Patent Publication Number: US-2023158285-A1

Title: System and method for cannula fiber lumen strain relief

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Patent App. No. 63/282,407, filed Nov. 23, 2021, the contents of which are incorporated by reference herein in their entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to intravascular blood pumps having one or more sensors for measuring, such as for measuring pressures within a patient&#39;s vascular system. 
     BACKGROUND 
     Intravascular blood pumps can be introduced into a patient either surgically or percutaneously and used to deliver blood from one location in the bean or circulatory system to another location in the heart or circulatory system. For example, when deployed in the left heart, an intravascular blood pump can pump blood from the left ventricle of the heart into the aorta. Likewise, when deployed in the right heart, an intravascular blood pump can pump blood from the inferior vena cava into the pulmonary artery. Examples of such blood pumps include the Impella® family of devices (Abiomed, Inc., Danvers, Mass.). 
     Blood pump may have one or more sensors for measuring the patient&#39;s vascular system. For example, intravascular blood pumps may include one or more optical sensors for measuring pressures within a patient&#39;s vascular system, and particular a patient&#39;s ventricular cavity, which may be used for operating the blood pump and/or for assessing the state of health of the patient&#39;s heart. 
     BRIEF SUMMARY 
     A first aspect of the present disclosure is drawn to a system including a cannula and a flexible hypotube with specific geometric relationships. The cannula (which may be a flexible flow cannula) has an inner surface and an outer surface, which define a cannula wall having a thickness, the inner surface of the cannula defining a first lumen therethrough. The flexible hypotube is attached to the cannula, and has an outer surface and an inner surface, where the inner surface defines a second lumen therethrough. The system is configured to provide a ratio R1 of a diameter of the outer surface of the hypotube to a diameter of the inner surface of the cannula is 1:5&gt;R1&gt;1:25. The second lumen is arranged to slidably receive an optical fiber therethrough. 
     Advantageously, the optical fiber is arranged to freely move within the second lumen. In some embodiments, a ratio R2 of a diameter of an outer surface of the optical fiber to a diameter of the inner surface of the flexible hypotube is 1:3&gt;R2&gt;1:1.1 
     In some embodiments, the system further includes an inflow cage connected at or near a distal portion of the cannula. In some embodiments, a distal portion of the optical fiber is attached to the inflow cage. In some embodiments, the optical fiber includes an optical fiber sensor head at a distal end of the optical fiber, where the sensor may be configured to, e.g., measure ventricular pressure. 
     In some embodiments, the system further includes a pump operably connected to a proximal portion of the first lumen. 
     In some embodiments, the flexible hypotube may be positioned within the first lumen. In some embodiments, the flexible hypotube may be positioned outside the first lumen. In some embodiments, at least one portion of the flexible hypotube is positioned within the first lumen and at least one portion of the flexible hypotube is positioned outside the first lumen. 
     In some embodiments, the flexible hypotube has a distal end, a proximal end, and a tubular portion between the distal end and the proximal end, the tubular portion containing at least one laser cut that extends at least partially through a wall of the flexible hypotube, such as from the outer surface towards the inner surface. In some embodiments, the cuts (or a subset of the cuts) may extend all the way through the wall of the hypotube. In some embodiments, each cut my have a width of between 0.01 mm and 0.1 mm. In some embodiments, the tubular portion may extend all the way between the distal and proximal ends. In such embodiments, the entire hypotube may include cuts other than the distal and proximal ends. In other embodiments, the tubular portion includes a portion of the length of the hypotube between the distal and proximal ends. For example, the tubular portion may be between 20% and 80% of the length of the hypotube. In some embodiments, the tubular portion is centered between the distal and proximal ends. In that regard, the tubular portion may be a central portion of the hypotube. 
     As will be appreciated, the hypotube and tubular portion may have any suitable cross-sectional shape, although shown as being circular in cross section. For example, in other embodiments, the hypotube and tubular portion may be ovular, triangular, square, other polygonal or other suitable shape. 
     As described herein, the at least one cut (e.g., laser cut) can exist in a variety of configurations. In some embodiments, the at least one cut defines a helical cut extending axially along the tubular portion of the flexible hypotube. 
     In some embodiments, the at least one cut comprises a plurality of identical laser cuts. In some embodiments, each of the plurality of identical laser cuts may be offset only axially from all other laser cuts of the plurality of identical laser cuts. In some of these embodiments, each of the plurality of identical laser cuts may be offset axially from all other laser cuts of the plurality of identical laser cuts, and at least one laser cut is offset circumferentially from a neighboring laser cut, such as being offset circumferentially by 45°, 90°, or 180° from a neighboring laser cut. In some of these embodiments, the plurality of identical laser cuts may define at least two helical patterns, such as two helical patterns that are offset circumferentially. 
     A second aspect of the present disclosure is drawn to a system having a cannula and a flexible hypotube, where the flexible hypotube contains laser cuts in the hypotube. The cannula (which may be a flexible flow cannula) has an inner surface and an outer surface, which define a cannula wall having a thickness, the inner surface of the cannula defining a first lumen therethrough. The flexible hypotube may be attached to the cannula, and has an outer surface and an inner surface, where the inner surface defines a second lumen therethrough. The flexible hypotube includes a tubular portion containing at least one cut extending from the outer surface at least partially through the sidewall of the flexible hypotube, each cut having a maximum width of between 0.01 mm and 0.1 mm. The second lumen is arranged to slidably receive an optical fiber therethrough. 
     As described herein, the optical fiber may be arranged to freely move within the second lumen of the hypotube. In some embodiments, the system is configured to provide a ratio R2 of a diameter of an outer surface of the optical fiber to a diameter of the inner surface of the flexible hypotube is 1:3&gt;R2&gt;1:1.1. In some embodiments, the system is configured to provide a ratio R1 of a diameter of the outer surface of the hypotube to a diameter of the inner surface of the cannula is 1:5&gt;R1&gt;1:25. 
     In some embodiments, the flexible hypotube may include a coating or jacket. 
     In some embodiments, the system also includes an inflow cage connected at or near a distal portion of the cannula. In some embodiments, a distal portion of the optical fiber may be attached to the inflow cage. In some embodiments, the optical fiber includes an optical fiber sensor head at a distal end of the optical fiber, where the sensor may be configured to, e.g., measure ventricular pressure. 
     In some embodiments, the system further includes a pump operably connected to a proximal portion of the first lumen. 
     In some embodiments, the flexible hypotube may be positioned within the first lumen. In some embodiments, the flexible hypotube may be positioned outside the first lumen. In some embodiments, at least one portion of the flexible hypotube is positioned within the first lumen and at least one portion of the flexible hypotube is positioned outside the first lumen. 
     In some embodiments, the flexible hypotube includes a distal portion, a proximal portion, and a tubular portion between the distal portion and the proximal portion, the tubular portion containing at least one cut extending at least partially through the wall of the flexible hypotube, from the outer surface towards the inner surface, each cut having a maximum width of between 0.01 and 0.1 mm. In some embodiments, the cuts may extend all the way through the hypotube. 
     As with the above, the at least one cut may include a variety of configurations. In some embodiments, the at least one cut defines a helical cut extending axially along the tubular portion of the flexible hypotube. In some embodiments, the at least one cut includes a plurality of identical laser cuts. In some of these embodiments, each of the plurality of identical laser cuts are offset only axially from all other laser cuts of the plurality of identical laser cuts. In some of these embodiments, each of the plurality of identical laser cuts are offset axially from all other laser cuts of the plurality of identical laser cuts, and at least one laser cut is offset circumferentially from a neighboring laser cut, such as being offset circumferentially by 45°, 90°, or 180° from a neighboring laser cut. In some of these embodiments, the plurality of identical laser cuts may define at least two helical patterns, such as two helical patterns that are offset circumferentially. 
     A third aspect of the present disclosure is drawn to an intravascular blood pump. The pump will generally include a catheter, a pumping device, and at least one sensor. The pumping device may be disposed distally of the catheter and has at its distal end a cannula (which may be a flexible flow cannula) through which blood is either sucked or discharged by the pumping device during operation of the intravascular blood pump. The at least one sensor has at least one optical fiber slidably disposed in a flexible hypotube, the flexible hypotube being at least partially attached to the cannula, the flexible hypotube having a tubular portion containing at least one cut extending from an outer surface of the flexible hypotube towards an inner surface of the flexible hypotube, at least partially through a wall of the flexible hypotube. In some embodiments, the cut(s) may extend all the way through the flexible hypotube wall. In some embodiment, each cut includes a width of between 0.01 mm and 0.1 mm. In some embodiments, the flexible hypotube is configured to minimize and/or prevent breakage of the at least one optical fiber during bending of the flexible hypotube and cannula while the blood pump is guided through a vascular system of a patient. 
     Advantageously, the optical fiber is arranged to freely move within the second lumen. In some embodiments, the system is configured to provide a ratio R2 of a diameter of an outer surface of the optical fiber to a diameter of the inner surface of the flexible hypotube is 1:3&gt;R2&gt;1:1.1. In some embodiments, the system is configured to provide a ratio R1 of a diameter of the outer surface of the hypotube to a diameter of the inner surface of the cannula is 1:5&gt;R1&gt;1:25. 
     In some embodiments, the system also includes an inflow cage connected at or near a distal portion of the cannula. In some embodiments, a distal portion of the optical fiber is attached to the inflow cage. In some embodiments, the optical fiber has an optical fiber sensor head at a distal end of the optical fiber, where the sensor may be configured to, e.g., measure ventricular pressure. 
     In some embodiments, the system further includes a pump operably connected to a proximal portion of the first lumen. 
     In some embodiments, the flexible hypotube may be positioned within the first lumen. In some embodiments, the flexible hypotube may be positioned outside the first lumen. In some embodiments, at least one portion of the flexible hypotube may be positioned within the first lumen and at least one portion of the flexible hypotube is positioned outside the first lumen. 
     In some embodiments, the flexible hypotube includes a distal portion, a proximal portion, and a tubular portion having at least one cut extending at least partially through the flexible hypotube (e.g., from the outer surface towards the inner surface). For example, the cut may extend all the way through the hypotube wall. In some embodiments, each cut includes a maximum width of between 0.01 mm and 0.1 mm. The at least one cut may include a variety of configurations. In some embodiments, the at least one cut defines a helical cut extending axially along the tubular portion of the flexible hypotube. In some embodiments, the at least one cut includes a plurality of identical laser cuts. In some of these embodiments, each of the plurality of identical laser cuts are offset only axially from all other laser cuts of the plurality of identical laser cuts. In some of these embodiments, each of the plurality of identical laser cuts are offset axially from all other laser cuts of the plurality of identical laser cuts, and at least one laser cut is offset circumferentially from a neighboring laser cut, such as being offset circumferentially by 45°, 90°, or 180° from a neighboring laser cut. In some of these embodiments, the plurality of identical laser cuts define at least two helical patterns, such as two helical patterns that are offset circumferentially. 
     A fourth aspect of the present disclosure is a method of reducing strain on an optical fiber during insertion and use of a blood pump. The method includes providing a blood pump having (i) a cannula (which may be a flexible flow cannula) having an inner surface and an outer surface, the inner surface defining a first lumen therethrough, (ii) a flexible hypotube attached to the cannula, the flexible hypotube having an outer surface and an inner surface, the inner surface defining a second lumen therethrough, the flexible hypotube having a tubular portion containing at least one cut extending from the outer surface of the flexible hypotube towards an inner surface of the flexible hypotube at least partially through the flexible hypotube, each opening having a width of between 0.01 and 0.1 mm, and (iii) an optical fiber having an outer surface, the optical fiber laid slidably in the flexible hypotube. The method then includes moving the blood pump through a patient&#39;s vascular system, while allowing the optical fiber to move axially within the flexible hypotube while the blood pump is moving. 
     In some embodiments, the method further includes receiving as an input at an evaluation device a transmitted optical signal from the optical fiber sensor head, and then determining a pressure using the transmitted optical signal. 
     In some embodiments, the optical fiber is arranged to freely move within the second lumen. In some embodiments, the blood pump of the method is configured to provide a ratio R2 of a diameter of an outer surface of the optical fiber to a diameter of the inner surface of the flexible hypotube is 1:3&gt;R2&gt;1:1.1. In some embodiments, the blood pump of the method is configured to provide a ratio R1 of a diameter of the outer surface of the hypotube to a diameter of the inner surface of the cannula is 1:5&gt;R1&gt;1:25. 
     In some embodiments, the blood pump of the method further includes an inflow cage connected at or near a distal portion of the cannula. In some embodiments, a distal portion of the optical fiber is attached to the inflow cage. In some embodiments, the optical fiber has an optical fiber sensor head at a distal end of the optical fiber, where the sensor may be configured to, e.g., measure ventricular pressure. 
     In some embodiments, the blood pump of the method further includes a pump operably connected to a proximal portion of the first lumen. 
     In some embodiments, the flexible hypotube may be positioned within the first lumen. In some embodiments, the flexible hypotube may be positioned outside the first lumen. In some embodiments, at least one portion of the flexible hypotube is positioned within the first lumen and at least one portion of the flexible hypotube is positioned outside the first lumen. 
     In some embodiments, the flexible hypotube has a distal portion, a proximal portion, and a tubular portion between the distal portion and the proximal portion, the tubular portion containing at least one cut at least partially through the flexible hypotube extending from the outer surface towards the inner surface, each cut having a width of between 0.01 and 0.1 mm. 
     As with the above, the at least one cut may include a variety of configurations. In some embodiments, the at least one cut defines a helical cut extending axially along the tubular portion of the flexible hypotube. In some embodiments, the at least one cut includes a plurality of identical laser cuts. In some of these embodiments, each of the plurality of identical laser cuts are offset only axially from all other laser cuts of the plurality of identical laser cuts. In some of these embodiments, each of the plurality of identical laser cuts are offset axially from all other laser cuts of the plurality of identical laser cuts, and at least one laser cut is offset circumferentially from a neighboring laser cut, such as being offset circumferentially by 45°, 90°, or 180° from a neighboring laser cut opening. In some of these embodiments, the plurality of identical laser cuts define at least two helical patterns, such as two helical patterns that are offset circumferentially. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a depiction of a blood pump laid through the aorta, extending through the aortic valve into the left ventricle and having an integrated pressure sensor. 
         FIG.  2 A  is a cross-section schematic representation of an embodiment of a flexible hypotube. 
         FIG.  2 B  is a cross-section schematic representation of an embodiment of a cannula, flexible hypotube, and optical fiber. 
         FIG.  2 C  is a cross-section schematic representation of an embodiment of a cannula where the flexible hypotube is disposed inside the cannula. 
         FIG.  3 A  is a schematic representation of a flexible hypotube with cuts as disclosed. 
         FIGS.  3 B- 3 G  are depictions of side views of alternate examples of cuts made in a flexible hypotube. 
         FIG.  3 H  is an axial cross-sectional view of a portion of a flexible hypotube coupled to a cannula. 
         FIG.  3 I  is a magnified or enlarged image of a flexible hypotube coupled to a cannula. 
         FIG.  4    is a depiction of a pumping device of the blood pump from  FIG.  1    in greater detail. 
         FIG.  5    is a flowchart of a disclosed method. 
     
    
    
     DETAILED DESCRIPTION 
     As is known, blood pumps may have sensors for monitoring a patient. For example, intravascular blood pumps may include optical sensors, such as for measuring pressures within a patient&#39;s vascular system, and particular a patient&#39;s ventricular cavity, which may be used for operating the blood pump and/or for assessing the state of health of the patient&#39;s heart. 
     As appreciated by the inventors, the cannula, on its way to placement in the heart, may be subjected to great bends or flexions which can exert non-negligible tensile and compressive stresses on an optical fiber laid along the cannula, which may cause damage to the optical fiber. For example, in an illustrative example, the optical fiber may become detached from the pump housing during insertion due to tensile and compressive stresses. This also may apply to optical fibers made of glass. Although such optical fibers are normally covered with a thin plastic coating, such as polyimide (Kapton), which offers some protection from breakage, the danger of breakage during insertion due to tensile and compressive stresses could still be problematic. For example, such damage may result in the entire blood pump having to be replaced (e.g., if the optical fiber breaks). 
     Accordingly, the inventors have recognized the advantages of a system and method for relieving the strain of an optical fiber associated with a cannula, such as a flexible flow cannula. As described herein, in some embodiments the system may include a flexible hypotube within which an optical fiber is slidably disposed. In this regard, the hypotube may form a protective sleeve within which the optical fiber may be seated. In some embodiments, the hypotube is associated with a cannula. For example, the hypotube may be disposed inside or outside the cannula. The hypotube may include one or more cuts (e.g., laser cuts). 
     Turning now to the figures,  FIG.  1    shows an exemplary intravascular blood pump having a catheter  10  which may be introduced into a patient&#39;s heart. For example, as show in this figure, the pump may be inserted into the descending aorta  11  retrograde in some embodiments. As is known, the descending aorta is part of the aorta  12  which first ascends from the heart and then descends and has the aortic arch  14 . At the beginning of the aorta  12  there is located the aortic valve  15  which connects the left ventricle  16  to the aorta  12  and through which the intravascular blood pump may extend. As will be appreciated, blood pumps may be inserted into other suitable portions of the    
     As shown in  FIG.  1   , the intravascular blood pump may include a rotary pumping device  50  fastened at the distal end of the catheter hose  20  and having a motor section  51  and a pump section  52  (sometimes referred to herein as simply the “pump”) disposed at an axial distance therefrom, as well as a cannula  53  (which may be a flexible flow cannula) protruding in the distal direction from the inflow end of the pump section  52  and having a suction inlet  54  located at its end. Distally of the suction inlet  54  there is provided a soft-flexible tip  55 , which can be configured for example as a “pigtail” or in a J shape. Through the catheter hose  20  there may extend different lines and devices which may be important for operating the pumping device  50 . 
     In some embodiments, the pump may include two optical fibers  28 A,  28 B that may be attached at their proximal end to an evaluation device  100 . These optical fibers  28 A,  28 B may be respectively part of an optical sensor (such as a pressure sensor) whose sensor heads  30  and  60  may be located in the vicinity of the suction inlet  54 , on the one hand, and on the outside on the housing of the pump section  52 , on the other hand.  FIG.  1    shows the sensor head  30  as being on the outside of the blood pump, but the sensor head could also be located internal to the blood pump, preferably within an inflow cage, the inflow cage having lumens therethrough that define the suction inlet  54 . In such embodiments, information (e.g., pressure information) may be transmitted by the sensor heads  30  and  60  to the evaluation device  100  and may be converted into electrical signals in the evaluation device  100  and displayed e.g., on a display screen  101 . 
     According to an aspect of the present disclosure, and as shown in  FIGS.  2 A and  2 B , the intravascular pump may include a flexible hypotube  27  for receiving an optical fiber. For example, the optical fiber may be slidably received in the flexible hypotube. As will be appreciated in view of these figures, the hypotube may be extend along an inner or outer surface of the cannula. As will be further appreciated, in some embodiments, the hypotube may extend partially along the inside and partially along the outside surfaces of the cannula. For example, in some embodiments, one or more portions of the flexible hypotube may be disposed on the inside of the cannula, while one or more other portions of the flexible hypotube may be disposed on the outside of the cannula. One or more portions of the flexible hypotube also may extend on a portion of the blood pump other than the cannula (e.g., on or in the inflow cage). 
     In some embodiments, the flexible hypotube may have a distal end, a proximal end, and a tubular portion including one or more cuts as described herein. As described herein, the tubular portion may extend along a length of the flexible hypotube, between the proximal and distal ends. In some embodiments, the tubular portion may extend along an entire length of the hypotube. In other embodiments, the tubular portion may extend along only a portion of the length of the hypotube. For example, in some embodiments, the tubular portion may include a middle portion of the hypotube. In such embodiments, the hypotube may include a distal portion, a middle portion, and the proximal portion. See, e.g.,  FIG.  3 A , in which the flexible hypotube  100 A includes a proximal portion  120 A, a middle portion  130 A, and a distal portion  140 A. 
     As shown in  FIGS.  2 A and  3 A , for example, flexible hypotube may be attached to the flexible flow cannula. The flexible hypotube may have an outer surface  111  and an inner surface  112 , where the inner surface defines a lumen extending from a proximal end  170 A to a distal end  171 A. In some embodiments, the hypotube may extend along a portion of the outer surface of the flow cannula (see, e.g.,  FIG.  2 A ). In other embodiments, the hypotube may extend along a portion of the inner surface of the flow cannula (see, e.g.,  FIG.  2 B ). In still other embodiments, the hypotube may extend along a portion of each of the inner and outer surfaces of the flow cannula. 
     The flexible hypotube  27  in which the optical fibers  28 A,  28 B are laid can, in some embodiments, extend shortly (e.g., less than 6 inches) into the catheter hose  20 , but can also extend completely through the catheter hose  20  (see  FIG.  1   ) and end in a corresponding plug at the end of the line for insertion of the relevant pressure sensor into a connection of the evaluation device  100 . 
     In some embodiments (see, e.g.,  FIG.  4   ), the cannula  53  may have a precurvature which may facilitate the laying of the device in the patient&#39;s vascular system. Due to this precurvature, the cannula  53  may have an inner radius of curvature and an outer radius of curvature between which, substantially in the middle, a neutral bending plane extends. In such embodiments, the hypotoube may be configured to bend with the precurvature of the flow cannula. 
     The flexible hypotube may include a single walled, hollow tube. In some embodiments, the hypotube may include one or more coatings around a single walled, hollow tube. For example, as seen in  FIG.  2 C , in some embodiments, the hypotube  27  may comprise an outer jacket  161  external to a single walled, hollow tube  162 , the single-walled hollow tube having one or more cuts described herein. In some embodiments, the hypotube  27  may comprise an inner coating  163  internal to a single walled, hollow tube  162 . In some embodiments, the hypotube  27  may comprise both an outer jacket  161  and an inner coating  163 . As will be appreciated, in some embodiments, the flexible hypotube may include only an inner jacket or only an outer jacket. In some embodiments, the outer jacket and inner coating are comprised of the same material. In some embodiments, the outer jacket and inner coating are comprised of different materials. 
     The flexible hypotube will have a length  113 . In some embodiments, the hypotube may be between 4 and 8 cm in length, such as between 5 and 7 cm in length. 
     As shown in  FIGS.  2 A and  3 A , the flexible hypotube may have an outer surface  111  defining an outer diameter  114  from a proximal end to the distal end. The flexible hypotube also may include an inner surface  112  having an inner diameter  115  that defines a lumen therethrough (e.g., from the proximal end  170  to the distal end  171 ). In some embodiments, the flexible hypotube may have an inner diameter between 0.130 mm and 0.275 mm, such as between 0.140 mm and 0.160 mm. The difference between the outer diameter  114  and the inner diameter  115  may define a wall thickness of the flexible hypotube. In some embodiments, the wall thickness may be between 0.045 mm and 0.090 mm, such as between 0.050 mm and 0.070 mm. 
     Referring briefly to  FIGS.  2 A and  2 B , an optical fiber  28 A may be present within a lumen of a flexible hypotube  27 , which is attached to the cannula  53 . For example, in some embodiments, the hypotube may be attached to an outer surface of the hypotube (see  FIG.  2 A ), while in other embodiments, the hypotube may be attached to an inner surface of the cannula (see  FIG.  2 B ). Accordingly, in  FIG.  2 A , the flexible hypotube and optical fiber may be positioned outside the first lumen, while in  FIG.  2 B , the flexible hypotube and optical fiber may be positioned within the first lumen. As will be appreciated, a first portion of the flexible hypotube may be positioned within the first lumen while a portion of the flexible hypotube is positioned the first lumen. 
     As represented in these views, an outer diameter  114  of the flexible hypotube  27  may be smaller than the inner diameter  117  which defines a lumen through the cannula  53 . In some embodiments, these components may be configured such that a ratio R1 of a diameter  114  of the outer surface of the hypotube  27  to a diameter  117  of the inner surface of the cannula  53  is 1:5&gt;R1&gt;1:25. That is, that the inner diameter of the cannula may be between 5 and 25 times larger than the outer diameter of the hypotube, such as between 15 and 25 times larger than the outer diameter of the hypotube (that is, 1:15&gt;R1&gt;1:25). 
     Further, the inner diameter  115  of the flexible hypotube  27  may be larger than the outer diameter  116  of the optical fiber  28 A. In some embodiments, these components are configured such that a ratio R2 of a diameter  116  of an outer surface of the optical fiber  28 A to a diameter  115  of the inner surface of the flexible hypotube  27  may be 1:3&gt;R2&gt;1:1.1, such as 1:2&gt;R2&gt;1:1.1. 
     In some embodiments, the optical fiber may be arranged to freely move within the second lumen, such that the optical fiber can move, axially, independent of movement of the flexible hypotube. In some embodiments, this freedom may be a result of the optical fiber not being connected to the flexible hypotube. In some embodiments, this freedom may be a result of there being slack, or excess, optical fiber within the flexible hypotube. For example, in some embodiments, the optical fiber may be attached to the hypotube (i.e., adhered to the hypotube, or otherwise restricted from moving axially independently of the hypotube) at or near the proximal end of the hypotube, while a linear length of optical fiber within the flexible hypotube may be longer (e.g., up to 1.1-1.2 times longer) that the linear length of the flexible hypotube, such that when the cannula and flexible hypotube bend, there may be sufficient excess optical fiber within the hypotube that the optical fiber does not experience substantial tension. As will be appreciated, the optical fiber also may be attached to other suitable portions of the hypotube and/or to the pump (e.g., at an inflow cage). 
     As shown in  FIGS.  3 A- 3 G , the flexible hypotube may include a tubular portion with at least one cut. As described herein, the cut(s) may be configured to control the ease (or resistance) the hypotube exhibits when bending in certain directions. In some embodiments, the cuts may be arranged such that the hypotube may bend in only one direction, such as in a prescribed bend direction of the cannula on or within which the hypotube is placed. The hypotube also may be configured to bend in all directions. 
     As seen in  FIG.  3 A , in some embodiments of the system, the flexible hypotube may include a distal portion  140 A at or near a distal end  171 , a proximal portion  120 A at or near a proximal end  170 , and a tubular portion  130 A having at least one cut  150 A extending at least partially through the flexible hypotube from the outer surface  111  towards the inner surface  112  (e.g., only partially through the wall of the flexible hypotube). In some embodiments, the distal portion may extend a distance from a distal end and the proximal portion may extend a distance from the proximal end. In some embodiments, each cut may extend completely through the wall of the flexible hypotube (e.g., from the outer surface through to the inner surface). 
     While the length of each cut may vary, each cut may have a width w  155  of between 0.01 and 0.1 mm. For purposes herein, a cut made between point A and point B along the surface of the hypotube may follow a pathline that is a straight, a curved, or a freeform path. The pathline may have a distance (i.e., the length of the pathline), and the means of forming the cut (such as a laser cut) may define the width w of the cut. In some embodiments, the width w of a cut may be constant along the entire pathline. In other embodiments, the width w of a cut may vary. For example, in some embodiments, the width of a cut may be constant except for the very ends  180  of each cut (which may be rounded, etc.). In other embodiments, the width of the cut may vary in other suitable portions 
     As shown in  FIGS.  3 A- 3 G , different patterns of cuts may be utilized. 
     As seen in  FIGS.  3 A and  3 B , in some embodiments, the at least one cut  150 A,  150 B comprises a single cut that defines a helical (or spiral) cut extending axially along a cut length  130 A,  130 B of the flexible hypotube  100 A,  100 B. The spiral pattern may have a constant pitch or may have a varying pitch. In some embodiments, the pitch may be between 0.3 mm and 1.0 mm. In one embodiment, the pitch may be 0.5 mm. 
     As will be appreciated, the length of the cut (e.g., the length of the tubular portion) may extend along an entire length of the hypotube (e.g., in  FIG.  3 B , between the distal end  171 B and proximal end  170 B of the hypotube  100 B). In other embodiments, such as those depicted in  FIG.  3 A , the length of the cut (e.g., a length of the tubular portion) may include a central portion of the hypotube. For purposes herein, the central portion  130 A may include between 20% and 80% of a length of the hypotube. In some embodiments, the central portion is centered between the distal end  171 A and proximal end  170 A of the hypotube. 
     While some embodiments utilize only a single cut, in some embodiments, the at least one cut may comprise a plurality of identical cuts, such as a plurality of identical laser cut openings. 
     For example, as shown in  FIGS.  3 C and  3 D , the cut may include partial spiral cuts. As will be appreciated, the plurality of cuts may extend around the circumferences of the hypotube and along a length of the hypotube. As seen in  FIG.  3 C , in some embodiments, a first partial spiral cut  150 C and a second partial spiral cut  151 C may be configured such that if the pathline of the first spiral cut and the pathline of the second spiral cut were extended, they would intersect and form a continuous spiral pattern. As seen in  FIG.  3 D , in some embodiments, the pathlines of a first partial spiral cut  150 D and a second partial spiral cut  151 D may be parallel to each other but not intersect if extended. Rather, the partial cuts may be configured such that a portion of each cut (such as a bottom edge, a top edge, a center point, etc.), if connected by an imaginary line  181 , would define a spiral pattern. In some embodiments, each cut may be configured such that a pathline of the cut is linear. In some embodiments, each cut may be configured such that a pathline of the cut is non-linear. In some embodiments, each cut may be made such that the pathline of the cut is in a plane normal to the axis of the hypotube. In some embodiments, each cut may, independently, be made such that the pathline of the cut is in a plane that is not normal to the axis of the hypotube. 
     As seen in  FIG.  3 E , the at least one cut may include a repeating pattern of interrupted helical or spiral patterns or cuts, including first spiral cut  150 E, an identical second spiral cut  151 E, an identical third spiral cut  152 E, and an identical fourth spiral cut  153 E. The spiral pattern(s) may have a constant pitch or may have a varying pitch. In some embodiments, the pitch may be between 0.3 mm and 1.0 mm. For example, the pitch may be 0.5 mm. 
     As shown in  FIG.  3 E , the first cut  150 E and second cut  151 E may start at the same axial distance  156 E from a distal end of the flexible hypotube, but may be offset circumferentially from each other (that is, the end of each cut is the same axial distance from the distal end of the hypotube, but the patterns are “rotated” around the axis of the hypotube in relation to each other). In some embodiments, the circumferential offset is ±45°, ±90°, or 180° from a neighboring laser cut opening. Neighboring laser cut opening can generally be considered as two different laser cut openings where there is no intervening other laser cut opening between them. In  FIG.  3 E , the first cut  150 E and the third cut  152 E may be only offset axially from each other, not circumferentially, while the first cut  150 E and fourth cut  153 E may be offset circumferentially and axially from each other. As such, in  FIG.  3 E , at least one cut of the plurality of cuts (e.g., third cut  152 E) may be offset only axially from at least one other cut (e.g., first cut  150 E), at least one other cut (e.g., second cut  151 E) of the plurality of cuts may be offset only circumferentially from the at least one other cut, and at least one additional cut (e.g., fourth cut  153 E) of the plurality of cuts is offset both axially and circumferentially from the at least one other cut. 
     While  FIG.  3 E  shows interrupted spirals, where each spiral or helical pattern or cut ( 150 E,  151 E,  152 E,  153 E) may extend only a portion of the length of the tubular portion  130 C, in other embodiments, the plurality of identical laser cuts can define at least two helical patterns, that each extends substantially the entire length of the tubular portion of the hypotube, or substantially the entire length of the hypotube. For example, in some cases, two or more helical patterns may be cut into the hypotube, where the patterns are only offset circumferentially. 
     Combinations of these cuts are also envisioned in other embodiments. For example, in some embodiments, one first long spiral cut may extend substantially the entire length of the tubular portion. In another embodiment, the hypotube may include a plurality of additional interrupted spiral cuts that are each offset circumferentially and/or axially from the first long spiral cut. 
     As seen in  FIG.  3 F , in some embodiments, the flexible hypotube  100 F may include a tubular portion with at least one cut having a repeating pattern of cuts ( 150 F,  151 F,  152 F,  153 F), where each cut is made orthogonal to the axis of the flexible hypotube (e.g., the cut is made only in a circumferential direction). In such embodiment, each cut may include first cut  150 F, an identical second cut  151 F, an identical third cut  152 F, and an identical fourth cut  153 F. As seen in  FIG.  3 F , each of the plurality of identical laser cut openings may be offset axially from all other laser cut openings of the plurality of identical laser cut openings. Further, as seen in  FIG.  3 F , at least one laser cut opening may be offset circumferentially from a neighboring laser cut opening. For example, in  FIG.  3 F,  151 F  is offset from both neighboring laser cut openings,  150 F and  152 F. In  FIG.  3 F , each laser cut opening may be offset axially by a small amount and circumferentially by 90 degrees from a previous laser cut opening in the pattern. That is, after  150 F is cut, the hypotube can be rotated 90 degrees, optionally moved axially a small amount, and identical second cut  151 F can be made. 
     In some embodiments, the at least one laser cut opening may be offset circumferentially by ±45°, ±90°, or 180° from a neighboring laser cut opening. 
     In some embodiments, at least one laser cut opening may be only offset circumferentially from a neighboring laser cut, and at least one laser cut opening may be offset circumferentially and axially from a neighboring laser cut. 
     As seen in  FIG.  3 G , in some embodiments, the flexible hypotube  100 G may include a cut length  157 G (as discussed previously, this cut length may be some or all of the entire length of the hypotube) with at least one cut comprises a repeating pattern of cuts ( 150 G,  151 G,  152 G,  153 G), where at least one laser cut opening ( 151 G) is only offset circumferentially from a neighboring laser cut ( 150 G), and at least one laser cut opening ( 152 G,  153 G) is offset circumferentially and axially from the neighboring laser cut ( 150 G). In  FIG.  3 G , the repeating pattern consists of two pairs of cuts ( 150 G and  151 G,  152 G and  153 G), where each cut in a pair are the same axial distance along the hypotube (i.e., they are not offset axially from each other), but are offset circumferentially 180 degrees from each other. For example, first cut  150 G may be circumferentially offset 180 degrees from second cut  151 G. The second pair of cuts may be offset axially from the first pair of cuts and offset circumferentially 90 degrees. That is, a third cut  152 G may be offset axially by a small amount and offset circumferentially 90 degrees from first cut  150 G, and fourth cut  153 G may be offset axially by a small amount and offset circumferentially −90 degrees (or offset +270 degrees) from first cut  150 G. 
     As seen in  FIGS.  3 H and  3 I , in some embodiments, the gaps  190  formed by the cuts in the hypotube  100 H,  100 I may be filled in, such as with a polymer. For example, in some embodiments, the gaps  190  may be filled with a urethane material, such as polyurethane (e.g., a thermoformed polyurethane). In some embodiments, the gaps may be filled by coating the hypotube with the polymer material. In some embodiments, the hypotube may include a polymer jacket. In such embodiments, the hypotube may have a smooth inner and/or outer surface. As seen in  FIG.  3 H , in some embodiments, a surface  166  of the hypotube  100 H may be coupled to a surface  167  of a cannula  53 . The hypotube  100 I may comprise an inner coating  163 , such as a low-friction coating (which may be, e.g., polytetrafluoroethylene (PTFE)) or a polyurethane, that defines the lumen  160  therethrough. The gaps  190  may be filled in, such as with a polymer layer  161 . In some embodiments, the polymer layer may not only form an outer layer of the hypotube  100 H and may also form an outer coating or layer of the cannula  53 . In some embodiments, the outer layer of the hypotube may be separate from the outer layer of the cannula, and thus the outer layer of the hypotube may be in contact with an outer layer of the cannula  53 . In some embodiments, the outer layer  161  of the hypotube may be comprised of the same material forming an outer coating or layer  165  of the cannula  53 . In some embodiments, the outer layer  161  of the hypotube may be comprised of a different material forming an outer coating or layer  165  of the cannula  53 . 
     Referring to  FIG.  4   , a pump may be operably connected to a proximal portion of the first lumen of cannula  53  (which may be a flexible flow cannula). The cannula preferably has a suction inlet  54  located at its distal end. In preferred embodiment, the suction inlet  54  may comprise a plurality of apertures formed on an inflow cage  70  that is coupled to the cannula  53 . In some implementations, the inflow cage may be comprised of stainless steel. 
     In some embodiments, a distal portion of the optical fiber is attached to the inflow cage  70 , and in some embodiments, attached to an internal surface of the inflow cage. 
     Referring to  FIGS.  1  and  4   , also disclosed is an intravascular blood pump. The blood pump may comprise a catheter, a pumping device, and at least one sensor. 
     The pumping device  50  may be disposed distally of the catheter  10  and may have at its distal end, a cannula  53  (which may be a flexible flow cannula) through which blood either sucked or discharged by the pumping device  50  during operation of the intravascular blood pump. The at least one sensor having at least one optical fiber  28 A may be laid slidably in a flexible hypotube  27 , the flexible hypotube being at least partially attached to the cannula (e.g., on an inner or outer surface of the cannula. As described herein, the flexible hypotube may include a tubular portion containing at least one cut extending from an outer surface of the flexible hypotube towards an inner surface of the flexible hypotube at least partially through the flexible hypotube, each cut having a width of between 0.01 and 0.1 mm. In some embodiments, the flexible hypotube may be configured to minimize or prevent breakage of the at least one optical fiber during bending of the flexible hypotube and/or cannula, and/or to minimize or prevent detachment of an optical sensor from the pump (e.g., an optical sensor attached to an inlet housing) while the blood pump is guided through a vascular system (e.g., 11, 12, 14, 15, 16) of a patient. 
     The components of the blood pump, including the cannula, flexible hypotube, and sensor (optical fiber, sensor head, etc.) may be configured as described in any of the previous embodiments. 
     Also disclosed is a method of reducing strain on an optical fiber during insertion and use of a blood pump. Referring to  FIG.  5   , the method  200  generally comprises providing  210  a blood pump with an optical fiber as described above. For example, in some embodiments, the blood pump may comprise (i) a cannula having an inner surface and an outer surface, the inner surface defining a first lumen therethrough, (ii) a flexible hypotube attached to the cannula (e.g., on the inner and/or outer surface), the flexible hypotube having an outer surface and an inner surface, the inner surface defining a second lumen therethrough, the flexible hypotube having a tubular portion containing at least one cut extending from the outer surface of the flexible hypotube towards an inner surface of the flexible hypotube at least partially through the wall of the flexible hypotube, each opening having a width (e.g., maximum width) of between 0.01 and 0.1 mm, and (iii) an optical fiber having an outer surface, the optical fiber laid slidably in the flexible hypotube. In other embodiments, the blood pump may comprise (i) a cannula having an inner surface and an outer surface, the inner and outer surface defining a cannula wall having a thickness, the inner surface of the cannula defining a first lumen therethrough, and (ii) a flexible hypotube attached to the cannula, the flexible hypotube having an outer surface and an inner surface, the inner surface of the flexible hypotube defining a second lumen therethrough. In some embodiments, the second lumen may be arranged to slidably receive an optical fiber therethrough, with the cannula and flexible hypotube being configured such that a ratio R1 of a diameter of the outer surface of the hypotube to a diameter of the inner surface of the cannula may be 1:5&gt;R1&gt;1:25. 
     After the blood pump has been provided, the blood pump can then be moved through a patient&#39;s vascular system. Rather than keeping the optical fiber from moving, the optical fiber may be allowed 220 to move axially within the flexible hypotube while the blood pump is moving. 
     After the blood pump is moved, an evaluation device (c.f.  FIG.  1   , device  100 ) may receive 230 as an input an optical signal transmitted from an optical fiber sensor head, through the optical fiber. The evaluation device can then use that received input in order to determine  240  a pressure and/or signal-to-noise ratio (SNR). 
     In some embodiments, the process of moving the blood pump and measuring pressures is repeated at least once. In some embodiments, it is repeated until the determined pressure indicates the blood pump is positioned correctly. 
     Referring again to  FIG.  4   , in some embodiments, the glass membrane  32  in the sensor head may be pressure-sensitive and be deformed in response to the amount of pressure acting on the sensor head  60  (or  30 ). For example, the deformation of the glass membrane  32  may cause the light to be reflected and coupled back into the optical fiber  28 A. Optical fiber  28 A transmits the optical signal from the optical fiber sensor to an evaluation device. For example, as mentioned above, the optical signals transmitted by the sensor heads  30  and  60  can be converted into electrical signals in the evaluation device  100  and displayed, e.g., on a display screen  101 . 
     As seen in  FIG.  4   , the optical fiber  28 A the pressure-measuring catheter may have a sensor head  30  having a head housing  31  which contains a thin glass membrane  32  which terminates a cavity  33 . The glass membrane  32  may be pressure-sensitive and be deformed in dependence on the size of a pressure acting on the sensor head  30 . Through the reflection on the membrane the light exiting from the optical fiber  28 A may be reflected modulatingly and coupled back into the optical fiber. The coupling can be effected either directly into the optical fiber  28 A or indirectly via a bottom  37  terminating the cavity  33  in a vacuum-tight manner. In some embodiments, the bottom  37  may be an integral part of the head housing  31 . Thus, the specification of the pressure in the cavity  33  can be effected independently of the mounting of the optical fiber  28 A. At the proximal end of the optical fiber  28 A, i.e., in the evaluation device  100 , there may be located a digital camera, such as e.g., a CCD camera or a CMOS, which evaluates the incoming light in the form of an interference pattern. In dependence thereon, a pressure-dependent electrical signal may be generated. The evaluation of the optical image or optical pattern delivered by the camera and the computation of the pressure may be affected through the evaluation unit  100 . The latter passes the already linearized pressure values to the control means, which also controls the power supply to the motor-operated pumping device  50  in dependence on the effected evaluation of the pressure signal. 
     In some embodiments, the evaluation device  100  may alternatively, or additionally, calculate a signal-to-noise ratio (SNR) based on the transmitted optical signal. For example, the optical signal that is transmitted from the distal sensor head  60  to the evaluation device  100  using optical fiber  28 A can be used by the evaluation device  100  to calculate the SNR of the optical signal. The SNR can be linked to the mechanical vibrations of a pumping device  50 . When the pumping device  50  is stopped, the motor current is zero and the mechanical vibrations of the pumping device  50  are at a minimum. During this state, the SNR may be relatively large because the noise level of the optical signal is low. When the pumping device  50  is running, the motor current is greater than zero and the mechanical vibration of the pumping device  50  increases. During this state, the SNR may be relatively low because the noise level of the optical signal is large. 
     The pumping device  50  from  FIG.  1    is represented in further detail in  FIG.  4   . As seen in  FIG.  4   , a drive shaft  57  may protrude from the motor section  51  into the pump section  52 , which drives an impeller  58  by means of which, during operation of the blood pump, blood may be sucked through the blood pass-through openings  54  at the distal end of the cannula  53  and discharged proximally of the impeller  58  through the blood-flow pass-through openings  56 . The pumping device  50  can also pump in the reverse direction when it is adapted accordingly. Leading through the catheter hose  20  of the catheter  10  to the pumping device  50  may be the above-mentioned optical fibers  28 A,  28 B, on the one hand, and a power-supply line  59 A for the motor section  51  and a purge-fluid line  59 B. 
     Instead of the optical pressure sensor described with reference to  FIG.  4   , which may work on, e.g., the Fabry-Pérot principle, other optical sensors (including other optical pressure sensors) with one or more optical fibers can also be employed. For example, in some embodiments, the optical sensor may be configured to measure a ventricular pressure. 
     The components of the blood pump, including the cannula, flexible hypotube, and sensor (optical fiber, sensor head, etc.) may be configured as described in any of the previous embodiments. 
     Those skilled in the art will recognize or be able to ascertain using no more than routine experimentation many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the following claims.