No description available.

Les travaux présentés dans ce mémoire s’inscrivent dans un projet visant à fabriquer des valves aortiques bioartificielles de remplacement pour des patients atteints de maladies cardiaques. La méthode globale étudiée consiste à produire un moule sacrificiel en sucre vitrifié produit par fabrication additive, prenant la forme d’une valve aortique et injecté avec un échafaudage cellulaire. En soumettant la valve moulée aux conditions physiologiques ressenties par une valve aortique réelle, il est espéré qu’une valve aortique fonctionnelle sera développée. Un des éléments importants dans ce procédé est l’échafaudage cellulaire. Puisque ce biomatériau contient des cellules vivantes, il doit être à l’abri de toutes sources de contamination. De plus, il doit permettre aux cellules de survivre et de sécréter de la matrice extracellulaire, dans le but d’éventuellement transformer l’échafaudage cellulaire en un tissu biologique fiable. Ce mémoire présente une technique de fabrication d’échafaudages cellulaires qui tient compte des enjeux liés à l’utilisation de cellules vivantes. Il s’agit d’une preuve de concept visant à s’intégrer au projet de valves aortiques bioartificielles. Afin de tester la méthode, une expérience in vitro de fabrication et de culture dynamique fut menée. Celle-ci démontra que cette méthode de fabrication fut adaptée au contexte de travail en environnement stérile, que les cellules ensemencées dans les spécimens furent distribuées de manière homogène, et que les moules en sucre vitrifié fabriqués par impression 3D ne causèrent pas de mortalité cellulaire dans ce contexte. Toutefois, des dommages mineurs furent observés après plusieurs semaines de culture, et les taux de viabilité cellulaire furent plus bas qu’attendu à cause d’un défaut au niveau de la perfusion des spécimens. Ainsi, la technique développée est prometteuse pour le projet de fabrication de valves aortiques, mais des améliorations doivent être apportées au niveau de la perfusion et du maintien de l’intégrité physique des tissus. / The work presented in this thesis is part of a project which aims at fabricating bioartificial aortic replacement valves for patients suffering from cardiac diseases. The global method studied to achieve this consists of fabricating sacrificial molds made of carbohydrate glass, produced by additive manufacturing, replicating the geometry of an aortic valve, and injected with a cellular scaffold. By exposing the molded valve to the physiological conditions a real aortic valve would experience, it is hoped that a functional aortic valve will be developed. One important aspect of this process is the cellular scaffold. Since this biomaterial contains live cells, it has to be isolated from all possible sources of contamination. Moreover, it has to favor cell survival, as well as extracellular matrix secretion, in order to eventually transform the scaffold into a reliable biological tissue. This thesis presents a fabrication technique for cellular scaffold that takes into account all the challenges linked to the use of live cells. It is a proof of concept with the aim of being included to the artificial aortic valve project. To validate this process and its aspects, an in vitro experiment of fabrication and dynamic culture was conducted. The results of this experiment showed that this method is adapted to the sterile work environment context, and that the cells seeded in the specimens were distributed homogeneously. This experience also demonstrated that the carbohydrate molds fabricated by additive manufacturing did not cause cell mortality in this context. However, minor damage was observed after several weeks of dynamic culture, and the cell viability rates were lower than expected because of suboptimal perfusion rates. This fabrication technique for cellular scaffolds is promising for the artificial aortic valves project, but improvements in terms of perfusion and preservation of physical integrity should be made.

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.

The automotive industry has been in a marathon of advancement over the past decades. This is partly due to global environmental concerns about increasing amount of air pollutants such as NOx (oxides of nitrogen), CO (carbon monoxide) and particulate matters (PM) and decreasing fossil fuel resources. Recently due to stringent emission regulations such as US EPA (Environmental Protection Agency) and CARB (California Air Resource Board), improvement in fuel economy and reduction in the exhaust gas emissions have become the two major challenges for engine manufacturers. To fulfill the requirements of these regulations, the IC engines including gasoline and diesel engines have experienced significant modifications during the past decades. Incorporating the fully flexible valvetrains in production IC engines is one of the several ways to improve the performance of these engines. The ultimate goal of this PhD thesis is to conduct feasibility study on development of a reliable fully flexible hydraulic valvetrain for automotive engines. Camless valvetrains such as electro-hydraulic, electro-mechanical and electro-pneumatic valve actuators have been developed and extensively studied by several engine component manufacturers and researchers. Unlike conventional camshaft driven systems and cam-based variable valve timing (VVT) techniques, these systems offer valve timings and lift control that are fully independent of crankshaft position and engine speed. These systems are key technical enablers for HCCI, 2/4 stroke-switching gasoline and air hybrid technologies, each of which is a high fuel efficiency technology. Although the flexibility of the camless valvetrains is limitless, they are generally more complex and expensive than cam-based systems and require more study on areas of reliability, fail safety, durability, repeatability and robustness. On the contrary, the cam-based variable valve timing systems are more reliable, durable, repeatable and robust but much less flexible and much more complex in design. In this research work, a new hydraulic variable valve actuation system (VVA) is proposed, designed, prototyped and tested. The proposed system consists of a two rotary spool valves each of which actuated either by a combination of engine crankshaft and a phase shifter or by a variable speed servo-motor. The proposed actuation system offers the same level of flexibility as camless valvetrains while its reliability, repeatability and robustness are comparable with cam driven systems. In this system, the engine valve opening and closing events can be advanced or retarded without any constraint as well as the final valve lift. Transition from regenerative braking or air motor mode to conventional mode in air hybrid engines can be easily realized using the proposed valvetrain. The proposed VVA system, as a stand-alone unit, is modeled, designed, prototyped and successfully tested. The mathematical model of the system is verified by the experimental data and used as a numerical test bench for evaluating the performance of the designed control systems. The system test setup is equipped with valve timing and lift controllers and it is tested to measure repeatability, flexibility and control precision of the valve actuation system. For fast and accurate engine valve lift control, a simplified dynamic model of the system (average model) is derived based on the energy and mass conservation principles. A discrete time sliding mode controller is designed based on the system average model and it is implemented and tested on the experimental setup. To improve the energy efficiency and robustness of the proposed valve actuator, the system design parameters are subjected to an optimization using the genetic algorithm method. Finally, an energy recovery system is proposed, designed and tested to reduce the hydraulic valvetrain power consumption. The presented study is only a small portion of the growing research in this area, and it is hoped that the results obtained here will lead to the realization of a more reliable, repeatable, and flexible engine valve system.

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.

Background: The etiology of congenital heart valve defects is not well understood; little is known about the risk factors that contribute to the survival and mortality outcomes of children with these defects. Methods: Using data from the Texas Birth Defects Registry (TBDR) we conducted a retrospective cohort study of 2070 singleton infants with congenital aortic, pulmonary, or tricuspid valve atresia or stenosis born in Texas between January 1, 1996 and December 31, 2007 to Hispanic, Non-Hispanic (NH) black, and NH white women. TBDR data were death-to-birth matched by the Texas Vital Statistics Unit for deaths between January 1, 1996 and December 31, 2008. Using Kaplan-Meier survival estimates with log rank tests and Cox proportional hazards regression model hazard ratios (HR) with 95% confidence intervals (CI), we examined whether infant sex and maternal race/ethnicity affected early childhood survival or risk of mortality for children with congenital heart valve defects. Covariates included birth weight and gestational age, maternal age, maternal education, and number of co-occurring birth defects. Results: In children with aortic valve atresia and aortic valve stenosis, we found males had higher early childhood survival than females (55.0% vs. 41.5%, P=0.0451 and 91.6% vs. 82.5%, P=0.0492, respectively). Early childhood survival for males (94.9%) with pulmonary valve stenosis was slightly lower than females (97.1%, P=0.0116), and was also lower for NH black (94.1%) and Hispanic (95.3%) children than NH white children (97.8%, P=0.0340). After adjusting for covariates, early childhood mortality in children with pulmonary valve atresia with hypoplastic right ventricle was greater in NH black than NH white children (HR=2.93, CI 1.09-7.85, P=0.0329) and greater in NH black males than NH white males (HR=4.63, CI 1.12-19.19, P=0.0349). For children with tricuspid valve atresia, early childhood survival was lower in NH black males (35.7%) and Hispanic males (64.0%) than NH white males (81.0%, P=0.0269); after adjusting for covariates, risk for early childhood mortality was higher in NH black than NH white children (HR=3.39, CI 1.41-8.13, P=0.0062), and higher in NH black males than NH white males (HR=5.23, CI 133-20.58, P=0.0179). Conclusions: Our findings demonstrate there are disparities in early childhood survival and risk of mortality by infant sex and maternal race/ethnicity for children with congenital heart valve defects. These findings provide a foundation for further investigation to better understand why these disparities exist and what can be done to improve the outcomes for children with these defects.

The automotive industry has been in a marathon of advancement over the past decades. This is partly due to global environmental concerns about increasing amount of air pollutants such as NOx (oxides of nitrogen), CO (carbon monoxide) and particulate matters (PM) and decreasing fossil fuel resources. Recently due to stringent emission regulations such as US EPA (Environmental Protection Agency) and CARB (California Air Resource Board), improvement in fuel economy and reduction in the exhaust gas emissions have become the two major challenges for engine manufacturers. To fulfill the requirements of these regulations, the IC engines including gasoline and diesel engines have experienced significant modifications during the past decades. Incorporating the fully flexible valvetrains in production IC engines is one of the several ways to improve the performance of these engines. The ultimate goal of this PhD thesis is to conduct feasibility study on development of a reliable fully flexible hydraulic valvetrain for automotive engines. Camless valvetrains such as electro-hydraulic, electro-mechanical and electro-pneumatic valve actuators have been developed and extensively studied by several engine component manufacturers and researchers. Unlike conventional camshaft driven systems and cam-based variable valve timing (VVT) techniques, these systems offer valve timings and lift control that are fully independent of crankshaft position and engine speed. These systems are key technical enablers for HCCI, 2/4 stroke-switching gasoline and air hybrid technologies, each of which is a high fuel efficiency technology. Although the flexibility of the camless valvetrains is limitless, they are generally more complex and expensive than cam-based systems and require more study on areas of reliability, fail safety, durability, repeatability and robustness. On the contrary, the cam-based variable valve timing systems are more reliable, durable, repeatable and robust but much less flexible and much more complex in design. In this research work, a new hydraulic variable valve actuation system (VVA) is proposed, designed, prototyped and tested. The proposed system consists of a two rotary spool valves each of which actuated either by a combination of engine crankshaft and a phase shifter or by a variable speed servo-motor. The proposed actuation system offers the same level of flexibility as camless valvetrains while its reliability, repeatability and robustness are comparable with cam driven systems. In this system, the engine valve opening and closing events can be advanced or retarded without any constraint as well as the final valve lift. Transition from regenerative braking or air motor mode to conventional mode in air hybrid engines can be easily realized using the proposed valvetrain. The proposed VVA system, as a stand-alone unit, is modeled, designed, prototyped and successfully tested. The mathematical model of the system is verified by the experimental data and used as a numerical test bench for evaluating the performance of the designed control systems. The system test setup is equipped with valve timing and lift controllers and it is tested to measure repeatability, flexibility and control precision of the valve actuation system. For fast and accurate engine valve lift control, a simplified dynamic model of the system (average model) is derived based on the energy and mass conservation principles. A discrete time sliding mode controller is designed based on the system average model and it is implemented and tested on the experimental setup. To improve the energy efficiency and robustness of the proposed valve actuator, the system design parameters are subjected to an optimization using the genetic algorithm method. Finally, an energy recovery system is proposed, designed and tested to reduce the hydraulic valvetrain power consumption. The presented study is only a small portion of the growing research in this area, and it is hoped that the results obtained here will lead to the realization of a more reliable, repeatable, and flexible engine valve system.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (p. 123-133).

AN ABSTRACT OF THE THESIS OF AMIT SHRESTHA, for the Master of Science degree in MECHANICAL ENGINEERING, presented on July 6th 2009, at the Southern Illinois University at Carbondale. TITLE: DEVELOPMENT AND PERFORMANCE EVALUATION OF A MONO-VALVE ENGINE MAJOR PROFESSOR: Dr. Suri Rajan A new Mono-Valve engine head was fabricated and assembled for a standard 4-stroke single cylinder Two-Valve gasoline engine with an aim to achieve an improved air flow characteristics than that of the Two-Valve engine. The Mono-Valve engine has only one valve in the cylinder head with the intake and exhaust ports controlled by an auxiliary Rotary-Valve. The two engines were tested under cold flow motoring conditions at engine speeds ranging from 1000 to 2500 rpm under fully open and half open throttle conditions in order to study and compare their volumetric efficiencies. Variable intake pipe lengths of 8.25, 25.5 and 39 inches were used to study their effect on volumetric efficiencies and in-cylinder pressure characteristics of both the engines. The results of the experiments showed that the average in-cylinder peak pressure, intake and exhaust pressures characteristics are similar for both the engine heads. However, the volumetric efficiency of the new Mono-Valve engine head was found to be 2-7% less than that of the original Two-Valve engine head depending upon the length of the intake pipe. This is mainly due to the opening angle in the Rotary-Valve that mostly controls the duration of the intake and the exhaust processes, and also due to the timing of the opening and closing of the intake and exhaust ports.

Abstract The repair of degenerative mitral valve regurgitation has been shown to be an effective procedure with durable results. The techniques for mitral valve repair are not completely risk-free for late failure, and the identification of factors associated with this increased risk is of clinical relevance as it permits an appropriate selection of patients for whom mitral valve surgery should be offered and by which technique. The European system for cardiac operative risk evaluation score (EuroSCORE) has been used and demonstrated worldwide to be a valid tool for the prediction of immediate postoperative outcome after coronary artery bypass surgery. There are only a few studies which examine its value in heart valve surgery. Mitral valve repair has been shown to be associated with significant improvement in terms of functional capacity, but the late quality of life in these patients has not been adequately assessed, and there is no data on the quality of life of long-term survivors. The study population consisted of two groups of patients operated on at our institution. The first group included 164 patients who underwent isolated or combined mitral valve repair for mitral valve regurgitation during the period 1993 to 2000, while the second group consisted of 207 patients who underwent mitral valve repair (164 patients) or replacement (43 patients) for isolated mitral valve regurgitation during the same time-period. The first study aimed to identify preoperative variables which may have impact on the 30-day postoperative outcome. In the second study, the long-term outcome after mitral valve repair was evaluated in order to identify the risk factors associated with late failures. The third study analyzed quality of life after valve repair and compared it to that of an age- and gender-adjusted Finnish general population. In the fourth study, the validity of EuroSCORE was tested in predicting the immediate and late outcome of patients who had undergone mitral valve repair or replacement for isolated valve regurgitation. Patient age, a history of prior cardiac surgery and NYHA functional class were independent predictors of poor outcome. A residual regurgitation grade of more than one immediately after primary repair and chronic pulmonary disease were independent predictors of mitral valve reoperation. After valve repair, quality of life was similar to the age- and sex-adjusted general Finnish population. Both additive and logistic EuroSCOREs were predictors of the immediate and late outcomes of patients after surgery for mitral valve regurgitation.