| Development of miniature implantable axial flow blood pump and numerical simulation for the dynamo temperature fieldObjective:The treatment of terminal heart failure has recently become great challenge for cardiovascular clinical physicians. The limitations of the routine medical therapy and surgical interventions, as well as the shortage of donor hearts have led to rapid development of mechanical circulation support devices. Through the joint research and development of electric machine, fluid mechanics, mechanical engineering, materials science, automatic control engineering, and medical science, exploring a new type of long term implantable miniature axial flow blood pump has become a hot topic in research. In this project we had designed and developed a kind of implantable axial flow blood pump. The construction features, the basic parameters of the blood pump had been investigated. Finally the simulation experiment was made to illustrate the change of electric machine temperature field of blood pump.Methods:The temperature of stator winding, stator core, flow channel intine, and pump housing were measured respectively, based on a simplified electric machine model. A finite element analysis software ANSYS WORKBENCH was used to divide grid, establish the boundary conditions and governing equations. Graphics were used to demonstrate the change of interior temperature field.Results:The numerical simulation showed that the temperature would tend to be stable after blood pump having been worked for 20 minutes.It was shown that the highest temperature of the generator winding and stator core were respectively 3.9 and 3.7℃in respective area. The whole temperature rise of the blood pump was approximately 2.7 to 3.9℃.Conclusion:In the whole process of the blood pump design, the international study on new pattern blood pump was considered. It was believed that the idea of design is new, and the structure is rational. Since the new materials and technology were applied, the blood pump showed reliable mechanical performance. The total design of electric machine was reasonable based on the analysis and computation of the blood pump by a finite element analysis software ANSYS WORKBENCH. The temperature rise of blood pump reached the implantable requirement of the artificial heart. Hydrodynamics and hemolysis test of miniature implantable axial flow blood pump in vitroObjective:To explore hydrodynamics and hemolytic characteristics of the self-made implantable axial flow blood pump through mock circulatory loop in vitro.Methods:This study included two parts:hemolysis test and the analysis of relationship of pressure and flow. The relationship of pressure and flow were tested in mock circulatory loop in vitro,30% glycerin in water was used as circulatory mediator. The inlet pressure of blood pump was adjusted by changing liquid level height, the outlet pressure was adjusted by changing damping valve, and pump rotation speed was adjusted by control system. Recorded the relationship curves of pressure and flow at different pump speeds. Hemolysis test:500ml blood reservoir was placed into thermostatic water bath which the temperature was set at 37℃. After axial flow blood pump was assembled in a mock circulatory loop and worked, pump rotation speed and damping valve were adjusted to make it run normally with a outflow of 5L/min and mean pressure of 100mmHg.Blood samples were collected at different time point before and after pump working 30,60,120,180,240,300 and 360min respectively. Supernate was collected after samples were centrifuged at twice, and the level of plasma free hemoglobin was measured by UV-2401PC ultraviolet spectrophotometer. Normalized index of haematolysis (NIH) was calculated to indicate the perniciasm degree of red blood cell during mechanical circulation support in vitro.Results:Analysis of the relationship of pressure and flow:there was a negative correlation and linear function between the pressure and flow, when the blood pump had a constant rotation speed, flow rate increased with the decrease of pressure. Furthermore flow increased with the increase of rotation speed when pressure was fixed.30% glycerin in water was used as circulatory mediator, when rotation speed was 13000rpm and afterload pressure was 100mmHg, the flow rate was 5.08L/min in correspondence. Hemolysis test:NIH was 0.01644±0.00018 g/100LConclusion:Axial flow blood pump has good hydrodynamics performance to substitute for left ventricle, which can meet the demand of assisted circulation in congestive heart failure patients. Hemocompatibility was in acceptable range and close to third generation blood pump, but it had still some disparity. Moreover the blood pump had qualifications for future acute animal experiments. Animal test of miniature implantable axial flow blood pump in vivoObjective:To investigate hydrodynamics characteristics and hemocompatibility in acute animal models on the basis of hydrodynamics and hemolysis test in vitro through mock circulatory loop in the previous study, and to investigate implant methods and announcements about blood pump. Furthermore, pathological changes of main organs and thrombogenesis in pump are investigated following the acute experiment.Methods:Blood pump was implanted in 7 healthy sheep through left thoracotomy, and circuit was established via left ventricular-blood pump-descending aorta. Pressure and flow monitor pipe were inserted, hydrodynamics performance and hemocompatibility were measured. In the condition that mean arterial pressure were controlled between 90 and 100mmHg, pump outflow and pulse pressure were recorded when rotation speed was adjusted to 11000,12000,13000 rpm respectively. Mean arterial pressure, left atria pressure and pulmonary arterial pressure were recorded when pump outflow was adjusted to 2.0L/min. The level of hemoglobin, free hemoglobin and other biochemical parameters reflecting liver and kidney function were detected before the operation and after the implantation of 0.5,2,4,8,12 and 24h, respecively. After blood pump worked for 24 hours continuously the experiment was end, and sheep were killed. Hearts, lungs, livers and kidneys were taken off for pathology observation with light microscope. Blood pump was removed to investigate shaft bearing wear and thrombogenesis.Results:The blood pump was implanted to left ventricular directly without cardiopulmonary bypass,which worked for 24 hours continuously without mechanical failure and had stable working performance. While mean arterial pressure was controlled between 90 and 100mmHg, pump outflow averaged 2.0±0.4L/min,3.4±0.4L/min, 5.0±0.3L/min at pump speeds of 11000,12000,13000rpm.Pulse pressure averaged 26±3 mmHg,18±2 mmHg,9±3mmHg in correspondence of pump speeds of 11000,12000, 13000rpm. When pump outflow was adjusted to 2.0L/min, mean arterial pressure, left atria pressure and pulmonary arterial pressure were in a stable level. In the period of blood pump working the content of free hemoglobin increased step by step. Preimplantation baseline of FHb was 3.7±1.6g/100L,there was obvious increase to 79.3±7.1g/100L at 24 hour after implantation, which was still clinically acceptable. The content of hemoglobin decreased and became steadily at 4 hour after implantation. The changes of other hematologic factors, such as total bilirubin and direct bilirubin were also within normal limits. Histopathology observation suggested that there was no thromboembolism and parenchymal organ hemorrhage in hearts, lungs, livers and kidneys. While the pump was detected instantly after the experiments were finished, shaft bearing wear was not seen and no thrombosis was formed in pump housing and either sides of impeller,except that punctiform thrombosis was seen in one example in the joint of pump outlet and artificial blood vessel due to insufficient anticoagulation.Conclusion:Our self-made axial flow blood pump is implanted easily, it has stable performance and good hydrodynamics characteristic for temporary circulation support, which can meet the demand of assisted circulation in congestive heart failure patients. The hemocompatibility of blood pump is also acceptable. However, the structural design need further optimize because of the high demand of the pump for anti-thrombus and the strict anticoagulation request.
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