Abstract:
A method for assisting blood circulation in a patient includes drawing a flow of blood from a patient&#39;s heart into a blood flow channel formed by a housing. The flow of blood is passed through a motor stator to a rotor disposed within the blood flow channel. The motor stator is arranged circumferentially around the blood flow channel. The rotor has permanent magnetic poles for magnetic levitation and rotation of the rotor. The motor stator is controlled to act as a radial bearing for magnetic levitation of the rotor and to rotate the rotor within the blood flow channel. The rotor is levitated within the blood flow channel in the direction of the rotor axis of rotation via passive magnetic interaction between the rotor and the motor stator. The flow of blood is output from the blood flow channel to the patient.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. application Ser. No. 14/735,990, filed Jun. 10, 2015, and titled “Implantable Blood Pump,” which application is a continuation application of U.S. application Ser. No. 13/212,813, filed Aug. 18, 2011, and titled “Implantable Blood Pump,” which application claims the benefit of U.S. Provisional Application Ser. No. 61/375,504, filed Aug. 20, 2010, and titled “Implantable Blood Pump,” the entire contents of which are incorporated herein by reference in their entirety. 
     
    
     FIELD 
       [0002]    This description relates to implantable blood pumps. 
       BACKGROUND 
       [0003]    Ventricular assist devices, known as VADs, are implantable blood pumps used for both short-term and long-term applications where a patient&#39;s heart is incapable of providing adequate circulation. For example, a patient suffering from heart failure may use a VAD while awaiting a heart transplant. In another example, a patient may use a VAD while recovering from heart surgery. Thus, a VAD can supplement a weak heart or can effectively replace the natural heart&#39;s function. VADs can be implanted in the patient&#39;s body and powered by an electrical power source outside the patient&#39;s body. 
       BRIEF SUMMARY 
       [0004]    In one general aspect, an implantable blood pump includes a housing and a blood flow conduit. Within the housing, the blood pump includes a stator located about the blood flow conduit and a magnetically-levitated rotor. 
         [0005]    In another general aspect, an implantable blood pump includes a housing defining an inlet opening and an outlet opening. Within the housing, a dividing wall defines a blood flow conduit extending between the inlet opening and the outlet opening of the housing. The blood pump has a rotary motor that includes a stator and a rotor. The stator is disposed within the housing circumferentially about the dividing wall such that the inner blood flow conduit extends through the stator. 
         [0006]    In another general aspect, an implantable blood pump includes a puck-shaped housing having a first face defining an inlet opening, a peripheral sidewall, and a second face opposing the first face. The blood pump has an internal dividing wall defining an inner blood flow conduit extending between the inlet opening and an outlet opening of the housing. The puck-shaped housing has a thickness from the first face to the second face that is less than a width of the housing between opposing portions of the peripheral sidewall. The blood pump also has a motor having a stator and a rotor. The stator is disposed in the housing circumferentially about the blood flow conduit and includes magnetic levitation components operable to control an axial position and a radial position of the rotor. The rotor is disposed in the inner blood flow conduit and includes an impeller operable to pump blood from the inlet opening to the outlet opening through at least a portion of the magnetic levitation components of the stator. 
         [0007]    Implementations of the above aspects may include one or more of the following features. For example, the stator is disposed circumferentially about at least a part of the rotor and is positioned relative to the rotor such that in use blood flows within the blood flow conduit through the stator before reaching the rotor. The rotor has permanent magnetic poles for magnetic levitation of the rotor. A passive magnetic control system is configured to control an axial position of the rotor relative to the stator, and an active electromagnetic control system is configured to radially center the rotor within the inner blood flow conduit. An electromagnetic control system controls at least one of a radial position and an axial position of the rotor relative to the stator, and the electromagnetic control system has control electronics located within the housing about the dividing wall. 
         [0008]    The control electronics are located between the inlet opening and the stator. The control electronics can be configured to control the active magnetic control system. The rotor has only one magnetic moment. The stator includes a first coil for driving the rotor and a second coil for controlling a radial position of the rotor, and the first coil and the second coil are wound around a first pole piece of the stator. The housing has a first face that defines the inlet opening, a second face opposing the first face, and a peripheral wall extending from the first face to the second face. The housing includes a rounded transition from the second face to the peripheral wall. The housing defines a volute located such that in use blood flows within the blood flow conduit through the stator before reaching the volute. The volute can be located between the stator and the second face. The housing can also include a cap that includes the second face, defines at least part of the volute, and defines at least part of the outlet. The cap is engaged with the peripheral wall of the housing. The housing also includes an inlet cannula extending from the first face and in fluid communication with the inlet opening. The inlet cannula can be inserted into the patient&#39;s heart. The outlet opening is defined in the second face and/or the peripheral wall. A thickness of the housing between the first face and the second face is less than a width of the housing. 
         [0009]    In another general aspect, a method includes inserting a puck-shaped blood pump housing into a patient&#39;s body. The blood pump is inserted such that an opening defined in a first flat face of the housing that is proximate to a stator of the blood pump faces the patient&#39;s heart. Additionally, the blood pump is inserted such that a second rounded face of the housing that is proximate to an impeller of the blood pump faces away from the patient&#39;s heart. The first face is disposed against a portion of the patient&#39;s heart such that the second face of the housing faces away from the heart of the patient. In some implementations, the method includes inserting an inlet cannula of the housing into the patient&#39;s heart. 
         [0010]    In another general aspect, making a blood pump includes assembling a motor stator and control electronics in a puck-shaped housing circumferentially about an internal dividing wall. The internal dividing wall defines an inner blood flow conduit that extends from an inlet opening to an outlet opening of the housing. The stator is assembled in the housing such that the inner blood flow conduit extends through the motor stator. Disposed within the inner blood flow conduit is a magnetically-levitated rotor. The rotor is surrounded by the stator such that impeller blades carried by the rotor are downstream of the stator from the inlet opening. In use, the impeller pumps blood from the inlet opening to the outlet opening through the stator. 
         [0011]    Implementations may include one or more of the following features. For example, the rotor has only one magnetic moment. The stator includes at least one first coil for driving the rotor and at least one second coil for controlling a radial position of the rotor, the at least one first coil and the at least one second coil being wound around a first pole piece of the stator. The housing includes a first face that defines the inlet opening, and further comprising engaging an end cap with a peripheral wall of the housing, the end cap including a second face, defining at least part of a volute, and defining at least part of the outlet opening. The housing includes a rounded transition from the second face to the peripheral wall. The housing further includes an inlet cannula extending from the first face and in fluid communication with the inlet opening. A thickness of the housing between the first face and the second face is less than a width of the housing. 
         [0012]    In another general aspect, a method of pumping blood includes magnetically rotating a centrifugal pump impeller of a blood pump device to draw blood from a patient&#39;s heart through an inlet opening of a housing of the blood pump device into an inner blood flow conduit within a stator in the housing, through the inner blood flow conduit, and through an outlet opening of the housing. The method includes selectively controlling a radial position of the impeller within the inner blood flow conduit. 
         [0013]    The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is an illustration of a blood pump in a use position implanted in a patient&#39;s body. 
           [0015]      FIG. 2  is a cross-sectional view of the blood pump of  FIG. 1 . 
           [0016]      FIG. 3  is a partial cut-away perspective view of a stator of a blood pump. 
           [0017]      FIG. 4  is a bottom perspective view of a blood pump. 
           [0018]      FIG. 5  is a top perspective view of the blood pump of  FIG. 4 . 
           [0019]      FIG. 6  is a front view of the blood pump of  FIG. 4 . 
           [0020]      FIG. 7  is a back view of the blood pump of  FIG. 4 . 
           [0021]      FIG. 8  is a right side view of the blood pump of  FIG. 4 . 
           [0022]      FIG. 9  is a left side view of the blood pump of  FIG. 4 . 
           [0023]      FIG. 10  is a bottom view of the blood pump of  FIG. 4 . 
           [0024]      FIG. 11  is a top view of the blood pump of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    With reference to  FIGS. 1 and 4-11 , a left ventricular assist blood pump  100  having a puck-shaped housing  110  is implanted in a patient&#39;s body with a first face  111  of the housing  110  positioned against the patient&#39;s heart H and a second face  113  of the housing  110  facing away from the heart H. The first face  111  of the housing  110  includes an inlet cannula  112  extending into the left ventricle LV of the heart H. The second face  113  of the housing  110  has a chamfered edge  114  to avoid irritating other tissue that may come into contact with the blood pump  100 , such as the patient&#39;s diaphragm. To construct the illustrated shape of the puck-shaped housing  110  in a compact form, a stator  120  and electronics  130  of the pump  100  are positioned on the inflow side of the housing toward first face I 11 , and a rotor  140  of the pump  100  is positioned along the second face  113 . This positioning of the stator  120 , electronics  130 , and rotor  140  permits the edge  114  to be chamfered along the contour of the rotor  140 , as illustrated in at least  FIGS. 2, 4, and 6-9 , for example. 
         [0026]    Referring to  FIG. 2 , the blood pump  100  includes a dividing wall  115  within the housing  110  defining a blood flow conduit  103 . The blood flow conduit  103  extends from an inlet opening  101  of the inlet cannula  112  through the stator  120  to an outlet opening  105  defined by the housing  110 . The rotor  140  is positioned within the blood flow conduit  103 . The stator  120  is disposed circumferentially about a first portion  140   a  of the rotor  140 , for example about a permanent magnet  141 . The stator  120  is also positioned relative to the rotor  140  such that, in use, blood flows within the blood flow conduit  103  through the stator  120  before reaching the rotor  140 . The permanent magnet  141  has a permanent magnetic north pole N and a permanent magnetic south pole S for combined active and passive magnetic levitation of the rotor  140  and for rotation of the rotor  140 . The rotor  140  also has a second portion  140   b  that includes impeller blades  143 . The impeller blades  143  are located within a volute  107  of the blood flow conduit such that the impeller blades  143  are located proximate to the second face  113  of the housing. 
         [0027]    The puck-shaped housing  110  further includes a peripheral wall  116  that extends between the first face  111  and a removable cap  118 . As illustrated, the peripheral wall  116  is formed as a hollow circular cylinder having a width W between opposing portions of the peripheral wall  116 . The housing  110  also has a thickness T between the first face I 11  and the second face  113  that is less than the width W. The thickness T is from about 0.5 inches to about 1.5 inches, and the width W is from about 1 inch to about 4 inches. For example, the width W can be approximately 2 inches, and the thickness T can be approximately 1 inch. 
         [0028]    The peripheral wall  116  encloses an internal compartment  117  that surrounds the dividing wall  115  and the blood flow conduit  103 , with the stator  120  and the electronics  130  disposed in the internal compartment  117  about the dividing wall  115 . The removable cap  118  includes the second face  113 , the chamfered edge  114 , and defines the outlet opening  105 . The cap  118  can be threadably engaged with the peripheral wall  116  to seal the cap  118  in engagement with the peripheral wall  116 . The cap  118  includes an inner surface  118   a  of the cap  118  that defines the volute  107  that is in fluid communication with the outlet opening  105 . 
         [0029]    Within the internal compartment  117 , the electronics  130  are positioned adjacent to the first face  111  and the stator  120  is positioned adjacent to the electronics  130  on an opposite side of the electronics  130  from the first face  111 . The electronics  130  include circuit boards  131  and various components  133  carried on the circuit boards  131  to control the operation of the pump  100  by controlling the electrical supply to the stator  120 . The housing  110  is configured to receive the circuit boards  131  within the internal compartment  117  generally parallel to the first face Ill for efficient use of the space within the internal compartment  117 . The circuit boards also extend radially-inward towards the dividing wall  115  and radially-outward towards the peripheral wall  116 . For example, the internal compartment  117  is generally sized no larger than necessary to accommodate the circuit boards  131 , and space for heat dissipation, material expansion, potting materials, and/or other elements used in installing the circuit boards  131 . Thus, the external shape of the housing  110  proximate the first face  111  generally fits the shape of the circuits boards  131  closely to provide external dimensions that are not much greater than the dimensions of the circuit boards  131 . 
         [0030]    With continued reference to  FIG. 2  and with reference to  FIG. 3 , the stator  120  includes a back iron  121  and pole pieces  123   a - 123   f  arranged at intervals around the dividing wall  115 . The back iron  121  extends around the dividing wall  115  and is formed as a generally flat disc of a ferromagnetic material, such as steel, in order to conduct magnetic flux. The back iron  121  is arranged beside the control electronics  130  and provides a base for the pole pieces  123   a - 123   f.    
         [0031]    Each of the pole piece  123   a - 123   f  is L-shaped and has a drive coil  125  for generating an electromagnetic field to rotate the rotor  140 . For example, the pole piece  123   a  has a first leg  124   a  that contacts the back iron  121  and extends from the back iron  121  towards the second face  113 . The pole piece  123   a  also has a second leg  124   b  that extends from the first leg  124   a  towards the dividing wall  115  proximate the location of the permanent magnet  141  of the rotor  140 . Each of the pole pieces  123   a - 123   f  also has a levitation coil  127  for generating an electromagnetic field to control the radial position of the rotor  140 . 
         [0032]    Each of the drive coils  125  and the levitation coils  127  includes multiple windings of a conductor around the pole pieces  123   a - 123   f  Particularly, each of the drive coils  125  is wound around two adjacent ones of the pole pieces  123 , such as pole pieces  123   d  and  123   e,  and each levitation coil  127  is wound around a single pole piece. The drive coils  125  and the levitation coils  127  are wound around the first legs of the pole pieces  123 , and magnetic flux generated by passing electrical current though the coils  125  and  127  during use is conducted through the first legs and the second legs of the pole pieces  123  and the back iron  121 . The drive coils  125  and the levitation coils  127  of the stator  120  are arranged in opposing pairs and are controlled to drive the rotor and to radially levitate the rotor  140  by generating electromagnetic fields that interact with the permanent magnetic poles S and N of the permanent magnet  141 . Because the stator  120  includes both the drive coils  125  and the levitation coils  127 , only a single stator is needed to levitate the rotor  140  using only passive and active magnetic forces. The permanent magnet  141  in this configuration has only one magnetic moment and is formed from a monolithic permanent magnetic body  141 . For example, the stator  120  can be controlled as discussed in U.S. Pat. No. 6,351,048, the entire contents of which are incorporated herein by reference. The control electronics  130  and the stator  120  receive electrical power from a remote power supply via a cable  119  ( FIG. 1 ). 
         [0033]    The rotor  140  is arranged within the housing  110  such that its permanent magnet  141  is located upstream of impeller blades in a location closer to the inlet opening  101 . The permanent magnet  141  is received within the blood flow conduit  103  proximate the second legs  124   b  of the pole pieces  123  to provide the passive axial centering force though interaction of the permanent magnet  141  and ferromagnetic material of the pole pieces  123 . The permanent magnet  141  of the rotor  140  and the dividing wall  115  form a gap  108  between the permanent magnet  141  and the dividing wall  115  when the rotor  140  is centered within the dividing wall  115 . The gap  108  may be from about 0.2 millimeters to about 2 millimeters. For example, the gap  108  is approximately 1 millimeter. The north permanent magnetic pole N and the south permanent magnetic pole S of the permanent magnet  141  provide a permanent magnetic attractive force between the rotor  140  and the stator  120  that acts as a passive axial centering force that tends to maintain the rotor  140  generally centered within the stator  120  and tends to resist the rotor  140  from moving towards the first face Ill or towards the second face  113 . When the gap  108  is smaller, the magnetic attractive force between the permanent magnet  141  and the stator  120  is greater, and the gap  108  is sized to allow the permanent magnet  141  to provide the passive magnetic axial centering force having a magnitude that is adequate to limit the rotor  140  from contacting the dividing wall  115  or the inner surface  118   a  of the cap  118 . The rotor  140  also includes a shroud  145  that covers the ends of the impeller blades  143  facing the second face  113  that assists in directing blood flow into the volute  107 . The shroud  145  and the inner surface  118   a  of the cap  118  form a gap  109  between the shroud  145  and the inner surface  118   a  when the rotor  140  is levitated by the stator  120 . The gap  109  is from about 0.2 millimeters to about 2 millimeters. For example, the gap  109  is approximately 1 millimeter. 
         [0034]    As blood flows through the blood flow conduit  103 , blood flows through a central aperture  141  a formed through the permanent magnet  141 . Blood also flows through the gap  108  between the rotor  140  and the dividing wall  115  and through the gap  109  between the shroud  145  and the inner surface  108   a  of the cap  118 . The gaps  108  and  109  are large enough to allow adequate blood flow to limit clot formation that may occur if the blood is allowed to become stagnant. The gaps  108  and  109  are also large enough to limit pressure forces on the blood cells such that the blood is not damaged when flowing through the pump  100 . As a result of the size of the gaps  108  and  109  limiting pressure forces on the blood cells, the gaps  108  and  109  are too large to provide a meaningful hydrodynamic suspension effect. That is to say, the blood does not act as a bearing within the gaps  108  and  109 , and the rotor is only magnetically-levitated. 
         [0035]    Because the rotor  140  is radially suspended by active control of the levitation coils  127  as discussed above, and because the rotor  140  is axially suspended by passive interaction of the permanent magnet  141  and the stator  120 , no rotor levitation components are needed proximate the second face  113 . The incorporation of all the components for rotor levitation in the stator  120  (i.e., the levitation coils  127  and the pole pieces  123 ) allows the cap  118  to be contoured to the shape of the impeller blades  143  and the volute  107 . Additionally, incorporation of all the rotor levitation components in the stator  120  eliminates the need for electrical connectors extending from the compartment  117  to the cap  118 , which allows the cap to be easily installed and/or removed and eliminates potential sources of pump failure. 
         [0036]    In use, the drive coils  125  of the stator  120  generates electromagnetic fields through the pole pieces  123  that selectively attract and repel the magnetic north pole N and the magnetic south pole S of the rotor  140  to cause the rotor  140  to rotate within stator  120 . As the rotor  140  rotates, the impeller blades  143  force blood into the volute  107  such that blood is forced out of the outlet opening  105 . Additionally, the rotor draws blood into pump  100  through the inlet opening  101 . As blood is drawn into the blood pump by rotation of the impeller blades  143  of the rotor  140 , the blood flows through the inlet opening  101  and flows through the control electronics  130  and the stator  120  toward the rotor  140 . Blood flows through the aperture  141   a  of the permanent magnet  141  and between the impeller blades  143 , the shroud  145 , and the permanent magnet  141 , and into the volute  107 . Blood also flows around the rotor  140 , through the gap  108  and through the gap  109  between the shroud  145  and the inner surface  118   a  of the cap  118 . The blood exits the volute  107  through the outlet opening  105 . 
         [0037]    A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the claimed invention. For example, the cap  118  can be engaged with the peripheral wall  116  using a different attachment mechanism or technique, including snap-fit engagement, adhesives, or welding. Additionally, while the cap  118  has been described as defining the outlet opening  105  and the chamfered edge  114 , the outlet opening  105  and/or the chamfered edge  114  can be defined by the peripheral wall  116  or by both the peripheral wall  116  and the cap  118 . Similarly, the dividing wall  115  can be formed as part of the cap  118 . 
         [0038]    Additionally, the rotor  140  can include two or more permanent magnets. The number and configuration of the pole pieces  123  can also be varied. The operation of the control electronics  130  is selected to account for the number and position of pole pieces of the stator and permanent magnets of the rotor. Also, the cap  118  can be engaged with the peripheral wall using other techniques, such as adhesives, welding, snap-fit, shrink-fit, or other technique or structure. Similarly, the first face Ill may be formed from a separate piece of material than the peripheral wall  116  and the first face  111 , including the inlet cannula  112 , can be attached to the peripheral wall  116 , such as by welding, after the control electronics  130  and the stator  120  have been mounted in the internal compartment  117 . The shroud  145  may be omitted and optionally replaced by other flow control devices to achieve a desired pump efficiency. As another option, the control electronics  130  can be located external to the pump  100 , such as in a separate housing implanted in the patient&#39;s abdomen, or external to the patient&#39;s body. 
         [0039]    In some implementations, the dimensions of the housing  110  can be larger or smaller than those described above. Similarly, the ratio of the width W of the housing  110  to the thickness T of the housing can be different than the ratio described above. For example, the width W can be from about 1.1 to about 5 times greater than the thickness T. Additionally, the permanent magnet  141  of the rotor  140  can include two or more pairs of north and south magnetic poles. While the peripheral wall  116  and the dividing wall  115  are illustrated as cylinders having circular cross-sectional shapes, one or both can alternatively be formed having other cross-sectional shapes, such as oval, or an irregular shape. Similarly, the peripheral wall  116  can be tapered such that the housing does not have a constant width W from the first face Ill to the second face  113 . 
         [0040]    As mentioned above, in some implementations, the blood pump  100  can be used to assist a patient&#39;s heart during a transition period, such as during a recovery from illness and/or surgery or other treatment. In other implementations, the blood pump  100  can be used to partially or completely replace the function of the patient&#39;s heart on a generally permanent basis, such as where the patient&#39;s aortic valve is surgically sealed. 
         [0041]    Accordingly, other embodiments are within the scope of the following claims.