Abstract:
A catheter enabling a reduced puncture hole size into the skin and blood vessel is disclosed. In one embodiment, the catheter has an elongate body having an expandable sheath extending at least a portion of its length. A pressure constraining sheath is positioned to surround the expandable sheath, at a selected region to prevent expansion of the inner sheath at the region of the constraining sheath. In one preferred use, the constraining sheath is positioned at the puncture hole. During use, the catheter increases in cross-section by an expandable sheath expanding from a first diameter to a second diameter. However, the outer sheath does not expand, maintaining a small diameter at the puncture site.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to angiography and/or particularly to an improved catheter for injecting medical fluids such as radiographic contrast fluid into living organisms. 
     BACKGROUND OF THE INVENTION 
     Angiography is a procedure used in the treatment of cardiovascular conditions including abnormalities or restrictions in blood vessels of a human or animal body. During angiography, a radiographic contrast material is injected through a catheter into a vein or artery, which then passes to vascular structures in fluid communication with the vein or artery. When X-rays are passed through the region of the body into which the contrast material is injected, they are absorbed by the contrast material, providing radiographic images of the desired vascular structure(s). The images can be recorded on film or video tape and/or displayed on a fluoroscope monitor. The images can be used for many purposes, as for example diagnostics, and for operative procedures such as angioplasty, wherein a balloon is inserted into a vascular system and inflated to open a stenosis. 
     The contrast material can be injected into the catheter by either manual or automated injection systems. Although the apparatus for injecting the contrast material can vary, many current systems include a syringe operatively connected with the catheter. The syringe has a chamber for holding the contrast material and a plunger reciprocally moveable within the chamber. An example of one such apparatus is U.S. Pat. No. 5,573,515, the entire disclosure of which is incorporated herein by reference. In this apparatus, the contrast material is suctioned into the chamber when the plunger is moved to create a partial vacuum within the chamber. A reversal of the plunger direction first forces air out of the chamber and then delivers the contrast material to the catheter at a rate and volume determined by the speed of movement of the plunger. 
     In a manual system the user or operator loads the syringe and ejects air from the chamber before connecting the syringe to the catheter. The user of a manual system adjusts the rate and volume of injection by altering the manual force applied to the plunger. The maximum injection pressure for manual systems is typically limited to 200 p.s.i. (i.e. the maximum pressure that can be applied by the human hand), and the maximum quantity of fluid is about 12 cc. 
     Angiography can include the injection of fluids other than the contrast material. For example, a saline flush and/or the injection of fluid medications may be desired. 
     The catheter through which the contrast agent or other fluid is supplied is typically inserted percutaneously and into the desired artery or vein. When inserted percutaneously, a puncture hole is created in both the skin and blood vessel wall at the insertion point in order to correctly position the catheter. It is preferable to use a puncture hole that is as small as possible, to avoid leakage around the catheter and to minimize the subsequent wound size. Additionally, the larger the puncture hole, the greater the opportunity for complications and the more time needed to stop the bleeding after the catheter is removed. 
     Many presently available catheters have a fixed size (diameter) that extends the entire length of the catheter. Resistance to fluid flow in the catheter is determined by the inside diameter. Therefore, the size of catheter chosen for a specific procedure is based upon the inside diameter needed to achieve the particular flow rates associated with the procedure. However, such fixed diameter catheters have the same outside diameter at the puncture site as at other points on the catheter. As a result of this design, the wound at the puncture site may be unduly large for the particular procedure to be performed. 
     Although the presently available catheters are well accepted by the medical profession and function as required, it is desirable to have a catheter that minimizes the vascular puncture site diameter, but allows minimal resistance to fluid flow. In other words, it is desirable to provide a catheter that minimizes the trauma to a patient but provides versatility to the user for many varied applications and uses of the catheter. 
     OBJECTS OF SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the present invention to overcome the deficiencies of existing catheters. 
     It is a further object of the present invention to provide a catheter that minimizes the wound size for use of the catheter and yet still provides a wide variety of potential uses. 
     It is a further object of the present invention to provide a catheter that is economical to produce. 
     It is a further object of the present invention to provide a method of ensuring adequate fluid flow through a catheter with the smallest diameter patient incision as possible. 
     The present invention attempts to address these objects and other objects not specifically enumerated herein through the use of a catheter that has an outer surface, a portion of which is compliant and has an adjustable diameter and another portion which is not adjustable, or non-compliant. It further may include a backbone, a compliant and expandable sheath surrounding the backbone, and an outer non-compliant sheath which covers a portion of the expandable sheath. At least a portion of the outer non-compliant sheath is not expandable. 
     The backbone allows the catheter to retain a predetermined shape for ease of manipulation and placement of the catheter. The outer non-compliant, nonexpandable sheath limits the expansion of the catheter and is positioned at the insertion point into the patient. The adjustable sheath, however, expands. Thus, the catheter retains the narrow insertion point but expands at either side of the insertion point. 
     The catheter sheath selectively expands to provide an expanded area and a non-expanded area, which expansion may occur either during, or prior to, the injection of a fluid. This selective expansion is advantageous because the puncture hole at the entry site into the patient is minimized. 
     In a preferred method of inserting the catheter, the flexible catheter tip and body are compressed, folded or otherwise manipulated to be smaller in diameter than the diameter of outer non-compliant sheath. The outer sheath can be inserted through the skin and vascular wall after which the body of the catheter is inserted through the constraining outer sheath. The body is then expanded to the desired size. 
     In a second embodiment, there may be no discrete inner expandable sheath at the position where the outer non-compliant sheath is located. Instead, the nonexpandable sheath may be integral with the expandable sheath. 
     In a further embodiment, the backbone can be removable and replaceable with a different backbone in order to provide a different shape to the catheter. 
     In yet a further embodiment, the outer non-compliant sheath may be expandable on demand, for example by mechanical structures. This option may be desired when a large device, such as an atherectomy catheter, needs to be inserted through the catheter. Alternately, the outer sheath may be replaceable with an outer sheath having a larger diameter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a catheter of the invention inserted into a blood vessel of a patient; 
     FIG. 2 is a perspective side view of a catheter of the invention in an unexpanded, first position; 
     FIG. 3 is a perspective side view of the catheter of FIG. 2 in an expanded, second position; 
     FIG. 4 is a cross-sectional view of a catheter of the invention taken along line  4 — 4  of FIG. 2; 
     FIG. 5 is a cross-section view of another embodiment of the invention taken along line  4 — 4  of FIG. 2; 
     FIG. 6A is a perspective side view of a spring in expanded form; 
     FIG. 6B is a perspective side view of a spring in unexpanded form; 
     FIG. 7A is a perspective side view of a coil in expanded form; and 
     FIG. 7B is a perspective side view of a coil in unexpanded form. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, a catheter  10  in one embodiment of the present invention is shown inserted into a patient to supply fluids, for example a contrast agent, to the blood stream. The catheter  10  is inserted into the patient through a puncture hole in the patient&#39;s skin  20  and in a blood vessel wall  22 . 
     Referring to FIGS. 1,  2  and  3 , the catheter  10  has a hollow elongate body  12  that extends from the patient&#39;s exterior and terminates inside the blood vessel. The distal end  21  of the catheter  10  is the end inserted into the patient whereas the proximal end of the catheter  10  is the end closest to the user (usually a physician or clinician). 
     Located internally in the catheter  10  is a backbone  14 , which serves to shape the catheter  10 . The backbone  14  is shown as an interior structure of the catheter  10  and is encompassed by the conduit  15  of the catheter  10 , which conduit is the outermost portion of the catheter  10 . The backbone  14  further provides strength, structure and integrity to the catheter  10  to allow insertion of the catheter  10  into the patient. The backbone  14  is generally sufficiently rigid to penetrate the patient&#39;s skin and vessel wall into the lumen of the vessel. However, the backbone  14  is also fairly thin so that unnecessary bulk and thickness are not added to the catheter  10 . 
     The conduit  15  of the catheter  10  includes an outer sheath  16  and an inner sheath  18  wherein the outer sheath  16  is a noncompliant, non-expandable sheath and wherein the inner sheath  18  is a compliant, expandable sheath that can readily stretch or expand or both, for example by the pressure of fluid flowing therethrough. 
     The interior of the conduit  15  is a hollow passage and is designed to provide a passage for fluid or a medical device, for example contrast agent or angioplasty catheter, respectively, or any other applicable liquid or device. In the case of fluid, the fluid enters the catheter  10  at an inlet  17  located at the proximal end of the catheter  10 , passes through the interior of the conduit  15 , and exits the catheter  10  at an outlet  19  at the distal end  21  of the catheter  10 . The inlet  17  can include typical connector systems such as Luer® locks, threads, and other known systems. The pressure of the fluid passing through the catheter  10  may be sufficient to expand expandable sheath  18 , but is insufficient to expand outer sheath  16 . 
     The outer sheath  16  is located at the point on the catheter  10  where the catheter  10  passes through the skin and vascular wall. The outer sheath  16  is rigid, non-compliant and non-expandable, and should be able to withstand pressures of at least about 500 p.s.i., preferably at least about 750 p.s.i., and more preferably at least about 1200 p.s.i. without radially expanding or deforming. The diameter of the outer sheath  16  is directly related to the diameter of the puncture hole needed for insertion of the catheter  10  into the patient. It is preferable to have the outer sheath  16  as small as possible so as to minimize the puncture hole. Preferably, the outer diameter of the outer sheath  16  is about 0.8 to 5 mm. 
     An inner expandable sheath  18  extends the length of the catheter&#39;s elongate body  12  and surrounds and covers the backbone  14 . If the backbone  14  is in the interior of catheter  10 , the inner sheath  18  is preferably connected to the backbone  14  in several spots, for example, at the tip  19 . Alternatively, the backbone  14  may be integral with the inner sheath  18 , that is, the backbone  14  may be located within the wall of the inner sheath  18 . 
     FIG. 2 shows catheter  10  of the present invention in a first, or non-expanded position prior to insertion in a patient. The inner sheath  18  has a diameter less than or equal to the outer sheath  16 . Preferably, the tip  19  of the catheter (at distal end  21 ) and the inner sheath  18  have a diameter less than the outer sheath  16 . 
     FIG. 3 shows the catheter  10  in a second, or expanded position. In this position, the inner sheath  18  has expanded to a diameter greater than that of the outer sheath  16 . The inner sheath  18  has expanded from its first position in FIG. 2 to a second position in FIG.  3 . The outer sheath  16  has not expanded or distorted, but has retained the same diameter and shape as before the inner sheath  18  was expanded. 
     Having described the general structure of a first embodiment of the present invention, the various components and variants thereof are now discussed in greater detail. It will be understood that a catheter in accordance with the present invention may incorporate any number of combinations of the specific aspects of the disclosed components. 
     Backbone 
     The backbone  14  of the catheter  10  extends longitudinally along the body and provides the catheter  10  with much of its structural properties. Additionally, the backbone  14  will allow the catheter  10  to be advanced to the preferred location in the blood vessel or may allow for rotation of the catheter  10  once in position. 
     The backbone  14  of the catheter  10  may be similar to the backbones used in conventional catheters. Moreover, the backbone  14  is typically about 60 to 100 cm long and generally extends the length of the catheter  10 . 
     The backbone  14  is generally located within the conduit  15  of the catheter  10 . That is, it is embedded in the catheter  10 , either in the interior of the conduit  15  or within a wall of the conduit  15 ; that is, the backbone  14  is positioned transmurally. Alternatively, the backbone  14  may be centrally located in the hollow interior of the conduit  15  or it may be displaced to one side or another of the interior. FIGS. 4 and 5 show the backbone  14  placed to one side of the interior area of conduit  15 . 
     Another alternative embodiment is to provide the backbone  14  within a lumen of the catheter  10 ; that is, the backbone  14  is positioned intralumenally. If positioned in a lumen, the backbone  14  is typically loosely held so that the backbone  14  can be rotated and advanced as desired. The lumen may be positioned inside or outside of the inner and outer sheaths  16 ,  18 . Generally, when a backbone  14  is said to be “removable” and/or “replaceable”, the backbone  14  is positioned in a lumen, however backbones  14  located in the interior of the catheter  10  may also be removable and replaceable. 
     Examples of typical backbone  14  materials include thermoplastic and thermoset polymers, such as nylon, polypropylene, polyethylene, polycarbonate, metals and alloys, such as titanium, stainless steel, ceramics, and composite materials, which can include combinations of ceramics, organic polymers, inorganic materials, and metals. A preferred material is a Ni—Ti shape-memory alloy commonly known as “nitinol”. 
     In one embodiment, the backbone  14  is removable from the catheter  10  after insertion in a patient and replaceable with a different backbone  14 , one that, for example, changes the shape of the catheter  10 . When exchanging the backbone  14 , it is not necessary to replace or move the catheter  10 . In particular, it is not necessary to disturb the puncture hole where the outer sheath  18  is positioned. 
     Outer Sheath 
     At least a portion of the outer sheath  16  is a rigid, noncompliant, non-expandable section. This non-compliant outer sheath  16  maintains a minimal puncture hole in the skin and vascular wall through which the catheter  10  is passed. Preferably, the puncture hole is less than about 3 mm. 
     The outer sheath  16  constrains the inner sheath  18  such that the inner sheath  18  is constrained from expanding beyond a predetermined limit established by the outer sheath  16 . The outer sheath  16  is positioned at least at the site of entry of the catheter  10  into the body and the vessel. The outer sheath  16  maintains the diameter of the catheter  10  minimally small at the puncture hole, yet allows expansion of the catheter  10  (in particular the compliant sheath  18 ) along its length either on both the distal and proximal sides of the outer sheath  16  or on one side of the outer sheath  16 . The unexpanded area created by the outer sheath  16  restricts the flow of the contrast agent through the catheter  10  yet allows sufficient volume flow of the agent. 
     The outer sheath  16  may be permanently affixed to the inner expandable sheath  18  it may be movable along the length of the catheter  10 . For example, when a movable outer sheath  16  is used, the user is capable of positioning the outer sheath  16  in the desired position on the catheter  10 . This may be particularly useful in patients where it is not possible to get a deep penetration of the catheter  10  into and along the blood vessel. Additionally, a movable outer sheath  16  may be completely removed from the catheter  10  and replaced with a different diameter outer sheath  16 . 
     In some embodiments it may be desirable to provide an outer sheath  16  that is expandable at some location or locations along its length. For example, the outer sheath  16  may be designed to remain at its unexpanded diameter at the outer sheath  16  mid-point and then expand gradually each direction along its length. This configuration may increase the stability of the catheter at the puncture point. 
     Controlled expansion of portions of the outer sheath  16  or of the entire outer sheath  16  itself may be accomplished by material selection, or by mechanical means. For example, once the catheter  10  is correctly positioned, the portion of the outer sheath  16  immediately on each side of the puncture point may be expanded, for example by a “twist and lock” or other mechanism. Any expansion of the outer sheath  16  may be directly controllable by the user, or may be a function of the fluid pressure flowing through the catheter  10 . The expandable portions may have a single expanded position or may be incrementally expandable. However, at least some portion of the outer sheath  16  usually remains unexpanded from its initial diameter. 
     The outer sheath  16  is preferably a cylindrical tube, but other shapes may be utilized if desired. The length of the outer sheath  16  is typically about 5 to 30 cm. Generally, the outer sheath  16  will be positioned so that it is located at the skin  20  and vessel puncture hole and extends minimally in either direction past this point. Preferably, the non-compliant, non-expanding outer sheath  16  extends at least 5 mm past the puncture point in the skin  20  and blood vessel wall  22 . 
     The diameter of the outer sheath  16  should be as small as feasible to provide as small of a puncture hole as possible insofar as the diameter of the outer sheath  16  is directly related to the diameter of the puncture hole needed for insertion of the catheter  10  into the patient. The outer sheath  16  should not, however, be so small as to prevent insertion of the compliant sheath  18  and catheter backbone  14  therethrough. 
     Typically, the outer sheath  16  will have an outer diameter between about 1 and 4 mm, preferably 1 to 2 mm. Different sizes of the outer sheath  16  can be available for different uses. The inner wall diameter should be minimally less than the outer diameter. That is, it is preferable to have the wall of the outer sheath  16  as thin as possible without compromising strength and integrity. Typical wall thickness include 0.004 to 0.010 mm, but other thickness may be utilized depending on the specific outer sheath  16  material used. 
     The outer sheath  16  is preferably manufactured from medically acceptable materials such as metals (for example stainless steel or nitinol), plastics (for example nylon, urethane or Polyethylene Terephthalate (ET)), and composites. The material of the outer sheath  16  may be reinforced, for example by fibers or other strengthening agents, so as to further increase the tensile strength and decrease any distortion possibilities. The outer sheath  16  should be capable of constraining pressure in excess 500 p.s.i., preferably more than 750 p.s.i. more preferably more than 1200 p.s.i. (approximately 8 atmospheres) in the radial direction without expanding or distorting in shape or size. In another preferred embodiment, the outer sheath  16  is capable of resisting pressures between about 1200-1500 p.s.i. without distorting. Many materials can have their properties, such as elasticity and stiffliess, etc., altered by various processing methods. 
     Inner Expandable Sheath 
     Placed within the outer non-compliant sheath  16  is an inner expandable sheath  18  that generally extends the length of the catheter  10 . In embodiments where the backbone  14  is located in the interior of the catheter  10 , the inner sheath  18  surrounds the backbone  14 . It is through the inner sheath  18  that the fluid being administered, for example the contrast fluid, passes. The expandable sheath  18  is radially expandable, preferably by the pressure of the fluid flowing therethrough, preferably in a controlled and repeatable manner. The amount of expansion, or diameter change, can be designed to be responsive to the needs of the user. 
     The expandable sheath  18  can be radially adjusted from a first diameter to a second diameter with the use of fluid pressure, mechanical means, or other forces. The first diameter of the inner sheath  18  is generally less than the smallest diameter of the outer sheath  16 , whereas the second diameter of the inner sheath  18  is greater than the largest diameter of the outer sheath  16 . The expansion of the inner sheath  18  to the second diameter may either be a permanent or temporary deformation, that is, it may be capable of returning to the first diameter without any permanent deformation. Any expansion may be incremental. 
     The expandable sheath  18  can be manufactured from medically acceptable materials such as metals, plastics, and composites, however polymeric materials are preferred. Insofar as the expandable sheath  18  must be capable of expanding from one diameter to at least a second diameter, it is preferable that the material used for the expandable sheath is elastic. However, expandability may be achieved by other methods, such as by providing an inner sheath  18  that has sufficient non-elastic material to provide a circumference related to the second diameter. The inner sheath  18  is then folded upon itself inside the outer sheath  16 . 
     FIGS. 4 and 5 show cross-sectional views of two embodiments of the inner sheath  18  placed within the outer sheath  16 . FIGS. 4 and 5 are taken from line  4 — 4  in FIG.  2 . FIG. 4 shows the inner sheath  18  flatly and continuously disposed within the outer sheath  16 . In such an embodiment, the inner sheath  18  is elastic and will expand radially at the points where the outer sheath  16  is not present when pressure is applied from the inside. 
     The inner sheath  18  of FIG. 5 will likewise expand radially at the points where the outer sheath  16  is not present, however, the inner sheath  18  is not elastic or is likely less elastic than that disclosed in FIG.  4 . Rather, extra material of the inner sheath  18  is folded on itself so that when pressure is applied, the inner sheath  18  will unfold, thus providing an expanded diameter. 
     Methods of Expanding the Expandable Sheath 
     The expandable sheath  18  may be expanded by mechanical means, fluid pressure, or other feasible methods. In a first embodiment, the expandable sheath  18  expands simply as a result of an increase in fluid pressure passing through the catheter  10 . The initial pressure of the fluid causes the inner sheath  18  to expand at locations where it is not constricted by the outer sheath  16 . The catheter  10  remains in this expanded configuration for the duration of the procedure after which the catheter  10  collapses or is simply pulled out through the narrower outer sheath  16 . 
     In another embodiment, mechanical means, such as a spring  24  or coil  26 , as shown in FIGS. 6A,  6 B,  7 A and  7 B, can be used to expand the inner sheath  18 . For example, a tightly wound spring  24  may be part of the catheter  10  between the backbone  14  and the expandable sheath  18 . The spring  24  may be actuated by mechanical manipulation, such as a twisting or pulling, in order to increase the diameter of the catheter  10 . 
     In yet another embodiment, the backbone  14  of the catheter  10  may also be used as a “key” or other device to alter the catheter&#39;s  10  shape. The backbone  14  may be removed and inserted in a manner that distorts the expandable sheath  18  so that a second diameter is obtained. Alternately, a stylet (other than the backbone  14 ) can be placed inside the catheter  10  for manipulation of the catheter&#39;s  10  shape and size. 
     And in another embodiment, the expandable inner sheath  18  may be made from a material that is expandable when heated, such as nitinol. Application of heat to the catheter  10  may cause the inner sheath  18  to expand whereas removal of the heat, or cooling, will cause the inner sheath  18  to retract to, or close to, its original diameter. Alternatively, the patient&#39;s body temperature (typically 98.60° F.) may be sufficient to cause the inner sheath  18  to expand. 
     The foregoing description addresses embodiments encompassing the principles of the present invention. The embodiments may be changed, modified and/or implemented using various types of arrangements. Those skilled in the art will readily recognize various modifications and changes which may be made to the invention without strictly following the exemplary embodiments and applications illustrated and described herein, and without departing from the scope of the invention which is set forth in the following claims.