Patent Publication Number: US-2023149692-A1

Title: Percutaneous circulatory support system facilitating reduced hemolysis

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Provisional Application No. 63/279,936, filed Nov. 16, 2021, which is herein incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to percutaneous circulatory support systems. More specifically, the disclosure relates to percutaneous circulatory support devices that facilitate reduced hemolysis. 
     BACKGROUND 
     Percutaneous circulatory support devices such as blood pumps can provide transient support for up to approximately several weeks in patients with compromised heart function or cardiac output. Operation of such blood pumps, however, may cause some amount of hemodynamic shear, which in turn may result in hemolysis (that is, the rupture or destroying of blood cells). High rates of hemolysis can in turn cause acute kidney injury or other complications. Accordingly, there is a need for improved blood pumps that facilitate reduced hemolysis. 
     SUMMARY 
     In an Example 1, a percutaneous circulatory support device comprises a housing; a shaft rotatably fixed relative to the housing; an impeller disposed within the housing and rotatably supported by the shaft, the impeller configured to rotate relative to the shaft and the housing to cause blood to flow through the housing; and a keeper coupled to the shaft distally relative to the impeller, the keeper inhibiting axial motion of the impeller relative to the shaft. 
     In an Example 2, the percutaneous circulatory support device of Example 1, wherein the keeper acts as a thrust bearing. 
     In an Example 3, the percutaneous circulatory support device of either of Examples 1-2, wherein the percutaneous circulatory support device lacks a support coupling the shaft to the housing and disposed distally relative to the impeller. 
     In an Example 4, the percutaneous circulatory support device of any of Examples 1-3, further comprising a motor being operable to rotatably drive the impeller relative to the shaft and the housing and thereby cause blood to flow through the housing. 
     In an Example 5, the percutaneous circulatory support device of any of Examples 1-4, further comprising a thrust bearing coupling the impeller to the housing. 
     In an Example 6, the percutaneous circulatory support device of Example 5, wherein the thrust bearing is a proximal thrust bearing, and further comprising a distal thrust bearing coupling the impeller to the housing. 
     In an Example 7, the percutaneous circulatory support device of any of Examples 1-6, further comprising an impeller assembly, the impeller assembly comprising the impeller and an inner tube rotatably supported by the shaft, and the impeller is rotatably fixed relative to the inner tube. 
     In an Example 8, the percutaneous circulatory support device of Example 7, further comprising a motor; a drive magnet operably coupled to the motor; and a driven magnet operably coupled to the drive magnet, and the inner tube and the impeller being rotatably fixed relative to the driven magnet; wherein the motor is operable to rotatably drive the impeller, via the drive magnet and the driven magnet, and thereby cause blood to flow through the housing. 
     In an Example 9, a percutaneous circulatory support device comprises a motor; a housing; a shaft rotatably fixed relative to the housing; a keeper coupled to the shaft; an impeller disposed within the housing, rotatably supported by the shaft, and axially restrained relative to the shaft by the keeper; and wherein the motor is operable to rotatably drive the impeller relative to the housing and thereby cause blood to flow through the housing. 
     In an Example 10, the percutaneous circulatory support device of Example 9, wherein the keeper acts as a thrust bearing. 
     In an Example 11, the percutaneous circulatory support device of either of Examples 9 and 10, wherein the keeper is disposed distally relative to the impeller. 
     In an Example 12, the percutaneous circulatory support device of any of Examples 9-11, wherein the percutaneous circulatory support device lacks a support coupling the shaft to the housing and disposed distally relative to the impeller. 
     In an Example 13, the percutaneous circulatory support device of any of Examples 9-12, further comprising a thrust bearing coupled to the impeller. 
     In an Example 14, the percutaneous circulatory support device of any of Examples 9-13, further comprising an impeller assembly, the impeller assembly comprising the impeller and an inner tube rotatably supported by the shaft, and the impeller is rotatably fixed relative to the inner tube. 
     In an Example 15, the percutaneous circulatory support device of Example 14, further comprises a drive magnet operably coupled to the motor; and a driven magnet operably coupled to the drive magnet, the inner tube and the impeller being rotatably fixed relative to the driven magnet; wherein the motor is operable to rotatably drive the impeller, via the drive magnet and the driven magnet, and thereby cause blood to flow through the housing. 
     In an Example 16, a percutaneous circulatory support device comprises a housing comprising an inlet and an outlet; a shaft rotatably fixed relative to the housing; an impeller disposed within the housing and rotatably supported by the shaft, the impeller configured to rotate relative to the shaft and the housing to cause blood to flow into the inlet, through the housing, and out of the outlet; and a keeper coupled to the shaft distally relative to the impeller, the keeper inhibiting axial motion of the impeller relative to the shaft. 
     In an Example 17, the percutaneous circulatory support device of Example 16, wherein the keeper acts as a thrust bearing. 
     In an Example 18, the percutaneous circulatory support device of Example 16, wherein the percutaneous circulatory support device lacks a support coupling the shaft to the housing and disposed distally relative to the impeller. 
     In an Example 19, the percutaneous circulatory support device of Example 16, further comprising a motor being operable to rotatably drive the impeller relative to the shaft and the housing and thereby cause blood to flow into the inlet, through the housing, and out of the outlet. 
     In an Example 20, the percutaneous circulatory support device of Example 16, further comprising a thrust bearing coupling the impeller to the housing. 
     In an Example 21, the percutaneous circulatory support device of Example 20, wherein the thrust bearing is a proximal thrust bearing, and further comprising a distal thrust bearing coupling the impeller to the housing. 
     In an Example 22, the percutaneous circulatory support device of Example 16, further comprising an impeller assembly, the impeller assembly comprising the impeller and an inner tube rotatably supported by the shaft, and the impeller is rotatably fixed relative to the inner tube. 
     In an Example 23, the percutaneous circulatory support device of Example 22, further comprises a motor; a drive magnet operably coupled to the motor; and a driven magnet operably coupled to the drive magnet, and the inner tube and the impeller being rotatably fixed relative to the driven magnet; wherein the motor is operable to rotatably drive the impeller, via the drive magnet and the driven magnet, and thereby cause blood to flow into the inlet, through the housing, and out of the outlet. 
     In an Example 24, a percutaneous circulatory support device comprises a motor; a housing comprising an inlet and an outlet; a shaft rotatably fixed relative to the housing; a keeper coupled to the shaft; an impeller disposed within the housing, rotatably supported by the shaft, and axially restrained relative to the shaft by the keeper; and wherein the motor is operable to rotatably drive the impeller relative to the housing and thereby cause blood to flow into the inlet, through the housing, and out of the outlet. 
     In an Example 25, the percutaneous circulatory support device of Example 24, wherein the keeper acts as a thrust bearing. 
     In an Example 26, the percutaneous circulatory support device of Example 24, wherein the keeper is disposed distally relative to the impeller. 
     In an Example 27, the percutaneous circulatory support device of Example 24, wherein the percutaneous circulatory support device lacks a support coupling the shaft to the housing and disposed distally relative to the impeller. 
     In an Example 28, the percutaneous circulatory support device of Example 24, further comprising a thrust bearing coupled to the impeller. 
     In an Example 29, the percutaneous circulatory support device of Example 28, wherein the thrust bearing is a proximal thrust bearing, and further comprising a distal thrust bearing coupled to the impeller. 
     In an Example 30, the percutaneous circulatory support device of Example 24, further comprising an impeller assembly, the impeller assembly comprising the impeller and an inner tube rotatably supported by the shaft, and the impeller is rotatably fixed relative to the inner tube. 
     In an Example 31, the percutaneous circulatory support device of Example 30, further comprises a drive magnet operably coupled to the motor; and a driven magnet operably coupled to the drive magnet, the inner tube and the impeller being rotatably fixed relative to the driven magnet; wherein the motor is operable to rotatably drive the impeller, via the drive magnet and the driven magnet, and thereby cause blood to flow into the inlet, through the housing, and out of the outlet. 
     In an Example 32, A method of manufacturing a percutaneous circulatory support device comprises coupling a shaft to a housing such that the shaft is rotatably fixed relative to the housing; coupling an impeller to the shaft such that the impeller is disposed within the housing and rotatably supported by the shaft; coupling a keeper to the shaft such that the impeller is axially restrained relative to the shaft; and operatively coupling the impeller to a motor. 
     In an Example 33, the method of Example 32, further comprising coupling a thrust bearing to the shaft and the housing before coupling the impeller to the shaft. 
     In an Example 34, the method of Example 32, further comprising coupling an inner tube to the impeller such that the impeller is rotatably fixed relative to the inner tube, and wherein coupling the impeller to the shaft comprises together coupling the inner tube and the impeller to the shaft. 
     In an Example 35, the method of Example 34, further comprising coupling a driven magnet to the inner tube such that the driven magnet is rotatably fixed relative to the inner tube, and wherein together coupling the inner tube and the impeller to the shaft comprises together coupling the inner tube, the driven magnet, and the impeller to the shaft. 
     While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a side sectional view of an illustrative mechanical circulatory support device (also referred to herein, interchangeably, as a “blood pump”), in accordance with embodiments of the subject matter disclosed herein. 
         FIG.  2    is an enlarged side sectional view of the blood pump within line  2 - 2  of  FIG.  1   , in accordance with embodiments of the subject matter disclosed herein. 
         FIG.  3    is a flow diagram of an illustrative method of manufacturing a blood pump, in accordance with embodiments of the subject matter disclosed herein. 
         FIG.  4    is a side sectional view of a first housing assembly provided according to the method of  FIG.  3   , in accordance with embodiments of the subject matter disclosed herein. 
         FIG.  5    is a side sectional view of an impeller assembly provided according to the method of  FIG.  3   , in accordance with embodiments of the subject matter disclosed herein. 
         FIG.  6    is a side sectional view of a second housing assembly provided according to the method of  FIG.  3   , in accordance with embodiments of the subject matter disclosed herein. 
         FIG.  7    is a side sectional view of another illustrative blood pump, in accordance with embodiments of the subject matter disclosed herein. 
         FIG.  8    is a side sectional view of yet another illustrative blood pump, in accordance with embodiments of the subject matter disclosed herein. 
         FIG.  9    is a side sectional view of yet another illustrative blood pump, in accordance with embodiments of the subject matter disclosed herein. 
     
    
    
     While the invention is amenable to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described in detail below. The intention, however, is not to limit the invention to the particular embodiments described. On the contrary, the invention is intended to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION 
       FIG.  1    depicts a side sectional view of an illustrative mechanical circulatory support device  100  (also referred to herein, interchangeably, as a “blood pump”) in accordance with embodiments of the subject matter disclosed herein. The blood pump  100  may form part of a percutaneous circulatory support system, together with a guidewire and an introducer sheath (not shown). More specifically, the guidewire and the introducer sheath may facilitate percutaneously delivering the blood pump  100  to a target location within a patient, such as within the patient&#39;s heart. 
     With continued reference to  FIG.  1    and additional reference to  FIG.  2   , the blood pump  100  generally includes an impeller housing  102  and a motor housing  104 . The impeller housing  102  and/or the motor housing  104  may be constructed of various materials, such as stainless steel or nitinol. In some embodiments, the impeller housing  102  and the motor housing  104  may be integrally or monolithically constructed. In other embodiments, the impeller housing  102  and the motor housing  104  may be separate components configured to be removably or permanently coupled. In some embodiments, the blood pump  100  may lack a separate motor housing  104  and the impeller housing  102  may be coupled directly to the motor  122  described below, or the motor housing  104  may be integrally constructed with the motor  122  described below. 
     The impeller housing  102  carries an impeller assembly  106  therein. The impeller assembly  106  generally includes an inner tube  108  (for example, a hypotube constructed of stainless steel) and an impeller  110  having one or more impeller blades  112 . The inner tube  108  and the impeller  110  rotate together relative to the impeller housing  102  to drive blood through the blood pump  100 . More specifically, the impeller  110  causes blood to flow from a blood inlet  114  formed on the impeller housing  102 , through the impeller housing  102 , and out of a blood outlet  116  formed on the impeller housing  102 . As shown in  FIGS.  1  and  2   , the inlet  114  and/or the outlet  116  may each include multiple apertures. As shown, apertures of the outlet  116  may be formed between adjacent struts  118  of a plurality of struts  118  of the impeller housing  102 . In other embodiments, the inlet  114  and/or the outlet  116  may each include a single aperture. As shown in  FIGS.  1  and  2   , the inlet  114  may be formed on an end portion of the impeller housing  102  and adjacent to a distal support  120  coupled to the impeller housing  102 . As shown in  FIGS.  1  and  2    the outlet  116  may be formed on a side portion of the impeller housing  102 . In other embodiments, the inlet  114  and/or the outlet  116  may be formed on other portions of the impeller housing  102 . In some embodiments, the impeller housing  102  may couple to a distally extending cannula (not shown), and the cannula may receive and deliver blood to the inlet  114 . 
     With continued reference to  FIGS.  1  and  2   , the motor housing  104  carries a motor  122 , and the motor  122  is configured to rotatably drive the impeller  110  relative to the impeller housing  102 . In the illustrated embodiment, the motor  122  rotates a drive shaft  124 , which is coupled to a drive magnet  126  (for example, a samarium cobalt magnet). Rotation of the drive magnet  126  causes rotation of a driven magnet  128  (for example, a samarium cobalt magnet), which is connected to the impeller assembly  106 . More specifically, the impeller  110  rotates with the driven magnet  128 . In other embodiments, the motor  122  may couple to the impeller assembly  106  via other components. 
     In some embodiments, a controller (not shown) may be operably coupled to the motor  122  and configured to control the motor  122 . In some embodiments, the controller may be disposed within the motor housing  104 . In other embodiments, the controller may be disposed outside of the motor housing  104  (for example, in a catheter handle, an independent housing, etc.). In some embodiments, the controller may include multiple components, one or more of which may be disposed within the motor housing  104 . In some embodiments, the controller may be, may include, or may be included in one or more Field Programmable Gate Arrays (FPGAs), one or more Programmable Logic Devices (PLDs), one or more Complex PLDs (CPLDs), one or more custom Application Specific Integrated Circuits (ASICs), one or more dedicated processors (e.g., microprocessors), one or more central processing units (CPUs), software, hardware, firmware, or any combination of these and/or other components. Although the controller is referred to herein in the singular, the controller may be implemented in multiple instances, distributed across multiple computing devices, instantiated within multiple virtual machines, and/or the like. In other embodiments, the motor  122  may be controlled in other manners. 
     With further reference to  FIGS.  1  and  2   , the blood pump  100  includes various components and features that provide reduced device-induced hemolysis compared to conventional devices. More specifically, the blood pump  100  includes a bearing shaft  130 , (also referred to herein, interchangeably, simply as a “shaft”—for example a pin or rod constructed of stainless steel, a ceramic, or the like) that is rotatably fixed relative to the impeller housing  102 . More specifically, the shaft  130  is fixedly coupled to a proximal hub  132  of the impeller housing  102  and an inner sleeve  134  of the distal support  120  (for example, a silicon sleeve). The bearing shaft  130  rotatably supports the impeller assembly  106  and reduces or eliminates impeller vibrations and other undesirable impeller rotational dynamics, which can cause relatively high shear and hemolysis in conventional blood pumps. 
     The bearing shaft  130  facilitates use of relatively simple proximal and distal bearings for rotatably coupling the impeller assembly  106  to the impeller housing  102  and the distal support  120  because such bearings do not need to radially capture the impeller assembly  106 . More specifically, the blood pump  100  may include one or more proximal thrust bearings and one or more distal thrust bearings. In some embodiments and as illustrated, the blood pump  100  includes a first proximal thrust bearing  136  that abuttingly engages the proximal hub  132  of the impeller housing  102  and a second proximal thrust bearing  138  that abuttingly engages the first proximal thrust bearing  136 , the driven magnet  128 , and the inner tube  108 . In some embodiments and as illustrated, the blood pump  100  includes a first distal thrust bearing  140  that abuttingly engages the impeller  110  and the inner tube  108  and a second distal thrust bearing  142  that abuttingly engages the first distal thrust bearing  140  and the distal support  120 , more specifically the inner sleeve  134  of the distal support  120 . 
     The thrust bearings  136 ,  138 ,  140 , and  142  may take various specific forms and may be constructed of various materials. For example, the first proximal thrust bearing  136 , the second proximal thrust bearing  138 , the first distal thrust bearing  140 , and/or the second distal thrust bearing  142  may be flat bearings. As another example, the first proximal thrust bearing  136  and the second proximal thrust bearing  138  may be constructed of a relatively hard material (that is, the bearings  136  and  138  may have a “hard-on-hard” arrangement). As another example, one of the first proximal thrust bearing  136  and the second proximal thrust bearing  138  may be constructed of a relatively hard material and the other may be constructed of a relatively soft material (that is, the bearings  136  and  138  may have a “hard-on-soft” arrangement). As another example, the first distal thrust bearing  140  and the second distal thrust bearing  142  may be constructed of a relatively hard material. As another example, one of the first distal thrust bearing  140  and the second distal thrust bearing  142  may be constructed of a relatively hard material and the other may be constructed of a relatively soft material. As another example, the first proximal thrust bearing  136 , the second proximal thrust bearing  138 , the first distal thrust bearing  140 , and/or the second distal thrust bearing  142  may be constructed of one or more ceramics, such as silicon nitride, or one or more jewel materials, such as sapphire. 
     The bearings  136 ,  138 ,  140 , and  142  may provide one or more advantages over those of conventional blood pumps. For example, the proximal bearings  136  and  138  could reduce or eliminate gaps at the proximal side of the driven magnet  128 , and the distal bearings  140  and  142  could reduce or eliminate gaps at the distal side of the impeller assembly  106 . As a result, the bearings  136 ,  138 ,  140 , and  142  could reduce or eliminate potential thrombus formation at those locations, which could lead to premature pump failure. As another example, the bearings  136 ,  138 ,  140 , and  142  have relatively large contact areas, which mitigates wear. As another example, the proximal bearing  136  and  138  may be relatively thin in an axial direction and thereby facilitate providing a relatively short distance between the drive magnet  126  and the driven magnet  128 , which in turn provides relatively high torque transmission to the impeller assembly  106 . As yet another example, and in contrast to conventional blood pumps, a compressive load would not need to be applied to the impeller assembly  106  to ensure the bearings  136 ,  138 ,  140 , and  142  remain seated during pump operation because radial capture of the impeller assembly  106  is provided by the bearing shaft  130 . This lack of a compressive load reduces friction and wear. 
     In some embodiments, the blood pump  100  also includes further advantages compared to conventional blood pumps. For example, the bearing shaft  130  is reinforced along its entire length by the impeller  110 , the bearings  136 ,  138 ,  140 , and  142 , the driven magnet  128 , the distal support  120 , and the impeller housing  102 . These components reduce stress on the bearing shaft  130  and increase the overall strength of the blood pump  100 . 
     In some embodiments, the inner sleeve  134  acts as a compression spring and applies a thrust force to the bearings  136 ,  138 ,  140 , and  142 . In these embodiments, the second distal thrust bearing  142  may be axially slidable within the distal support  120 . In other embodiments, the blood pump  100  lacks the inner sleeve  134 . 
       FIG.  3    illustrates a flow diagram of an exemplary method  200  of manufacturing a blood pump, in accordance with embodiments of the subject matter disclosed herein, and  FIGS.  4 - 6    illustrate intermediate assemblies associated with the method  200 . The method  200  describes features of the blood pump  100 , although it is understood that any of the blood pumps contemplated herein could be used in a similar manner. At step  202  and as also shown in  FIG.  4   , the method begins by providing a first housing assembly  144 . More specifically, providing the first housing assembly  144  includes coupling the bearing shaft  130  to the impeller housing  102  such that the shaft  130  is rotatably fixed relative to the impeller housing  102 . As illustrated, the shaft  130  may be received in a through opening  146  of the proximal hub  132  of the impeller housing  102 . In some embodiments, the bearing shaft  130  is welded or adhesively bonded within the proximal hub  132  of the impeller housing  102 . As also shown in  FIG.  4   , providing the first housing assembly  144  also includes sliding the first proximal thrust bearing  136  over the bearing shaft  130  and abutting the proximal hub  132  of the impeller housing  102 . In some embodiments, the first proximal thrust bearing  136  is adhesively bonded to the proximal hub  132  of the impeller housing  102 . Next or simultaneously and at step  204  and as shown in  FIG.  5   , the method includes providing the impeller assembly  106 . More specifically, providing the impeller assembly  106  includes coupling the impeller  110 , the driven magnet  128 , the second proximal thrust bearing  138 , and the first distal thrust bearing  140  to the inner tube  108  such that these components are rotatably fixed relative to each other. In some embodiments, the impeller  110  is overmolded onto the inner tube  108 . In some embodiments, the driven magnet  128  is slid over the proximal end of the inner tube  108  and adhesively bonded to the proximal end of the impeller  110 . In some embodiments, the second proximal thrust bearing  138  is slid over the inner tube  108  and adhesively bonded to the proximal end of the driven magnet  128 . In some embodiments, the first distal thrust bearing  140  is slid over the distal end of the inner tube  108  and adhesively bonded to the distal end of the impeller  110 . Next or simultaneously and at step  206  and as shown in  FIG.  6   , the method includes providing a second housing assembly  148 . More specifically, providing the second housing assembly  148  includes coupling the sleeve  134  and the second distal thrust bearing  142  to the distal support  120  such that these components are rotatably fixed relative to each other. In some embodiments, the sleeve  134  is inserted in a blind opening  150  of the distal support  120 , and the second distal thrust bearing  142  abuts the proximal end of the sleeve  134  and is adhesively bonded to the distal support  120 . 
     With continued reference to  FIG.  3    and further general reference to  FIGS.  4 - 6   , the method continues at step  208  by coupling the impeller assembly  106  ( FIG.  5   ) to the first housing assembly  144  ( FIG.  4   ). More specifically, coupling the impeller assembly  106  to the first housing assembly  144  includes sliding the inner tube  108  along the bearing shaft  130  such that the second proximal thrust bearing  138  loosely abuts the first proximal thrust bearing  136  (that is, without applying a load between the bearings) and the impeller assembly  106  is rotatable relative to the first housing assembly  144 . In some embodiments, coupling the impeller assembly  106  to the first housing assembly  144  additionally includes providing a lubricant between the inner tube  108  and the bearing shaft  130 . Next, the method continues at step  210  by coupling the second housing assembly  148  ( FIG.  6   ) to the impeller assembly  106  and the first housing assembly  144 . More specifically, coupling the second housing assembly  148  to the impeller assembly  106  and the first housing assembly  144  includes inserting the bearing shaft  130  into the sleeve  134  and the distal support  120  such that the first distal thrust bearing  140  loosely abuts the second distal thrust bearing  142  (that is, without applying a load between the bearings). In some embodiments, coupling the second housing assembly  148  to the impeller assembly  106  and the first housing assembly  144  includes welding or adhesively bonding the sleeve  134  of the distal support  120  to the bearing shaft  130 . In some embodiments, coupling the second housing assembly  148  to the impeller assembly  106  and the first housing assembly  144  includes welding or adhesively bonding one or more radially extending arms  152  of the distal support  120  to the impeller housing  102 . The method concludes at step  212  by operatively coupling the impeller assembly  106  to the motor  122  ( FIGS.  1  and  2   ) and coupling the impeller housing  102  to the motor housing  104  ( FIGS.  1  and  2   ). In some embodiments, operatively coupling the impeller assembly  106  to the motor  122  includes magnetically coupling the driven magnet  128  to the drive magnet  126  ( FIGS.  1  and  2   ). In some embodiments, coupling the impeller housing  102  to the motor housing  104  includes welding or adhesively bonding the impeller housing  102  to the motor housing  104 . 
       FIG.  7    depicts a partial side sectional view of another illustrative mechanical circulatory support device or blood pump  300  in accordance with embodiments of the subject matter disclosed herein. The blood pump  300  is generally similar to the blood pump  100  described above. That is, the blood pump  300  includes an impeller housing  302  that fixedly couples to a bearing shaft  304 . The bearing shaft  304  rotatably supports, via thrust bearings  306 , an impeller assembly  308 . The impeller assembly  308  is rotatably driven by a motor  310 , and the motor  310  is carried in a motor housing  312  coupled to the impeller housing  302 . The impeller housing  302  also includes an inlet  314  and an outlet  316  that facilitate blood flow through the blood pump  300 . Unlike the blood pump  100  described above, however, the impeller housing  302  includes a proximal impeller housing portion  318  and a distal impeller housing portion  320  that are completely disposed apart and thereby form the outlet  316  therebetween. Stated another way, the proximal impeller housing portion  318  and the distal impeller housing portion  320  are only indirectly coupled via the bearing shaft  304 , and the proximal impeller housing portion  318  and the distal impeller housing portion  320  thereby form the outlet  316  therebetween. Stated yet another way, the impeller housing  302  lacks struts (see, for comparison and for example, the struts  118  of the blood pump  100 ) coupling the proximal impeller housing portion  318  and the distal impeller housing portion  320 . As a result, shear induced by struts is eliminated, which results in reduced hemolysis. 
       FIG.  8    depicts a partial side sectional view of another illustrative mechanical circulatory support device or blood pump  400  in accordance with embodiments of the subject matter disclosed herein. The blood pump  400  is generally similar to the blood pump  100  described above. That is, the blood pump  400  includes an impeller housing  402  that fixedly couples to a bearing shaft  404 . The bearing shaft  404  rotatably supports, via bearings (one bearing  406  being visible), an impeller assembly (an inner tube  408  of the impeller assembly being visible). The impeller assembly is rotatably driven by a motor  410  via a drive magnet  412  and a driven magnet  414 , and the motor  410  is coupled to the impeller housing  402 . Additionally, and unlike the blood pump  100  described above, the impeller housing  402  also carries a protector  416 , which may also be referred to as a proximal seal. As illustrated, the protector  416  may be positioned both radially outwardly and distally relative to the driven magnet  414 . As such, the protector  416  may inhibit blood from contacting the driven magnet  414  and thereby inhibit corrosion and/or other wear. In some embodiments, the protector  416  may be configured to maintain a volume of protective fluid in contact with the driven magnet  414 . The protective fluid may be, for example, a hydrophobic lubricant. The protective fluid may be any type of hydrophobic lubricant suitable for use in a blood pump. For example, the protective fluid may be a modified silicone lubricant such as a modified Polydimethylsiloxane (PDMS). In other embodiments, the protective fluid may be an oil-based lubricant, a synthetic oil, a carbon-based lubricant, and/or the like. In some embodiments, the protector  416  may rotate with the impeller assembly and the driven magnet  414  relative to the impeller housing  402 . In some embodiments, the protector  416  may be fixed relative to the impeller housing  402 . 
     Generally, the blood pump  300  may be manufactured according to the method  200  except that providing the second housing assembly (step  206 ) may include coupling the distal support  322  to the distal impeller housing portion  320 , for example, via welding or adhesive bonding. The second housing assembly may be subsequently coupled to the first housing assembly and the impeller assembly. 
       FIG.  9    depicts a partial side sectional view of another illustrative mechanical circulatory support device or blood pump  500  in accordance with embodiments of the subject matter disclosed herein. The blood pump  500  is generally similar to the blood pump  100  described above. That is, the blood pump  500  includes an impeller housing  502  that fixedly couples to a bearing shaft  504 . The bearing shaft  504  rotatably supports, via proximal thrust bearings  506  and a first distal thrust bearing  508 , an impeller assembly  510 . The impeller assembly  510  is rotatably driven by a motor  512 , and the motor  512  is carried in a motor housing  514  coupled to the impeller housing  502 . The impeller housing  502  also includes an inlet  516  and an outlet  518  that facilitate blood flow through the blood pump  500 . Unlike the blood pump  100  described above, however, the blood pump  500  lacks a support coupling the shaft  504  to the impeller housing  502  and disposed distally relative to the impeller assembly  510 , such as the distal support  120  of the pump  100  (shown elsewhere). To inhibit axial motion of the impeller assembly  510  relative to the bearing shaft  504 , the bearing shaft  504  carries a distal keeper  520  near the inlet  516 . The keeper  520  may be, for example and as illustrated, a snap ring carried by the bearing shaft  504 . Alternatively, the keeper  520  may take other forms. In some embodiments and as illustrated, the keeper  520  may abuttingly engage the first distal thrust bearing  508  and thereby act as a second distal thrust bearing 
     Generally, the blood pump  500  may be manufactured according to the method  200  except that providing the second housing assembly (step  206 ) is omitted, and coupling the second housing assembly to the impeller assembly and the first housing assembly (step  210 ) is replaced by coupling the keeper  218  to the impeller assembly and the first housing assembly, for example, via snap fitting, welding, or adhesive bonding. 
     Various modifications and additions can be made to the exemplary embodiments discussed without departing from the scope of the present invention. For example, while the embodiments described above refer to particular features, the scope of this invention also includes embodiments having different combinations of features and embodiments that do not include all of the described features. Accordingly, the scope of the present invention is intended to embrace all such alternatives, modifications, and variations as fall within the scope of the claims, together with all equivalents thereof.