## 4 Results and Discussion
### Measurement of Energy Consumption and Flow Rate  
The results of the energy consumption (power consumed) obtained with the constructed measuring system are shown in Figure 7. Two configurations can be distinguished:  
* Servo amplifier configuration powering a servo motor (supplied directly from the 230 V AC). The power of this configuration is designated as \(P_{2}\);
* Configuration with a 12 V DC to 24 V DC converter and a sensor for determining the position of the compressor system base point and with a 12 V DC to 5 V DC converter to power the ODROID computer (powered by a set of 12 V DC batteries). The power of this configuration designated as \(P_{1}\).  
Figure 5: Pressures \(p\) in the hydraulic-pneumatic system for different operating frequencies \(f\) of the device for case 1—first stage of the reduction of the blood vessel lumen. (**a**) Fluid pressures in the hydraulic system as measured by the sensors. (**b**) Pressure \(p\) in the pneumatic system measured by a pressure sensor placed near the balloon assembly. (**c**) Maximum pressure values \(p_{max}\).  
Figure 6: Pressures \(p\) in the hydraulic-pneumatic system for different operating frequencies \(f\) of the device for case 2—second stage of the reduction of the blood vessel lumen. (**a**) Fluid pressures in the hydraulic system as measured by the sensors. (**b**) Pressure \(p\) in the pneumatic system measured by a pressure sensor placed near the balloon assembly. (**c**) Maximum pressure values \(p_{max}\).  
The power \(P_{2}\) consumed by the servo amplifier system, which powers the servo motor, varies linearly with the frequency \(f\) of the balloons. More specifically, at a frequency of \(f=60\) cyc/min, \(P_{2}\) varies from about 20 W to 50 W at a frequency of \(f=160\) cyc/min. The power requirements of this configuration can be approximated by a linear function of the following form:  
\[P_{2}=2+0.3\,f\qquad\text{W} \tag{1}\]  
where \(f\) is the frequency in cyc/min.  
The power of the configuration with the 12 V DC to 24 V DC converter and the sensor for determining the compressor system base point position and the 12 V DC to 5 V DC converter feeding the ODROID computer \(P_{1}\) is the same for all tests (around 6.4 W).  
Reducing the lumen of the blood vessels (simulated by closing the control valve) significantly affects the value of the mass flow rate \(\dot{m}\) (Figure 8). Very large differences in the mass flow rate \(\dot{m}\) between cases occur at the maximum heart rate (160 cyc/min) compared to the minimum heart rate (60 cyc/min). It can be seen that the flow rate variation in the hydraulic system when controlling the valve from fully open (0--no reduction) to partially closed (1--first stage of reduction) is as high as approximately 0.5 kg/min. In contrast, the change in the mass flow rate during valve setting from partially closed (1--second stage of reduction) to even more closed (2--second stage of reduction) is as high as approximately 0.6 kg/min. Meanwhile, for a frequency of 60 cyc/min, the differences in mass flow rate for individual cases do not exceed 0.2 kg/min. It is also important to note that increasing the operating frequency above 140 cyc/min does not generally increase the mass flow rate, except in the case where there is no reduction of the vessel lumen. In all cases, the greatest changes occur in the frequency range of 60 to 100 cyc/min. Increasing the frequency from 60 to 160 cyc/min increases the flow rate by 50% in the case of no reduction of the lumen of the vessels. In the case of lumen reduction, the values are smaller.