Flow rate estimation of a centrifugal blood pump using the passively stabilized eccentric position of a magnetically levitated impeller

Abstract

Flow rate estimation for ventricular assist devices without additional flow sensors can improve the quality of life of patients. In this article, a novel flow estimation method using the passively stabilized displacement of a magnetically levitated impeller is developed to achieve sufficient accuracy and precision of flow estimation for ventricular assist devices in a simple manner. The magnetically levitated impeller used is axially suspended by a magnetic bearing in a centrifugal blood pump that has been developed by our group. The radial displacement of the impeller, which is restricted by passive stability, can be correlated with the flow rate because the radial hydraulic force on the impeller varies according to the flow rate. To obtain the correlation with various blood viscosities, the relationships between the radial displacements of the magnetically levitated impeller and the pressure head-flow rate characteristics of the pump were determined simultaneously using aqueous solutions of glycerol with a potential blood viscosity range. The measurement results showed that accurate steady flow rates could be estimated with a coefficient of determination of approximately 0.97 and mean absolute error of approximately 0.22 L/min without fluid viscosity measurements by using the relationships between the impeller displacement and the flow rate. Moreover, a precision of approximately 0.01 (L/min)/µm was obtained owing to a strong estimation indicator signal provided by the large displacement of the passively stabilized impeller; thus, the proposed estimation method can help ensure sufficient accuracy and precision for ventricular assist devices in a simple manner, even if the blood viscosity is unknown.

Effects of gravity on flow rate estimations of a centrifugal blood pump using the eccentric position of a levitated impeller

“…Details of the PSDM were reported in our previous study. 11 In the previous report, it was shown that the radial component of the gravity force vector (F Gr ) was not exerted on the impeller due to horizontal operation of the device. This was because the gravity direction was the same as the actively controlled direction of the axial axis; therefore, the correlation between Q and (x, y), which is the basis of the PSDM, was not affected by gravity.…”

“…Recently, our group developed a novel flow rate estimation method using passively stabilized radial displacement of a magnetically levitated (maglev) impeller in a centrifugal blood pump with an axial magnetic suspension system (hereinafter referred to as the passively stabilized displacement method (PSDM)). 11 The PSDM is a simple system that does not require blood viscosity measurements, but showed high performance. The blood viscosity measurements compromised the simplicity of the flow rate estimation with the conventional flow rate estimation method using the motor current.…”

Estimation Methods for Viscosity, Flow Rate and Pressure from Pump-Motor Assembly Parameters

“…Various groups have already shown the feasibility of Q and ∆p estimation for heart assist devices from other signals such as ω and motor power-P [10,11], ω, and motor torque-τ [12,13], ω and I [14][15][16][17][18], or even impeller radial displacement [19]. Almost all also considered the effects of blood viscosity µ [10][11][12][14][15][16][17][18][19][20]. Most of the efforts are focused on steady state estimation or averaging over many samples [10,11,19].…”

“…Almost all also considered the effects of blood viscosity µ [10][11][12][14][15][16][17][18][19][20]. Most of the efforts are focused on steady state estimation or averaging over many samples [10,11,19]. However, some efforts have been put into dynamic estimations with high bandwidth [15,16], e.g., Moscato et al reported an root mean squared error (RMSE) of 252 mL .…”

Dynamic motion analysis of impeller for the development of real-time flow rate estimations of a ventricular assist device

“…Recently, we developed a novel flow rate estimation method using passively stabilized radial displacement of a magnetically levitated (maglev) impeller in a centrifugal blood pump with an axial magnetic suspension system (hereinafter, referred to as the passively stabilized displacement method (PSDM)). 11,12 The PSDM is a simple system that does not require blood viscosity measurements but yields high performance. Therefore, reliable and real-time flow rate estimation can be achieved with PSDM.…”