Note: Descriptions are shown in the official language in which they were submitted.
CA 02617284 2008-01-31
GUIDEWIRE HAVING LINEAR CHANGE IN STIFFNESS
BACKGROUND OF THE INVENTION
This invention relates to the field of guidewires for advancing
intraluminal devices such as stent delivery catheters, balloon dilatation
catheters,' atherectomy catheters and the like within body lumens.
In a typical coronary procedure a guiding catheter having a
preformed distal tip is percutaneously introduced into a patient's
peripheral artery, e.g. femoral or brachial artery, by means of a
conventional Seldinger technique and advanced therein until the distal tip
of the guiding catheter is seated in the ostium of a desired coronary
artery. There are two basic techniques for advancing a guidewire into the
desired location within the patient's coronary anatomy, the first is a
preload technique which is used primarily for over-the-wire (OTW) devices
and the bare wire technique which is used primarily for rail type systems.
With the preload technique, a guidewire is positioned within an inner
lumen of an OTW device such as a dilatation catheter or stent delivery
catheter with the distal tip of the guidewire just proximal to the distal tip
- of the catheter and then both are advanced through the guiding catheter .
to the distal end thereof. The guidewire is first advanced out of the distal
end of the guiding catheter into the patient's coronary vasculature until
the distal end of the guidewire crosses the arterial location where the
interventional procedure is to be performed, e.g. a lesion to be dilated or a
dilated region where a stent is to be deployed. The catheter, which is
slidably mounted onto the guidewire, is advanced out of the guiding
catheter into the patient's coronary anatomy over the previously
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2
introduced guidewire until the operative portion of the intravascular
device, e.g. the balloon of a dilatation or a stent delivery catheter, is
properly positioned across the arterial location. Once the catheter is in
position with the operative means located within the desired arterial
location, the interventional procedure is performed. The catheter can then
be removed from the patient over the guidewire. Usually, the guidewire is
left in place for a period of time after the procedure is completed to
ensure reaccess to the arterial location is it is necessary. For example, in
the event of arterial blockage due to dissected lining collapse, a rapid
exchange type perfusion balloon catheter such as described and claimed
in U.S. Patent 5,516,336 (McInnes et al), can be advanced over the in-
place guidewire so that the balloon can be inflated to open up the arterial
passageway and allow blood to perfuse through the distal section of the
catheter to a distal location until the dissection is reattached to the
arterial
wall by natural healing.
With the bare wire technique, the guidewire is first advanced by
itself through the guiding catheter until the distal tip of the guidewire
extends beyond the arterial location where the procedure is to be
performed. Then a rail type catheter, such as described in U.S. Patent
No. 5,061, 273 (Yock) and the previously discussed McInnes et at. which
is mounted onto the proximal portion
of the guidewire which extends out of the proximal end of the guiding
catheter which is outside of the patient. The catheter is advanced over
the catheter, while the position of the guidewire is fixed, until the
operative means on the rail type catheter is disposed within the arterial
location where the procedure is to be performed. After the procedure the
intravascular device may be withdrawn from the patient over the
guidewire or the guidewire advanced further within the coronary anatomy
for an additional procedure.
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3
Conventional guidewires for angioplasty, stent delivery, atherectomy
and other vascular procedures usually comprise an elongated core member
with one or more tapered sections near the distal end thereof and a
flexible body such as a helical coil or a tubular body of polymeric material
disposed about the distal portion of the core member. A shapable
member, which may be the distal extremity of the core member or a
separate shaping ribbon which is secured to the distal extremity of the
core member extends through the flexible body and is secured to the
distal end of the flexible body by soldering, brazing or welding which
forms a rounded distal tip. Torquing means are provided on the proximal
end of the core member to rotate, and thereby steer, the guidewire while
it is being advanced through a patient's vascular system.
Further details of guidewires, and devices associated therewith for
various interventional procedures can be found in U.S. Patent 4,748,986
(Morrison et al.); U.S. Patent 4,538,622 (Samson et al.): U.S. Patent
5,135,503 (Abrams); U.S. Patent 5,341,818 (Abrams et al.); U.S. Patent
5,345,945 (Hodgson, et al.) and U.S. Patent 5,636,641 (Fariabi)
For certain procedures, such as when delivering stents around
challenging take-off, e.g. a shepherd's crook, tortuosities or severe
angulation, substantially more support and/or vessel straightening is
frequently needed from the guidewire than normal guidewires can provide.
Guidewires have been commercially introduced for such procedures which
provide improved distal support over conventional guidewires, but such
guidewires are not very steerable and in some instances are so stiff that
they can damage vessel linings when advanced therethrough. What has
been needed and heretofore unavailable is a guidewire which provides a
high level of distal support with acceptable steerability and little risk of
damage when advanced through a patient's vasculature.
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In addition, conventional guidewires using tapered distal core
sections as discussed above can be difficult to use in many clinical
circumstances because they have an abrupt stiffness change along the
length of the guidewire, particularly where the tapered portion begins and
ends. As a guidewire having a core with an abrupt change in stiffness is
moved through tortuous vasculature of a patient, the physician moving
the guidewire can feel the abrupt resistance as the stiffness change is
deflected by the curvature of the patient's vasculature. The abrupt
change in resistance felt by the physician can hinder the physician's
ability to safely and controllably advance the guidewire through the
vasculature. What has been needed is a guidewire, and particularly a
guidewire core member, that does not have an abrupt change in stiffness,
particularly in the portions of the distal section that are subject to bending
in the vasculature and guiding catheter. The present invention satisfies
these and other needs.
SUMMARY OF THE INVENTION
The present invention is directed to an improved guiding device
providing enhanced distal support while having a flexible distal tip to
provide acceptable steerability and little risk of damage to vessel or
chamber linings when advanced through a patient's body lumen such as
veins and arteries.
The guiding member of the present invention has an elongated core
member with proximal and distal core sections and a flexible tubular body
such as a helical coil disposed about and secured to the distal section of
the core member. The distal core section has a plurality of distally
tapering contiguous core segments having tapers of up to 25 and lengths
of up to 15 cm. As used herein the measurement.of tapers is the angle of
a line tangent to the surface of the segment in line with the longitudinal
axis of the core member. The first tapered core segment, which typically
CA 02617284 2008-01-31
has a circular transverse cross-section, preferably tapers from the
diameter of the adjacent proximal core section to a diameter of about half
to about three quarters of the diameter of the adjacent proximal core
section. The second tapered core segment, which also has a circular
5 transverse cross-section, tapers from the smallest diameter of the first
tapered core segment to a diameter of not more than one-half the smallest
diameter of the first tapered core segment.
One presently preferred embodiment includes a first core segment
with a taper in the distal direction and a distally contiguous second core
segment having a taper in the distal direction greater than the taper of the
first core segment. The taper of the first or proximal segment generally
can be up to about 5 , preferably about 0.01 to about 10, more
preferably about 0.011 to about 0.2 . The taper of the second or distal
core segment can be up to about 6 , preferably about 0.01 to about
1.1 , more preferably about 0.015 to about 0.45 .
In another presently preferred embodiment, the second tapered core
segment has a length greater than the first tapered core segment , with
the distal segment generally ranging about 1 to about 1.2 cm, preferably
about 2 to about 10 cm and the distal segment generally about 1 to about
8 cm, preferably about 2 to about 6 cm. The tapered core segments may
have circular transverse cross-sections and straight exterior surfaces, e.g.
frusto-conical shape. However, other shapes are contemplated, e.g.
curved exterior surfaces. Indeed, the taper of the contiguous core
segments may have a continuously changing taper over all or part of both
core segments.
The flexible tubular body such as a helical coil is secured by its
distal end to the distal tip of the distal core section or to the distal tip
of a
shaping ribbon secured to the distal core section in a conventional
fashion. The helical coil may be secured by its distal end by soldering,
CA 02617284 2008-11-27
6
brazing or welding to form a rounded distal tip to the guiding member as
done with commercially available guidewire for procedures within a
patient's coronary artery.
In one presently preferred embodiment of the invention, the
guidewire has an elongated proximal core section having a length of about
65 to about 280 cm and a circular transverse cross-section with a
diameter of generally about 0.010 to about 0.035 inch (0.30-0.46 mm),
typically about 0.012 to about 0.018 inch (0.30-0.46 mm) for coronary
anatomy.
In one presently preferred embodiment of the invention, the second
tapered core segment is preferably followed distally with a manually
shapable flattened core segment of about 1 to 4 cm in length which
preferably has essentially constant transverse dimensions, e.g. 0.001 by
0.003 inch (mm). A helical coil having transverse dimensions about the
same as the proximal core section is secured by its distal end to the
flattened distal tip of the core member, e.g. solder, and by its proximal
end at an intermediate position on the second tapered segment so that
the distal end of the second tapered segment resides within the interior of
the coil. The coil may have a length of about 2 to about 40 cm or more,
but typically will have a length of about 2 to about 10 cm in length.
In one presently preferred embodiment of the invention, the guidewire has
a longitudinal section which tapers proximally to a more flexible proximal
section.
The guidewire of the invention provides the enhanced distal and
proximal support needed for stent deployment, advancement of
atherectomy devices and the like and provides a smooth transition
between the proximal core section and the flattened distal tip of the core
member while exhibiting excellent steerability.
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6a
In another aspect of the invention, an intracorporeal device,
preferably a guidewire, has an elongated member with at least one
longitudinal section having a substantially linear change in stiffness over a
length thereof. A substantially linear change in stiffness of a section of
15
25
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an elongate intracorporeal device may be achieved with an elongate core
member having a tapered profile, tapering distally to a smaller transverse
dimension and configured to produce a linear change in stiffness. The
distal taper of the elongate core may be in the form of a taper having a
continuously changing taper angle, i.e. a curvilinear taper profile, or may
be achieved by a plurality of tapered segments which are longitudinally
short in comparison to the longitudinal length of the tapered section as a
whole.
In embodiments where a plurality of tapered segments are used, the
tapered segments are preferably contiguous or adjacent each other and
have a substantially constant taper angle over the length of each tapered
segment. In a preferred embodiment, the taper angle of each tapered
segment is greater than the taper angle of the segment proximally
adjacent to it. The taper angle and segment length can be controlled from
tapered segment to tapered segment to produce the desired bending
characteristics of the longitudinal section of the core member.
A core member may be ground to a profile which is calculated
mathematically to produce a linear change in stiffness. A useful formula
for generating a substantially linear change in stiffness is
Di 64CL + Do' Q
= 4C
where DL is the diameter of an elongate core member at length L from a
position of starting diameter Do , E is the modulus of elasticity of the
material from which the elongate core member is made , and C is a
constant.
This formula may be used to generate smooth continuous profiles,
or multiple tapered segments where each individual tapered segment has
a substantially constant taper angle. In the latter instance, the taper angle
and length of each tapered segment can vary to produce the overall
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desired effect by having the segmented contour substantially follow the
formula above. In a preferred embodiment, the points between two
adjacent tapered segments, or transition points, have diameters that
substantially follow the formula above for DL. As the number of tapered
segments increases, this embodiment gradually approaches the smooth
continuous curvilinear embodiment. That is, in the limiting case where
the number of tapered segments is large, there is little or no difference in
stiffness between the segmented core and the smooth curvilinear profile
core.
Another approach to generating linear stiffness change in an
elongate intracorporeal involves controlling the moment of inertia at any
given point in a longitudinal section. A useful formula for such an
approach is
IL = CL +10
E
where IL is the moment of inertia of the elongate core member at length L
from a position of starting inertia to , E is the modulus of elasticity of the
core material, and C is a constant that is derived from the boundary
conditions of the longitudinal section, specifically, a desired starting
moment of inertia, finish moment of inertia, length of section of linear
change in stiffness.
A core member with a linear change in stiffness over its length
provides improved advancement and control of the distal end of an
intracorporeal device through a patient's body lumen. The improvement
in handling characteristics results in part from the absence of abrupt
changes in flexibility that can obscure the tactile feedback to the
physician holding the proximal end of the device. In addition, the abrupt
changes in stiffness can cause the device to resist smooth and
controllable advancement because a step or threshold force must be
applied to overcome the abrupt change in stiffness.
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9
These and other advantages of the invention will become more
apparent from the following detailed description of the invention when
taken in conjunction with the accompanying exemplary drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevational view partially in section of a guidewire
embodying features of the invention.
FIG. 2 is a transverse cross-sectional view of the guidewire shown
in Fig. 1 taken along the lines 2-2.
FIG. 3 is a transverse cross-sectional view of the guidewire shown
in Fig. 1 taken along the lines 3-3.
FIG. 4 is an enlarged view of the distal portion of the guidewire
shown in Fig. 1 which indicates the tapers of the distal core section.
FIG. 5 is a partial elevational view of the distal core section of an
alternative embodiment of the invention which has a separate shaping
ribbon extending from the distal extremity of the core member to the
distal end of the coil.
FIG. 6 is an elevational view of a portion of a guidewire having
features of the invention.
FIG. 7 is a transverse cross sectional view of the guidewire of FIG.
6 taken at lines 7-7 of FIG. 6.
FIG. 8 is a transverse cross sectional view of the guidewire of FIG.
6 taken at lines 8-8 of FIG. 6.
FIG. 9 is an elevational view of a portion of a guidewire having
features of the invention in partial section.
FIG. 10 is an elevational view in partial section of a portion of a
guidewire having features of the invention.
FIG. 11 is a graphic depiction of the diameter of -a typical guidewire
core member versus the axial position or length from a fixed reference
point of that diameter along the core member.
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FIG. 12 is a graphic depiction of relative bending stiffness values of
a typical guidewire core member versus length from a reference point
along the core member.
FIG. 13 is a graphic depiction of the diameter of a typical guidewire
5 core member versus the length from a fixed reference point or longitudinal
position of that diameter.
FIG. 14 is a graphic depiction of relative stiffness values of a typical
guidewire core member versus longitudinal position or length along the
core member.
10 FIG. 15 is a graphic depiction of relative stiffness values of a typical
guidewire core member versus longitudinal position or length along the
core member.
FIG. 16 is an elevational view of a section of a guidewire having
features of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Figs 1-3 depict a guidewire 10 which is a presently preferred
embodiment thereof which has a core member 11 with a proximal core
section 12, a distal core section 13 and a helical coil 14. The distal core
section 12 has a first tapered segment 15 and a second tapered core
segment 16 which is distally contiguous to the first tapered core segment.
The second tapered segment 16 tapers at a greater degree than the first
tapered segment and this additional taper provides a much smoother
transition when the distal portion of the guidewire 10 is advanced through
a tortuous passageway. The degree of taper of the first tapered core
segment 15, i.e. the angle between the longitudinal axis 17 and a line
tangent to the first tapered core segment 15 is about 2 to about 10 ,
whereas the taper of the second tapered core segment 16, i.e. the angle
between the longitudinal axis and the second tapered core segment is
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11
larger than the first angle and is about 5 to about 10 0 such as is shown
in the enlarged view of the guidewire 10 in Fig. 4. While only two
tapered core segments are shown in the drawings, any number of tapered
core segments can be employed. Moreover, all of a multiple of tapered
core segments need not have increasing degrees of tapers in distal
direction. However, two or more contiguous tapered core segments over
a length of about 5 to 15 cm should have distally increasing degrees of
tapering.
Typically, the first tapered segment is about 3 cm in length and the
second tapered segment is about 4 cm in length. In a presently preferred
embodiment, the guidewire 10 has a proximal core section 12 of about
0.014 inch (0.36 mm) in diameter, the first tapered core segment has a
diameter ranging from 0.014 inch down to about 0.008 inch (0.36-0.20
mm) and the second tapered core segment has a diameter ranging from
about 0.008 to about 0.002 inch (0.20-0.05 mm). A flattened distal tip
18 extends from the distal end of the second tapered core segment 16 to
the body of solder 20 which secures the distal tip 18 of the core member
11 to the distal end of the helical coil 14. A body of solder 21 secures
the proximal end of the helical coil 14 to an intermediate location on the
second tapered segment 16.
The core member 11 is coated with a lubricious coating 19 such as
a fluoropolymer, e.g. TEFLON available from DuPont, which extends the
length of the proximal core section 12. The distal section 13 is also
provided a lubricous coating, not shown for purposes of clarity, such as a
MICROGLIDE T" coating used by the present assignee, Advanced
Cardiovascular Systems, Inc. on many of its commercially available
guidewires. Hydrophilic coating may also be employed.
The core member may be formed of stainless steel, NiTi alloys or
combinations thereof such as described in U.S. Patent No. 5,341,818
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12
(Abrams et al) . Other materials such
as the high strength alloys described in U.S. Patent No. 5,636,641
(Fariabi), , may also
be used.
The helical coil 14 is formed of a suitable radiopaque material such
as platinum or alloys thereof or formed of other material such as stainless
steel and coated with a radiopaque material such as gold. The wire from
which the coil is made generally has a transverse diameter of about 0.003
inch (0.05 mm). The overall length of the coil 14 is typically about 3 cm.
Multiple turns of the distal portion of coil 14 may be expanded to provide
additional flexibility.
In an alternative embodiment shown in Fig. 5, the flattened distal
segment of the core member shown in Fig. 1 is replaced with a shaping
ribbon 30 which is secured by its distal end to the distal end of the coil
14 and by its proximal end to the distal extremity of the core member 11.
While the specific embodiments described above are directed to
tapered segments with constant tapers along their lengths, the taper need
not be constant. For example, the tapers of contiguous core segments
may be gradually increasing in the distal direction, with the taper, i.e. a
tangent line, crossing the junction between the two adjacent tapers being
a continuous function. Guidewires are generally about 90 to about 300
cm in length, and most commercially available guidewires for the coronary
anatomy are either 175 cm or 190 cm in length.
Multiple tapers may be ground simultaneously or as separate
operations. A centerless grinder with profile capabilities may be used to
grind the tapers simultaneously. A manual centerl'ess grinding may be
employed to create separate tapers in separate operations. Tapers may
also be formed by other means such as chemical means, e.g. etching, or
laser means.
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Another aspect of the invention can be seen in FIG. 6 which is a
distal portion of an.intracorporeal device in the form of a guidewire 40.
The guidewire 40 has an elongated core member 41, with a longitudinal
section 42, the longitudinal section having a substantially linear change in
stiffness along its length 43. The length 43 of the longitudinal section
can be up to 60 cm, preferably about 5 to about 35 cm, more preferably
about 10 to about 25 cm. The longitudinal section 42 tapers distally to a
smaller transverse dimension or diameter to a more flexible distal
segment. A flexible body 44 having a proximal end 45 and a distal end
46 is secured at its distal end 46 to a distal end 47 of a distal segment 48
of the elongate core member 41 by a first body of solder 51. The
proximal end 45 of the flexible body 44 is secured to the. longitudinal
section 42 of the elongate core member by a second body of solder 52.
The longitudinal section 42, and preferably the entire elongate core
member 41 of the guidewire 40 is made from high tensile stainless steel,
or hi-ten 304 stainless steel. The longitudinal section 42 can also be
made from other high strength metals, some of which are precipitation
hardenable, including 304 stainless steel, MP35N, L605. The longitudinal
section 42 may also be made from pseudoelastic alloys, such as NiTi.
The longitudinal section 42 has a curvilinear profile with a smooth
continuous change in taper angle over its length 43. The curvilinear
profile of the longitudinal section 42 preferably substantially follows the
formula
DL=[64cL + D04]4
E;r
where DL is the diameter of the longitudinal section at length L from a
position of starting diameter Do, E is the modulus of elasticity of the core
member material, and C is a constant that is determined by the boundary
conditions of the longitudinal section.
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The constant C is determined by the boundary conditions of a
desired section using the equation
C irEDL-Do)
=
64 L
where a desired starting diameter Do, finish diameter DL, length of the
section having a linear change in stiffness L, and modulus of elasticity E
of the section material are inserted into the equation which is then solved
for C.
A typical modulus of elasticity for 304 stainless steel is
approximately 28 x 106 psi. An example of a set of values for a
longitudinal section 42 having features of the invention are 0.002 inches
for a starting diameter Do , 0.013 inches for a finish or ending diameter
DL, 20 cm for the length of the longitudinal section L, and 28 x 106 psi for
the modulus of elasticity of the core member E. Solving for C yields a
constant value of about 0.005 pound-inches. Another example of a set of
values for a longitudinal section 42 having features of the invention are
0.0025 inches for a starting diameter D0 , 0.0076 inches for a finish or
ending diameter DL, 25 cm for the length of the longitudinal section L, and
30 x 106 psi for the modulus of elasticity of the core member E. Solving
for C yields a constant value of about 0.00049 pound-inches.
Another more generalized approach for achieving a substantially
linear change in stiffness in a longitudinal section 42 or elongate core
member 41 is to vary the moment of inertia along the longitudinal section
according to the formula
IL= CL +10
E
where IL is the moment of inertia of the elongate core member at length L
from a position of starting inertia 10 , E is the modulus of elasticity of the
core material, and C is a constant that is derived from the boundary
conditions of the longitudinal section. The constant C is determined by
CA 02617284 2008-01-31
inserting the values of a desired starting moment of inertia 10, finish
moment of inertia IL, length of section of linear change in stiffness L, and
modulus of elasticity E into the equation and solving for C.
The moment of inertia of a point on a longitudinal section 42 or
5 elongate core member 41 can be varied by controlling the diameter in a
round cross section as discussed above. Other variations in transverse
cross section shape and configuration can be made in embodiments
having non-round transverse cross sections. Finally, because bending
stiffness is equal to the modulus of elasticity multiplied by the moment of
10 inertia, the bending stiffness may be controlled by adjusting the modulus
of elasticity along the length of a longitudinal section 42 or elongate core
member 41.
FIG. 7 is a transverse cross sectional view of the guidewire 40 of
FIG. 6 taken at lines 7-7 of FIG. 6. The elongated core member 41
15 preferably has a round cross section. The core member 41 may optionally
be coated with a lubricious coating 53. The coating 53 is preferably a
hydrophyllic polymer, but may also be made of polymers such as TFE or
the like. FIG. 8 is a transverse cross sectional view of the guidewire 40 in
FIG. 6 taken at lines 8-8 of FIG. 6. The flexible body 44 is in the form of
a helical coil which is disposed about the distal segment 48 of the
elongate core member 41. The distal segment 48 of the elongate core
member is flattened to improve shapability of the distal segment.
FIG. 9 is an elevational view of a guidewire 60 having features of
the invention. The guidewire 60 has an elongated core member 61 with a
longitudinal section 62 having a plurality of tapered segments 63 tapering
distally to a more flexible distal segment 64. Transition points 65 are
disposed between adjacent tapered segments 63. A flexible body
member 66 is disposed over the distal segment 64 and a portion of the
longitudinal section 62. The flexible body 66 has a proximal end 67 and a
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16
distal end 68 with the distal end 68 of the flexible body being secured to
a distal end 71 of the distal segment 64 of the elongated core member 61
with a first body of solder 72. The proximal end 67 of the flexible body
66 is secured to the longitudinal section 62 with a second body of solder
73. In a preferred embodiment, each tapered segment 63 of the
longitudinal section 62 has a substantially constant taper angle with the
taper angle of each tapered segment being greater than the tapered
segment proximally adjacent thereto. Preferably, the diameter of the
longitudinal section 62 at the transition points 65 or alternatively
midpoints 74 of the tapered segments substantially follows the formula
DL=[64CL+D0]4
En
where DL is the diameter of the longitudinal section at a transition point at
length L from a position of starting diameter Do, E is the modulus of
elasticity of the core member material, and C is a constant that is
determined by the boundary conditions of the longitudinal section. The
determination of the constant C is performed in a manner similar to the
determination of the constant C discussed above with regard to the
embodiment of FIG. 6. The tapered segments 63 of the longitudinal
section 62 or core member 61 can be up to 10 inches in length,
preferably about 0.1 to about 5 inches in length, more preferably about
0.25 to about 3 inches in length.
FIG. 10 is an elevational view of a guidewire 80 having features of
the invention. The guidewire 80 is similar to the guidewire 40 of FIG. 6
except that the elongate core member 81 does not extend to a distal end
82 of a flexible body 83. Instead, a shaping ribbon 84 having a proximal
end 85 and a distal end 86 has its distal end 86 secured to the distal end
82 of the flexible body 83 with a first body of solder 88. A proximal end
91 of the flexible body 83 and the proximal end 85 of the shaping ribbon
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84 are secured to a longitudinal section 92 with a second body of solder
93. The guidewire 80 has a longitudinal section 92 configured to produce
a substantially linear change in bending stiffness similar to the longitudinal
section 42 of FIG. 6.
FIG. 11 is a graph of values determined for a typical guidewire core
member with diameter in inches along the vertical axis and length or axial
distance from a starting point on the core member in inches along the
horizontal axis. At the starting point A of the graph, the diameter of the
core member is approximately 0.0022 inches. Point A represents the
core at a distal end of a distal segment. The distal segment of the core
member continues proximally until the distal end of the tapered
longitudinal section of the elongate core is reached, which is represented
by point B on the graph. Moving proximally from the junction of the distal
segment and the tapered longitudinal section, the diameter of the core
member increases proportionally with a length from the junction. This
type of tapered longitudinal section is representative of a typical tapered
guidewire section having a constant taper angle over the length of the
section. The taper diameter increases proximally until the junction
between the tapered longitudinal section meets the constant diameter
section of the elongate core which is represented by point C on the graph.
FIG. 12 is a graph of relative bending stiffness values of the
elongate core member of FIG. 11 along its axial length. As can be seen
from the graph of FIG. 12, the plot of bending stiffness of the tapered
longitudinal section starting at point B and proceeding proximally to point
C is not a straight line. There is a curvature to the plot which becomes
progressively steeper as point C is approached. Near point C, the plot
becomes quite steep, which represents an abrupt change in bending
stiffness in the vicinity of point C.
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FIG. 13 is a plot or graph of the diameter of a guidewire core versus
the axial position of the diameter in a core having a longitudinal section
with a substantially linear change in bending stiffness. The graph begins
at point B at length 0 with the core member having a diameter of about
0.002 inches. Point B of FIG. 13 has a similar starting diameter to point B
in FIG. 11. FIG. 13 is representative a graph of stiffness values for an
embodiment of the invention having a plurality of. tapered segments, with
each tapered segment having a substantially constant taper angle. The
change in diameter or taper angle of the tapered segments is greater at
the distal end of the longitudinal section and decreases proximally. The
slope of the graph or taper angle for each tapered segment is less than
that of the tapered segment that is distally adjacent. The profile of
transition points between each pair of adjacent tapered segments of the
longitudinal section depicted by the graph of FIG. 13 substantially follows
the formula
DL = C 64 CL + D04]4
LEir
where DL is the diameter of the longitudinal section at a transition point at
length L from a position of starting diameter Do, E is the modulus of
elasticity of the core member material, and C is a constant that is
determined by the boundary conditions of the longitudinal section.
FIG. 14 depicts typical relative bending stiffness values of a core
member versus axial or longitudinal position along the length of the core
member. The core member has a longitudinal section with a taper profile
configured to generate a linear change in bending stiffness. The plot from
point B to point C does not change appreciably in slope which indicates a
constant change in stiffness over that section. This graph is not
indicative of the progressively steeper slope found on the stiffness curve
CA 02617284 2008-01-31
19
of FIG. 12 where an abrupt change in stiffness is noted at point C, in
addition to other points.
Bending stiffness can be measured in a variety of ways. Typical
methods of measuring bending stiffness include extending *a portion of the
sample to be tested from a fixed block with the sample immovably
secured to the fixed block and measuring the amount of force necessary
to deflect the end of the sample that is away from the fixed block a
predetermined distance. A similar approach can be used by fixing two
points along the length of a sample and measuring the force required to
deflect the middle of the sample a fixed amount. Those skilled in the art
will realize that a large number of variations on these basic methods exist
including measuring the amount of deflection that results from a fixed
amount of force on the free end of a sample, and the like. Although the
graph of FIG. 14 shows relative bending stiffness in terms of grams per
millimeter, the values shown were derived from a specific test apparatus
using the methods discussed above. Other methods of measuring
bending stiffness may produce values in different units of different overall
magnitude, however, it is believed that the overall shape of the graph will
remain the same regardless of the method used to measure bending
stiffness.
FIG. 15 depicts typical relative bending stiffness values of a
longitudinal section of another embodiment of a core member versus axial
position along the core member. The slope of the graph from point A to
point B is essentially constant, indicating a substantially constant change
in bending stiffness from point A to point B.
Unless otherwise described herein, conventional materials and
manufacturing methods may be used to make the guiding members of the
present invention. Additionally, various modifications may be made to the
present invention without departing from the scope thereof.
CA 02617284 2008-01-31
It may be desirable to have multiple tapered longitudinal sections or
sections having a varied flexibility. Any combination of multiple
longitudinal sections may be used including sections having a substantially
constant taper angle, sections having a substantially linear change in
5 stiffness along a length thereof, or sections of substantially constant
diameter along a length thereof. In FIG. 16, a preferred embodiment of an
elongate core member 99 has a longitudinal section 100 of substantially
linear change in stiffness intermediate. to a distal segment 101 having a
substantially constant diameter and a constant taper section 102 with a
10 constant taper angle increasing in diameter proximally. The distal
segment 101 has a diameter of about 0.002 to about 0.003 inches, and a
length of about 3 to about 6 cm. The longitudinal section 100 having a
substantially linear change in stiffness is about 15 to about 25 cm in
length and tapers to an increased diameter proximally from about 0.002
15 to about 0.003 inches at a distal end to about 0.0065 to about 0.0085
inches at a proximal end. The constant taper section 102 tapers
proximally from a diameter of about 0.0065 to about 0.0085 inches at its
distal end to an increased diameter of about 0.012 to about 0.014 inches
at its proximal end.
