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Dissertations / Theses on the topic 'Heart valves'

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Author: Grafiati

Published: 4 June 2021

Last updated: 29 July 2024

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1

Chan, Gene Yel. "Cryopreservation of porcine heart valves." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ60420.pdf.

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2

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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3

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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4

Barsanti, Stephen. "Observations on the mechanical behaviour of polyurethane heart valves." Thesis, University of the West of Scotland, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265928.

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5

Reynolds, Karen Jane. "Acoustic monitoring of prosthetic heart valves." Thesis, University of Leicester, 1994. http://hdl.handle.net/2381/34209.

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The aim of the work presented in this thesis was to examine the possibility of detecting structural changes to an implanted prosthetic heart valve by spectral analysis of the sounds produced by the valve. On closure, mechanical heart valves produce a distinct sound as the occluder strikes the metal frame of the valve. Any change in the mechanical state of the valve will produce changes in the modes of vibration of the entire structure, causing the spectrum of the closing sounds to change. Initial recordings were made in a large tank of water providing ideal valve actuation and recording conditions. Results showed that all valves produce a stable averaged spectrum, and that each valve has a unique averaged spectrum. A digital filtering technique was developed whereby a baseline spectrum recorded from each valve is used for comparison with all subsequently recorded spectra from that valve. Using this technique, averaged spectra from individual valves were found to be highly reproducible. However, a minor structural alteration to a valve (added mass, or strut fracture) caused significant spectral changes, readily detected by digital filtering. To investigate the effect of a finite recording volume, recordings were made in a tank with dimensions approximating those of a human thorax. Standing waves generated by reverberations were clearly visible in the results. Structural changes to a valve were still detectable. Recordings were also made from prosthetic valves implanted in patients. To reduce sound distortion at the thoracic surface, recordings were made with the patient submerged in water. Results showed that reproducible averaged spectra could be obtained from implanted valves provided recording conditions were kept constant. The technique has not yet been developed to the point where it can be applied clinically. Nevertheless the technique shows promise as a method of screening patients at risk.

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6

Zhang, Yinxing. "Bioprosthetic heart valves : ultrastructure and calcification." Master's thesis, University of Cape Town, 1998. http://hdl.handle.net/11427/26921.

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Sumaary in English.
Includes bibliographical references.
Background: Due to the geographic distance between abattoirs and commercial valve plants delays between harvest and fixation usually range from 48 to 72 hours. In order to assess the pre-fixation tissue damage arising from the hypoxic period and the resulting calcific degeneration after implantation, we used an ultrastructural damage score and transmission electron microscopy. Materials and Methods: In a step by step manner, three major issues were clarified: 1) The degree of pre-fixation tissue damage was determined in the four most widely used commercially produced tissue heart valves. Since stentless bioprostheses represent the latest promising trend in the development of biological heart valves, stentless models of the following makes were compared: Baxter, Medtronic, St. Jude and Biocor. Due to the fact that the aortic wall component of these valves proved most resistant to all anticalcification treatments, aortic wall tissue stood in the centre of our analyses. 2) Subsequently, three main determinants of the fixation process namely: delay, temperature and fixative-concentration were varied with the goal of significantly improving the ultrastructural preservation of the bioprosthetic tissue. 3) Eventually, the influence of improved ultrastructural preservation on calcific degeneration was evaluated under in vivo conditions in the non-human primate and the rat model. Results: The comparison of the four most commonly used stentless bioprosthetic heart valves revealed a disturbing degree of tissue damage in all valves. Using a damage score from 1 to 21 (21 being the worst), aortic wall tissue of commercial valves ranged from 10 to 18 and that of leaflet tissue from 12 to 20. When fixation conditions were permutated, tissue damage could almost be abolished by immediate fixation (within 30 minutes of slaughter), low-temperature fixation(4°C) and high glutaraldehyde concentrations (> 1 %). Our in vivo experiments confirmed that commercially used fixation (delayed fixation, room-temperature and I ow concentrations of glutaraldehyde) with its concomitant high degree of tissue damage results in high levels of calcification. Apart from a distinctly improved calcification potential in ultrastructurally well preserved tissue, there was also an inverse correlation between tissue calcification and the concentration of glutaraldehyde used for fixation. Conclusion: We could demonstrate that commercially produced bioprosthetic heart valves uniformly show badly damaged tissue and that tissue damage contributes to the calcific degeneration of these valves. We were also able to determine ideal fixation conditions which in turn significantly reduced tissue calcification.

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7

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.

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8

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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9

Gallocher, Siobhain Lynn. "Durability Assessment of Polymer Trileaflet Heart Valves." FIU Digital Commons, 2007. http://digitalcommons.fiu.edu/etd/54.

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The durability of a polymer trileaflet valve is dependent on leaflet stress concentrations, so valve designs that reduce stress can, hypothetically, increase durability. Design aspects that are believed to contribute to reduced leaflet stress include stent flexibility, parabolic coaptation curvature, and leaflet anisotropy. With this in mind, the purpose of this investigation was to elucidate what specific combinations of these parameters promote optimal acute and long-term valve function. A combination of four stent designs, seven leaflet reinforcement materials, and three coaptation geometries were evaluated through a combination of experimentation and modeling. Static tensile and Poisson’s ratio tests and dynamic tensile fatigue testing were used to evaluate the individual leaflet components; and hydrodynamic testing and accelerated valve fatigue was used to assess complete valve prototypes. The two most successful designs included a 0.40 mm thick knit-reinforced valve with a fatigue life of 10.35 years, and a 0.20 mm thick knit-reinforced valve with a 28.9 mmHg decrease in pressure drop over the former. A finite element model was incorporated to verify the impact of the above-mentioned parameters on leaflet stress concentrations. Leaflet anisotropy had a large impact on stress concentrations, and matching the circumferential modulus to that of the natural valve showed the greatest benefit. Varying the radial modulus had minimal impact. Varying coaptation geometry had no impact, but stent flexibility did have a marked effect on the stress at the top of the commissure, where a completely rigid stent resulted in a higher peak stress than a flexible stent (E = 385 MPa). In conclusion, stent flexibility and leaflet anisotropy do effect stress concentrations in the SIBS trileaflet valve, but coaptation geometry does not. Regions of high stress concentrations were linked to failure locations in vitro, so a fatigue prediction model was developed from the S/N curves generated during dynamic tensile testing of the 0.20 mm knit-reinforced leaflets. Failure was predicted at approximately 400 million cycles (10 years) at the top of the commissure. In vitro fatigue of this valve showed failure initiation after approximately 167 million cycles (4.18 years), but it was related to a design defect that is subsequently being changed.

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10

Weind, Kirsten L. "Potential oxygenation routes of aortic heart valves." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ58247.pdf.

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11

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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12

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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13

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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14

Thalassoudis, Kym. "Numerical studies of flow through prosthetic heart valves /." Title page, contents and summary only, 1987. http://web4.library.adelaide.edu.au/theses/09PH/09pht365.pdf.

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15

Ridgway, Andrea Janina. "Ultrasound doppler evaluation of mechanical aortic heart valves." Thesis, Georgia Institute of Technology, 1986. http://hdl.handle.net/1853/10213.

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16

D'Souza, Selwyn Stephen. "Accelerated testing of synthetic flexible leaflet heart valves." Thesis, University of Leeds, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270895.

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17

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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18

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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19

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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20

Shah, Sagar R. "Glycosaminoglycan stabilization reduces tissue buckling in bioprosthetic heart valves." Connect to this title online, 2007. http://etd.lib.clemson.edu/documents/1193080409/.

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21

Singer, C. "The development of prototype prosthetic synthetic fibre heart valves." Thesis, University of Leeds, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235412.

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22

Sierad, Leslie Neil. "A pulsatile bioreactor for conditioning tissue engineered heart valves." Connect to this title online, 2009. http://etd.lib.clemson.edu/documents/1249065889/.

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Thesis (M.S.) -- Clemson University, 2009.
Title from first page of PDF file. Document formatted into pages; contains x, 84 p. ; also includes graphics (some col.). Contains additional supplemental file.

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23

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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24

Chatzimavroudis, George P. "Quantification of valvular regurgitation with magnetic resonance phase velocity mapping." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/11808.

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25

Hopmeyer, Joanne. "Effect of physiologic parameters on the quantification of mitral regurgitation using the flow convergence method." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/10969.

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26

Everaerts, Fransiscus Joannes Leonardus. "A novel approach in cross-linking of bioprosthetic heart valves." Enschede : University of Twente [Host], 2007. http://doc.utwente.nl/58023.

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27

Watson, Stuart Kent. "Carbon deposition for artificial heart valves using liquid reagent CVD." Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/16908.

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28

Yeh, Han Hung. "Computational analysis of fluid structure interaction in artificial heart valves." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/44921.

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The development of heart valve stenosis and sclerosis can lead to the development of fatal complications such as congestive heart failure. Therefore, severe valve stenosis requires a surgical operation with artificial heart valve replacement. Given that the geometrical differences between artificial valves would significantly influence hemodynamic performance around the implanted valve, additional knowledge for the interactions between blood flow and the artificial valve is necessary. Therefore, in order to proceed, this study proposes an advanced computational fluid dynamics (CFD) simulation using a fluid-structure interaction (FSI) technique to investigate artificial valve leaflet motion under different physiological conditions. Among various FSI technique, it is proposed to simulate the motion of the artificial heart valve with a fully-coupled algorithm and arbitrary Lagrangian-Eulerian formulation (ALE) using a monolithic solver. Models are constructed using a realistic aortic root for both the bileaflet and bioprosthetic valves with additional modifications and considerations for the flexible arterial wall. Normal physiological blood pressure and conditions are used to simulate healthy scenarios, which are compared with experiments. Validation is conducted by analysing particle image velocimetry (PIV) experimental data from ViVitro Lab. Hemodynamic performance analyses are conducted and found that both velocity and maximum von Mises stress are higher if calculated using a rigid wall model. The leaflet dynamics, on the other hand, is relatively the same for rigid or flexible wall model. Clinically relevant scenarios are also simulated for both mechanical and bioprosthetic valves. The clinical focus for the mechanical valve is on the malfunction of the valve due to leaflet restrictions. In addition, the clinical focus for the bioprosthetic valve is on the systolic deficiency due to different tissue properties.

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29

Москаленко, Роман Андрійович, Роман Андреевич Москаленко, Roman Andriiovych Moskalenko, I. Iashlichyn, and E. Chernov. "Amyloidosis in aorta wall and heart valves afected by atherosclerosis." Thesis, Sumy State University, 2015. http://essuir.sumdu.edu.ua/handle/123456789/41234.

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30

Elliott, Catherine. "Complications of anticoagulation in pregnant women with mechanical heart valves." Master's thesis, University of Cape Town, 2012. http://hdl.handle.net/11427/3043.

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31

Raghavan, Devanathan. "ECM stabilization strategies for bioprosthetic heart valves for improved durability." Connect to this title online, 2008. http://etd.lib.clemson.edu/documents/1239896171/.

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32

Hinds, Heather C. "Evaluating terminal differentiation of porcine valvular interstitial cells in vitro." Link to electronic thesis, 2006. http://www.wpi.edu/Pubs/ETD/Available/etd-050506-113014/.

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33

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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34

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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35

Korossis, Sotirios Anastasios. "Biomechanics and hydrodynamics of decellularised aortic valves for tissue engineering." Thesis, University of Leeds, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270873.

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36

Forsythe, R. N. "A partitioned approach to fluid-structure interaction for artificial heart valves." Thesis, Queen's University Belfast, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438630.

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37

Leefe, Simon Edric. "Pulsatile flow testing and development of prosthetic heart valves in conduits." Thesis, University of Nottingham, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335930.

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38

Friebe, Vincent Morris. "Neomycin enhances glutaraldehyde crosslinking and glycosaminoglycan stability in bioprosthetic heart valves." Connect to this title online, 2009. http://etd.lib.clemson.edu/documents/1263397247/.

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39

Southern, Lisa Jane. "Identification of glutaraldehyde induced structures in bioprosthetic heart valves using mass spectrometry : an insight into valve failure." Thesis, University of Sheffield, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366113.

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40

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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41

Brito, Flavia Carneiro. "Melanocytes in the developing and adult atrioventricular valves of the murine heart." FIU Digital Commons, 2008. http://digitalcommons.fiu.edu/etd/2246.

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The Neural Crest (NC) is a multipotential group of cells that arises from the dorsal aspect of the neural tube early in development. It is well established that a group of NC cells named Cardiac Neural Crest (CNC) migrates to the heart and plays a critical role in the remodeling of the aortic arch arteries and septation of the outflow tract. In this study, using the mouse mutant Pax3sp/sp that has CNC deficits I have identified a putative novel role for the CNC in regulating apoptosis in the atrioventricular (AV) endocardial cushion. The AV endocardial cushion undergoes remodeling to give rise to the cardiac AV valves. Using a transgenic mouse that carries the LacZ reporter gene under the control of the Dopachrome tautomerase promoter (Dct-LacZ), I found that another NC derived population, melanocyte precursors, also contribute to the AV endocardial cushion and developing AV valves. The analysis of Dct-LacZ embryos at different stages showed that NC cells already committed to the melanocytic fate migrate to the heart along the same initial pathway taken by those that will populate the skin. Hypopigmented mice carrying mutations in the Kit and Endothelin receptor b genes, that are critical for the proper development of skin melanocytes, do not have cardiac melanocytes indicating that cardiac and skin melanocyte precursors share the same initial signaling requirements. The analysis of murine adult hearts showed that melanocytes are mostly found in the atrial sides of the tricuspid and mitral valve leaflets. The distribution of melanocytes in the AV valves corresponds exactly to areas of high Versican B expression, a proteoglycan essential for the process of AV valve remodeling. To evaluate a potential role for melanocytes in the AV valves, a nanoindentation analysis of the tricuspid valves of wild type, hypopigmented and hyperpigmented mice was performed. The storage modulus, a measure of stiffuess, for the leaflets obtained from hyperpigmented mice was considerably higher (10.5GPa) than that for the leaflets from wild type (7.5GPa) and hypopigmented animals (between 3.5 and 5.5 GPa) suggesting that melanocytes may contribute to the mechanical properties of the A V valves.

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42

Aliabadi, Ardavan. "Numerical simulation of fluid-structure interaction for tilting-disk mechanical heart valves." Thesis, Wichita State University, 2013. http://hdl.handle.net/10057/6803.

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According to the United States Department of Health and Human Services, 27.1 million non-institutionalized adults were diagnosed with heart disease in 2010. The number of deaths associated with heart disease in 2009 was reported to be 599,413, claiming the lives of 195 out of every 100,000 people, which makes heart disease the number one killer in the U.S. Even though mechanical heart valves (MHVs) have proven to save lives in many of these cases, they are still not perfect, and complications arising from their design have reduced their application. To better understand the important factors and pursue remedies, numerous experimental investigations have been conducted; however, despite impressive improvements, small-scale studies suffer from lower levels of accuracy and sometimes are very costly to conduct. As in many other areas of research, numerical simulations can be helpful in reducing costs and supplementing such experimental work. The computational effort in this thesis focused on the numerical analysis of current tilting-disk MHVs. In this work, an implicit fluid-structure interaction (FSI) simulation of the Bjork-Shiley design was carried out using in-house codes implemented in the commercial code software FLUENT. In-house codes in the form of journal files, schemes, and user-defined functions (UDFs) were integrated to automate the inner iterations and enable communication between the fluid and the moving disk at the interfaces. Based on the investigation of the current simulations, a new design aiming at improving the hemodynamic performance is suggested. The hemodynamics of flow in current tilting-disk valves was compared with the suggested design, and it is concluded that the suggested design has a better hemodynamic performance in terms of shear stress values and residence times.
Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering

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43

Rahmani, B. "Development of the next generation heart valves using a novel nanocomposite material." Thesis, University College London (University of London), 2015. http://discovery.ucl.ac.uk/1460756/.

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Replacement heart valves offer substantial benefits to the patients with severe valvular heart disease. However, current prosthetic heart valves are still unable to meet the needs for more durable tissue valves and less thrombogenic mechanical valves. The aim of this research was to develop and evaluate a new generation heart valves made from a new shape-memory nitinol scaffold and a novel nanocomposite material known as polyhedral oligomeric silsesquioxanes poly(carbonate−urea) urethane (POSS-PCU). During the course of this research, the biomechanical properties of POSS-PCU nanocomposite were evaluated and compared to those of the materials currently used to fabricate bioprosthetic valves. Moreover, POSS-PCU nanocomposite was chemically engineered to improve its oxidative stability and minimise biodegradation. A novel artificial aortic valve was devised and transferred from a stented design into a semi-stented concept and then a retrievable and repositionable valve suitable for transcatheter implantation. The proposed surgical and transcatheter valves were manufactured by an innovative automated dip-coating technique. An industrial-scale automated dipping mechanism was designed to improve the reproducibility of polymeric valve leaflets with no need to suturing or adhesives. The POSS-PCU valves were assessed in vitro for their hydrodynamic performance in a test setup complying with ISO 5840 standards and were shown to have an advanced function compared to clinically available prosthetic valves. The transcatheter POSS-PCU valves (Triskele valves) were then subjected to preliminary acute animal study in ovine model and successfully implanted, retrieved and repositioned in orthotopic position with excellent valve function. The promising results from the in vitro functional tests and the preliminary in vivo study encourage the use of POSS-PCU nanocomposite material and superelastic nitinol wire-frame to develop a new generation transcatheter heart valves which can overcome the main limitations experienced with current solutions. Although further durability and long-term animal studies are required which are currently under investigation.

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Tuladhar, Sugat Ratna. "Development and characterisation of bioengineered percutaneous heart valves using xenogeneic decellularised pericardia." Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3424734.

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Heart valve disease (HVD) represents a major health problem, causing significant morbidity and mortality worldwide. The gold standard for treating HVD is surgical replacement of the diseased valve with a prosthetic one. However, many patients affected by HVD cannot receive surgical treatment due to their old age or multiple comorbidities, such as poor left ventricular function, coronary artery disease, kidney failure or chronic lung diseases. The alternative solution for these patients is transcatheter implantation of a valve prosthesis, i.e. a percutaneous heart valve (PHV), by minimally invasive techniques. Current heart valve prostheses for this approach are composed of chemically treated xenogeneic tissue. As such, a limitation common to all of them is the inability of remodelling, repair, and regeneration, which are particularly problematic in case of paediatric patients. Decellularised scaffolds presenting a natural histoarchitecture have been shown to be a good alternative to chemically processed xenograft. Decellularisation is a process, which removes cells and other xenogeneic components from the treated tissue while retaining the integrity of its extracellular matrix components, which are essential for supporting cell engraftment and function. Importantly, decellularisation has the potential to remove immunogenic factors rendering decellularised xenografts potentially biocompatible in an in-human implantation. In this project, decellularised pericardium has been applied with the aim to develop bioengineered percutaneous heart valves (bioPHVs) with possibly superior potential of long-term performance in comparison to conventional cardiac valve prostheses. Porcine and bovine pericardia were decellularised using an established protocol combining Triton X-100, sodium cholate and endonucleases. Decellularisation was verified through histology, immunofluorescence, and biochemistry. BioPHVs were fabricated by sewing the decellularised pericardia onto commercially available stents. The bioPHVs were as first evaluated by hydrodynamic performance according to ISO 5840-3 standard requirements. Second, the possible effects of valve crimping on bioPHV decellularised pericardial tissues were assessed through histological and morphometrical analysis. Histology, immunofluorescence, and biochemical analyses revealed TRICOL to be equally successful for the decellularisation of both porcine and bovine pericardia. Hydrodynamic tests showed that bioPHVs satisfied the minimum performance requirements indicated by ISO 5840-3. The hydrodynamic behaviour of the bioPHVs was comparable, or even superior, to the one exhibited by the control valves. BioPHVs were also able to withstand extreme back pressure conditions without any severe regurgitations. Examination, both macroscopic and microscopic, of the valve samples after crimping showed no major trauma or injury on the pericardial cusps. This study demonstrated the suitability of the decellularised pericardium, either bovine or porcine, as an alternative to the glutaraldehyde-treated equivalent. Among the two types of pericardial species tested, preliminary results indicated that the porcine tissue would be preferable to fabricate advanced PHV replacements.
La malattia della valvola cardiaca (HVD) rappresenta un grave problema di salute, causando una significativa morbilità e mortalità in tutto il mondo. Il gold standard per il trattamento di HVD è la sostituzione chirurgica della valvola malata con una protesica. Tuttavia, molti pazienti affetti da HVD non possono ricevere un trattamento chirurgico a causa della loro vecchiaia o multiple comorbidità, come scarsa funzione ventricolare sinistra, malattia coronarica, insufficienza renale o malattie polmonari croniche. La soluzione alternativa per questi pazienti è l'impianto transcatetere di una protesi valvolare, cioè una valvola cardiaca percutanea (PHV), con tecniche minimamente invasive. Le attuali protesi valvolari cardiache per questo approccio sono composte da tessuto xenogenico trattato chimicamente. Come tale, una limitazione comune a tutti loro è l'incapacità di rimodellamento, riparazione e rigenerazione, che sono particolarmente problematici nel caso di pazienti pediatrici. Gli scaffold decellularizzati che presentano un'istologia architettonica naturale hanno dimostrato di essere una buona alternativa allo xenoinnesto trattato chimicamente. La decellularizzazione è un processo che rimuove le cellule e altri componenti xenogenici dal tessuto trattato, mantenendo l'integrità dei componenti della matrice extracellulare, essenziali per supportare l'attecchimento e la funzione delle cellule. È importante sottolineare che la decellularizzazione ha il potenziale per rimuovere i fattori immunogenici rendendo xenotrapianti decellularizzati potenzialmente biocompatibili in un impianto in-umano. In questo progetto, il pericardio decellularizzato è stato applicato con lo scopo di sviluppare valvole cardiache percutanee bioingegnerizzate (bioPHV) con possibilmente un potenziale superiore di prestazioni a lungo termine rispetto alle protesi valvolari cardiache convenzionali. La pericardia suina e bovina è stata decellularizzata usando un protocollo stabilito che combina Triton X-100, sodio colato e endonucleasi. La decellularizzazione è stata verificata attraverso l'istologia, l'immunofluorescenza e la biochimica. I BioPHV sono stati fabbricati cucendo la pericardia decellularizzata su stent disponibili in commercio. I bioPHV sono stati valutati per la prima volta dalle prestazioni idrodinamiche secondo i requisiti dello standard ISO 5840-3. In secondo luogo, i possibili effetti della crimpatura della valvola sui tessuti pericardici decellularizzati di bioPHV sono stati valutati mediante analisi istologica e morfometrica. Istologia, immunofluorescenza e analisi biochimiche hanno rivelato che TRICOL ha ugualmente successo per la decellularizzazione della pericardia suina e bovina. I test idrodinamici hanno dimostrato che i bioPHV soddisfacevano i requisiti minimi di prestazione indicati dalla norma ISO 5840-3. Il comportamento idrodinamico dei bioPHV era comparabile, o addirittura superiore, a quello mostrato dalle valvole di controllo. I BioPHV erano anche in grado di resistere a condizioni estreme di contropressione senza rigurgiti gravi. L'esame, sia macroscopico che microscopico, dei campioni delle valvole dopo la crimpatura non ha mostrato traumi o traumi maggiori alle cuspidi pericardiche. Questo studio ha dimostrato l'idoneità del pericardio decellularizzato, sia bovino che porcino, in alternativa all'equivalente trattato con glutaraldeide. Tra i due tipi di specie pericardiche testate, i risultati preliminari hanno indicato che il tessuto suino sarebbe stato preferibile per fabbricare sostituzioni avanzate di PHV.

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Xing, Yun. "Effects of Mechanical Forces on the Biological Properties of Porcine Aortic Valve Leaflets." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6828.

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Cardiac valves are dynamic, sophisticated structures which interact closely with the surrounding hemodynamic environment. Altered mechanical stresses, including pressure, shear and bending stresses, are believed to cause changes in valve biology, but the cellular and molecular events involved in these processes are not well characterized. Therefore, the overall goal of this project is to determine the effects of pressure and shear stress on porcine aortic valve leaflets biology. Results from the pressure study showed that elevated constant pressure (140 and 170 mmHg) causes significant increases in collagen synthesis. The increases were 37.5% and 90% for 140 and 170 mmHg, respectively. No significant differences in DNA and sGAG synthesis were observed under constant pressure. In the cyclic pressure study, the effects of both pressure magnitude and pulse frequency were studied. With the frequency fixed at 1.167 Hz, collagen and sGAG synthesis increased proportionally with mean pressure level. At a fixed pressure level (80-120 mmHg), collagen and sGAG synthesis were slightly increased by 25% and 14% at 0.5 Hz, respectively. DNA synthesis was significantly increased by 72% at 2 Hz. An experiment combining high magnitude (150-190 mmHg) and high frequency (2 Hz) demonstrated significant increases in collagen and sGAG synthesis (collagen: 74%, sGAG: 56%), but no significant changes in cell proliferation. Shear levels ranging from 1 to 80 dyne/cm2 were studied. Scanning electron microscopy results indicated that 48 hrs exposure to shear stress did not alter the circumferential alignment of endothelial cells. Collagen synthesis was significantly enhanced at 9 and 25 dyne/cm2, but not different from static controls under other shear conditions. Leaflets denuded of the endothelium were exposed to identical shear stress and showed very different responses. Collagen synthesis was not affected at any shear levels, but sGAG content was increased at shear of 9, 25 and 40 dyne/cm2. Further studies showed that the increases in collagen synthesis under pressure or shear stress was concurrent with a decline in the expression and activities of cathepsins L and S. This converse relationship between collagen synthesis and cathepsin activity indicated that cathepsins might be involved in valvular ECM remodeling.

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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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47

Suleiman, David. "Measurement and prediction of phase equilibrium properties at infinite dilution : alkanes in natural gases and organic solvents in aqueous solutions." Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/10270.

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Cape, Edward Gene. "Theoretical and experimental analysis of intracardiac jets : new techniques for noninvasive quantification of valvular insufficiency." Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/11310.

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Lapierre, Isabelle. "Recherche thématique sur le vocabulaire des valvulopathies : étude terminologique de 50 dossiers terminographiques /." Thèse, Chicoutimi : Université du Québec à Chicoutimi, 1994. http://theses.uqac.ca.

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Simon, Helene A. "Influence of the implant location on the hinge and leakage flow fields through bileaflet mechanical heart valves." Thesis, Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-04012004-192539/.

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Thesis (M.S.)--Chemical Engineering, Georgia Institute of Technology, 2004.
Sambanis Athanassios, Committee Member ; Sotiropoulos Fotis, Committee Member ; Yoganathan Ajit, Committee Chair. Includes bibliographical references (leaves 239-243).

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