U.S. patent application number 14/080104 was filed with the patent office on 2014-03-13 for cuff electrode having tubular body with controlled closing force.
This patent application is currently assigned to Advanced Neuromodulation Systems, Inc., d/b/a St. Jude Medical Neuromodulation Division, Advanced Neuromodulation Systems, Inc., d/b/a St. Jude Medical Neuromodulation Division. The applicant listed for this patent is Advanced Neuromodulation Systems, Inc., d/b/a St. Jude Medical Neuromodulation Division, Advanced Neuromodulation Systems, Inc., d/b/a St. Jude Medical Neuromodulation Division. Invention is credited to Ralph Cardinal, Hans Neisz, Jason A. Shiroff, Jason J. Skubitz.
Application Number | 20140074213 14/080104 |
Document ID | / |
Family ID | 45922169 |
Filed Date | 2014-03-13 |
United States Patent
Application |
20140074213 |
Kind Code |
A1 |
Neisz; Hans ; et
al. |
March 13, 2014 |
CUFF ELECTRODE HAVING TUBULAR BODY WITH CONTROLLED CLOSING
FORCE
Abstract
Nerve cuff electrode including a tubular body having a
longitudinal slit having electrodes disposed within the body. Wedge
shape slits are formed into at least one of the interior wall and
the exterior wall of the body, whereby the number and location of
slits provided to facilitate the adjustment of the amount of
compressive force of nerve cuff electrode about the nerve.
Inventors: |
Neisz; Hans; (Coon Rapids,
MN) ; Cardinal; Ralph; (White Bear Lake, MN) ;
Skubitz; Jason J.; (Arden Hills, MN) ; Shiroff; Jason
A.; (Minneapolis, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Advanced Neuromodulation Systems, Inc., d/b/a St. Jude Medical
Neuromodulation Division |
Plano |
TX |
US |
|
|
Assignee: |
Advanced Neuromodulation Systems,
Inc., d/b/a St. Jude Medical Neuromodulation Division
Plano
TX
|
Family ID: |
45922169 |
Appl. No.: |
14/080104 |
Filed: |
November 14, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13413509 |
Mar 6, 2012 |
8612025 |
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14080104 |
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12181214 |
Jul 28, 2008 |
8155757 |
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13413509 |
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61036429 |
Mar 13, 2008 |
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60952219 |
Jul 26, 2007 |
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Current U.S.
Class: |
607/118 |
Current CPC
Class: |
A61N 1/0556
20130101 |
Class at
Publication: |
607/118 |
International
Class: |
A61N 1/05 20060101
A61N001/05 |
Claims
1. A self-sizing cuff electrode, comprising: a tubular shaped body,
said body comprising a first end, a second end, a length, an inner
surface and an outer surface, the body further comprising: a hinge
portion configured to provide resilient support along at least a
portion of the length of the body; a longitudinal split, said split
defining a first edge, and a second edge, said first edge and
second edge configured to slidably overlap each other such that the
body substantially circumferentially encloses at least a portion of
a nerve; a plurality of wedge shaped slits formed into at least one
of the inner surface and the outer surface; and a plurality of
electrodes positioned within the body proximate the inner surface,
said electrodes comprising at least one anode and at least one
cathode, said at least one anode and at least one cathode are
located proximate the nerve when the nerve is enclosed by the body;
wherein in response to an electrical signal, the at least one anode
and at least one cathode form an electrically coupled anode-cathode
pair with an electrical pathway therebetween; and wherein the body
is configured to provide a compressive force effective to maintain
contact between the electrodes and the nerve, with the compressive
force at least partially dependent upon the number wedge shaped
slits, such that the electrical pathway between the electrodes and
the nerve is maintained.
2. The cuff of claim 1, wherein the compressive force is maintained
in a range of about 10 mm to about 30 mm Hg.
3. The cuff of claim 1, wherein the compressive force is maintained
in a range of about 2 mm to about 30 mm Hg.
4. The cuff of claim 1, wherein the hinge portion further comprises
at least one elastic member.
5. The cuff of claim 1, wherein the hinge portion includes a first
member which fails in response to an applied force exceeding a
limit.
6. The cuff of claim 1, wherein the hinge portion is configured to
yield before the force of the cuff on the nerve exceeds about 30 mm
Hg.
7. The cuff of claim 1, wherein there are a plurality of
anode-cathode pairs.
8. The cuff of claim 7, wherein a distance between the electrically
coupled anode and cathode in an anode-cathode pair is substantially
the same as a distance between the anode and cathode in any other
electrically coupled anode-cathode pair.
9. The cuff of claim 1, wherein at least one of the electrodes is
recessed relative to the inner surface.
10. The cuff of claim 1, wherein in response to an applied
electrical signal, an electrical pathway is formed by an
anode-cathode pair, such that current effectively traverses a
cross-sectional profile of the nerve.
11. The cuff of claim 1, in which the cuff applies no less than
about 2 mm Hg at 5 degrees of cuff opening and no more than about
30 mm Hg at 90 degrees of cuff opening.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 13/413,509, filed Mar. 6, 2012, which is a divisional of U.S.
application Ser. No. 12/181,214, filed Jul. 28, 2008, now U.S. Pat.
No. 8,155,757, which claims the benefit of U.S. Provisional
Application No. 61/036,429, filed Mar. 13, 2008 and U.S.
Provisional Application No. 60/952,219, filed Jul. 26, 2007, the
disclosures of which are fully incorporated herein by
reference.
TECHNICAL FIELD
[0002] The present application is related to medical nerve
electrodes. More specifically, the present invention is related to
nerve cuff electrodes which find use in both nerve stimulation and
sensing.
BACKGROUND
[0003] The nervous system comprises billions of neurons, organized
into structural and functional assemblages, that perform a wide
range of functions For example, some neurons relay information from
the central nervous system (CNS) to other parts of the body, while
others collect information from peripheral sensors either for use
by reflexive systems or for interpretation by the CNS.
[0004] One type of organized structure of the nervous system is
that of nerves. Nerves are bundles of axons, and may include
additional support cells, such as glial cells. A single nerve can
contain thousands to upwards of a million individual axons, each
axon being a specialized structural modification of a neuronal
cell. The body comprises a number of nerves, each one typically
serving particular functions or relaying particular types of
information to and from particular parts of the body. In general,
the relay of information through the nervous system is carried out
by the activity of excitable cells such as neurons. Neurons are
characterized by the ability to respond to stimuli, to conduct
impulses, and to communicate with each other or with other types of
responsive cells.
[0005] In neurons, this ability arises due to structural and
biochemical specializations, the most important of which is the
ability to maintain an electrical potential across the cellular
membrane of the neuron. This membrane potential is due to the
action of integral membrane ion "pumps" that produce and maintain
an asymmetric distribution of sodium and potassium ions across the
membrane, in which 3 sodium ions are pumped out of the cell in
exchange for 2 potassium ions pumped inwards. The net effect in a
typical neuron is that the electric potential difference across the
membrane is typically in the range of -70 mV, referred to as a
resting potential.
[0006] In addition to mechanisms that produce the asymmetric
distribution of sodium and potassium ions that create the resting
potential, excitable cells like neurons also have structural and
biochemical mechanisms that result in depolarization of the cell
membrane, resulting in a wave of electrical activity that
propagates along the surface of the neuron.
[0007] Depolarization can be caused either by chemical or direct
electrical stimulation of the cell. Typically depolarization occurs
initially as a localized event on the neuron cell surface that
results in the opening of voltage-gated sodium channels. Opening of
these channels allows sodium to diffuse into the cell driven along
its electrochemical gradient. This results in a reduction in the
potential difference across the membrane, which in turn opens more
voltage-gated sodium channels, allowing more sodium into the cell,
which further depolarizes the cell. Once a threshold level is
reached, the cells will completely depolarize, leading to the
production of an action potential.
[0008] Once initiated, an action potential will be propagated down
the length of the neuron, for example, down the axonal portion of
the cell. The speed of conduction is dependent on the diameter of
the axon, as well as other factors, such as whether the nerve is
myelinated or non-myelinated. Larger diameter neurons generally
conduct action potentials more rapidly, as do fibers that are
myelinated. Stimulation of neuronal signaling can occur naturally
in a number of ways. For example, some neurons have cell surface
receptors that bind to specific signaling molecules. In response to
ligand binding, the receptors in turn signal ion channels to open
or close, which can lead to depolarization or hyperpolarization of
the neuron. Hyperpolarization leads to de-sensitization of the
nerve, while depolarization sensitizes the nerve and increases the
likelihood that a stimulus will result in the production of an
action potential.
[0009] Neurons can be artificially stimulated to depolarize by
application of an electrical signal. In these cases, the electrical
signal directly acts on voltage-gated channels in the cell membrane
leading to depolarization. If a signal of sufficient intensity is
applied, an action potential can be evoked.
[0010] In addition to the production of an electrical signal,
neurons in particular are also able to provide information coding,
depending on the frequency at which depolarization occurs, the
timing of depolarization or even simply on whether the neuron is
firing or not.
[0011] Cuff electrodes are well known in the neurostimulation
field. Cuff electrodes can be used to stimulate and/or measure the
response of peripheral nerves. A cuff electrode can wrap around the
nerve to be stimulated and/or sensed.
[0012] At least one prior art nerve cuff includes a sheet biased to
curl into a tubular spiral when released or wrapped around a nerve.
Applicants believe this design is less than optimal for at least
two reasons. The first reason is manufacturability. A nerve cuff
may have nominal dimensions of 1 cm by 1 cm. One method for biasing
the sheet to curl is to stretch a first sheet and adhere the first
stretched sheet to a second sheet, allowing them to securely bond.
Electrodes would presumably be secured to the first sheet or within
recesses in the first sheet. Applicants are unsure as to the
reproducibility of such a process with respect to the inwardly
directed force on a nerve, among other properties.
[0013] A nerve may be teased out of the surrounding tissue, often
using blunt dissection tools. This isolation of the nerve may
irritate the nerve, which may lead to swelling of the nerve, as
would be expected with many other tissues. This swelling can
increase the outer diameter of the nerve.
[0014] During placement of the nerve cuff, the inwardly directed
pressure of the cuff should fall between two extremes, both
disadvantageous. If the cuff applies too much pressure on the
nerve, the nerve can be damaged. If the cuff applies an initially
proper amount of pressure and the nerve swells, then too much
pressure may be applied if the cuff does not expand enough.
[0015] If the cuff does not apply enough pressure on the nerve,
this often means that the cuff is not closely fitted to the nerve,
and the cuff can become dislodged from the nerve, particularly
during placement. This can allow an undesirable amount of fibrotic
tissue ingrowth. This can also force the current applied to the
cuff electrode to be larger than optimal, shortening battery life
and perhaps even allowing stray currents to effect nearby tissue.
If the cuff is initially properly situated, and the nerve later
returns to normal size, then the cuff should shrink in order to
maintain the proper fit around the nerve.
[0016] What would be advantageous is a nerve cuff which can be
easily placed using minimally invasive techniques. What would be
beneficial is a nerve cuff which is self sizing yet efficient and
has a well defined closing force.
SUMMARY
[0017] It is of interest to specifically stimulate individual
nerves in order to selectively probe physiological functions, or to
produce desired physiological effects, or to mimic selected
physiological states. For example, stimulation of the sympathetic
nerve, and in particular the splanchnic nerve, can be used to
produce neuronal signals that create a sense of satiety.
[0018] In some instances, an external signal generator, or an
implantable pulse generator (IPG), generates an electrical impulse
that is transmitted to the nerve through an electrode placed, near,
or in direct contact with the nerve surface. While this approach
generally results in neural stimulation, the design of the
electrodes result in limitations in the effectiveness and
specificity of stimulation.
[0019] For example, in using electrodes to simulate nerves, it is
desirable to secure the electrodes to the nerve in some fashion, in
order to maintain a consistent electrical pathway between the
electrode and the nerve to be stimulated. This is especially
important where the electrode is designed for long-term use, for
example in providing electrical stimulation to a nerve as part of a
medical therapeutic regime, or where a specific region in the body,
or portion of a nerve is to be stimulated. One approach is
preparing various types of electrodes that can be wrapped around a
portion of the nerve to be stimulated, so-called cuff electrodes.
By wrapping the electrode around the nerve, movement of the
electrode is limited, and contact between the nerve and electrode
is potentially improved. A number of different cuff electrode
configurations exist in the prior art, including rigid cuffs,
flexible cuffs, and helical electrodes.
[0020] Some embodiments described herein provide a self-sizing cuff
electrode that maintains a relatively even contact pressure between
the electrically conducting surfaces of the electrode and the
nerve. In addition, and as disclosed herein, some embodiments of
the present electrodes can be effective to provide an electrical
pathway between the conducting surfaces (for example, an anode and
cathode) that results in current flow cross-sectionally through the
nerve, as opposed to along the surface, as in some electrode
designs.
[0021] Some embodiments of the present invention provide a cuff
electrode which can be used to stimulate a wider range of nerve
sizes, when compared to many other cuff electrodes. The present
invention cuff electrodes can provide an efficient electrode which
allows for long term use with an implanted battery. The design of
such cuffs can provide resistance to fibrotic ingrowth.
[0022] The improved design of some embodiments of the present
invention provide both a large electrode surface area encircling
much of the nerve while providing a flexible cuff which can gently
adjust to the nerve size, as the nerve changes size to a post
operative inflamed state and back to a smaller diameter state.
[0023] The present invention includes self-sizing cuff electrodes
for use in stimulating a nerve, the cuff electrode including a cuff
portion configured to adopt a generally tubular shape, the cuff
portion being configured to contact a nerve over a contact area.
The cuff portion can also include a hinge portion configured to
provide resilient support along substantially the length of the
cuff portion. The cuff portion can include a longitudinal split,
forming a first edge and second edge configured to slidably overlap
each other such that the cuff portion substantially
circumferentially encloses at least a portion of the nerve. The
cuff may also include a plurality of electrodes including at least
one anode and at least one cathode, located on substantially
opposite sides of the nerve when the nerve is enclosed by the cuff
portion. In response to an electrical signal, the anode and cathode
can form an electrically coupled anode-cathode pair with an
electrical pathway therebetween, wherein the cuff portion is
configured to provide a compressive force effective to maintain
contact between the electrodes and the nerve, such that the
electrical pathway between the electrodes and the nerve is
maintained.
[0024] In some cuffs the compressive force is maintained in a range
of about 10 mm to about 30 mm Hg, and in others the compressive
force is maintained in a range of about 2 mm to about 30 mm Hg.
Some cuffs have a hinge portion including at least one elastic
member. The hinge portion is configured to yield before the force
of the cuff on the nerve exceeds about 20, 25, or 30 mm Hg, in
various embodiments.
[0025] Some cuff electrodes according to the present invention
include a first elongate conductor, a second elongate conductor, a
first pair of opposed curved electrically conductive plates
electrically coupled to each other and to the first conductor, a
second pair of opposed curved electrically conductive plates
electrically coupled to each other and to the second conductor, and
a third pair of opposed curved electrically conductive plates
electrically coupled to each other and to the first conductor. The
first, second, and third pairs of curved electrically conductive
plates each can have an electrically exposed interior surface. The
cuff electrode can also have an elongate flexible shaft having a
proximal region and can be operably coupled to the shaft distal
region, with the cuff including a tubular body having an interior
region and an exterior region. The first, second, and third curved
electrically conductive plates may be operably coupled to the cuff
tubular body interior region such that the electrically conductive
plate interior conductive surface is electrically exposed within
the cuff tubular body interior. The cuff tubular body can include a
tubular body wall having a longitudinal slit therethrough allowing
the cuff tubular body to open to expose the cuff tubular body
interior, and in which the cuff tubular body is biased to urge the
tubular body to close the slit.
[0026] In some such embodiments, the opposed curved electrically
conductive plates are electrically coupled to each other through
electrically conductive wires, where the wires may be biased to
urge the opposed plates closer together. Some cuffs further a flap
secured to the tubular body on a first side of the slit, in which
the flap wraps around the tubular body and covers the slit, and in
which the flap tapers to a free end of the flap. Some tapered
regions include at least one removable flexible member which is
adapted to being grasped to pull the tapered flap region under a
nerve. The removable flexible member may include a loop of suture
material secured to the flap tapered region.
[0027] In some such embodiments the opposed plates have
longitudinal edges near the slit and opposite the slit, where the
edges near the slit and opposite the slit are disposed about the
same distance from the opposing plate respective longitudinal edge
when the slit is closed. The opposed plates can have longitudinal
edges near the slit and opposite the slit, where the edges near the
slit are disposed a greater distance from the opposing plate
respective edges than the edges opposite the slit, when the slit is
closed. In other embodiments, the edges near the slit are disposed
a lesser distance from the opposing plate respective edges than the
edges opposite the slit, when the slit is closed. The cuff tubular
region between the opposed plates and opposite the slit is
substantially free of electrode material in some embodiments.
[0028] Some cuffs can open to varying degrees to receive a nerve,
and the cuff tubular region between the opposed plates and opposite
the slit form a hinge region having a non-linear spring constant,
wherein the spring constant is substantially greater at small
degrees of opening degree than at large degrees of opening. Some
cuffs have at least about 2 mm Hg closing force at 5 degrees of
opening and no greater than about 30 mm Hg at 90 degrees of
opening. Some cuffs have a hinge region which includes a first
element providing cuff closing force, where the first element
substantially decreases in closing force past a first degree of
opening limit. The hinge region may also include a second element
providing closing force, where the second element continues to
provide cuff closing force past the first cuff opening limit. Some
cuff have a hinge region which includes a weakened region
susceptible to folding a large degrees of opening, the hinge region
further having an inner wall disposed between the hinge weakened
region and an outer wall disposed away from the weakened area and
inner wall, such that the first element includes the hinge region
outer wall.
[0029] Some embodiments include jumper wires coupling the opposed
plates and are biased to close the cuff tubular body. The jumper
wires can be biased to close the cuff tubular body in a non-linear
fashion, such that the jumper wires have a spring constant which
decreases with increasing cuff tubular body opening.
[0030] Some cuff embodiments have a spring force provided at least
in part by a longitudinal channel in a tubular cuff wall region
substantially opposite the cuff opening, in which the tubular wall
region includes an inside wall and an outside wall, such that the
inside wall provides a tension closing force and the outside wall
provided a compressive closing force, where the outside wall
buckles under a compressive force at an opening limit and wherein
the inner wall tension force continues with further cuff opening
after buckling. In some embodiments, a compressible element is
disposed within the hinge region lumen, such that buckling of the
hinge region outer wall allows the hinge region lumen to decrease
in at least one dimension, which can allow the hinge region lumen
walls to bring radial, compressive forces to bear on a compressible
member disposed within. In some embodiments, the compressible
member includes a shaft. In other embodiments the compressible
member includes a tube having a tube lumen within. When the tube
lumen walls have been sufficiently compressed and forced inward,
then the inner member can itself compress and/or buckle, depending
on the embodiment. In various embodiments elastomeric foam shafts
and/or tubes are used, as are resilient elastomeric member tubes.
Spring members may be included within the hinge region lumen in
some embodiments. Some embodiments have a gap between the inner
member and the hinge region lumen inner wall. In this way the hinge
region wall can buckle and force the hinge region lumen wall to
close in on the inner member and to apply a compressive force on
the inner member. In still other embodiments, at least the cuff
hinge region is co-extruded, allowing different materials to be
used for the inner vs. outer wall in the hinge region. Some
embodiments include a thicker outer wall then inner wall in the
hinge region. This can provide a larger initial closing force with
initial cuff opening.
[0031] The present invention also includes methods for disposing a
nerve cuff about a nerve, one such method including advancing a
nerve cuff selected from any of the embodiments disclosed herein,
toward the nerve, at least partially freeing the nerve from nearby
tissue, advancing the cuff flap under the nerve, allowing the cuff
tubular body to close over the nerve, and allowing the cuff flap to
wrap around the tubular body to cover the tubular body slit. Some
methods further include pulling the cuff flap under the nerve using
a flexible graspable material. Methods may also include pulling the
cuff tubular body open about the slit by pulling on graspable
flexible members secured to the cuff on either side of the slit.
Some embodiment methods further include pulling the cuff tubular
body open about the slit by pulling on a first graspable flexible
member secured to the cuff tubular body near one side of the slit
and pulling on a second graspable flexible member secured to the
cuff flap which is secured to the cuff tubular body on an opposite
side of the slit from the first graspable member. In some of these
methods, the cuff is advanced minimally invasively, through a hole
less than 1/2 inch in maximum extent.
DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a diagram comparing the effects of nerve
stimulation using an unenclosed electrode and an enclosed
electrode.
[0033] FIG. 2 depicts the difference between surface and
cross-sectional activation of a nerve.
[0034] FIG. 3 illustrates a perspective view of one embodiment of a
self-sizing cuff style electrode showing one possible placement of
electrodes.
[0035] FIG. 4 illustrates a view of one embodiment of a self-sizing
cuff electrode in an open configuration prior to placement around a
nerve.
[0036] FIG. 5 is a cross-sectional end view of one embodiment of a
self-sizing cuff electrode showing the overlap region.
[0037] FIG. 6 depicts the effect of recessed electrode placement on
charge profile.
[0038] FIGS. 7A-D provide additional views of one embodiment of a
self-sizing cuff electrode.
[0039] FIG. 8 depicts additional views of one embodiment of a
self-sizing cuff.
[0040] FIG. 9 depicts cuff closing pressures as a function of cuff
opening.
[0041] FIG. 10A depicts an end view of a simplified cuff and
hinge.
[0042] FIG. 10B depicts an exploded view of a multi-element elastic
member.
[0043] FIG. 11A depicts embodiments of a cuff, and an exploded view
of a multi-element elastic member.
[0044] FIG. 11B depicts embodiments of a cuff with a multi-element
elastic member installed.
[0045] FIGS. 12A-C depict a portion of a cuff with an elastic
member comprising various numbers of elements.
[0046] FIGS. 13A-D depict embodiments of a cuff with a hinge area
comprising a longitudinal passage and load bearing portion.
[0047] FIG. 14A-B depicts a cuff like that of FIG. 13 at various
opening angles, showing compression and buckling of the hinge
passage wall as the cuff is laid open.
[0048] FIGS. 15A-15C illustrates the buckling of hinge regions.
[0049] FIG. 16 is a perspective view of a lead according to the
present invention, having a proximal connector, an intermediate
yoke, and a distal cuff.
[0050] FIG. 17 is a fragmentary, perspective view of the yoke of
FIG. 16, connecting a proximal lead body to distal lead bodies.
[0051] FIG. 18 is a fragmentary, perspective view of a cuff
electrode having interior, recessed, conductor plates disposed
within a tubular body closed about a slit and having a flap
covering the slit and wrapping around the tubular body.
[0052] FIG. 19 is a perspective view of a cuff electrode
sub-assembly having a flap with a tapered free edge and jumper
wires/springs electrically coupling the curved electrode
plates.
[0053] FIG. 20 is a side view of the cuff of FIG. 19, better
illustrating the jumper wires/springs coupling the curved electrode
plates.
[0054] FIG. 21 is a fragmentary, perspective view of a cuff
electrode subassembly better illustrating the opposed, curved plate
electrodes and the conductor wires coupled to the plates.
[0055] FIG. 22 is a fragmentary, perspective view of the curved
electrode plates and jumper wires of FIG. 21.
[0056] FIG. 23 is an end view of the subassembly of FIG. 22,
showing the conductor wires at the top and one jumper wire at the
left side.
[0057] FIG. 24 is a top, photographic view of a nerve cuff pulled
apart by the suture loops, showing the opposed curved electrode
plates coupled by the jumper wires.
[0058] FIGS. 25A and 25B are fragmentary, cross sectional views of
tubular cuff electrodes having material sections removed in the
tube cuff wall opposite the tube slit.
DETAILED DESCRIPTION
[0059] Neural stimulation can be accomplished by directly applying
an electrical charge via an electrode (or electrodes) to a surface
of a nerve. In general, electrodes comprise a holder of some type
into which electrically conductive materials are placed, as well as
points of contact on which to attach lead wires that connect the
electrodes to the signal generator or IPG. In addition, where the
electrode is designed for long-term use, for example when used in
an implantable system for medical or research use, there must also
be some way in which to keep the electrode in position and in
contact with the nerve of interest.
[0060] FIG. 1 illustrates a simple case, in which the electrodes
can be bare material laid on or around a nerve. For example, the
open stimulation lead coils shown in FIG. 1 (upper panel), can be
used to stimulate a nerve. A serious drawback of an open lead
system, however, is that current is free to flow into surrounding
tissue, and not all current is directed to the nerve to be
stimulated. The surrounding tissue in FIG. 1 includes some open
nerve endings in the tissue, represented as circles drawn in the
tissue.
[0061] In an open lead system, stimulating current can produce
stimulation of nerve fibers in the surrounding tissue. Depending on
the type of fibers, inadvertent stimulation may be perceived, for
example by a patient, and may lead to discomfort, or the
inappropriate activation of other neuronally regulated systems.
This can lead to reduced selectivity or specificity with respect to
the neural system that one is attempting to regulate with the IPG
system. To compensate, it may be necessary to reduce the
stimulation intensity in order to avoid stimulating unwanted nerve
fibers. This in turn may reduce the effectiveness of stimulation of
the nerve that is intended to be stimulated.
[0062] In some embodiments, electrodes may be electrically
insulated by means of an external shield in order to prevent
current leakage outside the area of interest. As shown in FIG. 1
(lower panel), this results in more effective energy delivery to
the nerve of interest and increased selectivity and specificity of
the stimulation regime. In addition, as shielding results in a
greater proportion of the total energy being delivered to the
desired nerve, less overall input energy is needed for effective
stimulation. Where the device is an IPG, this will tend to improve
the service life of the device due to lower overall energy
consumption from the IPG power source (e.g., an implanted battery)
over time.
[0063] FIGS. 2-4 illustrate embodiments of a self-sizing cuff
electrode assembly 10. In some embodiments, the shielding function
is provided by the enclosing member, or cuff 100 portion of the
assembly. The assembly further comprises electrodes 150, which in
some embodiments can be anodes 152 or cathodes 154.
[0064] Conveniently, in some embodiments the cuff 100 can be made
from a material, such as silicone rubber, that is resilient,
electrically insulative, and biocompatible. By placing an
insulative material between the electrodes 150, which are located
on the inner surface 140 of the cuff 100, current flow (indicated
at 290) is more likely to flow between the electrodes 152 and 154
and through the nerve 280, as opposed to leaking away from the
nerve where it could otherwise result in unwanted stimulation of
surrounding tissue and/or other nerve fibers.
[0065] A challenge in electrode design is in providing an electrode
placement that is effective to stimulate as many neurons within a
nerve as possible so that the full effect of stimulating the
particular nerve can be realized while minimizing unwanted
stimulation of adjacent nerves fibers or excitable tissues (e.g.,
muscle). As in other types of electrical circuits, the electrical
pathway formed when applying electrical energy to a nerve via
electrodes will be the path of least resistance. Consequently, the
placement of electrodes with respect to each other is
important.
[0066] Many stimulation devices use an electrode arrangement that
results in an electrical pathway oriented along the surface of the
nerve, as shown in FIG. 2 (left panel). For example, U.S.
Application 200610030919 by Mrva et al., the entirety of which is
incorporated by reference herein, discloses a cuff-style electrode
in which the electrical contacts are arranged either axially or
longitudinally with respect to the nerve bundle. In the Mrva
device, the electrodes are situated such that the shortest distance
between electrodes (i.e., the pathway for current) is along the
surface of the nerve. Similarly, in U.S. Pat. No. 5,282,468 to
Klepinski, the entirety of which is incorporated by reference
herein, the electrodes are arranged circumferentially, with the
result that the electrical pathway will be along the nerve surface.
However, the limitation resulting from electrodes that create a
surface-oriented electrical pathway is that a significant number of
the neurons in the interior of the nerve will not be adequately
stimulated. Thus, to fully stimulate the nerve requires increased
signal intensity, which in turn leads to several problems already
identified and discussed above.
[0067] As a result, it may be desirable to configure the device
such that the placement of the electrical contacts (i.e., the
electrodes) results in an electrical path that is oriented
cross-sectionally across the nerve, as opposed to along the nerve
surface, as illustrated in FIG. 2 (right panel). In embodiments of
the present disclosure, the electrodes are arranged such that the
electrical path for the stimulation current is oriented to pass
cross-sectionally, rather than along the nerve surface as in prior
art devices. Thus, in embodiments presently disclosed, the
electrodes are effectively horizontally opposed, such that each
anode-cathode "pair" is situated on substantially opposite sides of
the nerve to be stimulated. In this arrangement, the electrical
pathway between an anode-cathode pair may be cross-sectionally
across the nerve, while less desirable surface stimulation will be
reduced or non-existent.
[0068] For example, in one embodiment, as shown in FIG. 3, the
electrode cuff comprises a silicone enclosure that further
comprises three electrodes. In the illustrated embodiment, the cuff
includes a centrally located cathode, and two anodes located
towards each end of the cuff. This arrangement results in each
anode between equidistant from the cathode and placed in such a way
that the stimulation current will flow across the nerve as opposed
to along the surface of the nerve, as is the case with prior art
cuff electrodes.
[0069] While the embodiment illustrated in FIG. 3 depicts one
cathode and two anodes, other electrode arrangements are possible
that will fall within the scope of the disclosure as presented
herein. For example, it is possible to provide a cuff with a
centrally located anode, and two distally located cathodes, and
still retain an equidistant relationship between anodes and
cathodes, with the result that the current path will flow
cross-sectionally through the nerve.
[0070] In some embodiments, a plurality of anodes and cathodes can
be provided and arranged such that the equidistant, cross-sectional
arrangement is preserved between a plurality of anode-cathode
pairs. As used herein the term "anode-cathode pair" is intended to
have its plain and ordinary meaning, which includes, without
limitation, an anode and cathode that are configured to be
electrically coupled such that current passes between them and
through the nerve when a current is applied by a signal generator
or IPG to the electrodes.
[0071] Thus, the present disclosure is not limited to neural
stimulation devices with particular numbers of anodes or cathodes,
and all such devices are intended to fall within the scope of the
present disclosure. It should also be understood that the term
"equidistant" as used herein does not mean exactly the same
distance, but rather the various anode-cathode distance in the
assembly are substantially the same. The distribution of
stimulation current in the nerve is to a great extent determined by
the electrical resistance of the current pathway between respective
anodes and cathodes. If the distance between anodes and cathodes
varies, a higher current density will be observed at the region
where the anode is closest to the cathode. As a result, stimulation
of nerve fibers between the anode and cathode will be more
variable, and in some cases, significant numbers of fibers may be
less adequately stimulated, leading either to a loss or reduction
of the desired physiological response. In contrast, by shaping the
anodes and cathodes, such that an equal distance is maintained over
a greater area, more effective stimulation of a greater number of
neurons within the nerve will occur. Such a pattern of current flow
is not possible with prior art devices.
[0072] As shown in FIGS. 3 and 4, the electrodes can comprise
shapes other than simple strips of material. In addition, the
respective shapes of anodes and cathodes can be configured to
optimize the equidistant relationship between anodes and cathodes.
This can increase the "width" of the electrical pathway, while
still maintaining a relatively equidistant relationship between
anodes and cathodes. Thus, shaping the electrodes can provide
additional advantages.
[0073] Providing a plurality of anodes and cathodes, for example
the tri-polar arrangement depicted in the illustrated embodiments
of FIGS. 3 and 4, also provides useful advantages. For example, a
centrally located cathode will distribute current across a greater
section of the nerve, thus activating a greater volume than would
result from a conventional bi-polar design. In addition, providing
multiple electrodes allows for more complex stimulation
patterns.
[0074] For example, in a device such as that illustrated in FIG. 3,
it is possible to vary the stimulation pattern and intensity to the
anodes independently. This enables one to recruit different
afferent and efferent fibers within the same nerve using a single
electrode assembly. In such a case, the IPG or other signal
generator would comprise circuitry such that each anode (or
cathode, if multiple cathodes were used) would be controlled by an
independent channel, such that a number of independently controlled
electrical simulation pathways could be produced in the nerve.
Alternatively, the electrodes could be electrically linked, such
that a stimulation pattern could be effectively applied over a
greater area of the nerve. In some embodiments, the circuitry could
be configured to change between linked and independent modes of
stimulation to provide the greatest number of stimulation options.
The supporting structure for the electrodes comprises a cuff 100
configured to spontaneously form a generally tubular structure. The
self-curling feature of the cuff is a property that can be provided
by the material used to fashion the cuff, as well as the shape of
the cuff. For example, the cuff can be molded as a split tube using
a compliant material such as silicone rubber or a biocompatible
compliant polymer.
[0075] Thus, the cuff can be manufactured in the shape it will
assume when placed around the nerve. Conveniently, the use of a
compliant material and providing a longitudinal split region 250,
permits the cuff 100 to be laid open for placing under a nerve,
using surgical forceps or other suitable instruments capable of
grasping the first and second edges, as illustrated in FIG. 4. To
complete the placement of the cuff 100, the edges would be released
in a controlled manner, such that the first and second edges would
overlap, as in FIG. 5, and the cuff would assume its original
tubular shape, thus enclosing the nerve and placing the electrodes
150 in contact with the surface of the nerve.
[0076] In some embodiments, as shown in FIG. 3, the cuff 100
comprises a sheet of an elastomeric material, for example silicone
rubber, that is electrically insulative, compliant, and
biocompatible. The cuff 100 comprises a first end 110 and a second
end 120, an outer surface 130, and an inner surface 140. Electrodes
150 are located either on, or embedded into the inner surface 140
of the cuff 100. The cuff 100 is configured to perform a number of
functions. First, the cuff provides a structure onto, or into,
which the electrodes 150 can be situated. In some embodiments, the
electrodes 150 are placed on the inner surface 140 of the cuff 100.
In these embodiments the electrodes 150 can be secured with
biocompatible adhesives, or with other forms of securement well
known in the art. In some embodiments, for example those shown in
FIG. 6, the electrodes can be located within a recess 220 in the
inner surface 140 of the cuff 100. Recessed electrode surfaces
provide an advantage in that they facilitate better cross-sectional
current distribution across a nerve as well as more uniform charge
injection into the tissue (e.g., a nerve) being stimulated (FIG. 6;
Suesserman et al., IEEE Trans. Biomed. Eng. 38: 401-408, 1991, the
entirety of which is incorporated herein by reference).
[0077] The cuff 100 comprises an enclosing member that is
configured to spontaneously adopt a generally tubular shape that
encloses the nerve 280, and in turn places the electrodes 150 in
contact with the surface of the nerve 280. The cuff is preferably
made from a resilient material such as silicone rubber, although
other materials known to those of skill in the art will perform the
necessary functions of the cuff 100. As shown in FIG. 4, the cuff
100 is in effect a sheet of material that is shaped such that it
will form the tubular structure shown in FIG. 3. The cuff 100 is
thus easy to install at the desired site along a nerve, and once in
place, it is allowed to roll up and form a tube with the nerve
situated inside the cuff.
[0078] In addition, the cuff 100 is inherently self-sizing, such
that it will accommodate range of nerve sizes, while maintaining
the integrity of the nerve/electrode interface. Moreover, the cuff
can be designed that it will maintain a contact pressure within a
range of about 10 mm Hg to about 30 mm Hg, over at least a two-fold
range of internal diameters, in some embodiments. Significantly,
the self-sizing feature also addresses a problem of many cuff style
electrode assemblies. It is important in some electrode devices to
have an intimate contact between the electrode(s) and the nerve, to
ensure that stimulation energy is efficiently delivered. However,
the need for "firm" contact must be balanced against the
physiological realities of a living tissue such as a nerve. Thus,
it is desirable that an electrode device does not impose excessive
pressure on the nerve in order to maintain contact, as pressure
can, and does, interrupt blood and nutrient supply, which in turn
can lead to nerve atrophy.
[0079] Therefore, the pressure exerted on the nerve by the cuff can
be maintained within a range of pressure which allow on one hand
for consistent electrical contact between the electrodes and the
nerve, while avoiding physically damaging the nerve. In embodiments
of the present disclosure, the cuff is configured such that when it
encloses the nerve, a relatively even pressure is maintained over
substantially the entire contact area between the cuff 100 and
nerve 300. In some embodiments, the pressure is maintained with a
range from about 2 mm Hg to about 30 mm Hg.
[0080] This is achieved in part by the composition of the cuff
material, but as well is provided by additional features of the
cuff design. Embodiments of the cuff of the present disclosure
include a first edge 230 and second edge 240 that are configured to
overlap with each other at 250, when the cuff 100 assumes its
tubular conformation, as shown in FIGS. 3-5, 7, and 8. When viewed
end on, as in FIG. 5, the overlap of the first edge 230 and second
edge 240 that slidably engage each other along a longitudinal split
region 250. In some embodiments the cuff 100 comprises a notch 210
into which the first edge 230 can nest. The point at which the
first edge abuts the notch 210 can define the smallest effective
interior radius of a cuff.
[0081] FIGS. 13A-C show that, with respect to the cuff center
longitudinal axis 205, the first edge 230 and notch 210 form an
angle, or as defined herein, an opening angle 207. In the
embodiment shown in FIG. 5, where the first edge 230 and notch 210
are in contact, the opening angle will be about 0.degree.. As the
cuff is expanded, the first edge 230 and second edge 240 will slide
relative to each other, and a space 209 will form between the first
edge 230 and the notch 210. In the expanded state, the first edge
230 and notch 210 will now define an angle relative to the cuff
axis 205 that is greater than zero, as shown in FIG. 9. When the
cuff is laid open, the opening angle will be about 180.degree., and
the first edge 230 and second edge 240 will not contact each other,
as shown in FIGS. 4 and 14B. When the cuff is installed, the length
of overlap is chosen to provide a wide enough range of opening
angles, while maintaining effectively even pressure over the
contact area. Another way to view the interaction of the cuff with
the object it encloses is that the cuff resists the expansion that
results from a change in diameter due to the enclosed object. The
degree of resistance is observed as a pressure exerted by the cuff
on the object, for example a nerve, and the design of the cuff is
such that this resistance will range from about 2 mm to about 30 mm
Hg, when the cuff is installed.
[0082] Thus, because the cuff is resilient, as the opening angle
increases from about 0.degree., the cuff will exert an increased
pressure (i.e., it will increasingly resist) around any object it
encloses. The cuff of the present disclosure is thus designed that
as the opening angle increases to about 30.degree., the pressure of
the cuff on the nerve will increase no greater than about 30 mm Hg.
The cuff is also designed such that at greater opening angles, the
cuff yields so that the value of 30 mm Hg is never exceeded. Nerves
swell during the post-operative period, and then over a period of
weeks, they shrink back to the pre-operative size. In some cases,
the degree of swelling can be as much as 30% of the original
diameter. Embodiments of the cuff electrode as disclosed are
capable of maintaining a contact pressure between about 2 mm Hg and
about 30 mm Hg upon initial placement of the cuff, and during the
period of postoperative swelling, and resolution of the
post-operative swelling of the nerve, over the range of size
changes that are seen in vivo. The length of the overlap region is
selected to permit this degree of diameter change, while
maintaining effective contact between the electrode(s) and the
nerve, and at same avoiding over-compression of the nerve.
[0083] Thus, in order to effectively maintain electrical
conductivity between the electrodes and the nerve, while avoiding
over-compressing the nerve, the cuff must be both resilient (to
maintain pressure) and compliant (to avoid over-compression). At
the same time, to permit relatively easy installation of the cuff
around a nerve, it is an advantage to be able to effectively lay
open the cuff (as shown in FIG. 4), so that the cuff can be placed
under the nerve at a desired location, for example by sliding the
cuff into place, without damaging the resilient components of the
cuff that produce the tubular form, and which engage the nerve at
the desired pressure (i.e., resistance).
[0084] One way in which to accomplish these features would be to
include a bias member, such as a spring, that compliantly resists
opening of the cuff. However, typical spring behavior is such that
as the cuff is opened, the amount of force needed to further open
the cuff increases. At extreme opening angles, such as when laying
open the cuff for installation, the large opening angle might
damage the spring and/or cuff could be damaged. Moreover, the
spring member would need to exert relatively low forces, and should
not exceed, for example, about 30 mm Hg at any opening angle.
[0085] In the present disclosure the resiliency is provided by an
elastic hinge 260. The elastic hinge 260 is designed such that it
has complex elastic properties. At low opening angles (0.degree. to
about)30.degree., the elastic hinge 260 is operative such that the
pressure exerted by the cuff on the enclosed nerve will range from
about 2 mm Hg to about 30 m Hg. At higher opening angles, the
elastic hinge 260 is configured to yield, due to the action of a
release member 265, such that the pressure exerted by the cuff
never rises above, for example, about 30 mm Hg. In the embodiment
illustrated, release member 265 includes an outer wall alongside
the longitudinal lumen 266 in the hinge region. When the angle of
opening exceeds a limit, the outside wall can buckle, for example,
bulge outward. This failure of the outer wall to provide a force to
resist the hinge opening can remove some of the closing pressure on
the cuff. When the cuff is closed again, the outer wall preferably
resiliently regains its shape to provide closing force on the cuff
again. As some nerves can swell to a diameter 30% greater than the
pre-operative diameter, the cuff is designed to expand to opening
angles in excess of 100.degree. without exceeding the 30 mm Hg
pressure limitation. The inner wall of the hinge region can
continue to provide an elastic force in tension in some
embodiments, even after the outer wall has buckled. This force can
be finely selected through the wall thickness and even co-extrusion
of a different material than the outer wall, in some
embodiments.
[0086] In some embodiments, depicted in FIGS. 10A and B, 11A and B,
and 12A-C, the elastic hinge 260 includes a hole 266 running
substantially the length of the cuff. Into the hole can be inserted
one or more elastic members 267. In some embodiments, the elastic
members 267 are telescoping such that they can be easily placed in
the hole, either as a group of elements or individually. Thus, as
shown in FIGS. 12A-C, the elastic hinge 260 can comprises one
elastic member 267 or a plurality of the same.
[0087] The elastic members 267 can be fashioned from the same
material as the cuff or from a different material, depending on the
mechanical properties one wishes to impart and/or the nerve
diameter to be enclosed. The number of members will likewise be
selected based on the desired elastic properties of the cuff, as
well as the degree to which one wishes the cuff to resist expansion
by an enclosed object. In some embodiments, as shown in FIGS. 13A-D
and FIG. 14 A and B, the elastic hinge comprises a relatively
thickened region 268, with a hole 266 located within the interior
of the thickened region. Here, increasing the opening angle
eventually result in the collapse of the relatively thinner outer
wall that defines the hole 266, such that the elastic hinge 260
yields, as best seen by comparing FIGS. 14A and 14B.
[0088] The electrodes used in the device can be made from a variety
of conductive materials well known in the art. For example,
electrodes can be fashioned from, without limitation, metals such
as platinum, iridium, or rhodium or gold, or from any other
electrically conductive biologically compatible material. The leads
can be made from similar materials to the electrodes, or from any
other materials suitable for use in nerve stimulation systems.
Typically leads will be insulated to prevent current leakage
between the signal generator or IPG and the electrodes. A variety
of signal generators or IPGs are also suitable for use with the
presently disclosed electrode.
[0089] In some embodiments, electrodes can be mounted on the inner
surface of the cuff portion of the device such that the electrode
is effectively flush with the inner surface of the cuff. In these
cases, the electrode will make intimate physical, and hence direct
electrical contact with the nerve surface. In some embodiments, it
is an advantage to provide electrodes that are recessed with
respect to the inner surface of the cuff portion. Studies have
shown that recessed electrodes more effectively inject charge, and
produce a more uniform electrical field across the surface on the
electrode, as compared to those mounted co-planar with the surface
of the surrounding matrix holding the electrodes (See, e.g.,
Suesserman et al., 1991, IEEE 38: 401-408).
[0090] The recess can comprise walls with varying geometries. For
example, in some embodiments a recess is configured such that the
walls are effectively perpendicular to the surface of the
electrode. In some embodiments, the walls of the recess are
exponentially recessed. In some embodiments, the walls of the
recess are conically recessed. In some embodiments, the walls are
recessed in a stepwise configuration that mimics a conically
recessed electrode. Exemplary embodiments of recessed electrodes
are depicted in FIG. 6.
[0091] In the case of a recessed electrode configuration,
conduction between the electrode and the nerve occurs via a
conductive material spanning the gap between the electrode surface
and the nerve surface. This depth of the recess 220 can vary. In
some embodiments, the depth of the recess ranges from about 10% to
about 125% of the diameter of the electrode. The conductive
material spanning the gap between the electrode surface and nerve
surface can comprise any suitable fluid, gel, or even solid that is
capable of effective conduction of electrical current from the
electrode to the nerve surface. Such materials can include, without
limitation, normal saline, electro-conductive gels, and the like.
For example, U.S. Pat. No. 5,178,143 to Kwak et al. (the entirety
of which is incorporated by reference herein) discloses an
electrically conductive gel comprising a cross-linked, neutralized
copolymer of maleic anhydride and a C1-05 alkyl vinyl ether. The
conductive material is applied to the recessed region prior to
placement of the cuff around the nerve. Sufficient material is
applied to prevent the occurrence of air gaps, which could
otherwise disrupt or alter the current pathway from the electrode
to the nerve.
[0092] FIG. 15A illustrates a hinge region including a wall 620, a
longitudinal lumen 621, and inner wall region 622, and an outer
wall region 623. During cuff opening, inner wall region 622 is in
tension while outer wall region 623 in is compression, in some
embodiments. Outer wall region 623 can fail in compression, and
either buckle inward or outward, in various embodiments. In varying
embodiments, lumen 621 can be round or oblong, either in the
direction of the wall or transverse to the wall circumference.
[0093] FIG. 15B illustrates another embodiment, having a wall
region 625, inner wall region 627, and buckled outer wall region
628, next to lumen 626. FIG. 15C illustrates yet another
embodiment, having wall region 630, having compressed lumen 631,
having an inner member 632 within. As lumen 626 is further
compressed, it can in turn apply compressive forces against inner
member 632. Why any gap surrounding the inner member is crossed,
the outer forces may eventually cause the inner member to
elastically compress and/or fail itself. In this way, the inner
member can serve as yet another spring constant which can resist
the further opening of the cuff. The inner member can be an elastic
solid shaft in some embodiments and a hollow tube in others.
[0094] FIG. 16 illustrates one embodiment of the invention in a
lead 330 having a proximal portion 334 and a distal portion 332.
Lead 330 includes a proximal connector 336 which can be an IS1
connector. A proximal lead body 344 extends distally from connector
336 and is coupled to a yoke 338. A distal lead body (or bodies)
346 extends distally from yoke 338 and is coupled to a cuff 340
through a strain relief 342.
[0095] In some embodiments, lead 330 proximal lead body 344
includes two electrically insulated conductors which are
electrically coupled at yoke 338 to two distal conductors. The
proximal conductor can be, for example, an electrically conductive
coil having two insulated conductors. Distal lead body 346 can be
two distinct insulated wires or cables in some embodiments, and can
be joined over their entire lengths or at certain distinct
positions by a polymeric substance. The design of lead 330 allows a
standard IS1 connector and coupled lead body to be coupled to a set
of finer, distal lead conductors. In the embodiment illustrated,
proximal lead body 344 is larger and more robust than the finer
wires found in the distal lead body 346. In some embodiments, yoke
338 also serves as a suture point for fixing the position of the
lead within the human body.
[0096] FIG. 17 illustrates yoke 338 in more detail. Proximal lead
body 344 may be seen to include coiled conductors 350 which are
electrically coupled within the yoke to two distinct proximal
conductor wires 354 and 356, both included within a polymeric body.
Yoke 338 can also include a suture hole 352, as illustrated.
[0097] FIG. 18 illustrates a cuff 340 having a proximal lead body
346 coupled to strain relief 342. Inspection of FIG. 18 shows a
cuff tubular body 360 having a slit 362 therethrough. Slit 362
allows the tubular body to be opened and placed over a nerve. A
flap 364 can be secured at flap region 366 to tubular body 360.
Flap 364 extends over slit 362 and around a tubular body 360 and
terminating in a flap free region 368. In some embodiments, flap
free region 368 is tapered. Cuff tubular body 360 has a tube
interior region 369 opposite slit 362 and between the conductor
plates. In the embodiment illustrated, there are generally opposed
distal conductor plates 374, an intermediate pair of conductor
plates 372, and proximal conductor plates 370. The conductor plates
can be recessed within the tube interior wall, to provide for
improved performance. In one embodiment, intermediate conductor
plates 372 form the cathode, and distal and proximal conductor
plates 374 and 370 form the anodes. In this embodiment cathode 372
is electrically coupled to one elongate conductor, for example,
distal conductor 354, while the distal and proximal conductor
plates 374 and 370 are coupled to the other distal conductor, for
example, distal conductor 356. If flap free region 368 were peeled
clockwise and free of tubular body 360, this would open the tubular
body about slit 362 and allow nerve cuff 340 to be placed over a
nerve. FIG. 19 illustrates yet another cuff 380, shown as a
subassembly not including the lead bodies. Cuff 380 is coupled to
strain relief 342. A flap 384 may be seen to wrap around the
tubular body and terminate in a free edge tapered flap 382. The
free edge tapered flap can provide a more suitable leading edge for
inserting under a nerve in a body. The pair of opposed distal
recessed conductor plates 374 may be seen in FIG. 19. A distal
jumper wire or spring 375 may also be seen in this embodiment,
located opposite of slit 362 in the tubular body.
[0098] FIG. 20 again illustrates cuff 380 of FIG. 19, from the
side. The free or leading a flap edge 382 is shown as are center
curved electrode plates 372, the proximal curved electrode plates
370, and the distal electrode plates 374. Jumper wires or springs
371, 373, and 375 may also be seen.
[0099] FIG. 21 illustrates a cuff subassembly 400 including a first
or anode conductor wire 402 coupled through a weld tube to top
cathode curved plate 406. Jumper wire or spring 373 may be seen to
electrically couple the first or top cathode plate 406 to the
bottom or second cathode plate 407. A second conductor or cathode
wire 404 may be seen electrically coupled through a weld tube or
otherwise welded to the proximal, top curved electrode plate 408.
Second conductor or cathode wire 404 extends past the middle
cathode plate and couples to the distal, top curved cathode plate
410. Top, proximal plate 408 is coupled through a jumper wire or
spring 371 to the bottom proximal conductor plate 409. Similarly,
the distal conductor top plate 410 is electrically coupled through
a jumper wire or spring 375 to the bottom conductor plate 411.
[0100] The middle conductor plates 406 and 407 are illustrated as
longer than each of the other plates. In one embodiment, the
cathode has a surface area about twice that of each of the adjacent
anode curved conductor plates. The total cathode surface area is
equal to the total anode surface area is some embodiments. In one
embodiment, both anode plates are spaced the same at distance from
the middle cathode plate. This means that, for example, distal
conductor plates 410 and 411 are the same distance from plates 406
and 407 as are plates 408 and 409.
[0101] Cuff subassembly 400 also includes a boxed or foldover
region 420. This can be used to receive the jumper wires, the weld
attachment tubes, and may also function to secure the cuff tubular
polymeric body to the conductor plates after the polymer is
added.
[0102] FIG. 22 again illustrates cuff subassembly 400, in greater
detail. Curved conductor plates 408, 406, and 410 are shown as
before. The second or cathode conductor wire 404 is coupled to the
top cathode plate 406 through a weld attachment tube, with the
conductor wire terminating at 428. Weld attachment tube 424 may
also be seen. In some embodiments, the conductor wire is inserted
within the tube and laser welded to the tube. The tube can then be
laser welded to the curved electrode plate. Conductor jumper wire
373 can be also laser welded to weld tubes and the jumper wire bent
into a curve shape on a bending jig. This subassembly can then be
inserted into the folded over region of the cathode curved
conductor plates and then laser welded to each of the conductor
plates. Similarly, the other elongate conductor wire 402 can be
electrically and physically coupled through a weld to the anode
curved electrode plates 408 and 410. This again can be performed
through the weld tubes previously discussed. In some embodiments,
the curved electrode plates are formed of platinum iridium alloy,
which can be about 0.001 inch in thickness. The jumper wires can be
formed of MP35N material, which can be about 0.0065 inch OD in some
embodiments. The weld tubes can be formed of stainless steel in
some embodiments. In some embodiments, the jumper wires and
conductor wires are laser welded more toward the free end of the
jumper wire or conductor wire within the weld tube. Referring again
to FIG. 22, the curved plate electrodes have fold over regions 120.
The conductor plates also have mooring slots 421 and mooring holes
426. During manufacture, when molten or pre-polymer solution is
infused over the curved plates and jumper wires, the material can
flow at least partially into the holes and slots and provide
polymeric anchoring points for the structure.
[0103] In some embodiments of the invention, the jumper wires, for
example, jumper wire 373 provides little in the way of mechanical
structural support of the finished cuff. In this embodiment, the
jumper wires neither substantially inhibit nor bias the opposed
curved plates to open or close about the nerve. In another
embodiment, the jumper wires can provide a spring like a function
to the overall cuff. In this embodiment, the jumper wires can
function as springs which serve to urge the opposed plate
electrodes back together when the electrodes are splayed far apart.
In one such embodiment, the polymeric material forming the cuff has
an elastic, non-linear spring constant such that the polymeric
material provides a stronger closing force when the cuff is nearly
closed and a weaker closing force as the cuff is splayed further
and further apart. In such an embodiment, the spring function of
the jumper wires can be engineered to have another spring constant
which provides lesser force as the opposed plates are splayed
further and further apart. Engineered springs are well known to
those skilled in the art and can be designed to meet the required
criteria. Some types of engineered springs are formed of multiple
filars which provide a spring constant. The orientation of the
filars and the surrounding structure can be such that the filars
are forced into a taller but narrower structure as the two opposed
conductor plates are splayed further apart. This increases the
thickness of the spring and hence the spring constant as well.
Pairing a nonlinear polymeric spring constant which decreases with
increasing opening of the cuff; with a nonlinear jumper wire spring
constant which increases with increased opening of the cuff
effectively creates a linear composite spring function. This
composite spring function decreases over most or all of the range
of cuff opening in some embodiments. In some embodiments, the
jumper wire function is served by different materials which may
separately serve the mechanical and electrical properties. E.g.
super elastic Nitinol wire having a separate more electrically
conductive wire or a coating.
[0104] FIG. 23 illustrates cuff 400 of FIG. 22 from the end. Cuff
400 includes anode conductor wire 402, a cathode wire 404, and
recessed curved plates 406 and 407, having foldover regions 420.
Jumper wire 373 and slit 430 are also illustrated. A polymeric body
423 is generally indicated as well. Inspection of FIG. 23 shows
jumper wire 373 enclosed within the polymeric material in the
embodiment illustrated. The curved plate electrodes 406 and 407 are
facing each other, leaving the sides in between the curved
electrodes free of surface electrode material. While jumper wire
373 may function as a weak electrode, this will likely be an
insubstantial contribution due to the additional insulating
material covering jumper wire 373. As discussed herein, embodiments
such as those illustrated in FIG. 22 and FIG. 23 may be said to be
substantially free of electrode material opposite the silt, or
substantially free of electrode material between the opposed curved
electrodes opposite the slit. A cursory inspection of FIG. 22 shows
that the surface area of jumper wire 373 contributes very little
compared to the surface area of the two opposed curved electrode
plates. This, coupled with the added insulation of the polymer in
some embodiments decreases further the electrode contribution of
the jumper wires.
[0105] FIG. 23 also shows that the curved electrode plates are not
forced to flex opposite slit 430 as the cuff is opened and shut
about the nerve. FIG. 23 shows that the polymeric region opposite
slit 430 can be substantially free of metallic material, allowing
the polymer to determine the physical properties of this hinge
region opposite slit 430. In some embodiments, the durometrer of
the polymeric material and the material itself can determine the
elastic properties of this hinge area. As previously discussed,
jumper wire 373 can contribute to the closing force when the cuff
is very much open, in some embodiments. In one example of the
invention, a 70 D material is used as the polymeric material.
Silicone rubber is a polymeric material used in some
embodiments.
[0106] FIG. 24 illustrates a top, a photographic view of one cuff
assembly 500 made according to the present invention. FIG. 24 has
some edges darkened with a pencil in order to highlight the edges
of some features. Cuff assembly 500 includes a strain relief 502, a
tapered flap 504, and a suture hole 527 in flap 504, with the flap
held open with a suture loop 506. The cuff assembly 500 also
includes a second suture 510 pulling at the edge of the tubular
cuff. The distal end 508 of the cuff is pulled further apart than
the more proximal end of the cuff, a causing the curved plate
electrodes to appear larger in the photograph on the distal left
side of the cuff. A proximal curved electrode pair 516 is coupled
by a jumper wire 517, as is an intermediate curved electrode pair
518 coupled by a jumper wire 519, and a distal curved electrode
pair 520 coupled by a jumper wire 521. A first elongate conductor
wire 512 is seen coupled to the intermediate electrode pair 518. A
second elongate conductor wire 514 is seen electrically coupling
proximal electrode pair 516 and distal electrode pair 520. As
previously discussed, elongate conductor 512 can be a cathode wire
and elongated electrical conductor 514 can be an anode wire, in
some embodiments.
[0107] FIGS. 25A and 25B illustrate other embodiments of the
invention which can provide a tube closing force which varies of
the extent of opening of the tube. FIG. 25A illustrates a
fragmentary portion of a tubular cuff electrode 600, having a
tubular wall portion 602 located substantially opposite the tube
slit and between the opposed plates. Tube wall 602 has an interior
wall surface 604 and an exterior wall surface 606. In the
embodiment illustrated, several wedge shaped slits 608 have been
formed into interior wall surface 604. The removal or absence of
material can provide a different closing force relative to a
similar tube not having the material removed. In one example, the
removed material can provide a weaker closing force when the tube
is almost entirely closed about the slit. Some embodiments have a
single section of material removed or never formed, while other
have several sections of material removed.
[0108] FIG. 25B illustrates a fragmentary portion of another
tubular cuff electrode 610, having a tubular wall portion 612
located substantially opposite the tube slit. Tube wall 612 has an
interior wall surface 614 and an exterior wall surface 616. In the
embodiment illustrated, several wedge shaped slits 618 have been
formed into exterior wall surface 616. The removed or missing
material can provide lesser closing force relative to a similar
tubular cuff not having the material removed. In yet another
embodiment, material sections are removed from both the interior
and exterior wall surfaces.
[0109] In use, the targeted nerve or nerve bundle can be teased
away from surrounding tissue, until the bottom of the nerve is free
of the tissue. Then suture loop 506 can be pulled under the nerve,
and cuff 500 unwrapped to assume a configuration which may be
similar to that shown in FIG. 24. Suture loop 506 can then be
pulled under the nerve, followed by tapered flap 504. With the
nerve disposed over the electrodes, suture loop 510 can be
released, allowing the tubular cuff to close over the nerve body.
Suture loop 506 can then be released allowing tapered flap 504 to
cover the slit and curl over the now at least partially closed
tubular body. The suture loops can then be cut and pulled from the
cuff in some embodiments.
[0110] Referring again to FIG. 23, another aspect of the invention
can be described. In some embodiments, the nerve may be irritated
by the surgical manipulation. The nerve may swell slightly or swell
later after the nerve cuff is in place. Slit 430 may not be fully
closed when the tubular cuff is first placed over the nerve. The
opened lead 430 will still preferably be covered by the flap (not
shown in FIG. 23). In some embodiments, the curved electrode plates
424 are symmetrical as shown in FIG. 23. In other embodiments, the
curved plate electrodes are closer opposite the slit than near the
slit. In other embodiments, the curved plate electrodes are closer
together near the slit than opposite the slit. In this latter
embodiment, the curved plate electrodes can be more nearly
symmetrically opposed to each other when the slit is still a part,
for example, due to an undersized cuff or a swollen nerve.
[0111] The cuff can be manufactured using methods well known to
those skilled in the art. In one method, a mandrel or core pin is
provided, and the curved plates temporarily adhered to the core
pin, for example, you using a cyanoacrylate adhesive. The jumper or
wires can be laser welded to the weld tubes and the jumper
wire-weld tube assembly can be inserted into the foldover region of
the curved electrode plates and the weld tubes laser welded to the
curved electrode plates. The elongate conductors to the cathode and
anode can also be laser welded to the curved electrode plates, for
example, by again using weld tubes. The mandrel or core pin now
carrying the curved electrode plates and a jumper wires can be
placed in a two-part mold. A molten polymer or a pre-polymeric
solution can be infused into the mold. The interior core pin or
mandrel can prevent the polymer from flowing too far into the
future cuff interior. The interior surface of the mold will prevent
the polymer from flowing too far outside of the future cuff. After
the polymer has cured or solidified, the interior of the mandrel or
core pin can be removed, leaving the cuff assembly. In some
methods, the proximal lead bodies can also be formed in this
process, for example, formed with the strain relief and the cuff.
The cuff subassembly can be coupled to the proximal
subassembly.
[0112] While the disclosed embodiments have generally been
described in the context of contacting a nerve with a self-sizing
cuff electrode, there are other physiological application for the
device as disclosed. For example, in addition to electrical
stimulation of nerves, other tissues can also be subjected to
simulation with electrical energy, and in some cases enclosing the
tissue in a resilient cuff can provide an advantage. For example,
the healing of difficult bone fractures using electrical current or
ultrasound is well known. The present cuff and electrode
combination can be readily adapted to a scale effective for use in
orthopedic applications.
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