Patent Publication Number: US-2018036022-A1

Title: Device for improving electrohydraulic lithotripsy probe stiffness

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present patent document claims the benefit of the filing date under 35 U.S.C. §119(e) of Provisional U.S. Patent Application Ser. No. 62/371,437 filed Aug. 5, 2016, which is hereby incorporated by reference. 
    
    
     FIELD 
     The present disclosure relates to medical devices and more specifically to electrohydraulic lithotripsy probes. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Electrohydraulic lithotripsy is a procedure used as a means to break up stones within the biliary tree and urinary tract. While many stones may naturally pass through and out of the patient, some stones are too large to be passed on their own. These stones may become stuck in the biliary tree or urinary tract, thereby requiring medical intervention. A common way to remove stones is with lithotripsy: a medical procedure that involves breaking up the stones into smaller pieces that are then able to be passed naturally out of the patient&#39;s body. One specific subset of lithotripsy is electrohydraulic lithotripsy, which employs high energy shock waves to fragment the stones. These shock waves can be generated and targeted at the stone from outside of the patient&#39;s body or with a device that is inserted into the patient&#39;s body—either percutaneously or through a natural body cavity. 
     Electrohydraulic lithotripsy can use a shock wave generating device that is inserted into the patient&#39;s body. The device, or probe, is most commonly passed through an accessory channel of a scope or other similar introducer device until the probe is adjacent to the stone. A shock wave is then generated through the probe towards the stone. Eventually, the shock waves cause the stone to fragment and the probe and scope may then be removed while the stone fragments naturally pass through and out of the patient&#39;s body. Alternatively, the fragments may be removed by a vacuum, basket, or other fragment collection device inserted through or with the scope. 
     The scope, which is often a cholangioscope, must have an outer diameter small enough to allow it to be safely advanced through a body lumen of a patient. Sometimes, the cholangioscope is advanced through a working channel of a larger duodenoscope that also must have a diameter small enough to allow it be safely advanced through a body lumen of a patient. Since the probe is passed through a working channel of one of these scopes, the outer diameter of the probe must be fairly small. However, these probes are generally quite long, with lengths often exceeding 230 centimeters. Because of the high length to diameter ratio, one common problem associated with electrohydraulic lithotripsy is the buckling or kinking of the probe as it is advanced through the working channel of the scope and into a patient&#39;s body lumen. Kinking and buckling of the probe can be caused by the friction generated between the probe and the working channel of the scope or various structures in the patient&#39;s body lumen. As the physician advances the probe further into the scope, the friction between the scope and probe increase, thus requiring a greater force to further advance the probe. However, as the physician applies more force to the proximal end of the probe, the probe is more likely to kink or buckle, as it cannot withstand a large force due to its small diameter and low strength. When the probe kinks or buckles, the physician may have increased difficulty in advancing the probe towards the stone. Additionally, the probe must also maintain sufficient flexibility as it must be navigated through the twists and turns of the patient&#39;s body lumen. 
     Thus, it is desirable to provide a lithotripsy probe that is resistant to kinking and buckling while maintaining a small outer diameter with sufficient flexibility that may be passed through the working channel of a scope. 
     SUMMARY 
     In one form of the present disclosure, a lithotripsy probe is provided. The lithotripsy probe comprises an elongate body comprising a proximal end, a distal end, and a lumen extending therethrough. The lithotripsy probe also comprises a stiffening element comprising a proximal end, a distal end, and a length extending from the proximal end to the distal end. The stiffening element is disposed within the lumen of the elongate body. Further, the stiffening element comprises a stiffness that varies along the length of the stiffening element, wherein the stiffness of the proximal end of the stiffening element is greater than the stiffness of the distal end of the stiffening element. 
     The lithotripsy probe may further comprise first and second conductive wires extending through the lumen of the elongate body, the first and second conductive wires configured to deliver electrical energy to the distal end of the elongate body. Also, the stiffening element of the lithotripsy probe may increase along the length of the stiffening element from a lower stiffness at the distal end of the stiffening element to a greater stiffness at the proximal end of the stiffening element. Additionally, the proximal end of the stiffening element may be substantially coterminous with the proximal end of the elongate body and the distal end of the stiffening element may be substantially coterminous with the distal end of the elongate body. The stiffening element may also comprise a proximal portion and a distal portion, the proximal portion comprising a substantially constant outer diameter and the distal portion comprising a substantially constant outer diameter that is smaller than the outer diameter of the proximal portion, the stiffening element further comprising a step at a transition point between the proximal and distal portions. The stiffening element may include a proximal portion, a distal portion, and a first and second stiffener, the first stiffener extending from the proximal end of the stiffening element to the distal end of the stiffening element, the second stiffener extending through the proximal portion of the stiffening element. The stiffening element could also comprise a proximal portion comprising a first material and a distal portion comprising a second material, the first material having a greater stiffness than the second material. Alternatively, the stiffening element may comprise a proximal portion and a distal portion, the proximal portion being heat treated to increase the stiffness of the proximal portion, the proximal portion having a stiffness that is greater than the stiffness of the distal portion. 
     In another form of the present disclosure, a lithotripsy kit is provided. The lithotripsy kit comprises a scope comprising a proximal end, a distal end, and a working channel extending therethrough, the scope further comprising a proximal entrance to the working channel. The lithotripsy kit further comprises a probe comprising an elongate body comprising a proximal end, a distal end, and a lumen extending therethrough, the probe further comprising a stiffening element comprising a proximal end, a distal end, and a length extending from the proximal end to the distal end, the stiffening element disposed within the lumen of the elongate body. The probe is advancable through the working channel of the scope, the stiffening element comprising an adjacent point that is adjacent to the proximal entrance of the working channel, the adjacent point varying in position along the length of the stiffening element as the probe is distally advanced through the working channel, the probe further comprising a force required to advance the probe through the working channel of the scope, the force increasing as the adjacent point moves proximally along the length of the stiffening element. Also, the stiffening element further comprises a stiffness that varies along the length of the stiffening element, the stiffness increasing along the length of the stiffening element from the distal end to the proximal end, wherein the stiffness of the stiffening element at the adjacent point is proportional to the instant force required to advance the probe through the working channel of the scope at the adjacent point&#39;s current position along the length of the stiffening element. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a drawing of a lithotripsy probe, duodenoscope, and cholangioscope inserted into a patient&#39;s duodenum in accordance with the teachings of the present disclosure; 
         FIG. 2  is a drawing of a lithotripsy probe, duodenoscope, and cholangioscope inserted into a patient&#39;s duodenum; 
         FIG. 3  is a graph showing the relationship between the force required to advance the probe distally and the position of the distal end of the probe; 
         FIG. 4  is a cross-sectional view of a lithotripsy probe with a stiffening element; 
         FIG. 5  is an embodiment of a stiffening element with a varying diameter; 
         FIG. 6A  is an embodiment of a stiffening element with a tapered distal portion; 
         FIG. 6B  is an embodiment of a stiffening element with a stepped distal portion; 
         FIG. 6C  is an embodiment of a stiffening element with a tapered central portion and tapered distal portion; 
         FIG. 6D  is an embodiment of a stiffening element with a stepped central portion and a stepped distal portion; 
         FIG. 7A  is an embodiment of a stiffening element with two stiffeners; 
         FIG. 7B  is an embodiment of a stiffening element with three stiffeners; 
         FIG. 7C  is an embodiment of a stiffening element with two stiffeners with tapers; 
         FIG. 8A  is an embodiment of a stiffening element made up of two materials; 
         FIG. 8B  is an embodiment of a stiffening element with a coated proximal portion; and 
         FIG. 8C  is an embodiment of a stiffening element with heat treated portions. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. It should also be understood that various cross-hatching patterns used in the drawings are not intended to limit the specific materials that may be employed with the present disclosure. The cross-hatching patterns are merely exemplary of preferable materials or are used to distinguish between adjacent or mating components illustrated within the drawings for purposes of clarity. 
       FIG. 1  shows a lithotripsy probe  10  with a proximal end  15  and a distal end  17  inserted into a working channel  13  of a cholangioscope  11 , which is in turn inserted into a working channel  12  of a duodenoscope  14 . In this example, the duodenoscope  14  is inserted into the mouth of a patient and through the digestive track until the distal end  16  of the duodenoscope  14  is near the papilla of Vater  18  in the duodenum  20 . The papilla of Vater  18  is a mound-like structure that extends into the duodenum  20  and serves as the exit point for the common bile duct  22  and pancreatic duct  24 . A stone  26  may be lodged in the common bile duct  22 , and thus the probe  10  must be inserted through the papilla of Vater  18  until the distal end  17  of the probe  10  is near the stone  26 . Before the probe  10  is inserted, the cholangioscope  11  may be inserted through the working channel  12  of the duodenoscope  14  and then pushed through the papilla of Vater  18  until the distal end of the cholangioscope  11  is adjacent to the stone  26 . The probe  10  may then be inserted through a working channel  13  of the cholangioscope  11  until the distal end  17  of the probe  10  is near the stone  26 . Alternatively, the probe  10  can be at least partially preloaded into the working channel  13  of the cholangioscope  11  and the probe  10  and cholangioscope  11  can be advanced through the working channel  12  of the duodenoscope  14  together. Once the distal end  17  of the probe  10  is near the stone  26 , shock wave energy is applied through the probe  10  and towards the stone  26  which causes the stone  26  to fragment. The fragments of the stone  26  may either be collected and removed from the patient, or allowed to naturally pass through the patient&#39;s body. The probe  10 , cholangioscope  11 , and duodenoscope  14  may then be withdrawn from the patient&#39;s body, together or separately. 
     As the probe  10  is advanced through the working channel  13  of the cholangioscope  11 , the frictional resistance between the working channel  13  and the probe  10  steadily increases the further the probe  10  is advanced due to the increasing amount of surface area contact between the probe  10  and working channel  13 . Therefore, as the probe  10  is advanced the physician must apply an increasingly larger force to the proximal end of the probe  10  to overcome the increasing frictional forces. Due to the increasingly larger force that the physician must apply, the probe  10  may be at risk of kinking or buckling throughout this procedure. Further, the probe  10  is at a significant risk of buckling when the distal end  17  of the probe  10  reaches and then extends past the side port  28  of the duodenoscope  14  ( FIG. 2 ). The cholangioscope  11  and the probe  10  are deflected near the side port  28  by an elevator (not shown) within the duodenoscope  14 . The elevator can be manipulated by the physician to control the deflection of the cholangioscope  11  and probe  10  and thus steer the cholangioscope  11  and probe  10  towards the papilla of Vater  18  or other body structure. The elevator may deflect the cholangioscope  11  and probe  10  at this deflection point  30  as much as or more than 90 degrees. When the distal end  17  of the probe  10  reaches the elevator, the force necessary to further advance the probe  10  through the cholangioscope  11  increases due to the high amount of friction between the working channel  13  of the cholangioscope  11  and the probe  10  at the deflection point  30 . Thus, the physician must apply a greater force to the proximal end of the probe  10  to continue to advance the probe  10  than was previously necessary. 
     When all or part of the probe  10  is disposed within the working channel  13 , the portion of the probe  10  that is within the working channel  13  may be less prone to kinking or buckling due to the additional support provided by the low tolerance between the working channel  13  and the probe  10 . However, at any point in the procedure, an exposed portion  34  of the probe  10  (which varies in length based on the position of the probe  10  with respect to the cholangioscope  11 ) that has not yet been advanced into the working channel  13  of the cholangioscope  11  does not have the benefit of the support provided by the working channel  13 . Thus, when the physician applies an increased force to the exposed portion  34  of the probe  10  to advance the probe  10  past the elevator and deflection point  30 , the exposed portion  34  is prone to buckling, especially immediately proximal to the proximal entrance  36  to the working channel  13 . A rough graph showing the relationship between the force required by the physician to distally advance the probe  10  and the position of the distal end  17  of the probe  10  is shown in  FIG. 3 . 
     To help minimize the risk of buckling, a stiffening element  46  may be used with the probe  10 . As shown in  FIG. 4 , the lithotripsy probe  10  may include a flexible tubular body  40  with a lumen  41  running therethrough. The flexible tubular body  40  may be made of a variety of biocompatible materials, including but not limited to: polytetrafluoroethylene. Two conductive wires  42 ,  44  may run along the length of the lumen  41  to deliver the electrical current that is necessary to create the shockwaves at the distal end  17  of the probe  10 . The stiffening element  46  may also be placed within the lumen  41  of the probe  10 . The stiffening element  46  may be secured to the body  40  of the probe  10  through a variety of methods, including but not limited to: adhesives. A variety of materials may be used for the stiffening element  46 , including but not limited to: nitinol. The stiffening element  46  may provide extra support to the flexible body  40  of the probe  10 , thereby making the probe  10  less likely to buckle or kink. 
     However, the addition of a stiffening element  46  may be accompanied by the sacrifice of probe  10  flexibility. The flexibility of the probe  10  is an important design consideration since the probe must be advanced through the twists and turns of the gastrointestinal tract and then deflected 90 degrees or more at the elevator of the duodenoscope  14 . Therefore, it may be preferable to design the stiffening element  46  in such a way that minimizes the loss of flexibility while still providing the necessary added stiffness to prevent or limit kinking and buckling of the probe  10  during advancement through the cholangioscope  11 . As shown in the graph in  FIG. 3 , the force required to advance the probe  10  through the working channel  13  of the cholangioscope  11  increases as the distal end  17  of the probe  10  advances further distally into the working channel  13 . Further, as the force required to advance the probe increases, the need for a stiffening element  46  increases due to the increased likelihood of the exposed portion  34  buckling. Thus, the need for a stiffer stiffening element  46  that provides sufficient support to the probe  10  increases the further the probe  10  is distally advanced. 
     Therefore, it may be desirable to use a stiffening element  46  with a varying diameter or thickness along the length of the probe  10 . For example, as shown in  FIG. 5 , a stiffening element  46  with a proximal end  50 , distal end  52 , and length  54  is shown. The stiffening element  46  further includes a distal portion  58 , a proximal portion  60 , and a central portion  62 . As can be seen, the diameter  56  of the stiffening element  46  varies along the length  54  of the stiffening element  46 . Specifically, the diameter  56  is at its largest diameter at the proximal end  50  and tapers down to its smallest diameter at the distal end  52 . As the diameter  56  (or alternatively thickness) of the stiffening element  46  increases, the greater strength and support it provides to the probe  10 . However, the flexibility of the probe  10  decreases as the diameter  56  of the stiffening element increases. Therefore, since maximum flexibility is desired for the probe  10  while still maintaining enough stiffness to resist kinking or buckling of the exposed portion  34  of the probe  10 , the diameter  56  of the stiffening element  46  may be varied along the length of the probe  10  proportionally to the stiffness required to prevent kinking or buckling of the exposed portion  34 . Therefore, since the probe  10  is at a low risk of kinking or buckling when the distalmost portion of the probe  10  is inserted into the working channel, the diameter  56  and proportional stiffness of the distal portion  58  of the stiffening element  46  may be small, therefore allowing the distalmost portion of the probe  10  to maintain maximum flexibility. However, since the exposed portion  34  of the probe  10  is at a high risk of buckling when the distal end  17  of the probe  10  is advanced past the deflection point  30 , the diameter  56  and proportional stiffness of the proximal portion  60  of the stiffening element  46  may be large. The diameter  56  may slowly increase from the distal end  52  to the proximal end  50  in a manner proportional to the force required to advance the probe  10  distally. 
       FIGS. 6A-6D  show several more exemplary embodiments of the stiffening element  46 .  FIG. 6A  shows a stiffening element  46  with a diameter  56 , a proximal end  50 , distal end  52 , and a length  54  extending from the proximal  50  to distal end  52 . The proximal portion  60  of the stiffening element  46  has a constant diameter  56 . However, the distal portion  58  includes a taper from the transition point  70  (where the proximal portion  60  and distal portion  58  meet) to the distal end  52 . In  FIG. 6B , the diameter  56  of the proximal portion  60  is constant. The diameter  76  of distal portion  58  is constant, but is smaller than the diameter  56  of the proximal portion  60 . A step  71  may be included at the transition point  70  between the proximal portion  60  and distal portion  58 .  FIG. 6C  shows a stiffening element  46  with a proximal portion  60  having a constant diameter  56 . The central portion  62  tapers from a larger diameter  56  at the first transition point  72  to a smaller diameter  56  at the second transition point  74 . The distal portion  58  also tapers from a larger diameter  56  at the second transition point  74  to a smaller diameter  56  at the distal end  52 . However, the rate of taper for the distal portion  58  is greater than the rate of taper for the central portion  62 . Alternatively, the rate of taper for the central portion  62  may be greater than the rate of taper for the distal portion  58 .  FIG. 6D  shows a stiffening element  56  with a proximal portion  60  having a constant diameter  56 , a central portion  62  having a constant diameter  78  smaller than the constant diameter  56  of the proximal portion  60 , and a distal portion  58  having a constant diameter  76  smaller than the constant diameter of the central portion  62 . Steps  71  between the proximal portion  60  and central portion  62 , and the central portion  62  and distal portion  58  are located at the first and second transition points  72 ,  74 , respectively. 
       FIGS. 7A-7C  show additional embodiments of the stiffening element  46 . Specifically, the embodiments of  FIGS. 7A-7C  use multiple pieces of material to vary the stiffness of the stiffening element  46  instead of a single piece of material with a varying diameter.  FIG. 7A  shows a stiffening element  46  with a first stiffener  86  and a second stiffener  88 . The first stiffener  86  extends from the proximal end  50  to the distal end  52  of the stiffening element  46  and may have a constant diameter  82 . The second stiffener  88  extends through only a proximal portion  60  of the stiffening element  46  and may have a constant diameter  80 . Since both the first and second stiffeners  86 ,  88  extend at least through the proximal portion  60  of the stiffening element  46  the proximal portion  60  has a greater stiffness than the distal portion  58 . The first and second stiffeners  86 ,  88  may be attached together using a variety of methods, including but not limited to: adhesives.  FIG. 7B  shows a stiffening element  46  with a first stiffener  86 , second stiffener  88 , and third stiffener  90 . The first stiffener  86  extends from the proximal end  50  to the distal end  52  of the stiffening element  46  and may have a constant diameter  82 . The second stiffener  88  may have a constant diameter  80  and extends through the proximal portion  60  of the stiffening element  46 . The third stiffener  90  may have a constant diameter  84  and extends through the proximal and central portions  60 ,  62  of the stiffening element  46 . Since all three stiffeners  86 ,  88 ,  90  extend through the proximal portion  60 , the proximal portion  60  has a high stiffness. The central portion  62  has a lower stiffness than the proximal portion  60 , since only the first and third stiffeners  86 ,  90  extend through the central portion  62 , and the distal portion  58  has the lowest stiffness since only the first stiffener  86  extends through the distal portion  58 .  FIG. 7C  shows a stiffening element  46  with a first stiffener  86  and a second stiffener  88 . The first stiffener  86  extends from the proximal end  50  to the distal end  52  of the stiffening element  46 . The first stiffener  86  further includes a distally tapered diameter  80 . The second stiffener  88  extends through the proximal portion  60  of the stiffening element  46  and has a distally tapered diameter  82 . The above embodiments are just three examples of using multiple pieces of material for a stiffening element  46  with varying stiffness, additional variations are contemplated, including the use of more than three separate stiffeners  46 , along with varying the materials or diameters used for each stiffener. 
     Further, rather than varying the thickness of the stiffening element  46  to vary the stiffness along the length  54  of the stiffening element  46 , the material properties of the stiffening element  46  may be varied instead as shown in  FIGS. 8A-8C . Therefore, the stiffening element  46  may have a constant outer diameter  56  with varied material properties that provide maximum stiffness at the proximal end  50  of the stiffening element  46  while providing minimum stiffness and maximum flexibility at the distal end  52  of the stiffening element  46 .  FIG. 8A  shows a stiffening element  46  with a proximal portion  60  and a distal portion  58 . The proximal portion  60  of the stiffening element  46  includes a first material  90  while the distal portion  58  of the stiffening element  46  includes a second material  92 . The two materials  90 ,  92  may be attached together using a variety of methods. The materials  90 ,  92  may have varying stiffness properties, with the first material  90  having a greater stiffness than the second material  92 .  FIG. 8B  shows a stiffening element  46  made of a single piece of material. The proximal portion  60  further includes a coating  94  that increases the stiffness of the proximal portion  60 . Examples of coatings  94  include shrink tubing and other polymer wraps.  FIG. 8C  shows a stiffening element  46  made of a single piece of material. However, the portions  60 ,  62 , and  58  may be heat treated in various ways to increase or decrease the stiffness of those portions  60 ,  62 ,  58 . In one example, the proximal portion  60  may be heat treated to have a high stiffness, while the central portion  62  is heat treated to have a stiffness that is lower than the stiffness of the proximal portion  60 . The distal portion  58  may remain untreated and have a lower stiffness than the proximal and central portions  60 ,  62 . The above embodiments are just three examples of using multiple materials or heat treatment to vary the stiffness of the stiffening element  46 . Additional variations on these embodiments are contemplated, including the use of more than two materials and heat treatment in combination with multiple materials. 
     While the above embodiments describe stiffening elements  46  that extend along the entire length of the probe  10 , the stiffening element  46  may extend along only a portion of the probe  10 . For example, the stiffening element  46  may extend from the proximal end of the probe  10  to a point proximal the distal end of the probe  10 . Alternatively, multiple separate stiffening elements  46  may be used within a single probe  10 , each with properties similar to the stiffening elements  46  described above. Further, various design features of the stiffening element  46  in the above mentioned embodiments may be mixed and matched with other embodiments as desired. 
     The probe  10  and stiffening element  46  may be used in a variety of applications with varying lengths and designs. In one example, the probe  10  may be around 200-300 centimeters in length. The length of the working channel  12  of the duodenoscope  14  may be about 140-160 centimeters and the length of the working channel  13  of the cholangioscope  11  may be around 200-250 centimeters. The proximal portion  60  of the stiffening element may be 15 centimeters in length or greater. It may be preferable for the distal portion  58  to range from 5-35 centimeters in length; however, it may extend as far as or greater than half the length of the working channel  13  of the cholangioscope  11 . The central portion  62  may extend between the proximal and distal portions  60 ,  58 , and may vary widely in length. In one example, the central portion  62  may range from 30-120 centimeters in length. These dimensions are merely exemplary, and the lengths of the probe  10 , stiffening element  46 , and the portions  58 ,  60 ,  62  of the stiffening element  46  may be further varied. 
     The embodiments described above show just several potential designs of a stiffening element. Many other stiffening elements with varying diameters or thicknesses may be used. Further, the stiffening element need not be cylindrical in shape with a circular cross section. For example, the stiffening element may have a rectangular, square, ovular, or other shaped cross-section. The cross-section of the stiffening elements may also include grooves configured to accommodate the conductive wires  42 ,  44 , thus allowing for an overall reduction in the diameter of the probe  10 . The grooves may also aid in preventing the conductive wires from contacting each other, thereby reducing the possibility of electrical shorting. 
     Additionally, while the stiffening elements  46  may be made of a metallic material, they may also be made of a non-metallic, or non-conductive material. Non-conductive stiffening elements  46  may be desirable to prevent or limit the risk of shorting the conductive wires. Similarly, the stiffening elements  46  may instead or also be coated or wrapped in a non-metallic material to limit the risk of shorting the conductive wires. 
     While the present disclosure describes the embodiments in terms of a lithotripsy probe used during a biliary procedure, the stiffening element  46  may be used in any lithotripsy procedure to limit kinking and buckling of the probe when inserted into a patient. Further, the anti-kinking and buckling improvements may be used with a variety of other medical devices unrelated to lithotripsy, such as catheters used in a variety of medical procedures. Also, the improvements described above may be used in a variety of non-medical applications. 
     The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the substance of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.