# Influence of Impeller Speed Patterns on Hemodynamic Characteristics and Hemolysis of the Blood Pump
## 4 Discussion  
Assisted therapy of implementing pulsatile flow on a rotary impeller blood pump has always been a research hotspot. In this study, the impeller speed pattern waveform was modulated according to the blood pressure output characteristics of the native heart and the steady-state H-Q curve of the pump. The effects of an impeller with three speed patterns on the blood flow characteristics and HI were compared and analyzed under the condition of heart failure. On the basis of satisfying the normal blood demand of a patient body, the pulsating flow generated by periodic changes in the impeller speed could effectively increase the fluctuation of blood pressure in the aorta, which helped in improving the effect of peripheral blood vessel perfusion. A blood pump with three speed patterns made the H-Q change into a dynamic counterclockwise closed loop. The hydraulic power consumption in sinusoidal and pulsatile speed patterns was greater than that in the constant speed pattern. Under the sinusoidal and pulsatile speed patterns, the flow field of the blood pump was similar. The flow field in the spiral groove of hydrodynamic bearing varied pulsatively, but the flow path was uniform and no local flow field existed that was prone to thrombosis, such as eddy current and flow stagnation zone. Compared with the constant speed pattern, the high shear stress in the spiral groove of the sinusoidal and pulsatile speed patterns varied with time. When blood flowed through the blood pump, the shear stress and HI  
Figure 16: Shear stress variation characteristics of sinusoidal and constant speed patterns at different moments. Red dotted frames in panels (**a-c**) show the time-varying characteristics of scalar shear stress in the sinusoidal speed pattern; panels (**d–f**) show that the amplitude and distribution of scalar shear stress were almost unchanged in the constant speed pattern. increased slightly within a reasonable range, not causing obvious blood damage. Therefore, reasonable control of the impeller speed range is an important aspect to improve the hemolysis performance of a blood pump. The pulsatility of intra-aortic blood pressure could be improved by impeller speed modulation. The impeller speed modulation method produced pulsatile blood flow, which was similar to the natural heart physiological characteristics of the human body. It could effectively eliminate the complications such as hemorrhage and aortic insufficiency caused by the constant speed pattern, and improved the assisting effect of the blood pump to a certain extent. An impeller is the key component of a blood pump. Its speed not only affects not only the output of blood flow and pressure, but also affects the hemolysis characteristics of the blood pump. Therefore, the method of blood pump speed modulation plays an important role in the design of blood pump structure and physiological adaptive control. The narrow liquid film gap at the hydrodynamic bearing is the main area causing blood damage. Therefore, compared with the effect of speed waveform modulation on blood compatibility, the structure design of a blood pump might have a greater impact on blood compatibility. In addition, blood compatibility is more complex and affected by several factors. Further, blood compatibility experiments and clinical verification are needed. In addition, modulating the amplitude and phase of the blood pump impeller speed waveform according to the LVP waveform is also one of the difficulties. Therefore, in future research, it is necessary to study the influence of impeller speed pulsation characteristics on the performance of the blood pump, so as to design a pulsating rotary blood pump with low hemolysis characteristics, to achieve blood output in line with the native heart blood flow characteristics and to improve the quality of life of patients with heart failure. [PERSON] and [PERSON] conceptualized this study. [PERSON] and [PERSON] did the formal analysis. [PERSON] worked on the methodology and software-related evaluations.