| This dissertation focuses on the research of in vitro mock circulatory systems (MCS) and the physiological control of a left ventricular assist device (LVAD). These two aspects both concern about the performance of the LVAD. The former is a performance evaluating platform for a LVAD, whereas the latter makes the performance of a LVAD much better. Meanwhile, a MCS is also useful in the control strategy validation of a LVAD. In summary, the research content of this paper mainly centre on the performance of a LVAD, which is the key point during the development of a LVAD.First, the basic physiology of the blood circulation system is introduced, with features and functions of the main parts detailed. Based on these knowledge, the mathematic models of the blood circulation and the arterial baroreflex regulation are both provided. Then numerical simulations are carried out to reproduce the hemodynamics under different physiological conditions including normal, heart failure and abrupt aortic pressure change. Good results are yielded, demonstrating the effectiveness of the mathematical models. Secondly, a pneumatic adult MCS is designed, in which the baroreflex regulation is implemented for the first time through the combination of hardware and software. A simple and economic pediatric MCS is also constructed, and the afterload and preload sensitivities of the mock ventricle are reproduced by a feedback control method. In order to further validate the pediatric MCS, a pediatric LVAD is inserted and tested on it. At last, a physiological controller for rotary blood pumps, which is based on fuzzy logic and speed modulation, is proposed in an attempt to maintain the mean aortic pressure and meanwhile enhance the pulse pressure. Numerical simulations and in vitro experiments are both performed to validate the robustness and feasibility of the controller, respectively.The main contents of this dissertation are as follows:1. Mathematical modeling of the baroreflex-cardiovascular system. Time-varying elastance model is established for both ventricles and atriums. Blood vessel is modeled as resistance, compliance and inertance using lumped parameter method. Following the classical idea of electric-fluid analogue, an electric circuit is then used to represent the blood circulation. Besides, the baroreflex regulation model is also provided. Simulations are performed to reproduce hemodynamics in both normal and heart failure conditions, and the response when aortic pressure changes abruptly is investigated too. Results demonstrate the effectiveness of these models. They provide not only the guidance for the construction of a MCS, but also a numerical platform for control research of a LVAD.2. Research on adult MCS. Adopting hydraulic components to replicate the characteristics of the blood circulation system, a pulsatile pneumatic adult MCS is constructed. Hemodynamic waveforms such as pressure and blood flowrate are measured and displayed in computer. Experiments are carried out to simulate hemodynamic characteristics in both normal and heart failure conditions, demonstrating the capibility of the MCS to provide a similar environment as human circulation. Moreover, baroreflex regulation is introduced into the MCS based on the baroreflex model, through a combination method of hardware and software. This is achieved by driving the physical valves in the MCS appropriately according to the measured aortic pressure. It will enable the MCS to be a better platform for interaction investigation between LVAD and the blood circulation.3. Research on pediatric MCS. A novel method to construct a pediatric MCS quickly and economically is presented. This method employs a combination of off-the-shelf fluid components to simulate the ventricular contractility. In addition, a simple feedback control is introduced to reproduce the physiological afterload and preload sensitivities of the mock ventricle. Furthermore, a pediatric LVAD prototype is inserted for testing to further verify the effectiveness of the pediatric MCS. The experimental results indicate that this pediatric MCS is capable of reproducing basic hemodynamic characteristics of a child in both normal and heart failure conditions, and it’s sufficient for testing a pediatric LVAD.4. Physiological controller design of rotary blood pumps. A fuzzy control method for rotary blood pumps using active speed modulation is proposed to maintain the mean aortic pressure to provide sufficient perfusion while simultaneously enhance the pulse pressure. An additional algorithm is also included to prevent regurgitation. The controller is tested both in the baroreflex-cardiovascular model and in a preliminary in vitro experiment. Simulation results demonstrate that the controller is able to increase the pulse pressure to20mmHg and at the same time maintain the mean pressure at100mmHg, when heart failure occurs. It is also quite robust under various physiological disturbances. In vitro experimental results show that the controller is feasible in practice. |
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