Abstract:
A pump drive unit has an openable housing that accommodates a disposable impeller unit which is pre-connected with tubing, while maintaining the tight tolerances and close spacing. A levitation system (magnets and sensors), drive motor and drive magnets, and control electronics are all re-usable and housed within relatively permanent structures. In one embodiment, a hinged top separates the levitating magnets to allow the impeller unit to be captured and retained with positional accuracy and in close proximity to the desired locations when the hinged top is closed. The top may be separated into sections covering unequal arcs to coincide with the organization of the magnetic subcomponents in the upper drive unit housing.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. provisional application Ser. No. 60/963,841, filed Aug. 7, 2007. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     The present invention relates in general to centrifugal pumps for pumping blood in an extracorporeal blood circuit, and, more specifically, to a pump with a magnetically levitated impeller and with disposable and reusable portions that is applicable to blood pumps for short-term heart assist, especially following heart surgery. 
     During cardiac bypass surgery, if a patient&#39;s heart is slowed or stopped for surgical repair, his or her blood must be artificially oxygenated and pumped through the body using an extracorporeal support circuit. Using this system, venous blood is diverted from entering the right chambers of the heart and is instead directed through a series of tubes, pumps, and filters, which provide fresh oxygen to the blood and return it to the body&#39;s systemic circulation at the aorta. The oxygenated blood is then circulated throughout the body. The circuit thus ensures that the patient continues to be nourished by oxygenated blood flow while the heart is unable to function. 
     In performing such a procedure, a complicated apparatus is required. One or two blood reservoirs, an oxygenator (possibly combined with a heat exchanger), a blood pump, and multiple tubes to connect the various components are needed and must be assembled and arranged before surgery may begin. Typically a significant amount of time must be spent just prior to surgery to accomplish the set-up, and great attention must be paid to the details of this complicated task. In order to ease this task, a nearly complete support circuit is often assembled by the manufacturer in a sterile condition and packaged in a manner that protects sterility until the time that it is needed for a procedure. An assembly pack having a frame for supporting the individual disposable processing elements (e.g., filters, pump, oxygenator) and the interconnecting tubing is shown in U.S. Pat. No. 6,811,749, which is incorporated herein by reference in its entirety. Such a frame pack provides for quick set-up and integration into a complete extracorporeal support system, thus enhancing operating room efficiency. 
     Most of the components of the extracorporeal blood circuit are disposed of following the surgical procedure as medical waste since they have been exposed to the blood of the patient. Even relatively more expensive components such as a centrifugal pump are disposed of because the difficulty and cost of re-sterilization would be too great. 
     Centrifugal blood pumps are increasingly used in artificial heart/lung units for extracorporeal blood circulation. Centrifugal pumps of the magnetic coupling type wherein a driving torque from an external motor is transmitted to an impeller through magnetic coupling are commonly used because the physical communication between the blood chamber of the pump and the exterior can be completely excluded and invasion of bacteria is prevented. The centrifugal blood pump includes a chamber having a blood inlet port and a blood outlet port and an impeller rotatably accommodated in the housing to increase the difference between inlet and outlet fluid pressure by means of centripetal acceleration generated during its rotation. The impeller has one or more permanent magnets disposed thereon which are acted upon by attracting magnets of a drive motor that is disposed adjacent to the impeller chamber. Typically, the impeller rotates without contacting the housing by magnetically levitating above the bottom of the chamber. A separate set of levitating magnets that may include electromagnets is disposed axially and/or radially relative to the impeller in order to provide a precisely controlled levitating field. Position sensors are used to provide position feedback to a controller which drives the electromagnets. Tight tolerances and close distances between the impeller and the levitating magnets and sensors must be maintained in order to achieve proper pump functioning. Examples of magnetically levitated centrifugal blood pumps include U.S. Pat. Nos. 6,575,717; 6,589,030; 7,212,550; and 7,128,538, and U.S. patent application publication 2005/0014991 A1, all of which are incorporated herein by reference in their entirety. 
     It is often preferable to locate the levitating magnets and position sensors above (i.e., at the top of) the impeller chamber, opposite from the driving motor, especially when device volume is to be minimized, as in an implant application. However, with the impeller chamber sandwiched between other structures, it has not generally been segregated as a separate disposable element. Making a disposable impeller chamber (i.e., pump head) which is insertable into a nondisposable pump drive unit is especially difficult with drive components above and below the pump head, because of the desire to have all the tubing for the circuit pre-connected to the pump as part of a frame pack. Therefore, centrifugal pumps of this type have typically been used for long-term applications and have been disposed of with the rest of the hardware components. 
     SUMMARY OF THE INVENTION 
     The invention provides an openable pump drive unit housing that accommodates a disposable impeller unit which is pre-connected with tubing, while maintaining the tight tolerances and close spacing that are required when the unit is closed for use. The levitation system (magnets and sensors), drive motor and magnets, and control electronics are all re-usable and housed within relatively permanent structures. In one embodiment, a hinged top separates the levitating magnets to allow the impeller unit to be captured and retained with positional accuracy and in close proximity to the desired locations when the hinged top is closed. The top may be separated into sections covering unequal arcs to coincide with the organization of the magnetic subcomponents in the upper drive unit housing. 
     In one aspect of the invention, a blood pump comprises a disposable pump head having an inlet and an outlet formed in a sealed impeller unit housing. The pump head further comprises an impeller contained within the sealed impeller unit housing having a top disk and a bottom disk with impeller blades mounted therebetween. The top and bottom disks have respective magnetic structures. A re-usable levitation/drive unit is provided having relatively movable upper and lower housing sections. These housing sections are movable to an open position for allowing insertion of the disposable pump head and a closed position for retaining the disposable pump head in a predetermined position. The re-usable levitation/drive unit includes a levitation magnet in one of the housing sections and a drive magnet in the other one of the housing sections. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top, perspective view of one embodiment of a pump system with a housing section opened and an impeller unit inserted. 
         FIG. 2  is a side, perspective view of the pump system of  FIG. 1  with the impeller unit removed from the housing section. 
         FIG. 3  is a rear, perspective view of the pump system of  FIG. 1  with the impeller unit exploded. 
         FIG. 4  is a bottom, perspective view of the pump system of  FIG. 1 . 
         FIG. 5  is a front, perspective view with the housing section closed. 
         FIG. 6  is a top, perspective exploded view of an impeller unit (pump head). 
         FIG. 7  is a bottom, perspective exploded view of a pump head. 
         FIG. 8  is a top, perspective exploded view of an impeller section. 
         FIG. 9  is a bottom, perspective view of the exploded impeller of  FIG. 8 . 
         FIG. 10  is a cross-sectional view through the pump head. 
         FIG. 11  is a cross-sectional view through an alternative embodiment of a bottom disk and magnet portion of the impeller section. 
         FIG. 12  is a top view of the magnet disk of  FIG. 11 . 
         FIG. 13  is a cross-sectional view through an embodiment of the top disk of an impeller section including a magnet portion. 
         FIG. 14  is an exploded view of an alternative embodiment of an impeller section. 
         FIG. 15  is a side view of an alternative embodiment of the housing section in an open state. 
         FIG. 16  is a perspective view of the pump system of  FIG. 15  in a closed state. 
         FIG. 17  shows a pump system pre-connected to tubing for an extracorporeal blood circuit. 
         FIGS. 18-21  illustrate other alternative embodiments for providing an openable housing section. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The invention utilizes a magnetic levitation (mag-lev) type of pump architecture as is used in the implantable DuraHeart® left ventricular assist system available from Terumo Heart, Inc., of Ann Arbor, Mich. Although it may be used in extracorporeal blood circuit applications, the control system for obtaining levitation and a desired rate of flow through the pump can be substantially similar to the known controller utilized in the DuraHeart® system. However, the present invention uses a plastic cassette for an impeller chamber with inlet and outlet ports and an internally-located plastic impeller disk with integral magnets to form a disposable impeller unit (i.e., blood pump). The disposable unit may be substantially disk-shaped about 3 inches in diameter and one inch tall. An increased pump impeller diameter over the implantable DuraHeart® version enables higher outlet pressure capability and overall size of the unit does not need to be minimized in the disposable application. The non-disposable components of the invention are contained in an openable housing so that the disposable unit is removable. The housing may open and close using different constructions, such as a sideways splittable top, a splittable and raisable top, and a clamshell, for example. 
     Referring to  FIG. 1 , one embodiment of the invention includes a pump system  10  having a disposable impeller unit (or pump head)  11  and a re-usable levitation/drive unit  12 . Impeller unit  11  has an inlet port  13 , an outlet port  14 , and an impeller section  15  which preferably includes a plurality of impeller blades. Levitation/drive unit  12  includes a support rod  16  to which its lower housing  17  is attached. Housing  17  contains a drive motor  18  which is driven by an externally generated motor drive signal from a controller (not shown). Drive motor  18  has a spinning rotor carrying a plurality of magnets that magnetically couple with magnets in the impeller section. Impeller unit  11  fits into lower housing  17  so that the spinning rotor and impeller section  15  are located in proper relationship. In this disposable device version, where external volume constraints are reduced, stronger driving electromagnets could be used than in an implantable version to enable greater separation between driving and driven magnets. This would allow thicker housing wall sections for a more robust and reliable pump head cassette. 
     Sideways jaws  20  and  21  hingedly extend from support rod  16  and contain an electronic assembly  22  that includes levitation magnets (both permanent magnets and electromagnets) and position sensors. Jaws  20  and  21  may comprise discrete magnets and sensors embedded within a plastic molded matrix. Alternatively, they could be fabricated using a layered material process to embed sensors and magnets and to construct wiring for electromagnets or signal transmission within a solid body, such as the Ultrasonic Consolidation technology used by Solidica, Inc., of Ann Arbor, Mich. This type of CNC-based fabrication provides advantages to the drive unit housing of added ruggedness, reliability, and overall physical integrity which are of high importance in a heart-assist device. Other advantages include precise locations of magnetic material, highly consistent magnetic fields, and improved consistency of unit-to-unit performance. The driving motor/rotor may also be fabricated in this way to obtain added precision of built-in magnetic regions. 
     Control electronics (e.g., for calculating and generating precisely determined currents needed within the various electromagnets to properly levitate the impeller section in vertical and axial center positions) may also be housed within jaws  20  and  21  or support rod  16 , or they may be remotely located. In any case, a cable (not shown) is provided through rod  16  for supplying power. The cable may also carry operator command (e.g., pump speed) and/or other control signals. 
     Jaws  20  and  21  spread apart (e.g., rotate about rod  16 ) in order to provide space for impeller unit  11  to be placed within lower housing  17 . Then jaws  20  and  21  are closed into an engaged position which captures inlet port  13  between jaws  20  and  21  and locates the levitating magnets and position sensors in a predetermined spatial relationship with impeller section  15 . In addition to rotation in the plane perpendicular to rod  16  for spreading apart, it may also be desirable to provide for movement of jaws  20  and  21  or certain components thereof up and down (along the longitudinal axis of rod  16 ) so that they can be clamped in precise and close proximity to impeller unit  11  when in the closed position. Up/down and sideways motions can be used simultaneously so that jaws  20  and  21  follow slanted paths by providing appropriate cam surfaces within the supporting hinges in rod  16 . These hinge and translation combinations can also be combined with various rigid linkages to better control both the elevated/offset and lowered/locked positioning of jaws  20  and  21  in the interest of minimizing impeller unit  11  installation time and effort. 
     The levitating magnets and sensors contained within jaws  20  and  21  are deployed around 360° with respect to the central rotational axis of the impeller. Individual electromagnets each occupy a respective arcuate segment of the 360° total and are closely packed together with the position sensors. Typically, potential sites for separation points to allow the jaws to spread apart are not diametrically opposed (i.e., the jaws cannot be broken into two 180° segments. Instead, there is more likely a three-fold symmetry which allows the jaws to separate into 120°, 240° and smaller segments. With use of the current DuraHeart® levitation control electromagnet subassemblies, the preferred included angle for the smaller segment is 86°. 
       FIGS. 2-4  show impeller unit  11  removed from lower housing  17 . In order to fix impeller unit  11  in the proper orientation, a notch  23  formed in the side wall of lower housing  17  receives outlet port  14 . In addition, a centrally-located post  24  raises from lower housing  17  to mate with a matching depression  25  in the bottom of impeller unit  11  which is coaxial with inlet port  13 . 
       FIG. 5  shows the pump system in a closed position with the impeller unit captured in position so that the necessary tight tolerances and close spacing between magnets are achieved. 
       FIG. 6  shows a top, front, perspective exploded view of impeller unit  11 . A bottom cover  30  and a top cover  31  are joined to create an impeller pumping chamber for retaining impeller section  15 . Impeller section  15  includes bottom and top disks  32  and  33  with a plurality of impeller blades  34  disposed therebetween. A hole  35  in disk  33  distributes blood from inlet port  13  to impeller blades  34 . When impeller blades  34  are rotated about the impeller central axis, they generate a radial pressure gradient that produces a pressurized blood flow between inlet port  13  and outlet port  14 . 
     Impeller section  15  is preferably levitated by interaction of an external magnetic field with magnetic structures in top disk  33 , and is preferably rotated by interaction of another external magnetic field with magnets in bottom disk  32 . More specifically, attraction to a levitating magnetic field generated in the upper housing levitates impeller section  15 . A motor-driven circular array of magnets within the lower housing section transfers rotational energy to impeller section  15  by attraction/repulsion coupling with the magnets in bottom disk  32 . Other arrangements are also possible. 
       FIG. 7  shows a bottom, front, perspective exploded view of impeller unit  11 . Bottom disk  32  has a plurality of permanent magnets  36  mounted (e.g., glued) around the periphery of its bottom side or embedded within disk  32  by integral molding. They are preferably glued or embedded in such a manner that adjacent magnets have alternating magnetic polarities all the way around the periphery. In this embodiment, magnets on a rotor driven by the drive motor interact with magnets  36  from below in order to cause impeller section  15  to also rotate. 
       FIGS. 8 and 9  show an alternative embodiment of impeller section  15 ′. Top disk  33  is preferably formed separately from blades  34  and is adhesively bonded to them. Blades  34  may be integrally molded with bottom disk  32  or they may be welded or adhesively bonded in place. A magnet ring  37  is mounted in a toroidal recess  39  formed on the lower side of bottom disk  32  and is retained in recess  39  by a cover plate  38 . Magnet ring  37  may have separate magnet pieces (not shown) glued to it or embedded within it, for example. Cover plate  38  may be glued or welded to bottom disk  32 . 
       FIG. 10  is a vertical cross section through the housing and pump head wherein the impeller section is constructed according to the embodiment of  FIGS. 8 and 9 . 
       FIG. 11  shows an alternative embodiment for bottom disk  32  wherein the magnets are formed in a continuous disk made of a magnetic material with appropriate magnetic domains formed within it. Thus, a toroidal plastic channel  40  is shown in cross section receiving a magnet disk  41 . A cover  42  is joined (e.g., glued or ultrasonically welded) to channel  40  so that magnet disk  41  is captured in place. Magnet disk  41  is preferably formed of a molded magnetic material such as fine grained rare earth (e.g., neodymium) magnetic material in a plastic matrix. The magnetic particles are present throughout the disk and are initially magnetized in random directions. Permanently magnetized areas  43  as shown in  FIG. 12  are produced by applying high-flux magnetic fields to the disk while located in a fixture (e.g., containing electrodes energized by capacitive discharges so that strong, precisely located permanent magnetic fields having the desired polarity are created in disk  41 ). 
       FIG. 13  shows a cross section of one embodiment of top disk  33 . As is known in the art, it is desirable to create a uniform levitating magnetic field using a magnetic sheet at the top of the impeller. Thus, a circular plastic channel  44  receives a magnetic disk  45  that is locked in place by a cover  42 . Disk  45  may comprise a metal sheet or may comprise a molded magnetic material having its magnetic domains appropriately oriented. Rather than being embedded within top disk  33 , a magnetic disk  47  can be attached directly to top disk  33  as shown in  FIG. 14 . 
       FIGS. 15 and 16  show an alternative embodiment of the levitation/drive unit housing section using a re-usable clam shell housing to retain a disposable cassette (i.e., impeller unit). A lower clam shell  50  is joined to an upper clam shell  51  by a hinge  52 . A disposable cassette  53  sets into lower clam shell  50  when the shell is in the open position ( FIG. 15 ) and is clamped between lower and upper clam shells  50  and  51  when in the closed position ( FIG. 16 ). Cassette  53  and lower clam shell  50  may have the same overall shapes as in the previous embodiments. Upper clam shell  51  may be a continuous ring since it receives inlet port  54  axially. 
     The clam shell embodiment of  FIGS. 15 and 16  does not accommodate a pump head cassette that is pre-installed with closed loop tubing of a frame pack, for example, because of the need to insert inlet port  54  axially through upper clam shell  51 . However, a clam shell is useful in other applications of extracorporeal blood circuits, such as a temporary cardiac assist application as shown in  FIG. 17 . A venous cannula  55  for removing blood from a patient is coupled to inlet port  54  by a tube  56 . An arterial cannula  57  is coupled by a tube  58  to pump outlet port  60 . Since the tubing does not form a closed loop, cannula  55  and tube  56  can be “snaked” through the central hole in upper clam shell  51 , and then cassette  53  can be closed between clam shells  50  and  51 . Advantageously, a single latching/locking mechanism (not shown) can securely hold this type of assembly in its closed position. Disposable plastic shields can be provided on the clam shells, such as a shield  61  on upper clam shell  51 , to protect them and their internal components from the sterile or post-use blood-contaminated cannulae. As represented in  FIGS. 15 and 16 , certain features of the pump head cassette, such as the outlet and associated housing details, tend to provide indexing features useful for proper rotational positioning within the drive unit housing. Features of this type may also be exaggerated axially and/or radially to better enable easier and more rapid pump system assembly. Alternatively, the drive unit housing may be modified to reduce or eliminate the need for pump head indexing to a preferred rotational position. Axial movement of magnet and sensor elements into close proximity with the impeller unit housing also provides lockdown security for the entire assembly, as the impeller unit becomes mechanically trapped in its operating position. This adds a type of attitude insensitivity to the overall operating unit, allowing rapid and secure placement into the desired location against or near the patient. 
       FIG. 18  shows an embodiment wherein the top cover containing the levitation magnets and position sensors is separated into a section  65  and a section  66 . Section  65  is attached by a hinge  67  to lower housing  68  so that section  65  rotates upward and away from lower housing  68  to allow insertion of the disposable impeller unit. A guide rod  70  extends vertically from lower housing  68  through a receiver  71  fixedly mounted to the side of section  66 . Section  66  slides vertically upward so that the impeller unit can be installed or removed. A locking mechanism (not shown) may be provided to lock sections  65  and  66  in place when they are closed over the impeller unit. 
       FIG. 19  shows an embodiment wherein the top cover containing the levitation magnets and position sensors is separated into a section  75  and a section  76 . Section  75  is attached by a hinge  77  to lower housing  78  so that section  75  rotates upward and away from lower housing  78  to allow insertion of the disposable impeller unit. Section  76  is attached by a hinge  80  to lower housing  78  so that section  76  rotates upward and away from lower housing  78  to allow insertion of the disposable impeller unit. One or both of these hinges may be part of extension arms, making insertion of the disposable impeller unit faster and easier by moving the upper housing section(s) farther away from their common axis. A locking mechanism (not shown) may be provided to lock sections  75  and  76  in place when they are closed over the impeller unit. 
       FIG. 20  shows another alternative embodiment wherein a support rod  81  mounted to a lower housing  82  retains a first upper housing section  83  for vertical movement and a second upper housing section  84  for rotational movement. 
       FIG. 21  illustrates an impeller locking feature obtained by providing a flange  90  on inlet port  91  of an impeller unit  92 . When impeller unit  92  is placed within lower housing  93  and when upper housing sections  94  and  95  are rotated into a closed position, a pair of tabs  96  and  97  are captured beneath flange  90 . Consequently, the top of the impeller unit is constrained from upward and downward movement that could otherwise result from pressure changes within the impeller unit. If allowed to occur, such axial distortion might interfere with the performance of the levitating magnets or position sensors, or with impeller rotation. Similarly related features on the bottom of the impeller unit and also on and/or within the drive unit housing may constrain similar possible movements below the impeller.