Hydrodynamic thrust bearings for rotary blood pumps
A rotary blood pump includes a casing defining a pumping chamber. The pumping chamber has a blood inlet and a tangential blood outlet. One or more motor stators are provided outside of the pumping chamber. A rotatable impeller is within the pumping chamber and is adapted to cause blood entering the pumping chamber to move to the blood outlet. The impeller has one or more magnetic regions. The impeller is radially constrained in rotation by magnetic coupling to one or more motor stators and is axially constrained in rotation by one or more hydrodynamic thrust bearing surfaces on the impeller.
1. A rotary blood pump comprising:
a pumping chamber having an interior wall;
a rotatable impeller within said pumping chamber, said impeller having a plurality of sectors, adjacent sectors adjoining a blood flow path therebetween;
each of said sectors having a peripheral surface spaced by a gap from a portion of said interior wall of said pumping chamber when said impeller is rotating;
one or more of said peripheral surfaces of said impeller having a first inclined tapered region for capturing blood flow and a second oppositely inclined tapered region for ejecting blood flow, said first and second tapered regions being in tandem fluid flow communication across a flat bridging surface area therebetween, the taper depth of each of said tapered regions varying along its length in the direction of rotation of said impeller, each of said first and second tapered regions having a leading end and a trailing end, the leading end of said first tapered region being substantially perpendicular to the trailing end of said second tapered region, the taper depth of said first tapered region increasing hydrodynamic pressure on blood in said gap acting axially on said impeller when said impeller rotates, the taper depth of said second tapered region relieving hydrodynamic pressure on blood in said gap when said impeller rotates.
2. The blood pump of claim 1 in which each of said first and second tapered regions is substantially adjacent the periphery of said impeller.
3. The blood pump of claim 1 in which each of said first and second tapered regions is tapered in an axial direction relative to said impeller rotational axis.
4. The blood pump of claim 1 in which the depth of said gap is within the range of from approximately 0.003 inches to 0.020 inches when said impeller is rotating.
5. The rotary blood pump of claim 1 in which each of said one or more peripheral surfaces of each of said sectors of said impeller has said first and second tapered regions.
6. The rotary blood pump of claim 1 in which said rotatable impeller is made from an alloy of approximately 77.6% platinum by weight and 22.4% cobalt by weight.
7. The rotary blood pump of claim 1 in which each of first and second tapered regions is substantially flat in the radial direction relative to said impeller.
8. The rotary blood pump of claim 1 in which said impeller is made from titanium.
9. The blood pump of claim 1 comprising at least four of said sectors, adjacent ones of said sectors being separated by one of said blood flow paths, each of said blood flow paths extending to and defining a peripheral exit from said impeller.
10. The blood pump of claim 9 in which the peripheral exits from said impeller are substantially 90 degrees apart.
11. The blood pump of claim 9 in which each of said blood flow paths comprises a ramped bottom surface extending inwardly from substantially the bottom surface of said impeller at an inclined angle of substantially 32 degrees.
12. The blood pump of claim 1 comprising a plurality of said tandem first and second inclined tapered regions.
13. The blood pump of claim 12 in which said second tapered regions are each substantially triangular, an outside edge of which is at the circumference of said impeller.
14. The blood pump of claim 12 in which the leading end of each of said second tapered regions is adjacent the trailing end of one of said first tapered regions and the trailing end of each of said second tapered regions defines an inner edge at a sidewall of one of said blood flow paths.
15. The blood pump of claim 12 in which the leading end of each of said first tapered regions comprises an entrance edge at a trailing sidewall of one of said blood flow paths, the radius of curvature of each of said entrance edges being less than about 0.010 inches.
16. The rotary blood pump of claim 12 in which the angle of taper of each of said second tapered regions is more severe than the angle of taper of each of said first tapered regions.
17. The blood pump of claim 16 in which the angle of taper of each of said first tapered regions is less than 1 degree from its leading to trailing end.
18. The blood pump of claim 17 in which the angle of taper of each of said second tapered regions is within the range of from 2 to 4 degrees from its leading to trailing end.