Centrifugal blood pump impeller and flow path
An impeller and rotor structure for a magnetically levitated pump define a smooth primary flow path and U-shaped secondary flow path, which extends around an annular magnetic rotor. The u-shaped secondary flow path is defined by a large outer side gap along an outer surface of the rotor, a large bottom gap along a bottom surface of the rotor and a large inner gap along an inner surface of the rotor. Shroudless impeller blades are purely radial and overhung from a thin peripheral ring attached to the annular magnetic rotor. A center post having a low aspect ratio extends through the annular rotor. The low aspect ratio is configured to prevent flow in the primary flow path from colliding directly with flow in the secondary flow path at the inner radial gap.
1. A magnetic levitation pump apparatus, comprising:
a housing portion defining an axial inlet and including a center post and an annular cavity concentric with the center post;
an annular magnetic rotor located in the annular cavity;
an impeller coupled to the annular magnetic rotor and including:
a peripheral ring including a central aperture concentrically aligned with the annular magnetic rotor, and
blades extending from the peripheral ring inwardly into the central aperture and towards an axis of rotation of the annular magnetic rotor, wherein each of the blades includes a blade root surface facing the annular magnetic rotor and located in a first plane normal to the axis of rotation, and a blade tip surface facing away from the annular magnetic rotor and located in a second plane that is parallel to the first plane;
a nose cone portion extending from the center post towards the axial inlet, wherein a curved central portion of the nose cone extends axially through the impeller beyond the blades into the axial inlet; and
a secondary flow path in the annular cavity, wherein the secondary flow path has a U-shaped cross-section and extends around the annular magnetic rotor.
2. The apparatus of claim 1 , wherein the secondary flow path is defined by a first gap disposed between the annular magnetic rotor and an outer surface of the annular cavity, a second gap disposed between the annular magnetic rotor and a bottom surface of the annular cavity, and a third gap disposed between the annular magnetic rotor and an inner surface of the annular cavity.
3. The apparatus of claim 2 , wherein each of the first, second and third gaps is between about 0.010 inches and about 0.020 inches.
4. The apparatus of claim 2 , wherein each of the first, second and third gaps is between about 0.005 inches and about 0.030 inches.
5. The apparatus of claim 2 , wherein a height of the annular magnetic rotor is greater than a thickness of the annular magnetic rotor.
6. The apparatus of claim 2 , wherein a height of the annular magnetic rotor is about two times a thickness of the annular magnetic rotor.
7. The apparatus of claim 2 , wherein a height of the annular magnetic rotor is greater than two times a thickness of the annular magnetic rotor.
8. The apparatus of claim 2 , wherein an outside diameter of the center post is greater than the height of the center post.
9. A method for reducing cell damage caused by a magnetic levitation blood pump, the method comprising:
directing blood through a primary flow path from an axial inlet cannula to a peripheral volute of the magnetic levitation blood pump by rotating an impeller having blades about a nose cone portion extending from a center post towards the axial inlet, wherein a curved central portion of the nose cone extends axially through the impeller beyond the blades into the axial inlet, wherein the impeller includes a peripheral ring including a central aperture concentrically aligned with an annular magnetic rotor, and the blades extend from the peripheral ring inwardly into the central aperture and towards an axis of rotation of the annular magnetic rotor, wherein each of the blades includes a blade root surface located in a first plane normal to the axis of rotation, and a blade tip surface located in a second plane that is parallel to the first plane; and
directing a portion of the blood through a U-shaped secondary flow channel surrounding the annular magnetic rotor in the magnetic levitation blood pump.
10. The method of claim 9 , wherein the impeller is a shroudless inducerless impeller attached to the annular magnetic rotor.