Patent Publication Number: US-2021170162-A1

Title: Percutaneous heart pump

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/345,597, filed on Jan. 6, 2012, entitled  Percutaneous Heart Pump,  which claims priority to U.S. Provisional Application Ser. No. 61/430,537 filed Jan. 6, 2011, entitled  Percutaneous Heart Pump,  the contents of each of which are hereby incorporated by reference herein for all purposes. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This application is directed to heart pumps that can be applied percutaneously. 
     Description of the Related Art 
     Heart disease is a major health problem that claims many lives per year. After a heart attack, only a small number of patients can be treated with medicines or other non-invasive treatment. However, a significant number of patients can recover from a heart attack or cardiogenic shock if provided with mechanical circulatory support. 
     In a conventional approach, a blood pump having a fixed cross-section is surgically inserted a heart chamber, such as into the left ventricle of the heart and the aortic arch to assist the pumping function of the heart. Other known applications involve providing for pumping venous blood from the right ventricle to the pulmonary artery for support of the right side of the heart. The object of the surgically inserted pump is to reduce the load on the heart muscle for a period of time, which may be as long as a week, allowing the affected heart muscle to recover and heal. Surgical insertion, however, can cause additional serious stresses in heart failure patients. 
     Percutaneous insertion of a left ventricular assist device (“LVAD”), a right ventricular assist device (“RVAD”) or in some cases a system for both sides of the heart (sometimes called “biVAD”) therefore is desired. Conventional fixed cross-section ventricular assist devices designed to provide near full heart flow rate are too large to be advanced percutaneously, e.g., through the femoral artery. There is an urgent need for a pumping device that can be inserted percutaneous and also provide full cardiac rate flows of the left, right, or both the left and right sides of the heart when called for. 
     SUMMARY OF THE INVENTION 
     In one embodiment, a heart pump is provided that includes a catheter body, a housing, an impeller, and a diffuser. The catheter body includes a proximal end, a distal end, and an elongate body extending therebetween. The housing is coupled with the distal end of the catheter body and comprises a distal opening and a proximal opening. The impeller assembly is coupled with the distal end of the catheter body and positioned within the housing. The diffuser can include a flow directing surface. The diffuser is disposed between the distal end of the catheter body and the impeller. The diffuser is configured to be positioned within the housing and adjacent the proximal opening. 
     In another embodiment, a heart pump is provided that includes a catheter body comprising a proximal end, a distal end, and an elongate body extending therebetween. The pump also includes an impeller coupled with the distal end of the catheter body and comprising an axial lumen passing through a distal end of the impeller. The impeller comprises a tip positioned at the distal end of the impeller, the tip comprising a resealable member having a resealable path. 
     In another embodiment, a heart pump is provided that comprises a catheter body, an impeller, and a sheath. The catheter body has a proximal end, a distal end, and an elongate structure extending therebetween. The impeller is coupled with the distal end of the catheter body. The sheath is disposed over at least a portion of the distal end of the catheter body. The sheath also has an expandable distal end. 
     In another embodiment, a catheter assembly is provided that includes a catheter body, an impeller, and a deployment device. The catheter body comprises a proximal end, a distal end, and an elongate structure extending therebetween. The impeller is configured for relative motion in an axial direction, and is located at the distal end of the catheter body. The deployment device is located at the proximal end of the catheter assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the subject matter of the present inventions and the various advantages thereof can be realized by reference to the following detailed description, in which reference is made to the accompanying drawings in which: 
         FIG. 1  illustrates one embodiment of a heart pump configured for percutaneous application and operation; 
         FIG. 1A  is a plan view of one embodiment of a catheter assembly adapted to be used with the heart pump of  FIG. 1 ; 
         FIG. 2  is a detail view of a distal portion of the catheter assembly illustrated in  FIG. 1A ; 
         FIG. 3  is an exploded view of a portion of an impeller assembly of the catheter assembly of  FIG. 1A ; 
         FIG. 4A  is a cross-sectional view of a distal portion of the catheter assembly, taken through the section plane  4 A- 4 A shown in  FIG. 2 ; 
         FIG. 4B  is a detail view of the distal portion of the catheter assembly, taken at  4 B- 4 B shown in  FIG. 4A ; 
         FIG. 5  is a cross-sectional perspective view of a bearing assembly of the catheter assembly of  FIG. 1A ; 
         FIG. 6  is a cross-sectional view of a bearing housing of the bearing assembly of  FIG. 5 ; 
         FIG. 7  is a perspective view of one embodiment of a catheter body that can be used to house a drive shaft and to convey an infusant to the bearing housing of  FIG. 5 ; 
         FIGS. 7A-7C  show variations of the catheter body of  FIG. 7 ; 
         FIG. 8  illustrates a surface configuration of one embodiment of a bearing adapted to enhance or control flow of an infusant in the bearing assembly of  FIG. 5 ; 
         FIG. 9  illustrates one embodiment of an impeller assembly; 
         FIGS. 9A, 9B-1, 9B-2, 10 and 10A  illustrate details of further embodiments of impeller blades; 
         FIG. 11  is a cross-sectional view of a proximal portion of the catheter assembly, taken through the section plane  11 - 11  on  FIG. 1A ; 
         FIGS. 12, 12A, and 12B  are cross-section views similar to that of  FIG. 11 , illustrating an infusant outflow path; 
         FIGS. 13A-B  are cross-sectional views of two embodiments of a blood pump that includes a diffuser; 
         FIGS. 14A-B  are partial cross-sectional views illustrating one embodiment of a blood pump including a retractable impeller assembly in deployed and retracted configurations, respectively; 
         FIGS. 15A-B  illustrate a deployment device disposed at the proximal end of a catheter assembly illustrated in  FIGS. 14A-B  in deployed and retracted configurations, respectively; 
         FIG. 15C  is a cross-sectional view of a structure for actuating the deployment device illustrated in  FIGS. 15A-B ; 
         FIGS. 15D-F  illustrate further embodiments of deployment devices that can actuate the catheter assembly between deployed and retracted configurations; 
         FIGS. 16A-C  are cross-sectional views of three embodiments of a self-sealing impeller tip; and 
         FIGS. 17A-D  are perspective views of variations of a sheath assembly having an expandable distal portion. 
     
    
    
     A more detailed description of various embodiments of components for heart pumps useful to treat patients experiencing cardiac stress, including acute heart failure, are set forth below. 
     DETAILED DESCRIPTION 
     Major components of heart pumps that can be applied percutaneously to a patient are described below in Section I. Section II describes various structures that facilitate the rotatable support of a cantilevered impeller. Section III describes various structures that facilitate deployment and/or retrieval of one or more components of the distal end  108  of the heart pump  10  within the cardiovascular system. Section IV describes various methods and techniques in connection with specific structures of heart pumps 
     I. Overview of Heart Pumps 
       FIG. 1  illustrates one embodiment of a heart pump  10  that includes a catheter assembly  100  having a proximal end  104  adapted to connect to a motor  14  and a distal end  108  (see  FIG. 1A ) adapted to be inserted percutaneously into a patient. The motor  14  is connected by a signal line  18  to a control module  22  that provides power and/or control signals to the motor  14 . As discussed further below, the heart pump  10  in various embodiments has an infusion system  26  and a patient monitoring system  30 . 
     The infusion system  26  can provide a number of benefits to the heart pump  10  which are discussed below. In one embodiment, the infusion system  26  includes a source of infusant  34 , a fluid conduit  38  extending from the infusant source  34  to the proximal end  104  of the catheter assembly  100  and a fluid conduit  42  extending from the proximal end of the catheter assembly  100  to a waste container  46 . The flow of infusant to and from the catheter assembly  100  can be by any means, including a gravity system or one or more pumps. In the illustrated embodiment, the infusant source  34  includes an elevated container  50 , which may be saline or another infusant as discussed below. Flow from the elevated container  50  can be regulated by a pressure cuff  54  to elevate the pressure of the fluid in the container  50  to increase flow or by a pinch valve  58  or by other means. 
     The patient monitoring system  30  can be used to monitor the operation of the patient and/or the pump  10 . For example, the patient monitoring system  30  can include a user interface  60  coupled with a source of data  64 . The data source  64  can include one or more patient conditions sensors, such as pressure sensors  68  that are in pressure communication with the patient and/or operating components within the patient. In one embodiment, the pressure sensors  68  fluidly communicate by a conduit  72  that extends between the sensors and a proximal portion of the catheter assembly  100 . The conduit  72  can include a plurality of separable segments and can include a valve  76  to enable or disable the pressure communication to the sensors  68 . 
     The heart pump  10  is adapted to provide an acute or other short-term treatment. A short-term treatment can be for less than a day or up to several days or weeks in some cases. With certain configurations the pump  10  can be used for a month or more. 
     The catheter assembly  100  extends between the proximal end  104  and the distal end  108 . An impeller assembly  116  disposed at the distal end  108  is configured to pump blood to convey blood from one body cavity to another. In one arrangement, the impeller assembly  116  conveys blood proximally through or along a portion of the catheter assembly  100  to provide assistance to the left ventricle of the heart. In another embodiment, the impeller assembly  116  conveys blood distally through or along a portion of the catheter assembly  100  to provide assistance to the right ventricle of the heart. The heart pump  10  is useful as a heart assist device for treating patients with acute heart failure or other heart maladies. The heart pump  10  also can be used in connection with a surgical treatment to support the patient without providing full cardiovascular bypass. A patient could be supported on the device for longer term with proper controls and design. 
     The catheter assembly  100  is provided with a low profile configuration for percutaneous insertion. For example, the distal end  108  of the catheter assembly  100  can be configured to have about an 11 French (approximately 3.5 mm) size in a first configuration for insertion and an expanded configuration, such as up to about 21 French (approximately 7 mm), once positioned in the body. The larger size facilitates greater flow rates by the impeller assembly  116  as discussed below. 
     The catheter assembly  100  is configured to enable the distal end  108  to reach a heart chamber after being inserted initially into a peripheral vessel. For example, the catheter assembly  100  can have a suitable length to reach the left ventricle and sufficient pushability and torquability to traverse the intervening vasculature. The catheter assembly  100  may includes a multilumen catheter body  120  that is arranged to facilitate delivery and operation of the impeller assembly  116 . Further details concerning various embodiments of the catheter body  120  are discussed below in connection with  FIGS. 7-7C . 
     A drive system is provided to drive an impeller within the impeller assembly  116 . The drive system includes a motor  14  and a suitably configured drive controller (not shown) disposed within the control module  22 . The motor  14  is in various embodiments is configured to be disposed outside the patient, e.g., adjacent to the proximal end  104  of the catheter assembly  100 . In one advantageous embodiment, the drive system employs a magnetic drive arrangement. The motor  14  is arranged to generate magnetic fields that will be sensed by permanent magnets disposed within the proximal end  104  of the catheter assembly  100 . This arrangement facilitates very efficient generation of torque used to drive the impeller assembly  116 , as discussed below. 
     Some embodiments described herein could be incorporated into a system in which a motor is miniaturized sufficiently to be inserted into the patient in use, including into the vasculature. Such an embodiment could be operated by disposing control signal lines within the proximal portion of the catheter body  120 . Also, it may be useful to provide the capability to measure blood pressure at the distal end  108  using a device disposed at the proximal end  104 . For example, a pressure sensor at the distal end can communicate with a device outside the patient through a lumen of the catheter body  120 . Various details of these optional features are described in U.S. Pat. No. 7,070,555, which is incorporated by reference herein for all purposes and in its entirety. 
     In another embodiment, a mechanical interface can be provided between the motor and the proximal end  104  of the catheter assembly  100 . The mechanical interface can be between the motor  14  and a drive shaft positioned at the proximal end of the catheter assembly  100 . 
     A torque coupling system is provided for transferring torque generated by the drive system to the impeller assembly  116 . The torque coupling system is discussed further in Section II(C)—Torque Coupling System (as discussed below), but in general can include magnetic interface between the motor  14  and a drive assembly  146  disposed at the proximal end  104  of the catheter assembly  100 . The drive assembly  146  is coupled with a proximal end of an elongate drive shaft  148  in one embodiment. The drive shaft  148  extends between the drive assembly  146  and the impeller assembly  116 . A distal portion of the drive shaft  148  is coupled with the impeller assembly  116  as discussed below in connection with one embodiment illustrated in  FIGS. 4A and 4B .  FIG. 11  shows one manner of coupling the proximal end of the drive shaft  148  with the drive assembly  146 . 
     As discussed above, the heart pump  10  may also includes an infusion system  26 . Figure lA shows that the infusion system  26  can include an infusion inflow assembly  150  provided adjacent to the proximal end  104  in one embodiment. The infusion assembly  150  can be one component of an infusion system that is configured to convey one or more fluids within the catheter assembly  100 . The fluids can be conveyed distally within the catheter assembly  100 , e.g., within the catheter body  120 , to facilitate operation of the impeller assembly  116 , some aspect of a treatment, or both. In one embodiment, the infusion system is configured to convey a lubricant, which can be saline, glucose, lactated Ringer&#39;s solution, acetated Ringer&#39;s solution, Hartmann&#39;s solution (e.g., including compound sodium lactate), and D5W dextrose solution. In another embodiment, the infusion system is configured to convey a medication, or a substance that both acts as lubricant and medication. As sometimes used herein “infusant” is intended to be a broad term that includes any fluid or other matter that provides performance enhancement of a component of the heart pump  10  or therapeutic benefit, and can be wholly or partly extracted from the system during or after operation of the pump. 
     In one embodiment, the infusion inflow assembly  150  includes a catheter body  154  having a luer or other suitable connector  158  disposed at a proximal end thereof and an inflow port in fluid communication with one or more lumens within the catheter assembly  100 . A lumen extending through the catheter body  154  is adapted to be fluidly coupled with a fluid source connected to the connector  158  to deliver the fluid into the catheter assembly  100  and through one or more flow paths as discussed below in connection with  FIGS. 4A, 4B, and 7-7C . 
       FIGS 1A and 12  show that the catheter assembly  100  in various embodiments also includes an outlet positioned at a location that is outside the patient when the heart pump  10  is in use to allow infusant to be removed from the pump and from the patient during or after the treatment. The outlet can be fluidly coupled with an infusant return flow path in the catheter body  120  through a fluid port  144  disposed at the proximal end  104 . 
     The catheter assembly  100  can also include a sheath assembly  162  configured to constrain the impeller assembly  116  in a low profile configuration in a first state and to permit the impeller assembly  116  to expand to the enlarged configuration in a second state. The sheath assembly  162  has a proximal end  166 , a distal end  170 , and an elongate body  174  extending therebetween. In one embodiment, the elongate body  174  has a lumen extending between the proximal and distal ends  166 ,  170 , the lumen being configured to be slidably disposed over the catheter body  120 . The arrangement permits the sheath assembly  162  to be actuated between an advanced position and a retracted position. The retracted position is one example of a second state enabling the impeller assembly  116  to expand to an enlarged configuration. The advanced position is one example of a first state that enables the impeller assembly  116  to be collapsed to the low profile configuration. In some embodiments, a luer  102  or other suitable connector is in fluid communication with the proximal end  166  of the sheath assembly  162 . The luer  102  can be configured to deliver fluids to the catheter assembly  100 , such as priming fluid, infusant, or any other suitable fluid. 
       FIG. 1A  illustrates a retracted position, in which the distal end  170  of the elongate body  174  is at a position proximal of the impeller assembly  116 . In an advanced position, the distal end  170  of the elongate body  174  is positioned distal of at least a portion of the impeller assembly  116 . The sheath assembly  162  can be configured such that distal advancement of the distal end  170  over the impeller assembly  116  actuates the impeller assembly  116  from an enlarged state to a more compact state (or low profile configuration), e.g., causing a change from the second state to the first state, as discussed above. 
       FIGS. 4A &amp; 4B  show the elongate body  174  as a single layer structure from the inner surface to the outer surface thereof. In another embodiment, the elongate body  174  has a multilayer construction. In one arrangement, the elongate body  174  has a first layer that is exposed to the catheter body  120  and a second layer exposed that corresponds to an outer surface of the catheter assembly  100 . A third layer can be disposed between the first and second layers to reinforce the elongate body  174 , particularly adjacent to the distal end thereof to facilitate collapse of the impeller assembly  116 . In another construction, a reinforcing structure can be embedded in an otherwise continuous tubular structure forming the elongate body  174 . For example, in some embodiments, the elongate body  174  can be reinforced with a metallic coil. 
       FIG. 2  show that an impeller housing  202  is disposed at the distal end  108 . The impeller housing  202  can be considered part of the impeller assembly  116  in that it houses an impeller and provides clearance between the impeller and the anatomy to prevent any harmful interactions therebetween. The housing  202  and the impeller are also carefully integrated to maintain an appropriate flow regime, e.g., from distal to proximal or from proximal to distal within the housing. 
       FIGS. 1A and 2  also show that the distal end  108  of the catheter assembly  100  includes an atraumatic tip  182  disposed distal of the impeller assembly  116  in one embodiment.  FIG. 1A  shows that the atraumatic tip  182  can have an arcuate configuration such that interactions with the vasculature are minimally traumatic. The tip  182  can also be configured as a positioning member. In particular, the tip  182  can be rigid enough to help in positioning the impeller assembly  116  relative to the anatomy. In one embodiment, the tip  182  is rigid enough that when it is urged against a heart structure such as the ventricle wall, a tactile feedback is provided to the clinician indicating that the impeller assembly  182  is properly positioned against the heart structure. 
     II. Impeller Rotation and Support 
     The impeller assembly  116  can take any suitable form, but in various embodiments includes an impeller  200  adapted to move a fluid such as blood from an inlet to an outlet of the catheter assembly  100 . In certain embodiments the impeller  200  can be cantilevered or otherwise supported for rotation primarily at one end. 
       FIG. 3  shows that the impeller  200  includes a shaft  204 , a central body or hub  208 , and one or more blades  212 . 
     The shaft  204  and hub  208  can be joined in any suitable fashion, such as by embedding a distal portion of the shaft within the hub  208 . The blades  212  can be spaced out proximal to distal along the axis of the shaft. In some embodiments, the blades  212  are provided in blade rows.  FIG. 9  shows that the distal end of the shaft  204  can extend at least to an axial position corresponding to one of the blade rows. In some embodiments, the shaft  204  can be solid. In other embodiments, the shaft  204  has a lumen extending axially through the hub so that a guidewire can be passed through the catheter assembly  100 . Details of variations with a lumen are discussed further in U.S. application Ser. No. 12/829359, filed Jul. 1, 2010, titled  Blood Pump With Expandable Cannula,  which is hereby incorporated by reference herein in its entirety and for all purposes. 
     A. Infusant Delivery and Removal System 
     The operation and duty cycle of the impeller assembly  116  can be lengthened by providing a hydrodynamic bearing for supporting the shaft  204 . A hydrodynamic bearing can be supported by a lubricant, such as isotonic saline, which can be delivered in a continuous flow. The lubricant can be delivered through the infusion system to an outside surface of the shaft  204 . The infusant may be directed onto the shaft from a radially outward location. In some arrangements, the lubricant flow is controlled such that of a total lubricant volume introduced into the proximal end of the cannula, a first portion of the total volume of the lubricant flows proximally along the shaft  204 . In some embodiments, a second portion of the total volume flows distally along the shaft, the first volume being different from the second volume. The second portion of the total volume can be substantially equal to the total volume introduced into the proximal end of the cannula less the first volume. 
       FIGS. 3 to 8  show various structures for providing rotational support of a proximal portion of the shaft  204  within the distal portion of the catheter assembly  100 . For example, as shown in  FIG. 3 , a bearing assembly  220  can be disposed at a distal end  224  of the multilumen catheter body  120 . In one embodiment, the bearing assembly  224  includes a housing  228  (as shown in  FIG. 4B ) and one or more bearings configured to support the proximal portion of the shaft  204 . The bearing assembly  224 , as illustrated in more detail in  FIG. 4B , includes a plurality of bearings  232   a,    232   b  disposed within the bearing housing  228 . Various materials that can be used for the bearings are discussed below. 
       FIG. 6  shows that the bearing housing  228  has a lumen  234  extending therethrough with a proximal enlarged portion  236   a  and a distal enlarged portion  236   b.  The housing  228  comprises a shoulder defining a narrow portion  240  of the lumen  234  disposed between the enlarged portions  236   a,    236   b.  The first and second bearings  232   a,    232   b  can be disposed within the enlarged portions  236   a,    2366   b  of the bearing housing  228 . 
     In one arrangement, the proximal end of the shaft  204  (e.g., as shown in  FIG. 4A ) is received in and extends proximally of the second bearing  232   b.  In some embodiments there can be one bearing (e.g., only bearing  232   a ), while in other embodiments both bearings  232   a  and  232   b  can be used. In some embodiments, the bearing(s), e.g., bearings  232   a  and/or  232   b,  can be friction fit or interference fit onto the impeller shaft  204 . Accordingly, the shaft  204  can be supported for rotation by the bearings  232   a,    232   b  as well as in the narrow portion  240  of the housing  228 . In embodiments where the bearing(s)  232   a ,  232   b  are friction or interference fit onto the shaft, the bearing(s)  232   a,    232   b  can be configured to rotate with the shaft  204  relative to the bearing housing  228 . Further, the bearing(s)  232   a,    232   b  can have a relatively large clearance with the bearing housing  228 . The clearance between the shaft  204  and the bearing housing  228 , at regions that are not coupled with the bearing, can be in the range of about 0.0005 to about 0.001 inch. In certain embodiments, the clearance can be within a larger range, such as at least about 0.0005 inches, about 0.001 inches or up to about 0.005 inches. In embodiments with multiple bearing(s)  232   a,    232   b,  the clearance can be different for the bearings  232   a,    232   b,  such as providing a larger clearance at the proximal bearing  232   a.    
     In other embodiments, such as in  FIG. 5 , the bearing(s)  232   a,    232   b  may not be friction or interference fit onto the shaft  204 . In these embodiments, the bearing(s)  232   a,    232   b  may be disposed within the bearing housing  228 , for example by an interference or press fit. The shaft  204  may then rotate with respect to the bearing(s)  232   a,    232   b,  and there can be a clearance between the shaft  204  and the bearing(s)  232   a,    232   b.  The clearance between the shaft  204  and the bearings  232   a,    232   b  can be in the range of about 0.0005 to about 0.001 inch. In certain embodiments, the clearance can be within a larger range, such as at least about 0.0005 inches, about 0.001 inches or up to about 0.005 inches. The clearance can be different for the bearings  232   a,    232   b,  such as providing a larger clearance at the proximal bearing  232   a.  In certain embodiments, the bearing housing  228  may provide a thrust surface for bearing axial loads. In other embodiments, there may be other bearings located either distally or proximally of the bearing housing  228  that are configured to bear axial loads. In other embodiments, the fit between the bearings  232   a,    232   b  and the shaft  204  can be tight, which can also assist in bearing axial loads in some aspects. 
     At least the proximal portion of the shaft  204  can be made of a material that will not corrode or otherwise be made to be inert when immersed in the lubricant or other infusant. The material may be one that will not corrode in isotonic saline. Suitable materials may include a wide variety of metals, including alloys, and at least saline-resistant stainless steel and nickel-based alloys. Also, the shaft  204  could be made as a composite to include advantageous properties of a plurality of materials. In some cases the shaft  204  could be formed as a polymer. The class of polymers selected would include those that can form a shaft  204  of a certain stiffness suitable in this application. For example, polycarbonate or PEEK could be used. In certain configurations, the polycarbonate, PEEK, or other suitable polymer can provide enhanced performance by being combined with a second material or structure. A glass or carbon filled polycarbonate or other stiff polymer could also be used. 
     As discussed above, a hydrodynamic bearing between the shaft  204  and the bearings  232   a,    232   b  may be utilized in various embodiments. In one such arrangement, a continuously replenished fluid film is provided at least between the inner wall of the bearing housing and an adjacent moving structure, such as the impeller shaft or an outer surface of a bearing. For example, the bearing housing  228  can be configured to permit a lubricant to be delivered therethrough into the lumen  234 . The bearing housing  232  can include a plurality of channels  260  disposed therein extending proximally from a plurality of ports  264  located at the narrow portion  240  of the housing  228 . Each port  264  can communicate with one of the channels  260  to provide fluid communication into the lumen  234 . 
     As shown in  FIG. 5 , the channels  260  can be formed in the wall of the housing  228 . In one embodiment, the channels  260  are formed as open depressions, e.g., as flutes, extending along the housing  228 . In this embodiment, the channels  260  can be enclosed by a separate structure, such as a separate outer sleeve, that is disposed around the housing  228 .  FIG. 4B  shows that a proximal portion  268  of the impeller housing  202  can be sized to tightly fit over the outer surface of the bearing housing  228 , enclosing the radially outward portion of the channels  260 . In this arrangement, at least a portion of a flow path is formed between an outer surface of the bearing housing  232  and a separate outer sleeve. 
     Fluid communication between the port  264  in the bearing housing  228  and the infusion inflow assembly  150  can be by any suitable combination of lumens within the catheter assembly  100 . For example, in one embodiment, each of the channels  260  has a proximal port  272  that communications with an annular space  274  formed in the catheter assembly  100 . The annular space  274  can be formed between a plurality of separate overlaid structures in the catheter assembly  100 .  FIG. 4A and 4B  show that the annular space  274  is formed between an outer surface  278  of the multilumen catheter body  120  and an inner surface of the proximal length  268  of the housing  202 . 
     Fluid communication is provided in the catheter assembly  100  between the space  274  and the infusion inflow assembly  150 . For example, a plurality of lumens  282  formed in the multi-lumen catheter body  120  can be dispersed circumferentially about the catheter body  120  at a peripheral circumferential region  284 , as illustrated in  FIGS. 7-7C . The peripheral position of the lumens  282  enables a central area of the catheter body  120  to be dedicated to a central lumen  286 . By providing a plurality of smaller lumens  282  located at the periphery, a relatively large flow rate can be delivered through a relatively small circumferential band (when considered in cross-section) of the catheter body  120 . Each of the lumen  282  has a distal port  290  that communicates with the space  274 . 
     A proximal portion of the lumens  282  can take any suitable form. For example, the lumens  282  can communicate at their proximal end with a flow diverting structure (not shown) that is in fluid communication with the infusion inflow assembly  150 . As described herein, in some embodiments the lumen  282  can be disposed circumferentially about the central lumen  286 . The catheter assembly  100  can include a flow diverting structure or connector, e.g., disposed about the proximal end of the catheter body  120  that is configured to divert the infusant into the lumens  282  for distally directed flow therein. In other embodiments, the catheter assembly  120  can include a flow diverting structure disposed adjacent the distal end thereof that is configured to divert the infusant into the lumens  282  from the central lumen  286  for proximally directed flow in the lumens  282 . 
       FIG. 5  includes arrows that illustrate the flow of infusant into the bearing assembly  220 . In one arrangement, the inflow of infusant is indicated by an arrow  300  which is shown pointing distally within one of the channels  260  of the bearing housing  228 . The infusant flow enters the bearing housing through the ports  264 . Although flow is shown in one channel  260 , corresponding flow may be provided in each of a plurality of channels  260  disposed around the central lumen  234 . An arrow  304  illustrates that at least a portion of the infusant delivered through the port  264  may flow generally proximally within the bearing housing  228 . An arrow  308  illustrates that at least a portion of the infusant delivered through the port  264  may flow generally distally within the bearing housing  228 . 
       FIG. 5  illustrates the arrows  304 ,  308  as proximally and distally directed, respectively. However, the high speed rotation of the impeller shaft  204  within the housing  228  will create a thin film of lubricant spacing the impeller shaft  204  from the surfaces of the bearings  232   a,    232   b.  This thin film will extend all the way around the shaft  204  and thus each portion of the flow will have a spiral or helical flow direction. 
     The bearings  232   a,    232   b  can have different configurations to enhance the performance of the pump  10 . For example, the proximal bearing  232   a  can be longer along the longitudinal axis of the bearing housing  228  than the distal bearing  232   b.  A longer proximal bearing  232   a  is believed to better control runout of the shaft  204 . Better runout control on the shaft  204  is believed to enhance the control of the position of the blades  212  relative to the housing  202 . Less runout reduces excessive variation in the gap between the blades  212  and the housing  202 , providing biocompatibility benefits such as reduced hemolysis. 
     In some embodiments, such as those in  FIG. 5  where the bearings  232   a,    232   b  are not friction fit or interference fit onto the shaft  204 , the distal bearing  232   b  has a smaller inner diameter than the proximal bearing  232   a.  If the shaft  204  has a constant diameter, the smaller inner diameter should provide greater control of angular deflection of the shaft. Controlling angular deflection can enhance relative position control of the blades  212  and housing  202 , providing blood handling benefits such as reduced hemolysis. A smaller clearance could also be provided by enlarging the diameter of the shaft  204  at the axial position of the distal bearing. In some embodiments, the larger inner diameter of the bearing  232   b  enables a larger volume of lubricant to flow proximally and a lesser volume to flow distally in the lumen  234 . 
     The continuous introduction of lubricant maintains a constant, predictable and durable rotational bearing state between stationary component, e.g., the bearing housing  282 , and a moving component, e.g., the shaft  204 , a component of the bearings  232   a,    232   b,  or both the shaft  204  and a component of the bearings  232   a,    232   b.  Also, continuous lubricant inflow provides a means for removing heat generated by the relative motion between the shaft  204  and the bearings. Also, the infusant can create fluid pressure within the catheter assembly  100  that can push debris generated within or by the pump  10  out of the bearing housing  220 . Enhancing the volume of infusant that flows along the path indicated by the arrow  304  enhances the likelihood that debris generated by or present in the pump will be removed from the proximal end rather than to be trapped inside the distal portion of the catheter assembly  100 . 
     Another technique for controlling infusant flow in the lumen  234  is to locate the port  264  between the bearings  232   a,    232   b  and closer to one of the bearing. For example, the ports  264  can be located adjacent to the proximal bearing  232   a  in one embodiment. This provides a shorter path of egress out of the narrow portion  240  of the bearing housing  228  in the proximal direction. 
     Other strategies for controlling the flow of infusant within the bearing housing  228  include modifying a surface within one or more of the bearings  232   a,    232   b.    FIG. 8  shows a surface modification  233  provided in a bearing  232   a  to enhance proximally directed flow. The surface modification  233  comprises a plurality of axially oriented grooves  235  in one embodiment. In another embodiment, the surface modification  233  includes one or more spiral grooves. The spiral grooves can be formed with a groove entrance that is substantially parallel with a flow direction of infusant between the bearings  232   a,    232   b  such that a reduction of velocity of the flow is minimized. In one embodiment, each spiral groove includes at least about 3 turns disposed on the inner surface of the bearing between the proximal and distal ends of the bearing. In another embodiment, each spiral groove has adjacent turns that are spaced apart by a minimum pitch of 0.125 inches (3.2 mm). In another embodiment, each spiral groove has an axial density of about 32 turns per inch (about 1.3 turns per mm). The grooves are formed in the surface  237  of the bearing  232   a  upon which the impeller shaft  204  is supported. The grooves  235  locally enlarge the clearance between the shaft  204  and the surface  237  so that a greater volume of infusant can flow distal-to-proximal across the bearing  232   a.  The surface modification  233  reduces back-pressure limiting the distal-to-proximal flow across the bearing  232   a.    
     In other embodiments, it may be desirable to enhance distally directed flow. For example, the infusant may be provided with a fluid intended to be delivered to the patient. In such embodiments, the surface modification  233  can be provided on the distal bearing  232   b.  In certain embodiments, both proximal and distal bearings  232   a,    232   b  are provided with flow enhancing modifications to enhance heat transfer or purging of the bearing assembly  220 . In such embodiments, one of the bearings may have a greater degree of flow enhancement provided on the bearing surface. 
     The arrangement of the bearing assembly  220  can be a factor in selecting an appropriate infusant. Saline is a preferred infusant, but other sufficiently biocompatible infusants could be used. Other embodiments are configured such that little or no infusant flows out of the pump into the patient. For such embodiments, other infusant fluids can be used, such as glucose. 
       FIG. 7  illustrates further features of the catheter body  120 . The catheter body  120  comprises an inner most portion  320  that defines the central lumen  286 . The inner most portion  320  is disposed within, e.g., circumferentially surrounded by, the peripheral circumferential region  284 . A continuous outer circumferential region  324  can be provided around the peripheral circumferential region  284  to fully enclose the lumens  282 , discussed above.  FIGS. 4A and 4B  illustrate that a distal end of the inner most portion  320  is configured to be received and secured within a proximal portion of the lumen  234  within the bearing housing  228 .  FIG. 4B  illustrates that a region of overlap can be provided between a distal portion of the inner most portion  320  and a proximal portion of the bearing housing  228 . This construction provides a continuous lumen defined in part by the central lumen  286  of the catheter body  120  and in part by the lumen  234  of the bearing housing. In another arrangement, the bearing housing  228  and the catheter body  120  are joined by a coupler that enhances the sealing between infusant inflow through the lumens  282  and the channels  260  and the infusant outflow through the central lumen  286 . As discussed further below, this continuous lumen provides a space for the rotation of the shaft  204  of the impeller assembly  116  and the drive shaft  148  of the torque coupling system. 
     The physical connection between the bearing housing  228  and the catheter body  120  can be achieved in any suitable manner.  FIG. 3  illustrates that in one arrangement, a slideable connection is provided. In this arrangement, a rod  332  is provided between the bearing housing  228  and the catheter body  120 . The rod  332  can have any suitable configuration, but may have a proximal end configured to be received in a recess or lumen formed in the catheter body  120  and a distal end  340  configured to couple with the bearing housing  228 .  FIG. 3  shows that the distal end  340  of the rod  332  can be configured to engage with a feature of the bearing housing  228  so that a limited range of sliding is permitted. 
     In one embodiment, the bearing housing  228  has an elongate channel  342  configured to receive a middle portion of the rod  332  and an enlarged depression  344  located at the distal end of the channel  342 . The depression  344  has a width W that is sufficient to receive a wide distal end of the rod  332 . The depression  344  can be configured to have an axial length along the housing  228  that can define a range of motion of the bearing housing  228  relative to the catheter body  120 . 
     In one arrangement, the bearing housing  228  is positioned relative to the catheter body  120  and the rod  332  such that the distal portion of the rod  332  is located at the distal end of the depression  344 . Thereafter, the catheter assembly  100  can be manipulated such that the bearing housing  228  moves distally relative to the catheter body  120  and the rod  332  such that the distal portion of the rod  332  is located at the proximal end of the depression  344 . In the distal position, the impeller assembly  116  is located more distally than in the proximal position. As discussed further below, this enables a variety of techniques for unfurling the impeller blades  212  within the housing  202 . 
     B. Bearing Configurations 
     Any suitable bearing can be used in the catheter assembly  100 . The provision of an infusant for hydrodynamic support enables a wide range of bearing materials to be used. If saline or other more corrosive infusant is used, the bearing must be carefully configured to not degrade within the expected duty cycle of the pump  10 . Some polymeric materials are advantageously not degraded by isotonic saline, and are acceptable materials from this perspective. Under the fluid-dynamic conditions, a hydrodynamic bearing that is supported by a biocompatible infusant such as isotonic saline is preferred. It is believed that certain polymer bearings in combination with isotonic saline can support such conditions as 35,000-50,000 psi-ft/min for an appropriate duty cycle. Other aspects that can guide the choice of bearing configurations include minimizing thermal expansion, given the heat that could be generated in the heart pump  10 , and minimizing moisture absorption. 
     Any suitable polymeric material may be used for the bearings  232   a,    232   b.  The polymeric material can include a homopolymer, a copolymer, or a mixture of polymers. The polymeric material can include thermoplastic or thermoset polymers. Examples of polymers that can be used for bearings  232   a,    232   b  include, but are not limited to, one or more of a polyketone, a polyether, a polyacetal, a polyamide-imide, a polyacetal, polyether ether ketone (PEEK), polytetrafluoroethylene (PTFE), and polyphenylene sulfide (PPS). 
     The polymeric material can also include (e.g., can be mixed, combined, and/or filled with) one or more additives such as a reinforcer and a lubricant. Specific additives include, but are not limited to, graphite, carbon fiber, glass fiber, and PTFE. Those of ordinary skill in the art may appreciate that the additives may be polymeric or non-polymeric. In some embodiments, the polymeric material used for bearings  232   a  and/or  232   b  can include PEEK, carbon fiber, PTFE, and graphite. In other embodiments, the polymeric material can include PPS and glass fiber. In yet other embodiments, the polymeric material can include a polyamide-imide polymer, carbon fiber, and graphite. The polymeric material can include any suitable amount of additive(s). For example, the polymeric material can include a total amount of additive(s) in the range of from about 1 wt % to about 50 wt %, based on the total weight of the polymeric material. In other embodiments, the polymeric material used for bearings  232   a,    232   b  may not include any additives. 
     The polymeric material chosen for bearings  232   a,    232   b  can have particular characteristics that advantageously affect the performance of the bearings. For example, in order to minimize thermal expansion caused by the heat generated in the heart pump  10 , a preferred material would be subject to a minimum of dimensional change, and can have a coefficient of thermal expansion in the range of from about 1.2×10 −5  ° F −1  to about 25.2&gt;10 −5  ° F 1 . In other embodiments, the polymer used for bearings  232   a,    232   b  has a coefficient of friction in the range of from about 0.15 to about 0.3. In another example, in order to minimize or prevent water absorption, the selected polymeric material can have a water adsorption in the range of from about 0.01% to about 0.4% over a 24 hour period. In yet another example, the polymeric material can be suitable for high pressure and velocity performance, and can have a limiting pressure-velocity (PV) in the range of from about 20,000 psi-ft/min to about 50,000 psi-ft/min. 
     The polymeric material used for bearings  232   a,    232   b  may be commercially available. Examples of suitable, commercially-available polymeric materials include, but are not limited to, Ketron PEEK-HPV, Turcite A, Turcite X, Turcite T X, Rulon L R, Rulon J, Rulon 641, Rulon A R, Techtron HPV PPS, Ryton PPS, Torlon 4301, and Torlon 4501. In some embodiments, the polymeric material used for bearings  232   a,    232   b  is Ketron PEEK-HPV. 
     Of course, other bearing configurations and/or materials would be suitable under other conditions, e.g., with less corrosive infusants or if a hydrostatic or non-hydraulic bearing is used. 
     C. Torque Coupling Systems 
     A torque coupling system is provided to rotate the impeller  200  at a high rate to move blood from inside a heart camber to a location within a patient&#39;s vasculature in amounts sufficient to sustain the patient or provide treatment to the patient. The torque coupling system couples the impeller  200  with the motor  136 , which may be disposed outside the patient. It is expected that the impeller  200  and the drive shaft  148  are to be rotated at 25,000-30,000 revolutions per minute for a period of seven to ten days. To provide reliable performance under these conditions, isotonic saline or other lubricant is provided between the drive shaft  148  and stationary components therearound. 
       FIGS. 11 and 4B  illustrate proximal and distal portions  400 ,  404  of the drive shaft  148 . The proximal portion  400  is coupled with the drive assembly  146  such that rotation of the drive assembly  146  rotates the drive shaft  148 . The distal portion  404  of drive shaft  148  is coupled with the impeller shaft  204  such that rotation of the drive shaft  148  causes rotation of the impeller shaft  204 . The drive shaft  148  also includes an elongate body  408  that extends between the proximal and distal portions  400 ,  404 . The elongate portion  408  comprises a lumen  412  extending therethrough. 
     The size of the elongate body  408  may be as small as possible to minimize the cross-sectional profile of the catheter assembly  100 . The cross-sectional profile of the catheter assembly  100  corresponds to the crossing profile of the catheter assembly, which limits where the system can be inserted into the vasculature. The lumen  412  is sized to permit a guidewire to be advanced therethrough in some embodiments. The use of a guidewire is optional, but may simplify insertion. 
     In one embodiment, the elongate body  408  comprises a multi-layer construction. In some embodiments, each layer can include at least one coil wire or a plurality of coil wires all wound in a same orientation. For example, a two-layer, counter-wound wire construction is particularly advantageous. A first layer (e.g., an inner layer) of the elongate body  408  is provided by a coiled wire of nickel-molybdenum-chromium alloy, such as 35NLT or MP35N. In other embodiments, the wire material can be MP35N LT. In one embodiment, the wire has a 0.008 inch diameter and the coil has a 5 filar right-hand wound construction. The outer diameter of the first layer may be about 0.071 inch. A second layer (e.g., an outer layer) of the elongate body  408  can include the same material as the first layer, disposed on the outside of the first layer. The first and second layers can be wound in the same direction, or in opposite directions. For example, in some embodiments the first layer (e.g., an inner layer) can be left-hand wound and the second layer (e.g., an outer layer) can be right-hand wound, or vice versa. In other embodiments, both the first and second layers can be left-hand wound. In yet other embodiments, both the first and second layers can be right-hand wound. The wound coil wire construction can advantageously facilitate proximal and/or distal flow of infusant along the outer layer of the elongate body  408 . For example, the outer layer can be constructed such that the infusant travels along the coil and/or in the direction of the winding. Those skilled in the art may appreciate that, depending on the direction of rotation of the elongate body  408 , the infusant flow can advantageously be directed either proximally or distally. The second layer may be a 5 filar left-hand wound construction. In one embodiment, each layer is formed using a 0.008 inch diameter wire, in the above-noted coiled configuration. In other embodiments, the elongate body  408  can include three or more coil wire layers, wherein the layers are wound in alternating directions. In some embodiments, the outer diameter of the second layer can be between about 0.072 inch and about 0.074 inch, while in other embodiments the diameter can be much larger or smaller. In some aspects, for example, the outer diameter of the second layer can be about 0.073 inch. The inner diameter of the elongate body  408  can be at least about 0.039 inch in some implementations. In some embodiments, one or more ends of the elongate body  408  can be welded and square cut, for example, with a 0.1 inch maximum weld length on each end. The length of the elongate body  408  can vary, but in some embodiments, the length can be between about 47 inches and 48 inches, for example, about 47.5 inches. 
     Other materials and other constructions are possible. The elongate body  408  can be made of other non-ferrous metals or other corrosion resistant material or constructions with appropriate modulus. Other materials that could meet the corrosion requirements include stainless steel (e.g.,  302 ,  304 , or  316 ). In certain embodiments, the elongate body  408  can have a structure that enables other materials to be used. For example varying at least one of coil layers, filars, wire diameter, and coil diameter may enable an otherwise less robust material to operate below the fatigue stress of that material. 
     In another embodiment, a four layer construction is provided. The four layers comprise three wire-wound layers, e.g., similar to the arrangement described above, but included a third wound layer on the outer surface of the second layer. A low friction layer can be disposed on the outside surface of the elongate body  408 . One material that could be used as a low-friction layer is PTFE, known commercially as Teflon®. The low-friction layer should be configured to have sufficient wear resistance, such as by selection of the appropriate PTFE material, e.g. polyphenylene sulphone-filled PTFE, and/or by insuring appropriate infusant flow is maintained during the entire duration of use of the device in order to prevent undesirable local elevated temperature of the PTFE material. 
     The drive shaft  148  operates within the multilumen catheter body  120 . Because the drive shaft  148  is rotated at a very high rate when in use within the multilumen catheter body  120 , the configuration of the surface forming the central lumen  286  is important. In some embodiments, this inner surface has high lubricity and high wear resistance. One material that can be used for the inner surface of the catheter body  120  is high density polyethylene (HDPE), which provides sufficient lubricity and wear resistance. In one embodiment, the entire multilumen catheter body  120  is formed of HDPE. PTFE provides good lubricity and could be used if made sufficiently wear resistant. One way to increase the wear resistance of PTFE is to impregnate it with polyphenylene sulphone (PPSO 2 ), another is to gamma irradiate the material. One way to increase the lubricity of Polyimide materials is to impregnate it with Graphite, another is to impregnate it with Graphite and PTFE. 
       FIG. 4B  shows a clearance  412  between the elongate body  408  of the drive shaft  148  and the inner surface of the multilumen catheter body  120 . The clearance  412  may be about 0.005 inch. Along a diameter between opposite sides of the inner surface of the central lumen  286  and outer surface of the elongate body  408  includes about 0.010 inch of space or diametric clearance. A larger minimum clearance may be desirable if the crossing profile can be enlarged or if other structures of the catheter assembly  100  can be made thinner or eliminated to allow more room between the elongate body  408  and the central lumen  286 . 
       FIGS. 11 and 12  show further details of the drive assembly  146 , which is disposed at the proximal end  104  of the catheter assembly  100 . The drive assembly  146  includes a drive housing  450  having a recess or cavity  454  disposed therein. The cavity  454  is configured for mounting a rotor support shaft  458  for rotation therein. The support shaft  458  has a proximal end and a distal end and a plurality of components mounted thereon. The distal end of the support shaft  458  has a recess  462  formed therein to receive a proximal end of the drive shaft  148 . The support shaft  458  may also have a lumen  466  disposed therein for slideably receiving a guidewire. 
     A rotor  470  is mounted on an outer surface of the support shaft  458  between sleeve bearings  474   a,    474   b,  as shown in  FIG. 12 . The rotor  470  can take any suitable form, but in one embodiment includes an elongate magnet  476  disposed between proximal and distal flywheels  478   a,    478   b.    
     The proximal end of the support shaft  458  has a tapered port  480  for receiving the guidewire. The proximal end can be configured for engaging the motor  136  in some embodiments. In other embodiments, a magnetic field is induced by the motor  136  in a manner that creates torque and rotation of the shaft  458 . 
     An infusant outflow path  482  is provided within the drive assembly  146 . The outflow path  482  is provided between an outer surface of the support shaft  458  and an inner surface  486  of the distal bearing. The flow path  482  continues from the distal bearing  474   b.  radially outwardly along thrust surfaces  490   a.  The flow path continues proximally between the outer surface of the rotor  470  and the inner surface defining the cavity  454 . The flow path  482  continues radially inwardly along the thrust surface  490   a  toward the support shaft  458 . The flow path  482  continues proximally between the support shaft  458  and the proximal bearing  474   a.  Proximal of the bearing  474   a,  the flow of infusant exits the catheter assembly  100  through an outflow port  144  through which it can be directed to the waste container  46  or discarded. The flow path is shown in more detail in  FIGS. 1, 12, 12A, and 12B . 
     III. Structures that Facilitate Deployment and Retreival 
     The catheter assembly  100  can include one or more features that facilitate the deployment and/or retrieval of one or more components of the distal end  108  of the heart catheter assembly  100  (e.g., the impeller assembly  116  or a portion thereof). 
     A. Optionally-Expandable Diffuser 
     As shown in  FIGS. 13A and 13B , the pump can include a diffuser  502   a,    502   b.  As illustrated in  FIG. 13A , in some embodiments the diffuser  502   a  is connected to the impeller hub  208 . For example, the diffuser  502   a  can be integral, or form a unitary structure, with the impeller hub  208 . In another example, the proximal end of the impeller hub  208  can include the diffuser  502   a.  As illustrated in  FIG. 13B , in other embodiments, the diffuser  502   b  is separate from (e.g., not connected to) the impeller hub  208 . 
     The diffuser  502   a,    502   b  can be disposed between the distal end of the elongate body of the catheter body and the impeller. The diffuser  502   a,    502   b  can be configured to be positioned within the housing  202  and adjacent to the proximal opening of the housing. In some embodiments, the diffuser  502   a,    502   b  can be axially aligned with the proximal opening of the housing  202 . Advantageously, this configuration can maximize the flow directing capabilities of the diffuser  502   a,    502   b,  as discussed further herein. The diffuser  502   a,    502   b  can be located adjacent the proximal end of the hub  208 . The diffuser  502   a,    502   b  can include a proximal end  504   a,    504   b.  and a distal end  505   a,    505   b.  The proximal end  504   a,    504   b.  of the diffuser  502   a,    502   b  can be positioned adjacent the distal end of the bearing housing  228  (e.g., over a bearing  516  and/or a front thrust washer  518 ). As shown in  FIG. 13A , the proximal end  504   a  can be separated from the bearing  516  by a gap  522 . The gap  522  can have an axial length generally equal to the length of the bearing  516 . The gap  522  can also be generally cylindrical with a longitudinal axis that is aligned with the longitudinal axis of the impeller shaft  204 . The distal end  505   a,    505   b  can be located adjacent the proximal end of the impeller hub  208 . The diffuser  502   a,    502   b  can include a flow directing surface. For example, an outer surface  513  of the diffuser  502   a,    502   b  can form a curved line from the proximal end  504   a,    504   b.  to the distal end  505   a,    505   b,  as illustrated in  FIGS. 13A-B . As viewed from the proximal or distal end, the diffuser  502   a,    502   b  can have a generally circular cross sectional shape. As shown in  FIGS. 13A and 13B , the diameter of the diffuser  502   a,    502   b  can be greatest in the mid section and can taper to a smaller diameter in the distal and/or proximal directions. The diffuser  502   a,    502   b  can have a maximum diameter that is generally greater than the diameter of the hub  208  and/or the bearing housing  228 . The diameter of the proximal end  504   a,    504   b.  can be generally equal to the diameter of the bearing housing  228 . The diameter of the distal end  505   a,    505   b  can be generally equal to the diameter of the hub  208 . The diffuser  502   a,    502   b  may be referred to herein as a bulge, and in various embodiments can have a radially enlarged portion disposed downstream of the impeller. 
     Advantageously, the relatively large diameter and/or the curved outer surface can assist in directing (e.g., diffusing) fluid flow out of the housing  202 . The geometry of the diffuser  502   a,    502   b  (e.g., the radius of curvature of the outer surface) can be optimized to control desired fluid properties such as boundary layer flow, laminar flow, and pressure gradients and to reduce outlet flow losses. 
     The diffuser  502   a,    502   b  can include a wall  511 . The wall  511  can include an inner surface  512  and the outer surface  513 , described above. The wall  511  can have a thickness extending from the inner surface  512  to the outer surface  513 . In some embodiments, the wall  511  can have a generally uniform thickness along the axial length of the diffuser  502   a,    502   b.  One advantage of a generally uniform wall thickness is that the diffuser  502   b  can be more easily expanded and/or collapsed, as described herein. In other embodiments, the wall  511  can have a variable thickness along the axial length of the diffuser  502   a,    502   b.  For example, as illustrated in  FIG. 13A , the thickness of the wall  511  can increase in the distal direction. One advantage of a variable thickness wall is that it can have variable structural strength. For example, a wall having a thickness that increases distally can advantageously have greater strength in areas that are most exposed to oncoming blood flow. 
     The inner surface  512  can define a chamber  506  through which the impeller shaft  204  can pass. As shown in  FIG. 13A , the diffuser  502   a  can form part of the proximal end of the hub  208  of the impeller  200  (e.g., the hub  208  can be connected to the diffuser  502   a ). Thus, the diffuser  502   a  can rotate with the rotating hub  208 . The diffuser  502   a  can also include a proximal cavity outlet  508 . As shown in  FIG. 13B , the diffuser  502   b  can be a component separate from the impeller  200 . In this embodiment, the diffuser  502   b  can be stationary when the hub  208  is rotating. The diffuser  502   b  can also include a distal cavity outlet  510 . 
     There can be many advantages to including a diffuser  502   a  that is connected to the impeller hub  208 . For example, the unitary construction can be easier to manufacture and/or assemble. As described herein, the distal end of the diffuser  502   a  can be relatively thick and strong (e.g., stiff). In addition, it can be advantageous for the infusant to exit the catheter assembly  100  at the proximal outlet  508 , which is generally at the downstream end of the diffuser  502   a.    
     There can also be advantages to including a diffuser  502   b  that is a structure separate from and not directly attached to the impeller hub  208 . In some embodiments, the diffuser  502   b  can be made from a material that is different from the material used to make impeller hub  208 . For example, the diffuser  502   b  can be made from a material that is relatively more flexible (softer) than the material of the impeller hub  208 . In other embodiments, the wall  511  of diffuser  502   b  can have a generally uniform thickness. These features of diffuser  502   b  can facilitate the expansion and/or contraction of the diffuser  502   b,  described further herein. 
     As shown in  FIGS. 13A and 13B , the diffuser  502   a,    502   b  can be generally hollow, as defined by the chamber  506 . The diffuser  502   a,    502   b  can be sufficiently hollow and can be made of a relatively flexible material (e.g., a polymer or elastomer) to be expandable and/or collapsible. For example, the maximum diameter of the diffuser  502   a,    502   b  can expand from a first diameter to a second diameter. Advantageously, the collapsible diffuser  502   a,    502   b  can have a deployed, expanded configuration, and a retracted, collapsed configuration. In the deployed, expanded configuration, the diffuser  502   a,    502   b  can have a maximum diameter (e.g., as measured at the mid-section or bulge) that is generally greater than the diameter of the hub  208  and/or the bearing housing  228 . In the retracted, collapsed configuration, the diffuser  502   a,    502   b  can have a reduced diameter. For example, in the retracted, collapsed configuration, the diffuser  502   a,    502   b  can have a maximum diameter that is generally less than or equal to the diameter of the hub  208  and/or the bearing housing  228 . Although described as having a diameter, those skilled in the art may appreciate that while retracted and/or collapsed, the diffuser  502   a,    502   b  may not have a generally circular cross section. A collapsible diffuser can be advantageous compared to a non-collapsible diffuser because a collapsible diffuser can allow the overall structure to maintain and low profile for the purpose of retracting back into a sheath and for insertion into and/or removal from a patient. 
     In some embodiments, the relatively flexible material itself may not be significantly expandable (e.g., stretchable and/or elastic). Rather, the terms “expandable” and “collapsible” can refer to the overall expansion and/or collapse of the chamber  506  of the diffuser  502   a,    502   b.  In other embodiments, the relatively flexible material itself may be significantly expandable (e.g., balloon-like). 
     The chamber  506  can be configured (e.g., sized) to allow fluid (e.g., infusant) flow through the diffuser  502   a,    502   b.  The diffuser  502   a,    502   b  can be configured for fluid communication with a fluid, such as an infusant, that passes through the bearing assembly  220 . The bearing assembly  220  illustrated in  FIGS. 13A and 13B  can have many, if not all, of the same features as described with respect to the bearing assembly  220  illustrated in  FIG. 5 . As shown in  FIGS. 13A and 13B , the infusant can follow an infusant path  514   a,    514   b.  out of the bearing assembly  220  and into the diffuser  502   a,    502   b  via a passage or cavity  520  between the bearing  516  and the washer  518 . For at least a portion of the infusant path  514   a,    514   b,  the infusant can travel distally. In some embodiments, at least a portion of the infusant path  514   a,    514   b.  can be non-helical (e.g., generally linear). In other embodiments, at least a portion of the infusant path  514   a,    514   b.  can be generally helical. The helical shape of the infusant path  514   a,    514   b.  can be caused at least in part by rotation of one or more components of the impeller assembly  116  (e.g., the impeller shaft  204  and/or impeller hub  208 ). 
     As illustrated in  FIG. 13A , the infusant path  514   a  can extend from the proximal end  504   a  to the distal end  505   a  and can return back to the proximal end  504   a  to exit the proximal outlet  508  via the gap  522 . The portion of the infusant path  514   a  that extends from the proximal end  504   a  to the distal end  505   a  is helical (e.g., can encircle the impeller shaft  204  one or more times along the axial length of the path). The return portion of the infusant path  514   a  can be non-helical (e.g., generally linear). The return portion of the infusant path  514   a  can be non-helical at least in part because the return portion can follow the curved interior surface  512  of the diffuser wall  511 . In use, the infusant can exit the bearing assembly  220  at the cavity  520  to enter the chamber  506 . At least a portion of the infusant can then follow infusant path  514   a  to travel helically around the impeller shaft  204  in the distal direction until the distal end  505   a  is reached. The infusant then changes direction and turn around to flow proximally along the non-helical return portion of the infusant path  514   a  and through the gap  522  to exit the pump via the proximal cavity outlet  508 . Although shown as a single distal-to-proximal line, in some embodiments, exit flow can be induced along and generally following the shape of the inner surface  512  to the proximal cavity outlet  508 . In use, as the infusant passes through the gap  522 , the infusant can act as a hydrodynamic bearing (e.g., in addition to the hydrodynamic bearing that may be present between the impeller shaft and the bearing housing as described herein). This hydrodynamic bearing can generally be in the shape of a cylinder that extends axially, as defined by the gap  522 . Advantageously, this hydrodynamic bearing can reduce friction between the diffuser  502   a  and the bearing housing  228 . 
     As illustrated in  FIG. 13B , the infusant path  514   b.  can extend from the proximal end  504   b.  to the distal end  505   b.  As illustrated in  FIG. 13B , the infusant path  514   b.  is helical (e.g., can encircle the impeller shaft  204  one or more times along the axial length of the path). In use, as shown in  FIG. 13B , generally all of the infusant flows proximally to distally within a distal portion of the bearing assembly  220  and exits the bearing assembly at the cavity  520  to enter the chamber  506 . In various embodiments, a portion of the infusant flows proximally within a proximal portion of the bearing assembly  220  through a space between the drive shaft  148  and the catheter body  120 . This return flow is discussed above, e.g., in connection with arrow  304  in  FIG. 8 . At least a portion of the infusant then follows the infusant path  514   b.  to travel helically around the impeller shaft  204  in the distal direction and out through the distal cavity outlet  510 . As illustrated in  FIG. 13B , the distal cavity outlet  510  defines a gap between the distal end  505   b  of diffuser  502   b  and the proximal end of impeller hub  208 . In use, as the infusant passes through the distal cavity outlet  510 , the infusant can act as a hydrodynamic bearing. This hydrodynamic bearing can generally be in the shape of a cylinder having a length extending axially along the length of the gap and a radius corresponding to the cross sectional radius of the gap. Advantageously, this layer of infusant between the diffuser and the impeller hub can reduce friction between the diffuser  502   b  and the impeller hub  208  when the pump is in operation. 
     As described herein, the diffuser  502   a,    502   b  can be expandable. In some embodiments, one or more forces exerted by the infusant can be used to expand the diffuser  502   a,    502   b.  The flow rate of the infusant can be sufficient to establish an area of positive pressure within the diffuser  502   a,    502   b,  thereby allowing at least a portion of the infusant to exit adjacent to a distal end of the device. In some embodiments, the static pressure of the infusant entering the chamber  506  can cause the diffuser  502   a,    502   b  to expand. In any of these embodiments, an inflated diffuser  502   a,    502   b  can be deflated by interrupting and/or discontinuing the flow of infusant into the diffuser  502   a,    502   b  and by allowing the infusant to exit the diffuser via the proximal outlet  508  or the distal outlet  510 . In some embodiments, the wall is elastic but the pliability is relatively low such that upon removal of the infusant flow a transition from expanded to low profile is rapid. The diffuser  502   a,    502   b  self-collapses displacing the infusant out of the chamber  506  through one or more small apertures. In addition to promoting quick deflation, the relatively low pliability will provide a uniform diffuser profile, e.g., will not be deformed or deflected by any varying pressure or flow rate of the blood from the impeller  200 . A lower infusant pressure configuration can also be provided by increasing the pliability of the structure forming the diffuser  502   a,    502   b.  The structure can be of enhanced pliability by material selection or constructions (e.g., by being thinner or adopting other balloon-like features). 
     In other embodiments, the centrifugal force exerted by the infusant as it travels along the helical path  514   a,    514   b.  can be used to expand the diffuser  502   a,    502   b.  As illustrated in  FIG. 13A , the diffuser  502   a  can be connected to the impeller assembly  116 . 
     In these embodiments, the diffuser  502   a  and the impeller assembly  116  can be rotated. In use, when the impeller assembly  116  and the diffuser  502   a  are rotated, the infusant can also rotate due to, e.g., shear forces generated from the fluid contact with the rotating diffuser  502   a  and/or the rotating impeller shaft  204 . The rotating infusant can exert a pressure on the inner surface  512  to thereby expand the diffuser  502   a  from the collapsed configuration to the expanded configuration. Thus, in some embodiments, the diffuser  502   a  can be centrifugally expanded. In yet other embodiments, the diffuser  502   a  can be expanded using a combination of static and centrifugal forces. 
     As illustrated in  FIG. 13B , the diffuser  502   b  may not be rotatable. In these embodiments, when the impeller shaft  204  is rotated, the infusant can also rotate due to, e.g., shear forces generated from the fluid contact with the rotating impeller shaft  204 . As described herein, the rotating infusant can exert a pressure on the inner surface  512  to thereby expand the diffuser  502   b  from the collapsed configuration to the expanded configuration. Thus, in some embodiments, the diffuser  502   b  can be centrifugally expanded. In yet other embodiments, the diffuser  502   b  can be expanded using a combination of static and centrifugal forces. 
     Infusant exiting the diffuser  502   a,    502   b  can be continuously replenished with additional infusant via the flow path  514 . If the impeller shaft  204  stops rotating, the pressure generated from rotation can decrease to match the pressure acting on the outside of the diffuser  502   a,    502   b,  thereby allowing the diffuser  502   a,    502   b  to collapse. 
     In yet other embodiments, the diffuser  502   a,    502   b  can be expanded and/or inflated by a combination of static and centrifugal forces. For example, the diffuser  502   a,    502   b  can be expanded and/or inflated by a combination of the static force of the infusant as it enters the chamber  506  and the centrifugal force of the infusant as it travels along the helical path  514 . 
     B. Relatively Axially-Moveable Impeller Housing 
     As illustrated in  FIG. 14B , when the impeller and the diffuser  502  are in the proximal position, at least a portion of the impeller (e.g., the blades  212  and/or the hub) and/or the diffuser  502  may be relatively positioned in a portion of the housing  202  having minimal or no coating, such as an outlet  802  of the housing  202  (e.g., the outlet through which blood is pumped). In some embodiments, the housing  202  can be moved axially relative to the impeller and/or the diffuser  502 . In some embodiments, the housing  202  is moved axially over the impeller and the impeller is stationary. Those skilled in the art may appreciate that in some embodiments, the housing  202  may not be configured to move axially relative to the impeller and/or the diffuser  502  (e.g., housing  202  is fixed or stationary relative to impeller and/or the diffuser  502 ). For example, the housing  202  and the diffuser  502  can be spaced apart by a relatively constant axial distance in all operational states, or at least in a collapsed and an expanded state. 
     As illustrated in  FIGS. 14A and 14B  and as described herein, the rod  332  provided between the catheter body  120  and the bearing housing  228  enables a slideable engagement between the catheter body  120  and the bearing housing  228 . The distal end of the catheter body  120  can be connected to the proximal portion  268  of the impeller housing  202 . The catheter body  120  can translate distally from a proximal position to a distal position, and vice versa, by the application of an axial force described further herein. As described herein, for example with respect to  FIGS. 4A-4B , the catheter body  120  can be coupled to the proximal portion  268  of the impeller housing  202 . For example, the proximal portion  268  of the impeller housing  202  can be fitted over the distal end of the catheter body  120 . 
     In the proximal position, illustrated in  FIG. 14A , the axial position of the outlet  802  can be proximal of the axial position of the proximal-most blade  212 . In the distal position, illustrated in  FIG. 14B , the axial position of the outlet  802  can generally correspond to the axial position of the proximal-most blade  212 . Advantageously, the rod  332  and the enlarged depression  344  can control the axial distance over which the impeller housing  202  is capable of sliding. The rod  332  can also advantageously prevent the bearing housing  228  from rotating with the impeller shaft  204 . 
     Those skilled in the art may appreciate that the axial movement of the catheter body  120  and the impeller housing  202  relative to the impeller and/or the diffuser  502  can have the same relative effect as axially moving the impeller and/or the diffuser  502  relative to the catheter body  120  or the impeller housing  202 , even if the impeller and/or the diffuser are not actually moved axially. Accordingly, in some embodiments the catheter body  120  in the proximal position can be referred to as the deployed position of the impeller and/or the diffuser  502 . The catheter body  120  in the distal position can be referred to as the retracted position of the impeller and/or the diffuser  502 . 
     The ability of the impeller and/or the diffuser  502  to be retracted and deployed relative to the impeller housing can have many advantages. For example, axial movement of the impeller housing relative to the impeller and/or the diffuser can reduce the profile of the pump to ease insertion and retrieval. In some embodiments, in the retracted position, the impeller hub  208 , blades  212 , and/or diffuser  502  can be positioned at the same axial location as a portion of the housing  202  that does not have a covering (e.g., the outlet  802 ). Accordingly, the cross-sectional area of the catheter assembly  100  measured at the axial position of the diffuser  502  in the retracted position, for example, is comparatively smaller than when it is in the deployed position. The smaller cross sectional area can be advantageous for minimizing trauma to a user during insertion into and/or retrieval from the body. 
     In other embodiments, the retracted position of the impeller and/or the diffuser can be distal of the deployed position of the impeller and/or the diffuser. In some embodiments, the impeller housing can have a rigidity that varies axially. For example, the impeller housing can have a proximal portion that is more rigid (e.g., less flexible) than a distal portion. In these embodiments, the impeller and/or the diffuser can reside in the proximal, rigid portion while in the deployed position. The impeller and/or the diffuser can reside in the distal, flexible portion while in the retracted position. Advantageously, when the impeller and/or the diffuser reside in the flexible portion of the impeller housing, this portion of the pump may be collapsed to a lower profile than would otherwise be achievable if the impeller and/or the diffuser remained in the rigid portion of the impeller housing. 
     As described herein, the catheter body can be coupled to the impeller housing. The retraction and deployment (e.g., movement between proximal and distal positions) of the impeller housing can be controlled by manipulation of a proximal end of the catheter assembly that results in an application of axial force to the catheter body. For example, the impeller housing can be moved axially by the rotational force applied by a nut disposed at the proximal end of the catheter assembly. A section of the proximal end of the catheter assembly is illustrated in  FIGS. 15A and 15B . 
     In some embodiments, axial force is applied to the catheter body via an impeller deployment assembly  800 . The impeller deployment assembly includes a nut  804  that is engaged with a portion of the catheter assembly, such as a flow diverter  806 . As described herein, the flow diverter  806  can be a part of the infusion inflow assembly  150 , illustrated in  FIG. 1 . The distal end of the flow diverter  806  can be connected to a proximal portion of the catheter body. In some embodiments, the nut  804  can be engaged with a pin  808 . The pin  808  can penetrate through the wall of the drive housing  450  and can be coupled with or fixedly attached to the flow diverter  806 . The nut  804  can be disposed over at least a portion of the drive housing  450  and/or the flow diverter  806 . The nut  804  can include an internal engagement structure that is configured to engage the flow diverter  806  (e.g., via the pin  808 ). In some embodiments, the internal engagement structure can include internal threading. In other embodiments, the internal engagement structure can include a cam track  812  having first and second ends (e.g., a proximal end and a distal end), as illustrated in  FIG. 15C . In these embodiments, the pin  808  can be configured to travel along the cam track  812 . The internal engagement structure can be generally helical. The drive housing  450  can also include a longitudinal channel  810  along which the pin  808  can travel. 
     As illustrated in  FIGS. 15A and 15B , the drive housing  450  can contain the support shaft  458  and the drive shaft  148 . The drive housing  450  can also capture the nut  804 . For example, a retention structure can be formed in the outside surface of the housing  450  to prevent the nut  804  from slipping proximally or distally relative to the housing  450 . One embodiment of a retention structure is illustrated below in connection with the deployment device of  FIGS. 15D-F  but can be included with the deployment device  800  as well. The pin  808  can penetrate the wall of the drive housing  450  and permit axial translation of the flow diverter  806  by acting as a cam. In some embodiments, the support shaft  458  and the thread advance nut  804  may be rotatable but not translatable relative to the drive housing  450 . 
     In use, a rotational force can be applied to the nut  804 . This application of rotational force can be converted into an axial force that is applied to the flow diverter  806  and the catheter body. As described herein, the pin  808  can be fixedly attached to the flow diverter  806  at one end and have a second end disposed within the inner surface of the nut  804  along the cam track thereof. The rotation of the nut  804  in a first direction (e.g., clockwise or counter-clockwise) can cause the pin  808  to translate from a proximal position (e.g., proximal end) to a distal position (e.g., distal end) in the longitudinal channel  810 . Accordingly, the flow diverter  806 , the catheter body, and the impeller housing can also translate from a proximal position to a distal position. As described herein, the distal translation of the catheter body and the impeller housing can improve the ease of the retraction of the impeller hub and the blades into the impeller housing. In embodiments where the outlet  802  is generally free of a polymeric coating, relative movement of at least a portion of the impeller and/or the diffuser proximally into the outlet  802  or distally into a more flexible region of the impeller housing (i.e., mid section of the housing where there is less strut material) can advantageously reduce the profile of the pump upon collapsing into the sheath. In addition, axial adjustment of the impeller housing relative to the impeller can advantageously promote more efficient flow dynamics. In some embodiments, the impeller is positioned closer to the outlet  802  than the middle portion of the housing in order to improve flow dynamics. 
     A rotational force applied to the nut  804  in a second direction (e.g., counter-clockwise or clockwise) can cause the pin  808  to translate from the distal position to the proximal position. Accordingly, the flow diverter  806 , the catheter body  120 , and the impeller housing  202  can also translate from a distal position to a proximal position. As described herein, the proximal translation of the catheter body  120  and the impeller housing  202  can effectively result in the deployment of the impeller hub  208  and the blades  212 . 
       FIGS. 15D-F  illustrate another embodiment of a deployment device  850  that can be used to manipulate or deploy a distal structure of the catheter assembly and/or the impeller housing. As with the deployment device  800 , the deployment device  850  can be used to actuate the impeller  200  between retracted and deployed configurations. 
     As discussed above, the catheter assembly can include a flow diverter  852  that is part of the infusion system. The flow diverter  852  may be coupled with a proximal portion  122  of the catheter body  120 . In one embodiment, the proximal end of the proximal portion  122  is inserted into a recess  854  formed at a distal  852   a  end of the flow diverter  852 . The connection between the proximal portion  122  of the catheter body  120  the flow diverter  852  can be further made secure by a strain relief  856  disposed at the junction and extending distally thereof. The strain relief  856  overlaps a proximal length of the proximal portion  122  and absorbs movements of the portions of the catheter assembly to isolate the connection between the flow diverter  852  and the catheter body. A cap  860  can be used to securely couple strain relief  856  to the flow diverter  852 . A proximal portion  862  of the flow diverter  852  is received within a recess  864  of the housing  450 . A seal device  866 , such as an  0 -ring, may be provided between the proximal portion  862  of the flow diverter  852  and inside surface of the recess  864  to prevent infusion from exiting the housing  450  in an undesirable manner. 
     The flow diverter  852  also includes a lumen  868  that extends from a proximal end  852   b  to the distal end  852   a  thereof. The lumen  868  is configured to permit a proximal portion of the drive shaft  148  to reside therein. In some embodiments, flow diverter  852  is configured to cause some infusant to flow proximally in the lumen  868  between the drive shaft  148  and the inner surface of the flow diverter  852  that forms the lumen  868  to lubricate and cool the drive shaft. The flow diverter  852  can be configured to cause most or substantially all of the infusant entering the diverter through the lumen in the catheter body  154  to flow distally between the catheter body  120  and the drive shaft  148 . In one arrangement, the lumen  868  is enlarged from a location proximal of where the catheter body  154  couples with the flow diverter  852  toward the distal end  852   a  of the flow diverter. This enlargement creates a path of least resistance toward the distal direction to divert the flow distally. In one embodiment, the lumen  868  is further enlarged at a location between where the catheter body  154  couples with the flow diverter  852  and the recess  854  such that a substantially continuous lumen can be formed to keep flow resistance at the junction between the flow diverter  852  and the proximal portion  122  of the catheter body  120  to a minimum. 
     The deployment device  850  includes a guide track  872  on a proximal portion  862  of the flow diverter  852 , a guide member  874 , and an actuator  876 . The guide track  872  can comprise an axially oriented slot or recess formed in the outside surface of the proximal portion  862 . The guide track  872  may be configured to slidably receive a guide member  874  such that relative movement can be provided between the guide track  872  and a guide member  874 . A portion of the guide member  874  may extend through sidewall of the drive housing  450  such that the axial position of the guide member  874  can be fixed and relative movement is provided by movement of the flow diverter  852  relative to the guide member. In one embodiment the guide member  874  is a pin that has one end received in a small hole in the drive housing  450  and the other end disposed in the guide track  872 . 
     The actuator  876  is configured to translate rotational motion thereof into axial motion of the flow diverter  852 . For example, the actuator  876  can comprise a nut that includes internal threads that are engaged with external threads on the outside surface of the flow diverter  852 . In various embodiments, a proximal portion of the actuator  876  is anchored to the drive housing  450  to prevent the actuator  876  from moving axially along the drive housing. In one embodiment a retention structure  882  is provided between the actuator  876  and the drive housing  450 . One embodiment of the retention structure  882  is illustrated in detail B of  FIG. 15D . In particular, the retention structure  882  includes an inwardly protruding member  884  that is received in an annular recess formed in the outside surface of the drive housing  450 . The protruding member  890  can include an inwardly protruding ring having n diameter that is less than the diameter of the actuator  876  distally and proximally of the protruding member  884 . 
       FIGS. 15E-F  illustrate operation of the deployment device.  FIG. 15E  corresponds to an expanded configuration of the catheter assembly  100 . In this position, the pin  874  is positioned at the distal end of the guide track  872  and the flow diverter  852  is in a proximal position. Because the flow diverter  852 , the catheter body  120 , and the impeller housing are coupled together so that they move in unison, the catheter body  120  and the impeller housing are also positioned in a relatively proximal position. Relative axial movement is permitted between the impeller and the catheter body, as well as between the diffuser and the catheter body. Also, because the catheter body  120 , the flow diverter  852 , and the impeller housing move in unison, relative axial movement is permitted between the impeller (and/or diffuser) and the impeller housing. As a result, the impeller will be in a more distal position relative to the impeller housing when the catheter assembly  100  is in the configuration of  FIG. 15E . The more distal position moves the impeller into the largest volume portion of the impeller housing enabling the impeller to expand. 
       FIG. 15F  corresponds to a collapsed configuration of the catheter assembly  100 . In this position, the pin  874  is positioned at the proximal end of the guide track  872  and the flow diverter  852  is in a distal position. This causes the impeller to be in a more proximal position relative to the housing when the catheter assembly is in the configuration of  FIG. 15F . This more proximal position moves the impeller into engagement with the inside surface of the housing tending to collapse the impeller. 
     To move from the expanded configuration of  FIG. 15E  to the collapsed configuration of  FIG. 15F , the actuator  876  is rotated in a manner that causes the threads to act upon each other which creates axial movement of the catheter body  120  and the impeller housing  202 . 
     C. Impellers Having Self-Sealing Impeller Tips and Lumens With Valves 
     In some embodiments, the tip  602  of impeller hub  208  can be self-sealable or resealable (e.g., configured to automatically effectively form a seal to substantially stop the flow of a fluid in the absence of direct action by a user or operator to form the seal), as illustrated in  FIGS. 16A-C . As illustrated in  FIGS. 16B-C , the tip  602  of impeller hub  208  can include a resealable member having a resealable path therethrough. 
     As shown in  FIG. 16A , the impeller tip  602  can be made of an elastomeric material (e.g., a silicone or polyisoprene polymer). As shown in  FIG. 16A , the tip  602  can include a resealable path  604  that extends along the length of the tip. The resealable path  604  can extend from the outer surface at the distal end of tip  602  to the impeller shaft, which can be hollow. The hollow shaft extension  606  is shown in  FIGS. 16A and 16B  connected by the resealable path  604  to the tip  602  and is connected at its proximal end to the impeller shaft  204 . Thus, the resealable path  604  can extend from the impeller shaft  204  to the outer surface of the tip  602 . The resealable path  604  can be configured for guidewire passage. The resealable path  604  can generally pass through the center of rotation of the impeller tip  602 . 
     The resealable path  604  can be created using a very small diameter, e.g., a 32 gauge (0.00925 inch or 0.235 mm) wire or pin. In some embodiments, the resealable path  604  can be created without coring the impeller tip  602  (e.g., without punching out or otherwise removing a cylinder of material). The resealable path  604  can be self-sealable. For example, the resealable path  604  can close or seal automatically, without the use of additional tools or implements. The resealable path  604  can be self-sealable due to the elastomeric properties of the material used for impeller tip  602  (e.g., a silicone or polyisoprene polymer) and/or the diameter of the resealable path  604 . In some embodiments, circumferential and radial forces of the tip material and/or external pressure forces (illustrated with arrows at  612 ) exerted while the catheter assembly  100  is implanted can also contribute to sealing the resealable path  604 . 
     In some embodiments, the tip  602  or resealable member  622 ,  624  can be made of the same material as the rest of the impeller system (e.g., hub, blades, shaft, and/or shaft extension). In other embodiments, the tip  602  or resealable member  622 ,  624  can be made from a different material than the rest of the impeller system (e.g., hub, blades, shaft, and/or shaft extension). For example, the tip  602  or resealable member  622 ,  624  can be made of a material that is more elastomeric (e.g., has greater elasticity) than the material from which the impeller shaft  204  and/or shaft extension  606  are formed. In another example, the tip  602  or resealable member  622 ,  624  can be made from a polyisoprene polymer and at least a portion of the impeller shaft  204  (e.g., the distal end) and/or shaft extension  606  are formed from an acrylonitrile butadiene styrene (ABS) polymer or a polycarbonate polymer. 
     In some embodiments where the impeller tip  602  comprises a resealable member  622  that is made separately from the rest of the impeller system, the resealable member  622  can include one or more proximally-extending tabs  616 . The one or more tabs  616  can be disposed about the proximal end of resealable member  622 . In some embodiments, the resealable member  622  can include one generally cylindrical tab  616  that is disposed about the proximal end of the resealable member  622 . The one or more tabs  616  can be configured to mate with (e.g., can engage and/or be disposed within) one or more of the corresponding recesses  618  disposed on the distal end of a portion of the impeller assembly  116  (e.g., the hub  208 , shaft  204 , and/or shaft extension  606 ). As illustrated in  FIG. 16B , the recess  618  can be bounded by the surfaces of the hub  208  and the shaft extension  606 . The one or more recesses  618  can be disposed about the distal end of impeller assembly  116 . In some embodiments, the distal end of the impeller assembly  116  can include one recess  618 . For example, the recess  618  can be a generally cylindrical channel surrounding at least a portion of the shaft extension  606 . 
     Engagement of the resealable member  622  with the distal end of the impeller assembly  116  as illustrated in  FIG. 16B  can have many advantages. For example, an interface  620  between the resealable member  622  and the distal end of the impeller assembly  116  can be non-planar. Accordingly, a non-planar interface  620  can have a greater surface area than an otherwise similar interface that is planar. The increased surface area can advantageously increase the connection strength between the resealable member  622  and the distal end of the impeller assembly  116 . In one embodiment, the interface  620  can be much longer than the radial distance from the lumen  610  to the outer surface of the hub  208 . For example, the interface  620  can be at least about twice as long as this radial distance. 
     As illustrated in  FIG. 16B , resealable member  622  can include a valve  608  that extends proximally into an axial lumen  610 . One valve structure that can be used is a duck bill valve. The lumen  610  can pass through one or more components of the distal end of the impeller assembly  116 , such as the impeller shaft  204 , the impeller shaft extension  606 , and/or the hub  208 . The lumen  610  can have a diameter that is greater than the diameter of the resealable path  604 . The lumen  610  may also not be self-sealing. The valve  608  can be tapered or otherwise have a reduced cross section compared to the lumen  610 . As a result, the impeller tip can also include one or more corners  614  where the lumen  610  extends distally to overlap with the valve  608 . The outer surface of valve  608  can be separated by a distance from the inner surface of the resealable member  622 . Advantageously, where the pressure within the lumen  610  is greater than the pressure outside the catheter assembly  100 , the internal pressure can be exerted on valve  608  to close resealable path  604 . The proximal extension of the valve  608  into the lumen  610  can also promote easier entry of a guidewire into the lumen  610  when the guidewire is introduced from the distal end of the pump. Other valves structures that may be used in place of the valve  608  are discussed in US application Ser. No. 12/829,359 and in U.S. Pat. No. 7,022,100, which are incorporated by reference herein for all purposes and in its entirety. 
     Another embodiment of an impeller tip  602  that includes a resealable member  624  is illustrated in  FIG. 16C . The resealable member  624  can have a resealable path  630  therethrough. The resealable member  624  can optionally include a distal tapered portion. As described herein, the impeller can be coupled with the catheter body through a drive shaft  148 , which can be disposed or received within the axial lumen of the impeller or within the impeller shaft  204 . As illustrated in  FIG. 16C , a distal portion of a shaft, e.g., the drive shaft  148  or the impeller shaft  204 , can be disposed or received within the resealable member  624 . The impeller tip  602  can further include a non-resealable portion  626  having a non-resealable path  628  extending therethrough (e.g., a path that generally does not seal or close once it has been opened or created, and/or remains permanently open allowing fluid to pass therethrough). The resealable path  630  and the non-resealable path  628  can be co-linear (e.g., coaxial). As illustrated in  FIG. 16C , the non-resealable portion  626  can extend distally of the resealable member  624 . In some embodiments, the non-resealable portion  626  can partially or fully surround an outer surface of the resealable member  624 . For example, the resealable member  624  can be partially or entirely contained within the non-resealable portion  626 . As illustrated in  FIG. 16C , the non-resealable portion  626  can include the distal-most portion of the impeller tip  602 . In some embodiments, the non-resealable portion  626  can be a unitary structure that includes the hub and one or more blades of the impeller. In one embodiment, the non-resealable portion  626  can include the entire impeller body except for the resealable member  624 . For example, as discussed above, the impeller can include a hub disposed between the impeller blades and the impeller shaft  204 . The impeller hub can surround the resealable member  624 . 
     Advantageously, the impeller tip  602  can be configured to receive a guidewire through both the resealable path and the non-resealable path  628 . In some embodiments, the resealable path (when open) and/or the non-resealable path can have a diameter that is no more than one-half the diameter of the guidewire. Where the impeller tip  602  includes a resealable member  624  disposed therein, the resealable member can be advantageously protected from the trauma to which the outer surface of the impeller tip  602  may be exposed. In addition, the distally-extending non-resealable path can act as a guide or channel that directs the guidewire through the impeller. Furthermore, as discussed herein, the tapered shape of the distal portion of the resealable member  624  can help to reseal the resealable member  624 , as radial forces extending inwards can surround the tapered portion and help to close the resealable path. Note in this case that the non-resealable member, also made of an elastomeric material (but different actual material), retains a level of elasticity that can stretch to a lesser degree than the resealable material to accommodate passage of the guidewire. 
     The impeller tip  602  illustrated in  FIG. 16C  can be manufactured by first molding a soft and/or elastomeric material over at least a portion of the drive shaft  148  of the impeller shaft  204  to form the resealable member  624 . Some suitable materials for forming the member  624  include polyurethane and silicone. Some materials having low durometer, e.g., below  60 A, can be used for the resealable member  624 . In some embodiments, the material can have a durometer in the range of from about  25 A to about  55 A. For example, the material can be a polyurethane or a silicone polymer having a durometer below  60 A (e.g., in the range of from about  25 A to about  55 A). In some embodiments with a polyurethane material, the hardness can be for example, about  25 A, about  35 A, about  45 A, or about  55 A. In other embodiments, a silicone material can be used for the tip  602  and/or the resealable member  622 ,  624 . The silicone material can have a hardness ranging from about  20 A to about  60 A. In some embodiments, the hardness can be about  38 A. As described above, the resealable member  624  can optionally be formed to include a distal tapered portion. The rest of the impeller, or a portion thereof, can then be molded over the resealable member  624  and the drive shaft  148 . The remainder of the impeller tip  602  can be formed from a second material (e.g., a second polymer) that is different from the material used to form the resealable member  624 . The non-resealable path  628  and the resealable path  630  can be created after the impeller is molded over the drive shaft  148  or the impeller shaft  204 . A variety of methods and/or tools can be used to create these paths, including but not limited to a drill, a needle, or a small gauge screw. In some embodiments, the paths  628 ,  630  can be formed from a proximal end to a distal end of a wall of the impeller hub, e.g., distal of the distal most blade. In other embodiments, the paths  628  can be formed from a distal end of the impeller toward a proximal end of the impeller. 
     In use, those skilled in the art may appreciate that non-sealable (e.g., non-resealable or non-self-sealing) devices may require a constant flow of infusant in the distal direction to prevent the proximal flow of fluid or blood into the device. Advantageously, a resealable tip can allow for guidewire passage through the center of the catheter assembly  100  to ease insertion without requiring a constant flush of infusant. The tip in various embodiments the resealable tip self-seals when the guidewire is removed. Valves discussed herein provide the advantage of preventing blood from entering other portions of the catheter assembly  100 , such as the impeller shaft  204  or the lumen  234  or the bearing housing  228 . In various embodiments, valves are configured to be actuated from an at least partially open configuration to a closed configuration, such as by application of a force or pressure on one side thereof. 
     D. Sheath Having Expandable Distal End 
     As described herein, the pump can include a sheath assembly. The sheath assembly can control the collapse and expansion of the impeller and/or the impeller housing. In some embodiments, the distal end of the sheath assembly can optionally include one or more structures that aid in the deployment and/or retrieval of the impeller assembly. 
     In some embodiments, as shown in  FIGS. 17A to 17D , the sheath assembly can include an expandable distal end  170   a,    170   b,    170   c.  For example, the distal end can expand when a radial force is applied, and can contract when the radial force is removed. The distal end may also be able to expand and/or contract repeatedly. When expanded, the distal end  170   a,    170   b,    170   c  can have a conical and/or funnel-like configuration. When not expanded, the distal end  170   a,    170   b,    170   c  can have a generally cylindrical (e.g., generally constant diameter) configuration, for example as illustrated in  FIG. 17A . To assist with expansion and/or contraction, the distal end  170   a,    170   b,    170   c  or portions thereof may be made from materials having a different flexibility and/or elasticity (e.g., more or less flexible and/or elastic) than the material(s) used for all or a portion of the remainder of the sheath assembly. In some embodiments, the sheath assembly  162  can have at least one configuration where it is at least partially disposed over the impeller housing, catheter assembly, and/or impeller assembly. Advantageously, the conical and/or funnel-like configuration can aid the deployment and/or retraction of the impeller assembly and/or impeller housing as described herein. 
     As illustrated in  FIG. 17A , the distal end  170   a  can include one or more axial slits  702  (e.g., 2, 3, or 4 slits). Slit  702  can extend proximally from the distal end  170   a  at least partially along the length of the elongate body  174 . The distal end  170   a  can also include a plurality of elongate members  704  (e.g., 2, 3, or 4 elongate members). Each elongate member  704  can be joined at one end (e.g., proximal end) to the sheath assembly. Each elongate member  704  can also have a distal end  705  that is outwardly deflectable away from axis  708 . The elongate members  704  can be separated from each other by the slits  702 . Each elongate member  704  can have a width that is defined by the distance between slits  702  and a length defined by the length of each adjacent slit  702 . In some embodiments, the elongate members  704  and slits  702  can be generally equally spaced circumferentially about the elongate body  174 . In some embodiments, the elongate members  704  can each have a length that is generally equal to or greater than the axial length of the outlet portion of the impeller housing. For example, in some embodiments, the elongate members  704  can each have a length in the range of from about 0.25 in. up to about 2.0 in. In other embodiments, the elongate members  704  can each have a length in the range of from about 0.5 in to about 0.75 in. The elongate members  704  and/or at least a portion of the sheath assembly  162  (e.g., the portion of the sheath assembly  162  that connects to elongate members  704 ) can be made from a relatively elastic material (e.g., any of the elastomeric polymers described herein). 
     In use, an outwardly-acting radial force resulting from the radial stiffness of the impeller housing can be applied to the elongate members  704  which causes the elongate members  704  to deflect outwards, as illustrated in  FIG. 17B . For example, the axial movement of the impeller housing in the proximal direction into the sheath assembly (or distal movement of the sheath over the expanded impeller housing) can cause the elongate members  704  to deflect outwards. The outward deflection of the elongate members  704  can result in the conical or funnel-like configuration of the distal end  170   a  when sheathed over an expanded section of the impeller housing. When the elongate members  704  are deflected outwards, the width of each slit  702  can increase at the distal end to define a gap  709 . In some embodiments, the elongate members  704  can be self-collapsing. For example, the elongate members  704  can be configured to return to their original configuration when the internal outward-acting radial forces are released (e.g., where the elongate members  704  are made of a relatively elastic material). 
     As illustrated in  FIG. 17C , the distal end  170   b  of the sheath assembly can include an deformable structure  706  (e.g., a webbing) that at least partially covers one or more slits  702 . In some embodiments, the deformable (e.g., stretchable, expandable, flexible, and/or elastic) structure  706  can surround, coat, and/or cover at least a portion of the distal end  170   b  (e.g., the elongate members  704 ). As illustrated in  FIG. 17C , the deformable structure  706  can be an elastomeric coating (e.g., incorporating those elastomeric materials described herein). In other embodiments, the deformable structure  706  can include a spring, such as a semi-circular spring member having a straight or oscillatory pattern. In use, the deformable structure  706  can be configured to return the elongate members  704  to their original, non-conical configuration and/or prevent over-deflection of the elongate members  704  beyond their elastic limit. 
     In some embodiments, the elongate members  704  can be stiffer (in the circumferential and/or axial direction(s)) than the proximally-adjacent portion of the sheath assembly. Advantageously, the stiffer material can prevent or inhibit the distal-most end of the sheath assembly from folding over itself when it encounters resistance (e.g., advancing the sheath over an expanded cannula housing). In one embodiment, one or more elongate members  704  can be reinforced with a plurality of wires that extend to the distal-most tip of the elongate member  704 . In another embodiment, one or more elongate members  704  can be made from a polymer that is stiffer than the material (e.g., a second polymer) of the proximally-adjacent portion of the sheath assembly. 
     As illustrated in  FIG. 17D , in some embodiments the distal end  170   c  of sheath assembly  162  can include an integral funnel  710  having a distal, conically-shaped portion  711 . As described further herein, the integral funnel  710  can be expandable and/or collapsible. Advantageously, the integral funnel  710  can assist in deployment and retraction of the housing while minimally increasing the profile of the pump. The integral funnel  710  can be connected to a non-expandable portion  712  of the sheath, for example, at a distal-most tip  714 . The integral funnel  710  can include an outer layer  713  and an inner layer  715  that converge at an interface  717 . The integral funnel  710  can be layered over an outer surface  716  and over an inner surface  718  of the non-expandable portion  712 . Accordingly, as illustrated in  FIG. 17D , at least a portion of the inner layer  715  can reside, at least temporarily, within the lumen of the sheath assembly  162 . The integral funnel  708  can be connected to either the outer surface  716  or the inner surface  718  of the sheath. In some embodiments, the funnel  710  can be a distal extension of distal end  170  that is folded over the non-expandable portion  712 . 
     The integral funnel  710  can be slideable over the outer surface  716  and/or the inner surface  718  of the non-expandable portion  712 . The contact surfaces between the non-expandable portion  712  and the integral funnel  710  and/or between the outer layer  713  and the inner layer  715  can be lubricated, e.g., using a silicone lubricant, to establish and/or maintain slideability and/or low friction. The integral funnel  710  can be made from a thin, flexible material, such as a polyurethane polymer. In some embodiments, the integral funnel  710  can be made from a material that is more flexible and/or elastic than the material that is used for all or a portion of the remainder of the sheath assembly. In some embodiments, the material used for the integral funnel  710  can have one or more membrane-like qualities. In use, the axial movement of the housing  202  (not shown) can frictionally engage the integral funnel  710 , causing the integral funnel  710  to deploy or retract. For example, in embodiments where the outer layer  713  is affixed to the non-expandable portion  712  of the sheath, axial movement of the housing  202  in a distal direction can cause the inner layer  715  to translate distally (e.g., slide distally along the inner surface  718  of the sheath), thus deploying the conical portion  711  (e.g., pulling the conical portion  711  out of the sheath). Axial movement of the housing in a proximal direction can cause the inner layer  715  to translate proximally (e.g., slide proximally along the inner surface  718  of the sheath), thus retracting the conical portion  711  into the sheath (e.g., pulling the conical portion  711  into the sheath). The thin, flexible material of the conical portion  711  can advantageously allow the conical portion  711  to deform upon retraction into the sheath. 
     In embodiments where the inner layer  715  is affixed to the non-expandable portion of the sheath, axial movement of the housing  202  can cause the outer layer  713  to translate. For example, distal movement of the housing can cause the outer layer  713  to slide distally along the outer surface  716  of the sheath. Proximal movement of the housing can cause the outer layer  713  to slide proximally along the outer surface  716  of the sheath. 
     In some embodiments where the funnel  710  is a distal extension of the non-expandable portion  712  that is folded over the non-expandable portion  712 , the funnel  710  can slide distally as the non-expandable portion  712  is moved proximally. In use, as the non-expandable portion  712  is moved proximally, the funnel  710  can slide distally to unfold and surround the impeller assembly  116 . 
     IV. Methods 
     Various methods and techniques are discussed above in connection with specific structures of heart pumps. The following elaborates on some aspects of these techniques and methods. The following discussion is to be read in light of and freely combined with the foregoing discussion. 
     A. Retracting and Deploying the Impeller Housing By Way of the Impeller Deployment Assembly at the Proximal End of the Catheter Body 
     As discussed above, in various embodiments the heart pump  10  is inserted in a less invasive manner, e.g., using techniques that can be employed in a catheter lab. Various general techniques pertinent to the heart pump  10  are described in U.S. patent application Ser. No. 12/829,359, filed on Jul. 1, 2010, and entitled Blood Pump With Expandable Cannula, which is incorporated by reference herein in its entirety and for all purposes. 
     Because the catheter assembly  100  is to be delivered through a small access site, it can be important to ensure that the impeller housing is reliably deployed and retracted, as described above. A clinician may begin a heart pumping procedure by introducing the catheter assembly  100  into the patient percutaneously, e.g., by urging the catheter assembly through the femoral artery and into a heart chamber. Because the impeller and impeller housing are advanced through a narrow artery in some embodiments, the impeller and impeller housing can initially be inserted into the patient in a retracted, or collapsed (or low profile), state, as described above. Once the distal end of the catheter assembly  100  (including the impeller housing) has reached the desired operating location (e.g., a heart chamber), the clinician can deploy the impeller housing into an advanced or expanded configuration. 
     One method of deploying the impeller and/or diffuser is by using the impeller deployment assembly  800 , which can be located near the proximal end of the catheter assembly. As shown in  FIGS. 15A and 15B , the clinician can rotate the nut  804  (clockwise or counter-clockwise depending on the threading) such that the nut  804  translates from a distal position to a proximal position. In turn, the flow diverter  806 , the catheter body, and the impeller housing can also translate from a distal position to a proximal position and thereby advance the impeller distally into a wider portion of the impeller housing to allow for deployment of the impeller hub  208  and blades  212 . Thus, in some embodiments, the clinician can deploy the impeller, located at a distal end of the catheter assembly, by rotating a nut disposed near the proximal end of the catheter assembly. 
     In some embodiments, the impeller  200  and housing  202  can be axially displaced relative to their operational positions during delivery of the distal end to the heart (e.g., the impeller and housing can be delivered to the vasculature in an axially separated configuration). As used in this context, “axially displaced” includes configurations where there is axial movement of the impeller  200  relative to any portion of the housing  202  prior to or during the process of delivery. For example, axial displacement includes conditions in which the impeller  200  is moved from a first position near a proximal end port (outlet for left side support or inlet for right side support) of the housing  202  to a second position distal the first position. The second position can be one that is still between the proximal end port and a distal end port (inlet for left side support or outlet for right side support) of the housing  202 . The first position may be the operational position of the impeller  200  relative to the housing  202 . Axial displacement also includes conditions in which the impeller is located proximal of an operational position, e.g., at a location proximal of a proximal end port of the housing  202 , including being disposed within a non-expandable portion of the heart pump. When the clinician delivers the distal end of the heart pump to the heart chamber, rather than delivering the distal end with the impeller housing disposed over the impeller blades, the impeller housing can be in a proximally displaced position or retracted configuration (or distally displaced position or advanced configuration in other embodiments) with respect to the impeller, such that it is axially moved from the operational position, as discussed above. 
     In some embodiments, the impeller and the housing can be delivered in series (with the impeller being delivered before the housing, or vice versa). For example, in one embodiment, the impeller housing  202  is first advanced into position, e.g., in the heart. The housing  202  may then be expanded if the housing has expanded and compressed configurations. Thereafter the impeller  200  may be positioned, e.g., advanced through a catheter body similar to the catheter body  120  to be positioned within the impeller housing  202 . Thereafter the impeller  200  can be rotated by a source of rotational energy. In various embodiments, the source of rotational energy can comprise a motor positioned outside of the patient to drive a shaft similar to the shaft  148 . In other embodiment, the source of rotational energy can comprise a motor that is miniaturized to be positionable within the patient, as discussed in U.S. Pat. No. 7,070,555, which is incorporated by reference herein for all purposes and in its entirety. In another embodiment, the distal end of the impeller  200  can be configured to be advanced into position in the patient and, at a later stage of a procedure, the impeller housing  202  can be positioned thereover. In one technique, the impeller  200  is positioned in the heart chamber (or wherever the procedure is to occur), the clinician can then advance the impeller housing over the impeller blades and begin operating the heart pump. For removal of the catheter assembly from the patient after the procedure, the clinician can retract or displace the impeller housing proximally to axially displace and/or separate the impeller from the impeller housing. 
     The configurations enabling displaced or serial delivery also can decouple the design of the impeller housing  202  from the complexities of the design of the impeller  200 . For example, the impeller housing  202  can have a greater range of expansion from a collapsed state to an expanded state. If no structures are disposed inside the housing  202  in the collapsed state, greater compression and a lower crossing profile can be achieved compared to where the housing  202  must be sized in the collapsed state to accommodate the impeller  200  in its collapsed state. This provides one or more of the benefits of access through smaller vessels, in smaller patients, or a larger expanded size in standard patients through typical access (e.g., femoral vessel). Similarly, greater compression of the impeller  200  may be possible if the impeller  200  is delivered using a dedicated compression sheath or device that is not required to expand and/or to be present around the impeller during operation. As a result, larger blades may be delivered from the same collapsed profile, providing the advantages of higher flow discussed above. More details of serial delivery of blood pumps are discussed in U.S. Pat. No. 7,022,100, which is incorporated by reference herein for all purposes and in its entirety. 
     Once the impeller is deployed, the clinician can conduct the procedure, e.g., by running the heart pump within a heart chamber. Once the procedure is finished, the clinician can remove the catheter assembly from the patient by retracting the impeller. The clinician can simply rotate the nut  804  in a direction opposite to that rotated for deploying the impeller. The nut can then translate from the proximal position to the distal position, which in turn can cause the flow diverter  806 , the catheter body, and the impeller housing to also translate from the proximal position to the distal position. The impeller can thereby be retracted proximally into an area near the outlet  802  to reduce the profile of the pump upon collapsing into the sheath. Thus, the clinician can both deploy and retract the impeller by rotating a nut located near the proximal end of the catheter assembly. 
     B. Controlling the Collapse and Deployment of the Impeller Housing with the Sheath Assembly 
     As mentioned above in Section IV(A), it can be advantageous in certain embodiments to enable a clinician to deploy and retract the impeller assembly prior to and after a heart procedure. One method of collapsing the impeller housing can be performed by advancing the sheath assembly  162  distally over the impeller housing to collapse the impeller assembly, e.g., for removal of the catheter assembly from the patient after a heart procedure. As mentioned above, elongate body  174  of the catheter assembly  162  can be slidably disposed over the catheter body  120 . The clinician can distally advance the elongate body  174  over the impeller housing, or alternatively proximally retract the catheter body  120  such that the impeller housing collapses into the elongate body  174  of the sheath assembly  162 . 
     As  FIGS. 17A-D  illustrate, the sheath assembly can have expandable distal ends  170   a,    170   b,    170   c,  that expand when a radial force is applied. Thus, when the clinician advances the elongate body  174  of the sheath over the impeller housing, the impeller housing can contact the distal end  170  and can induce a radial force that causes the distal ends  170   a,    170   b,    170   c,  to expand in order to aid in retraction of the impeller assembly. Similarly, when the clinician slides the elongate body  174  in a proximal direction, the impeller assembly can deploy through the distal end  170  of the catheter assembly  162 , because the distal ends  170   a,    170   b,    170   c,  can contract when a radial force is removed (or not applied). Thus, the clinician can reliably deploy and retract the impeller assembly by sliding the elongate body  174  of the sheath relative to the catheter body  120 . In other embodiments, the sheath assembly need not have expandable distal ends as described above. The clinician can therefore simply deploy the impeller assembly  116  by providing relative motion between the elongate body  174  of the sheath and the impeller assembly, e.g., by retracting the elongate body  174  from the impeller assembly, and can collapse the impeller assembly by providing relative motion between the elongate body  174  of the sheath and the impeller assembly  116 , e.g., by advancing the elongate body over the impeller assembly. The distal end of the elongate body  174  can therefore effectuate collapse of the impeller assembly  116  without using the expandable distal ends described above. In embodiments where the impeller assembly is self-expanding, the retraction of the elongate body  174  from the impeller assembly  116  or extension of the impeller assembly  116  out of the elongate body  174  can release the impeller assembly to self-expand. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present embodiments without departing from the scope or spirit of the advantages of the present application. Thus, it is intended that the present application cover the modifications and variations of these embodiments and their equivalents.