Patent Application
20060084939
The present invention pertains generally to catheters. More particularly, the present invention pertains to articulating segments that can be used to conform a catheter to the tortuous paths and configurations that are operationally necessary for the catheter to be positioned in, or to pass through the vasculature of a patient. The present invention is particularly, but not exclusively, useful as a fluid-tight articulating segment that can effectively serve as a cryo-chamber in the operation of a cryo-catheter.
In general, a catheter is any hollow, flexible tube that can be inserted into a body cavity, duct or vessel for any of a variety of purposes. In each case, to be effective, the catheter must be somehow controllable so that it can be properly positioned in the body. Additionally, a catheter must have the structural capability of performing its intended purpose once it has been properly positioned. Of the many different types of medical catheters that are presently being used, the so-called cryo-catheters are of particular interest for the present invention. As is well known, these catheters are used primarily for the purpose of cryo-ablating tissue in the vasculature of a patient.
Unlike other types of catheters, a cryo-catheter is unique in that it has a cooling segment. Preferably, the cooling segment of a cryo-catheter is capable of being cooled to temperatures as low as approximately eighty-five Kelvin. With this requirement in mind, several competing structural characteristics for the cooling segment of a cryo-catheter become of particular importance. For one, the cooling segment of a cryo-catheter needs to be made of a thermally conductive material. Such materials without modification, however, do not typically have the flexibility that is required for maneuvering a catheter through the vasculature of a patient. Thus, if a thermally conductive material such as stainless steel is to be used, it needs to be somehow structurally modified to achieve the required flexibility. This however, in turn, leads to a consideration of other requirements such as fluid confinement in the cooling segment, and resistance to increases in fluid pressure.
Whatever modifications may be required to construct an effective cryo-catheter, it is clear the resulting structure must be sufficiently strong to confine a pressurized fluid refrigerant in the cooling segment. With this in mind, appreciate that a cryo-catheter is essentially nothing more than a tube. Thus, to accomplish certain of the requirements mentioned above, it must have good “hoop strength” for confining the pressurized fluid. Further, because pressurized fluids are involved, the structure of the cooling segment must also be fluid-tight to prevent any leakage of the fluid refrigerant. At the same time, the cryo-catheter must remain sufficiently flexible so it can be maneuvered while being advanced through the vasculature of a patient. Finally, it must also be sufficiently strong to resist kinking.
In light of the above, it is an object of the present invention to provide an articulating segment for a cryo-catheter that is made with a thermally conductive material which is structurally modified to provide the required flexibility for use in an invasive catheter. Another object of the present invention is to provide an articulating segment for a cryo-catheter which is thermally conductive, is flexible and is sufficiently strong to contain a pressurized refrigerant fluid. Still another object of the present invention is to provide an articulating segment for a cryo-catheter which is relatively simple to manufacture, is easy to use and is comparatively cost effective.
In accordance with the present invention, an articulating segment for use in the cooling chamber of a cryo-catheter includes a tube shaped member that has an outer surface and an inner surface. The tube shaped member defines an axis and it is formed with a helical cut that goes around the axis. Specifically, the cut extends through the wall of the tube shaped member between its outer surface and its inner surface. In addition to this tube shaped member, the articulating segment includes a flexible coating that is positioned on the outer surface of the tube shaped member. This flexible coating covers the helical cut and provides a fluid-tight condition for the lumen that is created in the articulating segment of the tube shaped member.
Structurally, the helical cut in the articulating segment defines a pitch angle (α) that is measured between the cut and the axis of the tube shaped member. Preferably, this pitch angle (α) is in a range between forty-five and ninety degrees. Within this range, the pitch angle (α) can be varied during manufacture to achieve a predetermined flexibility for the segment. More specifically, an increase in the pitch angle (α) will provide increased flexibility for the segment. As a practical matter, this flexibility can be increased to a point where the predetermined flexibility for the articulating segment allows the tube shaped member to be bent with a radius of curvature of approximately fifteen mm.
In line with the description given above, the articulating segment can be thought of as being formed by a flat, narrow, ribbon-like band that is wound into a spiral. Importantly, for enhanced strength, this band has a substantially rectangular-shaped cross-section that is bounded by the upper and lower surfaces, and by opposed first and second edges. In this structure, the helical cut is formed as a gap between the first and second edges of the band. For disclosure purposes, this gap has a depth between the outer and inner surfaces that is in a range of 0.1 mm to 0.2 mm, and it has a width substantially perpendicular to the depth that is formed in a range of 10 microns and 100 microns. As a practical matter, however, unless the articulating segment is being bent, the edges of the band will generally be in contact with each other and, consequently, there will be no effective gap width.
Preferably, the tube shaped member is made of stainless steel or Nitinol and the flexible coating is made of nylon or of a polymer material.
The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which:
Referring initially to
Still referring to
With reference to
Several operational benefits result from the rectangular shaped cross-section of the tube shaped member 20 in distal segment 14. For one, this configuration effectively maximizes the amount of material that is available to resist “hoop stress” in the distal segment 14. Thus, the tube shaped member 20 is able to contain higher fluid pressures inside the lumen 34 of tube shaped member 20 than might otherwise be possible. Further, the surface area 36 of flexible coating 22 in gap 24 that may be directly exposed to fluid pressures in lumen 34 is minimized.
As is also to be appreciated with reference to
Still referring to
As disclosed above, a flexible coating 22 is positioned on the outer surface 26 of the tube shaped member 20 to cover the outer surface 26 and the gap 24. This then effectively provides a fluid-tight condition for the lumen 34. Additionally, as indicated above, the flexible coating 22 provides a degree of lubricity that will assist in the advancement of the catheter 10 into the vasculature of a patient.
In operation, the distal segment 14 of catheter 10 needs to be articulated for several reasons. These reasons include, steerability for the catheter 10 as it is being advanced to position the distal segment 14 at a site in the vasculature of a patient. Also, if the catheter 10 is a cryo-catheter, the distal segment 14 must be able to confine pressurized fluid refrigerants and be configurable to conform with tissue that is to be cryo-ablated. As envisioned for the present invention, these objectives are met by the ability of the structure for distal segment 14 to be bent on a curve of radius “R” as shown in
While the particular Articulation Segment for a Catheter as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.
