# Influence of Impeller Speed Patterns on Hemodynamic Characteristics and Hemolysis of the Blood Pump
## 1 Introduction  
A ventricular assist device helps the native heart to pump blood to meet the normal demand of patients with heart failure. It is an effective method for treating heart failure in a clinic. At present, a ventricular assist device has developed from the first generation of a total artificial heart to the third generation of a suspension rotary blood pump. Additionally, the structure of a blood pump has been further reduced to be implantable into the thoracic cavity of a human body. In clinical application, a blood pump is the core component of a ventricular assist device that needs to not only satisfy the hemodynamic characteristics of the blood flow rate and pressure output of a wide range of patients, but also have good blood compatibility to prevent hemolysis and thrombosis. At present, commercial blood pumps used for treating heart failure are divided mainly into two forms: total artificial heart and continuous-flow blood pump (CFBP). The output blood flow form of a pulsatile-flow blood pump (PFBP) is consistent with the native heart of the human body, but the structure is complex and the volume is large, making its implantation into a patient body difficult; it also has a high failure rate. Moreover, PFBP is prone to cause thrombosis, infection, and other symptoms in clinical applications. A CFBP realizes the continuous output of blood flow rate and blood pressure by controlling the impeller speed. This kind of blood pump has the advantages of small size, stable performance, andgood implantability. Therefore, the continuous development of a PFBP or a CFBP has always been a hot topic for researchers [1; 2]. A CFBP provides a specific blood pressure at a constant speed pattern to meet the blood demand. Although it has been widely used in clinically treating patients with heart failure and has achieved a good auxiliary effect, some complications still exist, such as bleeding, aortic valve insufficiency, and thrombosis, in patients with heart failure, seriously affecting the treatment effect and the quality of life [3]. Therefore, some studies have explored the possibility that the blood flow rate and pressure at the outlet of CFBP can be similar to the pulsatile-flow output by means of impeller speed modulation [4; 5; 6], and investigated the differences in the hemodynamic characteristics between a CFBP and a PFBP. Professor [PERSON] designed a PFBP impeller with low hemolysis based on the ternary theory [7; 8]. The experimental result showed that the pulsating flow was produced when the impeller speed changed periodically. Compared with diaphragm pumps and other types of PFBP, it had a lower hemolysis value. [PERSON] et al. studied the effects of different speed patterns of a blood pump on hemodynamic characteristics through animal experiments. The results showed that the speed modulation of the blood pump directly affected the left ventricular pressure and volume, and the arterial pressure, while the coronary blood flow was not affected. The synchronized pulsatile control of the impeller speed of the blood pump helped in ventricular unloading, resulting in more physiological blood flow and better blood perfusion effect [9]. [PERSON] compared the advantages and disadvantages between a CFBP and a PFBP, and pointed out that a CFBP could cause complications in long-term assistance and reduce blood pressure pulsatility, which was not conducive to myocardial recovery [10]. Therefore, the best solution was to achieve pulsating blood flow on the basis of a CFBP. In addition, the author also pointed out that it was necessary to study the physiological response, end-organ function, and left ventricular remodeling at different levels of pulsation and assistance. [PERSON] [11] studied the hemolysis performance of PFBP using the Lagrange particle tracking method, and the effects of trapezoidal and sinusoidal speed patterns on the flow rate and hemolysis were analyzed.