U.S. patent application number 13/692455 was filed with the patent office on 2013-04-18 for introducer sheath with encapsulated reinforcing member.
This patent application is currently assigned to Cook Medical Technologies LLC. The applicant listed for this patent is Cook Medical Technologies LLC. Invention is credited to William L. Howat, David Christian Lentz.
Application Number | 20130095228 13/692455 |
Document ID | / |
Family ID | 41401928 |
Filed Date | 2013-04-18 |
United States Patent
Application |
20130095228 |
Kind Code |
A1 |
Howat; William L. ; et
al. |
April 18, 2013 |
INTRODUCER SHEATH WITH ENCAPSULATED REINFORCING MEMBER
Abstract
An introducer sheath and a method for making the sheath. The
sheath includes a fluoropolymer liner having a passageway extending
longitudinally therethrough. An inner jacket is positioned
longitudinally over the liner, and the inner surface of the inner
jacket is bonded to the outer surface of the liner. An outer jacket
is positioned longitudinally over the inner jacket, and the inner
surface of the outer jacket is bonded to the outer surface of the
inner jacket. A reinforcing coil is encapsulated within the inner
jacket and the outer jacket.
Inventors: |
Howat; William L.; (Laconia,
NH) ; Lentz; David Christian; (Bloomington,
IN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Cook Medical Technologies LLC; |
Bloomington |
IN |
US |
|
|
Assignee: |
Cook Medical Technologies
LLC
Bloomington
IN
|
Family ID: |
41401928 |
Appl. No.: |
13/692455 |
Filed: |
December 3, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12198484 |
Aug 26, 2008 |
8343136 |
|
|
13692455 |
|
|
|
|
Current U.S.
Class: |
427/2.28 |
Current CPC
Class: |
A61M 25/0045 20130101;
A61M 25/00 20130101; A61M 25/0012 20130101; A61M 25/005 20130101;
A61M 25/0662 20130101 |
Class at
Publication: |
427/2.28 |
International
Class: |
A61M 25/00 20060101
A61M025/00 |
Claims
1. A method for forming an introducer sheath, comprising:
positioning an inner liner over a mandrel, said inner liner having
a passageway extending therethrough, and having an outer surface;
applying a solution comprising a polymer dissolved in a solvent to
said outer surface of said inner liner; evaporating the solvent,
leaving a layer of the polymer on the outer surface of the inner
liner, said layer comprising an inner polymer layer; positioning a
reinforcing member around the inner polymer layer; applying an
outer polymer layer over the reinforcing member; and exposing an
assembly comprising the inner liner, inner polymer layer,
reinforcing member and outer polymer layer to sufficient heat to at
least partially melt the inner polymer layer and outer polymer
layer such that a bond is formed therebetween, and such that said
inner polymer layer is bonded to said liner outer surface, said
reinforcing member being encapsulated within said inner and outer
polymer layers.
2. The method of claim 1, wherein said solution is applied to said
liner outer surface by at least one of submersion of the liner and
mandrel into the solution, spraying the solution onto the outer
surface of the liner, and coating the solution on the outer surface
of the liner.
3. The method of claim 1, wherein said layer of polymer on the
outer surface of the inner liner has a thickness between about
0.0001 and 0.001 inch (0.0025 and 0.025 mm) after evaporation of
the solvent.
4. The method of claim 3, wherein said thickness is about 0.001
inch (0.025 mm).
5. The method of claim 2, wherein said liner comprises a lubricious
fluoropolymer having a roughened outer surface, and said inner
polymer layer bonds with said roughened outer surface upon said
exposure to heat.
6. The method of claim 2, wherein said dissolved polymer comprises
at least one of a polyether block amide, nylon, and
polyurethane.
7. The method of claim 6, wherein said inner liner comprises a
fluoropolymer, and said solvent comprises a non-polar solvent.
8. The method of claim 7, wherein said fluoropolymer comprises
PTFE.
9. The method of claim 1, wherein said solvent comprises a phenolic
solvent.
10. The method of claim 2, wherein each of said inner and outer
polymer layers comprises at least one of a polyether block amide,
nylon, and polyurethane, and wherein said reinforcing member
comprises a helical coil.
11. The method of claim 10, wherein each of said inner and outer
polymer layers comprises the same polymer composition.
12. The method of claim 1, wherein said inner polymer layer extends
substantially the length of said liner outer surface.
13. The method of claim 1, wherein the assembly is exposed to said
heat in a heat shrink enclosure.
14. The method of claim 13, wherein the assembly is heated to a
temperature of between about 400-500.degree. F. (204-260.degree.
C.).
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of U.S. patent application
Ser. No. 12/198,484, filed Aug. 26, 2008, which is incorporated
herein by reference in its entirety.
BACKGROUND
[0002] 1. Technical Field
[0003] This invention relates to a medical apparatus suitable for
accessing a target site within the body of a patient, and more
particularly, to an introducer sheath suitable for use in
introducing an interventional device into a bodily passageway of a
patient.
[0004] 2. Background Information
[0005] Introducer sheaths are in widespread use in the medical
field for delivering a medical interventional device, such as a
stent, to a target site within a bodily passageway of a patient,
such as the vasculature. In order to reach the target site, the
sheaths are often required to traverse tortuous pathways having
sharp bends and angles. In some instances, and particularly when
traversing such tortuous pathways, the sheaths exhibit a tendency
to kink. Kinking reduces, and often collapses, the effective inner
diameter of the sheath, thereby typically rendering the sheath
unsuitable for its intended use.
[0006] The tendency of a sheath to kink is increased when the
sheath is used to introduce the interventional device into one of
the many smaller vessels that branch off from major vessels. In
this event, the sheath may have insufficient flexibility at the
very point where flexibility is most desired in order to enable
proper positioning of the interventional device. In order to
traverse the narrow confines of, e.g., the vascular system, the
introducer sheath is typically formed of thin-wall construction.
However, thin wall sheaths often have difficulty tracking narrow
vessels, and exhibit an increased propensity to kink. Increasing
the thickness of the sheath wall can minimally improve the level of
kink resistance, as well as the trackability of the sheath. Any
such increase in thickness, however, is inherently undesirable. The
thickness increase limits the ability of the sheath to enter a
narrow vessel, and reduces the diameter of the lumen when compared
to the lumen of an otherwise similar thin-walled sheath. In
addition, a larger diameter sheath necessitates the use of a larger
entry opening than would otherwise be required or desirable.
[0007] One introducer sheath with improved kink resistance is
disclosed in U.S. Pat. No. 5,380,304 to Parker. The introducer
sheath described in the '304 patent comprises an inner liner formed
of a lubricious fluoropolymer, such as polytetrafluoroethylene
(PTFE). A coil is fitted around the inner PTFE liner, and an outer
jacket formed of a heat-formable material, such as nylon or a
polyether block amide, surrounds the inner liner and coil. The
heat-formable material is heat shrunk onto the PTFE outer surface
by enveloping it in a heat shrink tube, and heating the entire
assembly until the material melts. As the heat-formable material
melts, it flows between the spacings of the coil turns, and bonds
to the outer diameter of the PTFE layer. The use of the coil in
this device reinforces the sheath wall, and provides enhanced
kink-resistance to an otherwise thin-walled introducer sheath.
[0008] The introducer sheath described in the '304 patent has
proven to be particularly effective in delivering medical devices
and medicaments to remote areas of a patient's vasculature without
kinking. In order to minimize the cross-sectional profile (i.e.,
the outer diameter) of the sheath, the coil is generally formed of
flat wire, as shown in FIG. 2 of the patent. By utilizing a flat
wire coil, the sheath achieves a high level of kink resistance, and
at the same time, maintains a low cross-sectional profile. The
sheath described in the '304 patent enables the physician to
routinely access, without kinking, target areas of the vasculature
that had previously been difficult, or impossible, to reach.
[0009] With the continuous advances in the medical arts, more and
more features have been developed to enhance the use of such
introducer sheaths. For example, in order to improve the
trackability of such sheaths, introducer sheaths have been
developed wherein the proximal end of the sheath has a higher
stiffness, while the distal end has a lower stiffness. One such
sheath is disclosed in U.S. Patent Publication No. 2001/0034514.
Since the distal portion of the sheath has a lower stiffness (and
therefore is more flexible) than the proximal portion, the sheath
is able to traverse portions of the anatomy that would have been
difficult, if not impossible, to traverse with stiffer sheaths.
Since the proximal portion has a higher stiffness (and is therefore
less flexible) than the distal portion, the sheath maintains the
trackability to traverse tortuous areas of the anatomy. This
presence of the coil reinforcement also enables this sheath to be
kink resistant through a wide range of bending angles.
[0010] U.S. Pat. No. 6,939,337 discloses a sheath having a coil
reinforcement, as well as a braid reinforcement positioned over
(i.e., radially outwardly of) the coil. This sheath utilizes a coil
for the purposes of providing kink resistance in the same manner as
the '304 patent and the patent publication recited above, and also
includes a braid to enhance torqueability and pushability of the
sheath. Each of the patent references cited above is incorporated
herein by reference.
[0011] The improvements cited above have enabled the medical
professional to more easily access areas of the vasculature that
had previously been difficult, if not impossible, to reach. It is
desired to continue to make advancements to enhance usage of such
devices.
BRIEF SUMMARY
[0012] In one form thereof, the present invention is directed to an
introducer sheath. The introducer sheath includes a liner having a
passageway extending longitudinally therethrough. An inner jacket
is positioned longitudinally over the liner, wherein the inner
surface of the inner jacket is engaged with the outer surface of
the liner. An outer jacket is positioned longitudinally over the
inner jacket. The outer jacket has an inner surface bonded to the
outer surface of the inner jacket. A reinforcing member is
encapsulated along a length of the inner jacket and the outer
jacket.
[0013] In another form thereof, the invention is directed to a
method for forming an introducer sheath. An inner liner having a
passageway extending therethrough is provided. A solution
comprising a polymer dissolved in a solvent is applied to the outer
surface of the inner liner. The solvent is evaporated, leaving a
layer of the polymer on the outer surface of the inner liner, which
layer comprises an inner polymer layer. A reinforcing member is
positioned around the inner polymer layer, and an outer polymer
layer is applied over the reinforcing member. The assembly
comprising the mandrel, inner polymer layer, reinforcing member and
outer polymer layer is exposed to sufficient heat to at least
partially melt the inner polymer layer and outer polymer layer such
that a bond is formed therebetween, and such that the reinforcing
member is encapsulated within the inner and outer polymer
layers.
[0014] In yet another form thereof, the invention is directed to an
introducer sheath. A lubricious liner for the sheath is formed of
PTFE. An inner jacket formed of a polyether block amide, nylon, or
polyurethane, is positioned longitudinally over the lubricious
liner. The inner surface of the inner jacket is bonded to a
roughened outer surface of the liner. The inner jacket has a
thickness of about 0.001 inch (0.025 mm). An outer jacket is formed
of the same polymer composition as the inner jacket. The outer
jacket is positioned longitudinally over the inner jacket, and
bonded thereto. A flat wire coil is encapsulated in the inner
jacket and the length of the outer jacket.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a side view of a flexible, kink-resistant
introducer sheath of the present invention, shown in combination
with a dilator and a hub;
[0016] FIG. 2 is a longitudinal cross-sectional view of a portion
of the wall of the introducer sheath of FIG. 1, taken along line
2-2; and
[0017] FIG. 3 is a transverse cross-sectional view of the
introducer sheath of FIG. 1 taken along line 3-3, with the dilator
removed.
DETAILED DESCRIPTION OF THE DRAWINGS AND THE PRESENTLY PREFERRED
EMBODIMENTS
[0018] For the purposes of promoting an understanding of the
principles of the invention, reference will now be made to the
embodiments illustrated in the drawings, and specific language will
be used to describe the same. It should nevertheless be understood
that no limitation of the scope of the invention is thereby
intended, such alterations and further modifications in the
illustrated device, and such further applications of the principles
of the invention as illustrated therein being contemplated as would
normally occur to one skilled in the art to which the invention
relates.
[0019] In the following discussion, the terms "proximal" and
"distal" will be used to describe the opposing axial ends of the
inventive sheath, as well as the axial ends of various component
features. The term "proximal" is used in its conventional sense to
refer to the end of the apparatus (or component thereof) that is
closest to the operator during use of the apparatus. The term
"distal" is used in its conventional sense to refer to the end of
the apparatus (or component thereof) that is initially inserted
into the patient, or that is closest to the patient during use.
[0020] FIG. 1 shows an illustrative flexible introducer sheath 10
according to an embodiment of the present invention. Introducer
sheath 10 includes an outer tube 12, having a distal portion 13 and
a proximal portion 15. Preferably, distal portion 13 tapers to a
tapered distal end 14. An inner passageway 16 (FIG. 3) extends
through sheath 10 in well-known fashion.
[0021] In FIG. 1, sheath 10 is shown in combination with an
optional dilator 18 and connector hub 22. Dilators and connector
hubs for use with introducer devices, such as sheath 10, are well
known, and the particular dilator and hub illustrated in FIG. 1 may
be replaced with various other dilators and hubs known in the art.
As shown herein, dilator 18 extends longitudinally through the
passageway of the sheath. The dilator includes a tapered distal end
19 for accessing and dilating a vascular access site, e.g., over a
wire guide (not shown) by any conventional vascular access
technique, such as the well-known Seldinger technique. .A Luer lock
connector 20 may be attached at the proximal end of the dilator for
connection to a syringe or other medical apparatus in well known
fashion.
[0022] Connector hub 22 is attached about the proximal end of the
sheath during use. Connector hub 22 may include one or more
conventional silicone disks (not shown) for preventing the backflow
of fluids therethrough. Connector hub 22 may also include a side
arm 23, to which a polymeric tube 24 and a conventional connector
25 may be connected for introducing and aspirating fluids
therethrough in conventional fashion.
[0023] FIG. 2 is a longitudinal cross-sectional view of a portion
of the wall of introducer sheath 10 of FIG. 1. This figure
illustrates the layered structure of the sheath wall. FIG. 3 is a
transverse cross-sectional view of introducer sheath 10. The views
of introducer sheath 10 in FIGS. 2 and 3 do not include the
optional dilator 18. As illustrated, sheath 10 comprises a liner
31, having a radially outer surface 32. A thin-walled inner layer
or jacket 35 shields or otherwise covers outer liner surface 32. A
conventional reinforcing member, such as coil 40, is wound or
otherwise fitted around the radially outer surface 36 of the
thin-walled inner jacket 35. A polymeric outer layer or jacket 44
is bonded to the outer surface 36 of inner jacket 35 through the
spaced turns of the coil 40.
[0024] Liner 31 is typically formed of a lubricious material.
Preferably, the lubricious material comprises a fluoropolymer, such
as PTFE or FEP. Lubricious liners for sheaths are well known in the
medical arts, and those skilled in the art can readily select an
appropriate liner for a particular use. The lubricious material
provides a slippery, low friction inner surface 33 to ease
insertion and/or withdrawal through passageway 16 of the dilator or
medical interventional device, such as a stent. Liner 31 preferably
has a substantially uniform inner diameter that extends the entire
length of passageway 16, to allow passage therethrough of an
interventional device having the largest possible diameter.
Preferably, the radially outer surface 32 of liner 31 is roughened
in any conventional manner, such as by machine grinding or chemical
etching, to form an irregular surface to facilitate bonding with
inner jacket 35. The wall of the liner will also preferably have
sufficient structural integrity to prevent the inner jacket and/or
coil turns from protruding into inner passageway 16.
[0025] Inner jacket 35 may comprise a polymeric material capable of
forming a secure bond with liner 31, and more preferably, with the
roughened outer surface 32 of liner 31. Preferably, the inner
jacket comprises a thin layer of a polymeric material, such as a
polyether block amide (PEBA), nylon, or polyurethane. The material
of the inner jacket will preferably be formed from the same, or a
chemically similar, polymeric material as that of the outer jacket
44, to enhance formation of a secure bond therebetween, in a manner
to be described.
[0026] The coil may be formed from well-known materials for such
use in the medical arts, such as a metal, a metal alloy (e.g.,
stainless steel or a shape memory composition such as nitinol), a
multi-filar material, or a composite material. In order to minimize
the cross-sectional profile (i.e., outer diameter) of the sheath,
it is preferred to provide a coil with a conventional flat wire
construction. However, those skilled in the art will appreciate
that coil materials of other cross-sectional configurations, such
as round, oval, and various other geometric configurations, may be
substituted.
[0027] Outer jacket 44 may generally be formed from any composition
commonly used for such purposes in a medical device. As stated, it
is preferred to form outer jacket 44 from the same or a similar
composition as that of inner jacket 35, e.g., a polyether block
amide, nylon, or polyurethane. As a result, a very secure bond can
be formed between these materials. Other outer layer compositions
that are capable of securely bonding, adhering, or otherwise
securely engaging the inner jacket 35 may be substituted.
[0028] One particularly preferred method of forming the inventive
sheath will now be described. Initially, the liner 31 is positioned
over a supporting mandrel in well-known fashion. The ends of the
liner may be knotted or otherwise manipulated in a manner to
prevent the solvent solution (as described hereinafter) from
contacting the mandrel.
[0029] A solution of the inner jacket 35 composition dissolved in a
suitable solvent is prepared for application to the outer surface
32 of liner 31. Typically, the inner jacket material is in a
powdered, pelletized, or other form that promotes dissolution of
the material in the solvent.
[0030] Those skilled in the art will appreciate that the inner
jacket composition is soluble in many common solvents that are
suitable for use herein. Preferably, phenolic solvents such as
meta-cresol and cresylic acid, or various other non-polar solvents
will be utilized. However, many polar solvents, such as
N,N-dimethylacetamide (DMAC) and tetrahydrofuran (THF), are also
generally suitable. Those skilled in the art are well aware of
suitable solvents for dissolving a particular polymer, and may
prefer solvents other than those specifically listed here in a
particular case. Generally, a non-polar solvent is preferred for
use with fluoropolymer inner jacket compositions.
[0031] Preferably, the solvent and the polymer are introduced into
a suitable container, and the container is sealed. The sealed
container is placed in, e.g., a barrel roller to mechanically mix
the solvent and the polymer, thereby promoting dissolution of the
polymer. Alternatively, other conventional mixing methods may also
be appropriate, such as an ultrasonic bath. As still another
alternative, the mixture may be exposed to controlled heat, with
some agitation. Those skilled in the art are well aware of suitable
mixing techniques, and may prefer techniques other than those
specifically identified herein in a particular case.
[0032] In most cases, it is preferred to maintain the concentration
of the polymer in the solvent at 10% by weight, or less. However,
higher amounts (e.g., up to about 50%), may be used in a particular
case. If the concentration of any particular solvent solution
becomes too concentrated, the layer may be too thick to fill the
etchings of the PTFE liner, thereby resulting in a bonding problem.
If the solution has a low polymer concentration (e.g., less than
about 5%), the resulting inner jacket layer may be too thin to
accomplish the objectives of the invention.
[0033] Once the polymer is dissolved in the solvent, this solution
is applied to the liner. Any conventional technique for applying a
solvent solution to a substrate may typically be utilized.
Preferred techniques for applying the solution to the liner include
one or more of the following well-known techniques: submersion of
the liner and mandrel in the solution; spraying the solution onto
the outer surface of the liner; and wiping or otherwise directly
coating the solution onto the outer surface of the liner. Following
application of the solution to the liner by any suitable means, the
solvent is evaporated away from the polymer, e.g., by air drying or
by the application of heat, leaving a layer of the inner jacket
polymer on the liner.
[0034] Following evaporation, the inner jacket will preferably have
a wall thickness between about 0.0001 and 0.001 inch (0.0025 and
0.025 mm). Most preferably, the jacket will have a wall thickness
of about 0.001 inch (0.025 mm). Those skilled in the art can
readily determine an acceptable concentration level of polymer in
the solvent solution, and an acceptable manner of applying the
solution onto the inner liner in order to achieve the desired wall
thickness without undue experimentation. Although the recited range
of wall thicknesses is preferred, those skilled in the art will
appreciate that wall thicknesses greater than, or less than, those
specified here may be suitable in a particular case.
[0035] Those skilled in the art will appreciate that the desired
wall thickness of the inner jacket may be conveniently achieved by
controlling the number of repetitive immersions, sprayings,
coatings, etc., as required in order to arrive at the target
thickness. Although, in theory, the technique described herein can
be used to prepare an inner jacket of virtually any wall thickness,
it will generally be preferred in most instances to maintain the
wall thickness within the optimal ranges described above, so as to
not appreciably increase the outer diameter of the completed
sheath.
[0036] Following application of the inner jacket 35 to the liner 31
as described, the coil 40 may be wrapped, wound, compression
fitted, or otherwise applied around the outer surface 36 of inner
jacket 35 in a conventional fashion. Techniques for applying a coil
to a substrate in an introducer sheath are now well known, and
various conventional techniques will be suitable for use herein.
Non-limiting examples of such techniques are described in the
incorporated-by-reference citations.
[0037] Outer jacket 44 is then applied to the outer surface of the
inner jacket. Generally speaking, any conventional technique for
engaging the outer jacket 44 with the inner jacket 35 may be
utilized. In one preferred technique, outer jacket 44 comprises a
sleeve formed of a composition that is the same or a similar
composition as that of inner jacket 35, in order to promote bonding
therebetween. Those skilled in the art will appreciate, however,
that virtually any composition that is capable of forming a secure
bond with the inner jacket material may be utilized. The sleeve is
positioned over the structure comprising the coil, inner jacket,
liner and the mandrel.
[0038] The entire assembly (comprising the outer sleeve, coil,
inner jacket, liner and mandrel) is then placed in a heat shrink
enclosure formed of a material commonly utilized for such purposes,
such as fluorinated ethylene propylene (FEP). The heat shrink
enclosure is then placed in an oven, and heated to a temperature
(e.g., 400-500.degree. F. (204-260.degree. C.)) sufficient to at
least partially melt the outer jacket composition and the inner
jacket composition. The melted compositions flow into each other,
between the turns of the coil, resulting in the formation of a
secure bond between the inner jacket composition and the outer
jacket composition. Additionally, melting of the inner jacket 35
enhances formation of a bond between the inner jacket and the
roughened outer surface 32 of liner 31. Following formation of the
bonds as described above, the assembly is allowed to cool, and
thereafter removed from the heat shrink enclosure. The mandrel is
then removed from the inner liner.
[0039] As illustrated in FIGS. 2 and 3, when the sheath is formed
in the manner described herein, coil 40 does not directly contact
the outer surface of the liner along a discrete length of the
sheath. Rather, coil 40 is encapsulated within the bonded
compositions that comprise inner jacket 35 and outer jacket 44. As
used herein, the term "encapsulated" means that the coil is
enclosed within the portion of the sheath defined by the inner
jacket and the outer jacket along a length of the sheath. A minor
amount of contact between the coil and the lubricious layer may be
permissible in some instances, and may not appreciably detract from
the objectives of the invention. However, in the most preferred
embodiment the coil is completely encapsulated in the sheath
portions 35, 44.
[0040] Since the inner jacket 35 directly contacts the liner 31
along its outer surface length 32, the entire length of this liner
outer surface is available for bonding with the inner jacket.
Accordingly, a very secure bond may be formed between the liner and
the inner jacket. Since the inner jacket 35 and outer jacket 44 are
formed from compositions that are readily capable of forming a
secure bond therebetween, there is little likelihood of
disengagement of this bond, notwithstanding the presence of the
coil intermediate, or within, the respective layers.
[0041] Although the sheath described hereinabove preferably
utilizes a conventional flat wire coil reinforcement, the teachings
of the present invention are also applicable to sheaths or other
devices having other structures disposed therewithin, such as other
reinforcements. For example, in some embodiments, a braided
reinforcement formed of interwoven wires may be used. Rather than
having any portion of the interwoven wires in direct contact with
the liner, such as the PTFE liner described herein, the wire would
be positioned over an inner jacket applied over the liner as
described. The outer layer then would be bonded in the manner
described above, such that the wire is encapsulated in the heat
shrinkable layer(s), and wherein the innermost layer bonds directly
to the outer surface of the liner along the length of that
liner.
[0042] Those skilled in the art will appreciate that all
dimensions, compositions, etc., described herein are exemplary
only, and that other appropriate dimensions, compositions, etc.,
may be substituted in an appropriate case. For example, other than
the inner jacket described herein, the respective thicknesses of an
inner liner and an outer jacket for an introducer sheath are
conventional, and may be varied based upon the intended use of the
sheath. If desired, the sheath can be formed to have one or more
segments of varying durometer along its length, typically aligned
in a sequence of decreasing durometer from the proximal end to the
distal end in well-known fashion. Additionally, other features
commonly found in sheaths, such as radiopaque markers, rings,
coatings, etc., may also be incorporated into the inventive
structure in well-known manner.
[0043] It is therefore intended that the foregoing detailed
description be regarded as illustrative rather than limiting, and
that it be understood that it is the following claims, including
all equivalents, that are intended to define the spirit and scope
of this invention.
* * * * *