Sensorless Viscosity Measurement in a Magnetically‐Levitated Rotary Blood Pump

Abstract

Controlling the flow rate in an implantable rotary blood pump based on the physiological demand made by the body is important. Even though various methods to estimate the flow rate without using a flow meter have been proposed, no adequate method for measuring the blood viscosity, which is necessary for an accurate estimate of the flow rate, without using additional sensors or mechanisms in a noninvasive way, has yet been realized. We have developed a sensorless method for measuring viscosity in magnetically levitated rotary blood pumps, which requires no additional sensors or mechanisms. By applying vibrational excitation to the impeller using a magnetic bearing, we measured the viscosity of the working fluid by measuring the phase difference between the current in the magnetic bearing and the displacement of the impeller. The measured viscosity showed a high correlation (R(2) > 0.992) with respect to a reference viscosity. The mean absolute deviation of the measured viscosity was 0.12 mPa·s for several working fluids with viscosities ranging from 1.18 to 5.12 mPa·s. The proposed sensorless measurement method has the possibility of being utilized for estimating flow rate.

Mechanical antithrombogenic properties by vibrational excitation of the impeller in a magnetically levitated centrifugal blood pump

“…The radial gap between the impeller and the bottom housing is 300 μm, which is the minimum gap inside the pump. More details of the dimensions of the pump can be found in our previous study . Rotation of the impeller was realized by magnet coupling between permanent magnets inside the impeller and those inside the motor unit.…”

“…More details of the dimensions of the pump can be found in our previous study. 20 Rotation of the impeller was realized by magnet coupling between permanent magnets inside the impeller and those inside the motor unit. The position of the impeller in the X and Y directions was actively controlled using a 2-degrees of freedom magnetic bearing comprising 4 electromagnets and 3 eddy current displacement sensors (PU-05; Applied Electronics Corp., Kawasaki, Japan).…”

“…Therefore, there exists a need to develop an intelligent function for blood pumps that can prevent, detect, and treat pump thrombus, eliminating the need for costly and risky pump replacement procedures . In a previous study, we developed a method to measure the fluid viscosity inside a magnetically levitated blood pump by applying vibrational excitation to the impeller . This method has the potential to not only detect thrombus formation inside a pump, but may also be able to prevent thrombus by enhancing the washout effect.…”

“…19 In a previous study, we developed a method to measure the fluid viscosity inside a magnetically levitated blood pump by applying vibrational excitation to the impeller. 20 This method has the potential to not only detect thrombus formation inside a pump, 21 but may also be able to prevent thrombus by enhancing the washout effect. Although anticoagulation therapies are traditionally used to prevent thrombus formation, there exists a risk of bleeding episodes from an increase in prothrombin time, and anticoagulation medications must be carefully managed.…”

Artificial Organs 2015: A Year in Review

“…Wataru Hijikata et al of the Tokyo Institute of Technology, Yokohama, Japan reported on the development of a sensorless method for measuring viscosity (and in turn blood flow) in magnetically levitated rotary blood pumps. By applying vibrational excitation to the impeller using a magnetic bearing, the viscosity of the working fluid was measured by assessing the phase difference between the current in the magnetic bearing and the displacement of the impeller.…”