A Compact Highly Efficient and Low Hemolytic Centrifugal Blood Pump With a Magnetically Levitated Impeller

Abstract

A magnetically levitated (maglev) centrifugal blood pump (CBP), intended for use as a ventricular assist device, needs to be highly durable and reliable for long-term use without any mechanical failure. Furthermore, maglev CBPs should be small enough to be implanted into patients of various size and weight. We have developed a compact maglev CBP employing a two-degree-of-freedom controlled magnetic bearing, with a magnetically suspended impeller directly driven by an internal brushless direct current (DC) motor. The magnetic bearing actively controls the radial motion of the impeller and passively supports axial and angular motions using a permanent magnet embedded in the impeller. The overall dimensions of the maglev CBP are 65 mm in diameter and 40 mm in height. The total power consumption and pump efficiency for pumping 6 L/min against a head pressure of 105 mm Hg were 6.5 W and 21%, respectively. To evaluate the characteristics of the maglev CBP when subjected to a disturbance, excitation of the base, simulating the movement of the patient in various directions, and the sudden interception of the outlet tube connected with the pump in a mock circulatory loop, simulating an unexpected kink and emergent clamp during a heart surgery, were tested by monitoring the five-degree-of-freedom motion of the impeller. Furthermore, the hemolytic characteristics of the maglev CBP were compared with those of the Medtronic Biomedicus BPX-80, which demonstrated the superiority of the maglev CBP.

The Papworth Experience With the Levitronix CentriMag Ventricular Assist Device

“…4,5 Temporary cardiac mechanical assistance allows salvage of some patients who otherwise would have died from cardiogenic failure despite optimal medical management. Early experience with the Biomedicus bio-pump demonstrated a 20% to 30% survival rate.…”

“…The hemolysis rate of this pump is half that of the Biomedicus BP-80 (Medtronic, Minneapolis, MN). 5 Our aim was to achieve a cardiac index of 2 liters/m 2 or higher. The device has been approved for short-term use of up to 2 weeks in cardiogenic shock patients.…”

Development of a Compact Maglev Centrifugal Blood Pump Enclosed in a Titanium Housing

“…The impeller radial displacement signal is feedbacked by two eddy current type displacement sensors located between the electromagnets, allowing the MB to actively control the radial motion of the impeller and to passively support both the axial and angular motions (2) . The titanium cover of the impeller is used as the displacement sensor target.…”

“…This configuration reduces the number of displacement sensors and electromagnets needed for the MB, but leads to lower axial stiffness compared to the radial direction, which is actively controlled (2) . The lower axial stiffness, associated with hydraulic forces inside the pump, causes axial shifting of the impeller.…”

“…In our laboratory, a prototype maglev centrifugal blood pump called MedTech Heart, consisting of a controlled two-degrees-of-freedom radial magnetic bearing (MB), a built-in brushless DC motor and a plastic housing was developed (2) . Since the impeller in this pump is magnetically levitated, there is no contact between the rotating and stationary parts, increasing its durability and decreasing the blood damage level (3) .…”