# Influence of Impeller Speed Patterns on Hemodynamic Characteristics and Hemolysis of the Blood Pump
## 3 Results  
### Analysis of Hemodynamic Characteristics  
Figure 9 shows the hemodynamic characteristics of the cardiovascular-coupled blood pump. The AOP could meet the normal physiological needs of the human body with the help of the impeller with three speed patterns, and the pressure fluctuated between 86 and 102 mm Hg. The AOP pressure pulsation range was small at a constant speed pattern, and the sinusoidal and pulsatile speed patterns provided a larger range of pressure pulsation for the blood input to the aorta. It was up to a max pulse pressure (PP) of 13 mm Hg, which was relative to the constant speed pattern. During the assistance process of the blood pump with three speed patterns, the aortic valve remained closed and the blood pump helped in pumping the blood, contributing to ventricular unloading and left ventricular function recovery.  
Figure 9: Changes in LVP and AOP when the left ventricle was assisted by the three kinds of speed patterns of the blood pump. The pressure difference between the dotted lines represents the maximum aortic pulse pressure (PP) As LVP was much lower than AOP, the aortic valve remained closed during the process of blood pump assistance.  
During a cardiac cycle, the trend of flow change in the blood pump with three speed patterns was basically consistent with that of AOP. Figure 10 shows that the flow fluctuated around 90 mL/s. It also shows that the blood flow through the blood pump was almost equal to the blood flow into the aorta, indicating that the aortic valve remained closed during the operation of the blood pump, and almost all the blood flowed through the blood pump to the aorta.  
The relationship between the pressure head and the flow rate of the blood pump was different from that in the steady state. In the transient state, the H-Q curve between the pressure head and the flow rate was a closed loop, consistent with the results of previous studies [24]. The pressure head generated by the blood pump varied counterclockwise with the flow rate. The starting point and the endpoint of the two closed loops were the same, as shown in Figure 11. The range of flow fluctuation corresponding to the pulsatile and sinusoidal speed patterns was larger than that of the constant speed pattern. The closed-loop area formed by the pressure head and the flow rate represented the hydraulic power consumed by the blood pump. The hydraulic power consumed by the pulsatile and sinusoidal speed patterns was larger than that by the constant speed pattern. Compared with the steady-state H-Q curve, the H-Q curve corresponding to the three speed patterns could display the hemodynamic changes in the blood pump in the real situation more dynamically, and facilitate the monitoring and further control of the actual working state of the blood pump.  
Figure 11: H–Q curve loop of the impeller with three speed patterns. Arrows indicate the trend of the blood flow rate and pressure changes with the impeller speed. The closed curve represents the hydraulic power consumed by the blood pump in a cardiac cycle.  
Figure 10: Blood flow rate variation characteristics with time; the curve in the frame indicates the difference between the blood pump flow rate and the blood flow rate in the aorta.  
The PP, energy equivalent pressure (EEP), and surplus hemodynamic energy (SHE) were used to evaluate blood pulsatility. Table 4 shows the blood output indicators under the three speed patterns of the blood pump. The cardiac output (CO) was about 5 L/min, which could meet the normal blood demand of the human body. The sinusoidal and pulsatile speed patterns could effectively increase the pressure pulsation value compared with the constant speed pattern. The difference between EEP and mean arterial pressure (MAP) was the largest; therefore, the SHE was correspondingly the largest. It indicated that the pulsatile and sinusoidal speed patterns had larger pulsating energy compared with the constant speed pattern, and could increase the degree of blood pulsation in the cardiovascular circuit.