U.S. patent application number 10/057708 was filed with the patent office on 2002-08-01 for guidewire for positioning a catheter against a lumen wall.
This patent application is currently assigned to PROLIFIX MEDICAL, INC.. Invention is credited to Huynh, Joan, Kupiecki, David J., Mah, Kathy M., McFann, Timothy B., Passafaro, James D., Patterson, Greg R., Perkins, Roger W., Williams, Ronald G..
Application Number | 20020103446 10/057708 |
Document ID | / |
Family ID | 23653111 |
Filed Date | 2002-08-01 |
United States Patent
Application |
20020103446 |
Kind Code |
A1 |
McFann, Timothy B. ; et
al. |
August 1, 2002 |
Guidewire for positioning a catheter against a lumen wall
Abstract
The present invention relates to a guidewire having a shaped
three dimensional guide section. In the preferred embodiment the
guide section is helical, and exerts an outward radial force on a
lumen the guidewire is constrained in. The outward radial force can
be measured or calculated according to methods of the present
invention. Also described is a system comprising a guidewire and
catheter where the force of the catheter exerts on a body lumen can
also be calculated. Apparatus and methods of making the guidewire
are also disclosed, as well as alternative embodiments of the
guidewire.
Inventors: |
McFann, Timothy B.; (Redwood
City, CA) ; Mah, Kathy M.; (Mountain View, CA)
; Passafaro, James D.; (Los Gatos, CA) ; Perkins,
Roger W.; (San Jose, CA) ; Huynh, Joan; (San
Jose, CA) ; Patterson, Greg R.; (Pleasanton, CA)
; Williams, Ronald G.; (Menlo Park, CA) ;
Kupiecki, David J.; (San Francisco, CA) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
PROLIFIX MEDICAL, INC.
680 West Maude Avenue, suite 2
Sunnyvale
CA
94086
|
Family ID: |
23653111 |
Appl. No.: |
10/057708 |
Filed: |
January 24, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10057708 |
Jan 24, 2002 |
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09417228 |
Oct 13, 1999 |
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09417228 |
Oct 13, 1999 |
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09289850 |
Apr 12, 1999 |
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09417228 |
Oct 13, 1999 |
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08966001 |
Nov 7, 1997 |
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09417228 |
Oct 13, 1999 |
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09290510 |
Apr 12, 1999 |
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09417228 |
Oct 13, 1999 |
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09389772 |
Sep 3, 1999 |
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60081631 |
Apr 13, 1998 |
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60081614 |
Apr 13, 1998 |
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60103447 |
Oct 7, 1998 |
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60081631 |
Apr 13, 1998 |
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60081614 |
Apr 13, 1998 |
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60103447 |
Oct 7, 1998 |
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60099079 |
Sep 4, 1998 |
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Current U.S.
Class: |
600/585 |
Current CPC
Class: |
A61B 2017/320766
20130101; A61B 2017/00867 20130101; A61B 17/320758 20130101; A61M
25/09 20130101; A61B 2017/22042 20130101; A61B 17/221 20130101;
A61M 2025/09175 20130101; A61B 2090/064 20160201; A61M 2025/09083
20130101; A61M 2025/09141 20130101; A61B 2017/2217 20130101; A61M
2205/0266 20130101 |
Class at
Publication: |
600/585 |
International
Class: |
A61B 005/00 |
Claims
What is claimed is:
1. A portable force resistance meter for determining a catheter
resistance value comprising: an aperture for receiving a catheter
distal end; a deflection lever for moving said catheter distal end
a quantifiable distance; a load cell linked to said deflection
lever for determining a beam stiffness value for said catheter
distal end; a microprocessor for converting said beam stiffness
value into a force resistance value using the quantifiable distance
and the length of the catheter distal end; and a display unit.
2. A method of determining the outward radial force of a helical
guide section comprising the steps of: (a) securing a helical guide
section in a force measuring device; (b) fixing each end of the
helical guide section in said force measuring device; (c) pulling
the ends of the helical guide section apart; (d) measuring the
force required to pull the helical guide section apart while
tracking the linear displacement of the helical guide section
during the pull; (e) measuring the corresponding radial
displacement of the guide section while the guide section is being
pulled; and (f) determining the radial force of the guide section
from the measured axial force, the measured linear displacement and
the measured radial displacement.
3. A method of determining the outward radial force of a catheter
over a helical guide section comprising the steps of: (a) measuring
the beam stiffness of a catheter; (b) measuring the beam stiffness
of a helical guide section; (c) measuring the axial force required
to elongated a helical guide section to one half the helical guide
section unconstrained diameter; and (d) determining P.sub.eff.
4. The method of claim 2, wherein said force measuring device is a
portable hand held device.
5. A method of matching a catheter to a guidewire for a medical
procedure requiring precision radial positioning comprising the
steps of: (a) determining a lumen diameter of a body lumen to be
treated; (b) selecting a catheter to be used in said body lumen;
(c) choosing the effective length of said catheter; (d) measuring a
catheter resistance value of said catheter over said effective
length; and (e) matching a guidewire having a compressible guide
section to said catheter resistance value to ensure said guidewire
has sufficient outward radial force when compressed to deflect said
catheter into said lumen wall.
6. The method of claim 5, wherein step (d) further comprises
measuring the beam stiffness in a portable force measuring device
and converting the beam stiffness of said catheter into said
catheter resistance value.
7. An apparatus for shape setting a wire with a curved three
dimensional guide section, said apparatus comprising: a mandrel
having a temperature stable core, at least one screw thread having
spaced apart roots capable of mechanically receiving a wire; and at
least one retaining device for securing said wire within said
spaced apart roots and preventing said wire from slipping or
shifting.
8. The apparatus of claim 7, wherein said mandrel has a minor
diameter between 0.5 and 20 mm.
9. The apparatus of claim 7, wherein said mandrel has a non-uniform
minor diameter.
10. The apparatus of claim 7, wherein said mandrel has a uniform
linear geometry.
11. The apparatus of claim 7, wherein said mandrel has a
non-uniform linear geometry.
12. The apparatus of claim 7, wherein the mandrel has a plurality
of cross section geometries.
13. The apparatus of claim 7, wherein said cross sectional
geometries are any combination of regular and irregular shapes.
14. The apparatus of claim 7, wherein the distance between said
roots is between 0.026 mm and 12.7 mm.
15. The apparatus of claim 7, wherein the distance between said
roots is preferably between 1 mm and 6 mm.
16. The apparatus of claim 7, wherein said mandrel is hollow.
17. The apparatus of claim 7, wherein said mandrel is made of
brass.
18. The apparatus of claim 7, wherein said mandrel is made of any
form of steel.
19. The apparatus of claim 7, wherein said mandrel is made of a
ceramic material.
20. The apparatus of claim 7, wherein the retaining device is a
clip.
21. The apparatus of claim 7, wherein the retaining device is a
tube slidably fit over said mandrel.
22. A system for shape setting a guidewire comprising: a rotatable
chuck; a mandrel having at least one screw thread engraved along at
least a portion of said mandrel axial length; at least one spring
tension arm for providing tension to a core wire as said core wire
is wrapped around a mandrel; and a heating element for heating said
core wire to a shape setting temperature.
23. The system of claim 22, wherein said rotatable chuck is mounted
on a lathe.
24. The system of claim 22, further comprising an automated
operation of the core wire winding and heating process through a
series of stepper motors .
25. The system of claim 22, wherein said spring tension arm is a
restraining means for securing said core wire about said
mandrel.
26. The system of claim 24, wherein the automated operation is
handled by a computer.
27. A method of manufacturing a guidewire with a curved three
dimensional guide section comprising the steps of: (a) wrapping a
core wire around a mandrel; (b) securing the core wire about the
mandrel; (c) heating the mandrel assembly to a temperature between
300 degrees C. and 800 degrees C.; (d) stopping the heating; (e)
cooling the mandrel assembly to room temperature; and (f)
unwrapping the core wire from the mandrel.
28. The method of manufacturing a guidewire as in claim 27, further
comprising the steps of: (g) coating the core wire with a
biocompatible material; (h) attaching a filament wire to the core
wire; and (i) providing an atraumatic tip at the distal end.
29. The method of claim 27, wherein step (a) comprises a core wire
composed at least partially of a shape memory material.
30. The method of claim 27, wherein step (a) comprises a core wire
composed at least partially of a shape memory alloy.
31. The method of claim 27, wherein step (a) comprises a core wire
composed of nickel-titanium.
32. The method of claim 27, wherein step (a) comprises a core wire
composed of stainless steel with a shape memory material laminate
coating.
33. The method of claim 27, wherein step (a) comprises a core wire
composed of a stainless steel and shape memory sandwich.
34. The method of claim 27, wherein step (a) comprises a core wire
composed of at least one wire within a shape memory material
matrix, said shape memory matrix being formed in particular to
operate as a guidewire.
35. The method of claim 27, wherein step (a) further comprises a
core wire having a diameter between 0.0005" and 0.020".
36. The method of claim 27, wherein the mandrel further comprises a
fixed channel for providing a predetermined shape setting.
37. The method of claim 36, further comprising a mandrel minor
diameter between 0.5 mm and 20 mm.
38. The method of claim 37, wherein the mandrel preferably
comprises a mandrel diameter of 1 to 6 mm.
39. The method of claim 27, wherein step (a) further comprises
ensuring the core wire is wound such that there is no slack in the
wire coils.
40. The method of claim 27, wherein step (b) further comprises a
means for securing the wire about the mandrel to assure the core
wire does not unravel or slip.
41. The method of claim 27, wherein step (c) further comprises
heating the mandrel assembly to a temperature between 450 and 550
degrees C.
42. The method of claim 41, wherein the mandrel assembly remains at
temperature from 1 to 10 minutes.
43. The method of claim 27, wherein step (e) further comprises
quenching the mandrel assembly.
44. The method of claim 28, wherein step (g) is omitted.
45. The method of claim 28, wherein step (h) is omitted.
46. The method of claim 28, wherein step (i) is omitted.
47. The method of claim 28, wherein step (g) further comprises
coating the core wire with a laminate material for reducing the
guidewire coefficient of friction.
48. The method of claim 28, wherein step (i) further comprises
attaching an atraumatic element to said core wire.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is a division from U.S. patent application
Ser. No. 09/417,228 (Attorney Docket No. 017903-000580) filed Oct.
13, 1999, which is a continuation-in-part of application Ser. No.
09/289,850 (Attorney Docket No. 017903-000560) filed Apr. 12, 1999,
which claimed the benefit of provisional application no.
60/081,631; (Attorney Docket No. 17903-000520), and No. 60/081,614
(Attorney Docket No. 017903-000510) both filed Apr. 13, 1998, and
No. 60/103,447 (Attorney Docket No. 017903-000530) filed Oct. 7,
1998; a continuation-in-part of application Ser. No. 08/966,001
(Attorney Docket No. 017903-000500) filed Nov. 7, 1997; of
application Ser. No. 09/290,510 (Attorney Docket No. 017903-000550)
filed on Apr. 12, 1999, which claimed the benefit of provisional
application Nos. 60/081,631; 60/081,614; and 60/103,447; and a
continuation-in-part of application Ser. No. 09/389,772 (Attorney
Docket No. 017903-001010) filed on Sep. 3, 1999; of which claimed
the benefit of provisional application No. 60/099,079 (Attorney
Docket No. 017903-001000) filed on Sep. 4, 1998. The full
disclosures of each of these prior regular and provisional
applications are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to an apparatus and
method of making a guidewire with a preformed three dimensional
profile for use in guiding a catheter or other medical device to a
desired location within a body lumen.
[0004] 2. Description of the Background Art
[0005] Medical guidewires are used primarily to facilitate the
placement of catheters and endoscopic instruments within the
tortuous paths of body conduits. For example, if it is desirable to
place a catheter within the vascular system of a patient, a
guidewire is first inserted into the vessel and then guided through
the tortuous path desired for the catheter. Then the catheter is
threaded over the guidewire. As the catheter is advanced it tends
to follow the direction of the guidewire so that it ultimately
negotiates the same tortuous path. Once the catheter is in its
final operative position, the guidewire can be removed leaving the
catheter to perform its desired function.
[0006] Guidewires are traditionally utilized to negotiate the
complex vascular system of a patient to guide a medical device,
(e.g., a catheter) to a desired location. It has been in the past
of paramount importance for the guidewire to have a shape which
provides for superior navigation a patient's vascular system.
Inventions in the field include guidewires with floppy tips,
improved methods of manufacturing, increased torqueability and
improved friction reducing features to help catheters move over the
guidewires. Thus the focus of the prior art has been to create a
guidewire with the ability to create a path along which a catheter
could follow to reach a particular site of the body.
[0007] Guidewires often use transition areas of changing diameter
along their length. A smooth transition gives the guidewire the
ability to better negotiate tight bends in the anatomy of the
patient. The transition area of a guidewire may be long or short,
that is the change from one diameter along the length of the
guidewire may occur over a few millimeters, or several centimeters.
In the past the use of transition areas has been combined with the
use of a filament wire which covers the narrower distal section of
the guidewire. The combination, well understood in the art,
provides the distal tip of the wire with a greater flexibility to
steer through the vasculature of a patient, while the filament wire
provides added strength and radiopacity. The filament wire can also
be used as a fastening point for the attachment of an atraumatic
tip. Examples of guidewires using the combination of transition
areas and filament wires are described in Colon et al., (U.S. Pat.
No. 5,402,799) and Ashby et al., (U.S. Pat. No. 5,622,184). Others
have modified the basic design by using other materials, such as
Johanson et al., (U.S. Pat. No. 5,596,996). However all of the
prior art to date has used guidewires for essentially the same
purpose, to navigate the anatomy of a patient and direct a catheter
to a particular sight within a body lumen. The medical procedure to
be carried out is then conducted by the catheter. There are
specialized guidewires which have been developed which attempt to
do the job of a catheter using a modified guidewire. Two examples
are guidewires with imaging and non-imaging sensors.
[0008] However there remains a need for a guidewire which can steer
a catheter more particularly to a precise position within the
vascular system of the patient. More particularly it would be
beneficial to be able to manufacture a guidewire able to direct a
catheter to a particular side of a lumen in the event a physician
wishes to treat one side of a body lumen and not another, or be
able to direct a catheter to precise locations of a body lumen.
Straight guidewires are unable to perform this feat, however a
novel guidewire has been disclosed in co-pending patent application
Ser. No. 08/966,001 which is capable of steering catheters to a
particular side of a body lumen. At least some of these objectives
will be met by the embodiments of the present invention described
below.
BRIEF SUMMARY OF THE INVENTION
[0009] The present invention relates to medical wires, specifically
guidewires and perfusion wires. In general the wires share a
generally straight proximal section and a distal section having a
curved three dimensional profile. The three dimensional profile
usually defines a helical section having a relaxed diameter and a
constrained diameter. The use of various materials and
manufacturing techniques produces the variety of wires
disclosed.
[0010] In a first embodiment, a guidewire for guiding another
device to a desired location within a body lumen is described. The
guidewire has a generally straight proximal section, and a guide
section which defines a helical or other curved three dimensional
profile. The three dimensional profile of the guide section is
diametrically larger than the profile of the proximal section. The
guide section is preferably made from a shape memory alloy and
provides a curved path for another medical device to follow. The
guide section has sufficient flexibility to assume a generally
straight configuration when the guide section is extended through
the lumen of a guiding member, such as a catheter, or is otherwise
constrained.
[0011] In a second embodiment, a guidewire having a generally
straight proximal section and a distal section having a helical
support section is described. The helical support section defines a
curved three dimensional profile that is diametrically larger than
the proximal section. The helical support section is capable of
elongation into a substantially straight profile when constrained
and expansion into a wider diameter when unconstrained. The helical
support section exerts an outward radial force (W.sub.r) less than
20 pounds per inch, preferably less than 15 pounds per inch,
usually less than 10 pounds per inch, and often less than 5 pounds
per inch when axially extended so the diameter of the helical guide
section is half the relaxed diameter. Exemplary ranges of outward
radial force are from 0.001 pound per inch to 3 pounds per inch,
usually from 0.01 pound per inch to 1 pound per inch.
[0012] In a third embodiment, a perfusion wire is disclosed with a
generally straight proximal section and a distal section having a
helical support section. The helical support section defines a
curved three dimensional profile that is diametrically larger than
the diameter of the proximal section. The helical perfusion section
is capable of elongation into a substantially straight profile hen
constrained and expansion to a larger diameter (W.sub.r) when
unconstrained. The helical perfusion section exerts an outward
radial force in excess of 10 pounds per inch, preferably 20 pounds
per inch, and often 100 pounds per inch, or higher, when axially
extended so the constrained diameter is half the unconstrained
diameter.
[0013] A system is described comprising a guidewire having a
straight proximal section and a distal section. The distal section
having a helical guide section capable of changing geometry when
constrained in a lumen. The helical guide section exerts and
outward radial force less than 15 pounds per inch, preferably less
than 15 pounds per inch, usually less than 10 pounds per inch, and
often less than 5 pounds per inch. Exemplary ranges of outward
radial force are from 0.001 pound per inch to 3 pounds per inch,
usually from 0.01 pound per inch to 1 pound per inch. A catheter is
included in the system that is capable of tracking over the
guidewire wherein the catheter is capable of following the three
dimensional profile of the helical guide section. The catheter
exerts an outward radial force (Peff) on a lumen at substantially
the point of entry of the guidewire into the catheter, thus causing
the catheter to exert an outward radial force less than 4 pounds
per inch, preferably less than 2 pounds per inch, usually less than
1 pound per inch. Exemplary ranges of outward radial catheter force
are from 0.0001 pound per inch to 2 pounds per inch, usually from
0.001 pound per inch to 1 pound per inch. The precise outward
radial force can be determined using an equation.
[0014] The guidewire of the present invention may be manufactured
using an apparatus comprising a mandrel with a heat stable core.
The mandrel has at least one screw thread having spaced apart roots
for receiving a guidewire. The mandrel also has at least one
retainer for ensuring the guide wire is securely fixed to the
mandrel. The method of using the apparatus follows the steps of
wrapping a guidewire around the mandrel, securing the wire about
the mandrel with the retaining device, heating the mandrel to a
desired temperature, stopping the heating, cooling the mandrel and
unwrapping the wire from the mandrel. A system for automating the
manufacturing process is also described.
[0015] These and other embodiments are further detailed in the
descriptions that follow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1A shows a plan view of a unconstrained guide
section.
[0017] FIG. 1B shows a constrained guide section.
[0018] FIG. 1C shows three key relationships in a simple visual
format.
[0019] FIG. 1D show the beam stiffness variables for a
catheter.
[0020] FIGS. 2A and 2B show a guidewire with a helical guide
section.
[0021] FIGS. 3A, 3B, and 3C shows a guide section with reference to
the elements for a low outward radial force (W.sub.r).
[0022] FIG. 4 shows the relationship between a catheter, guidewire
and lumen.
[0023] FIGS. 5 and 5I show two core wire geometries prior to
treatment according to the present invention.
[0024] FIGS. 5A-5H illustrate various mandrels and mandrel
assemblies.
[0025] FIGS. 5J and 5K show a system for automated manufacturing of
the guide section.
[0026] FIGS. 5L-5Q illustrate various cross sections of the guide
section wire.
[0027] FIG. 6 is a graph of the outward radial force (W.sub.r).
[0028] FIGS. 7A and 7B are graphs of the P.sub.eff value against
radius of the guide section.
[0029] FIG. 8 show various forms of the perfusion wire.
[0030] FIGS. 9A and 9B show a portable force resistance meter.
DETAILED DESCRIPTION OF THE INVENTION
[0031] The following detailed descriptions are the best presently
contemplated modes of carrying out the invention. This description
is not to be taken in a limiting sense, but is made merely for the
purpose of illustrating general principles of embodiments of the
invention. The scope of the invention is best defined by the
appended claims. In certain instances, detailed descriptions of
well-known devices, compositions, components, mechanisms and
methods are omitted so as to not obscure the description of the
present invention with unnecessary detail.
[0032] 1. Definitions and Table of Variables.
[0033] While common guidewire terminology is used herein,
clarification of certain terms are necessary. Terms used in the
field of guidewire manufacturing and guidewire usage often vary
among physicians and practitioners. The present invention is
designed to take a straight core wire and reshape it into a form
suitable for use in interventional procedures. The "core wire" is
the back bone of a guidewire. Frequently made from a bio-compatible
alloys such as stainless steel or nickel-titanium, these wires are
usually larger at the proximal side and tapered to a thinner
diameter at the distal end. The taper of the guidewire can be
constant along the length, or broken up into transition lengths.
Along the distal tip of the guidewire, a small coil is often slid
over and secured to the core wire. The small wire which is used to
make the coil is referred to herein as the "filament wire." The
diameter of a regular guidewire used in cardiology procedures at
the present time is generally about 0.014." For purposes of
discussion the core wires used in the present invention follow the
same geometries of the core wires used in other guidewires.
[0034] A tapered core wire is used as the starting material for
making a guidewire having a three dimensional profile. By "three
dimensional profile" we refer to the shape the wire assumes after
it has gone through the procedure detailed below. Once the shape
setting step is complete, the core wire can be modified as any
other guidewire may be by techniques well understood in the art.
While most guidewires are used to guide a catheter from a point of
entry from outside a patients body to a desired location, the
guidewire of the present invention is preferably utilized to direct
a catheter to precise locations in a body lumen after the catheter
has already been guided to the general site of interest using a
standard guidewire. The present invention may be used for both
introducing the catheter and for localized guidance if the
guidewire is composed of a two way shape memory material.
[0035] Shape memory alloys are commonly used in medical devices.
Shape memory alloys are often used for making guidewires and
stents. A wide variety of shape memory alloys are currently
available (see Table 1). Among the more common alloys used is
nickel-titanium. The principle feature these alloys possess is
their ability to deform in a super elastic range. This alloys these
alloys to change their shape to a greater degree than other
materials, without being permanently deformed. This ability makes
shape memory alloys a preferred material for the present invention.
However the present invention does not depend on super elastic
properties and can function with in the elastic range of standard
metal alloys such as stainless steel. Furthermore full recovery of
the material is not necessary so materials may also operate
according to the present invention with a small degree of plastic
deformation.
1TABLE 1 Shape Memory Alloys Transformation-Temp Range Alloy Sample
Composition (Degrees Celsius) Ag-Cd 44/49 at. % Cd -190 to -50
Au-Cd 46.5/50 at % Cd 30 to 100 Cu-Al-Ni 14/14.5 wt % Al 3 to 4.5
wt % Ni Cu-Sn 15 at. % Sn -120 to 30 Cu-Zn 38.5/41.5 wt % Zn -180
to -10 Cu-Zn-X (X = a few wt % -180 to 200 Si, Sn, Al) In-Ti 18/23
at % Ti 60 to 100 Ni-Al 36/38 at. % Al -180 to 100 Ni-Ti 49/51 at %
Ni -50 to 110 Fe-Pt 25 at % Pt -130 Mn-Cu 5/35 at % Cu -250 to 180
Fe-Mn-Si 32 wt % Mn, 6 wt % Si -200 to 150
[0036] Examples of superelastic metal alloys, including
nickel-titanium, which are usable to form the core of the guidewire
of the present invention are described in detail in U.S. Pat. No.
4,665,906. The disclosure of U.S. Patent No. 4,665,906 is expressly
incorporated herein by reference insofar as it describes the
compositions, properties, chemistries, and behavior of specific
metal alloys which are super elastic within the temperature range
at which the guide section of the guidewire of the present
invention operates, any and all of which super elastic metal alloys
may be usable to form the core of the guide section of the
guidewire.
[0037] Regardless of the materials used the helical guide section
or perfusion section according to the present invention will exert
an outward radial force (W.sub.r) when constrained to a helical
radius less than the unconstrained helical radius. The variables
that are used to determine the outward radial force (W.sub.r) of
the helical guide section and the perfusion section, as well as the
force a catheter exerts at the point of contact (Peff) over a
helical guide section are given in Table 2.
2TABLE 2 Variables for Determination of W.sub.r and P.sub.eff
Symbol Definition P.sub.eff Force the distal end of the catheter
exerts against the lumen wall D Diameter of the wire comprising the
guide section R Radius of guide section measured from axis of guide
section R.sub.0 Initial radius of guide section measured from axis
of guide section R.sub.k Distance between the axis of the helical
guide section and the center of the wire comprising the helical
guide section S.sub.tot Total length of wire used to make the
helical guide section N Number of active turns in guide section
E.sub.g Modulus of elasticity of the wire comprising the guide
section I.sub.g Moment of inertia of the wire comprising the guide
section G Shear modulus of elasticity of the wire comprising the
guide section F.sub.a Axial force .delta..sub.a Axial displacement
of the guide section R.sub.c Radius of the center lumen of the
catheter through which the guide wire passes L.sub.c Effective
length of the catheter in bending E.sub.c Modulus of elasticity of
the catheter I.sub.c Moment of inertia of the catheter
.delta..sub.c End displacement of catheter L.sub.eff Effective
length of contact between the distal section of the catheter and
the lumen wall W.sub.r Outward radial force of a helical support
section when constrained
[0038] By "outward radial force" the description means a force
exerted by a compressed helical guide section as it seeks to
recover the strain it has experienced while being compressed. There
are two predominate sources for compression of the helical guide
section. First the helical guide section may be deployed within a
lumen having a smaller diameter than the unconstrained diameter of
the helical guide section. Under this condition the entire helical
guide section may experience a uniform compression or constraining
force preventing the helical guide section from releasing the
strain energy it possesses. The outward radial force can be uniform
along the entire length of the helical guide section, or can vary
based on the amount of compression the guide section is
experiencing. The second manner a guide section experiences
compression, causing an outward radial force, is when a catheter
tracking over the guide section causes further compression of the
guide section. As the catheter advances, local deformations
immediately proximal and distal to the catheter appear on the
length of the guide section. These deformations are the result of
the strain the catheter exerts on the guidewire as it is advanced.
The guide section seeks to resist deformation and recover the
strain to return to its natural, relaxed shape. Any force the guide
section exerts as it seeks to recover its natural state is an
"outward radial force" with respect to the intended operation and
usage of the present invention. The outward radial force of the
guide section less the beam stiffness of the catheter and the
adjustments for the local deformations of the guidewire as the
catheter is tracking over it constitute the value (P.sub.eff).
[0039] A "catheter resistance force" is the force the catheter
exerts on the guide section. This resistive force is a result of
the catheter being displaced by the guide section off of its
natural axis. The catheter may be stiff or flexible in the distal
end as it moves over the guidewire. The stiffer the catheter, the
greater the force the catheter exerts on the guide section. Any
force the catheter exerts on the guide section at the distal tip of
the catheter moving forward is the "catheter resistance force" with
respect to the intended operation and usage of the present
invention.
[0040] Referring now to FIG. 1A, the helical guide section 202 is
shown in an unconstrained state. When the helical guide section 202
is unconstrained, it is possible to measure the radius R.sub.o of
the helical guide section 202. R.sub.o is measured from the center
axis of the guide section 212 to the outside of the wire comprising
the helical guide. The total length of the wire comprising the
helical guide section (S.sub.tot) can either be measured directly
from the straightened helical guide section or calculated using
geometric relationships and measured parameters of the helical
guide section 202. The total number of active coils of the helical
guide section (N) can be measured directly from the helical guide
section 202. The diameter of the wire 202d comprising the helical
guide section 202 can be measured directly from the wire comprising
the helical guide section. Lastly, the shear modulus of elasticity
of the wire (G) may be determined from any readily available
engineering reference manual.
[0041] FIG. 1B shows the helical guide section 202 axially extended
so the constrained radius R is half the unconstrained radius
R.sub.o. At this time it is possible to measure or calculate the
distance from the center axis of the helical guide section 212 to
the center of the wire comprising the helical guide section
(R.sub.k) (FIG. 1C). The axial displacement of the helical guide
section (.delta..sub.a) 216c is the axial extension of the helical
guide section 202 as a result of the helical guide section 202
being constrained by a lumen 300 of a certain radius (R). Because
the helical guide section 202 is in contact with the wall of the
lumen 302, the helical guide section 202 conforms to the radius of
R. Conversely, when an axial force F.sub.a is applied to the
helical guide section 202, the result is an axial displacement
.delta..sub.a that will also result in the helical guide section
202 reducing to the radius of R. The two situations are equivalent
in terms of the mechanical response of the helical guide section
202. The axial force (F.sub.a) applied to the helical guide section
202 results in the axial displacement .delta..sub.a.
[0042] The beam stiffness of the guidewire is needed to determine
the outward radial force (W.sub.r). In the system of the present
invention a determination of the catheter stiffness is also
required. Using a standard beam stiffness test it is possible to
calculate or measure the beam stiffness of a catheter. The
effective beam length of the catheter in bending (L.sub.c) can also
be measured. Finally it is necessary to determine the effective
length of contact between the catheter distal end 406 and the wall
of the lumen (L.sub.eff). Once the beam stiffness measurements or
calculations are completed, it is possible to determine the modulus
of elasticity and the moment of inertia for both the helical guide
section 202 and the catheter 400. These calculations produce the
necessary EI data to determine W.sub.r and P.sub.eff. The details
of determining W.sub.r and P.sub.eff are described below in section
7 and 8 respectively.
[0043] FIG. 1C shows the value of R.sub.k as the distance from the
axis of the helical guide section 212 to the center of the wire
comprising the helical guide section 202. FIG. 1C' shows R.sub.c as
the radius of the center lumen of the catheter 400 through which
the guidewire 200 passes. FIG. IC" shows .delta..sub.c as the
displacement of the catheter 400 from its neutral, undeflected
axis. The catheter is shown in the drawing in a perspective view
with the front along the lumen circumference. For clarity the
helical guide section 202 is not shown in this figure.
[0044] FIG. 1D shows the catheter under going a beam stiffness test
(also known as a cantilever test) where L.sub.c is the effective
beam length, F is the force applied to deflect the tip of the
catheter 402 a distance .delta..sub.c.
[0045] 2. Guidewire with Curved Three Dimensional Profile.
[0046] FIG. 2A illustrates an embodiment of a guidewire 200
according to the present invention. The guidewire 200 is preferably
provided with a configuration to enable it to guide, in a
controlled manner, a catheter distal tip 402 (not shown) at and
along the location of a body lumen 300.
[0047] Referring to FIGS. 2A and 2B; the guidewire 200 is provided
with a generally helical guide section 202 adjacent its distal end
204. As shown in FIG. 2A, the helical guide section 202 has a
three-dimensional configuration that approximates the configuration
of a cylindrical lumen wall. The distal end 204 of the guidewire
200 is generally straight and preferably has an atraumatic distal
tip 208. The remainder of the guidewire 200, and in particular, the
proximal section 206, is generally straight, as with conventional
guidewires. The distal section 204 and the proximal section 206 are
axially coplanar with each other, and are preferably coaxial with
respect to each other. In other words, the distal section 204 and
the proximal section 206 are oriented along the same longitudinal
axis. In addition, the distal section 204 and the proximal section
206 are concentric, and can also be eccentric, with respect to the
guide section 202. The proximal and distal extremities of the
helical guide section 202, or the entire helical section, are
preferably provided with sufficient radiopacity so that the helical
guide section 202 can be clearly viewed during fluoroscopic
visualization. The radiopacity can be provided by the use of a
radiopaque wire 203, as shown in FIG. 2B, which can be made of
platinum or gold alloys or other radiopaque wires, and which is
wound around the core wire 101.
[0048] The helical guide section 202 of the guidewire 200 can be
modified so that it has a generally tapered or stepped, or both
tapered and stepped, configuration (not shown).
[0049] For example, the helix of the guide section 202 can be
tapered from the proximal extremity to the distal extremity thereof
so that the helical diameter decreases from the proximal extremity
to the distal extremity. The helix can also be stepped at certain
discrete locations of the guide section 202. In addition, although
the helical guide section 202 of the guidewire 200 is illustrated
as having uniformly configured helixes, it is also possible to
provide the helixes in a manner that they are non-uniform to each
other across the helical length 202.
[0050] As yet another alternative, a plurality of guide sections
202 can be provided in spaced-apart manner at the distal end of the
guidewire 200. For example, two spaced-apart guide sections 202
would be helpful in treating body lumens where restenosis has
occurred at the locations of two spaced-apart implanted stents.
[0051] 3. Guidewire Having a Helical Guide Section with a Low
Radial Force.
[0052] FIGS. 3A, 3B, and 3C show the preferred embodiment of the
present invention. A guidewire 200 with an atraumatic tip 208 is
shown with a helical guide section 202 capable of exerting an
outward radial force (W.sub.r) 102 when compressed. The vectors
102, 102' and 102" represent the larger radial forces generated
from the increased compression of the helical guide section 202. It
is important to note that while the drawings show these as vector
arrows, the outward radial force (W.sub.r) is a distributed force
along the entire length of the 20 helical guide section 202. The
helical guide section 202 further comprises a plurality of helical
winds 214 with a proximal transition period 218 and a distal
transition period 220. The helical guide section 202 also has a
relaxed helical diameter 222 and an axis of extension 212. The
guidewire 200 has a core wire 101 made of a shape memory material
such as nickel-titanium or other shape memory alloy. The actual
outward radial force (W.sub.r) of the helical guide section 202
depends on the composition of the helical guide section 202 when it
is made, the shape it is fashioned into, and the amount of
constraint it experiences. In general for interventional procedures
the total outward radial force (W.sub.r) must be sufficient to
provide a force that can deflect a catheter tip 402 (not shown) in
a controlled manner to abut a lumen wall 302 while at the same time
not damaging the lumen wall 302. The helical guide section 30 202
exerts an outward radial force (W.sub.r) when compressed which is
proportional to the axial extension of the helical guide section
202. The outward radial force (W.sub.r) is distributed along each
helical wind 214 of the guide section 202 in proportion to the
radial compression of the particular wind. That is, those helical
winds 214 that are more compressed, will have a greater outward
force (W.sub.r). Since it is difficult to accurately measure the
force values of the helical guide section 202 in vivo (when it is
compressed inside a body lumen), the current description uses a
test model in an in vitro setting. That is a bench top test is used
to determine the force values of the helical guide section 202. In
general the helical guide section 202 has a maximum outward radial
force (W.sub.r) less than fifteen (15) pounds per inch when
constrained to a radius that is half the unconstrained radius.
Preferably the outward radial force (W.sub.r) is in between of
0.0001 pound and 3.0 pounds. The actual outward radial force
(W.sub.r) of the helical guide section 202 can be calculated using
the formula:
W.sub.r=(((E.sub.gI.sub.g)F.sub.a.delta..sub.a)/(2S.sub.totR.sub.kR.sub.oR-
.sup.2)).sup.1/2
[0053] Wherein the formula variables are defined above.
[0054] 4. System with Guidewire and Catheter.
[0055] FIG. 4 illustrates the relationship between the guide
section 202 and the catheter distal tip 402. Competing factors must
be considered when the helical guide section 202 is made. A helical
guide section 202 having a helical diameter 322 smaller than the
vessel it may operate in will not provide the necessary
relationship between the guidewire 200 and a catheter distal tip
402 to provide precision location of the catheter distal tip 402 in
a lumen 300. Likewise if the core wire 101 is too stiff, the
helical guide section 202 will not deform when the catheter distal
tip 402 tracks over it. In general the helical guide section 202 of
the present invention will operate using materials generally the
same as used for straight guidewires.
[0056] The use of a shape memory material in the helical guide
section 202 allows the helical guide section 202 to be deformed in
the elastic and super elastic range of the material and return to
the original shape of the helical guide section 202. The inherent
unloading of force, or relaxing of the helical guide section 202
when it is compressed, produces the outward radial force (W.sub.r).
The thicker the core wire 101 of the guidewire 200, the stronger
the outward radial force (W.sub.r), or the greater the resistance
to deformation the helical guide section 202 possesses. The
combination of elements and properties provide the guide section
202 of the guidewire 200 with an outward radial force (W.sub.r)
sufficient to deflect a catheter distal tip 402 into the lumen wall
302 as the catheter 400 is being advanced over the guide section
202. This relationship holds true as the helical diameter 322 of
the guide section 202 compresses from its free state to conform to
the lumen diameter.
[0057] When a catheter 400 is tracking over the guide section 202
while the guide section 202 is pushing against the lumen wall 302,
the outward radial force the catheter exerts (P.sub.eff) against
the lumen wall 302 is determined from the value of the force the
guide section exerts (W.sub.r) plus a term for the energy release
of the guide section and the torsional energy of the guide section
less the catheter beam stiffness. The relationship can be expressed
as:
P.sub.eff=(((E.sub.gI.sub.g)F.sub.a.delta..sub.a)/(2S.sub.totR.sub.kR.sub.-
oR.sup.2)).sup.1/2(L.sub.eff)+E.sub.gI.sub.g[((1/R.sub.o)-(1/R))
((1/R.sub.oR.sup.2)-(1/R.sub.cR.sup.2))].sup.1/2+((96F.sub.a.sup.2R.sup.2-
N)/(d.sup.4G))-((3(E.sub.cI.sub.c).delta..sub.c)/(L.sub.c.sup.3)).
[0058] Wherein the variables are defined above.
[0059] 5. Apparatus and Methods for Manufacturing Wire with a
Helical Guide Section.
[0060] FIGS. 5 and 5I illustrate a typical core wire 101 that has
been ground down for use in the present invention. The core wire
101 has a tapered region 120 that begins at the most proximal grind
down 116, or at the point the core wire begins to taper if the
grind down is a gradual and constant type 110. In a step down grind
configuration (FIG. 5I) of the core wire 101, the barrels 118
between step down grinds 116, 116' and 116" have a constant
diameter. In the preferred embodiment, three step down regions are
used. However the present invention may be made with a single grind
down that is either gradual along the entire length of the grind
down region, or of variable decreasing diameter along the length of
the grind down region. It should be appreciated that the strength
of the guide section of the wire will be decreased as the diameter
of the core wire 101 is reduced. Thus it is preferred to maintain
the core wire diameter along the length of the core wire to be
consistent. The most distal barrel is the distal tip 108. The
intermediate barrel 100 forms the guide section 202 after heat
setting in the preferred embodiment. The proximal barrel is the
proximal section 110. Proximal to the proximal grind 116 is
unmodified core wire 101.
[0061] FIG. 5A illustrates a plan view of a mandrel 500 in its
basic form. The mandrel 500 has a proximal end 502 and a distal end
504 for reference. A helical screw thread 505 is engraved into the
mandrel 500. The screw thread 505 has a defined pitch 508 used to
establish the distance between the coils of the core wire once the
shape setting procedure is complete. The screw thread 505 has
spaced apart roots 506 for receiving the core wire 101. It is
important the mandrel 500 be made from a temperature stable
material for the operation of making the shaped guidewire. The
mandrel 500 may be made of brass, steel, ceramics or any other
material which will retain its shape at temperatures up to 800
degrees Centigrade. The diameter of the mandrel between the bottom
of the roots 506 is the minor diameter 528. The minor diameter 528
determines the minimum inner diameter of the core wire 101 after
the shape setting is complete.
[0062] FIG. 5B shows a mandrel 500 with three different pitches
508, 508' 508" that can be used to produce a guidewire where the
pitch is uneven along the length of the three dimensional profile
of the wire. FIG. 5C shows another mandrel 500 where the diameter
of the helical winds may be varied. Because of the ability of shape
memory alloys to assume a tremendous assortment of shapes, the
mandrel 500 may be designed with any combination of cross section
geometries and diameters. However it should be apparent that the
smoother the outer perimeter of the wire during usage, the less
traumatic the guidewire will be to the patient. Thus it is
preferred to utilize a regularly curved helical structure when
possible.
[0063] FIGS. 5D and 5E show a series of drawings where the method
of the present invention is employed to produce a guidewire having
a shaped three dimensional profile. The mandrel 500 in FIG. 5D is
shown with a core wire 101 being introduced into the proximal end
502. The winding procedure may be done by hand. If done by hand,
the operator feeds a predetermined length of the core wire 101
through the wire entry port 518 on the proximal tip 502. Once the
appropriate amount is fed through the first wire entry port 518,
the core wire 101 is secured at the proximal end 502 with a
securing means 552. The core wire 101 is wound around the screw
threads 505 either by a machine or an operator, and the core wire
101 is wound tightly so tension remains in the core wire 101 during
the shape setting procedure. The operator must be careful to make
sure each wind in the roots 506 is tight. If the wire is not
tightly wound around the mandrel 500 during the shape setting step
the wire will not retain the shape of the mandrel 500.
Alternatively the operator may feed any length of the core wire 101
through the first wire entry port 518 and simply clip off any
excess core wire 101 that remains after the winding procedure.
[0064] FIG. 5E shows the core wire 101 fully wrapped around the
mandrel 500. The core wire 101 is fed through both wire entry ports
518 on the distal tip 502 and the distal end 504. Once the core
wire 101 is fully wrapped around the mandrel 500, a second core
wire securing means 552 is used at the distal end 504 to make sure
tension remains in the core wire 101 about the mandrel 500. The
core wire 101 and mandrel 500 together comprise the mandrel
assembly 550. The mandrel assembly 550 is then heated to the
appropriate shape setting temperature which corresponds to that of
the shape memory alloy being used. For nickel-titanium alloys, the
temperature is preferably between 200 and 800 degrees Centigrade.
In the case of two way shape memory alloys, the shape setting
temperature should also be between 200 and 800 degrees centigrade
while the transition temperature between austenite and martensite
phases can be any temperature which is not the same as the heat set
temperature.
[0065] FIG. 5F shows the mandrel 500 with a variety of wire entry
ports 518. The main consideration in the design of the wire entry
port 518 is simply to be able to secure the core wire 101 to the
mandrel 500 without damaging the core wire 101. Thus the wire entry
port 518 may be a simple channel, an eyelet 518', threaded pin 518"
or any other receptacle capable of holding the wire in place.
[0066] Alternatively, the core wire 101 may have a filament wire
attached to it before the shape setting procedure is done. In the
alternative method the core wire will have a filament wire tightly
wrapped around the core wire, then be wrapped about the mandrel 500
as detailed above. Either method will produce the guidewire of the
present invention. The completed shape set wire has a form similar
to that shown in FIG. 2A.
[0067] FIG. 5G shows another variation on the securing means used
to provide the tension fit between the core wire 101 and the
mandrel 500. A sleeve 520 with an inner diameter 522 frictionally
engages the outer diameter of the mandrel 500 when the core wire
101 is wrapped around the mandrel 500. Using this embodiment it is
necessary for the core wire 101 to be at least as high as the
mandrel 500 outer surface so the core wire 101 can also
frictionally engage the sleeve 520. Alternatively the sleeve 520
may have a heat stable cushion 524 (FIG. 5H) so that the cushion
524 may fill the gaps 526 in between the root 506 and the core wire
101. The sleeve 520 may be a cylinder or a foldable device which
can be wrapped around the mandrel assembly 550 and then itself
secured in place.
[0068] FIG. 5J shows a plan view of a system according to the
present invention. The system 580 comprises a rotatable chuck 582
for holding the mandrel 500, and a spring tension arm 584 for
maintaining the tension of the core wire 101 while the core wire
101 is loaded onto the mandrel 500. The system 580 also includes a
heating element 586 for providing the heat necessary for
accomplishing the shape setting step of the method described below.
The rotatable chuck 582 may be turned by hand or mounted on a
modified lathe 588. Furthermore the system 580 may be automated by
using a computer controller 590 for handling the rotational speed
of the chuck 582. Speed determination and the proper winding of the
core wire 101 around the mandrel 500 is handled by a plurality of
stepper motors 592. The heating element 586 need not be actual
heaters, but can be any means known in the art to increase thermal
temperatures, such as a salt bath, induction or RF system. An air
cooling fan or blower 594 can be used to cool the mandrel 500 after
the shape setting is finished. FIG. 5K shows an end view of the
system described in FIG. 5J.
[0069] FIGS. 5L through 5Q show alternative core wires 101 which
may be used in the present invention. Any material that can be
shape set at a particular temperature, and has a high degree of
elastic or super elastic behavior may be used in the current
invention. Aside from a core wire of a single material or single
alloy (FIG. 5L), the core wire may represent a complex structure
such as a shape memory alloy hypo-tube 244 with a high density
metal as the core 240 (FIG. 5M). An example would be a gold core
wire with a nickel-titanium hypo-tube, the combination then being
co-axial, and then the two being shape set using the method
described above. The advantage of using a core wire comprising a
sandwich or tube arrangement is greater radiopacity or lateral
strength may be imparted to the core wire, depending on the
particular desire of the manufacturer. FIG. 5N shows a shape memory
alloy 240 as the core element and a different material 244 as the
cladding. FIGS. 5O-5Q show three different cross sections for a
shape memory alloy core wire 101.
[0070] When using the methods below for determining the outward
radial force (W.sub.r) and the force a catheter exerts on a lumen
(P.sub.eff) it should be noted that only the method for the most
common wire diameter (FIG. 5L) has been detailed. The radial forces
for a guide section with a non-circular cross section can be
determined by simply adapting the methods below, and the formula to
adjust for the change in the core wire cross-section.
[0071] 6. Method of Determining the Outward Radial Force of a
Helical Guide Section.
[0072] A method of determining the outward radial force (W.sub.r)
of the guide section 202 using the physical and geometric
properties of the helical guide section 202 as defined above and
solving the following equation for Wr:
W.sub.r=(((E.sub.gI.sub.g))F.sub.a.delta..sub.a)/(2S.sub.totR.sub.kR.sub.o-
R.sup.2)).sup.1/2
[0073] As detailed above, the modulus of elasticity for the guide
section (Eg) can be found in published sources. The moment of
inertia for the guide section (Ig) can be calculated from the known
geometry of the wire comprising the guide section 202. If the wire
comprising the helical guide section 202 is a composite, the
effective E.sub.g and I.sub.g can be calculated for the composite.
The product of E.sub.g I.sub.g in the first term of the equation
for W.sub.r can alternately be determined empirically by performing
a beam stiffness test on a section of the wire comprising the
helical guide section 202.
[0074] The shear modulus of elasticity (G) for the guide section
202 can also be found in published sources. If the wire comprising
the helical guide section 202 is a composite, the effective shear
modulus of elasticity (G) can be calculated for the composite.
Alternately, the shear modulus of elasticity (G) can be determined
empirically by performing a torsional beam stiffness test on a
section of the wire comprising the helical guide section 202.
[0075] Utilizing geometric relationships, the axial displacement of
the guide section (.delta..sub.a) and the distance between the axis
of the helical guide section 202 and the center of the wire
comprising the helical guide section (R.sub.k) can be written in
terms of the radius of the guide section measured from the axis 212
of the guide section to the outer edge of the guide section
(R).
[0076] The axial force (F.sub.a) can be expressed as
F.sub.a=k.delta..sub.a, where k is the axial spring constant for
the helical guide section 202. As such, Fa can be written in terms
of R. Alternately, .delta..sub.a and F.sub.a can be determined
empirically as a function of R: The axial force is measured by
placing the guide section 202 in a force-displacement measuring
instrument (such as an Instron.TM. model 5543, using a 10-pound
load cell). The guide section 202 is subject to a standard axial
force displacement test, with the ends of the guide section 202
fixed in rotation. The load cell of the Instron.TM. is slowly moved
apart so that the guide section 202 of the guide section 202 is
slowly stretched. The Instron.TM. can be programmed to measure on
an incremental basis the force required to stretch the guide
section 202. For example, if the guide section 202 is stretched at
a rate of 1 cm per minute, force measurements can be taken every
millimeter or every six seconds. Once the guide section 202 is
extended to a point such that the guide section 202 is
substantially straight, the test should be stopped.
[0077] Following completion of the axial force and displacement
testing, the guide section 202 is removed from the Instron.TM. and
the radius of the guide section 202 measured using an optical
measurement device. The guide section 202 is displaced axially with
the ends of the guide wire fixed in rotation. The radius R is
recorded at axial displacements .delta..sub.a corresponding to
those at which the axial displacement .delta..sub.a and axial force
F.sub.a measurements were taken.
[0078] Using the experimental setup described above, we can exert
an axial force Fa on the guide section 202 over substantially its
full range of deflection. For example, when measuring a 1 cm length
guide section, use 10-50 discrete deflections. At each deflection,
measure and record the axial displacement .delta..sub.a, axial
force F.sub.a and radius R of the guide section 202. Utilizing this
data, .delta..sub.a and F.sub.a can be determined as a function of
R. Following the determination of the values and relationships
described above, calculate and graph W.sub.r as a function of R of
the helical guide section. An example of which is shown in FIG.
6.
[0079] 7. Method of Determining the Force Exerted by a Catheter
(P.sub.eff).
[0080] A method of determining the outward radial force P.sub.eff a
catheter distal tip 402 exerts against a lumen wall 302 while
traversing a given helical guide section 202 using the physical and
geometric properties of the helical guide section 202 and catheter
400 as defined above and solving the following equation for
Peff:
P.sub.eff=(((E.sub.gI.sub.g)F.sub.a.delta..sub.a)/(2S.sub.totR.sub.kR.sub.-
oR.sup.2)).sup.1/2(L.sub.eff)+E.sub.gI.sub.g[((1/R.sub.o)-(1/R))
((1/R.sub.oR.sup.2)-(1/R.sub.cR.sup.2))].sup.1/2+((96F.sub.a.sup.2R.sup.2-
N)/(d.sup.4G))-((3(E.sub.cI.sub.c).delta..sub.c)/(L.sub.c.sup.3))
[0081] The equation for P.sub.eff is comprised of four terms: the
first three terms are expressions of the outward radial force the
helical guide section 202 exerts on the distal end of the catheter
406, the fourth term is the resistive force of the catheter due to
its beam stiffness. Subtracting the resistive force of the catheter
from the total force exerted outwardly by the helical guide section
202 on the catheter 400 results in the net force of the distal end
of the catheter 406 against the lumen wall 302. If P.sub.eff is
positive the catheter 400 is exerting an outward force on the wall
of the lumen 302. If P.sub.eff is zero the resistive force of the
catheter distal tip 402 is balanced with the outward radial force
the helical guide section 202 is exerting on the catheter distal
tip 402 and the catheter distal tip 402 is resting on the wall of
the lumen 302 but not exerting any force on the wall of the lumen
302. If P.sub.eff is negative the resistive force of the catheter
exceeds the outward force of the helical guide section 202 on the
catheter distal tip 402 and the catheter distal tip 402 is no
longer in contact with the wall of the lumen 302.
[0082] The modulus of elasticity of the catheter (E.sub.c) can be
found in published sources. The catheter's moment of inertia
(I.sub.c) can be calculated from the known geometry of the
catheter. If the catheter is a composite, the effective E.sub.c and
I.sub.c can be calculated for the composite. The product E.sub.c
I.sub.c in the catheter (fourth) term of the equation for P.sub.eff
can alternately be determined empirically by performing a beam
stiffness test on the catheter 400.
[0083] When determining the effective length of the catheter in
bending (L.sub.c) careful consideration must be given to competing
factors. In practice, when using a catheter 400 in a body lumen
300, the maximum distance that the catheter can be deflected is
determined by the diameter of that lumen 300. The distance the
catheter 400 will be deflected in use in a body lumen 300 is
estimated to be between 0.5 mm and 5 mm. The specific maximum
deflection can be determined by the greatest radius of the largest
guide section 202 intended for use with this catheter 400. The
effective beam length of the catheter being used in a body lumen
300 varies depending on the body lumen 300 in which the catheter
400 is inserted. In the tortuous anatomy of the coronary arteries
the effective beam length of the catheter 400 may be short.
However, if the catheter 400 is inserted into a straight lumen, the
effective beam length 410 of the catheter 400 will be longer. Here,
the effective beam length L.sub.c of the catheter 400 in use is
estimated to be between 1 cm and 5 cm.
[0084] The intent of the cantilever beam test is to model the
effective beam length of the catheter in use. Determining an
effective beam length L.sub.c that models the actual use of the
catheter can be difficult. The effective beam length L.sub.c of the
catheter in the cantilever beam test should best be determined
based on its specific usage. Because the stiffness of a beam
increases inversely with length, a limit on the minimum length of
the catheter used during the cantilever beam test is defined. For
definition purposes in the present invention, it will be defined
that the minimum effective beam length L.sub.c of the catheter 400
will be that distance that the catheter 400 can be deflected in the
largest lumen 300 expected for use from the center axis of the
lumen 300 to the lumen wall 302 without permanent deformation to
the catheter 400. The maximum deflection distance is defined as the
largest radius of the largest guide section 202 intended for use
with the catheter 400.
[0085] The effective beam length L.sub.c of the catheter 400 for
the cantilever beam test will be determined based on competing
considerations involved for the specific use of the device. It will
be appreciated by those schooled in the art that if the catheter
distal tip 406 is a rigid section, the resistance value of the
catheter 400 could exceed the outward force of the guide section
202. Should the minimum deflection required above result in
permanent deformation to the catheter distal tip 406 during the
cantilever beam test, that effective beam length L.sub.c is too
short to be a representative model of the catheter 400 in actual
use.
[0086] To measure the force of the catheter, mount the catheter 400
in an instrument capable of measuring force and deflection (e.g.,
an Instron.TM.), with the catheter 400 having an effective beam
length L discussed above. The catheter 400 must be prepared such
that its stiffness will be that seen during its use. Thus if the
guide section 202 passes through a lumen in the catheter during
use, the guide section 202 must be inserted into the catheter 400
prior to testing in such a way that the guide section 202
contributes to the stiffness of the catheter 400 but does not
externally restrict the deflection of the catheter 400. Measure and
record the force required to deflect the catheter orthogonal to its
major axis from zero deflection (its natural, free state) to a
deflection at a minimum equal to the greatest free state 30 radius
of the largest guide section 202 intended for use with this
catheter 400.
[0087] To graph the equation of P.sub.eff for all possible R of the
helical guide section, there are several possible methods to
generate the dependent variables R.sub.k, .delta..sub.a, F.sub.a,
.delta..sub.c and L.sub.eff: Utilizing geometric relationships,
.delta..sub.a, R.sub.k and .delta..sub.c can be written in terms of
the R. L.sub.eff can be calculated using the theory of contacting
surfaces (e.g., Hertz contact theory) and as such, L.sub.eff can be
written in terms of R.
[0088] Alternately, L.sub.eff can be determined empirically (e.g.,
deploy the catheter 400 and helical guide section 202 in a plastic
tube and measure L.sub.eff using polarized light to visualize the
contact between the catheter distal end 406 and the tube wall).
[0089] Following the determination of the values and relationships
described above, calculate and graph P.sub.eff for all possible
values of R. If P.sub.eff is zero or positive for all possible
values of R (See FIG. 7A), the catheter distal end 406 will remain
in contact with the wall of the lumen 302 for all possible values
of R. If P.sub.eff is negative for any possible value or R (See
FIG. 7B), the distal end of the catheter 406 will not be in contact
with the lumen wall 302 for any value of R. The lower limit on R is
the radius from the center of the catheter to the outside of the
catheter. Because the helical guide section 202 conforms to the
lumen 300, a lumen 300 with a radius equal to the radius of the
catheter is the smallest lumen in which the catheter will fit. If
the lumen radius is smaller than that of the catheter 400, the
catheter 400 cannot operate within that lumen 300. As such, the
lower limit on R of the helical guide section is the radius of the
outside of the catheter. The upper limit on R is the free,
unconstrained radius of the helical guide section R.sub.0. At
R.sub.0 the helical guide section 202 is in its free, non-deformed
state and as such, the helical guide section 202 is no longer
capable of exerting a force against the wall of the lumen 300.
[0090] 8. Helical Perfusion Wire with a High Radial Force.
[0091] FIG. 8 shows an alternative embodiment of the present
invention. The perfusion wire 800 can be made having an outward
radial force (W.sub.r) in excess of 20 pounds per inch. Many of the
features of the perfusion wire are similar to the wire previously
described. However the perfusion wire requires a helical support
section 802 made of a more robust material than that of the helical
guide section 202. The wire cross sections illustrated in FIGS. 5M
and 5N provide greater structural integrity and outward radial
force (W.sub.r) when made of a strong inner material such as
stainless steel with a shape memory cladding like
nickel-titanium.
[0092] The perfusion wire 800 is designed for deployment within a
blood vessel 700 that is either diseased and substantially
occluded, or has been perforated and collapsed due to loss of local
blood pressure. In deployment of the perfusion wire a guide
catheter 801 is used to cross the region where the perfusion wire
800 is to be deployed. The guide catheter 801 is then retracted
while the perfusion section 802 is deployed. Once free of the
constraints of the guide catheter 801, the perfusion section 802
resumes its natural shape. The perfusions section exerts an outward
radial force (W.sub.r) sufficient to open a passage through a
collapsed blood vessel, or substantially occluded blood vessel
without danger of damaging the vessel further, or deforming the
guide catheter 801.
[0093] 9. Portable Force Resistance Meter.
[0094] FIGS. 9A and 9B illustrate a portable force measuring unit
900. The force measuring unit 900 of the present invention is used
for determining a catheter resistance force value. The preferred
embodiment is a small, hand held unit having a port 902 for
receiving the distal tip 404 of a catheter 402. The receiving port
902 is generally large enough to receive any catheter 402
ordinarily used in a body lumen with an adaptable entry collar 904
which can be secured around the catheter 402 to lock it in place.
The receiving port 902 leads to a test lumen 906 where the catheter
distal tip 404 extends into. The catheter distal tip 404 enters at
the proximal end 906' of the test lumen 906 and the distal tip 404
extends to the distal end 906' of the test lumen 906. At the distal
end 906' of the test lumen 906 a deflection gauge 908 can be used
to push the catheter tip 404 a precise distance off the axis 12 of
the test lumen 906. A load cell 910 is connected to the deflection
gauge 908 to determine the beam stiffness of the catheter 402.
[0095] A microprocessor 912 is used to collect and interpret the
data collected by the load cell 910 and the test lumen 906. A
display unit 914 then indicates the catheter beam stiffness value
for use in matching an appropriate guidewire 200 to the catheter
402. FIG. 9B illustrates the electronic element organization of the
hand held force meter 900.
[0096] While the present invention has been described in the above
description, the scope of the present invention is broader than can
be reasonably described in a single document as will be come clear
to an individual of skill in the art upon review of the present
disclosure and the appended claims.
* * * * *