Catheter with low-friction distal segment

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FIELD OF THE INVENTION

The present invention relates to an improved catheter and catheter device for accessing a tissue target site along a tortuous or highly curved path through small vessels. More particularly, the invention relates to a catheter comprised of a tube and a guidewire wherein the internal surface of at least a portion of the tube is designed so as to facilitate the relative movement of the guidewire with respect to bent or curved portions of the tube and thus prevent jamming, sticking or locking of the guidewire against the internal tube surface.

BACKGROUND OF THE INVENTION

Catheters are being used increasingly as a means for delivering diagnostic or therapeutic agents to internal target sites that can be accessed through the circulatory system. For example, in angiography, catheters are designed to deliver a radio-opaque agent to a target site within a blood vessel, to allow radiographic viewing of the vessel and blood flow characteristics near the release site. For the treatment of localized disease, such as solid tumors, catheters allow a therapeutic agent to be delivered to the target site at a relatively high concentration with minimum overall side effects.

Often the target site which one wishes to access by catheter is buried within a soft tissue, such as brain or liver, and can only be reached by a tortuous route (i.e., a route including repeated sharp curves) through small vessels or ducts----less than about 3 mm lumen diameter----in the tissue. The difficulty in accessing such regions is that the catheter must be quite flexible in order to follow the tortuous path into the tissue, and at the same time, stiff enough to allow the distal end of the catheter to be manipulated from an external access site, which may be as much as a meter or more from the tissue site.

Heretofore, two general methods for accessing such tortuous-path regions have been devised. The first method employs a highly flexible catheter having an inflatable, but pre-punctured balloon at its distal end. In use, the balloon is partially inflated and carried by blood flow into the target site. The balloon is continually inflated during placement to replenish fluid leaking from the balloon. A major limitation of this method is that the catheter will travel in the path of highest blood flow rate, so many target sites with low blood flow rates cannot be accessed.

In the second method, a torqueable guidewire and catheter are directed as a unit from a body access site to a tissue region containing a target site. The guidewire is bent at its distal end and may be guided, by rotating and advancing the wire, along a tortuous, small-vessel pathway, to the target site. Typically the guidewire and catheter are advanced along the tortuous pathway by alternately advancing the wire along a region of the pathway, then advancing the catheter axially over the advanced wire portion. An important advantage of this method is the ability to control the location of the catheter along a tortuous path.

It is frequently desirable, for example, in treating deep brain vessel abnormalities, to direct a small-diameter catheter along a tortuous, small-diameter pathway to the brain vessel site. The procedure may be advisable, for example, in treating an arteriovenous malformation, in order to introduce an embolic agent into the small capillaries connecting the arterial and venous vessels at a deep brain site. At a certain point along the pathway, when sharp bends are first encountered, the catheter is advanced by alternately guiding the flexibletip portion of the guidewire along the path, then threading the catheter over a portion of the advanced wire region.

One problem which may be encountered, as the guidewire and catheter are advanced, is that the guidewire can become stuck against the internal tubular surface of the catheter. Typically, this problem arises when a sharp bend, such as a hairpin loop, is encountered and/or where two or more sharp bends occur in succession. When the catheter and wire become locked together (i.e., the end of the guidewire is jammed against the internal surface of the catheter tube so as to prevent the relative movement of the guidewire and internal tubular surface) in the region of wire bending, it may be impossible to either advance or withdraw the wire. In this event, the wire and catheter must be pulled back as a unit along the pathway until both are straight enough to allow the wire to be moved axially within the catheter, and often, the physician may have to give up attempting to reach the site.

The problem of advancing a catheter over a guidewire in a region of sharp wire bend(s) has been addressed by the catheter construction disclosed in U.S. Pat. No. 4,739,768. This construction includes a relatively long, relatively rigid proximal segment, and a shorter, more flexible distal segment having a length of at least about 5 cm. The proximal segment provides sufficient torqueability and axial stiffness for guiding the catheter and internal guidewire from a body access site to the target tissue of interest. Once the tortuous tissue pathway is reached, the more flexible end segment allows the end region of the catheter to be advanced axially over sharp and/or frequent wire bends.

SUMMARY OF THE INVENTION

A catheter device is disclosed which is comprised of two basic components including (1) an elongated guidewire having a proximal and a distal end; and (2) a catheter in the form of an elongated tubular member. The catheter or tubular member is comprised of two sections. The first section is toward the proximal end of the tubular member where, in a catheter device, it is connected to a proximal end fitting. The first section has substantially less flexibility relative to a second section which is toward a distal end of the tubular member. The second section is sufficiently flexible to allow a high degree of bending as compared with the first section. A critical feature of the present invention is that the highly flexible second section of the tubular member includes an internal tubular wall portion which has been substantially modified. The internal wall portion can be modified in a variety of different manners in order to obtain the object of reducing the potential for jamming, sticking or locking the distal end of some other portion of the guidewire against the internal tubular wall portion.

In accordance with one embodiment of the invention, the internal tubular wall portion is constructed (i.e., physically structured) in a manner so as to deflect the distal end of the guidewire from applying significant forces in a direction normal to the surface of the internal tubular wall. This construction could be in the form of providing a braided sleeve or coil-like structure which wraps around the internal tubular wall. Other constructions might include regular and irregular shapes such as undulations formed in a serpentine pattern on the surface of the internal tubular wall. The coils or configuration of the braided sleeve are constructed so that when the guidewire contacts these constructions, the guidewire is deflected so that the guidewire does not provide substantial forces normal to the surface of the internal tubular wall and therefore does not become jammed or locked into a position on the surface of the internal tubular wall (especially when the second section is bent at an angle of 90.degree. or more).

In a second embodiment of the invention, the internal tubular wall is comprised of materials which minimize the frictional resistance between the internal tubular wall and the distal end portion of the guidewire. Examples of such materials include graphite and Teflon-like materials (i.e., tetrafluoroethylene and fluorocarbon polymers, fluorinated ethylene-propylene resins and other similar non-stick, anti-friction coating compounds) which provide a low coefficient of friction.

In a third embodiment of the invention, yet another tubular member is provided which is positioned within the elongated tubular member and may internally extend from the first section, but at least extends partly within the second tubular section and provides structural (i.e., deflecting normal forces) or material (i.e., anti-friction) features of the types described above which prevent the jamming, sticking or locking of the distal end of the guidewire against the internal tubular wall portion of the second section. The elongated internal tubular member may be movable so as to physically free a jammed end or portion of the guidewire.

A primary object of the invention is to provide a catheter comprised of a guidewire and an elongated tubular member wherein a more flexible section of the tubular member includes an internal wall surface which is constructed and/or comprised of materials so as to aid in preventing the distal end of the guidewire from jamming or locking against its surface.

A feature of the present invention is that the catheter includes a tubular member with a highly flexible section which includes an internal wall member having physical constructural features and/or anti-friction material capable of deflecting the guidewire from applying significant forces in a direction normal to the internal surface of the tubular wall and thus avoid jamming of the wire against the internal wall.

An advantage of the present invention is that the catheter can be used to enter highly curved areas with substantially reduced problems with respect to the jamming of the distal end of the guidewire against the internal tubular surface of the tubular member.

These and other objects, advantages and features of the present invention will become apparent to those persons skilled in the art upon reading the details of the construction, composition and usage as more fully set forth below, reference being made to the accompanying drawings forming a part hereof.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention may be better understood and its numerous objects, advantages and features will become apparent to those skilled in the art by reference to the accompanying drawings as follows:

FIG. 1 shows a catheter device, including a catheter constructed according to the present invention;

FIG. 2 is an enlarged, sectional view of the catheter, taken along the region 2--2 in FIG. 1, in an embodiment in which the internal tubular surface is a braided sleeve;

FIG. 2A is the same view as FIG. 2 showing the wire coil in place of the braided sleeve;

FIG. 3 is a cutaway view of a portion of the distal-end segment of a catheter similar to the one shown in FIG. 2, but where the braided sleeve has a reduced density and increased radial pitch on progressing toward the catheter's distal end;

FIGS. 4A and 4B are enlarged sectional views of a catheter constructed according to a second general embodiment, showing a distal-end segment of a catheter having a carbon-particle coating (4B) formed by drying a carbon slurry on the wall of the distal segment (4A);

FIG. 5 is an enlarged, sectional view of a catheter constructed according to a third general embodiment, where the distal-end segment includes a thin-walled, relatively stiff inner lining or coat and a thicker-walled, relatively more flexible outer tube;

FIG. 6 is a view of a catheter embodiment like that shown in FIG. 5, but where the thickness of the inner tube in the distal-end segment is tapered on progressing toward the distal end of the catheter;

FIG. 7 is an enlarged sectional view of a catheter device constructed according to a fourth general embodiment, where the distal-end segment has a chemically hardened inner coating;

FIG. 8 illustrates an enlarged, fragmentary sectional view of one preferred type of guidewire for use in the catheter of the invention;

FIG. 9 shows a test configuration for measuring the resistance of a catheter being advanced over a helically-wound wire;

FIG. 10 shows plots of the force required to advance a standard polymer-tube catheter (dashed lines) and a catheter constructed according to the invention (dash-dot lines) over a smooth-surface wire, as a function of the position of the catheter on the FIG. 9 helical wire turns;

FIG. 11 illustrates a typical small-vessel pathway in which a serpentine configuration like that illustrated in FIG. 11 is encountered; and

FIG. 12 is an enlarged cross-sectional view of the catheter of the invention being advanced over a serpentine portion of a guidewire.

DETAILED DESCRIPTION OF THE INVENTION

Before the present catheter, catheter device and process for using such is described, it is to be understood that this invention is not limited to the particular catheter devices, components, constructions and materials specifically recited as such may, of course, vary. It is to be understood that the terminology used herein is for purposes of describing particular embodiments only, and is not intended to be limiting since the scope of the present invention will be limited only by the appended claims.

It must be noted that as used in the specification and claims, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a coiled construction" includes a plurality of such constructions, reference to "an anti-friction material" includes a plurality of such materials and reference to "the bending" includes reference to a plurality of bends made by the catheter and/or guidewire and so forth.

FIG. 1 shows a catheter device 10 constructed according to the present invention. The device includes a catheter 12 in the form of an elongated tubular member which will be described below, and a guidewire, here indicated at 14. The catheter device is designed for accessing a target site which can be reached only along a small tunnel-like tortuous path within a target tissue, as will be described with reference to FIGS. 11 and 12 below.

With continued reference to FIG. 1, the catheter 12 includes an elongate outer tubular surface 16 having proximal end 18 connected at a fitting and a distal end. The tubular member 12 can be between about 50-300 cm in length, and is typically and more preferably between about 100-200 cm in length. The hollow cylindrical area inside the tube 12 or inner lumen 22 (FIG. 2) extending between the two ends has a preferred diameter of less than about 40 mil, and preferably between about 12-30 mil. One mil is one thousandth of an inch, i.e., 0.001 inch. In one embodiment, the diameter of the inner lumen is between about 2-7 mils greater than that of the diameter of the guidewire 14 carried within the catheter 12. The lumen 22 may have a substantially uniform cross-sectional area along its length, or may vary along the catheter length, for example, the distal end may taper toward a small diameter in a direction away from the proximal end.

As will be described in greater detail below, the catheter or tubular member 12 includes a relatively stiff proximal segment or segment means 24 (a first section) terminating proximally at end 18, and a relatively more flexible distal segment or segment means 26 (a second section) terminating distally at end 20. Thus the first segment or proximal segment 24 has greater structural integrity, a greater resistance to bending, and is more stiff than the second or distal segment 26 which has less structural integrity, greater flexibility, and less resistance to bending than the first section. Although either segment can be comprised of a variety of materials it is important that the materials be modified and/or structured so as to obtain the desired differential with respect to the flexibility of the two sections. The greater stiffness and less flexibility of the first section 24 relative to the softer or more flexible material of the second segment 26 can be measured quantitatively by the bending forces necessary to bend either segment through an equivalent angle. The distal segment is at least about 5 cm long, typically between about 5 cm in length, with the proximal segment providing the remainder of the length of the catheter tubular member. Typically, the proximal segment makes up between about 70%-90% of the total length of the tubular member, and the relatively flexible distal segment makes up the remaining 10%-30% of the length.

Throughout this disclosure, the first or proximal section of the catheter will be referred to as stiffer or less flexible than the second or distal section of the catheter which will be referred to as more flexible and bendable than the first or proximal section. The degree of stiffness, flexibility and/or bendability can be measured quantitatively using tests known to those skilled in the art such as the American Society for the Standard of Testing of Materials (hereinafter referred to as ASTM). In connection with the present invention, the materials used in the catheter were tested using ASTM D747. It should be pointed out that ASTM D747 is generally used in connection with the testing of rectangular pieces of material. Since the present invention is in the form of a tubular catheter, the D747 test was modified for use in connection with the testing of tubular pieces of material. For purposes of this disclosure the ASTM test designated a D747 is incorporated herein by reference for purposes of disclosing methods of testing material with respect to their flexibility.

The above referred-to ASTM D747 modified test was carried out in connection with sections of tubular material to be used for the first or proximal section of the catheter device. The proximal or first section tested under modified D747 testing procedures should give a result of 15,000 psi or more. Results as high as 60,000 psi or more are possible. However, it is more likely that the results will yield a reading of about 40,000 psi or more and are most preferably in the range of about 25 to 35,000 psi with one particular embodiment providing a result of 29,000 psi.

Tubular segments of material to be used in connection with the second section or distal section of the catheter were also tested using the ASTM modified D747 testing procedure. These more flexible or bendable segments gave a reading of 10,000 psi or less and are generally in the range of about 7,000 to 3,000 psi. Although some particularly flexible tubings may have readings below 3,000, e.g., about 1,000 psi, a particularly preferred material has a reading of about 5,500 psi.

Based on the above information, it can be seen that the most flexible D747 reading for the stiffer material (about 15,000 psi) is substantially greater than the least flexible material to be used in connection with the more flexible distal end (about 10,000 psi or less). In general, the modified D747 test reading for the stiffer or proximal section is at least 50 percent greater than the reading for the more flexible or distal segment, and is more preferably more than 100 percent greater. When given in terms of ranges, it can be pointed out that the stiffer or proximal segment is in the range of 2 to 30 times the D747 reading of the more flexible section and more preferably in the range of about 3 to 8 times greater than the D747 reading of the more flexible section.

The inner surface wall of the distal segment 26 of the catheter is constructed such that or comprised of a material such as a low-friction coat which allows the guidewire to be moved axially within the catheter through regions of sharp bends or turns. Four general embodiments of the internal surface of the distal segment are described below in Sections A-D.

The catheter device further includes a proximal end fitting 28 through which the guidewire is received, and through which fluid material can be introduced into the catheter lumen. One standard fitting which is suitable has a guidewire 0-ring seal 30 which can be compressed to provide a suitable seal about the guidewire, while still allowing the wire to be rotated (torqued) and advanced or retracted axially within the catheter, during a catheter placement operation. Fluid material can be introduced into the catheter lumen, for example, from a syringe, through port 32.

A. Catheter With Flexible-Sleeve Distal Segment

FIG. 2 shows an enlarged cross sectional view of a region of catheter 10 in the region of transition between the two segments, indicated at 2--2 in FIG. 1. As seen, proximal segment 24 is composed of inner 34 and outer 36 coaxial tubes which are tight-fitting and/or essentially integral with respect to each other. The stiffness in the proximal segment 24 is provided predominantly by an additional coaxial tube 34. The inner, stiffer tube 34 is preferably polypropylene or high-density polyethylene tubing having a wall thickness of between about 2-4 mils. The outer, more flexible tube is preferably low density polyethylene or silicone tubing, also having a preferred wall thickness of between about 2-4 mils. As defined herein, high- and low-density polyethylene have the usual trade meaning which is applied to the density grade of polyethylenes which are commonly used in extrusion. With respect to the present invention it is not critical that the materials be low and/or high density polyethylenes or silicon material. Any materials having differing properties of the type described above can be used to make up the two different tubular members. What is important is that the outer tube be comprised of a material of less flexibility and structural integrity and greater flexibility relative to the inner tube which is comprised of a material of greater structural integrity and stiffness and less ability to bend relative to the outer tube. By comprising the tubes of the different types of materials it is possible to include the first segment which is stiffer and less bendable