# Influence of Impeller Speed Patterns on Hemodynamic Characteristics and Hemolysis of the Blood Pump
## 2 Materials and Methods
### Hydrodynamic Characteristic Test and Result Analysis  
An experimental platform was built to measure the hydrodynamic characteristics of the blood pump (Figure 4a). The inlet and outlet pressures were measured using two pressure sensors (PX409-015 CGUSBH, \(\pm\)1 bar, 0.06% accuracy, Omega Engineering Inc., CA, USA). The outlet of the blood pump was connected with an ultrasonic flowmeter (CO.56/120, 0-12 L/min, 2% accuracy, SONOTEC Ultraschallsensorik Halle GmbH, Germany), which was used to measure the outlet flow rate of the blood pump. The blood reservoir was connected with rubber hoses (\(\varphi\)16 and \(\varphi\)14 mm, Dongguan Kuwei Medical Devices Co., Ltd., China) to simulate the actual human blood circulation circuit. An auxiliary water pump (DC50C-2480A, 0-2400 L/min, Shenzhen Zhongke Century Co. Ltd., China) was connected to the outlet of the blood reservoir to adjust the flow rate with a damper valve. When the steady-state characteristics of the blood pump were studied, the auxiliary water pump did not work, so the inlet flow of the blood pump was regulated by a damper valve. However, in the study of the dynamic hydraulic model of a blood pump, an auxiliary water pump worked to generate a pulsating blood flow at the inlet of the blood pump, which simulated the pulsating blood flow of patients with heart failure. Glycerol solution (40%) was used to replace blood as the fluid medium [20]. The normal human blood flow demand is 4-6 L/min, and the pressure range is 80-120 mm Hg. When the blood pump worked in a constant speed pattern, it ensured 5 L/min and 100 mm Hg of blood flow output. This was also a part of the reference index of the blood pump structure design. When the blood pump was partially or completely assisted, it was able to meet the normal output of the cardiovascular system; however, when the impeller speed was lower than 1800 rpm, the impeller could not suspend stably. Therefore, the selection of impeller speed and flow range was based on the stable operation of the blood pump and the widest range of patients' blood flow demand of the human body. After setting different speeds of the blood pump and reading the inlet flow rate and the pressure of the inlet and outlet of the blood pump, the pressure head under different working conditions was calculated. The H-Q curve of the blood pump was drawn according to the results of the measurement, as shown in Figure 4b.  
Figure 4: (**a**) An experimental platform for testing the hydrodynamic characteristics of blood pumps. (**b**) Pressure head versus blood flow rate curve.  
The experimental results in Figure 4b showed that the pressure head of the blood pump decreased with the increase in the flow rate and increased with the increase in the impeller speed. The shape of the H-Q curve was parabolic. When the impeller speed changed from 2400 to 3000 rpm, the pressure head increased from 47.6 to 131.9 mm Hg. In this impeller speed range, the pressure at the outlet of the blood flow better met the needs of the patients with heart failure; therefore, it was the main working area of the rotational speed. Figure 5 shows that the simulation results coincided with the experimental data at 4 and 5 L/min, while the simulation results far away from the main working nodes deviated from the measured values; the error was less than 10%. This showed that the simulation method could better reflect the influence of the operation parameters of the blood pump on the hydrodynamic characteristics of the blood pump [21]. Therefore, according to the relationship between the blood pump speed, flow rate, and pressure difference, the quality of life of patients with heart failure could be improved by adjusting the speed of the blood pump in a specific range, so as to avoid the problems of ventricular collapse and swelling caused by the pressure difference between the entrance of the blood pump and the ventricle.