Abstract:
The present disclosure pertains to devices and methods for diagnosis and treatment of biological tissue in which the tissue is accessed by a catheter through a working channel of an endoscope and in which the degree of extension of a distal tip of the catheter beyond a distal tip of the endoscope is controlled.

Description:
FIELD OF THE DISCLOSURE 
       [0001]    The present disclosure relates generally to devices, systems and methods wherein a catheter is introduced to a site within a subject via another device, and more particularly, to devices and methods for diagnosis and treatment of biological tissue in which the tissue is accessed by a catheter through a working channel of an endoscope. 
       BACKGROUND 
       [0002]    Endoscopes are employed in a wide variety of medical procedures. Examples of commonly employed endoscopes include the following, among others (listed along with the area or organ typically viewed): arthroscopes (joints), bronchoscopes (trachea and bronchi of the lungs), colonoscopes (colon and large intestine), colposcopes (vagina and cervix), cystoscopes (bladder), esophagoscopes (esophagus), gastroscopes (stomach and duodenum), laparoscopes (stomach, liver, or other abdominal organ, including female reproductive organs), laryngoscopes (larynx), neuroendoscopes (brain), proctoscopes (rectum and sigmoid colon), sigmoidoscopes (sigmoid colon), and thoracoscopes (pleura covering the lungs and structures covering the heart). 
         [0003]    In various medical procedures it is desirable to introduce a catheter to a site within a subject for purposes of diagnosis and/or treatment of biological tissue at the site. Examples of such catheters include tissue ablation catheters and drug delivery catheters, among others. Tissue ablation refers to the removal or destruction of tissue, or of tissue functions. Appropriate target tissue for ablation may include, for example, cancerous or precancerous lesions, tumors (malignant or benign), damaged epithelium, fibroses and any other healthy or diseased tissue for which tissue ablation is desired. 
         [0004]    Cryoablation is a relatively recent technique in which tissue ablation is conducted by freezing a target tissue of interest. Cryoablation may be performed by using a system that sprays low pressure cryogen on the target tissue. Such systems are often referred to as cryosurgery systems, cryosurgery spray systems, cryogen spray systems, and cryospray systems, among other terms. As used herein, “cryogen” refers to any fluid (e.g., gas, liquefied gas or other fluid known to one of ordinary skill in the art) that has a sufficiently low boiling point to allow for therapeutically effective cryotherapy and is otherwise suitable for cryogenic surgical procedures. For example, acceptable fluids may have a boiling point below approximately negative (−) 150° C. The cryogen may be liquefied nitrogen, as it is readily available. Other fluids such as argon and air may also be used. Additionally, liquid helium, liquid oxygen, liquid nitrous oxide and other cryogens can also be used. 
         [0005]    During typical operation of a cryosurgery system, a clinician, physician, surgeon, technician, or other operator (collectively referred to as “operator” herein), sprays cryogen on the target tissue via a delivery catheter. The spray of cryogen causes the target tissue to freeze or “cryofrost.” The physician may target the cryospray visually utilizing endoscopy, bronchoscopy, pleuroscopy, or other video assisted device or scope. 
       SUMMARY OF THE DISCLOSURE 
       [0006]    In the course of various procedures, it may be desirable to introduce a catheter to a site for treatment or diagnosis. In certain of these procedures, catheter access to the treatment or diagnosis site may be provided via a working channel of an endoscope. In such procedures, it may be desirable to provide improved control of a distance by which a distal tip of the catheter extends from a distal tip of the endoscope, for example, by improving the resistance to relative movement between the endoscope and catheter during treatment and/or navigation and, with regard to cryosurgery systems, by ensuring that the catheter is extended from the distal tip of the endoscope by a distance sufficient to avoid the formation of obstructive amounts of frost on a lens of the endoscope, among other improvements. 
         [0007]    The present disclosure provides devices, systems and methods that allow for precise positioning of a catheter tip during the course of treatment of tissue within a subject. The devices, systems and methods pertain to the use of an endoscope for the navigation and visualization of the target tissue, and the use of a catheter to diagnose and/or treat such target tissue after extending a distal tip of the catheter to one or more predetermined distances from a distal tip of the endoscope. In certain embodiments, the catheter may be part of a cryogen spray system in which the catheter is connected to a console that houses and delivers cryogen fluid to the catheter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a perspective view of a portion of a cryosurgery system, in accordance with an embodiment of the present disclosure. 
           [0009]      FIG. 2A  is a perspective view of a tubular member, in accordance with an embodiment of the present disclosure. 
           [0010]      FIG. 2B  is a perspective view of a catheter handle assembly, in accordance with an embodiment of the present disclosure. 
           [0011]      FIG. 3  is a perspective view of a catheter extension control assembly, in accordance with an embodiment of the present disclosure. 
           [0012]      FIGS. 4A and 4B  are partial cutaway views of the catheter extension control assembly of  FIG. 3 . 
           [0013]      FIG. 5A  shows perspective views of proximal and distal portions of a catheter extension control assembly in a first position, in accordance with an embodiment of the present disclosure. 
           [0014]      FIG. 5B  shows perspective views of proximal and distal portions of a catheter extension control assembly in a second position, in accordance with an embodiment of the present disclosure. 
           [0015]      FIG. 5C  shows perspective views of proximal and distal portions of a catheter extension control assembly in a third position, in accordance with an embodiment of the present disclosure. 
           [0016]      FIG. 5D  shows perspective views of proximal and distal portions of a catheter extension control assembly in a fourth position, in accordance with an embodiment of the present disclosure. 
           [0017]      FIGS. 5E and 5F  are perspective views further illustrating movement between a catheter handle assembly and a tubular member of a catheter extension control assembly, in accordance with the present disclosure. 
           [0018]      FIGS. 6 and 7  are perspective view of tubular members, in accordance with two embodiments of the present disclosure. 
           [0019]      FIG. 8  is a partial cutaway perspective view of a tubular member and a proximal portion of an endoscope, in accordance with an embodiment of the present disclosure. 
           [0020]      FIG. 9  is a partial cutaway perspective view of a portion of a catheter extension control assembly, in accordance with another embodiment of the present disclosure. 
           [0021]      FIG. 10  is an exploded view of the catheter extension control assembly shown in  FIG. 9 . 
           [0022]      FIG. 11  is cross-sectional view a portion of the catheter extension control assembly shown in  FIG. 9 . 
           [0023]      FIG. 12  is a perspective view of a portion of the catheter extension control assembly, in accordance with another embodiment of the present disclosure. 
           [0024]      FIG. 13A  is a cutaway of the portion of the catheter extension control assembly shown in  FIG. 12 .  FIG. 13B  is an enlarged view of a portion of  FIG. 13A . 
           [0025]      FIG. 14A  is a top view of a portion of the catheter extension control assembly, in accordance with an embodiment of the present disclosure. 
           [0026]      FIGS. 14B and 14C  are cutaway views of a portion of a catheter extension control assembly like that shown in  FIG. 14A . 
           [0027]      FIG. 15  is a perspective view of a portion of the catheter extension control assembly, in accordance with yet another embodiment of the present disclosure. 
           [0028]      FIG. 16A  is a side view showing a distal portion of a catheter extension control assembly in a position wherein a distal tip of the catheter is touching tissue, in accordance with an embodiment of the present disclosure. 
           [0029]      FIG. 16B  is a side view showing a distal portion of a catheter extension control assembly in a position wherein a distal tip of the catheter is withdrawn from tissue, in accordance with an embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]      FIG. 1  is a perspective view of a portion of a cryosurgery system  41  having a cryogen delivery apparatus  42 . Cryosurgery system  41  comprises a bronchoscope  40  and a catheter tip  42  exiting its working channel. As shown, bronchoscope  40  may be positioned in the trachea  44 , or bronchi—such as the principle bronchi  45  of patient. The catheter  48  is placed in the working channel lumen  46  of the scope  40  and exits the working channel at the distal tip of the scope. Cryogen delivery apparatus  42  comprises a radial spray cryogen delivery catheter at distal end  42 , and one or more holes  47 . After insertion of the cryogen delivery apparatus into the patient, cryogen is provided to cryogen delivery catheter  48  from a cryogen source. Catheter distal end with one or more holes  42  causes the cryogen to be sprayed on the target tissue via the hole(s)  42 . A gas egress tube  43  that surrounds the scope may be utilized to provide additional means to evacuate the treatment area of the cryogenic gas out of the patient  49 . Passive lumen egress  50  is also present via the management of the airway to ensure proper venting during the procedure. In certain beneficial embodiments, the cryogen delivery catheter  48  may include (1) a bayonet and hub for attachment to the console at its proximal end, (2) a layered polyimide and stainless steel braided shaft to minimize kinking and breaking, (3) insulation to protect the user from cold, (4) a strain relief to help prevent kinking when torqued by users and (5) an atraumatic tip at its distal end to prevent damage to tissue, as described in U.S. Patent Pub. No. 2015/0066005 to Wei Li Fan et al. 
         [0031]    In procedures where a catheter is advanced to a site in a subject through an endoscope,  FIG. 1  representing one specific example of such a procedure, it is beneficial for the operator to able to position the catheter tip at one or more predetermined distances from the distal tip of the endoscope and to maintain the catheter tip at such a position, if desired. In accordance with the present disclosure, a variety of devices, systems and methods are provided for doing so. 
         [0032]    Endoscopes useful for such procedures may be of any size suitable for the site being accessed. In certain embodiments, an endoscope having one or more one or more optical (e.g., fiber optic) and/or electronic (e.g., camera, led, etc.) elements may be provided in order to project light from a distal tip of the endoscope onto the site and to transmit an image of the site back from the distal tip, for example, to a monitor or a microscope, where the procedure can be visualized. Assisted by this visualization, an operator is able to perform diagnostic and/or therapeutic procedures via an inserted catheter beyond a distal end of the endoscope. Examples of endoscopes for use in conjunction with the present disclosure include arthroscopes bronchoscopes, colonoscopes, colposcopes, cystoscopes, esophagoscopes, gastroscopes, laparoscopes, laryngoscopes, neuroendoscopes, proctoscopes, sigmoidoscopes, and thoracoscopes, among others. 
         [0033]    Catheters useful for such procedures vary widely and may also be of any size suitable for the site being accessed. Although cryogen delivery catheters are specifically described herein, the present disclosure is not so limited and applies to any catheter used in conjunction with any type of endoscope. 
         [0034]    Turning now to  FIG. 2A , a tubular member  110  (also referred to as an introducer) is shown therein, which comprises an inlet  110   i , an outlet  1100 , a proximal end  110   p , a distal end  110   d , and a lumen extending between the inlet  110   i , and outlet  110   o . Tubular member  110  is configured for engagement with a working channel of an endoscope. For this purpose, tubular member  110  may be provided with an attachment feature  112 , which can be directly attached to a working channel of an endoscope, for example, as shown. In other embodiments, tubular member  110  may be attached to an additional component that is configured for attachment to a working channel of an endoscope, for instance, a biopsy cap. 
         [0035]    The tubular member  110  comprises a body portion  114  and a widened portion adjacent inlet  110   i , specifically, a cuff portion  118  in the embodiment shown, which eases introduction of a catheter assembly into the tubular member  110  as described in more detail below. A slot  116 , which extends through a sidewall of the tubular member  110 , is formed in the proximal end of the body portion  114  and extends into the widened portion  118 , where it serves as a keyhole feature for receiving an extension feature, as described in more detail below. Protrusions  114   p   1 ,  114   p   2 ,  114   p   3  extend from the body portion into the slot, forming regions of constricted slot width  116   c   1 ,  116   c   2 ,  116   c   3  in slot  116 , which lie between regions of expanded slot width  116   e   1 ,  116   e   2 ,  116   e   3 ,  116   e   4  in slot  116 . 
         [0036]    In some embodiments, the tubular member  110  may be designed to provide strain relief. For example, although not illustrated, in order to provide strain relief, a spiral cut may be provided in a sidewall of the body portion  114  for instance, in the region between the slot  116  and attachment feature  112 , among various other possible approaches. 
         [0037]    The tubular member  110  of  FIG. 2A  may be used in conjunction with an assembly that includes an inner member comprising a catheter and an extension feature extending radially outward from an axis of the catheter, in which case the inner member is positioned within the tubular member  110  such that the extension feature slidably fits within the slot  116  of the tubular member  110 . 
         [0038]    In some embodiments, such an inner member may comprise, for example, a catheter with an extension feature extending from and integrated into a sidewall of the catheter. 
         [0039]    In other embodiments, such an inner member may comprise, for example, an assembly which includes a mechanism whereby an extension feature is fixed at a predetermined position along a length of the catheter. One example of such a mechanism is a catheter handle assembly  120 , illustrated in  FIG. 2B , which comprises a hollow shaft portion  124  having a lumen  1241  and an extension feature  122 . A catheter (not shown) may be passed through the lumen  1241 . The hollow shaft portion  124  in the embodiment shown may be coupled to a tapered region  126  and/or a strain relief component  128 . The tapered region  126  may be further connected to a strain relief component  128 , which along with tapered region  126 , serves a handle function. Although not shown, in use, a catheter will pass through the lumen  1241  of the catheter handle assembly  120  (from right-to-left in the image shown). While the catheter handle assembly  120  may be in the form of an assembly of separate components in some embodiments, in other embodiments two, three, or all of the hollow shaft portion  124 , extension feature  122 , tapered region  126  and strain relief component  128  may be integrated into a single component. 
         [0040]    As seen from the catheter extension control assembly  200  illustrated in  FIG. 3 , a catheter  125  may be attached to and extend through the strain relief component  128 , tapered region  126  and shaft portion  124  of the catheter handle assembly  120 . As noted elsewhere, the catheter may be any of a wide range of catheters, which in certain embodiments may include cryospray catheters. The catheter  125  further extends through the tubular member  110  and into a working channel of an endoscope  130 . The extension feature  122  is configured to slidably fit within the elongated slot  116  of the tubular member  110 . Because the extension feature  122  is wider than the regions of constricted slot width  116   c   1 ,  116   c   2 ,  116   c   3 , the regions of constricted slot width act as stops with regard to the advancement of the extension feature  122  (and thus the catheter that is attached to the extension feature  122 ). By forming the tubular member  110  from a material that has appropriate elasticity, the extension feature  122  can be moved by an operator, through application of a suitable force, from the first region of expanded slot width  116   e   1 , through the first region of constricted slot width  116   c   1  (which acts as a first stop, until sufficient force is applied), and into the second region of expanded slot width  116   e   2 . Subsequently, the extension feature  122  can be moved from the second region of expanded slot width  116   e   2 , through the second region of constricted slot width  116   c   2  (which acts as a second stop, until sufficient force is applied) and into the third region of expanded slot width  116   e   3 . Thereafter, the extension feature  122  can be moved by from the third region of expanded slot width  116   e   3  through the third region of constricted slot width  116   c   3  (which acts as a third stop, until sufficient force is applied) and into the fourth and final region of expanded slot width  116   e   4 . 
         [0041]    As the extension feature  122  is advanced within the slot  116 , the catheter  125  is advanced within the endoscope  130 . The length of extension of the catheter  125  from the endoscope  130  is determined by the position of the regions of constricted slot width.  FIGS. 5A-5D  illustrate the proximal end of the system, including (a) the slot  116  of the tubular member  110  and (b) the shaft portion  124  with extension feature  122 , tapered region  126  and strain relief component  128  of the catheter handle assembly  120 .  FIGS. 5A-5D  also illustrate the distal end of the system, including (a) a distal tip  130   t  of endoscope  130  and (b) a distal tip  125   t  and first marker band of  125   b   1  of catheter  125 . Although not shown, in further embodiments, visually identifiable marks may be placed on a proximal end of the catheter  125  outside of the endoscope  130 , as an additional or alternative means of controlling and/or monitoring extension. 
         [0042]    In  FIG. 5A , the catheter handle assembly  120  has been moved relative to the tubular member  110  to a point where the extension feature  122  has been moved against the first region of constricted slot width  116   c   1  (see  FIG. 2A ), which acts as a first stop, corresponding to a position where the first marker band  125   b   1  begins to emerge from the distal tip  130   t  of endoscope  130 . 
         [0043]    By applying a sufficient force, the extension feature can be moved through the first region of constricted slot width  116   c   1 , into and through the second region of expanded slot width  116   e   2 , and against the second region of constricted slot width  116   c   2  (see  FIG. 2A ), which acts as a second stop. As seen in  FIG. 5B , the second stop corresponds to a position where the second marker band  125   b   2  begins to emerge from the distal tip  130   t  of endoscope  130 . 
         [0044]    By again applying a sufficient force, the extension feature  122  can be moved through the second region of constricted slot width  116   c   2 , into and through the third region of expanded slot width  116   e   3 , and against the third region of constricted slot width  116   c   3 , which acts as a third stop. As seen in  FIG. 5C , the third stop corresponds to a position where the third marker band  125   b   3  begins to emerge from the distal tip  130   t  of endoscope  130 . 
         [0045]    Finally, by yet again applying a sufficient force, the extension feature  122  can be moved through the third region of constricted slot width  116   c   3 , into and through the fourth region of expanded slot width  116   e   4 , and up to a point of maximum extension of the catheter handle assembly  120  relative to the tubular member  110 , as seen in  FIG. 5D . 
         [0046]      FIGS. 5E and 5F  further illustrate movement of the catheter handle assembly  120  relative the tubular member  110  of the catheter extension control assembly  200 . 
         [0047]    With reference now to  FIGS. 16A and 16B , during use, catheter extension control assemblies in accordance with the present disclosure may be used to perform a number of operations, including withdrawal and/or advancement of a catheter tip by a predefined distance. In this regard,  FIG. 16A  is a side view showing a distal portion of a catheter extension control assembly including an endoscope  130  having an endoscope tip  130   t  and a catheter  125  having a catheter tip  125   t  and marker bands (marker bands  125   b   1 ,  125   b   2 ,  125   b   3  are shown). In  FIG. 16A , the catheter distal tip  125   t  is in contact with tissue  300 . In  FIG. 16B , on the other hand, the catheter distal tip  125   t  is pulled back from contact with the tissue  300 . Catheter extension control assemblies in accordance with the present disclosure are useful for this task, for example, as the catheter tip  125   t  may be reliably and reproducibly retracted by a known distance D (e.g., 1 cm, among other distances) from the tissue  300 .  FIGS. 4A and 4B  show further construction details of the catheter extension control assembly, including a cutaway view of a proximal part of the shaft portion  124  and the tapered portion  126  of the catheter handle assembly  120  as well as three catheter portions  125   a ,  125   b  and  125   c  of varying diameter that are positioned in the interior of the catheter handle assembly  120 . 
         [0048]    An additional embodiment of a tubular member  110  in accordance with the present disclosure is shown in  FIG. 6  and includes a body portion  114 , flared widened portion  118 , attachment features  112   a  and  112   b , and a slot  116  formed in a proximal end of the body portion  114  which extends into the widened portion  118 . Protrusions  114   p   1 ,  114   p   2 ,  114   p   3  extend from the body portion  114  into the slot  116 , forming regions of constricted slot width  116   c   1 ,  116   c   2 ,  116   c   3  that lie between regions of expanded slot width  116   e   1 ,  116   e   2 ,  116   e   3 ,  116   e   4 , with the regions of constricted slot width  116   c   1 ,  116   c   2 ,  116   c   3  acting as stops for the catheter handle assembly  120  (not shown) when inserted into the tubular portion  110  in a fashion analogous to that described in conjunction with  FIGS. 5A-5D . 
         [0049]    Yet another embodiment of a tubular member  110  in accordance with the present disclosure is shown in  FIG. 7  and includes a body portion  114 , flared widened portion  118 , attachment features  112   a ,  112   b , and a slot  116  formed in a proximal end of the body portion  114  which extends into the widened portion  118 . Protrusions  114   p   1 ,  114   p   2 ,  114   p   3 ,  114   p   4  extend from the body portion into the slot  116 , forming regions of constricted slot width  116   c   1 ,  116   c   2 ,  116   c   3 ,  116   c   4  that lie between regions of expanded slot width  116   e   1 ,  116   e   2 ,  116   e   3 ,  116   e   4 ,  116   e   5  with the regions of constricted slot width  116   c   1 ,  116   c   2 ,  116   c   3 ,  116   c   4  acting as stops for the catheter handle assembly  120  (not shown) when inserted into the tubular portion  110  in a fashion analogous to that described in conjunction with  FIGS. 5A-5D . 
         [0050]    One or more attachment features may be configured to interface with complementary features associated with the endoscope. For example, one or more circumferential features selected from one or more circumferential protrusions and/or one or more circumferential recesses may be provided, which may interface with one or more complementary circumferential features associated with the endoscope and which may be selected from one or more complementary circumferential recesses and/or protrusions. In this regard, two circumferential protrusions may be employed as attachment features  112   a ,  112   b  as shown in  FIGS. 6 and 7 , which may interface with two complementary circumferential recesses associate with the endoscope. These complementary features may be formed in an entrance to a working channel of an endoscope or may be formed in another component that is configured for attachment to a working channel of an endoscope, for example, a biopsy cap  130   b  which is in turn attached to an endoscope  130  as shown in  FIG. 8 . 
         [0051]    Materials for forming the tubular member  110  described herein include suitable polymers, metals, and polymer-metal composites, which provide appropriate resistance to the movement of the extension feature  122  through the regions of constricted slot width, while also providing suitable shape memory to return to an original shape after passage of the extension feature  122  through the regions of constricted slot width. Particular examples of polymers for forming the tubular member  110  include acrylonitrile butadiene styrene copolymers and polycarbonates, among other possible materials, whereas particular examples of metals for forming the tubular member  110  include elastic metals such as nitinol, among other possible materials. 
         [0052]    Materials for forming the extension feature  122  (and also typically the shaft portion  124  and tapered region  110 ) include polymers, metals, and polymer-metal composites providing a stiffness sufficient to push through (i.e., spread) the regions of constricted slot width of the tubular member  110 . Particular examples of materials for forming the extension feature  122  (and also typically the shaft portion  124  and tapered region  110 ) include metals and polymers such as acrylonitrile butadiene styrene copolymers and polycarbonates, among other possible materials. 
         [0053]    Alternative assemblies for controlling an amount of catheter extension will now be described. Referring now to  FIG. 9  (assembled view) and  FIG. 10  (exploded view), catheter extension control assembly is shown which includes an endoscope  230  with biopsy cap  230   b , a first tubular member  210  having lumen  2101  extending therethrough, a second tubular member  220  having a lumen  2201  extending therethrough and a strain relief component  218  having a lumen  2181  extending therethrough. 
         [0054]    The first tubular member  210  has a proximal end  210   p , a distal end  210   d  and includes a distal sidewall portion  214  and a proximal sidewall portion  216 . The strain relief component  218  is configured to be attached to the proximal end  210   p  of the first tubular member  210 , and the lumens extending through the strain relief component  218  and the first tubular member  210  are configured to receive a catheter (not shown) which may be affixed to the first tubular member  210  and/or the strain relief component  218 . It is noted that the assembly comprising the strain relief component  218  and first tubular member  210  is somewhat analogous to the catheter handle assembly  120  illustrated in  FIG. 2 . An outer surface of the distal sidewall portion  214  comprises at least one circumferential feature formed therein, which may be selected, for example, from at least one circumferential protrusion and/or at least one circumferential recess. 
         [0055]    The second tubular member  220  has a proximal end  220   p , and a distal end  220   d  and includes a proximal sidewall portion  222  and a distal sidewall portion  224 . An outer surface of the second tubular member  220  forms a shoulder  220   s  adjacent to the distal sidewall portion  224 . An inner surface of the proximal sidewall portion  222  comprises at least one circumferential feature formed therein, which may be selected, for example, from at least one circumferential protrusion and/or at least one circumferential recess, and which is complementary to the at least one circumferential feature that is formed in the outer surface of the distal sidewall portion  214 . For example, with reference to  FIG. 11 , it can be seen that the inner surface of the proximal sidewall portion  222  of the second tubular member  220  comprises first, second and third circumferential protrusions  222   p   1 ,  222   p   2 ,  222   p   3  whereas the outer surface of the distal sidewall portion  214  of the first tubular member  210  comprises first, second and third circumferential recesses  214   r   1 ,  214   r   2 ,  214   r   3 , which are complementary to the circumferential protrusions  222   p   1 ,  222   p   2 ,  222   p   3 . As also seen from  FIG. 11 , wherein the lumen of the second tubular member  220  forms a funnel  220   f  in the proximal sidewall portion  222 , with a largest diameter of the funnel located at a proximal end  220   p  of the second tubular member  220 . In addition, the outer surface of the sidewall of the first tubular member  210  forms a flared configuration  210   f  that mates with the funnel  222   f.    
         [0056]    As also seen from  FIGS. 9-11 , the outer surface of the distal sidewall portion  224  of the second tubular member  220  may comprise at least one circumferential feature formed therein, which may be selected, for example, from at least one circumferential protrusion and/or at least one circumferential recess. An inner surface of an entrance to a working channel of the endoscope  230  (e.g., an inner surface of the biopsy cap  230   b ) may also comprise at least one circumferential feature formed therein, which is complementary to the at least one circumferential feature that is formed in the outer surface of the distal sidewall portion  224  of the second tubular member  220 , and which thus may be selected, for example, from at least one circumferential protrusion and/or at least one circumferential recess. For example, with reference to  FIG. 9 , it can be seen that the outer surface of the distal sidewall portion  224  of the second tubular member  220  comprises a single circumferential protrusion  224   p   1  which engages a complementary circumferential recess  230   r   1  provided on the inner surface of the entrance to the working channel of the endoscope  230 . 
         [0057]    As can be understood by those of ordinary skill in the art with reference to  FIG. 11 , when the distal end  210   d  of the first tubular member  210  is inserted into the flared proximal end  220   p  of the lumen  2201  of the second tubular member  220  and advanced, the first circumferential recess  214   r   1  of the first tubular member  210  will initially engage (at a first stop position) the complementary third circumferential protrusion  222   p   3  of the second tubular member  220 . Depending on the dimensions selected for the various components in this system, the first stop position may correspond to a catheter position analogous to that of  FIG. 5A  where a first marker band begins to emerge from a distal tip of the endoscope. 
         [0058]    Upon further distal advancement of the first tubular member  210  relative to the second tubular member  220 , the first circumferential recess  214   r   1  of the first tubular member  210  will engage (at a second stop position) with the complementary second circumferential protrusion  222   p   2  of the second tubular member  220 , and the second circumferential recess  214   r   2  of the first tubular member  210  will engage with the complementary third circumferential protrusion  222   p   3  of the second tubular member  220 . Depending on the dimensions selected for the various components in this system, the second stop position may correspond to a catheter position analogous to that of  FIG. 5B  where a second marker band begins to emerge from the distal tip of the endoscope. 
         [0059]    Still further distal advancement of the first tubular member  210  relative to the second tubular member  220  will lead to the a third stop position having the configuration shown in  FIG. 11 , in which the first circumferential recess  214   r   1  of the first tubular member  210  is engaged with the complementary first circumferential protrusion  222   p   1  of the second tubular member  220 , the second circumferential recess  214   r   2  of the first tubular member  210  is engaged with the complementary second circumferential protrusion  222   p   2  of the second tubular member  220 , and the third circumferential recess  214   r   3  of the first tubular member  210  is engaged with the complementary third circumferential protrusion  222   p   3  of the second tubular member  220 . Depending on the dimensions selected for the various components in this system, the third stop position may correspond to a catheter position analogous to that of  FIG. 5C  where a second marker band begins to emerge from the distal tip of the endoscope. Although not show, the first and second tubular members  210 ,  220  may be dimensioned such that the first tubular member  210  may be further distally advanced relative to the second tubular member  220  to a fourth stop position, which may correspond to a catheter position analogous to that of  FIG. 5D . 
         [0060]    Materials for forming the first tubular member  210  include polymers, metals, and polymer-metal composites that provide a stiffness sufficient to push the distal sidewall portion  214  of the first tubular member  210  into the lumen  2201  of the second tubular member  220 . Particular examples of materials for forming the first tubular member  210  include metals and relatively stiff polymers such as acrylonitrile butadiene styrene copolymers and polycarbonates, among other possible materials. 
         [0061]    Materials for forming the second tubular member  220  include suitable materials that that elastically accommodate movement of the distal sidewall portion  214  of the first tubular member  210  into the lumen  2201  of the second tubular member  220 , while also providing suitable shape memory to return to original form such that the complementary features on the first and second tubular members  210 ,  220  can engage one another. Particular examples of materials for forming the second tubular member  220  include elastomeric polymers, among other possible materials. 
         [0062]    In another embodiment, shown in  FIGS. 12, 13A and 13B , a first tubular member  210  having lumen  2101  extending therethrough and a second tubular member  220  having a lumen  2201  extending therethrough are illustrated. The lumens  2101 ,  2201  extend through first tubular member  210  and second tubular member  220 , respectively, are configured to receive a catheter (not shown) which may be affixed to the proximal end  210   p  of the first tubular member  210  or an additional component attached to the first tubular member  210 , for example, a strain relief component analogous to that shown in  FIGS. 9 and 10 . 
         [0063]    The first tubular member  210  has a proximal end  210   p , a distal end  210   d  and includes a proximal sidewall portion  216  and a distal sidewall portion  214 . An outer surface of the distal sidewall portion  214  comprises a circumferential feature in the form of a circumferential protrusion  214   p . The second tubular member  220  likewise has a proximal end  220   p , and a distal end  220   d  and includes a proximal sidewall portion  222  and a distal sidewall portion  224 . An outer surface of the second tubular member  220  forms a shoulder  220   s  at a transition between the proximal sidewall portion  222  and the distal sidewall portion  224 . As best shown in  FIG. 13B , which shows a more detailed view of section  200 B in  FIG. 13A , an inner surface of the proximal sidewall portion  222  of the second tubular member  220  comprises a plurality of circumferential features in the form of circumferential recesses formed therein (four circumferential recesses  222   r   1 ,  222   r   2 ,  222   r   3 ,  222   r   4  are numbered). Each of the circumferential recesses in the inner surface of the proximal sidewall portion  222  is complementary in shape to the circumferential protrusion  214   p  that is formed in the outer surface of the distal sidewall portion  214  of the first tubular member  210 . As also seen from  FIGS. 12, 13A and 13B , the lumen of the second tubular member  220  forms a funnel  220   f  in the proximal portion sidewall  222 , with a largest diameter of the funnel  220   f  located at a proximal end  220   p  of the second tubular member  220 . In addition, the outer surface of the sidewall of the first tubular member  210  forms a flared configuration  210   f  that mates with the funnel  220   f.    
         [0064]    As can be understood by those of ordinary skill in the art, and with reference to  FIGS. 12, 13A and 13B , when the distal end  210   d  of the first tubular member  210  is inserted into the flared lumen  2201  at the proximal end  220   p  of the second tubular member  220  and advanced, the circumferential protrusion  214   p  of the first tubular member  210  will initially engage the complementary first circumferential recess  222   r   1  of the second tubular member  220  at a first stop position. Upon, further advancement of the first tubular member  210  within the second tubular member  220 , (a) the circumferential protrusion  214   p  of the first tubular member  210  will engage the complementary second circumferential recess  222   r   2  of the second tubular member  220  at a second stop position, (b) followed by engagement of the circumferential protrusion  214   p  of the first tubular member  210  with the complementary third circumferential recess  222   r   3  of the second tubular member  220  at a third stop position, (c) followed by engagement of the circumferential protrusion  214   p  of the first tubular member  210  with the complementary fourth circumferential recess  222   r   4  of the second tubular member  220  at a fourth stop position, (d) and so forth, until a final position of maximum insertion is reached. As previously described, when employed in conjunction with a catheter extension control assembly, the differing stop positions will correspond to differing lengths from which a catheter will extend from a distal end of an endoscope. 
         [0065]    In a further embodiment shown in  FIGS. 14A-14C , a first tubular member  210  having a proximal end  210   p  and a distal end  210   d , and a second tubular member  220  having a proximal end  220   p  and a distal end  220   d  are shown. As above, lumens  2101 ,  2201  (see  FIG. 14B ) extending through first tubular member  210  and second tubular member  220  are configured to receive a catheter (not shown) which may be affixed to the proximal end  210   p  of first tubular member  210  or to an additional component that is attached to the first tubular member  210 , for example, a strain relief component analogous to that shown in  FIGS. 9 and 10 . 
         [0066]    The first tubular member  210  further includes a proximal sidewall portion  216  and a distal sidewall portion  214 . An outer surface of the distal sidewall portion  214  comprises a single circumferential feature in the form of a circumferential protrusion  214   p . The second tubular member  220  includes a proximal sidewall portion  222  and a distal sidewall portion  224 . An outer surface of the second tubular member  220  forms a shoulder  220   s  at a transition between the proximal sidewall portion  216  and the distal sidewall portion  224 . As best shown in  FIGS. 14B-14C , an inner surface of the proximal sidewall portion  222  comprises a plurality of circumferential features in the form of circumferential recesses  222   r   1 ,  222   r   2 ,  222   r   3 ,  222   r   4 ,  222   r   5  formed therein. Each of the circumferential recesses  222   r   1 ,  222   r   2 ,  222   r   3 ,  222   r   4 ,  222   r   5  in the inner surface of the proximal sidewall portion  222  is shaped to receive the circumferential protrusion  214   p  that is formed in the outer surface of the distal sidewall portion  214  of the first tubular member  210 . As also seen from  FIGS. 14A-14C , the lumen  2201  of the second tubular member  220  forms a funnel  220   f  in the proximal portion sidewall  222 , with a largest diameter of the funnel located at a proximal end  220   p  of the second tubular member  220 . In addition, the outer surface of the sidewall of the first tubular member  210  forms a flared configuration  210   f  that mates with the funnel  222   f.    
         [0067]    As can be understood by those of ordinary skill in the art, with reference to  FIGS. 14A-14C , when the distal end  210   d  of the first tubular member  210  is inserted into the flared lumen  2201  at the proximal end  220   p  of the second tubular member  220  and advanced, the circumferential protrusion  214   p  of the first tubular member  210  will initially engage, at a first stop position, the first circumferential recess  222   r   1  of the second tubular member  220  (see  FIG. 14B ). Upon, further advancement of the first tubular member  210  within the second tubular member  220 , (a) the circumferential protrusion  214   p  of the first tubular member  210  will engage the second circumferential recess  222   r   2  of the second tubular member  220  at a second stop position (see  FIG. 14C ), (b) followed by engagement of the circumferential protrusion  214   p  of the first tubular member  210  with the third circumferential recess  222   r   3  of the second tubular member  220  at a third stop position (see  FIG. 14A ), (c) followed by engagement of the circumferential protrusion  214   p  of the first tubular member  210  with the fourth circumferential recess  222   r   4  of the second tubular member  220  at a fourth stop position, (d) followed by engagement of the circumferential protrusion  214   p  of the first tubular member  210  with the fifth circumferential recess  222   r   4  of the second tubular member  220  at a fifth stop position. 
         [0068]    As seen from  FIG. 14A , the distal portion  214  of the first tubular member  210  may comprise one or more first visually identifiable markings (e.g., circumferential protrusion  214   p  is provided with a distinguishing color in the embodiment shown, among other possibilities) and the second tubular member may be made transparent (or alternatively, suitable cut-outs may be provided), the such that a position of the one or more first visually identifiable markings within the second tubular member  220  may be seen. Moreover, the proximal end  222  of the second tubular member  220  may comprise a plurality of second visually identifiable markings at differing longitudinal positions which allow a user to identify the relative longitudinal position of the first tubular member  210  within the second tubular member  220 . For example, second tubular member  220  may be provided with visually identifiable markings  220   m  that distinguish the stops from one another, for example, by employing one or more alphanumeric characters (numerals are employed in  FIG. 14A ). When employed in conjunction with a catheter extension control assembly, the differing stop positions will correspond to differing lengths from which a catheter will extend from a distal end of an endoscope, as previously discussed. 
         [0069]    In other embodiments of the present disclosure, a position of a catheter may be reversibly locked relative to an endoscope. In this regard, and turning to  FIG. 15 , a first tubular member  210  having an axis A, a proximal end  210   p  and a distal end  210   d , and a second tubular member  220  having an axis A (sharing a mutual axis A in  FIG. 5 ), a proximal end  220   p  and a distal end  220   d  are shown. As in the embodiments of  FIGS. 9 to 14C  above, lumens  2101 ,  2201  extend through the first tubular member  210  and the second tubular member  220 , respectively, and are configured to receive a catheter (not shown) which may be affixed to the proximal end  210   p  of first tubular member  210  or to an additional component attached to the first tubular member  210 , for example, a strain relief component analogous to that shown in  FIGS. 9 and 10 . 
         [0070]    The first tubular member  210  includes a proximal portion  216  that is provided with one or more actuators  217 . The first tubular member  210  also includes a distal portion  214  that is provided with one or more radially expandable and contractible engagement members  219  (e.g., pads) which can be radially expanded and contracted by operation of the one or more actuators  217 , which are configured to actuate the engagement members  219  between a radially expanded position and a radially contracted position. 
         [0071]    For example, radially inward movement of the one or more actuators  217  may place the one or more engagement members  219  in a first position in which the engagement members  219  are radially contracted, whereas radially outward movement of the one or more actuators  217  may place the one or more engagement members  219  in a second position in which the engagement members  219  are radially expanded. In certain embodiments, one or more springs (not shown) may be used to bias the one or more actuators  217  radially outward, thereby placing the one or more engagement members  219  in the second position as a default position and requiring radially inward compression of the one or more actuators  217  to move the one or more engagement members  219  radially inward (or vice versa). 
         [0072]    As another example, the one or more actuators  217  may be slidable longitudinally such that proximal movement of the one or more actuators  217  may place the one or more engagement members  219  in a first position in which the engagement members  219  are radially contracted, whereas distal movement of the one or more actuators  217  may place the one or more engagement members  219  in a second position in which the engagement members  219  are radially expanded. In certain of these embodiments, one or more springs (not shown) may be used to bias the one or more engagement members  219  in the second position as a default position and requiring a proximal force to be exerted on the one or more actuators  217  to move the one or more engagement members  219  radially inward (or vice versa). 
         [0073]    Conversely, the one or more actuators  217  may be slidable longitudinally such that distal movement of the one or more actuators  217  may place the one or more engagement members  219  in a first position in which the engagement members  219  are radially contracted, whereas proximal movement of the one or more actuators  217  may place the one or more engagement members  219  in a second position in which the engagement members  219  are radially expanded. In certain of these embodiments, one or more springs (not shown) may be used to bias the one or more engagement members  219  in the second position as a default position, requiring a distal force to be exerted on the one or more actuators  217  to move the one or more engagement members  219  radially inward (or vice versa). 
         [0074]    The second tubular member  220 , on the other hand, includes a proximal sidewall portion  222  and a distal sidewall portion  224 . An outer surface of the second tubular member  220  forms a shoulder  220   s  at a transition between proximal sidewall portion  222  and distal sidewall portion  224 . At least a portion  22010  of a length of the lumen  2201  of the second tubular member  220  is of substantially constant axial cross-section (typically circular in axial cross-section). Moreover, in the embodiment shown, a funnel is formed in a proximal portion  2201   p  of the lumen  2201  of the second tubular member  220 , with a largest diameter of the funnel located at a proximal end  220   p  of the second tubular member  220 . In addition, an outer surface of the first tubular member  210  lying proximal to a distal portion  214  of the first tubular member  210  forms a flared configuration  210   f  that mates with the funnel. 
         [0075]    Examples of materials that may be used to construct the first tubular member  210  and second tubular member  222  metals and polymers such as acrylonitrile butadiene styrene copolymers and polycarbonates, among other possible materials. Examples of materials that may be used to construct the engagement members  219  include various elastomers known in the art. 
         [0076]    When the distal portion  214  of the first tubular member  210  is inserted into the proximal portion  222  of the second tubular member  220 , so long as the one or more engagement members  219  of the first tubular member  210  are placed in a radially contracted first position wherein the one or more engagement members  219  do not engage the proximal sidewall portion  222  of the second tubular member  220 , the first tubular member  210  will be freely movable relative to the second tubular member  220  over a range of longitudinal positions. On the other hand, once the one or more engagement members  219  of the first tubular member  210  are placed in a radially expanded second position such that the one or more engagement members  219  engage the proximal sidewall portion  222  of the second tubular member  220 , relative longitudinal movement between the first tubular member  210  and the second tubular member  220  is resisted/prevented. Once the one or more engagement members  219  are again placed in a radially contracted first position, the first tubular member  210  will again be freely movable longitudinally relative to the second tubular member  220 . 
         [0077]    When employed in conjunction with a catheter extension control assembly, the configuration described provides a range of differing lengths that a catheter may be extended from a distal end of an endoscope. If desired, analogous to the embodiment of  FIGS. 14A-14C , the distal portion  214  of the first tubular member  210  may comprise one or more first visually identifiable markings (not shown) and the second tubular member  220  may be configured (e.g., may be made transparent, may be provided with cut-out portions, etc.) such that the position of the one or more first visually identifiable markings of the first tubular member  210  can be seen within the second tubular member  220 . Moreover, the proximal end  222  of the second tubular member  220  may comprise a plurality of second visually identifiable markings (e.g., one or more alphanumeric characters) (not shown) at differing longitudinal positions which allow a user to identify the relative longitudinal position of the first tubular member  210  within the second tubular member  220 . The plurality of second visually identifiable markings may correspond to different lengths of catheter extension beyond a distal end of an endoscope. 
         [0078]    Although various embodiments are specifically illustrated and described herein, it will be appreciated that modifications and variations of the present disclosure are covered by the above teachings and are within the purview of the appended claims without departing from the spirit and intended scope of the disclosure.