Design And Development Of Mock Circulation Systems For The Evaluation Of Mechanical Circulatory Assistance

Heart failure(HF) has become one of the biggest threats to human health and its incidence rate has being increasing on a yearly basis. Heart transplant is the most effective treatment for late stage HF patients. However, the severe shortage of donor heart has always been a serious limitation for the treatment. A large portion of patients would die before they get the heart transplant surgery. Therefore, the ventricular assist device(VAD) has already become an alternative therapy for late stage HF patients in some developed country. It can temporarily or permanently assist or substitute partial heart function, release heart load and drive the circulation of blood. Before the clinical practice, the performance evaluation of VAD generally consists of two phases which includes the in vitro(hemodynamic performance and hemocompatibility assessment) and in vivo test(animal experiments and clinical trials).For in vitro research, mock circulatory system(MCS) can be introduced to evaluate the performance of mechanical assistant device and provide valuable information for the design and optimization of VAD’s filling function. Massive researches have proved that MCS based in vitro test is a viable method to assess VAD’s hemodynamic function. The experiment not only has its own advantages in terms of controllability and repeatability, but can also save remarkable amount of cost in animal experiment.The object of this research is to develop a mock circulation system which has the function of simulating the human circulatory hemodynamic state. Different physiological condition including HF, healthy body in rest and movement will be mimicked by adjusting the parameters(heart rate, systolic and diastolic ratio, stroke volume, arterial compliance, flow resistance and venous pressure) of corresponding components in the MCS. The VAD will be integrated into the simulation for the purpose of quantitatively investigating respond from HF to ventricular support of multiple degree.Main research work of the thesis is as follows:1. MCS design: the MCS is comprised of hydraulic system and drive control unit which were integrated by the date acquisition interface. In the case of a full understanding of human body blood circulation and target hemodynamic parameters, the circulation was simplified as a lumped parameter model consisting of a group of hemodynamic components representing ventricle, vessel compliance and resistance respectively. The hydraulic systems can be simulated by: a linear motor derived piston pump acting as ventricle; one-way mechanical valves and flexible tube as natural valve and blood vessels, the resistance valve and inner hose friction as blood flow resistance, a water tank as human venous system and a compliance chamber as artery elasticity. Cardiac output, ventricular pressure, artery and vein pressure date were measured accordingly by flow or pressure sensors at each component and collected via the data acquisition interface. The drive unit in this research were designed to control the motion of piston pump(ventricle simulator). The periodic movement of piston was regulated by the displacement-time curve, by which corresponding pressure wave profile can be achieved.2. Regulation of MCS and baseline physiological condition: On the basis of the MCS hardware and structure design, the average index(mean arterial pressure and cardiac output) for different baseline physiological state(at rest, heart failure, in motion) were defined referring to clinical date. Besides, the appropriate pressure and flow rate were obtained by adjusting system parameters. Meanwhile, different parameters of mock circulatory system were analyzed, including the frequency of heart simulator, trajectory, arterial compliance, resistance and their influence on pressure or flow wave profile.3. VAD supported hemodynamic experiment: the fully magnetically levitated VAD developed previously by our group was fitted into the system and cooperated with ventricle in the experiment. For the purpose of evaluating the performance of VAD, the rotary speed was adjusted, by which to investigate its effect on pressure and flow.Results show that the MCS developed by this research has sufficient adjustability and ability to simulate the physiological condition within purposed range, which also proved that the system meets the requirement for hemodynamic research of VAD. Furthermore, VAD supported MCS experiment also indicated that the fully magnetically levitated VAD developed in previous study can be a viable therapy for late stage heart failure patients to improve their arterial pressure and cardiac output to healthy level,and realize different hemodynamic change under different assisting degree. In conclusion, the MCS in this research is capable of providing a useful tool for the design and performance assessment of VAD, and a comprehensive understanding of the influence of VAD to important organ filling function.