Patent Publication Number: US-2005119614-A1

Title: Irrigation and aspiration device

Description:
This application is a continuation application of U.S. patent application Ser. No. 10/242,370 filed Sep. 12, 2002 which is a continuation application of U.S. patent application Ser. No. 09/363,455 filed on Jul. 29, 1999 the contents of which are incorporated in their entirety into this disclosure by reference. 
    
    
     BACKGROUND OF THE INVENTION  
      The present invention relates to a tubular irrigation and aspiration device having an outer tubular sheath with an atraumatic tip.  
      Medical catheters generally comprise elongate tube-like members which may be inserted into the body, either percutaneously or via a body orifice, for any of a wide variety of diagnostic and therapeutic purposes. Such medical applications generally require the use of a catheter having the ability to turn corners, such as in ocular irrigation and aspiration applications, or to negotiate twists and turns, such as in certain cardiovascular applications.  
      For example, percutaneous transluminal coronary angioplasty (balloon angioplasty), requires manipulation of a catheter from a proximal position outside the patient&#39;s body through branched and tortuous portions of the patient&#39;s arterial system for the purpose of alleviating an obstruction by inflating a balloon. This particular procedure has been performed with increasing frequency over the past years in preference to open heart bypass surgery, when possible.  
      In another application, transluminal laser catheter angioplasty (laser angioplasty), the delivery of laser energy from an external source to an intraluminal site to remove plaque or thrombus obstructions in vessels is accomplished by providing a waveguide such as a fiber optic bundle within a catheter. The nature of laser angioplasty requires an even greater ability to precisely manipulate the catheter, to control and aim the laser light at the specific plaques or thrombi to be removed.  
      A variety of other medical applications require or would benefit from the use of a coil polymer composite housing, together with the steering mechanism disclosed herein, which may be coupled with or incorporated into an endoscope or other multi-functional catheter. For example, one ocular application involves removal of a diseased lens, and replacement with any of a variety of prosthetic intraocular lenses. The native lens is encased in a capsular bag, including a front portion closest to the cornea known as the anterior capsule and a rear portion known as the posterior capsule.  
      An irrigation and aspiration instrument is advanced through an incision in the cornea and through the anterior wall of the capsular bag. Due to the geometry involved, the distal tip of the irrigation and aspiration tool cannot conveniently reach various regions within the capsular bag. The irrigation and aspiration tool must be both flexible, and capable of transmitting either vacuum or fluid under pressure.  
      For each of the foregoing applications, there remains a need for a small diameter tubular housing structure, which may be readily adapted for use in the construction of steerable guidewires, catheters and other implements. For many applications, the catheter preferably has optimum flexibility and pushability, yet minimal outer diameter and wall thickness. In addition, the tubular wall is preferably fluid tight, to permit transmission of fluids or gas therethrough either under pressure or vacuum.  
     SUMMARY OF THE INVENTION  
      There is provided in accordance with one aspect of the present invention an irrigation and aspiration tool. The irrigation and aspiration tool comprises a tubular spring coil, having a flexible distal region. An elastomeric sheath surrounds at least a portion of the spring coil. An end cap is integrally molded with the elastomeric sheath.  
      In one embodiment, the elastomeric sheath comprises silicone. The end cap is preferably provided with an aperture therethrough, the aperture having a longitudinal axis. In some embodiments, the longitudinal axis of the aperture is angularly displaced from the longitudinal axis of the tubular spring coil.  
      In accordance with another aspect of the present invention, there is provided a medical device. The device comprises an elongate flexible tubular housing, having a proximal end and a distal end and at least one central passageway extending axially therethrough.  
      A spring coil is provided in the wall of at least a portion of the housing, and an elastomeric sheath surrounds at least a distal portion of the spring coil.  
      The sheath comprises a tubular sleeve for surrounding the spring coil and an end cap, intregally molded with the tubular sleeve.  
      Preferably, the sheath comprises silicone. The tubular sleeve has a wall thickness within the range of from about 0.0005″ to about 0.010″. In an intraocular irrigation and aspiration tool embodiment, the wall thickness of the sleeve is within the range of from about 0.001″ to about 0.005″. The outside diameter of the tubular housing is no more than about 0.060″.  
      In accordance with a further aspect of the present invention, there is provided a method of making an intraocular irrigation and aspiration tool. The method comprises the steps of providing a spring coil having a proximal end and a distal end. A sheath is provided, having a tubular sleeve with an inside diameter, a proximal end, a distal end, and an end cap on the distal end.  
      The method further comprises the step of coaxially sliding the spring coil within the tubular body, and reducing the inside diameter of the sleeve to fit the spring coil. The method preferably further comprises the step of expanding the inside diameter of the sleeve before the coaxially sliding step. In one embodiment, the expanding step comprises contacting the sleeve with an alcohol. In this embodiment, the reducing the inside diameter of the sleeve step comprises permitting alcohol to volatilize from the sleeve. Preferably, the tubular sheath comprises silicone, and the tubular sleeve and end cap are intregally molded together.  
      Further features and advantages of the present invention will become apparent from the detailed description of preferred embodiments which follows, when considered together with the attached claims and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a cross-sectional elevational view of the distal end of a steerable tubular sheath.  
       FIG. 2  is a cross-sectional view through lines  2 - 2  of  FIG. 1 .  
       FIG. 3  is a cross-sectional elevational view of the steerable sheath of  FIG. 1 , shown in a deflected configuration.  
       FIG. 4  is a cross-sectional elevational view of the distal end of a steerable aspiration device.  
       FIG. 5  is a cross-sectional view along linen  5 - 5  in  FIG. 4 .  
       FIG. 6  is a cross-sectional elevational view of a tubular spring coil body incorporating a coil polymer composite  
       FIG. 7  is a cross-sectional elevational view of a coil polymer composite irrigation and aspiration device.  
       FIG. 8  is a cross-sectional elevational view of a steerable tubular sheath incorporating a coil polymer composite.  
       FIG. 9  is a cross-sectional elevational view of a steerable tubular sheath in accordance with the present invention, having an integral outer sleeve and end cap. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      There is provided in accordance with one aspect of the present invention an embodiment of a steerable medical device in the form of a steerable tubular sheath, for gaining access to and/or pointing within the body. Any of a wide variety of working implements, such as fiber optics, irrigation, aspiration, balloon dilatation catheters, biopsy or other tissue removal apparatus, and the like can readily be adapted for use through the central lumen of the steerable sheath. Preferably, the steerable sheath is provided with a coil polymer composite tubular body, as discussed infra in connection with  FIGS. 6-8 .  
      Referring to  FIG. 1 , there is provided a steerable sheath  10 . Steerable sheaths and/or coil polymer composite housings in accordance with the present invention, coupled with or incorporated into an endoscope or other multifunctional catheter, can be used in any of a wide variety of medical and nonmedical applications. Medical applications of particular interest include gastroenterology, urology, gynecology, ear, nose and throat applications, orthopedics (arteroscopy), angioscopes, neurology and cardiology.  
      In general, the steerable sheath of the present invention is applicable in any environment in which it is desirable to controllably deflect the distal tip of a working implement. Alternatively, the coil polymer composite body can be readily incorporated into nonsteerable devices, as will be apparent to one of skill in the art. The steerable sheath embodiment illustrated in  FIGS. 1-3  can be readily adapted to a desired application by one of skill in the art. The embodiment illustrated in  FIGS. 4 and 5  has been particularly adapted for use as an ocular irrigation and aspiration tool, as will be discussed infra.  
      Steerable sheath  10  generally comprises an elongate tubular body  12  which is laterally flexible at least in the distal steering region  32  thereof. For certain applications, such as ocular surgical procedures, only the distal steering region  32  of the sheath  10  is preferably flexible. For other applications such as endoscopes and cardiovascular catheters, the sheath is preferably flexible as far proximally of steering region  32  as is desirable for the intended application.  
      Tubular body  12  generally comprises a spring coil portion  14 , as is well known in the art. Spring coil  14  may additionally be coupled to a proximal hypodermic needle tubing section, as is known in the art. Spring coil  14  defines a central elongate lumen  16  for guiding surgical implements, fluids or vacuum axially through the sheath  10  and out a distal opening  18 . Depending upon the intended application, the central lumen  16  can be readily divided into two or more passageways such as for carrying fiber optic illumination and visualization bundles, irrigation, aspiration, drug delivery, balloon inflation or other conduits as well as wiring for transducers and working channels for any of a wide variety of known medical implements.  
      In an embodiment of the steerable sheath useful in spinal endoscopy, the section of spring coil  14  extends approximately 16 inches or more in length. Adjacent windings of the spring coil  14  (“filars”) are typically “bottomed out” as is known in the art, with adjacent filars in the distal most one quarter to one half inch being spaced apart by about a 0.005-0.006 inch gap. The outside diameter of the steerable endoscope sheath is approximately 0.100 inches. In this embodiment, the spring coil extends the entire length of the sheath, and no proximal hypotube section is generally provided.  
      In one embodiment, an end cap  20  or other lateral force transmitting structure is provided at the distal opening  18 . End cap  20  in the illustrated embodiment comprises a radially extending annular flange  22  with a smooth outer surface for minimizing trauma as the tubular sheath  10  is advanced distally through the body. End cap  20  is preferably additionally provided with one or more axially extending support structures such as annular flange  24  which extends in a proximal direction through central lumen  16  to securely anchor cap  20 . Axial flange  24  and radial flange  22  provide convenient mounting surfaces for attachment of the deflection ribbon  26  and pull ribbon  34 , discussed infra.  
      End cap  20  may comprise any of a variety of configurations and materials, as will be apparent to one of skill in the art. Preferably, end cap  20  comprises a material which is readily securable to the deflection ribbon  26  and pull ribbon  34  such as by brazing or soldering techniques. Typically, end cap is also secured to the spring coil  14 .  
      Alternative structures to replace end cap  20  can be devised as needed for particular applications or manufacturing convenience. For example, axial flange  24  can be replaced by one or more support structures which extend less than the full circumference of spring coil  14 . Alternatively, the function of end cap  20  can be accomplished by fusing the distal most filars of spring coil  14  together such as by flowing solder therebetween in a manner that maintains patency of lumen  16 . In general, any structure that laterally transfers force between deflection ribbon  26  and pull ribbon  34 , and which preferably also resists axial collapse of the spring coil, is preferred.  
      The portion of spring coil  14  which extends around axial flange  24  is relatively inflexible. Thus, the axial length of axial flange  24  can be varied to affect the deflected profile of the steerable sheath  10 . Preferably, the axial flange  24  is less than about 0.5 inch long, and, more preferably, axial flange  24  is less than about 0.2 inch long. Too short an axial flange  24  may adversely impact the integrity of the joint between end cap  20  and spring coil  14 , and an annular flange  24  of at least about 0.100 inches long is preferred in a steerable sheath having a diameter of about 0.100 inches.  
      A deflection ribbon  26  is preferably secured with respect to the tubular body  12  at a proximal point  28 , and extends distally to a distal point of attachment  30 . The distal point of attachment may secure the deflection ribbon  26  to either or both of the spring coil  14  and end cap  20 . Deflection ribbon  26  bends upon axial displacement of pull ribbon  34 , with proximal point of attachment  28  functioning as a fulcrum or platform.  
      Proximal attachment  28  is preferably a solder, braze or weld joint, as is known in the art, with any excess on the radial outside surface of the tubular body  12  being trimmed or polished to minimize rough edges. Distal point of attachment  30  is similarly provided by any of a variety of conventional securing techniques which is appropriate for the construction materials of the steerable sheath  10 .  
      The length of the space between the proximal point of attachment  28  and distal point of attachment  30  affects the radius of the curve of the deflection ribbon  26  and hence of the region  32 , as will be appreciated by one of skill in the art. The deflection ribbon  26  in the preferred embodiment will tend to remain positioned along the exterior circumference of the curve during deflection of the steerable sheath  10 . Since the circumference in a given steerable sheath  10  will be a fixed distance, the radius of the curve during deflection will differ, depending upon the degree of deflection achieved.  
      For example, in a steerable sheath  10  as illustrated in  FIG. 1  having an exterior diameter of about 0.100 inches and a distance of 0.315 inches between the first and second points of attachment, a 45° bend in the steerable sheath  10  will produce a 7.5 mm inside curve radius (10 mm outside radius). In order to achieve a 7.5 mm inside curve radius for a bend of 90°, the distance between points of attachment  28  and  30  must be extended to 0.630 inches.  
      Deflection at steering region  32  of steerable sheath  10  is accomplished by providing a pull ribbon  34 . Pull ribbon  34  is preferably secured at a distal point of attachment  36  and extends proximally to the control end of the steerable sheath  10 . Axial displacement of the pull ribbon  34  will tend to pivot the steering region  32  of the tubular body  12  around proximal point of attachment  28 . Preferably, lateral displacement of steering region  32  is accomplished by axial proximal displacement of pull ribbon  34 .  
      Two or more pull ribbons  34  can be provided in accordance with the same basic principles. See, e.g., U.S. Pat. No. 5,108,368 to Hammerslag, et al., the disclosure of which is incorporated herein by reference. However, in a simplified, single plane steerable sheath  10 , a single pull ribbon  34  is sufficient.  
      Pull ribbon  34  is rotationally offset from deflection ribbon  26  by at least about 90°. Preferably, pull ribbon  34  is rotationally offset from deflection ribbon  26  by about 180°, as illustrated in  FIG. 1  and cross-sectional view  FIG. 2 . Among other advantages of this configuration, opposing placement of deflection ribbon  26  and pull ribbon  35  tends to maintain central lumen  16  open while the steering region  32  is laterally deflected in response to proximal displacement of pull ribbon  34 . This tends to prevent objects traveling through central lumen  16  from becoming entangled with pull ribbon  34  or deflection ribbon  26 .  
      In another embodiment, an interior tubular sleeve (not illustrated) is additionally provided to facilitate negotiation of objects or fluids through central lumen  16 . The interior sleeve is preferably in the form of a continuous, tubular flexible material, such as nylon or polyethylene. In an embodiment of the tubular sheath in which the catheter has an outside diameter of 0.100 inches (0.098 inch coil with a 0.001 inch thick outer sleeve) and an inside diameter of 0.078 inches, the interior tubular sleeve may have an exterior diameter in the area of about 0.074 inches and an interior diameter in the area of about 0.069 inches. The use of this thin wall plastic tube on the inside of the tubular sheath  10  is particularly useful for guiding a fiber through the tubular sheath  10 . The interior tube described above is additionally waterproof, and can be used to either protect the implements transmitted therethrough from moisture, or can be used to transmit fluids through the steerable sheath  10 .  
      In one embodiment of the steerable sheath illustrated in  FIG. 1 , the spring coil  14  is wound from a filar stock having a 0.010-inch diameter. The spring coil is tightly wound or “bottomed out” from its proximal end through the proximal point of attachment  28 . From the proximal point of attachment  28  to the distal point of attachment  30 , the adjacent loops of the spring coil are preferably spaced slightly apart (e.g., 0.005-0.006 inches) to facilitate flexibility and bending, as is well known in the art. However, it has been determined that in an embodiment utilizing an end cap  20 , as illustrated, wherein the end cap is secured to deflection ribbon  26  and pull ribbon  34  but not to the spring coil  14 , spring coil  14  can be bottomed out within the distance between proximal point of attachment  28  and distal point of attachment  30 .  
      In a preferred embodiment for carrying and aiming a fiber optic through the cardiovascular system, 0.010-inch wire stock is wound into a coil having an outside diameter of about 0.098 inches and an inside diameter of from about 0.078 to about 0.080 inches. The pull ribbon  34  comprises a flat ribbon of high-tensile strength stainless steel having a cross-sectional dimension of about 0.003 by about 0.010 inches. The deflection ribbon  26  preferably comprises a material such as spring-tempered stainless steel or Elgiloy®, available from Elgiloy Ltd. Partnership, Elgin, Ill. Elgiloy® may be desirable in embodiments required to permit relatively higher degrees of curvature, as it does not take a set as easily as the stainless steel deflection ribbon  26 . In general, materials such as Elgiloy® which will not exceed their elastic limit as easily as stainless steel are preferable in embodiments which are required to undergo particularly extreme curvature in use.  
      Preferably, an outer tubular sleeve is provided for surrounding the tubular body  12  at least throughout the length of spring coil  14 . The outer tubular sleeve may be provided in accordance with techniques known in the art and, in one embodiment, is a thin wall polyester heat shrink tubing such as that available from Advanced Polymers, Inc. in Salem, N.H. Such heat shrink tubings have a wall thickness of as little as about 0.0002 inches and tube diameter as little as about 0.010 inches. The outer tubular sleeve enhances the structural integrity of the sheath, and also provides a fluid seal and improved lubricity.  
      For example, the outer tubular sleeve tends to prevent the spring coil from collapsing under proximal force on pull wire  34 . In general, in an embodiment of the steerable sheath  10  for use with a 0.055 inch diameter central fiber bundle, a pulling force on pull wire  34  in the area of from about 2½ pounds to about 5 pounds may be necessary to bend the fiber optic. If the outer tubular sleeve is deleted, adjacent windings of spring coil  16  may become misaligned under these forces. The sleeve also improves pushability of the catheters, and improves torque transmission.  
      Referring to  FIGS. 4 and 5 , there is illustrated a modified embodiment of the steerable tubular sheath of the present invention, particularly adapted for irrigation and aspiration of interior regions of the human eye. However, any of the features of the embodiment of  FIGS. 4 and 5  can readily be adaptable or combinable into the previous embodiments disclosed herein, such as for application within the cardiovascular, gastrointestinal or other body lumens, tissue or organs, as desired.  
      A variety of medical conditions can give rise to a cataract or opaque lens. One method of treating the opaque lens is by removal, and replacement with any of a variety of prosthetic intraocular lenses.  
      A variety of instrumentation has been developed for removal of the lens material. For example, U.S. Pat. No. 5,084,012 to Kelman discloses both rigid linear and flexible precurved irrigation and aspiration catheters for this purpose. In general, the elongated catheter tip is inserted through an incision made in the cornea. The instrument is said to be capable of vibrating the operative tip at ultrasonic frequencies of variable amplitude and duration to break apart particles of the material, such as a cataracted lens. Sources of fluid and vacuum are provided at the proximal end of the instrument to dispense and withdraw fluid to and from the surgical site.  
      The opaque lens or cataract to be removed is encased in a membrane or capsular bag, including a front portion closest to the cornea, known as the anterior capsule and a rear portion known as the posterior capsule.  
      The removal instrument is advanced through the incision in the cornea and also through an incision in the anterior wall of the capsular bag. Due to the geometry involved, as is well understood in the art, the distal tip of the irrigation and aspiration tool can not conveniently reach various regions within the capsular bag, particularly around the peripheral portions at the junction of the anterior and posterior walls. The ability of the irrigation and aspiration tool disclosed herein to controllably bend in as far as a 180° or greater curve permits significantly improved access to all regions within the capsular bag, as will be apparent to one of skill in the art in view of the disclosure herein.  
      Referring to  FIG. 4 , the modified steerable sheath comprises an elongate tubular body  40  having a spring coil section  42  disposed on the distal end thereof. Spring coil section  42  may in an ocular application be considerably shorter than in a cardiovascular application, as will be understood by one of skill in the art.  
      Spring coil  42  defines a central lumen  44  for placing a distal opening  46  in fluid communication with a proximal vacuum or source of infusion media. The spring coil wall is rendered fluid tight such as by an outer shrink tubing (not illustrated) as has been discussed. Multiple infusion or vacuum lumen can readily be provided, as desired, such as for simultaneous irrigation and aspiration or other functions known in the art.  
      In one embodiment of the steerable sheath intended for ocular applications, an outer tubular irrigation sleeve is provided, spaced apart from and surrounding the spring coil  42 . The outer tubular sleeve in one embodiment has an inside diameter of about 0.060 inches and an outside diameter of about 0.075 inches for use on a steerable sheath having an outside diameter of spring coil  42  of about 0.040 inches. This configuration provides an annular flow passageway in the annular space between the spring coil  42  and the outer sheath (not illustrated). The distal end of the outer irrigation sleeve is positioned sufficiently close to the distal end of the device so that it will be positioned within the capsule of the eye when in use. In one preferred embodiment, the outer distal sleeve is positioned no more than about 2 mm from the distal tip of the catheter.  
      Preferably, the outer irrigation sleeve is axially reciprocally movable with respect to spring coil  42 . In addition, the irrigation sleeve is preferably secured at its proximal end with respect to pull wire  62 . In this manner, axial proximal displacement of the irrigation sleeve simultaneously causes lateral deflection of the steering region  60 . This configuration provides a preferred result of causing the spring coil  42  to simultaneously curve as it is advanced out of the distal end of the outer sleeve.  
      Distal opening  46  may be conveniently provided in an end cap  48  which is otherwise constructed in a manner similar to end cap  20  of the previous embodiment. Preferably, distal opening  46  is inclined with respect to the longitudinal axis of tubular body  40 . Preferably, an angle of about 45° is provided, although other angles can be used as will be understood by one of skill in the art.  
      In a steerable sheath adapted for the ocular irrigation and aspiration (IA) application, the steering region  60  extends approximately from the distal end of hypotubing  66  to the distal point of attachment  58  with respect to cap  48 . The steering region  60  in an IA device will typically be less than about 0.25 inches in length, and preferably less than about 0.200 inches.  
      In one particular embodiment, the distance between distal point of attachment  58  and distal end of hypotube  66  is approximately 0.175 inches. In that embodiment, the distance from distal point of attachment  58  to the distal tip of end cap  48  is approximately 0.040 inches. The outside diameter of the spring coil  42  is approximately 0.040 inches, and the inside diameter of spring coil  42  is approximately 0.033 inches. The inside diameter of hypotube  66  is approximately 0.026 inches. Preferably, the outside diameter of the tubular body  40  is substantially uniform throughout its length; however, only the distal most 0.5 inches is likely to be introduced within the eye. Portions of the tubular body  14  which are spaced more than about 0.75 inches from the distal end of end cap  48  therefore need not maintain the same exterior diameter.  
      Deflection of steering region  60  is accomplished in a manner similar to that previously described, with one or more deflection ribbons  54  extending from a proximal point of attachment  56  to a distal point of attachment  58 . Preferably, adjacent windings of the spring coil  42  throughout the steering region  60  are slightly spaced apart as has been previously described. The proximal point of attachment  56  may coincide with the distal end of hypotube  66 , and, preferably, comprises a solder joint or other secure junction which joins the spring coil  42 , proximal end of deflection ribbon  54 , and the distal end of hypotube  66 .  
      Deflection is further accomplished through the use of a pull ribbon  62 , which is secured at a distal point of attachment  64  to end cap  48  or other lateral force transmitting structure.  
      In one embodiment, the proximal end of pull wire  62  is soldered or otherwise secured with respect to the spring coil  42  at a point proximally of the distal end of hypotube  66 . In this manner, steering may be accomplished by grasping the proximal extension of hypotube  66  and axially sliding spring coil  42  in a proximal or distal direction with respect to hypotube  66 . The proximal end of spring coil  42  may be secured to any of a variety of friction enhancing structures or handles to facilitate axial manipulation of spring coil  42  with respect to hypotube  66 .  
      The concentric arrangement of the spring coil  42  with respect to hypotube  66  is further illustrated in  FIG. 5 . At the illustrated cross section, hypotube  66  is axially slideably received within spring coil  42 . An axially extending deflection ribbon flat  68  is milled, ground or otherwise provided along an exterior surface of hypotube  66 , for receiving deflection ribbon  54 . Deflection ribbon  54  is preferably secured to the hypotube at a proximal point of attachment  56  such as by soldering, or other attachment means which does not interfere with axial slidability of the hypotube  66  within spring coil  42 .  
      Similarly, an axially extending pull ribbon flat  70  is provided on the opposing side of hypotube  66 , for slideably receiving pull ribbon  62 . In an embodiment where pull ribbon  62  extends through a channel provided by pull ribbon flat  70 , straightening of a displaced steering region  60  can be achieved by distal axial displacement of pull ribbon  62  as will be understood by one of skill in the art.  
      In one preferred embodiment of the IA tool, the steering region  60  between proximal point of attachment  56  and distal point of attachment  58  is approximately 0.175 inches, which permits a 180° deflection of the steering region  60  with respect to the longitudinal axis of tubular body  40 , around an inside curve radius of about 0.015 inch. Deflections of as much as 180° or more are preferably obtainable for use in IA procedures, in order to insure access to the entire interior of the lens capsule as will be understood by one of skill in the art.  
      The IA tool tip is further provided with an interior and/or exterior tubular sleeve for efficiently transmitting vacuum or pressurized fluids from the proximal end of the tubular body  40  to the distal port  46 . In one preferred embodiment, an outer tubular sleeve is securely adhered around the outside of spring coil  42 , to provide an efficient seal. One preferred outer tubular sleeve is a thin wall low density polyethylene tubing such as that available from Medical Extrusion Technologies in Murietta, Ca. Alternatively, a polyester heat shrink tubular sleeve such as that available from Advanced Polymers, Inc., as has been previously discussed, can also be used. Alternatively, other techniques for waterproofing a spring coil can be devised.  
      Referring to  FIG. 6 , there is disclosed a coil polymer composite subassembly  80  in accordance with a preferred embodiment of the present invention. The illustrated coil polymer composite subassembly  80  comprises a tubular spring coil body  81  having a bottomed out region  82  in which adjacent coil filars are in contact with one another, and a stretched section  84  in which adjacent coil filars are spaced apart from one another. Although the utility of the present invention is maximized in a section of spring coil such as  84  where adjacent filars are spaced apart for optimum flexibility, the invention is also advantageous in bottomed out spring coil segments such as  82 .  
      A polymer coil  86  fills the spaces between adjacent coil filars in the stretched region  84 , to produce a fluid-tight tubular body. Preferably, the polymer additionally fills interstitial spaces  85  between adjacent coil filars in the bottomed out region  82 , on the radial exterior and/or radial interior surfaces of the coil, to produce a sealed tubular composite body  80 .  
      Adjacent segments of polymer coil  86  are preferably connected across the intervening filar by a connective layer  87  as described infra. Thus, the polymer component of the composite may take the form of a tubular sleeve having a radially inwardly extending spiraling flange or thread. The depth of the thread in the radial direction depends upon whether the corresponding spring coil filars are bottomed out or spaced apart at a given location.  
      Alternatively, depending upon the method of applying the polymer, an additional connective layer may extend along the radially interior surface of the spring coil. The polymer component in this embodiment will be in the form of a cylindrical wall having a central lumen therethrough and a wall thickness at least slightly larger than the spring coil filar diameter.  
      The polymer is preferably sufficiently elastic to withstand the stretching and compressive forces experienced during flexing of the subassembly  80  without compromising the seal. In addition, in a medical application, the polymer is preferably substantially biologically inert and sterilizable. Silicone has been found to be particularly well suited for this purpose, although other materials may be selected through routine experimentation.  
      The application of silicone or other suitable polymer in accordance with this aspect of the present invention produces a different structure than conventional heat shrinking of tubing around the periphery of a coil, although heat shrink tubing may in the future be developed which can accomplish the objectives of the present invention. In accordance with the present invention, a helical coil  86  of polymer is provided to continuously join adjacent spring coil filars into a composite tubular body. The polymer coil  86  is disposed substantially entirely between adjacent filars, generally with a relatively minor outer connective layer  87  extending across the radially outward most surface of the filar. The thickness of the outer connective layer  87  can be increased in an embodiment where the maximum desired exterior diameter permits.  
      Thus, polymer contacts substantially all and preferably all of the surface of the spring coil filar which is exposed in a direction parallel to the longitudinal axis of the tubular body. See  FIG. 6 . In between adjacent coil filars, the axially extending surfaces of the polymer coil  86  may be substantially parallel at rest as illustrated in  FIG. 6 . Alternatively, shrinkage or other factors may produce a thickness through the midpoint of one or more segments of polymer coil  86  which is slightly less than the filar diameter. This would produce a slightly concave outward meniscus like curve in the polymer segments between each filar. The thickness of the polymer coil in a radial direction can be varied to optimize desired physical properties of the finished device, such as torque transmission, pushability, flexibility, memory and burst strength or vacuum capacity.  
      In general, spring coil based medical devices for certain applications are advantageous over other designs for a variety of reasons. For example, coils are generally very flexible in a lateral direction which allows them to go easily around tight bends, yet they still transmit force very well in an axial direction which makes them very “pushable.” Coils can be curved in a tight radius without kinking or changing the dimension of the inner lumen because the coil filars can separate along the outside radius of the curve. In addition, the stiffness of a coil can be varied in a variety of ways to produce discrete flexibility sections such as by stretching the coil to create a space between adjacent filars.  
      On the other hand, one difficulty with coil guidewire and catheter bodies compared to a polymeric or metal tube is that the inner lumen is not hermetic. This is particularly true in the distal region  84  where adjacent coil filars are spaced axially apart. Many applications of a steerable sheath or guidewire require hermeticity of the inner lumen for irrigation or aspiration purposes. The coil polymer composite of the present invention is directed to achieve both the benefits of the spring coil tubular body, as well as the hermeticity of the solid walled polymeric or hypodermic tube body designs.  
      Referring to  FIG. 6 , the polymeric coil  86  and connection layer  87  extends over and between adjacent filars. When the coil is coated in this way with the appropriate polymer, it becomes hermetic but the other advantageous properties of the spring coil remain substantially unchanged. The polymeric coating can be any of a variety of medical grade polymeric materials, which exhibit sufficient adhesion to produce a seal between adjacent filars and which retains its integrity even following significant and repeated bending of the catheter. Such materials are generally convertible from a first, relatively fluid state to a second, cured state by the application of an outside influence such as heat, catalyst or light.  
      Silicone has been found to be advantageous for this application because of its relative nonreactivity in the biological environment, and its extreme elastomeric properties. Even a relatively thin layer of silicone can be stretched significantly without ripping, and still return to its original shape. It can also sustain a significant amount of compression and return to its original shape. In addition, silicone is sufficiently flowable in its precured state to provide a smooth outer and inner surface to the coil polymer composite. This advantageously minimizes trauma to tissue, and provides a smooth interior wall for the passage of implements or matter such as aspirated biological material.  
      One embodiment of the present invention was prepared using a two-part silicone dispersion system made by McGhan Nusil Corporation, Carpenteria, Ca., part No. MED2-4210. The silicone dispersion was thinned with 1,1,1-trichloroethylene to achieve a viscosity suitable for applying to the coil body.  
      The coil can be coated in any of a variety of ways. In the illustrated example, the silicone dispersion was painted onto the coil with a small piece of wire. The painted coil was thereafter positioned vertically and cured in an oven at about 300° F. for about 20 minutes. The coil can alternatively be coated such as by spraying or dipping into the silicone dispersion solution.  
      The silicone dispersion can be formulated in any of a variety of ways, as will be well known to one of skill in the art. For example, the dispersion can be formulated so that it will cure at room temperature, if desired. However, the working time in this formulation is greatly reduced. In addition, the surface tension and the viscosity of the silicone dispersion is preferably adjusted such as through the addition of 1,1,1,-trichloroethylene or other solvents to permit the dispersion to flow in between adjacent filars in the spaced region  84 , yet not run down the inside or outside of the coil.  
      Alternatively, a one-part silicone adhesive can be used which cures when exposed to ambient air at room temperature, or at elevated temperatures such as in an oven. A one-part medical grade silicone adhesive for this purpose can be obtained from Dow Corning.  
      The resulting coil polymer composite subassembly  80  can be incorporated into any of a wide variety of medical or nonmedical tubular devices, as will be apparent to one of skill in the art. The composite subassembly  80  can include a tightly packed region  82  throughout, or a spaced apart region  84  throughout, as desired, depending upon the intended application of the structure.  
      Referring to  FIG. 7 , there is disclosed an IA tool incorporating both a steering device and the coil polymer composite of the present invention.  
      The IA tool  88  is provided with a distal opening  90  in fluid communication by way of central lumen  92  with a proximal source of vacuum or infusate. The tubular body of IA device  88  comprises a proximal hypotube section  94  and a distal spring coil section  96 . The spring coil section  96  generally comprises a proximal portion  98  having tightly packed adjacent coil filars, and a distal portion  100  having adjacent coil filars spaced axially apart.  
      A deflection ribbon  102  extends from a proximal point of attachment  104  to a distal point of attachment  106  as has been previously discussed. In addition, a pull ribbon  108  extends proximally from a distal point of attachment  110  at end cap  112 . The proximal end of pull ribbon  108  is preferably secured to an axially reciprocally moveable annular pull sleeve  114 . Axial displacement of pull sleeve  114  will cause a lateral deflection of the distal portion of the IA tool  88  as has been previously discussed.  
      Following assembly of the mechanical structures identified above, a curable polymer is applied to produce a coil polymer composite IA tool. Preferably, an elongate mandrel having a diameter approximately equal to the inside diameter of hypotube section  94  is provided. The mandrel is preferably coated with a release agent such as polyvinylpyrrolidone (PVP) or other coating which will prevent adhesion between the polymer and the mandrel surface. Preferably, the pull wire  108  is also coated with PVP prior to installation. PVP is a water-soluble polymer obtainable, for example, from VWR Scientific, Inc., Cerritos, Ca., which may be mixed with ethyl alcohol as a carrier and applied to the mandrel and pull wire such as by dipping.  
      The mandrel is thereafter positioned within the IA tool by distal axial advancement through the proximal hypotube section and through the distal spring coil section. With the mandrel in place, a silicone or other suitable polymer is applied to the spring coil section of the IA tool  88  such as by dipping or painting as has been previously described. The silicone is cured as described, and the mandrel is thereafter axially withdrawn from the IA tool.  
      Optionally, the end cap  112  is molded from a polymer such as silicone. This may be accomplished in a discrete step, or simultaneously with the coating operation. This is accomplished by extending the mandrel axially slightly beyond the distal end of the spring coil and positioning a female mold cavity at the end of the coil having the desired interior shape. Preferably, the distal end of the mandrel and/or the interior of the mold is provided with a pin to produce distal opening  90 . All of the silicone components can be simultaneously formed, for example, by positioning the entire spring coil section of the device within a mold cavity and injecting the uncured silicone or silicone precursor.  
      This method produces a coil polymer composite IA tool having silicone or other suitable polymer segments  116  positioned between adjacent coil filars, as has been previously discussed. In addition, provision of the mandrel during the polymer coating process in combination with the use of a polymer having a sufficiently low viscosity to flow through the adjacent coil filars, produces a tubular sleeve  118  on the radial interior surface of the spring coil  100  which has a substantially uniform interior cross-sectional area throughout. This eliminates, for example, the shelf  120  formed in this embodiment at the distal end of hypotube  94 . In addition, interior tubular wall  118  encloses both the pull ribbon  108  and the deflection ribbon  102 .  
      Isolating the interior lumen  92  from the pull ribbon  108  and deflection ribbon  102  is advantageous for several reasons. For example, in the IA embodiment, material is aspirated from inside of the eye. Interior sleeve  118  minimizes the possibility of that material getting hung up in the pull ribbon or deflection ribbon, to create a blockage within the central lumen. In non-IA embodiments, the interior sleeve  118  minimizes the likelihood that fiber optics or other medical implements passed through the sheath will damage or get tangled in the deflection ribbon or pull ribbon.  
      In addition, entrapping the pull wire  108  within a silicone sleeve  118  resists bowing of the pull ribbon  108  into the central lumen  92  when the pull ribbon is pushed distally in order to straighten the tip.  
      In an actual embodiment produced in accordance with the illustration contained at  FIG. 7 , the outside diameter of the coil was 0.040 inches. The coil was wound from a filar having a diameter of 0.0035 inches. A 0.006 inch gap was provided between adjacent filars in the deflection section. Each of the deflection ribbon and pull ribbon were made from 0.001 inch by 0.003 inch stock.  
      Referring to  FIG. 8 , there is disclosed a steerable endoscope sheath incorporating the coil polymer composite of the present invention. Steerable sheath  124  generally comprises a coil body  126  having axially spaced adjacent filars in the distal steerable region  128  thereof. A deflection ribbon  130  extends from a distal point of attachment to end cap  132 , to a proximal point of attachment  134 . A pull ribbon  136  extends from a distal point of attachment to end cap  132 , to a proximal control.  
      A silicone coating  138  is provided in manners previously discussed, to fill the spaces between adjacent filars  128  in the distal region of the flexible endoscope  124 . In addition, the silicone coating  138  provides a smooth interior wall transition between the inside diameter at the distal end of the endoscope sheath and the interior diameter of an inner polyethylene tube  140 .  
      In an actual embodiment of the design illustrated in  FIG. 9 , the outside diameter of the coil was 0.098 inches. The filar diameter was 0.010 inches, with a 0.006 inch gap between adjacent filars in the deflection section. The deflection ribbon had cross-sectional dimensions of 0.004 by 0.020 inches, and the pull ribbon had cross-sectional dimensions of 0.003 by 0.011 inches.  
      In addition to, or in place of, the elastomeric layer or coil described above, the intraocular irrigation and aspiration tool or other flexible medical device may be provided with an outer sheath  142  as illustrated in  FIG. 9 . Thus, the discussion of the sheath  142  is to be understood as applicable to any of the steerable tools disclosed herein and to not just the specific embodiment illustrated in  FIG. 9 .  
      Referring to  FIG. 9 , an irrigation and aspiration tool  88  comprises a coil  96 , having a proximal portion  98  and a distal portion  100  as has been previously discussed. The coil  98  defines at least one lumen  92 , which is in communication by way of a distal opening  90  through a distal cap portion  146  with the exterior of the irrigation and aspiration tool  88 . A pull ribbon  108  extends axially through the irrigation and aspiration tool  88 , and, in the illustrated embodiment, through the central lumen  92 , to a distal point of attachment  110  to the distal portion  100  of coil  96 . A deflection ribbon as has been previously discussed is preferably also included, but has been omitted from  FIG. 9  for simplicity. Axial movement of the pull ribbon  108  causes a lateral deflection of the irrigation and aspiration tool  88  in at least the distal steering region  32 , as has been discussed in connection with previous embodiments. Distal point of attachment  110  may comprise any of a variety of attachments, such as soldering, brazing, welding, crimping, adhesives, and the like. Preferably, the pull ribbon  108  and coil  96  are both metals which can be soldered at distal point of attachment  110 .  
      The irrigation and aspiration tool  88  or other steerable medical device is provided with a flexible outer sheath  142 . In the illustrated embodiment, the outer sheath  142  comprises a proximal tubular sleeve portion  144  and an integral distal cap portion  146 . The proximal sleeve portion  144  and distal cap  146  may be integrally formed and thereafter assembled onto the irrigation and aspiration tool  88  as a unit. Alternatively, the cap portion  146  or the sleeve portion  144  can be attached to the irrigation and aspiration tool  88  first, with the other of the two sheath  142  components attached thereafter. Preferably, the proximal sleeve  144  and distal cap  146  are molded as an integral unit to form a sheath  142 , which is subsequently positioned on the irrigation and aspiration tool  88  as a unit, as will be discussed.  
      The sheath  142  may be molded such as through the use of liquid injection molding from a silicone such as that disclosed previously herein. Other polymeric, and generally elastomeric, polymers may alternatively be used, depending upon the physical requirements of the finished device. Optimization among different biocompatible polymers can be readily accomplished through routine experimentation in view of the disclosure herein. Other sheath manufacturing techniques include spraying silicone or other polymer dispersion onto a mandrel, or extruding a tube of thermoplastic elastomer material such as urethane or C-Flex and heat forming the distal tip. The sheath may also be formed slush molding. This process uses a female mold. Silicone or polymer dispersion of the desired viscosity is poured into the mold then poured out. Some of the dispersion remains coating the mold. The solvent is allowed to evaporate (and, in the case of silicone, the polymer is then cured). The finished part is removed from the mold. This process will allow the creation of sheaths with robust tip sections more easily then dip molding on a mandrel. Other techniques, such as dip molding with silicone in dispersion, will be understood by those of skill in the art in view of the disclosure herein.  
      In an injection-molded embodiment, the proximal sleeve portion  144  has a wall thickness within a range of from about 0.0005 to about 0.010 inches or greater. Wall thicknesses for the sleeve portion  144  can be varied outside of the foregoing range, depending upon the particular polymer utilized and the manufacturing technique. Typically, for use in an irrigation and aspiration tool  88 , the wall thickness will be ori the order of from about 0.002 to about 0.003 inches. The outside diameter of the proximal sleeve portion in the IA tool embodiment is about 0.032 inches.  
      The distal end of the IA tool  88  is provided with a distal cap portion  146  having an opening  90  therein. The opening  90  may be manufactured in any of a variety of ways, such as by drilling, punching, or molding (e.g., using a removable pin or mandrel) together with the distal cap portion  146 . In one preferred manufacturing technique, the distal opening  90  is punched through the distal cap portion  146  and has a diameter of about 0.013 inches.  
      The distal opening  90  has a longitudinal axis  148  which extends at an angle θ from the longitudinal axis  150  of the irrigation and aspiration tool  88 . The angle θ can be varied between 0° (i.e., coaxial or offset but parallel) and about 90° from the longitudinal axis  150 , depending upon the intended application and functionality of the IA tool  88 . In the illustrated embodiment, the distal opening axis  148  is inclined at an angle within the range of from about 35° to about 55°, and particularly, approximately 45°, from the longitudinal axis  150  and away from the direction of the pull wire  108 .  
      The outer sheath  142  having a distal opening  90  punched therein may thereafter be assembled onto the spring coil  96 . This may be facilitated by soaking the sheath  142  in a material or solution to facilitate expansion and/or increase lubricity of the sheath  142  material. Such solutions can be readily determined through routine experimentation. For a sheath  142  molded from silicone, the sheath  142  may be soaked in freons, xylene, toluene, alcohol or solutions thereof to cause expansion of the sheath. The expanded sheath may thereafter be axially pulled onto the distal end of the spring coil  96 , and left in place for the alcohol to volatilize thereby providing a secure fit between the outer sheath  142  and the coil  96 . It is generally preferably to manufacture the sheath  142  with an internal diameter slightly smaller than the outer diameter of the spring coil  96 . Manufactured in this manner, the sheath  142  will shrink snugly onto the spring coil  96  and will be firmly held in place.  
      In general, the foregoing techniques for creating a sheath, swelling it, placing it over the mechanical skeleton of a steerable tubular body and allowing the swelled sheath to recover is also applicable to devices such as those shown in  FIG. 1-6 . In this situation the sheath is simply a tube there is no need for an end cap on the tube since the end cap, if any, is already part of the mechanical skeleton.  
      Additional materials, features, combinations, and other design aspects of the IA tool  88  can be incorporated from any of the previously disclosed embodiments herein. Thus, the present invention provides a flexible sheath having an integral sleeve portion and cap portion which may be mounted on any of a wide variety of underlying flexible medical implements, which may desirably be protected or otherwise isolated from the surrounding environment except such as through distal opening  90  or other apertures where communication between the interior of the medical device and the surrounding environment may be desired.  
      Although this invention has been described in terms of certain preferred embodiments, other embodiments that are apparent to those of ordinary skill in the art are also within the scope of this invention. Accordingly, the scope of the invention is intended to be defined only by reference to the appended claims.