Abstract:
A pump for inducing motion of a fluid, the pump including a cannula adjustable between an operable configuration having a first diameter and a deployment configuration having a substantially smaller second diameter. An impeller is rotatable within the cannula about an axis. The impeller includes an at least semi-rigid support for a flexible web, and is positionable with respect to the cannula the operable configuration and the deployment configuration, the operable configuration extending the web to a first radial distance from the axis and the deployment configuration collapsing the web to a second substantially smaller radial distance from the axis.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/528,536 filed Aug. 29, 2011, the entirety of which is incorporated by reference herein. This application is related to U.S. application Ser. No. 13/______ to Evans et al., entitled EXPANDABLE VASCULAR PUMP and filed on even date herewith, the entirety of which is incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present disclosure relates to blood pumps for acute cardiac support. More particularly, the present disclosure relates to expandable blood pumps and methods of their deployment and use for quickly providing temporary circulatory support. 
       BACKGROUND 
       [0003]    A variety of cardiac problems result in the need for temporary cardiac support. These scenarios can range from contingency support during high risk cardiac surgery to immediate full support after a myocardial infarction. Acute pumps for temporary cardiac support differ from implantable pumps because the period of use may be measured short-term, in days or weeks, rather than long-term months or years. These situations requiring temporary cardiac support can benefit strongly from quick deployment in a range of anatomical locations. 
         [0004]    Thus, there exists a need in the art for blood pumps that can improve aspects of this type of therapy. Particularly, there is a need in the art for improved expandable blood pumps for acute cardiac support. 
       SUMMARY 
       [0005]    The present disclosure, in one embodiment, relates to expandable blood pumps and methods of their deployment and use for quickly providing temporary circulatory support. The blood pump may include a cannula constructed of an adjustable support member and flexible mesh cover allowing a deployment configuration of reduced or minimum collapsed size and an operable configuration of increased or maximum expanded size. In one embodiment, the cannula may vary in diameter along its axial length reducing or minimizing the interference between the expanded cannula and tissue openings. In addition, cannula diameter variation can allow for a leading narrow portion of the cannula which can improve maneuverability and permit an increased reach in anatomy. Further yet, cannula diameter variation can allow means for fixing the position of the pump with respect to a vessel opening or other port that it passes through. The cannula may include multiple openings, which can assist in preventing zero flow if a tissue collapses at the inlet end of the cannula. The cannula, in some embodiments, may be configured such that an outlet ejects flow generally perpendicularly to the pump&#39;s axis of rotation. The blood pump may be powered by a fluid system including catheter supply and return channels that cause a mechanical generator to rotate. The mechanical generator may be mechanically or magnetically coupled to an impeller of the blood pump. 
         [0006]    The present disclosure, in another embodiment, relates to a pump for inducing motion of a fluid relative the pump. The pump may include an elongated cannula having at least one section adjustable between an operable configuration having a first diameter and a deployment configuration having a substantially smaller diameter. The pump may also include an impeller positioned within the adjustable section of the cannula and rotatable therein about an impeller axis. The impeller can include a rigid or semi-rigid mast supporting a flexible web, the mast being separately positionable with respect to the cannula between an operable configuration and a deployment configuration, the operable configuration extending at least a portion of the web to a first radial distance from the impeller axis and the deployment configuration collapsing the portion of the web to a second radial position of substantially shorter distance from the impeller axis. In some embodiments, the cannula may include a spiral support member, the spiral support member spiraling about the impeller axis. The spiral support member may be adjustable from the operable configuration to the deployment configuration by twisting the spiral support member. Alternatively or additionally, the spiral support member may be adjustable from the operable configuration to the deployment configuration by axially positioning a proximal and distal end of the spiral support member further away from one another. The cannula may further include a cover supported by the spiral support member. The cover, in some instances, may comprise a plurality of inlet openings and/or an outlet opening permitting flow to exit the pump substantially perpendicularly to the impeller axis. In some embodiments, the cannula may also include a second section adjustable between an operable configuration having a second diameter and a deployment configuration having a diameter substantially smaller than the second diameter. In particular embodiments, the cannula can include a port fixation neck between the first and second cannula sections. 
         [0007]    In further embodiments, the impeller may have two rigid or semi-rigid masts supporting the flexible web, the masts in the operable configuration being substantially perpendicular to the impeller axis and in the deployment configuration being substantially parallel to the impeller axis. A distal catheter section may support a first one of the masts and a proximal catheter section may support a second one of the masts, at least one of the distal and proximal catheter sections being rotatable with respect to the other so as to radially offset the two masts. In other embodiments, a first end of the rigid or semi-rigid mast may be operably connected with a first catheter section of the impeller and a second end of the rigid or semi-rigid mast may be operably connected with a second catheter section, at least one of the first and second catheter sections being axially positionable with respect to the other, such that as the catheter sections are positioned toward each other, the mast is forced toward the operable configuration and as the catheter sections are moved away from each other, the mast is forced toward the deployment configuration. Additionally, at least one of the first and second catheter sections may be rotatable with respect to the other so as to radially offset the first and second mast ends. 
         [0008]    The pump may include a drive shaft for driving a rotating motion of the impeller. The drive shaft may include a proximal section having a first gear at its distal end and a distal section having a second gear at its proximal end, rotation of the proximal section being transferred to the distal section by adjacently positioning the first and second gears. In another embodiment, a power transmission system of the pump for driving a rotational motion of the impeller may include a mechanical generator for transferring fluid motion therethrough into rotational motion of the generator about the impeller axis and a first lumen driving fluid to the mechanical generator and a second lumen transferring fluid away from the mechanical generator. The mechanical generator may be operably connected with the impeller, thereby transferring rotational motion of the generator about the impeller axis to rotational motion of the impeller about the impeller axis. In a further embodiment, the power transmission system may further include one or more first magnets radially positioned about the impeller axis and operably connected at or near a distal end of the mechanical generator and rotatable therewith about the impeller axis and a magnet housing operably connected with the impeller and positioned adjacent the distal end of the mechanical generator, the housing having one or more second magnets radially positioned about the impeller axis interacting with the first magnets to magnetically transfer rotational motion of the first magnets to rotational motion of the second magnets about the impeller axis. 
         [0009]    The present disclosure, in yet a further embodiment, relates to a method of deploying a pump for acute cardiac support. The method may generally include providing a pump, such as that described above, inserting a catheter with the pump operably connected at or near the distal end thereof into a blood vessel with the cannula and impeller in their deployment configurations, guiding the pump to a desired location, and adjusting the cannula and impeller from their deployment configurations to their operable configurations. The method may also include adjusting the rigid or semi-rigid mast and flexible web to create a desired impeller blade angle. The impeller may be driven at a desired speed via a power transmission system. The method may also include adjusting the cannula and impeller back to their deployment configurations and removing the catheter and pump from the blood vessel. 
         [0010]    While multiple embodiments are disclosed, still other embodiments of the present disclosure will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the disclosure. As will be realized, the various embodiments of the present disclosure are capable of modifications in various obvious aspects, all without departing from the spirit and scope of the present disclosure. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter that is regarded as forming the various embodiments of the present disclosure, it is believed that the embodiments will be better understood from the following description taken in conjunction with the accompanying Figures, in which: 
           [0012]      FIG. 1  is a perspective view of an expandable blood pump according to one embodiment of the present disclosure. 
           [0013]      FIG. 2  is a schematic diagram of an expandable blood pump according to one embodiment of the present disclosure. 
           [0014]      FIG. 3  is a perspective view of an impeller according to one embodiment of the present disclosure. 
           [0015]      FIG. 4A  is a perspective view of an impeller according to another embodiment of the present disclosure. 
           [0016]      FIG. 4B  is an end view of the impeller of  FIG. 4A . 
           [0017]      FIG. 5A  is a perspective view of an impeller according to yet another embodiment of the present disclosure. 
           [0018]      FIG. 5B  is an end view of the impeller of  FIG. 5A . 
           [0019]      FIG. 6  is a perspective view of a cannula according to one embodiment of the present disclosure. 
           [0020]      FIG. 7  includes side and end schematic views of the cannula embodiment of  FIG. 6  in an expanded configuration and an end schematic view of the cannula embodiment of  FIG. 6  in a collapsed configuration. 
           [0021]      FIG. 8  includes side and end schematic views of a cannula according to another embodiment of the present disclosure in an expanded configuration and an end schematic view of the cannula in a collapsed configuration. 
           [0022]      FIG. 9  is a perspective view of a cannula according to still a further embodiment of the present disclosure having various diameters along its axial length. 
           [0023]      FIG. 10A  is a side view of a cannula according to yet another embodiment of the present disclosure having a port fixation feature. 
           [0024]      FIG. 10B  is a perspective view of the cannula of  FIG. 10A . 
           [0025]      FIG. 11A  is a side schematic view of an opening in a wall between any combination of heart chamber(s) and blood vessel(s). 
           [0026]      FIG. 11B  is a side schematic view of the cannula embodiment of  FIG. 10A  fixed within the opening of  FIG. 11A . 
           [0027]      FIG. 11C  is a side schematic view of the cannula embodiment of  FIG. 10A  fixed within the opening of  FIG. 11A , wherein the opening also has an intermediate device fixed at the wall opening. 
           [0028]      FIG. 12  is a perspective view of a catheter guidance system according to one embodiment of the present disclosure. 
           [0029]      FIG. 13  is a perspective view of a catheter guidance system according to another embodiment of the present disclosure. 
           [0030]      FIG. 14  includes a side view and exploded side views of a power transmission system of a pump according to one embodiment of the present disclosure. 
           [0031]      FIG. 15  is a perspective view of a power transmission system of a pump according to another embodiment of the present disclosure. 
           [0032]      FIG. 16  is a perspective view of a power transmission system of a pump according to still a further embodiment of the present disclosure. 
           [0033]      FIG. 17  is a perspective view of a power transmission system of a pump according to yet another embodiment of the present disclosure. 
           [0034]      FIG. 18  is a flow diagram of a method of deploying and using and expandable blood pump according to one embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    The present disclosure relates to novel and advantageous blood pumps for acute cardiac support. Particularly, the present disclosure relates to novel and advantageous expandable blood pumps and methods of their deployment and use for quickly providing temporary circulatory support. Example uses of the various embodiments of expandable blood pumps provided herein can range from contingency support during high risk cardiac surgery to immediate full support after a myocardial infarction. 
         [0036]    In general, a pump, with a cannula and impeller in a collapsed, deployment configuration, may be inserted into, for example, a major blood vessel and guided to the heart. Once the pump is placed in or near the desired location, e.g., desired chamber of the heart, the clinician or operator may use catheter controls to expand the pump&#39;s cannula. With the cannula expanded and a conduit created, the clinician or operator may then expand the pump&#39;s impeller within the cannula. Rotation of the impeller generates blood flow within the cannula between the cannula&#39;s inlet and outlet. The cannula may also provide separation between any surrounding tissue and the rotating impeller. The impeller may be driven via a power transmission system in the catheter and controlled from a control and/or power unit. The clinician or operator may enter therapeutic system parameters into the control unit, which drives the pump at the desired speed. The collapsed, deployment configuration may permit quick insertion to, and removal from, several anatomical positions while the expanded, operable configuration may permit appropriate therapy. 
         [0037]      FIG. 1  illustrates one embodiment of an expandable blood pump  100  according to the present disclosure. With additional reference to  FIG. 2 , an expandable blood pump  100  may generally include a catheter  102  with a pump  104  positioned at or near the inserted end of the catheter and a control and/or drive unit  106  operably connected at or to an external end of the catheter. The pump  104  may include an impeller  108 , a cannula  110 , and a guidance system  112 . The catheter  102  may include a power transmission system operably coupling the pump  104  and the control and/or drive unit  106 . Several of these components, such as but not limited to, the impeller  108 , cannula  110 , guidance system  112 , and power transmission system, can have various embodiments, which may be interchanged or interchangeable within the blood pump  100  to create a variety of different blood pump embodiments, which will be understood from the following description. 
       Impeller 
       [0038]    In general, the various embodiments of impellers of the present disclosure may include one or more impeller blades comprising a thin, flexible web or film of material suspended by or between one or more generally moveable, rigid or semi-rigid support members or masts. In the various embodiments of impellers disclosed herein, the impeller may be activated between a collapsed, deployment configuration and an expanded, operable configuration by changing the position of the moveable, rigid or semi-rigid support members, thereby stretching the flexible web into a desired position and creating an impeller blade surface. That is, by virtue of the flexible web and moveable, rigid or semi-rigid support members, the impeller may permit a collapsed, deployment configuration of reduced or minimum size and an expanded, operable configuration of increased or maximum size. In some embodiments, the impeller may be activated between a collapsed, deployment configuration and an expanded, operable configuration separately from an activation of the cannula (discussed in further detail below) between a collapsed, deployment configuration and an expanded, operable configuration. In various embodiments disclosed herein, the impeller blades&#39; geometries and scales can reduce hemolysis, thereby improving procedure outcomes due to improved therapy. 
         [0039]    In one embodiment, illustrated in  FIG. 3 , an impeller  300  may be comprised of one or more impeller blades  302 , each blade having a flexible web  304  suspended between rigid or semi-rigid, cantilevered support members  306  attached to the catheter  308 . The support members  306  may be rotated or adjusted between positions substantially parallel and perpendicular to the pump&#39;s rotational axis  310 . With the support members  306  in a position substantially parallel to the pump&#39;s rotational axis  310 , the flexible web  304  may be retracted therewith to a collapsed, deployment configuration. As the support members  306  are adjusted to a position substantially perpendicular to the pump&#39;s rotational axis  310 , as illustrated in  FIG. 3 , the flexible web  304  may be extended therewith to an expanded, operable configuration. 
         [0040]    The catheter  308  may include a catheter layer having a proximal section  312  and a distal section  314 , which may be rotated relative one another. Each blade  302  may have a support member  306  positioned at the proximal section  312  and a support member at the distal section  314 . In this manner, with the flexible web  304  in an expanded, operable configuration, the angle of the flexible web, and thus the impeller blade surface, may be created or modified by rotation of the proximal  312  and distal  314  sections of the catheter  308  relative one another. 
         [0041]    In another embodiment, illustrated in  FIGS. 4A and 4B , an impeller  400  may include a flexible web  402  suspended by or between a generally semi-rigid, but flexible support member  404  and optionally the catheter  406 . The generally semi-rigid, but flexible support member  404 , in some embodiments, may be but is not limited to a moderate stiffness wire, and may be attached at both ends  408 ,  410  to the catheter  406 . In one embodiment, the catheter  406  may include a sliding section  412  and a rotational section  414 , which may be rotated relative to the sliding section, and the support member  404  may be attached at both ends  408 ,  410  to the sliding section of the catheter. A portion of the support member  404  may also be generally held in place axially at a fixed location  416  along the rotational section  414 . For example, in one embodiment, the flexible support member  404  may pass through the rotational section  414 , as shown in  FIG. 4A , such that a portion of the support member is generally held in place axially at fixed location  416  along the rotational section. In another embodiment, the support member  404  may be split into two sections, each section having an end attached to the sliding section  412  and an end attached to the rotational section  414  at fixed location  416 . However, other suitable means for permitting proximal and distal ends of the flexible support member  404  to move axially relative one another are considered within the spirit and scope of the present disclosure. 
         [0042]    The sliding section  412  of the catheter  406  may be slid or axially adjusted along the rotational section  414  between axial positions toward and away from fixed location  416 . With the sliding section  412  slid to a position generally relatively away from fixed location  416 , portions of the support member  404  may be pulled closer to the pump&#39;s rotational axis  418 , thereby causing the flexible web  402  to be retracted therewith to a collapsed, deployment configuration. As the sliding section  412  is slid to a position generally relatively toward the fixed location  416 , portions of the support member  404  may be forced away from the pump&#39;s rotational axis  418 , thereby causing the flexible web  402  to be expanded therewith to an expanded, operable configuration, as illustrated in  FIG. 4A . With the flexible web  402  in an expanded, operable configuration, the angle of the flexible web, and thus the impeller blade surface, may be created or modified by rotation of the rotational section  414  of the catheter  406  with respect to the sliding section  412 , as illustrated in  FIG. 4B . 
         [0043]    In yet another embodiment, illustrated in  FIGS. 5A and 5B , an impeller  500  may include one or more impeller blades  502 , which may each include a flexible web  504  suspended by or between a generally semi-rigid, but flexible support member  506  and optionally the catheter  508 . The generally semi-rigid, but flexible support member  504 , in some embodiments, may be but is not limited to a moderate stiffness wire, and may be attached at both ends  510 ,  512  to the catheter  508 . In one embodiment, the catheter  508  may include a catheter layer having a distal section  514  and a proximal section  516 , with either or both sections axially positionable along the pump&#39;s rotational axis  518  and either or both sections rotatable about the pump&#39;s rotational axis, such that the distal and proximal sections may be axially positioned and rotated relative to one another. The support member  506  may be attached at one end  510  to the distal section  514  and at one end  512  to the proximal section  516 , thereby permitting the ends to also be axially positioned and rotated relative one another by means of the distal and proximal sections. However, other suitable means for permitting distal  510  and proximal  512  ends of the flexible support member  506  to move axially and/or rotationally relative one another are considered within the spirit and scope of the present disclosure. 
         [0044]    Either or both of the distal  514  and/or proximal  516  sections of the catheter  508  may be slid or axially adjusted along the pump&#39;s rotational axis  518  between axial positions toward and away from the other. With the distal  514  and proximal  516  sections adjusted to a position generally relatively away from each other, portions of the support member  506  may be pulled closer to the pump&#39;s rotational axis  518 , thereby causing the flexible web  504  to be retracted therewith to a collapsed, deployment configuration. As the distal  514  and proximal  516  sections are adjusted to a position generally relatively toward each other, portions of the support member  506  may be forced away from the pump&#39;s rotational axis  518 , thereby causing the flexible web  504  to be expanded therewith to an expanded, operable configuration, as illustrated in  FIG. 5A . With the flexible web  504  in an expanded, operable configuration, the angle of the flexible web, and thus the impeller blade surface, may be created or modified by rotation of either or both of the distal  514  and/or proximal  516  sections of the catheter  410  with respect to one another, as illustrated in  FIG. 5B . 
         [0045]    The flexible webs of the various embodiments of cannulas described above may be manufactured from any suitable materials. For example, the various embodiments of cannulas described above may be manufactured from, but are not limited by, a polymer, a metal or metal alloy, a shape memory material, or combinations of materials. 
       Cannula 
       [0046]    In general, the various embodiments of cannulas of the present disclosure may include a plurality of support members or ribs, and may be activated between a collapsed, deployment configuration and an expanded, operable configuration by changing the relative position of the ribs. In some embodiments, as noted above, the cannula may be activated between a collapsed, deployment configuration and an expanded, operable configuration separately from an activation of the impeller between a collapsed, deployment configuration and an expanded, operable configuration. In an expanded, operable configuration, a conduit may be created within which the pump&#39;s impeller may be expanded and operated. Operation of the impeller can generate blood flow within the cannula between the cannula&#39;s inlet and outlet, which may typically be provided at the proximal and distal ends, respectively, of the cannula. In some embodiments, the cannula may also provide separation between any surrounding tissue and the impeller. 
         [0047]    In one embodiment, illustrated in  FIG. 6  and schematically in  FIG. 7 , a cannula  600  may include a thin, flexible film or mesh cover  602  supported by or between one or more substantially rigid or semi-rigid support members  604  in spiral configuration, creating a plurality of ribs  606 . In an expanded, operable configuration, as illustrated in  FIG. 6 , the ribs  606  may stretch and/or support the cover  602  to create a conduit  608 , in which the impeller (e.g., impeller  500  as shown in  FIG. 6 ; although any of the above described impellers are suitable) may by expanded to its operable configuration. In some embodiments, the substantially rigid or semi-rigid support members  604  in spiral configuration may be biased to the expanded, operable configuration. 
         [0048]    The cannula  600  may be adjusted to a collapsed, deployment configuration, as illustrated at the bottom of  FIG. 7 . In one embodiment, with reference again to  FIG. 6 , the catheter  610  may include a catheter layer having a distal section  612  and a proximal section  614 , with either or both sections axially positionable along the pump&#39;s rotational axis  616 , such that the distal and proximal sections may be axially positioned relative to one another. The cannula  600 , or more particularly in some embodiments, the support members  604 , may be attached at one end  618  to the distal section  612  and at one end  620  to the proximal section  614 , thereby permitting the ends of the cannula  600 , or support members  604 , to also be axially positioned relative one another by means of the distal and proximal sections. Thus, in one embodiment, the cannula  600  may be adjusted to a collapsed, deployment configuration by causing the support members  604  to be adjusted axially generally relatively away from each other, thereby causing portions of the support members to be pulled closer to the pump&#39;s rotational axis  616 , and causing the flexible mesh cover  602  to be retracted therewith. 
         [0049]    In addition or alternatively, either or both of the distal  612  and proximal  614  sections may be rotatable about the pump&#39;s rotational axis  616 , such that the distal and proximal sections may be rotated relative to one another. In this regard, the ends of the cannula  600 , or support members  604 , may additionally or alternatively be rotatably positioned relative one another by means of the distal  612  and proximal  614  sections. Thus, in one embodiment, the cannula  600  may be adjusted to a collapsed, deployment configuration by additionally or alternatively causing the ends of the spiral support members  604  to be rotated relative one another other, thereby shrinking the size of the conduit  608  and collapsing the mesh cover  602  supported therebetween. 
         [0050]    However, any other suitable means for permitting distal  618  and proximal  620  ends of the support members  604  to move axially and/or rotatably relative one another are considered within the spirit and scope of the present disclosure. In a further embodiment, cannula  600  and/or catheter  610  may include a drawstring, which may be pulled to gather up any loose material of the retracted mesh cover  602  and hold the mesh cover relatively closer to the catheter body. 
         [0051]    In another embodiment, illustrated schematically in  FIG. 8 , a cannula  800  may include a thin, flexible film or mesh cover  802  supported by or between one or more substantially rigid or semi-rigid support members  804  in a linear, axial configuration, creating a plurality of ribs  806  that are generally aligned parallel to the catheter body. In an expanded, operable configuration, the ribs  806  may stretch and/or support the cover  802  to create a conduit  808 , in which the impeller may by expanded to its operable configuration. In some embodiments, the substantially rigid or semi-rigid support members  804  in a linear, axial configuration may be biased to the expanded, operable configuration. 
         [0052]    Similar to the embodiments of  FIGS. 6 and 7 , the cannula  800  may be adjusted to a collapsed, deployment configuration, as illustrated at the bottom of  FIG. 8 . In one embodiment, as discussed above, the catheter  810  may include a catheter layer having a distal section and a proximal section, with either or both sections axially positionable along the pump&#39;s rotational axis  812 , such that the distal and proximal sections may be axially positioned relative to one another. The cannula  800 , or more particularly in some embodiments, the support members  804 , may be attached at one end  814  to the distal section and at one end  816  to the proximal section, thereby permitting the ends of the cannula  800 , or support members  804 , to also be axially positioned relative one another by means of the distal and proximal sections. Thus, in one embodiment, the cannula  800  may be adjusted to a collapsed, deployment configuration by causing the support members  804  to be adjusted axially generally relatively away from each other, thereby causing portions of the support members to be pulled closer to the pump&#39;s rotational axis  812 , and causing the flexible mesh cover  802  to be retracted therewith. 
         [0053]    As with the above embodiments, any other suitable means for permitting distal  814  and proximal  816  ends of the support members  804  to move axially relative one another are considered within the spirit and scope of the present disclosure. In a further embodiment, cannula  800  and/or catheter  810  may include a drawstring, which may be pulled to gather up any loose material of the retracted mesh cover  802  and hold the mesh cover relatively closer to the catheter body. 
         [0054]    In some embodiments, as illustrated in  FIGS. 6-8 , the cannula may have a generally constant diameter axially along the catheter body. However, in other embodiments, as illustrated for example in  FIG. 9 , the cannula  900  may have a diameter that varies axially along the catheter body  902 . In such embodiments, the cannula  900  may have two or more axial sections  904 ,  906  of substantially constant diameters and one or more axial sections of transition  908  from one section of constant diameter to a different section of constant, but different, diameter. An impeller, such as those described above, may be provided in any suitable axial section. As illustrated, an impeller (e.g., impeller  500  as shown in  FIG. 9 ; although any of the above described impellers are suitable) may be provided within a proximal axial section  906  of relatively larger diameter than a distal axial section  904 . In such an embodiment, the transition from a relatively larger diameter conduit to a relatively smaller diameter conduit may also increase the rate of flow through the distal axial section  904  and out of cannula  900 . 
         [0055]    According to some embodiments, operation of an impeller within the various embodiments of cannulas described herein may cause a flow of fluid, e.g., blood, into an inlet opening at one end of the cannula, through the cannula, and out an outlet opening at an opposite end of the cannula. Generally, the flow of fluid may be substantially axial with the axis of rotation of the impeller. However, in some embodiments, a cannula may additionally, or alternatively include outlet openings that permit the flow of fluid out of the cannula substantially perpendicularly to the axis of rotation of the impeller. In still other embodiments, a cannula may include multiple inlets, and/or multiple outlets, which may assist in preventing blockages of the inflow and/or outflow of fluid to or from the pump. 
         [0056]    In still further embodiments, as illustrated in  FIGS. 10A and 10B , a cannula  1000  may include one or more features  1002  for port fixation. More specifically, as shown in cross-section in  FIG. 11A , where there is an opening  1102  in the wall, for example but not limited to, between any combination of heart chamber(s) and blood vessel(s), the cannula  1000  may be configured such that it can be placed in the opening, expanded as described in various manners above, and remain substantially affixed with respect to the opening by means of the one or more features  1002  for port fixation, as illustrated in cross-section in  FIG. 11B . In one particular embodiment, one end of the cannula  1000 , such as but not limited to, the distal end  1004 , may include an impeller conduit section  1006 , a neck section  1008 , and a port fixation section  1010 . As described with respect to the various cannula embodiments above, the cannula  1000 , including the impeller conduit section  1006 , neck section  1008 , and a port fixation section  1010 , may be adjusted between a collapsed, deployment configuration and an expanded, operable configuration. As illustrated in  FIGS. 10A and 10B , in the expanded, operable configuration, the neck section  1008  may be configured to expand to a diameter that is smaller than the expanded diameter of the impeller conduit section  1006  and the port fixation section  1010 , thereby forming a generally hourglass shape having a pocket  1012  created between the impeller conduit section and the port fixation portion at the neck section. As illustrated in  FIG. 11B , the cannula  1000  may be expanded at a position such that the pocket  1012  formed at the neck section  1008  upon expansion of the cannula may generally align with the wall opening  1102 . The relatively larger diameters of the impeller conduit section  1006  and the port fixation section  1010  can be designed such that they do not easily pass through the wall opening  1102  when the cannula is in the expanded, operable configuration, and thus cause the cannula  1000  to remain substantially affixed with respect to the opening by means of the pocket  1012 . In additional embodiments, as shown in  FIG. 11C , an intermediate device  1104 , such as a port or similar device, may be fixed at the wall opening  1102  to, for example only, improve the opening strength and/or improve the opening geometry. 
         [0057]    The flexible film or mesh covers of the various embodiments of cannulas described above may be manufactured from any suitable materials, such as but not limited to a polymer, a metal or metal alloy, a shape memory material, or combinations of materials. In further embodiments, the various embodiments of cannulas described above may be provided without the flexible film or mesh covers, thereby leaving the support members exposed. 
         [0058]    With reference again to  FIG. 1 , in one embodiment, the various embodiments of impellers and cannulas described in the present disclosure may be adjusted, for example to expand and retract the impellers and/or cannulas between the expanded, operable configuration and collapsed, deployment configuration, using a plurality of concentric layers or sheaths of the catheter, as will be described in further detail below. Generally, however, in one embodiment, the plurality of concentric layers may include, a drive shaft layer, translatable along the catheter&#39;s axial direction for adjusting the impeller, and a cannula sheath, translatable along the catheter&#39;s axial direction for adjusting the cannula. In alternative or additional embodiments, the drive shaft layer and/or the cannula sheath may be rotatable about the axis of rotation, so as to permit, for example, the variation in impeller blade angle and/or to assist in, for example, collapsing a spiral support member or flexible mesh cover, as described above. 
       Guidance System 
       [0059]    In general, the various embodiments of pumps disclosed herein may include a means or guidance system for directing the catheter and pump into and through the vasculature to the desired anatomical position, for example, at the heart. Such means or guidance system, according to one embodiment of the present disclosure, illustrated in  FIG. 12 , may include an opening or passageway  1202  through the central axis  1204  of the catheter  1206 , such that the catheter and pump  1208  may be inserted over and travel along a guidewire  1210  as will be understood by those skilled in the art. 
         [0060]    In another embodiment, illustrated in  FIG. 13 , a means or guidance system for directing the catheter and pump into and through the vasculature to the desired anatomical position may include a steerable catheter tip  1302 . More specifically, the catheter  1304  may include a generally flexible section  1306  at or near its distal end. The flexible section  1306  may have an adjustable curvature that permits the flexible section of the catheter to be adjusted to aim the catheter in the desired direction of travel. In one embodiment, the flexible section  1306  may have a bias for curvature in a predetermined direction, or in some embodiments may have a bias for no curvature. The flexible section  1306  may include a cable therewithin and anchored thereto for controlling the curvature of the flexible section, the cable running through the catheter to an external control system. In a particular embodiment, the cable is anchored at or near the tip  1308  of the flexible section  1306 , which may permit ease of control. The cable may be used to control the flexible section  1306  by, for example, manipulating or pulling the cable at the external control system to cause a desired curvature of the flexible section. Similarly, when the cable is manipulated in a different direction or released, the flexible section  1306  may return to its normal biased position. 
       Power Transmission System 
       [0061]    In general, the various embodiments of pumps disclosed herein may include a means or power transmission system in the catheter for driving the impeller. The transmission system may be controlled, for example, from a control and/or power unit operably connected at or to an external end of the catheter. The power transmission system may generally provide a means of transferring power from the external control and/or power unit to the mechanical power needed by the pump or impeller. 
         [0062]    In one embodiment, as illustrated in  FIG. 14 , the transmission system may include a drive shaft that connects the impeller directly with a drive motor of the control and/or power unit through a clutch. In one embodiment, as described briefly above, the catheter  1402  may include a plurality of concentric layers. In one embodiment, these layers in order of innermost to outermost, may include but are not limited to, a cable  1404 , an inner catheter sheath  1406 , a rotatable layer  1408  of the drive shaft, a drive shaft layer  1410  that is axially positionable with respect to the rotatable layer  1408  and may, in some embodiments, be rotatable therewith, and an axially positionable cannula sheath  1412 . The cable  1404  may be used, for example, to control the guidance system, such as a steerable catheter tip, described above; however, in other embodiments, the cable  1404  may be eliminated leaving a passageway for a guidewire along which the catheter travel may travel, as described above. The inner catheter sheath  1406  may surround the cable  1404 . The rotatable drive shaft layer  1408  may provide the rotational motion for the impeller and transfer the rotational motion thereto. The drive shaft layer  1410 , which is axially positionable with respect to the rotatable layer  1408 , may be used, as described above, to retract and deploy any of the impeller embodiments of the present disclosure. The cannula sheath  1412  may be axially positionable with respect to the inner catheter sheath  1406  and may be used, as described above, to retract and deploy any of the cannula embodiments of the present disclosure. 
         [0063]    In one embodiment, the drive shaft layers  1408 ,  1410  may be longitudinally-flexible, but torsionally rigid, thereby permitting the drive shaft to have flexibility when be maneuvered through the vasculature, but maintaining its ability for delivering rotational motion. One or both of the drive shaft layers  1408 ,  1410  may be lubricated with a lubricating fluid, such as but not limited to saline. The rotatable drive shaft layer  1408  or both drive shaft layers  1408 ,  1410 , as thus described, may be used to control the pump by delivering or transferring rotational motion to the impeller. 
         [0064]    In a further embodiment, illustrated in  FIG. 15 , the transmission system may include drive shaft means generally configured as that described above, except that at one or more locations along the drive shaft, a set of gears  1502  may be employed to permit relatively sharper bends or angles in the drive shaft between a distal drive shaft section  1504  and a proximal drive shaft section  1506 , while maintaining torque along the drive shaft. In some embodiments, the drive shaft sections  1504 ,  1506 , with gears  1502  at their adjacent ends can be brought into contact with one another or maintain contact with one another via tensioning means, such as but not limited to a cable or sheath. The angle between the drive shaft sections  1504 ,  1506  may be adjustable. 
         [0065]    In another embodiment, illustrated in  FIG. 16 , the transmission system may include a fluid driven or hydrostatic transmission system  1602  in combination with a magnetic coupling device  1604 . In general, an external system may drive a fluid to a mechanical generator, causing rotational motion of the mechanical generator, which is transferred to the impeller via a magnetic couple. In a particular embodiment, the hydrostatic transmission system  1602  may include a catheter body or outer sheath  1606  and an inner sheath  1608 , concentrically positioned within the outer sheath, the distal ends of which are operably connected with a mechanical generator  1610 . The inner sheath  1608  may provide an inlet channel or lumen by which to deliver fluid from the external system to the mechanical generator  1610 , while the outer sheath  1606  may provide an outlet channel or lumen by which to return fluid from the mechanical generator to the external system; of course, in other embodiments, the outer sheath may provide the inlet channel while the inner sheath may provide the outlet channel. The mechanical generator  1610  may convert the axial motion of the fluid passing therethrough to rotational motion of the generator about the central axis  1612  of the catheter. At or near a distal end of the generator  1610 , the generator may include a proximal end of the magnetic coupling device  1604 , including one or more magnets  1614 . The magnets  1614  may, by means of the rotational motion of the generator, also rotate therewith about the central axis  1612  of the catheter, creating a changing magnetic field at the distal end of the mechanical generator  1610 . 
         [0066]    Positioned at or near the distal end of the hydrostatic transmission system  1602  may be the distal end of the magnetic coupling device  1604  having a housing  1616  also including one or more magnets  1618  which interact with the magnets  1614  of the proximal end of the magnetic coupling device to cause rotational motion of housing  1616 . More specifically, the changing magnetic field created by the rotational motion of magnets  1614  of the proximal end of the magnetic coupling device  1604  interacts with the magnets  1618  in housing  1616  causing rotational motion thereof. 
         [0067]    An impeller  1620 , such as any of the various embodiments of impellers described herein, may be operably connected with the distal end of the magnetic coupling device  1604  or housing  1616  and thus rotate therewith. One advantage of such fluid driven or hydrostatic transmission system  1602  in combination with a magnetic coupling device  1604  is impeller interchangeability since the indirect connection provided by the magnetic coupling device between the transmission system and the impeller provides a relatively easy interconnect for changing between impeller embodiments. 
         [0068]    In another embodiment, illustrated schematically in  FIG. 17 , the transmission system may simply include a fluid driven or hydrostatic transmission system  1702  driving an operably connected impeller. In general, an external system may drive a fluid to a mechanical generator, causing rotational motion of the mechanical generator, which is transferred substantially directly to the impeller. In a particular embodiment, the hydrostatic transmission system  1702  may include a catheter body or outer sheath  1704  and an inner sheath  1706 , concentrically positioned within the outer sheath, the distal ends of which are operably connected with a mechanical generator  1708 . The inner sheath  1706  may provide an inlet channel or lumen by which to deliver fluid from the external system to the mechanical generator  1708 , while the outer sheath  1704  may provide an outlet channel or lumen by which to return fluid from the mechanical generator to the external system; of course, in other embodiments, the outer sheath may provide the inlet channel while the inner sheath may provide the outlet channel. The mechanical generator  1708  may convert the axial motion of the fluid passing therethrough to rotational motion of the generator about the central axis  1710  of the catheter. The mechanical generator  1708  may be directly connected to the impeller, such as any of the various embodiments of impellers described herein; however, it is recognized that any suitable means for indirectly or operably connecting the mechanical generator  1708  and impeller, such as but not limited to a gearing system, are within the spirit and scope of the present disclosure. 
         [0069]    With respect to the various fluid driven or hydrostatic transmission systems described above, a fluid driven or hydrostatic transmission system may be externally connected with, for example, a hydraulic connector or compressible tube, which mates the fluid driven or hydrostatic transmission system to an external controller for driving the fluid, as will be understood by those skilled in the art. The external controller may or may not be a component of the control and/or power unit, described herein. 
         [0070]    In yet another embodiment, the transmission system may be electrically driven. More specifically, the impeller, such as any of the various embodiments of impellers described herein, may be operably connected with a motor at or near the pump end of the catheter. An electrical system may be driven by the control and/or power unit operably connected at or to an external end of the catheter and may condition the energy for use in controlling the motor and rotating the impeller, as will be recognized by those skilled in the art. The electrical system, or a portion thereof, may be located at or near the motor or may be positioned at any other suitable location, including but not limited to at the control and/or power unit operably connected at or to an external end of the catheter. The electrical system and control and/or power unit may be operably connected by means of electrical connectors or conductors. 
         [0071]    A method of deploying and using an expandable blood pump according to the various embodiments described herein is described with reference to  FIG. 18 . As illustrated at step  1802 , a catheter with a pump at or near the distal end thereof may be inserted into a major blood vessel and guided to the desired location, such as at the heart. As described in detail above, the pump may include an impeller and cannula, and the impeller and cannula may be initially inserted in a collapsed, deployment configuration. The impeller and cannula may be biased in the deployment configuration, or alternatively, may be retracted to the deployment configuration using a control unit operably coupled at or near the external end of the catheter. Once the pump is positioned in or near the desired location, e.g., desired chamber of the heart, at step  1804 , the clinician or operator may use the control unit to adjust the pump&#39;s cannula, as described above, to an expanded, operable configuration, thereby creating a conduit for pump flow. With the cannula expanded and a conduit created, at step  1806 , the clinician or operator may adjust the pump&#39;s impeller within the cannula into its expanded, operable configuration. Although illustrated as separate steps  1804 ,  1806 , in some embodiments, the adjustment of the cannula and impeller into their expanded, operable configurations may be done substantially simultaneously. At step  1808 , if desired, the impeller blade angle may be adjusted, as described in detail above for each of the various impeller embodiments, to create the desired pump flow direction. At step  1810 , a power transmission system may be activated, for example using the control unit, to cause rotation of the impeller and generation of pump flow within the cannula between the cannula&#39;s inlet(s) and outlet(s). The clinician or operator may enter therapeutic system parameters into the control unit so as to drive the impeller at the desired speed. In general, the collapsed, deployment configuration may permit quick insertion to, and removal from, several anatomical positions while the expanded, operable configuration may permit appropriate therapy. 
         [0072]    Although the various embodiments of the present disclosure have been described with reference to preferred embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the present disclosure.