Pumps – Motor driven – Electric or magnetic motor
Reexamination Certificate
1999-04-28
2001-05-22
Freay, Charles (Department: 3746)
Pumps
Motor driven
Electric or magnetic motor
C417S420000, C417S423100, C415S900000, C604S151000
Reexamination Certificate
active
06234772
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to the field of blood pumps. More specifically, the invention pertains to pumps of rotary design, suitable for implantation in humans.
BACKGROUND OF THE INVENTION
Ventricular assist devices (“VAD”), based on sealless rotary blood pumps, do not have drive shafts for the transmission of torque. Transmission of torque can readily be accomplished with the use of magnetic or electromagnetic coupling, but supporting the impeller poses challenges because of the unique properties of blood.
Blood can be used for hydrodynamic support and surface lubrication in sealless rotary pumps. But, the use of blood for lubrication poses many challenges not encountered with conventional lubricants such as oil, graphite, etc. Blood is composed of cellular elements which can be adversely effected or destroyed by mechanical forces and heat. In addition, blood carries large molecules, such as proteins, enzymes and clotting precursors, which can be damaged, denatured or inactivated as a result of heat, shear, material surfaces, or bearing clearances found in rotary blood pumps. Also, the blood can form clots.
Thus, the use of blood for hydrodynamic support and surface lubrication imposes a very narrow range of operating conditions. To avoid cell injury, only very low levels of shear can be produced. To avoid protein denaturation, local heats must not exceed 45 degrees C. To avoid the formation of clots, surfaces must be made of blood compatible materials and rapid exchange of blood within narrow clearances must be ensured.
Accordingly, it is an object of the present invention to provide a rotary blood pump using hydrodynamic bearings, magnet bearings, hybrid hydrodynamic/magnetic bearings or combinations thereof.
It is yet a further object of the present invention to provide a rotary blood pump in which all the internal surfaces are regularly washed by fresh blood to prevent thrombosis from occurring.
It is another object of the present invention to provide a rotary blood pump which does not subject any blood to shear forces, temperatures or materials that would substantially damage blood or adversely react with blood.
It is another object of the present invention to provide a rotary blood pump in which the magnetic and hydrodynamic forces acting on the rotor provide sufficient support to allow elimination of the shaft.
Other objects and advantages will become apparent as the description proceeds.
SUMMARY OF THE INVENTION
In accordance with illustrative embodiments of the present invention, a rotary blood pump includes a pump housing and a rotor comprising an impeller within the housing. In some embodiments, the rotor also includes a shaft. However, it is presently preferred to design the pump in order to eliminate the necessity for a shaft.
The rotor is suspended within the housing by magnetic and hydrodynamic forces or a combination of magnetic and hydrodynamic forces such that under normal conditions there is little or no rubbing contact between the housing and the rotor. To that end, the pump is provided with hydrodynamic bearings, magnetic bearings, hybrid hydrodynamic/magnetic bearings and combinations of these types of bearings.
In certain embodiments of the invention, a rotary blood pump has a housing and a rotor within the housing. The rotor includes an impeller and a shaft. A radial bearing is provided using magnets carried on the shaft and magnets carried on the housing. A hydrodynamic thrust bearing is defined by a gap between the impeller and the housing. A second radial bearing is defined by a gap between the impeller and an inward extension of the housing. The clearance in the gap of the second radial bearing is greater than the clearance in the hydrodynamic thrust bearing in order to provide for greater blood flow in this gap.
In other embodiments of the invention, a portion of one face of the housing and a portion of one face of the impeller have complementary shaped surfaces and are separated by a gap with sufficient clearance that little or no radial hydrodynamic support is provided.
In other embodiments of the invention, the radial magnetic bearing in the area of the pump is eliminated. In certain of these embodiments, a rotary blood pump has a pump housing and a rotor within the housing. The rotor includes an impeller and a shaft. A hydrodynamic thrust bearing is defined by a gap between the impeller and the housing. A hydrodynamic radial bearing in the area of the impeller is defined by a gap between the impeller and an inward extension of the housing.
In further embodiments of the invention, the rotary blood pump is made shaftless. In certain of these embodiments, a rotary blood pump has a pump housing and a rotor comprising an impeller. A hydrodynamic thrust bearing is defined by a gap between the impeller and the housing. A hydrodynamic radial bearing is defined by a gap between the impeller and an inward extension of said housing.
In other embodiments of the invention employing a shaftless rotor, a magnetic radial bearing has one or more magnets carried by the impeller and one or more magnets carried by an inward extension of the housing. A hydrodynamic thrust bearing is defined by a gap between the impeller and the housing.
In certain alternative embodiments of the invention, the clearance of the magnetic radial bearing is reduced so that the bearing provides additional, hydrodynamic support. In other embodiments, the rotary pump includes more than one magnetic radial bearing each comprising one or more magnets carried by the impeller and one or more magnets carried by an inward extension of the housing.
In preferred embodiments of the present invention, the magnets and motor stators can be offset axially, radially or both to provide forces to hold the rotor and its parts in proper relation to the housing, to dampen or prevent eccentric movement of the rotor, or to preload bearings to counteract hydrodynamic pressure. In certain of these preferred embodiments, magnets or motor stators in one part of the pump are offset in such a way to provide opposing forces to magnets or motor stators offset in another part of the pump.
The present invention incorporates new discoveries relating to non-intuitive ways to support the rotor of a blood pump. One especially significant discovery relates to the improvements in the thrust bearings. It has been found that preloading the hydrodynamic thrust bearings by offsetting magnets or motor stators with approximately ½ to ¾ lbs. of force, employing a large bearing surface, and providing for high flow through the bearing achieves substantial benefits. With these improvements, the hydrodynamic thrust bearing provides an unexpected amount of both axial and moment-restoring force to support the rotor in the axial direction and to prevent tilting and eccentric motion of the rotor. The amount of support and stability is so substantial that it is possible to eliminate the forward magnetic bearings in the area of the pump inlet, and the shaft, spindle, spoke and hub of the pump shown in U.S. Pat. No. 5,840,070. Thus, the pump design can be simplified, the manufacturing costs can be reduced, and potentially stagnant areas in the pump can be eliminated.
Through the present invention, substantial improvements and benefits are also provided in the radial or journal bearings in the area of the impeller. The hybrid hydrodynamic/magnetic radial bearings of this invention allow large clearances and provide large blood flow in the journal area without resulting in anticipated increases in blood damage due to shear. It is believed that the magnetic force decreases the load on the bearing and, thus, decreases shear. Any transient loads caused by eccentric movements are counteracted by the spring forces in hydrodynamic thrust bearings and the hydrodynamic and magnetic forces in the hybrid hydrodynamic/magnetic bearings in the journal area. Again, these improvements in support for the rotor further allow for elimination of any forward magnetic bearings and the shaft, spindle, spoke and hub.
Indee
Lancisi David M.
Wampler Richard K.
Freay Charles
Gerstman George H.
Kriton Medical, Inc.
Shaw Seyfarth
Tyler Cheryl J.
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