomechanics to personalised heart valve tissue engineering: Convergence of biomimetic design approach and melt electrowriting." Thesis, Queensland University of Technology, 2020. https://eprints.qut.edu.au/200709/1/Navid_Toosisaidy_Thesis.pdf.
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This thesis presented a novel platform for the design and manufacture of tissue engineered heart valves to overcome the disadvantages of current heart valve prosthesis by providing an alternative valve capable of growth and remodelling. The convergence of a biomimetic design methodology and melt electrowriting was illustrated as a promising approach to embrace mechanical, structural, geometrical and functional complexities of a native heart valve, which has been challenging to achieve using currently available manufacturing technologies. This project provided a step forward toward addressing the urgent clinical need to develop functional tissue engineered heart valves.
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Talman, Eric A. "Internal shear properties of porcine aortic heart valve cusps." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0020/NQ58163.pdf.
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Dreger, Sally Anne. "Matrix remodelling : a requirement for heart valve tissue engineering." Thesis, Imperial College London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.510735.
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Grzymala-Lubanski, Bartosz. "Anticoagulation treatment in patients with a mechanical heart valve." Doctoral thesis, Umeå universitet, Institutionen för folkhälsa och klinisk medicin, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-128355.
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Background Every year about 2,500 patients in Sweden undergo surgery for heart valve disease, primarily in the aortic valve. In contrast to the mitral valve, which can be repaired in 70% of the cases, the aortic valve is normally replaced by a mechanical or biological prosthesis. A mechanical heart valve (MHV) necessitates lifelong anticoagulation treatment with a vitamin K antagonist, most commonly warfarin, due to the high thrombogenicity of the prosthesis. The quality of the warfarin treatment is crucial in these patients. Compared to other countries, treatment quality in Sweden is very high; nonetheless, there is always room for improvement. One of the ways to achieve this improvement is to implement computerized dosing assistance. Treatment recommendations for anticoagulation intensity are based on few and old studies, making these recommendations uncertain. There is therefore a need for studies designed to establish the appropriate level of anticoagulation therapy. Aim The aim of these studies was to investigate the efficacy and safety of anticoagulation treatment among patients with mechanical heart valve prostheses in Sweden; to assess whether computerized dosing can increase the treatment quality; to investigate the influence of the treatment quality, measured by Time in Therapeutic Range (TTR) and INR variability, on the risk of complications and, finally, to establish the optimal intensity of anticoagulation treatment in this group of patients. Methods Data were obtained from AuriculA – a national quality registry established in 2006, which currently includes approximately 50% of all patients treated with oral anticoagulation in Sweden. Study II used only data from AuriculA. 769,933 warfarin-dosing suggestions proposed by the dosing algorithm in AuriculA were analysed. Accepted dose suggestions (590,939) were compared with 178,994 manually-changed doses in regard to the resultant INR value, measured as mean error (deviation from target INR) and hit rate (number of INR samples within the target range 2-3). In study III, AuriculA was used to identify patients in Sundsvall and Malmö in the period 2008 – 2011 who were receiving warfarin for a mechanical heart valve prosthesis, as well as to retrieve their INR data. Data on background characteristics and bleedings or thromboembolic complications were manually retrieved from medical records by two investigators. A total of 534 patients with mechanical heart valve prostheses were divided into quartiles based on TTR and were compared regarding the risk of complications. For Studies I and IV, data from AuriculA were merged with the Swedish National Patient Register, SWEDEHEART/ Heart surgery, and the Swedish Cause of Death Register, comprising in total 77,423 patients on warfarin with 217,804 treatment years. Every treatment period registered in AuriculA was given an individual identification number. During the study period a patient could have any number of treatment periods. The number of complications in total and in different patient groups within the study population was investigated. Complications were defined by ICD-10 codes. Major bleeding was defined as an event necessitating hospital treatment and given a discharge diagnosis with one of the ICD-10 codes reflecting bleeding, as listed in the Appendix. Bleeding events were divided into intracranial, gastrointestinal and other bleedings. Thromboembolic complications consist of venous events (deep vein thrombosis, pulmonary embolism, venous stroke) or arterial events (stroke, TIA, acute myocardial infarction, peripheral arterial embolism). Data were analysed using both simple, descriptive statistical methods and various tests such as Mann-Whitney (or two sample Wilcoxon), T-test, Chi 2 test, ANOVA, multivariate analysis with logistic regression and survival analysis with Cox Regression with proportional hazard assumption. Results Treatment quality Mean TTR among all patients in Study I was 76.5% whereas patients with mechanical heart valve prostheses had a TTR of 74.5%. The annual incidence of major bleeding or thromboembolic events among all patients was 2.24% and 2.65%, respectively. The incidence of intracranial bleeding was 0.37% per year in the general population and 0.51% among patients with mechanical heart valve prostheses, who also had a higher bleeding rate in total (3.37% per year). Both the mean and median errors were smaller (0.44 vs. 0.48 and 0.3 vs. 0.4, respectively) and the hit rate was higher (0.72 vs. 0.67) when the dose suggested by the algorithm was accepted, compared to when it was manually changed. TTR In Study III there was no significant difference in the risk of thromboembolism regardless of TTR level. Risk of bleeding in quartiles I and II was more than two times higher than in the quartile with TTR >82.9. In Study IV, lower TTR (≤70%) was associated with a significantly higher rate of complications when compared with TTR >70%. Bleeding risk was higher in the group with lower TTR (HR=2.43, CI 2.02-2.89, p<0.001). After dividing patients into TTR quartiles, the rate of complications in total was significantly higher in quartiles I to III compared with quartile IV, which had the highest TTR. Risk of thromboembolism, major bleeding and death was higher in the first and second quartile compared to the quartile with the highest TTR. INR variability Higher INR variability above mean (≥0.40) was related to a higher rate of complications compared with lower INR variability (<0.40) as shown in Study IV. Bleeding risk was higher in the group with INR variability ≥0.40 (HR = 2.15, CI 1.75-2.61, p<0.001). Comparison of quartile IV, which had the lowest INR variability, with the other three revealed that quartiles I and II, which had the highest INR variability, had significantly worse outcomes for all complications except for thromboembolic events, plus also death in quartile II. TTR and INR variability combined High variability and low TTR combined was associated with a higher risk of bleedings (HR 2.50, CI 1.99-3.15), death (3.34, CI 2.62-4-27) and thrombosis (1.55, CI 1.21-1.99) compared to the best group. Level of anticoagulation Higher warfarin treatment intensity (mean INR 2.8-3.2 vs. 2.2-2.7) was associated with a higher rate of bleedings (HR 1.29, CI 1.06-1.58), death (1.73, CI 1.38-2.16) and complications in total (1.24, CI 1.06-1.41) after adjustment for MHV position, age and comorbidity. Conclusion Warfarin treatment quality is crucial for patients with mechanical heart valve prostheses. Computerized dosing assistance could help maintain high warfarin treatment quality. Well-managed treatment with TTR ≥70% and INR variability below mean <0.40 is associated with a lower risk of serious complications compared with a lower TTR and higher INR variability. No benefit of higher warfarin treatment intensity was found for any valve type or position.
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Mitchell, Stuart B. "Electrospinning controlled architecture scaffolds for tissue engineering & the effect of scaffold mechanical properties on collagen synthesis in tissue engineered mitral valves /." Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/8045.
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Leung, Wing-ki Vikki, and 梁頴琪. "The implications of transcatheter aortic valve implantation (TAVI) adoption." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B48424031.
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Aortic stenosis is a life-threatening valvular heart disease. At the onset of symptoms, a patient’s prognosis becomes poor and the risk of death rapidly increases. Aortic valve replacement surgery remains the gold standard in treatment for aortic stenosis. However, in the total population of patients with severe aortic stenosis, about one third are deemed inoperable due to their high surgical risk. In recent years, the development of transcatheter aortic valve implantation (TAVI), a non-invasive heart valve replacement procedure brought hope for the elderly, high-risk and inoperable aortic stenosis patient population pool. A literature review was performed to examine the safety, efficacy and effectiveness evidence for transcatheter aortic valve treatment option. The results showed that TAVI is a safe treatment option, however the effectiveness for the whole patient population is unknown. The adoption of this alternative treatment option is certainly coupled with multiple dimension of impact from a public health perspective. It remains inconclusive whether TAVI is an effective treatment option to be adopted.published_or_final_version
Public Health
Master
Master of Public Health
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Kemp, Iain Henry. "Development,testing and fluid interaction simulation of a bioprosthetic valve for transcatheter aortic valve implantation." Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/71710.
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Thesis (MScEng)--Stellenbosch University, 2012.ENGLISH ABSTRACT: Bioprosthetic heart valves (BHVs) for transcatheter aortic valve implantation (TAVI) have been rapidly developing over the last decade since the first valve replacement using the TAVI technique. TAVI is a minimally invasive valve replacement procedure offering lifesaving treatment to patients who are denied open heart surgery. The biomedical engineering research group at Stellenbosch University designed a 19 mm balloon expandable BHV for TAVI in 2007/8 for testing in animal trials. In the current study the valve was enlarged to 23 mm and 26 mm diameters. A finite element analysis was performed to aid in the design of the stents. New stencils were designed and manufactured for the leaflets using Thubrikar‟s equations as a guide. The 23 mm valve was manufactured and successfully implanted into two sheep. Fluid structure interaction (FSI) simulations constitute a large portion of this thesis and are being recognized as an important tool in the design of BHVs. Furthermore, they provide insight into the interaction of the blood with the valve, the leaflet dynamics and valve hemodynamic performance. The complex material properties, pulsating flow, large deformations and coupling of the fluid and the physical structure make this one of the most complicated and difficult research areas within the body. The FSI simulations, of the current valve design, were performed using a commercial programme called MSC.Dytran. A validation study was performed using data collected from a cardiac pulse duplicator. The FSI model was validated using leaflet dynamics visualisation and transvalvular pressure gradient comparison. Further comparison studies were performed to determine the material model to be used and the effect of leaflet free edge length and valve diameter on valve performance. The results from the validation study correlated well, considering the limitations that were experienced. However, further research is required to achieve a thorough validation. The comparative studies indicated that the linear isotropic material model was the most stable material model which could be used to simulate the leaflet behaviour. The free edge length of the leaflet affects the leaflet dynamics but does not greatly hinder its performance. The hemodynamic performance of the valve improves with an increase in diameter and the leaflet dynamics perform well considering the increased surface area and length. Many limitations in the software prevented more accurate material models and flow initiation to be implemented. These limitations significantly restricted the research and confidence in the results. Further investigation regarding the implementation of FSI simulations of a heart valve using the commercial software is recommended.
AFRIKAANSE OPSOMMING: Bio-prostetiese hartkleppe (Bioprosthetic Heart Valves - BHVs) wat gebruik word vir transkateter aortaklep-inplantings (Transcatheter Aortic Valve Implantation - TAVI) het geweldig vinnige ontwikkeling getoon in die afgelope tien jaar sedert die eerste klepvervanging wat van die TAVI prosedure gebruik gemaak het. TAVI is ʼn minimaal indringende klepvervangingsprosedure wat lewensreddende behandeling bied aan pasiënte wat ope-hart sjirurgie geweier word. Die Biomediese Ingenieurswese Navorsingsgroep (BERG) by Stellenbosch Universiteit het in 2007/8 ʼn 19 mm ballon-uitsetbare BHV vir TAVI ontwerp vir eksperimente met diere, en hierdie tesis volg op die vorige projekte. In die huidige studie is die klep vergroot na 23 mm en 26 mm in deursnee. ʼn Eindige element analise is gedoen om by te dra tot die ontwerp van die rekspalke vir die klep. Nuwe stensils is ontwerp en vervaardig vir die klepsuile, deur gebruik te maak van Thubrikar se vergelykings. Die 23 mm klep is vervaardig en suksesvol in twee skape ingeplant. Vloeistruktuur interaksie (Fluid Structure Interaction (FSI)) simulasies vorm ‟n groot deel van die tesis en word gesien as ʼn noodsaaklike hulpmiddel in die ontwerp van BHVs. Die simulasies verskaf ook insig in die interaksie van die bloed met die klep, die klepsuil-dinamika en die klep se hemodinamiese werkverrigting. Die komplekse materiaal eienskappe, polsende vloei, grootskaalse vervorming, die verbinding van die vloeistof en die fisiese struktuur maak van hierdie een van die mees gekompliseerde voorwerpe om te simuleer. Die FSI simulasies van die huidige ontwerp, is uitgevoer deur van kommersiële sagteware, MSC.Dytran, gebruik te maak. ʼn Geldigheidstudie wat data gebruik het vanaf die hartklop-nabootser, is uitgevoer. Die FSI model word geverifieer deur klepsuil dinamika visualisering en ʼn vergelyking van die drukgradiënt gebruik te maak. Verdere vergelykende studies is uitgevoer om te bepaal watter materiaal model om te gebruik, asook die uitwerking van die klepsuil-vrye rand en klepdeursnee op die klep se werkverrigting. Die resultate van die studie korreleer goed, in ag genome die beperkings wat ervaar is. Verdere navorsing is egter nodig vir ʼn volledige geldigheidstudie. Vergelykende studies het getoon dat die liniêre isotropiese materiaalmodel die meer stabiele materiaalmodel is wat kan gebruik word om klepsuilgedrag te simuleer. Die vrye-rand lengte van die klepsuil affekteer die dinamika van die klepsuil, maar belemmer nie die werkverrigting grootliks nie. Die hemodinamiese werkverrigting van die klep verbeter met die toename in deursnee en die klepsuil-dinamika vertoon goed in ag genome die verhoogde oppervlak area en lengte. Die vele beperkings in die sagteware het die implementering van meer akkurate materiaalmodelle verhoed. Hierdie beperkings het ʼn verminderde vertroue in die resultate tot gevolg gehad. Verdere ondersoek rakende die implementering van die FSI simulasies van ʼn hartklep deur kommersieel beskikbare sagteware te gebruik, word aanbevel.
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Padala, Sai Muralidhar. "Mechanics of the mitral valve after surgical repair-an in vitro study." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/39564.
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Mitral valve disease is widely prevalent among pediatric and adult population across the world, and it encompasses a spectrum of lesions which include congenital valve defects, degenerative valve lesions, and valve dysfunction due to secondary pathologies. Though replacement of the diseased mitral valves with artificial heart valves has been the standard of care until early 1990's, current trends have veered towards complete surgical repair. These trends are encouraging, but current repair techniques are plagued with lack of durability and high rates of failure within 10 years after repair. With increasing number of patients receiving mitral valve repair, there is now an immediate need to understand the mechanisms of repair failure, and assess the role of several clinical risk factors on valve repair. In this thesis, an in vitro pulsatile left heart simulator was developed to mimic the congenital and adult mitral valve pathological morphologies in normal porcine valves, and simulate the pathological valve hemodynamics and mechanics. Different surgical repair techniques were used to correct the valve lesions, and the post repair valve hemodynamics, mechanics and geometry were assessed using quantitative measurement techniques. The extent to which each repair restores physiological valve function and mechanics was assessed, and the impact of different pathological risk factors on repair failure mechanisms was investigated. It is expected that the knowledge from this thesis would play an important role in the evolution of mitral valve surgical repair, and guide the development of more effective and long-lasting heart valve repair technologies.
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Dye, Bailey Katherine. "Cellular Mechanisms of VIC Activation in Mitral Valve Prolapse." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1594995213439086.
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Grande, Kathryn Jane. "The aortic root-aortic valve relationship in the normal, diseased, and surgically repaired states /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/8114.
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Castellanos, Glenda L. "Cellular Events Under Flow States Pertinent to Heart Valve Function." FIU Digital Commons, 2015. http://digitalcommons.fiu.edu/etd/2285.
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Heart valve disease (HVD) or a damaged valve can severely compromise the heart's ability to pump efficiently. Balloon valvuloplasty is preferred on neonates with aortic valve stenosis. Even though this procedure decreases the gradient pressure across the aortic valve, restenosis is observed soon after balloon intervention. Tissue engineering heart valves (TEHV), using bone marrow stem cells (BMSCs) and biodegradable scaffolds, have been investigated as an alternative to current non-viable prosthesis. By observing the changes in hemodynamics following balloon aortic valvuloplasty, we could uncover a potential cause for rapid restenosis after balloon intervention. Subsequently, a tissue engineering treatment strategy based on BMSC mechanobiology could be defined. Understanding and identifying the mechanisms by which cytoskeletal changes may lead to cellular differentiation of a valvular phenotype is a first critical step in enhancing the promotion of a robust valvular phenotype from BMSCs.
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Brubert, Jacob. "A novel polymeric prosthetic heart valve : design, manufacture, and testing." Thesis, University of Cambridge, 2016. https://www.repository.cam.ac.uk/handle/1810/256312.
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In this thesis a flexible leaflet polymeric prosthetic aortic heart valve was designed, manufactured, and tested. The prosthesis was designed with the aim of overcoming the need for anticoagulant therapy, which is required for current mechanical prostheses; while also having lifelong durability, which current bioprosthetic heart valves are not able to achieve. Inspired by the anisotropic architecture of collagen in the natural valve, a shortlist of polystyrene based block copolymers (BCPs), which can be processed to yield mechanically anisotropic materials, was proposed. The shortlist was evaluated based upon processability, biostability, ex vivo haemocompatibility, and a novel material performance index comprising the flexural modulus and the cyclic fatigue stress predicted by fracture mechanics methods. Polystyrene-block-polyethylene-polypropylene-block-polystyrene with 22 mol% polystyrene (SEPS22) was selected for further testing and use in the design. Haemocompatibility and calcification of the BCPs was assessed against reference materials. In measures of coagulation and thrombogenicity the BCPs were better than polyester, but worse than expanded polytetrafluoroethylene and pericardium graft materials. In measures of inflammation, the BCPs and polytetrafluoroethylene were better than polyester and pericardium. A durable heparin coating gave SEPS22 superior haemocompatibility compared to all the reference materials. The BCPs calcified less than pericardium, but calcification still accelerated failure. The technique of injection moulding discs of the BCP from a point was used to create a novel biaxial structure of cylindrical polystyrene domains. A combination of modelling and bench-scale injection moulding was used to select a point from which the prosthetic heart valve injection tool cavity should be filled. By simultaneously injecting at a point at the centre of the free edge of each leaflet, a bioinspired orientation was produced. Based upon hydrodynamic testing, a spherical form leaflet design was selected. The hydrodynamic performance of the complied with the ISO 5840 standard for cardiac valve prostheses, but the fatigue performance was inadequate due to the leaflets being thinner than specified due to manufacturer error. Fatigue prediction and finite element analysis were used to conjecture that correctly manufactured polymeric valves could theoretically reach the ISO limit, indicating that there is potential for polymeric prostheses to overcome the issues of durability and need for anticoagulation.
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Scott, Michael J. "The elastin and collagen microstructure of aortic heart valve cusps." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ32327.pdf.
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Jones, Mark I. "Haemocompatibility and charactersation of candidate coatings for heart valve prosthesis." Thesis, University of Nottingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301695.
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Prosthetic cardiac valve surgery is a well-established technique, but the search continues for engineering materials with sup..e rior mechanical characteristics in order to extend the service life of the implant. The introduction of pyrolytic carbon was seen as a breakthrough in the development of wear resistant, non-thrombogenic materials for such applications. However, thrombo-embolic phenomena and the need for anticoagulation treatment following valve insertion remain the main problems associated with artificial materials in this application. The work carried out in this research has studied the haemocompatibility of a commercially available, wear resistant TiffiN/TiCfDLC multilayer structure, and a second TiN coating deposited by RF reactive sputtering of a titanium target in a ArIN2 environment, as candidate materials for a heart valve prosthesis. The structure of the RF deposited tiN coating was assessed as a function of deposition conditions, and was seen to develop a particular preferred crystallographic orientation. The nature of this texture was influenced by the condition of the underlying substrate. The effect of substrate condition on the biocompatibility of the tiN coating was studied by assessment of fibroblast attachment and spreading, and by haemolytic analysis of released haemoglobin. The results showed that the initial attachment and orientation of fibroblast cells was influenced by the substrate condition, but no influence on the degree of spreading and haemolytic nature was observed. Characterisation of the TiN coating and the components of the multilayer structure was carried out by Atomic Force Microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS), stylus profilometry and contact angle measurement. Haemocompatibility was studied by the interaction of the surfaces with plasma proteins, blood platelets and red blood ceUs. Cytotoxicity was studied using the MTT test. The degree of platelet activation on the surfaces correlated with their surface energy. The greatest degree of platelet spreading was observed on the more hydrophilic coatings. The lack of platelet activation seen on the DLC coating is attributed to its smooth surface and hydrophobic nature, resulting in higher levels of adsorption of anticoagulation proteins. The RF sputtered TiN coating caused significant levels of haemolysis and fibroblast cell death. None of the components of the multilayer structure caused such effects, although thrombus formation was observed to a degree on the Ti, TiN and TiC components of this structure. The toxic nature of the RF deposited TiN coating was not attributed to surface chemistry or roughness, but rather to a combination of the hydrophilic nature and the defect state of the surface.
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Rozeik, Monica Mary. "Development of a reinforced synthetic heart valve for precutaneous delivery." Thesis, University of Strathclyde, 2013. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=25550.
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Approximately 30% of patients with aortic stenosis over the age of 75 years are refused surgery on the grounds of technical or high risk complications. Following the onset of symptoms, prognosis is very poor if left untreated. Transcatheter aortic valves intervention (TAVI) has paved the way for valve replacement in high risk patients without the need for open heart surgery. The current market approved valves can be delivered percutaneously through the femoral artery or transapically to the beating heart, deployed over the calcified leaflets and begin functioning immediately. Complications with the current TAVI valves include a requirement for a large delivery sheath which leads to major vascular bleeding. Additionally, these valves use pericardial leaflets, which are too thick to collapse into a small catheter and have a propensity to calcify. It is therefore the objective of this thesis to develop an ultra-thin reinforced synthetic leaflet to reduce the delivery profile and facilitate deployment though a peripheral artery. Polyurethane films reinforced with multi-walled carbon nanotubes were solvent cast and tested for changes to the mechanical properties. Dip coated composite valves with varying content of carbon nanotubes were then developed and tested in a high cycle durability tester. The stiffness of composites was found to improve overall with increasing nanotube content. However, fatigue life was found to be compromised, with only the 0.125% MWNT-TPU composite material having similar fatigue life to the neat TPU. The durability of the leaflets was also severely compromised when the thickness was dropped below 50 μm. Leaflet stresses were also reportedly highest at the commissures and the belly region. A valve having sufficiently thin leaflets (130 μm) was developed from a harder grade of polyurethane and has survived 23 million cycles to date. It is believed that a thin and durable leaflet can be achieved using harder grades of polyurethanes reinforced with low carbon nanotube concentrations.
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Bentley, Paul Mark. "Time-frequency analysis of native and prosthetic heart valve sounds." Thesis, University of Edinburgh, 1996. http://hdl.handle.net/1842/10785.
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In the past, a number of researchers have applied various spectral estimation techniques in an attempt to analyse recorded heart sounds. The majority of these studies have used spectral estimation algorithms such as the Fourier transform and various autoregressive modelling techniques. Despite the definite potential these techniques have shown for the diagnosis of valvular heart disease, they are limited by their assumption of signal stationary and lack of relation to present stethoscope-based medical evaluation procedures. A solution to these limitations can be achieved by analysing the recorded sounds in the time-frequency domain rather than in the frequency-domain of time-domain independently. The research detailed in this thesis investigates the application of time-frequency techniques to the description and analysis of recorded heart sounds. Time-frequency is further investigated as a tool for the description of heart sounds in an attempt to diagnose valvular heart disease. Data used in the study was recorded from 100 subjects in four main valve populations. The four populations investigated were subjects with native heart valves, Carpentier-Edwards bioprosthetic heart valves, Bjork-Shiley metallic prosthetic heart valves and subjects before and after surgery for heart valve replacement. Prior to the analysis of these data sets, an investigation was performed into the suitability of various time-frequency techniques to the analysis of heart sounds. By comparing the short-time Fourier transform, wavelet transform, Wigner distribution and the Choi-Williams distribution it was found that the Choi-Williams distribution provides definite advantages over the other techniques due to its high resolution and reduced interference properties. Applying the Choi-Williams distribution to typical examples of each data set demonstrated that time-frequency offers definite potential as a heart sound descriptor. Typical results also demonstrate that time-frequency can be used as an aid to understanding the origins of heart sounds.
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Koch, Thorsten M. "Non-linear finite element analyses of the aortic heart valve." Thesis, University of Cape Town, 2004. http://hdl.handle.net/11427/6756.
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Includes bibliographical references.Finite element models of the aortic heart valve have been successfully used in the past to gain insight into the mechanics of the valve and to aid in understanding of valve failure. Moreover such models are indispensable tools for further developments in heart valve prosthetic design. In previous stress analyses linear elastic constitutive models have predominantly been used to model aortic valve leaflets, despite aortic valve tissue showing highly non-linear behaviour in tension tests. In view of recent developments towards tissue engineering of heart valves, these linear constitutive models of aortic valve leaflets are not likely to produce results sufficiently accurate to correlate cell behaviour with mechanical stimuli. To study how non-linear material behaviour affects the results of stress analyses of the aortic valve, static finite element analyses of the valve including the aortic root and leaflets have been carried out. An isotropic linear elastic material model was assigned to the aortic root with Young's modulus adjusted for the simulated compliance to match physiological values. Linear elastic models for the aortic valve leaflets with parameters used in previous studies were then compared with hyperelastic materials. The parameters used for the exponential strain energy function of the latter were obtained from fits of uniaxial tension test results of fresh porcine aortic valve leaflets. As natural leaflets show anisotropy with a pronounced stiff direction along the circumference of the valve, isotropic models of the leaflets were extended to account for this behaviour by incorporating transverse isotropy. The results display a stark impact of a transversely isotropic hyperelastic material on leaflet mechanics, Le. increased coaptation with peak values of stress and strain in the elastic limit. Interestingly, the alignment of maximum principal stress of all models seems to approximately follow the coarse collagen fibre distribution found ill aortic valve leaflets.
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Stepan, Lenka Lan-Sun. "Development and testing of a thin film nitinol heart valve." Diss., Restricted to subscribing institutions, 2007. http://proquest.umi.com/pqdweb?did=1324380381&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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