U.S. patent application number 13/326093 was filed with the patent office on 2012-07-12 for methods and apparatus for an adjustable stiffness catheter.
Invention is credited to Edward H. Cully, Jeffrey B. Duncan, Benjamin M. Trapp.
Application Number | 20120179097 13/326093 |
Document ID | / |
Family ID | 46455817 |
Filed Date | 2012-07-12 |
United States Patent
Application |
20120179097 |
Kind Code |
A1 |
Cully; Edward H. ; et
al. |
July 12, 2012 |
METHODS AND APPARATUS FOR AN ADJUSTABLE STIFFNESS CATHETER
Abstract
Apparatus and methods for an endovascular catheter that can be
inserted within tortuous body anatomies and then selectively
stiffened and fixed in place. In a particular embodiment, this
stiffness is reversible. The stiffness or a comparable mechanical
characteristic of the catheter assembly may be adjusted to a
relatively low value during insertion (so that it easily navigates
a guide wire or the like), and then subsequently adjusted to a
relatively high value in situ to keep the catheter assembly
substantially fixed in place (i.e., during delivery of an
interventional device).
Inventors: |
Cully; Edward H.;
(Flagstaff, AZ) ; Duncan; Jeffrey B.; (Flagstaff,
AZ) ; Trapp; Benjamin M.; (Flagstaff, AZ) |
Family ID: |
46455817 |
Appl. No.: |
13/326093 |
Filed: |
December 14, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61430303 |
Jan 6, 2011 |
|
|
|
Current U.S.
Class: |
604/95.05 ;
604/524; 604/95.01 |
Current CPC
Class: |
A61M 25/0053 20130101;
A61M 25/0012 20130101; A61M 2025/0025 20130101; A61M 25/005
20130101; A61M 25/0102 20130101; A61M 2205/0266 20130101; A61M
25/0045 20130101; A61M 25/0054 20130101; A61M 2025/0064 20130101;
A61M 25/0051 20130101 |
Class at
Publication: |
604/95.05 ;
604/524; 604/95.01 |
International
Class: |
A61M 25/092 20060101
A61M025/092; A61M 25/00 20060101 A61M025/00 |
Claims
1. A catheter apparatus comprising: a tubular body having a distal
end, a proximal end, and a lumen defined therein; and activation
means for selectably causing the tubular body to enter a first
state and a second state; wherein, in the first state, the tubular
body has a first value of a stiffness metric that is below a
predetermined navigatibility threshold; and wherein, in the second
state, the tubular body has a second value of the stiffness metric
that is above a predetermined rigidity threshold value.
2. A catheter apparatus comprising: a tubular body having a distal
end, a proximal end, and a lumen defined therein; and activation
means for selectably causing the tubular body to enter a first
state and a second state; wherein, in the first state, the tubular
body has a first value of a stiffness metric; wherein, in the
second state, the tubular body has a second value of the stiffness
metric that is greater than the first value; and wherein the
activation means includes a controller communicatively coupled to
the tubular body and adapted to place the tubular body in the
second state by subjecting at least a portion of the catheter
apparatus to a reduction or change in temperature.
3. A catheter apparatus comprising: a tubular body having a distal
end, a proximal end, and a lumen defined therein; and activation
means for selectably causing the tubular body to enter a first
state and a second state; wherein, in the first state, the tubular
body has a first value of a stiffness metric; wherein, in the
second state, the tubular body has a second value of the stiffness
metric that is greater than the first value; and wherein the
activation means includes a controller communicatively coupled to
the tubular body and adapted to place the tubular body in the
second state by subjecting at least a portion of the tubular body
to an increase in axial compression.
4. The catheter apparatus of claim 3, wherein the tubular body
comprises a plurality of axial segments responsive to the increase
in axial compression.
5. The catheter apparatus of claim 4, wherein the controller
includes at least one linkage component mechanically coupled to at
least one of the plurality of axial segments and extending to the
proximal end of the tubular body.
6. The catheter apparatus of claim 5, wherein the tubular body
includes an auxiliary lumen provided therein, and wherein the at
least one linkage component includes at least one wire component
extending through the auxiliary lumen.
7. The catheter apparatus of claim 6, wherein the tubular body
includes at least two auxiliary lumens distributed symmetrically
within the tubular body.
8. The catheter apparatus of claim 7, wherein the at least one wire
includes two or more wires, and the controller includes a gimble
component coupled to the two or more wires, the gimble component
configured to apply substantially equal tension on the two or more
wires.
9. The catheter apparatus of claim 8, wherein the two or more wires
includes four three wires.
10. A catheter apparatus comprising: a tubular body having a distal
end, a proximal end, and a lumen defined therein; and activation
means for selectably causing the tubular body to enter a first
state and a second state; wherein, in the first state, the tubular
body has a first value of a stiffness metric; wherein, in the
second state, the tubular body has a second value of the stiffness
metric that is greater than the first value; and wherein the
activation means includes a controller communicatively coupled to
the tubular body and adapted to place the tubular body in the
second state by subjecting at least a portion of the tubular body
to an increase in radial compression.
11. The catheter apparatus of claim 10, wherein: the tubular body
includes at least two fluid impermeable layers defining a
pressure-responsive chamber; the tubular body includes at least one
interstitial structure provided within the pressure-responsive
chamber; the controller is configured to cause a change in internal
pressure within the pressure-responsive chamber; and the at least
one interstitial structure is adapted to exhibit radial compression
in response to the change in internal pressure.
12. The catheter apparatus of claim 11, wherein the at least one
interstitial structure includes a plurality of laminar members
configured to be substantially slideable with respect to each other
during the first state, and be substantially non-slideable with
respect to each other during the second state.
13. The catheter apparatus of claim 12, wherein the plurality of
laminar members comprise a braid or a helically wrapped
structure.
14. The catheter apparatus of claim 10, wherein the tubular body
includes an outer layer, an inner layer, and one or more
interstitial structures provided therebetween; and wherein the
controller includes at least one linkage component mechanically
coupled to at least one of the interstitial structures and
configured to cause the at least on linkage component to expand and
contract radially.
15. The catheter apparatus of claim 12, wherein the at least one
interstitial component comprises a substantially cylindrical
braided structure.
16. The catheter apparatus of claim 12, wherein the at least one
interstial component comprises a helically-wrapped structure.
17. A catheter apparatus comprising: a tubular body having a distal
end, a proximal end, and a lumen defined therein; and activation
means for selectably causing the tubular body to enter a first
state and a second state; wherein, in the first state, the tubular
body has a first value of a stiffness metric; wherein, in the
second state, the tubular body has a second value of the stiffness
metric that is greater than the first value; and wherein the
tubular body includes at least two body segments, the activation
means includes a controller rotatably coupled to the at least two
body segments, and the controller is configured to apply a relative
rotational force between the at least two body segments to cause
the tubular body to enter the second state.
18. The catheter apparatus of claim 17, wherein the at least two
body segments includes an outer layer, an inner layer, and a
torsionally-responsive structure provided therebetween.
19. The catheter apparatus of claim 18, wherein the
torsionally-responsive structure comprises a substantially
cylindrical braided structure.
20. A catheter apparatus comprising: a tubular body having a distal
end, a proximal end, and a lumen defined therein; and activation
means for selectably causing the tubular body to enter a first
state and a second state; wherein, in the first state, the tubular
body has a first value of a stiffness metric; wherein, in the
second state, the tubular body has a second value of the stiffness
metric that is greater than the first value; and wherein the
tubular body includes at least one inner chamber, a selectably
solidifiable material provided within the inner chamber; and a
controller fluidly coupled to the at least one inner chamber.
21. The catheter apparatus of claim 20, wherein the solidifiable
material is adapted to substantially solidify in response to UV
radiation.
22. The catheter apparatus of claim 20, wherein the solidifiable
material is adapted to substantially solidify in response to
introduction of a catalyst within the inner chamber.
23. The catheter apparatus of claim 20, wherein the solidifiable
material is a polymer adapted to substantially solidify in response
to a temperature change.
24. The catheter apparatus of claim 20, wherein the solidifiable
material includes hydrophilic particles configured to expand when
contacting water, and the controller is configured to introduce a
volume of water into the inner chamber.
25. The catheter apparatus of claim 24, further including a
perfusion lumen provided within the inner chamber, the perfusion
lumen fluidly coupled to the controller.
26. The catheter apparatus of claim 20, wherein the solidifiable
material is an acoustically-active polymer.
27. The catheter apparatus of claim 20, wherein the solidifiable
material is an electroactive polymer (EAP).
28. A catheter apparatus comprising: a tubular body having a distal
end, a proximal end, and a lumen defined therein; activation means
for selectably causing the tubular body to enter a first state and
a second state; and a controller adapted to selectably dispense an
aqueous mixture; wherein, in the first state, the tubular body has
a first value of a stiffness metric; wherein, in the second state,
the tubular body has a second value of the stiffness metric that is
greater than the first value; wherein the tubular body includes a
chamber fluidly coupled to the controller and at least partially
bounded by a membrane; and wherein the membrane is configured to be
permeable to a liquid portion of the aqueous mixture and
impermeable to a solid portion of the aqueous mixture.
29. The catheter apparatus of claim 28, wherein the aqueous mixture
is a saline mixture.
30. A catheter apparatus comprising: a tubular body having a distal
end, a proximal end, and a lumen defined therein; activation means
for selectably causing the tubular body to enter a first state and
a second state; and a controller comprising a voltage source;
wherein, in the first state, the tubular body has a first value of
a stiffness metric; wherein, in the second state, the tubular body
has a second value of the stiffness metric that is greater than the
first value; and wherein the activation means includes at least one
shape-memory metallic structure provided within the tubular body
and communicatively coupled to the voltage source.
31. The catheter apparatus of claim 30, wherein the shape-memory
metallic structure comprises a Ni/Ti alloy.
32. The catheter apparatus of claim 30, wherein the stiffness
metric is a measurement of the bending stiffness of the tubular
body.
33. The catheter apparatus of claim 30, wherein the stiffness
metric is a catheter pull-out metric.
34. The catheter apparatus of claim 30, wherein the tubular body
has a plurality of zones, each zone having a corresponding
stiffness metric while in the second state.
35. The catheter apparatus of claim 34, wherein, within a first
zone, the stiffness metric of the tubular body varies continuously
along its length while in the second state.
36. The catheter apparatus of claim 35, wherein a first zone is
adjacent the distal end of the tubular body, and a second zone is
adjacent the first zone, further wherein the corresponding
stiffness metric of the first zone is less than the corresponding
stiffness metric of the second zone while in the second state.
37. The catheter apparatus of claim 30, wherein, while in the
second state, the tubular body has the second stiffness value along
a first curvature axis and a third stiffness value along a second
curvature axis that is orthogonal to the first curvature axis.
38. The catheter apparatus of claim 30, wherein the activation
means is coupled to a controller provided at the proximal end of
the tubular body.
39. The catheter apparatus of claim 30, wherein the activation
means is communicatively coupled to a controller configured to be
slideably inserted within the lumen.
40. The catheter apparatus of claim 30, wherein the activation
means is coupled to a controller that is remote from the tubular
body.
41. The catheter apparatus of claim 30, wherein the tubular body
includes a helical channel formed therein.
42. The catheter apparatus of claim 30, wherein the tubular body
includes a plurality of ring-shaped channels formed
circumferentially therein.
43. The catheter apparatus of claim 42, wherein the plurality of
ring-shaped channels are distributed irregularly along the tubular
body.
Description
CROSS-REFERENCE TO A RELATED APPLICATION
[0001] This application claims the priority benefit under 35 U.S.C.
.sctn.119(e) of U.S. Provisional Application No. 61/430,303 filed
on Jan. 6, 2011, the content of which is incorporated herein in its
entirety.
TECHNICAL FIELD
[0002] Embodiments of the subject matter described herein generally
relate to catheter systems, and more particularly relate to
catheters of the type used in the context of tortuous anatomic
features.
BACKGROUND
[0003] Catheters are useful in performing a wide range of medical
procedures, such as diagnostic heart catheterization, percutaneous
transluminal coronary angioplasty, and various endocardial mapping
and ablation procedures. It is often difficult, however, to
selectively catheterize certain vessels of the human body due to
the tortuous paths that the vessels follow. FIG. 1, for example, is
a conceptual diagram useful in depicting the human aortic arch 100.
As shown, the ascending aorta 110 rises from its origin at the
aortic valve (not shown). The right common carotid 104 and the
right subclavian 103 branch off of the brachiocephalic artery 102.
The left common carotid 105 and the left subclavian artery 106
branch and rise from the aorta just before it turns and descends to
the descending aorta 120. Dashed line 170 depicts a typical
catheter placement that might be desirable in this context.
[0004] Normal aortic arches such as that shown in FIG. 1 rarely
require intervention. Instead, interventionalists most often find
themselves viewing and navigating diseased and abnormal aortic
pathology, such as that shown in FIGS. 2A-2D, which depict assorted
variant conditions of the human aortic arch (201-204). It is clear
that navigation from the descending aorta 120, up over the arch,
and then back to gain access to the right brachiocepalic artery 102
can be extremely difficult in such cases, particularly when the
arteries are partially occluded with easily displaced and dislodged
build-ups of plaque.
[0005] As a result, catheterization procedures often require
multiple catheter exchanges--i.e., successively exchanging
catheters with different sizes and/or stiffness to "build a rail"
through which subsequent catheters can be inserted, eventually
resulting in a wire and guide stiff enough to allow delivery of the
intended interventional device (e.g., a stent, stent-graft, or the
like).
[0006] Flexibility is therefore desirable in a catheter to allow it
to track over a relatively flexible guidewire without causing the
guidewire to pull out. That is, the "navigatibility" of the
catheter is important. At the same time, the stiffness or rigidity
of the same catheter is desirable to allow the guiding catheter to
be robust enough to allow a relatively stiff device (such as a
stent) to be tracked through the guiding catheter without causing
the guiding catheter to lose position (i.e., becoming "dislodged").
If dislodgement occurs, the entire procedure of guide wire and
guide catheter exchanges must be performed again from the
beginning.
[0007] Often, an optimal balance is sought, such that the distal
end of the catheter is flexible, and the proximal end is stiff to
enable tracking. However, in order to move the stiff part of a
catheter in place, the flexible section typically needs to be
buried deep within the anatomy to get "purchase" and to hold
position. In many instances, the anatomy does not allow for deep
purchase. Accordingly, there is a need for catheter designs and
methods that overcome these and other shortcomings of the prior
art.
SUMMARY OF THE INVENTION
[0008] The present invention generally relates to a catheter
assembly having an adjustable stiffness during, for example,
endovascular procedures within the human body. That is, the
stiffness or a comparable mechanical characteristic of the catheter
assembly may be adjusted to a relatively low value during insertion
(so that it easily navigates a guide wire or the like), and then
subsequently adjusted to a relatively high value in situ to keep
the catheter assembly substantially fixed in place (i.e., during
delivery of an interventional device).
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] A more complete understanding of the subject matter may be
derived by referring to the detailed description and claims when
considered in conjunction with the following figures, wherein like
reference numbers refer to similar elements throughout the
figures.
[0010] FIG. 1 is a conceptual diagram depicting a human aortic arch
useful in describing the present invention;
[0011] FIGS. 2(a)-(d) depict various common aortic pathologies;
[0012] FIG. 3 is a conceptual cross-sectional diagram depicting a
catheter apparatus in accordance with one embodiment;
[0013] FIGS. 4 and 5 are qualitative graphs showing the value of a
stiffness metric as a function of length for catheters in
accordance with various embodiments;
[0014] FIG. 6 depicts a three-point bend test used for measuring a
stiffness metric;
[0015] FIGS. 7(a)-(c) depicts an alternate test used for measuring
a stiffness metric;
[0016] FIGS. 8(a)-(b) depicts a catheter apparatus in accordance
with one embodiment;
[0017] FIG. 9 depicts a catheter apparatus in accordance with one
embodiment;
[0018] FIGS. 10(a)-(b) and 11 depict a catheter apparatus in
accordance with one embodiment;
[0019] FIGS. 12-13 depict a catheter apparatus in accordance with
one embodiment;
[0020] FIGS. 14-15 depict a catheter apparatus in accordance with
one embodiment;
[0021] FIGS. 16-17 depict a catheter apparatus in accordance with
one embodiment;
[0022] FIGS. 18(a)-(c) depicts lumen configurations in accordance
with various embodiments; and
[0023] FIG. 19 depicts a qualitative graph showing the value of a
stiffness metric in accordance with one embodiment.
DETAILED DESCRIPTION
Overview
[0024] Referring to the longitudinal cross-section shown in FIG. 3,
a catheter apparatus (or simply "catheter") 300 in accordance with
one embodiment generally includes a generally tubular body (or
simply "body") 304 having a delivery lumen (or simply "lumen") 301
defined therein. Catheter 300 extends from a distal end 308
(generally, the end configured to be inserted first within an
anatomical feature) and a proximal end 310 opposite distal end 308.
A controller 320 communicatively coupled to catheter body 304
and/or lumen 301 will also typically be provided for controlling
the operation of catheter 300, as discussed in further detail
below.
[0025] An activation means (not illustrated in FIG. 3) is provided
for causing body 304 to enter two or more states, which may be
discrete states or states that vary continuously, or a combination
thereof. The activation means will generally include a variety of
mechanical, pneumatic, hydraulic, electrical, thermal, chemical,
and or other components as described in connection with the various
embodiments presented below, and may be incorporated into body 304,
lumen 301, controller 320, or a combination thereof. In various
embodiments, controller 320 is one component of the activation
means.
[0026] In general, body 304 can be selectably placed in at least
two states. In the first state, body 304 has a relatively low
stiffness and/or has other mechanical properties selected such that
catheter 300 can easily be inserted (e.g., via manual axial force
applied at proximal end 310) over a guide wire or the like without
substantially disturbing the placement of that guide wire. A
variety of conventional, commercially available guide wires are
known in the art, and need not be discussed in detail herein. In
the second state, body 304 has a relatively high stiffness and/or
other has mechanical properties selected such that catheter 300
remains substantially in place within the anatomical feature during
subsequent operations, including the removal of any guide wire used
during insertion. Stated another way, while in the first state,
body 304 has a stiffness metric that is equal to or less than a
predetermined "navigatibility threshold," and while in the second
state, body 304 has a stiffness metric that is greater than or
equal to a predetermined "rigidity threshold." This is illustrated
in FIG. 19, which qualitatively depicts two states (1902 and 1904)
and their corresponding stiffness threshold values (i.e.,
navigatibility threshold and rigidity threshold, respectively).
[0027] The term "stiffness metric" as used herein refers to a
dimensionless or dimensional parameter that may be defined in
various ways, as described in further detail below. However,
regardless of the nature of the stiffness metric, the
navigatibility threshold and rigidity threshold define the primary
modes of operation of catheter 300. In this regard, note that
"stiffness metric" is often used herein to refer to an actual
stiffness metric value.
Stiffness Metric and Thresholds
[0028] FIG. 4 presents a qualitative graphical representation of a
stiffness metric (S) as a function of distance along catheter 300
from its proximal end to its distal end. FIG. 4 corresponds to the
case where the stiffness metric is substantially uniform along its
length, but as will be seen below, the invention is not so limited.
Dashed line 412 indicates the navigatibility threshold, and dashed
line 410 represents the rigidity threshold for a given stiffness
metric. While in the first state (during insertion) catheter 300
has a stiffness metric 402 that is equal to or less than
navigatibility threshold 412. Similarly, while in the second state,
catheter 300 has a stiffness metric 410 that is greater than or
equal to rigidity threshold 410.
[0029] In one embodiment, the stiffness metric corresponds to the
flexural modulus of catheter 300--i.e., the ratio of stress to
strain during bending, as is known in the art. This value may be
determined empirically, for example, using a three-point bend test
as shown in FIG. 6, wherein catheter 300 (or a portion of catheter
300) is placed on a pair of supports 602 and 604 that are a known
distance apart, and a downward (radial) force 608 is applied to
catheter 300 via a third structure 606 that is situated between
supports 602 and 604.
[0030] In another embodiment, the stiffness metric corresponds to
an empirical measurement that more closely models the actual
operation of catheter 300. For example, FIGS. 7(a)-(c) depict a
"dislodgment" test that simulates the placement of a catheter 300
placed at approximately a 90-degree angle (although this angle may
vary depending upon the test). More particularly, stationary
supports 702, 704, and 706 are positioned in a predetermined
geometric relation such that catheter 300 (or a short segment cut
from catheter 300) must bend to fit between supports 702 and 704
while contacting support 706. Additional supports (not illustrated)
may also be used to assist in placing catheter 300.
[0031] During the start of the test, a probe 702 is inserted within
one end of catheter 300 as shown (FIG. 7(a)). Probe 702 might be
configured to approximate the stiffness of a typical stent-graft or
the like. As probe 702 is further inserted into the lumen 301 of
catheter 300, it makes contact with the inner surface of the lumen
301 and causes end 308 to move with respect to support 702.
Ultimately, when probe 702 is inserted with a sufficient force,
catheter 300 will be released entirely from between supports 702
and 704 as shown. The force necessary to dislodge catheter 300 in
this way then becomes the stiffness metric. The test is
advantageously conducted at approximately 37.degree. C. (body
temperature). Further, the test may be initiated with an exemplary
guide wire in place, thereby allowing the navigatibility threshold
to be determined.
Stiffness Metric Variation
[0032] While FIG. 4 depicts the stiffness metric as being invariant
over the length of catheter 300, the invention is not so limited.
FIG. 5 presents a qualitative graphical representation of stiffness
metric (S) as a function of distance along catheter 300 from its
proximal end to its distal end; however, in this embodiment,
catheter 300 includes two "zones" or segments, each having a
corresponding stiffness metric while in the second state. That is,
in zone 520, the stiffness metric in the second state (504) is
substantially the same as the stiffness metric in the first state
(502) (i.e., is generally below the navigatibility threshold 412).
Within zone 522, the stiffness metric in the second state (504) is
above the rigidity threshold 410.
[0033] Catheter 300 may include any number of such zones.
Furthermore, the stiffness metric within each zone may be constant
or vary continuously. In a particular embodiment, a first zone is
adjacent to the distal end of catheter 300, and a second zone is
adjacent to the first zone, wherein the stiffness metric of the
first zone is less than the stiffness metric of the second zone
while in the second state.
[0034] In an alternate embodiment, catheter 300 has one stiffness
metric value along a first curvature axis and another stiffness
metric value along a second curvature axis that is orthogonal to
the first curvature axis.
Catheter Body
[0035] Catheter body 304 may have any suitable structure, and be
fabricated using any suitable combination of materials capable of
achieving the selectable stiffness metric described above. For
example, in one embodiment, catheter body 304 includes a helical
(spiral) channel formed within its exterior and/or its interior.
The channel effectively weakens body 304 such that the stiffness
metric in the first state is lower than it would be if the body 304
were perfectly tubular. In another embodiment, catheter body 304
includes a plurality of ring-shaped channels formed
circumferentially therein. In a particular embodiment, the
plurality of ring-shaped channels are distributed irregularly along
the tubular body. Such an embodiment allows the baseline stiffness
metric to vary in a specified way along the length of catheter
300.
[0036] Catheter body 304 may comprise a variety of materials.
Typical materials used to construct catheters can comprise commonly
known materials such as Amorphous Commodity Thermoplastics that
include Polymethyl Methacrylate (PMMA or Acrylic), Polystyrene
(PS), Acrylonitrile Butadiene Styrene (ABS), Polyvinyl Chloride
(PVC), Modified Polyethylene Terephthalate Glycol (PETG), Cellulose
Acetate Butyrate (CAB); Semi-Crystalline Commodity Plastics that
include Polyethylene (PE), High Density Polyethylene (HDPE), Low
Density Polyethylene (LDPE or LLDPE), Polypropylene (PP),
Polymethylpentene (PMP); Amorphous Engineering Thermoplastics that
include Polycarbonate (PC), Polyphenylene Oxide (PPO), Modified
Polyphenylene Oxide (Mod PPO), Polyphenelyne Ether (PPE), Modified
Polyphenelyne Ether (Mod PPE), Polyurethane (PU), Thermoplastic
Polyurethane (TPU); Semi-Crystalline Engineering Thermoplastics
that include Polyamide (PA or Nylon), Polyoxymethylene (POM or
Acetal), Polyethylene Terephthalate (PET, Thermoplastic Polyester),
Polybutylene Terephthalate (PBT, Thermoplastic Polyester), Ultra
High Molecular Weight Polyethylene (UHMW-PE); High Performance
Thermoplastics that include Polyimide (PI, Imidized Plastic),
Polyamide Imide (PAI, Imidized Plastic), Polybenzimidazole (PBI,
Imidized Plastic); Amorphous High Performance Thermoplastics that
include Polysulfone (PSU), Polyetherimide (PEI), Polyether Sulfone
(PES), Polyaryl Sulfone (PAS); Semi-Crystalline High Performance
Thermoplastics that include Polyphenylene Sulfide (PPS),
Polyetheretherketone (PEEK); and Semi-Crystalline High Performance
Thermoplastics, Fluoropolymers that include Fluorinated Ethylene
Propylene (FEP), Ethylene Chlorotrifluroethylene (ECTFE), Ethylene,
Ethylene Tetrafluoroethylene (ETFE), Polychlortrifluoroethylene
(PCTFE), Polytetrafluoroethylene (PTFE), Expanded
Polytetrafluoroethylene (ePTFE), Polyvinylidene Fluoride (PVDF),
Perfluoroalkoxy (PFA). Other commonly known medical grade materials
include elastomeric organosilicon polymers, polyether block amide
or thermoplastic copolyether (PEBAX), Kevlar, and metals such as
stainless steel and nickel/titanium (nitinol) alloys.
[0037] The material or materials selected for catheter body 304 may
depend upon, for example, the nature of the activation means used
to effect a transition from the first state to the second state of
operation. Catheter body 304 may be manufactured, for example,
using conventional extrusion methods or film-wrapping techniques as
described in U.S. Pat. App. No. 2005/0059957, which is hereby
incorporated by reference. Additional information regarding the
manufacture of catheters may be found, for example, at U.S. Pat.
No. 5,324,284, U.S. Pat. No. 3,485,234, and U.S. Pat. No.
3,585,707, all of which are hereby incorporated by reference.
Activation Means (Generally)
[0038] Catheter 300 includes activation means for causing body 304
to enter two or more states as detailed above. The activation means
may make use of a variety of physical phenomenon and be composed of
any number of components provided within and/or communicatively
coupled to catheter 300, including for example, controller 320 as
illustrated in FIG. 1. The change of state may be accomplished, for
example, via mechanical activation, electrical activation,
pneumatic activation, chemical activation, and/or thermal
activation. Typically, activation will occur subsequent to catheter
placement--i.e., in situ. Various specific types of activation
means will now be discussed below in conjunction the exemplary
embodiments.
EMBODIMENT 1
Thermal Activation
[0039] In one embodiment, the activation means includes a
controller 320 communicatively coupled to body 304 as well features
within body 304 that are together adapted to place the body in the
second state by subjecting at least a portion of the catheter 300
to a reduction or change in temperature.
[0040] Referring now to FIGS. 8 (a)-(b) in conjunction with FIG. 1,
a catheter 300 in accordance with one embodiment generally includes
two auxiliary lumens or channels 802 and 804 that are
interconnected (e.g., fluidly coupled near a distal end) such that
the coolant travels through body 304. The channels 804 and 802 are
separated, for example, by a membrane (such as an ePTFE membrane)
806.
[0041] After delivery of catheter 300 (during which it is in the
first state), a coolant 805 such as liquid nitrogen is supplied to
channel 804 (e.g., via a coolant delivery system within controller
320), where it travels parallel to lumen 301 along the length of
(or a portion of) body 304. As the changes from liquid to gas at
membrane 806, it cools body 304 as well as membrane 806. The
materials for catheter body 304 and/or membrane 806 are selected
that their stiffness increases as the temperature is reduced.
Exemplary materials include, for example, urethane and the like. As
channel 804 is significantly smaller than channel 802, compressed
gas 803 is allowed to expand as it passes through membrane 806 into
channel 802.
[0042] As a result of heat transfer from the coolant, the coolant
(in the case of liquid nitrogen) changes to a gas phase and exits
through channel 802. In other embodiments, the coolant remains in
liquid form during operation. Suitable coolants include, for
example, chilled saline, liquid CO.sub.2, liquid N.sub.2, and the
like. Other approved medical chilling methods may also be
employed.
EMBODIMENT 2
Axial Compression
[0043] Referring now to FIGS. 16 and 17 in conjunction with FIG. 1,
in one embodiment, the activation means includes controller 320
communicatively coupled to the body 304 and components within body
304 that are adapted to place body 304 in the second state by
subjecting it to an increase in axial compression.
[0044] As shown in FIG. 16, one or more tension lines 1602 may be
used to selectively apply a compressive force to body 304. The
tension lines 1602 are attached at the distal end 308 of catheter
300 and are slideably received by corresponding accessory lumens
1402 that pass through a series of body segments 1605. The
accessory lumens 1402 are preferably sized to allow the free axial
movement of tension lines 1602. Depending upon the particular
design, body segments 1605 will typically be separated by a small
interstitial gaps 1607.
[0045] The tension lines 1602 are subjected to approximately zero
tension (i.e., are generally "slack") while navigating the anatomy
during the first state; however, when stiffening of all or a
portion of catheter 300 is desired, tension lines 1602 are pulled
substantially simultaneously as depicted in FIG. 17. Gaps and the
orientation between body segments 1605 may be optimized to reduce
(and/or increase the repeatability of) the foreshortening that
occurs when tension is applied. In one embodiment, tension wires
1602 are attached to a floating gimbal mechanism incorporated into
controller 320. Once tension is applied, the compressive force
tends to bind the catheter; thereby decreasing it's flexibility in
that section. Reduction in the axial length may accompany the
application of tension. That is, as illustrated, the interstitial
gaps 1607 may be reduced.
[0046] The tension lines may be made of any suitably strong and
flexible material, such as polymeric or metallic filaments or
ribbons. The force necessary to place catheter 300 in the second
state may vary depending upon the length, material, and
cross-section of tension lines 1602, as well as the structural
characteristics of body 304.
[0047] Any number of tension lines 1602 and accessory lumens 1402
may be used. FIGS. 18(a)-(c) present a cross-sectional view of
various designs for catheter body 304, including three equidistant
accessory lumens 1402 (FIG. 18(a)), two equidistant accessory
lumens 1402 (FIG. 18(b)), and four equidistant accessory lumens
(FIG. 18(c)). In addition, equidistant accessory lumens may be
distributed in any arbitrary fashion, and need not be symmetrical
or equidistant as illustrated.
[0048] In one embodiment, the column stiffness of body 304 is
modified to allow for tracking, then increased to deployment
without foreshortening during stiffening.
EMBODIMENT 3
Radial Compression
[0049] In one embodiment, the activation means includes controller
320 communicatively coupled to the body 304 and adapted to place
the body 304 in the second state by subjecting at least a portion
of the tubular body to an increase in radial compression. For
example, body 304 may include two fluid impermeable layers defining
a pressure-responsive chamber and at least one interstitial
structure provided within the pressure-responsive chamber. The
controller is configured to cause a change in internal pressure
within the pressure-responsive chamber; and the interstitial
structure is adapted to exhibit radial compression in response to
the change in internal pressure.
[0050] Referring now to FIG. 9, in the illustrated embodiment
catheter 300 includes an accessory lumen 902 extending from
chambers 906 to a hub 302. Hub 302 in this embodiment is configured
as a standard "Y" fitting, wherein negative pressure (i.e., a
reduction from some baseline pressure) is applied be attaching a
syringe to luer fitting 910. When negative pressure is applied,
chambers 906 collapse and apply pressure to corresponding body
segments 904 (as illustrated in FIGS. 12 and 13). The pressure is
preferably great enough to cause a change in stiffness metric of
the affected portion of catheter 300.
[0051] In an alternate embodiment shown in FIGS. 10A and 10B, the
body 304 comprises a layered structure 1002 (i.e., an interstitial
component) positioned between two or more layers of an
air-impermeable chamber 1004. To facilitate the use of negative
pressure, the chamber 1004 includes a flexible polymeric material
configured to be non-permeable while in the bloodstream. The
flexible polymeric comprise, for example, Polyethylene
Terephthalate (PET), Polyurethane, Fluorinated Ethylene Propylene
(FEP), Nylons or Flouropolymers, including Polytetrafluoroethylene
(PTFE) or Expanded Polytetrafluoroethylene (ePTFE), or combinations
thereof.
[0052] At atmospheric pressure, bending causes the individual
components of layers 1002 to slide across each other with minimum
friction. When the individual layers are allowed to slide and act
individually, the resulting stiffness metric is very low. Upon
application of negative pressure, however, a normal (i.e., radial)
force 1008 is created within structure 1002 by the collapse of the
flexible polymeric material 1004. This normal force is translated
through the layers, increasing the layer-to-layer friction and
limiting their ability to slide with respect to each other. As a
result, the stiffness metric of the structure is increased. In an
alternate embodiment, the pressure is increased in an adjacent
pressure chamber, thereby causing that chamber to press the
adjacent layered structure.
[0053] The layered structure 1002 of the present invention may be
manufactured using a variety of processes, including, for example,
tape wrapping, braiding, serving, coiling, and manual layup.
Suitable materials include, include, fibers/yarns (Kelvar, nylon,
glass, etc), wires (flat or round, stainless steel, nitinol,
alloys, etc), and/or thin slits of film (Polyester, Nylon,
Polyimide, Fluoropolymers including PTFE and ePTFE, etc.) In this
embodiment, the change in stiffness metric is easily reversed by
allowing the chamber pressure to increase (e.g., by relaxation of a
syringe attached to luer fitting 910), thereby decreasing the
applied normal force.
[0054] In an alternate embodiment depicted in FIG. 11, multiple
discrete air chambers 1102 are distributed along the length of
catheter 300 and can be toggled independently. Chambers 1102 may be
composed of differentiated layered structures, such as layers of
slit, thin film 1104. The distal air chambers may be controlled
independently through lumen 1109, while the proximal air chamber is
controlled through lumen 1108. This allows the operator to control
the segments independently to varying degrees of stiffness change.
The lumens 1108 and 1109 may be constructed in a variety of
conventional ways, including evacuation through the annular space
of the chamber, or individual lumens of tubing such as polyimide
that either have an open end in communication with the hub, or
holes through the sidewall allowing for unobstructed
evacuation.
EMBODIMENT 4
Torsional Activation
[0055] In one embodiment, the activation means includes a
controller rotatably coupled to at least two body segments (i.e.,
portions of body 304), wherein controller 320 is configured to
apply a relative rotational force between the body segments to
cause the tubular body to enter the second state. In one
embodiment, two body segments includes an outer layer, an inner
layer, and a torsionally-responsive structure provided
therebetween. In one embodiment, for example, the
torsionally-responsive structure comprises a substantially
cylindrical braided structure.
EMBODIMENT 5
Solidifying Material/Membrane
[0056] In one embodiment, body 304 includes at least one inner
chamber, a selectably solidifiable material provided within the
inner chamber; and a controller fluidly coupled to the at least one
inner chamber. The solidifiable material is adapted to
substantially solidify in response to, for example, UV radiation,
the introduction of a catalyst within the inner chamber, a
temperature change, the introduction of water (in the case of
hydrophilic particles), acoustic energy (in the case of an
acoustically-active polymer), or an electrical current or field (in
the case of an electroactive polymer).
[0057] FIGS. 14 and 15 depict an exemplary embodiment incorporating
a selectably solidifiable material to effect transition to the
second state. As shown in FIG. 14, body 304 is at least partially
filled with a medium 1404 (for example, within individual chambers
as illustrated) that together can alter the stiffness metric of
catheter 300. In this embodiment, the medium 1404 is injected
through accessory lumens 1402. Medium 1404 may be a substance that
hardens relatively quickly, such as a silicone or polyurethane. If
medium 1404 requires a catalyst to activate, that catalyst may
already reside within the walls of the body 304 or within the
material of catheter 300 itself.
[0058] In one embodiment, medium 1404 is a slurry of particles
suspended in solution as depicted in FIG. 15. In this case, the
walls of body 304 (or membranes provided therein) may be
selectively permeable so to allow a carrier liquid to escape (e.g.,
the chamber and/or catheter body walls) while confining the
particles themselves. Once these particles build up and "pack" into
the chamber they cause an increased stiffness metric in that
section. A variety of suitable particle materials and sizes can be
used. In one embodiment, the particle possesses neutral buoyancy in
the selected carrier liquid. A hydrophilic particle is advantageous
in that it swells during hydration, causing additional binding and
increased catheter stiffness.
EMBODIMENT 6
Memory Metal
[0059] In one embodiment, the activation means includes at least
one metallic structure having shape-memory properties provided
within body 304 and communicatively coupled to a power source (e.g.
a voltage and/or current source located within controller 320). In
one embodiment, the shape-memory metallic structure comprises a
Ni/Ti alloy (nitinol).
CONCLUSION
[0060] What has been described are methods and apparatus for an
endovascular catheter that can be inserted within tortuous body
anatomies and then selectively stiffened and fixed in place. In a
particular embodiment, this stiffness is reversible. In this
regard, the foregoing detailed description is merely illustrative
in nature and is not intended to limit the embodiments of the
subject matter or the application and uses of such embodiments. As
used herein, the word "exemplary" means "serving as an example,
instance, or illustration." Any implementation described herein as
exemplary is not necessarily to be construed as preferred or
advantageous over other implementations. Thus, although several
exemplary embodiments have been presented in the foregoing
description, it should be appreciated that a vast number of
alternate but equivalent variations exist, and the examples
presented herein are not intended to limit the scope,
applicability, or configuration of the invention in any way. To the
contrary, various changes may be made in the function and
arrangement of the various features described herein without
departing from the scope of the claims and their legal
equivalents.
[0061] Techniques and technologies may be described herein in terms
of functional and/or logical block components, and with reference
to symbolic representations of operations, processing tasks, and
functions that may be performed by various computing components or
devices.
[0062] While at least one exemplary embodiment has been presented
in the foregoing detailed description, it should be appreciated
that a vast number of variations exist. It should also be
appreciated that the exemplary embodiment or embodiments described
herein are not intended to limit the scope, applicability, or
configuration of the claimed subject matter in any way. Rather, the
foregoing detailed description will provide those skilled in the
art with a convenient road map for implementing the described
embodiment or embodiments. It should be understood that various
changes can be made in the function and arrangement of elements
without departing from the scope defined by the claims, which
includes known equivalents and foreseeable equivalents at the time
of filing this patent application.
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