Abstract： Among all kinds of heart diseases, heart failure is the leading cause of death. In recent years, the treatment of terminal heart failure has increasingly become a great challenge to cardiovascular clinical physicians. The limitations of routine medical therapy and surgical interventions, and the shortage of donor hearts have led to the rapid development of mechanical circulation support devices. As the joint research and development of electric machine, mechanical engineering, fluid mechanics, materials science, medical science and some other related subjects, exploring a new type of longterm implantable blood pump has become a hot issue. Axial flow blood pump has the advantages of simple structure, light weight, high flow and efficiency, easy implantation and removal, and at the same time, it does not need to install artificial valves, which can greatly reduce the risk of thrombosis. Compared with the centrifugal pump, axial flow blood pump is smaller and causes much less damage to the blood. At present, axial flow blood pump research has become a focus in cardiac surgery and biomedical engineering field. This article is going to review the operation principles and characteristics of axial flow blood pump, and some key technical issues of current axial flow blood pump research.
Abstract: The ventricle assist device has emerged as an important therapeutic option in the treatment of both acute and chronic heart failure. The blood pumps which are the major components of ventricle assist devices have also progressed to the third generation. The magnetic and/or liquid levitation technologies have been applied into the third generation blood pumps. The impellers which drive blood are levitated in the blood pumps. The third generation blood pumps are mainly composed of the levitation system and the driving system. The development of the third generation blood pumps has three stages: the stage of foreign motor indirectly driving the impeller with the levitation and driving system separated, the stage of motor directly driving the impeller with the levitation and driving system separated, and the stage of levitation system integrated with the driving system. As the impellers do not contact with other structures, the third generation blood pumps possess the advantages of low thrombosis, less hemolysis and high energy efficiency ratio. Currently most of the third generation blood pumps are in the research stage, but a few number of them are used in clinical trials or applying stage. In this article, the history, classification, mechanism and research situation of the third generation blood pumps are reviewed.
Objective To provide a ventricular assist device for patients with heart failure, Fu Wai （FW） axial blood pump was developed for partly or totally to assist the left ventricular function. Vitro hemolysis and animals tests were also employed to test the hydromechanics and hemocompatibility of the FW left ventricular assist devices developed in Fu Wai hospital. Methods Using vitro test loop, FW axial blood pump has been used to evaluate the performance of hemolysis， the pump has also been tested for hemolysis characteristic through five sheep experiments. Results At 8 400 r/min, the pump generates 5 L/min flow against 100 mm Hg, the normalized index of hemolysis (NIH) was0.17±0.06 mg/L. The plasma free hemoglobin of in vivo tests was around 30 mg/dl. Conclusion The results obtained in vitro and in vivo testing indicate an acceptable design for the blood pump, further in vivo tests will be performed before clinical use.
The impeller profile, which is one of the most important factors, determines the creation of shear stress which leads to blood hemolysis in the internal flow of centrifugal blood pump. The investigation of the internal flow field in centrifugal blood pump and the estimation of the hemolysis within different impeller profiles will provide information to improve the performance of centrifugal blood pump. The SST κ-ω with low Reynolds correction was used in our laboratory to study the internal flow fields for four kinds of impellers of centrifugal blood pump. The flow fields included distributions of pressure field, velocity field and shear stress field. In addition, a fast numerical hemolysis approximation was adopted to calculate the normalized index of hemolysis (NIH). The results indicated that the pressure field distribution in all kinds of blood pump were reasonable, but for the log spiral impeller pump, the vortex and backflow were much lower than those of the other pumps, and the high shear stress zone was just about 0.004%, and the NIH was 0.0089.
The purpose of this paper is to report the research and design of control system of magnetic coupling centrifugal blood pump in our laboratory, and to briefly describe the structure of the magnetic coupling centrifugal blood pump and principles of the body circulation model. The performance of blood pump is not only related to materials and structure, but also depends on the control algorithm. We studied the algorithm about motor current double-loop control for brushless DC motor. In order to make the algorithm adjust parameter change in different situations, we used the self-tuning fuzzy PI control algorithm and gave the details about how to design fuzzy rules. We mainly used Matlab Simulink to simulate the motor control system to test the performance of algorithm, and briefly introduced how to implement these algorithms in hardware system. Finally, by building the platform and conducting experiments, we proved that self-tuning fuzzy PI control algorithm could greatly improve both dynamic and static performance of blood pump and make the motor speed and the blood pump flow stable and adjustable.
The implantable miniaturized axial blood pump works at a high rotational speed, which increases the risk of blood damage. In this article, we aimed to reduce the possibility of hemolysis and thrombosis by designing a two-stage axial blood pump. Under the operation conditions of flow rate 5 L/min and outlet pressure of 100 mm Hg, we carried out the numerical simulation on the two-stage and single-stage blood pumps to compare the hemolysis and platelet activation state. The results turned out that the hemolysis index of two-stage axial blood pump was better while the platelet activation state was worse than those of single stage design. On the index of hemolysis level and platelet activation state, the design of the two-stage pump with the low and high-head impeller combination was better than the two-stage pump with the equal heads, or the high and low-head impeller combination. In terms of reducing the risk of blood damage for implantable miniaturized axial blood pump, the research result can provide some theoretical basis and new design ideas.
Heart failure is a leading cause of death in human populations. Because of the insufficient numbers of donor hearts, ventricular assist as a way for the treatment of heart failure and its clinical use is increasing. Initially ventricular assist devices were approved as a bridge-to-recovery indication, and these systems are now increasingly being used as a bridge-to-transplant (BTT) , destination therapy (DT) or permanent support. According to the different structure and working mechanism, ventricular assist device is generally divided into three generation. This review makes a summary on the type of blood pump and its research progress in clinical application.
The rotary left ventricular assist device (LVAD) has been an effective option for end-stage heart failure. However, while clinically using the LVAD, patients are often at significant risk for ventricular collapse, called suction, mainly due to higher LVAD speeds required for adequate cardiac output. Some proposed suction detection algorithms required the external implantation of sensors, which were not reliable in long-term use due to baseline drift and short lifespan. Therefore, this study presents a new suction detection system only using the LVAD intrinsic blood pump parameter (pump speed) without using any external sensor. Three feature indices are derived from the pump speed and considered as the inputs to four different classifiers to classify the pumping states as no suction or suction. The in-silico results using a combined human circulatory system and LVAD model show that the proposed method can detect ventricular suction effectively, demonstrating that it has high classification accuracy, stability, and robustness. The proposed suction detection system could be an important part in the LVAD for detecting and avoiding suction, while at the same time making the LVAD meet the cardiac output demand for the patients. It could also provide theoretical basis and technology support for designing and optimizing the control system of the LVAD.
An implantable axial blood pump was designed according to the circulation assist requirement of severe heart failure patients of China. The design point was chosen at 3 L/min flow rate with 100 mm Hg pressure rise when the blood pump can provide flow rates of 2-7 L/min. The blood pump with good hemolytic and anti-thrombogenic property at widely operating range was designed by developing a structure that including the spindly rotor impeller structure and the diffuser with splitter blades and cantilevered main blades. Numerical simulation and particle image velocimetry (PIV) experiment were conducted to analyze the hydraulic, flow fields and hemolytic performance of the blood pump. The results showed that the blood pump could provide flow rates of 2-7 L/min with pressure rise of 60.0-151.3 mm Hg when the blood pump rotating from 7 000 to 11 000 r/min. After adding the splitter blades, the separation flow at the suction surface of the diffuser has been reduced efficiently. The cantilever structure changed the blade gap from shroud to hub that reduced the tangential velocity from 6.2 m/s to 4.3-1.1 m/s in blade gap. Moreover, the maximum scalar shear stress of the blood pump was 897.3 Pa, and the averaged scalar shear stress was 37.7 Pa. The hemolysis index of the blood pump was 0.168% calculated with Heuser’s hemolysis model. The PIV and simulated results showed the overall agreement of flow field distribution in diffuser region. The blood damage caused by higher shear stress would be reduced by adopting the spindle rotor impeller and diffuser with splitter blades and cantilevered main blades. The blood could flow smoothly through the axial blood pump with satisfactory hydraulics performance and without separation flow.
The high rotational speed of the axial flow blood pump and flow separation of the centrifugal blood pump are the main causes for blood damage in blood pump. The mixed flow blood pump can effectively alleviate the high rotational speed and the flow separation. Based on this, the purpose of this study is to explore the performance of the mixed blood pump with a closed impeller. A mixed flow blood pump with closed impeller was studied by numerical simulation in this paper. The flow field characteristics and the pressure distribution of this type of blood pump were analyzed. The hydraulic performance of the blood pump and the possible damages to red blood cells were also discussed. At last, pump performance was compared with the mixed flow blood pump with semi-open impeller. The results show that the mixed flow blood pump with close impeller studied in this paper can operate safely and efficiently with a good performance. The pump can reach the pressure head of 100 mmHg at 5 L/min mass flow rate. Flow in the blood pump is uniform and no obvious separation or vortex occurs. Pressure distribution in and on the impeller is uniform and reasonable, which can effectively avoid the thrombosis of blood. The average mean value of hemolysis index is 4.99 × 10−4. The pump has a good biocompatibility. Compared with the mixed flow blood pump with semi-open impeller, the mixed flow blood pump with closed impeller has higher head and efficiency, a smaller mean value of hemolysis index prediction, a better hydraulic performance and the ability to avoid blood damage. The results of this study may provide a basis for the performance evaluation of the closed impeller mixed flow blood pump.