CA2240555A1

CA2240555A1 - Sealless rotary blood pump

Info

Publication number: CA2240555A1
Application number: CA002240555A
Authority: CA
Inventors: Richard K. Wampler
Original assignee: Kriton Medical Inc
Current assignee: Heartware Inc
Priority date: 1997-08-13
Filing date: 1998-06-12
Publication date: 1999-02-13
Also published as: DE69828926D1; US6080133A; US6688861B2; DE69828926T2; US20020102169A1; EP0901797B1; US6234998B1; EP0901797A2; US5840070A; ATE288770T1; JP4248626B2; IL124876A0; US7575423B2; KR19990023563A; US20040234397A1; IL124876A; US6368083B1; JPH11123239A; EP0901797A3

Abstract

An implantable rotary sealless blood pump is provided. The pump includes a housing having an inlet tube on one end and an impeller casing on the other end. A
rotor is mounted for rotation within the housing, with the rotor having an elongated shaft portion and an impeller attached to the shaft portion. The impeller is located within the impeller casing. Radial magnetic bearings are carried by the shaft portion and radial magnetic bearings are carried by the housing for maintaining the shaft portion of the rotor within the inlet tube of the housing. A rotor motor includes a plurality of permanent magnets carried by the impeller and a motor stator including an electrically conductive coil located within the housing. A ring of back iron is carried by the impeller to aid in completing a flux return path for the permanent magnets. A plurality of hydrodynamic thrust bearings are located outside of the axis of rotation of the rotor. The impeller uses large axially thick blade sectors with narrow blood channels extending through the impeller, to minimize hemolysis and to increase the working surface of the blades.

Description

Doeket No. 14233-CIP
SEALLI~SS ROTA~Y I~LOOD PUMP
This application is related to Canadian Application No. 2,218,342 filed February 14, 1997.

Field Of The Invention The invention relates generally to the field of blood pumps. More specifically, the invention pertains to continuous flow pumps of rotary design, 10 suitable for permanent implantation in humans, for use as chronic ventricular assist devices.

~3ack~round Of The Invention Thousands of heart patients who suffer from severe left ventricular 15 heart failure could benefit from eardiae transplantation. However, owing to ashortage of donor hearts, most of these patients faee a foreshortened life span characterized by frequent hospitalizations, severe physieal disability, and death from congestive failure or eardiogenie shock. If a left ventricular assist device ("LVAD") were available for chronie use, many of these patients could be returned to prolonged 20 and produetive lives.
Prior art LVADs, now in elinical trials, provide a cyclic or p~ tinE
delivery of blood, designe-l to emulate the natural pulsatile blood flow through the heart. This design approaeh has resulted in a variety of anatomic and engineering problems. Cyelic delivery systems tend to be physically large, m~king implantation 25 difficult or impossible for some patients. Cyclic delivery systems also employ artificial valves, having speeial material, longevity, and performanee requirements.
All of ~hese characteristics make cyelie blood pumping deviees both complex and expenslve.

CA 02240S~S 1998-06-12 It is apparent that if the requirement of pulsatile blood flow is elimin~ted, the LVAD could be much smaller, simpler, and less expensive. Rotary pumps, whether of centrifu~al or axial flow design, provide substantially continuous liquid flow, and potentially enjoy a number of the listed advantages over cyclic5 delivcry systems. However, thc prior art llas not devcloped a durable rotary blood pump, owing to unique problcms with the rotary pump's driveshaft seal. In a blood environment, such driveshaft seals have a short life, and contribute to a premature failure of the pump. Prior art driveshaft seals may also cause embolisms, resulting in a stroke or even deatll for the patient.
Accordingly, it is an object of the present invention to provide an improved rotary blood pump, by elimin:~ting the necessity for a driveshaft seal;It is a furthcr object of the present invention to providc a compact, rotary blood pump using passive, magnetic radial bearings to m~int~in an impeller and its support shaft for rotation about an axis;
It is yet a furtller object of the present invention to provide a rotary blood pump having bi-stable operation, in which the impeller and the support shaft shuttle as a unit, between two predetermined axial positions;
It is another object of the present invention to provide blood immersed axial thrust bearings which are regularly washed by fresh blood flow to prevent 20 thrombosis from occurring;
It is yet another object of the present invention to provide a unique thick bladed pump impeller, which houses both motor m~gn~t~ and radial bearing magnets, and includes narrow, deep, blood flow passages;
It is yet another object of the present invention to provide a pump 25 impeller which is effective pumping viscous liquids, such as blood, at low flow rates, and which minimi7rs hcmolysis of the blood by using only a few pump impeller CA 02240~ 1998-06-12 blades.

SumMary Of The Invention In accordance with illustrative embodiments of the prcsent invention, S a rotary blood pump includes a housing ànd a pump rotor. A centrifugal pump iml?cllcr is attached to an impeller support sllaft, or spindle, to form the pump rotor.
The pump housing includes an elongated inlet tube surrounding the shaft, and a scroll-shaped casing, or volute, with a discharge outlet, enclosing the impeller.
The shaft and the impeller are specially suspended within the housing.
10 Radial magnetic bearings of passive design, m~int~in the support shaft and the impeller about a rotational axis. The magnetic bearing which levitates the shaftincludes a plurality of permanent ring magnets and pole pieces arranged along surrounding portions of the inlet tubc, and a plurality of permanent disc magnets and pole pieces within the shaft itself. Radially adjacent pairs of these magnets are of like 15 polarity. One part of the magnetic bearing, wllich m~int~in~ the irnpeller about a rotational axis, includes a plurality of permanent rod or arcuate m~gn~ts disposed in spaced, circular relation around blade sectors of the impeller; another part of the bearing includcs a pair of permanent ring magnets outsidc the casing, on either side of the impeller. Adjacent portions of the rod and ring m~gnet~ are of opposite 20 polarity.
The shaft and impeller are axially restrained by a m~gn~tic and llydrodynamic forccs in combination witll mechanical thrust bearings, or touchdowns.
The magnets of the m~gn~tic bearing in the inlet tube and shaft may be arranged in slightly offset axial relation, to produce a translational loading force, or bias, along 25 the longitll~lin~l axis of the rotor. This bias substantially counteracts the axial force resulting from the hydraulic thrust of the rotating impeller. However, the hydraulic CA 02240~ 1998-06-12 thrust will vary as a function of the cardiac cycle and additional restraints are desirablc to cnsure that pump operation is stable and controlled. For this purpose, a pair of blood immersed thrust bearings is provided. These thrust bearings may belocated at either end of the rotor, altllough other arrangements are feasiblc.
One thrust bearing is includcd at the upstream end of the support shaft, and the otller thrust bearing is located on the bottom, or downstream side of the impeller. A spider within the inlet tube includes a touchdown, or thrust surface, against which tlle end of the shaft periodically touches. Another touchdown is provided on an inner surface of the casing base, adjacent a downstream terminus of 10 the impeller. A predetermined amount of spacing is included bctween the two touchdowns, so as to allow the shaft/impeller assembly axially to shuttle back and forth, in response to the user's cardiac cycle. This sh-~ttling motion will produce a pumping action, frequently exchanging blood in the touchdown area with fresh blood from the circulation. This pumping action minimi7f~s the likelihood of blood 15 tllrombosis in the thrust region, by m~int~ining the blood at an acceptable temperature and by shortening its residence time in the thrust bearing gap.
The impeller is of unique configuration and characteristics, owing to the special requirements of the present application. Contrary to conventional centrifugal pump design, thc present invention uses relatively few impeller blades, 20 generally resembling pie-shaped sectors. Moreover, the blades are made quite thick in an axial direction, having deep and narrow, arcuate channels between adjacentblades for the passage of blood through thc impeller. The substantial height of the blades provides a relatively large blade working surface, ensuring efficient pump opcration. These structural features decrease hemolysis of the blood, while 25 m~int~ining useful efficiency in a pump using so few impeller blades.

CA 02240~ 1998-06-12 Sealed, hollow chambers are provided within the thiek impeller blades to reduce the density of the impeller. These chambers reduce gravity indueed loads on the thrust bearings, which in turn reduces the likelihood of thrombosis of the blood used to lubricate the bearings.
The tllick impeller blades are also used advantageously to house magnets used in the pump drive system. Torque drive is imparted to the impeller by magnetic interaction between arcuate, permanent magnetie segments imbedded within each impeller blade seetor, and a eircular eleetromagnetie stator, affixed to the easing. Back-EMF sensing is used to commutate the brushless motor stator, providing 10 attractive and repulsive forees upon the magnetie segments. A eontrol unit and a portable power supply, worn on the user, power the pump drive system. The control unit allows the speed and drive eyele of the motor either to be programmed or interactively determined by the user's physieal activity or eondition.
In eertain embodiments of the invention, the motor includes a plurality 15 of permanent magnets earried by the impeller and a motor stator ineluding an electrically conductive eoil located within the housing. A ring of back iron is fixed to the easing to aid in completing a flux return path for the permanent m~gnPts and to decrease the axial thrust which results from the attraetion of the motor rotor magnets toward the motor rotor stator. The impeller has a forward side faeing the 20 inlet tube and a rear side downstream of the forward side. In one embodiment, the eonductive eoil of the motor stator is loeated adjaeent the rear side of the impeller, and a stator back iron ring is located outside of the eonduetive eoil, within the housing and fixed to the housing. In one embodiment, a second ring of baek iron is loeated on the forward side of the impeller and outside of the easing but inside of the 25 housing, with the second ring of back iron being fixed to the easing. In thatembodiment, a second motor stator having an electrically conductive coil is loeated CA 02240~ 1998-06-12 on the forward side of the impellcr outside of the casing but inside of the housing.
In that embodiment, the second ring of back iron is located forward of the second motor stator.
In certain embodiments, a plurality of hydrodynamic thrust bearings S are located outside of the axis of rotation of the rotor. The hydrodynamic bearings are wedge-shaped and, during rotation of the rotor and impeller, the hydrodynamic bearings are separated from the casing by a fluid film and are not in direct mechanical contact with the casing.
A more detailed explanation of the invention is provided in the 10 following description and claims, and is illustrated in the accompanying drawings.

Brief Description Of The Drawin~s Figure 1 is a left front perspective of the blood pump of the present invcntion;
Figure 2 is a fragmentary, cross-sectional view of the pump of Figure 1, showing a plurality of ring magnets comprising part of the m~gnetic bearing assembly;
Figurc 3 is a fragmentary, cross-sectional view of the pump of Figure 1, showing the shaft and an impeller;
Figure 4 is a view as in Figure 1, but with the shaft and impeller shown removed from the housing;
Figure 5 is a simplified, fragmentary, representation of a human heart, showing the pump implanted within the left ventricle of the heart;
Figure 6 is a transverse, cross-sectional view of the housing, impeller, 25 and impeller chamber, taken along the line 6-6, shown in Figure 1;
Figure 7 is a longitll~lin~l, cross-sectional view of the pump, taken CA 02240~ 1998-06-12 along the line 7-7, shown in Figure 1;
Figure 8 is a longitudinal, cross-sectional view of a simplified, schematic representation of the pump, showing respective polarities of the magnets and the pole pieces of the passive radial magnetic bearings, and the elements of the 5 pump motor, including rotor magnets and a motor stator;
Fig. 8a is a scllematic view, similar to Fig. 8, but showing another embodiment of the present invention;
Fig. 8b is a schematic vicw, similar to Fig. 8a, but showing another embodiment of the present invention.
Figure 9 is a longitudinal, cross-sectional view of an impeller constructed in accordance with the principles of the present invention;
Figure 10 is an end view tllercof, taken from the right side of Figure 9;
Figure 11 is a longitudinal, cross-sectional view of a simplified, 15 schematic representation of another embodiment of the pump;
Figure 11a is an enlarged view of the circled portion 11a from Figure 11;
Figure 12 is a cross-sectional end view of the Figure 11 pump with the end of the llousing and casing removed for clarity;
Figure 13 is a perspective view, partially broken for clarity, of the blood pump of Figure 11;
Fig. 13a is a perspcctivc view of a portion of Fig. 13, showing the slotted motor stator;
Fig. 13b is a perspective view, similar to Fig. 13a but showing a 25 slotless motor stator.

CA 02240~ 1998-06-12 Figure 14 is another perspective view, partially broken for clarity, of the blood pump of Figure 11;
Figure 15 is a longitudinal, cross-sectional view of another embodiment of the pump;
Figure 15a is an enlargcd view of the circled portion 15a from Figure 15;
Figure 16 is a cross-sectional end view of the Figure 15 pump, with the end of the housing and casing removed for clarity;
Figurc 17 is a longitudinal, cross-sectional view of another 10 cmbodiment of a blood pump;
Fi~gure 17a is an cnlarged view of thc circled portion 17a from Figure 17;
Figure 18 is a cross-sectional end view of the Figure 17 pump, with the end of the housing and casing rcmoved for clarity;
Figure 19 is a longitudinal, cross-sectional view of another embodiment of the present invention;
Figure 19a is an cnlargcd view of the circled portion 19a from Figure 19; and Figure 20 is a cross-sectional end view of the Figure 19 pump, with 20 the end of the housing and casing removed for clarity.

Det~iled DescriPtion Of The Preferred Embodiment Turning now to Figures 1-8 of the drawings, a sealless rotary blood pump 11 includes a housing 12, having an elongated inlet tube 13 and an irnpeller 25 casing or volute 14. A discharge tube 16 extcnds through the housing to commlmi~te with the interior periphery of casing 14. Tube 16 has a tangential orientation with CA 02240~ 1998-06-12 respect to a radius of the casing, for effectively channeling the blood output from the pump.
A pump rotor 17 is located within housing 12, within casing 14, and includes an elongated, right-circular cylindrical support shaft or spindle 18, attached 5 to a disc-shaped impeller 19. Rotor 17 is mounted for rotation about a longitllclin~l axis which extends both through shaft 18 and impeller 19. It should be noted that the preferred embodiment disclosed herein includes an impeller and a casing of centrifugal design. However, many of the structural features and aspects of operation of the present invention may also be adapted advantageously to rotary blood pumps 10 of axial flow design.
The pump 11 of the present invention includes a forward m:~gn~tic bearing 21 and a rearward magnetic bearing 22 to levitate rotor 17 and m~int~in it in proper radial alignment with respect to its longitudinal axis. A radial magnetic bearing construction is shown in U.S. Palcnt No. 4,072,370, issued to Wasson. The lS '370 Patent is hereby expressly incorporated by reference. The forward m~gnetic bearing 21 herein may be constructed entirely in accordance with the teachings of the '370 Patent. However, several simplifications and improvements to the construction shown in the '370 Patent are disclosed herein. For example, it has been determined that the radially polarized ring magnets (numerals 44 and 46) of the '370 device, are 20 not necess~ry for successful practice of the invention herein. In addition, as will be explained below, the axially magnetized ring magnets (numeral 22) of the '370 device may advantageously be replaced with axially magnetized disc m~gn~t~ for purposesof the present invention.
Accordingly, the forward m~gn~tic bearing 21 includes a plurality of 25 rings, comprising ferromagnetic pole pieces 23 and axially polarized pcrm~n~nt magnets 24. As shown most clearly in Figures 7 and 8, pole pieces 23 and m~gnets CA 02240~S 1998-06-12 24 are arranged in contingent, alternating fashion, and are located between outer sidcwall 26 and inner sidewall 27 of inlct tube 13. The polarization of opposingmagnets is the same, inducing an identical polarization into a respective pole piece therebetween. A combination of higll strength adhesive and surrounding tube 5 sidewalls, m~int~in~ the arrangement of magnets and pole pieces in contingent relation, despite strong magnet forces attempting to urge the rings apart.
Forward magnetic bearing 21 also includes a plurality of discs, comprising ferromagnetic pole pieces 28 and axially polarized permanent magnets 29.
Pole pieces 28 and magnets 29 are also arranged in contingent, alternating fashion, 10 so as to form a magnetic structurc which mirrors the polarity and axial position of respective pieces and magnets of the surrounding rings. This magnetic structure is first assembled and secured together using high strength adhesive, and is then installed within the hollow volume of shaft or spindle 17. The magnetic polarizations and repulsive forces produced by the magnets and the pole pieces of forward 15 magnetic bearing 21 are sucll that magnetic levitation of support shaft 18 results.
To provide additional radial restraint for rotor 17, rearward magnetic bearing 22 is also provided. Bearing 22 includes a first ring magnet 31 mounted on an outer wall of casing 14, and a second ring magnet 32 imbedded within a circular casing base 33. The bottom portion of casing 14 is attached and sealed to base 33, 20 to form a fluid impervious enclosure for impeller 19 (see Figure 7). Both magnets 31 and 32 are axially polarized, but cach has a different polarization facing impeller 19. Bearing 22 also includcs a plurality of rod magnets 34, transversely extending from an upper face portion 36 to a lower face portion 37 of impeller 19. Rod magnets 34 are arranged in spaced, circular fashion, adjacent an outer periphery 38 25 of impeller 19. The polarizations between tlle ends of magnets 34 and the adjacent surfaces of magnets 31 and 32 are respectively opposite, creating attractive, but equal CA 02240~ 1998-06-12 and opposite magnetic forces acting on the impeller. It can be seen that radial movement of the impeller (deflection from the axis of rotation) will result in arestoring force due to the attraction between the magnets 34 towards magnets 31 and 32. The magnetic force in the axial direction will largely be counterb~l~n~e-l to the S opposing magnetic attraction of magnets 34 to magnet 31 and magnets 34 to magnet 32. However, the action of the magnetic force in the axial direction would not be restoring.
It should also be noled that other configurations, locations, numbers, and polarization orientations may be used for the components forming rearward 10 magnctic bearing 22. ~or example, Magnets 34 may be arcuate segments, rather than rods. Also, the polarizations of the magnets 31, 32, and 34 may be arranged to effect respective repulsive forces, rather than the attractive forces specifically disclosed herein. In this manner, referring to Figs. 8a and 8b, the south pole of magnets 34 would be adjacent the south pole of magnet 31 and the north pole of magnets 34 15 would be adjacent the north pole of magnet 32. For the magnets to be restoring in tlle radial direction, the magnets would have to be offset. To this end, in the Fig.
8a embodiment magnets 34 would be more outward radially than magnets 31 and 32.
Alternatively, in the Fig. 8b embodiment magnets 34 are radially inside the radial dimension of magnets 31 and 32. If a repulsive configuration is used, as illustrated 20 in Figs. 8a and 8b, the action of the magnetic force would be restoring in both the radial and axial direction.
Although the drawings show magnets 32 and 34 as if portions thereof are directly immersed in blood, in actual practice, a thin-walled non-m~nPtic jacket or a plastic coating would be placed over these portions, to prevent contact between 25 the magnets and the blood. Such contact, if it were allowed, would likely cause an undesirable chemical reaction, to the detriment of the blood. However, for clarity, CA 02240~ 1998-06-12 the referenced jacket or coating, is not shown in the drawings.
To provide mechanical limitations Oll axial, translational excursions of the rotor, a first thrust bearing 39 and a second thrust bearing 41 are provided. First thrust bearing 39 includes a threaded plug 42, installed within casing base 33. Plug 5 42 is scrcw adjustablc along the longitudinal axis of rotor 17, and includes a recessed bearing surface 43. Surface 43 is contoured to accommodate a corresponding bearing tip 44, in the lower face portion of impeller 19. It should be noted that the particular configuration of bearing 39 is not critical, and planar bearing surfaces may alternatively be used in this application.
Second thrust bearing 41 is secured within the blood entry end of inlet tube 13, and includes a spider 46, adjustment knob 47, and ball 48. Rotation of knob 47 will translate ball 48 along the longitudinal axis of rotor 17.
Alternative locations and constructions for second thrust bearing 41 are also contemplated. For example, an annular thrust bearing surface could be provided on the inner wall of casing 14, adjacent the upper face portion 36 of impeller 19. In this arrangement, portion 36 would slidably contact the annular thrust bearing surface. By elimin~ting spider 46 and the associated components of the upstream thlust bearing, the possibility of blood deposits forming on thcse structures would be elimin~ted.
It will be appreciated that thrust bearings 39 and 41 are effective not only to provide limit stops to axial movement of rotor 17, but also to adjust certain operational aspects of the pump. In the drawings, the upstream end of support shaft 18 is shown in contact with ball 48. However, this will not always be the case during the course of operating the pump. For example, it is desirable for the two thrust 25 bearings to be adjusted so that the distance between them, is slightly greater than the overall length of the rotor. This will allow the rotor to "shuttle", back and forth CA 02240~ 1998-06-12 between the axial constraints provided by tl1e thrust bearings with each cardiac cycle of tlle uscr. Each SUClI cyclc Will producc a pumpin~ action, bringing fresh blood into the touchdown, or thrust bearing area.
Tlle prescnt invention does not use a journal bearing to restrain the S rotor. Of nccessity, a journal bearing radially encases at least a portion of the rotor's support shaft or spindle. It is within this thin, annular voluMe between the shaft and the bcaring surface, where thrombosis can occur in prior art deviccs as a consequence of heat and excessivc residence time within the bearing. The bi-stable operation of thc pump and rotor of thc prescnt invcntion, continuously flushcs the blood around 10 each thrust bcaring, avoiding thrombosis effects of prior art journal bearings.
There is also an im~ortant pllysical rclationship which exists between the rotor and the magnetic bearings of the device disclosed herein. This relationship is established and m~int~ined by proper axial placement of the adjustable thrustbearings. In operation of the pump, the pressure gradient produced by the rotating 15 impeller imparts an upstream axial force on the rotor. This force needs to besubstantially counterbalanced, to ensure that cardiac pulses will create sufficient pressure variances tllrough the pump, to effect bi-stable operation. By adjusting the axial relationship of the pole pieces 23 and the magnets 24 with respect to the pole pieces 28 and magnets 29, a downstream axial force will be produced. Since the 20 forces within forward m~gnPtic bearing 21 are repulsive, the desired downstream loading or bias will be effected when the magnets and pole pieces within the shaft are translated slightly downstream from the magnets and pole pieces in the inlet tube (See, Figures 7 and 8). Thus, second thrust bearing 41 is effective to shift, or offset the rotor downstream a sufficient amount so the resultant, repulsive magnetic forces 25 substantially counterbalance the hydrodynamic axial force produced by the rotating pump impeller.

~ CA 02240~ 1998-06-12 We can now turn to the special design considerations and operational ch~ractcristics of impellcr 19. As will bc notcd particularly in Figure 6, tllc impeller includes a plurality of lar~e blade sectors 49. Owing to its relatively high viscosity and susceptibility to damage from heat and mechanical action, blood is a uniquely S difficult liquid to pump.
It is generally prererable in a large centrifugal pump, to have a substantial number of thin, sharp impeller blades with relatively large voids orpassages, between the blades, for the passage of low viscosity liquid. However, such a conventional design is not desirable, for a small centrifugal pump which has to 10 pump a viscous liquid, such as blood.
When blood flows axially into the leading edges of impeller blades it tends to be damaged by the mechanical action and turbulence associated with the impeller blades. Thus, one of the design considerations of the present invention is to reduce such hemolysis, by minimi7.ing the number of impeller blades and leading 1~ edges.
To m~in~in efficiency in a small pump with so few blades, the effective working area of the blades needs to be increased. This was accomplished in the present design by modifying the size and configuration of conventional blades in two significant aspects. First, blade sectors 49 are made relatively wide or 20 expansive through a rotational aspect (see Figure 6). In other words, the outer periphery of each blade sector 49 assumes approximately 80 to 85 degrees of rotation. It should be noted tllat an alternative design contemplated herein includes only two blade sectors, each of which assumes approximately 175 degrees of rotation. In either case, the width of the impeller blade sectors of the present25 invention differ significantly from known prior art blades.

CA 02240~ 1998-06-12 The second modification pertains to the thickness or height of the blade sectors. As shown particularly in Figures 4 and 7, blade sectors 49 are relatively thick in an axial direction. As a consequence of these modifications, a narrow and deep impcller blood flow path or passageway 51 is defined between adjacent edges5 of blade sectors 49. By increasing thc thickness of the blade sectors and narrowing the blood passageway, the ratio between tllc area of working surface of the blades and the volume of the passageway is increased. Also, the average distance of theliquid in the passageway from the working surface of the blades is decreased. Both of these beneficial results provide a sn1all pump for blood which has few blades for 10 damaging blood, yet m~in~ins acceptable efficiency.
The size and configuration of the impeller blades also allows the structural integration of a number of features directly within the impeller 19. For example, the previously discussed rearward magnetic bearing 22 includes a plurality of rod magnets 34 of considerable length. Owing to the thickness of the blade 15 sectors, these magnets are readily accommodated within the sectors. The sectors may also be provided with respective hollow chambers 52, to reduce the mass of the impeller and the gravity induced loads on the thrust bearings (see, Figure 6).
Lastly, a brushless rotor motor 53 includes arcuate m~gnP~ic segments 54, imbedded within the upper face portion 36 of blade sectors 49. As discussed 20 above, the portions of segments 54 which would otherwise be in fluid communication with the pumped blood, are encased in a jacket or a coating (not shown) to prevent any chemical reaction betwcen thc blood and the magnetic segments. Making reference to Figures 6 and 8, segments 54 have alternating orientations in theirpolarities, and are directed toward an adjacent motor stator 56. Included within stator 25 56 are windings 57 and a circular pole piece or back iron 58, mounted on the outer surface of impeller casing 14. Windings 57 are interconnected by means of CA 02240~ 1998-06-12 percutaneous wires to a controller 59 and a power supply 61, as shown in Figure 5.
Alternative to using wires, transcutaneous power tr~n~mi~sion could be used. It is contemplated that controller 59 and power supply 61 may be worn externally by the user, or alternatively, they may be completely implanted in the user.
S Controller 59 may include circuitry as simple as a variable voltage or current control, manually adjusted or progMmmed to detennine the running rate ofpump. However, controller 59 may also have interactive and automatic capabilities.
For example, controllcr 59 may be interconnected to sensors on various organs of the user, automatically and instantaneously to tailor operation of the pump to the user's 10 physical activity and condition.
The windings 57 are energized by the electrical output of controller 59 to produce an electromagnetic field. This field is concentrated by pole piece 58, and is effective to drive magnets 54 and the rotor 17, in rotary fashion. The back EMF
resulting from the magnets 54 passing by the windings is detected by the controller.
15 The controller uses this back EMF voltage to continue generation of the electromagnetic field in synchronism with further rotation of the rotor. Brushless operation of thc molor 53 is effccted, then, by clectromagnetic interaction between the stator and magnets imbedded within the pump's impeller blades.
Motor 53, with windings 57 and pole piece 58, together with magnets 20 54, function not only to transmit torque but also provide a restoring radial magnetic forcc that acts as a radial bearing. As illustrated in Figures 7 and 8, m~gnetc 54 are carried by blade sectors 49 and are positioned in radial alignment with pole piece 58.
The magnets 54 have attraction with the iron pole piece 58 of the stator. Any attempt to deflect the impeller radially produces an increasing restoring force between 25 the pole piece 58 and the magnets 54 which would cause the impeller to return to a neutral position.

CA 02240~ 1998-06-12 Rotation of the rotor 17, including shaft 18 and impeller 19, causes blood to flow through inlet tube 13 in the direction of arrows 62. The blood continues its path from the upper edge of passage 51 to the interior of casing 14.
Discharge tube 16 allows the blood to be expelled from the casing an into the user's S cardiovascular system.
Anatomical placement of the pump 11 is shown in Figure 5. The simplified representation of a human heart 63, includes a left ventricle 64 and an aorta 67. The inlet tube 16 serves as the inflow calmula and is placed into the apex of the left ventricle 64. An arterial vascular graft 66 is connected on one end to tube 10 16 and on the other end to the aorta 67 througl1 an end to side anastomosis.
The centrifugal design of the pump allows a considerable amount of flexibility during implantation. Owing to the axial inflow and radial outflow of the pump, a 90 degree redirection of the blood is effected without the necessity of a flow-restrictive elbow fitting. Moreover, the pump can be rotated on its longitudinal 15 axis to adjust the orientation of thc discharge tube and minimi7.~ kinking and hydraulic losses in the vascular graft. Good anatomic compatibility is possible since the pump casing is comp~ct and disc-shapcd, ~Itting well between the apex of theheart and the adjaccnt diaphragm.
In a specific example although no limitation is intended, referring to 20 Figure 7, blood ~low path 62a is .06 inch to 0.1 inch in thickness. The fluid gap 70 comprising the clearance between the impeller and the housing is .005 inch to .02 inch. The impeller diameter is 1.0 inch to 1.5 inch. Thc rotor diameter is .025 inch to 0.4 inch. The outside diameter of the flow annulus is .35 inch to .S5 inch. The outer diameter of the housing adjacent the forward end of the pump is .85 inch to 25 1.25 inch. The axial length of the entire pump is 1.75 inch to 3.0 inch. The axial length of the rotor spindle is 1.0 inch to l.S inch and the axial length of the impeller CA 02240~5~ 1998-06-12 is 0.2 inch to 0.5 inch. ~y using a thick impeller (having a long axial length) the fluid gap 70 can be larger and still provide a highly efficient pumping action.
Enlarged views of an impeller used in the pump of the present invention are set forth in Figures 9 and 10. Referring to Figures 9 and 10, an S impeller 74 is shown therein having a number of blade sectors 76, 78 and 80. Blade sectors 76 and 78 are separated by slot 82; blade sectors 78 and 80 are separated by slot 84; and blade sectors 80 and 76 are separated by slot 86. By ll~ili7ing blade sectors 76, 78 and 80 that are relatively tllick in the axial direction, narrow and deep impeller blood flow paths are fonned by slots 82, 84 and 86 between the adjacent10 edgcs of thc bladc sectors. By increasing the tllickness of the blade sectors and narrowing the blood passageway, the ratio between the area of working surface ofthe blades and the volume of the passageway is increased. Also, the average distance of the liquid in the passageway from the working surface of the blades is decreased.
Both of these beneficial results allow a small pump for blood which has less blades~5 for potcntially d~m~ging blood, yet the small pump m:~int~in~ acceptable efficiency.
As a specific example although no limitation is intended, the diameter of the impeller is 1 inch to 1.5 inch, the blade depth bd (Fig. 9) is 0.2 inch to 0.5 inch, the magnet width mw (Fig. 9) is .15 inch to 0.3 inch, the spindle diameter sd (Fig. 9) is .25 inch to 0.5 inch, and the inner diameter id (Fig. 9) of the impeller 20 inlet is .45 inch to .6 inch. The width w of the slots (see Fig. 10) is approximately .075 inch and preferably ranges from .05 inch to 0.2 inch. The outlet angle a (Fig.
10) preferably ranges between 30~ and 90~.
Another benefit of the thick impeller is the ability to utilize magnetic pieces 88 that are inserted in a manner enabling the stators to be on opposite sides 25 of the impeller. Referring to Figures 11, 11a, 12, 13 and 14, the blood pump 11' shown therein is similar in many respects to blood pump 11 illustrated in Figures 1-8, CA 02240~ 1998-06-12 and includes housing 12 having an elongated inlet tube 13 and a scroll-shaped impeller casing or volute 14. A discharge tube 16 extends through the housing tocommunicate with the interior periphery of casing 14. Tube 16 has a tangential orientation with respect to a radius of the casing, for effectively channeling the blood 5 output from the pUMp.
Pump rotor 17 is located within housing 12, within casing 14, and includes an elongated, right-circular cylindrical support shaft or spindle 18, attached to impeller 74. Rotor 17 is mountcd for rotation about an longitudinal axis which extends both through shaft 18 and impeller 74.
Tlle n1agnetic bearings for Icvitating rotor 17 and m~in~:lining it in proper radial alignn1ent with respect to its longitudinal axis are not specifically shown but may be identical to those illustrated in the pump embodiment of Figures 1-8 and described above.
In the Figures 11-14 embodiment, a first motor stator 90, comprising 15 conductive coils or motor windings 91, is located at the rear of impeller 74. A ring of back iron 92 is located behind windings 91 and, as illustrated in Figure 9, first motor stator 90 and back iron 92 are fixed between housing 12 and casing 14.
A second motor stator 94, comprising windings 95, is positioned on the forward side of impeller 74. As illustrated in Figure 11, windings 95 are fixed 20 to casing 14 and a ring of back iron 96 is positioned forward of windings 95. As illustrated in Figures 13, 13A and 14, back iron 92 and back iron 96 have teeth 98 whicll extend into the stator windings to form the stator iron. Thus the windings 95 wrap around the teeth 98 in the intervening slots 99 (See Fig. 13a). In the Fig. 13A
embodiment, a slotless motor stator is illustrated. In that embodiment, the windings 25 91 are fixed to the back iron 96 and there are no teeth extending into the stator windings.

- CA 022405~ 1998-06-12 It can be seen that the motor stators 90 and 94 are placed on opposite sides of casing 14 such that each is adjacent to thc pole faces of the motor rotor magnets 98. Back iron 92 and back iron 96 serve to complete a magnetic circuit.
The windings 91 and 95 of the stators 90, 9~ can be in series or each stator 90, 94 5 can bc commutated independent of thc other. Tllcrc are scveral advantages to this approach:
First, as long as tllc l~ole faccs of the motor rotor magnets are centered between tl-e faccs of tlle motor stators, the nct axial force will be relatively low.
Second, the radial restoring force which results from the attractive 10 forcc of the motor rotor magnets to the motor stators will be nearly twice as large as the restoring force with only one stator. The total volume and weight of the motor will be smaller than a single stator design.
Third, the dual stator design is adapted to provide system red-ln~ncy for a fail safe mode, since each stator can be made to operate independently of the 15 other in the case of a system failure.
Fourth, hydrodynamic bearings can be located on the surface of the impeller to constrain axial motion and to provide radial support in the case of eccentric motion or shock on the device. Referring to Figures ll and 11a in particular, hydrodynamic bearings in the forrn of raised pads 100, 101 and contact 20 surfaces 102 and 103 are illustrated. Such hydrodynamic bearings are symrnetrically located about the impeller as illustrated in Figure 13, in which raised pads 100 are shown.
The raised pads could be rectangularly-shaped or wedge-shaped and are preferably formed of hardened or wear resistant materials such as ceramics, 25 diamond coatings or titanium nitride. Alternatively, the raised pads may be formed of a different material having an alumina or other ceramic coating or insert.

CA 02240~ 1998-06-12 The raised pads are carried by either the impeller or the casing, or an attachment to the casing. In the Figures 11 and 1 la embodiment, the raised pads 100 are carried by the impeller and the raised pads 101 are carried by a cup-shaped member 104 that is fastened to the casing. Cup-shaped member 104 is utilized as a S reinforcement for thc casing whicl1 would not be structurally stable enough to carry the raised pads itself.
The hydrodynamic bearings are formed by a raised pad spaced from a contact surface by the blood gap. Although at rest there may be contact between the impeller and the casing, once rotation begins each hydrodynamic bearing is 10 structured so that during relative movement between the raised pad and the contact surface the hydrodynamic action of the fluid film produces increased pressure within the bearing gap which forces the raised pad and the contact surface apart.
Depending upon the location of the hydrodynamic bearings, they can aid in axial support, radial support or both axial and radial support. For example, 15 if the bearings are perpendicular to the rotational axis, tlley aid primarily in axial support but if they are at an angle with respect to the rotational axis, they aid in both radial and axial support. In the embodiment of Figures 11-14, the hydrodynamic bearings are positioned outside the axis of rotation, as illustrated.
In the Figures 15-16 embodiment, there is a single axial motor and the 20 stator 90 is located at the rear end of impeller 74. Stator 90 comprises windings 91, and a ring of back iron 92 is located downstream of windings 91. The motor stator 90 and back iron arc fixed betwcen casing 14 and housing 12.
In the Figures 15-lG embodiment, a ring of back iron 106 is placed in the impeller, in axial alignment with the magnets, such that it completes the flux 25 return path for the motor rotor magnets in the impeller. Thus while motor stator 90 and back iron 92 are located downstream of the impeller and outside of casing 12, CA 02240~S~ 1998-06-12 back iron 106 is located within the impeller and within the casing 12. Using back iron to complete the magnetic circuit in this manner increases the overall efflciency of the motor.
Referring to the embodiment of Figures 17-18, a motor stator 90 and 5 back iron 92 arc provided at thc rear cnd of impeller 74 as with the Figures 9-14 embodiments, but another ring of back iron 108 is placed outside pump casing 12 on the front side of the impeller and is fixed to the casing. Back iron ring 108 serves two purposes. First, it serves to help complete the flux return path for the motor rotor magnets. Second, the attractive force between the motor rotor magnets and the 10 ring of back iron 108 substantially reduces the net axial force produced by the attraction of the motor rotor magnets for the stator iron. Third, the ring of back iron significantly increases tlle radial restoring force compared to just the interaction between the motor rotor magnets and the stator iron.
Although the Figures 1-18 embodiments utilize an axial flux gap 15 motor, in the Figures 19-20 embodiment a radial flux gap motor is utilized. To this end, a ring-shaped structure is placed on either side of the impeller to house a series of motor rotor magnets (an even number) oriented such that the m~gn~tic poles of the motor rotor magnets are radially, and alternately, aligned. The inner diameter of the magnets is located on the surface of a ring of back iron to provide a flux return path.
20 On the opposite end of the impeller, passive radial magnetic bearings are used.
It can be seen that in the Figure 19-20 embodiment the motor rotor magnets 110 arc radially aligned. Radially within the motor rotor magnets 110 is a ring of back iron 112. The inner diameter of m~gn~t~ 110 are located on the surface of back iron ring 112 (see Fig. 20) to provide a flux return path. The motor rotor 25 magnets 110 and ring of back iron 112 are carried by the impeller, within tlle casing 14. Outside of the casing 14 there is radially positioned a ring-shaped stator 114 CA 02240~ 1998-06-12 with motor windings 116.
A number of axial pcrmanent magnets 120 are carried by the impeller, at its rear end. A number of axial permanent magnets 122 are fixed to the casing 14 and housing 12, downstream of and partially offset from, magrlets 120. Magnets 120 5 and 122 scrve as passive magnctic bearings for thc impcller.
Therc are two significant differences rrom axial flux gap motors by using the radial flux gap motor. ~irst, there is very little axial force produced by the inter~ction between the motor rotor magnets and the stator. Second, there is no rcstoring force with the radial flux gap motor. Radial support is provided by 10 mechanical bearings or dedicated radial magnet bearings.
It will be appreciated, thcn, that I have provided an improved sealless blood pump including m~netic bearings and thrust bearing suspension to minimi7~
thrombosis, and an impeller having a blood flow path therethrough which is calculated to minimi~.e hemolysis.
Various elements from the Figures 1-8 embodiment can be used in the Figures 11-20 embodiments. For example, magnets 34 illustrated in Figures 3 and 4 could bc used in impeller 74 of the Figures 11-20 cmbodiments. Also, rotor 18 of the Figures 11-20 embodiments could be supported using front thrust bearings such as tllrust bearing 41 of the Figures 1-8 emoodiment. Various other elements may be 20 employed in the Figures 11-20 cmbodiments from the Figures 1-8 embodiment.
Although illustrative embodiments of the invention have been shown and described, it is to be understood that various modifications and substitutions may be made by those skilled in the art without departing from the novel spirit and scope of the present invention.

Claims

1. A sealless blood pump, comprising:
a pump housing, having an inlet tube on one end and an impeller casing on the other end, said casing including a outlet;
a rotor mounted for rotation within said housing, said rotor having an elongated shaft portion and an impeller attached to said shaft portion, said impeller being located within said impeller casing;
radial magnetic bearings carried by said shaft portion, and radial magnetic bearings carried by said housing for maintaining said shaft portion of said rotor within said inlet tube of said housing;
a rotor motor, said motor including a plurality of permanent magnets carried by said impeller and a motor stator including an electrically conductive coil located within said housing; and a ring of back iron fixed to said casing to aid in completing a flux return path for said permanent magnets.

2. A sealless blood pump as defined in claim 1, in which said conductive coil and said back iron are fixed to said casing and said housing rearwardly of said impeller.

3. A sealless blood pump as defined in claim 1, in which said impeller has a forward side facing said inlet tube and a rear side downstream of said forward side, said conductive coil being located adjacent said rear side and said back iron ring being located outside of said conductive coil, within said housing, and fixed to said housing.

4. A sealless blood pump as defined in claim 3, including a second ring of back iron located on the forward side of said impeller and outside of said casing but inside of said housing, said second ring of back iron being fixed to said casing.

5. A sealless blood pump as defined in claim 4, including a second motor stator having an electrically conductive coil located on the forward side of said impeller outside of said casing but inside of said housing.

6. A sealless blood pump as defined in claim 5, in which said second ring of back iron is located forward of said second motor stator.

7. A sealless blood pump, comprising:
a pump housing, having an inlet tube on one end and an impeller casing on the other end, said casing including a outlet;
a rotor mounted for rotation within said housing, said rotor having an elongated shaft portion and an impeller attached to said shaft portion, said impeller being located within said impeller casing;
radial magnetic bearings carried by said shaft portion, and radial magnetic bearings carried by said housing for maintaining said shaft portion of said rotor within said inlet tube of said housing;
a rotor motor, said motor including a plurality of permanent magnets carried by said impeller and a motor stator including an electrically conductive coil located within said housing; and a ring of back iron carried by said impeller to aid in completing a flux return path for said permanent magnets, said ring of back iron being located at the forward side of said impeller and within said casing.

8. A sealless blood pump as defined in claim 7, in which said rotor motor is a radial flux gap motor and said plurality of permanent magnets located within said impeller extend in radial alignment with said motor stator.

9. A sealless blood pump as defined in claim 7, in which said ring of back iron is generally aligned with said permanent magnets and is located radially inside said permanent magnets.

10. A sealless blood pump as defined in claim 7, including permanent magnetic bearings located at the rear side of said impeller.

11. A sealless blood pump as defined in claim 10, in which said permanent magnetic bearings comprise first permanent magnets carried by said impeller at the rear end thereof and second permanent magnets downstream of saidfirst permanent magnets and fixed to said casing and housing.

12. A sealless blood pump, comprising:
a pump housing, having an inlet tube on one end and an impeller casing on the other end, said casing including an outlet;
a rotor mounted for rotation within said housing, said rotor having an elongated shaft portion and an impeller attached to said shaft portion, said impeller being located within said impeller casing;
radial magnetic bearings carried by said shaft portion, and radial magnetic bearings carried by said housing for maintaining said shaft portion of said rotor within said inlet tube of said housing;
a rotor motor, said motor including a plurality of permanent magnets carried by said impeller and a motor stator including an electrically conductive coil located within said housing; and a plurality of hydrodynamic thrust bearings located outside of the axis of rotation of said rotor.

13. A sealless blood pump as defined in claim 12, in which said hydrodynamic bearings are wedge-shaped.

14. A sealless blood pump as defined in claim 12, in which during rotation of said rotor and impeller, said hydrodynamic bearings are separated from said casing by a fluid film and are not in direct mechanical contact with said casing.

15. A sealless blood pump as defined in claim 12, in which said hydrodynamic bearings are arcuate and are located on the forward side of said impeller.

16. A sealless blood pump as defined in claim 12, in which at least some of said hydrodynamic thrust bearings are carried by said impeller.

17. A sealless blood pump as defined in claim 12, in which at least some of said hydrodynamic thrust bearings are carried by said casing.

18. A sealless blood pump as defined in claim 12, including a casing reinforcement member on the rear side of said casing, carrying said hydrodynamic bearings.

19. A sealless blood pump, comprising:
a pump housing, having an inlet tube on one end and an impeller casing on the other end, said casing including an outlet;
a rotor mounted for rotation within said housing, said rotor having an elongated shaft portion and an impeller attached to said shaft portion, said impeller being located within said impeller casing;
said impeller comprising a disk-shaped member having a central, upper face portion attached to one end of said shaft, said impeller having a plurality of blade sectors, each of said sectors being separated from an adjacent sector by achannel extending from said upper face portion to a lower face portion;
said channels serving as a fluid path through the impeller and functioning to increase the effective working area of the impeller; and a plurality of hydrodynamic thrust bearings located outside of the axis of rotation of said rotor.

20. A sealless blood pump as defined in claim 19, including radial magnetic bearings carried by said shaft portion, and radial magnetic bearings carried by said housing for maintaining said shaft portion of said rotor within said inlet tube of said housing.

21. A sealless blood pump as defined in claim 19, including a rotor motor, said motor including a plurality of permanent magnets carried by said impeller and a motor stator including an electrically conductive coil located within said housing.

22. A sealless blood pump as defined in claim 21, including a ring of back iron fixed to said casing to aid in completing a flux return path for said permanent magnets.

23. A sealless blood pump as defined in claim 22, including a second ring of back iron located on the forward side of said impeller and outside of said casing but inside of said housing, said second ring of back iron being fixed to said casing.

24. A sealless blood pump as defined in claim 21, including a second motor stator having an electrically conductive coil located on the forward side of said impeller outside of said casing but inside of said housing.

25. A sealless blood pump, comprising:
a pump housing, said housing having an inlet tube on one end and an impeller casing on the other end, said casing including a discharge tube;
a rotor mounted for rotation within said housing, said rotor having an elongated shaft portion and an impeller attached to said shaft portion, said impeller being located within said impeller casing and having a diameter between 1 inch and 1.5 inch;
radial magnetic bearings carried by said shaft portion, and radial magnetic bearings carried by said housing for maintaining said shaft portion of said rotor coaxially within said inlet tube of said housing, a primary flow channel for blood being provided by an annular volume between said shaft and said radialmagnetic bearings carried by said housing, said primary flow channel having a thickness between .06 inch and .1 inch.

26. A sealless blood pump as defined in claim 25, in which the axial length of the entire pump is 1.75 inch to 3.0 inch.

27. A sealless blood pump as defined in claim 25, in which the rotor diameter is .025 inch to 0.4 inch and the axial length of the impeller is 0.2 inch to 0.5 inch.

28. A sealless blood pump, comprising:
a pump housing, having an inlet tube on one end and an impeller easing on the other end, said casing including an outlet;
a rotor mounted for rotation within said housing, said rotor having an elongated shaft portion and an impeller attached to said shaft portion, said impeller being located within said impeller casing;
a rotor motor, said motor including a plurality of permanent magnets carried by said impeller, a first motor stator including an electrically conductive coil located within said housing and a second motor stator including an electrically conductive coil located within said housing;
said first motor stator and said second motor stator being located on opposite sides of said impeller.

29. A sealless blood pump as defined in claim 28, including a ring of back iron fixed to said casing to aid in completing a flux return path for said permanent magnets.

30. A sealless blood pump as defined in claim 29, including a second ring of back iron located on the opposite side of said impeller from said first mentioned ring of back iron, said second ring of back iron being fixed to said casing.

31. A sealless blood pump as defined in claim 30, in which said rings of back iron are located outside of said casing but inside of said housing.

32. A sealless blood pump as defined in claim 28, including a plurality of hydrodynamic thrust bearings located outside of the axis of rotation of said rotor.

33. A sealless blood pump, comprising:
an impeller comprising a disk-shaped member having a diameter between 1 inch and 1.5 inch;
an impeller shaft;
said impeller including a central, upper face portion attached to one end of said shaft;
said impeller having a plurality of blade sectors, each of said sectors being separated from an adjacent sector by a channel extending from said upper face portion to a lower face portion;
said impeller blade depth being between 0.2 inch and 0.5 inch;
said channels having a width between .05 inch to 0.2 inch;
said channels serving as a fluid path through the impeller and functioning to increase the effective working area of the impeller.

34. A sealless blood pump as defined in Claim 33, in which said impeller carries plurality of permanent magnets.

35. A sealless blood pump as defined in Claim 33, including a pump housing, having an inlet tube on one end and an impeller casing on the other end, said casing including an outlet; a rotor mounted for rotation within said housing, said rotor comprising said impeller shaft, said impeller being located within said impeller casing.

36. A sealless blood pump, comprising:
a pump housing, having an inlet tube on one end and an impeller casing on the other end, said casing including an outlet;
a rotor mounted for rotation within said housing, said rotor having an elongated shaft portion and an impeller attached to said shaft portion, said impeller being located within said impeller casing;
a rotor motor, said motor including a plurality of magnets carried by said impeller and a motor stator including an electrically conductive coil and a pole piece located within said housing, said magnets and said stator being positioned to function to transmit torque and to provide a restoring radial magnetic force between said stator and magnets that would tend to return a radially deflected impeller to a neutral position.

37. A sealless blood pump as defined in Claim 36, in which said pole piece comprises teeth extending from a ring of back iron.

38. A sealless blood pump as defined in Claim 36, including a plurality of hydrodynamic thrust bearings located outside of the axis of rotation of said rotor.

39 A sealless blood pump as defined in Claim 36, in which said impeller comprises a disc-shaped member having a central, upper face portion attached to one end of said shaft, said impeller having a plurality of blade sectors, each of said sectors being separated from an adjacent sector by a channel extending from said upper face portion to a lower face portion, said magnets being positioned within said blade sectors in radial alignment with said pole piece.