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Ann Thorac Surg 2001;71:S191
© 2001 The Society of Thoracic Surgeons
a Department of Biomedical Engineering, Lerner Research Institute, The Cleveland Clinic Foundation, Cleveland, Ohio, USA
Address reprint requests to Dr Golding, Department of Biomedical Engineering/ND20, Lerner Research Institute, The Cleveland Clinic Foundation, 9500 Euclid Ave, Cleveland, OH 44195
e-mail: golding{at}bme.ri.ccf.org
Presented at the Fifth International Conference on Circulatory Support Devices for Severe Cardiac Failure, New York, NY, Sept 15–17, 2000.
The CorAide (The Cleveland Clinic Foundation, Cleveland, OH) blood pump is a third-generation permanent blood pump with a suspended rotor capable of continuous operation with no mechanical contact or wear. Its development was funded in part by the National Heart, Lung, and Blood Institute (N01-HV-58159), and the geometric design is now fixed. The finalized pump weighs 293 g and is characterized by having an inverted motor and a noncontacting rotating assembly supported in operation by a stable blood-lubricated fluid film bearing. The innovative simplicity of this design was validated by a cumulative 1.5 years of animal testing demonstrating the noncontacting, nonwearing, and nonthrombogenic characteristics of this pump. It consists of only three subassemblies: a pump housing, a stator assembly, and a rotating assembly.
The pumping element is a cylindrical rotating assembly (the only moving part) containing permanent magnet and impeller vanes on each axial end of the assembly. The magnet ring has been fabricated from a squirrel cage assembly of separate neodymium-iron-boron magnets, but in the most recent embodiment is a single cylindrical magnet that is magnetized in a squirrel cage pattern. The primary impeller end of the rotating assembly generates the majority of the pump flow through interaction of imparted centrifugal force and volute housing design. The opposite end has a smaller secondary impeller that helps to balance axial hydraulic forces and thus maintain stable rotating assembly position along the axis of rotation. The secondary impeller also helps to generate the differential pressure and thus blood flow through the fluid film bearing that supports the rotating assembly in the radial direction. The secondary fluid flow pathway passes over the outer surface of the rotating assembly and then ascends between the rotor and stator.
The stator assembly contains the motor windings surrounded by a thin-walled titanium cylinder, forming the post about which the rotating assembly spins. This proximity of the windings to blood allows for the rapid dissipation of any produced heat into blood. The outer diameter of this stator housing post acts as the stationary member of the fluid film bearing. A unique noncircular profile is used on the stator assembly bearing surface, which stabilizes the radial hydrodynamic forces acting on the rotating assembly and allows an axial passage through the center of the pump for blood circulation and thus wash of the fluid film load-bearing surfaces. A controlled bearing radial preload has proven to be essential in maintaining hydrodynamic stability. This is achieved by radially offsetting the steel stator winding laminations from the geometric center of the stator bearing to provide this intentional magnetic load.
The innovative, enabling technology is in the design of the inverted, blood-lubricated fluid film bearing, which radially supports the rotating assembly with a stable, hydrodynamic fluid film. The rotating assembly revolves, levitated on a cradle of blood, deriving lift from its own motion and providing for a thick fluid film. This fluid film of blood is located in the space between the rotating assembly inner diameter and the stator assembly outer diameter. Bearing design has limited the blood shear stress in the fluid film such that there has been no evidence of hemolysis during in vivo testing. With the rotating assembly levitated on this thick hydrodynamic fluid film, there is normally no surface contact in the bearing.
The rotating assembly is axially suspended by means of passive magnetic forces from the interaction of the rotating assembly magnet ring and the steel stator winding laminations. There is sufficient axial clearance, and axial magnetic stiffness, such that there is normally no axial surface contact either. This combination of hydrodynamic radial support by the blood-lubricated bearing and passive magnetic positioning in the axial direction again result in no contact between the rotating assembly and the stator assembly during normal operation. During axial mechanical shock loads, the large, radial primary and secondary impeller vanes momentarily act as thrust bearings. The pump has demonstrated a significant tolerance to mechanical shock while being subjected to intentional impact loading such as hammer blows and slamming onto a tabletop during operation on the bench.
The third component is the one-piece cast titanium pump housing, which contains the impeller cover, the volute section, the discharge diffuser, and the inlet and outlet ports. The latter are threaded for quick screw connection to the inlet and outlet cannulas. The stator assembly is attached to this housing by six titanium screws.
In vivo testing in 13 calves since June 1999 (551 cumulative days) at an average blood flow of 6 L/min has shown no hemolysis (free serum hemoglobin < 3 mg/dL) and no mechanical failures. Two of three planned 90-day implant validation studies have been successfully completed, and the third is proceeding uneventfully at day 70. The most recent implant was maintained without any anticoagulants for 32 days and had no pump deposition and no systemic emboli at complete autopsy. Two further implants without anticoagulants are planned.
This article has been cited by other articles:
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  K. Doi, L. A. R. Golding, A. L. Massiello, M. W. Kopcak Jr, R. L. Gerhart, S. Schenk, M. Inoue, Y. Ootaki, and K. Fukamachi Preclinical readiness testing of the arrow international CorAide left ventricular assist system Ann. Thorac. Surg., June 1, 2004; 77(6): 2103 - 2110. [Abstract] [Full Text] [PDF]
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Y. Ochiai, L. A.R. Golding, A. L. Massiello, A. L. Medvedev, R. L. Gerhart, J.-F. Chen, M. Takagaki, and K. Fukamachi In vivo hemodynamic performance of the Cleveland Clinic CorAide blood pump in calves Ann. Thorac. Surg., September 1, 2001; 72(3): 747 - 752. [Abstract] [Full Text] [PDF]
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