Metal working – Method of mechanical manufacture – Assembling or joining
Reexamination Certificate
1999-02-26
2001-03-13
Hughes, S. Thomas (Department: 3726)
Metal working
Method of mechanical manufacture
Assembling or joining
C156S293000, C156S257000, C264S544000, C604S532000, C604S525000
Reexamination Certificate
active
06199262
ABSTRACT:
FIELD THE INVENTION
The present invention relates to a guiding catheter that combines stiffness that resists bending stress or torque and elasticity that permits straightening without plastic deformation.
BACKGROUND OF INVENTION
Medical catheters generally comprise elongated 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 or aspiration applications, or to negotiate twists and turns, such as in certain cardiovascular applications.
Catheters are typically introduced to the patients body through an introducer sheath. The catheter must generally be straightened to fit through the introducer sheath. Therefore, the catheter must be constructed so that it is elastically resilient enough to go through the introducer sheath without plastic deformation, yet resilient enough to meet the performance needs of the particular medical procedure.
For some applications, an inner catheter having a preformed shape is straightened and placed in an outer guiding sheath. When the inner catheter is extended or the outer sheath withdrawn, the inner catheter assumes its original shape. Again, the inner catheter must be constructed so that it is elastically resilient enough to straighten without plastic deformation, yet resume its original configuration when the outer sheath is removed.
For example, percutaneous translumenal coronary angioplasty (PTCA) requires manipulation of a catheter from a proximal position outside the patient's body through branched or tortuous portions of the patients arterial system for purposes 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.
FIG. 1
illustrates the typical configuration of a conventional left coronary guiding catheter
20
with a dilation balloon
24
in the aorta when engaged with a stenosis
24
in the left main coronary artery during the performance of left coronary artery PTCA. The application of force
22
to advance a dilation balloon across the region of stenosis
26
increases the bending stress
28
on the bend
30
of the guiding catheter
20
. The pre-bent configuration of the guiding catheter
20
, in this situation a left Judkin's configuration, is unable to overcome the resistance at the stenosis
24
, causing distal end
32
to back away from the entrance of the left main coronary artery and the angioplasty balloon catheter
24
to prolapse in the accenting aorta, precluding further progress.
Inability to advance the angioplasty balloon across the coronary stenosis because of instability of the guiding catheter and subsequent prolapse of the angioplasty balloon catheter represents one of the most common reasons for failure during the performance of a coronary angioplasty procedure. The guiding catheter disengages in this circumstance because of its flexibility. The guiding catheter has intrinsic flexibility because it must conform to the configuration of the aorta and aortic arch, which contain both linear and curved segments, during introduction. Insertion of the guiding catheter requires that it be advanced over a guidewire up the aorta, which is relatively straight, and then over the aortic arch, which, as the name implies, is curvilinear.
The stability afforded by guiding catheters typically relates to the limited intrinsic stiffness of these catheters. The stiffness of these prior guiding catheters is subject to a “warm-up” phenomenon (becoming more flexible as they remain in the body and equilibrate to body temperature) and thus varies inversely with the temperature of the device. Hence, these catheters tend to be particularly stiff on introduction into the body, when flexibility is preferable, and yet relatively flexible and hence unstable following exposure to body temperatures during balloon catheter manipulation across a coronary stenosis when rigidity is preferable.
U.S. Pat. No. 4,909,787 (Danforth) discloses a catheter having a closed chamber eccentrically disposed along almost the entire length of the housing such that it virtually encompasses the housing. The catheter preferably contains a relatively elastic segment disposed preferentially along the outer circumference of the curvature of the catheter. The chamber may be filled with a fluid. The catheter is capable of asymmetric elongation when hydrostatic pressure is applied to the chamber, resulting in the development of bending stress and increased rigidity on the distal end as desired by the operator.
U.S. Pat. No. 5,456,674 (Bos et al.) discloses a catheter with variable longitudinal properties. The catheters are manufactured by simultaneously conveying a plurality of streams of different materials to a molding nozzle and merging the streams together to form a catheter. The catheter is manufactured with varying properties along its longitudinal axis corresponding to properties of the constituent streams of materials.
SUMMARY OF THE INVENTION
The present invention relates to a catheter comprising an elongated tube structure having a proximal end and at least one preset curved portion proximate a distal end. The preset curved portion comprising a first material located generally along an outer surface on the outer radius of the preset curved portion and a second material located generally along an inner surface on the inner radius of the preset curved portion. The present catheter is particularly useful as a guiding catheter that combines stiffness to resist bending stress and elasticity to permit straightening without plastic deformation.
The first material preferably has a modulus of elasticity greater than the modulus of elasticity of the second material. Alternatively, the modulus of elasticity of the second material may be greater than a modulus of elasticity of the first material. The first material preferably has a first stiffness greater than a second stiffness of the second material. A third material may be interposed between the first and second materials. The third material preferably has a third stiffness less than the first stiffness, but greater than the second stiffness.
The preset curved portion is capable of assuming a generally straight configuration without plastic deformation. The cross sectional area of at least a portion of the preset curved portion is about 50% of the first material and about 50% of the second material. The first and the second materials are preferably coextruded structure. Alternatively, the first material is bonded to the second material. An outer resilient layer may alternatively extend around the first and second materials. In one embodiment, the one preset curved portion has a bend configuration suitable for performing percutaneous coronary angioplasty.
The present invention is also directed to a method of forming a catheter. The method includes the step of forming an elongated tube structure having a proximal end and at least one preset curved portion proximate a distal end. The preset curved portion comprises a first material located generally along an outer surface of the preset curved portion and a second material located generally along an inside surface of the preset curved portion. In one embodiment, the step of forming the elongated tube structure includes interposing a third material between the first and second materials. The tube structure may be formed by coextrusion or joining discrete segments of material.
Stiffness refers to the ratio of a steady force acting on a deformable elastic medium to the resulting displacement. The modulus of elasticity refers to the ratio of the increment of some specified form of stress to the increment of some specified form of strain. In the catheter art, torque generally refers to a force that causes a catheter to kink or twist (torque failure). Bending stress refers to an internal tensile or com
Blount Steven A
Hughes S. Thomas
Medtronic Inc.
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