U.S. patent number RE45,718 [Application Number 12/816,802] was granted by the patent office on 2015-10-06 for systems and methods for reversibly blocking nerve activity.
This patent grant is currently assigned to BOSTON SCIENTIFIC CORPORATION. The grantee listed for this patent is Warren M. Grill, Kevin L. Kilgore, Cameron C. McIntyre, John T. Mortimer. Invention is credited to Warren M. Grill, Kevin L. Kilgore, Cameron C. McIntyre, John T. Mortimer.
United States Patent |
RE45,718 |
Kilgore , et al. |
October 6, 2015 |
Systems and methods for reversibly blocking nerve activity
Abstract
Systems and methods for blocking nerve impulses use an implanted
electrode located on or around a nerve. A specific waveform is used
that causes the nerve membrane to become incapable of transmitting
an action potential. The membrane is only affected underneath the
electrode, and the effect is immediately and completely reversible.
The waveform has a low amplitude and can be charge balanced, with a
high likelihood of being safe to the nerve for chronic conditions.
It is possible to selectively block larger (motor) nerve fibers
within a mixed nerve, while allowing sensory information to travel
through unaffected nerve fibers.
Inventors: |
Kilgore; Kevin L. (Avon Lake,
OH), Grill; Warren M. (Chapel Hill, NC), McIntyre;
Cameron C. (Cleveland, OH), Mortimer; John T. (Chagrin
Falls, OH) |
Applicant: |
Name |
City |
State |
Country |
Type |
Kilgore; Kevin L.
Grill; Warren M.
McIntyre; Cameron C.
Mortimer; John T. |
Avon Lake
Chapel Hill
Cleveland
Chagrin Falls |
OH
NC
OH
OH |
US
US
US
US |
|
|
Assignee: |
BOSTON SCIENTIFIC CORPORATION
(Natick, MA)
|
Family
ID: |
54203995 |
Appl.
No.: |
12/816,802 |
Filed: |
June 16, 2010 |
PCT
Filed: |
February 20, 2002 |
PCT No.: |
PCT/US02/04887 |
371(c)(1),(2),(4) Date: |
February 17, 2004 |
PCT
Pub. No.: |
WO02/065896 |
PCT
Pub. Date: |
August 29, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
60269832 |
Feb 20, 2001 |
|
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Reissue of: |
10468642 |
Feb 20, 2002 |
7389145 |
Jun 17, 2008 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61N
1/36171 (20130101); A61N 1/36178 (20130101); A61N
1/36071 (20130101); A61N 1/3605 (20130101); A61N
1/36164 (20130101) |
Current International
Class: |
A61N
1/34 (20060101); A61N 1/36 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Bowman et al., "Response of Single Alpha Motoneurons to
High-Frequency Pulse Trains," Appl. Neurophysiol. 49: 121-138
(1986). cited by applicant .
Shaker et al., "Reduction of Bladder Outlet Resistance By Selective
Sacral Root Stimulation Using High-Frequency Blockade in Dogs: An
Acute Study," Journal of Urology, vol. 160, 901-907, Sep. 1998.
cited by applicant.
|
Primary Examiner: Schaetzle; Kennedy
Attorney, Agent or Firm: Tarolli, Sundheim, Covell &
Tummino LLP
Government Interests
.Iadd.GOVERNMENT FUNDING.Iaddend.
.Iadd.This invention was made with government support under grant
No. EB002091, awarded by the NIH-National Institute of Biomedical
Imaging and Bioengineering. The government has certain rights in
the invention..Iaddend.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
.Iadd.This application is a broadening reissue of Ser. No.
12/272,394, now U.S. Pat. No. 7,389,145, entitled "SYSTEMS AND
METHODS FOR REVERSIBLY BLOCKING NERVE ACTIVITY," issued on Jun. 17,
2008, by KILGORE et al. .Iaddend.
This application is a national stage filing under 35 U.S.C. 371 of
International Application PCT/US02/04887, filed Feb. 20, 2002,
which claims priority from U.S. application Ser. No. 60/269,832,
filed Feb. 20, 2001, the specifications of each of which are
incorporated by reference herein. International Application
PCT/US02/04887 was published under PCT Article 21(2) in English.
Claims
The invention claimed is:
.[.1. A method for selectively blocking activity of a nerve in an
animal by application of an electric current, said method
comprising: generating an electrical waveform having a first phase
with a first polarity, a first duration, and a first amplitude,
that produces subthreshold depolarization of the nerve membrane and
a second phase after the first phase that has a second polarity, a
second duration, and a second amplitude; and applying the waveform
to a targeted nerve region, wherein the phases of said waveform are
delivered at a rate of at least 5 kilohertz (kHz), and the ratio of
the amplitude of the second phase to the amplitude of the first
phase is about 1:1 to about 1:5..].
.[.2. The method as set forth in claim 1, wherein said first and
second phases are charge balanced..].
.[.3. The method as set forth in claim 1, wherein said pulses of
said waveform are delivered at a rate of between about 5 kilohertz
(kHz) and 10 kilohertz (kHz) inclusive..].
.[.4. The method as set forth in claim 1, wherein said second
amplitude is greater than said first amplitude..].
.[.5. The method as set forth in claim 1, wherein said second
duration is less than said first duration..].
.[.6. The method as set forth in claim 1, wherein at least one of
said first and second amplitude are increased over time to block
conduction of said action potential in progressively smaller nerve
fibers..].
.[.7. The method as set forth in claim 1, wherein the first
amplitude is about 0 to 1 milliamps..].
.[.8. A method for selectively blocking conduction of an action
potential in a nerve of an animal such as a human, said method
comprising: delivering an electrical waveform to a nerve, said
waveform comprising a series of bi-phasic pulses that, when applied
to said nerve, block conduction of an action potential by said
nerve, wherein said nerve comprises h gates and m gates and wherein
said bi-phasic pulses of said waveform close said h gates and said
m gates sufficiently to block said nerve from conducting said
action potential, wherein each pulse of said electrical waveform
comprises: a first phase having a first polarity, a first duration
and a first amplitude, said first amplitude less than an activation
threshold of said nerve; and, a second phase having a second
polarity, a second duration and a second amplitude, wherein the
pulses of said waveform are delivered at a rate of at least 5
kilohertz (kHz), and the ratio of the amplitude of the second phase
to the amplitude of the first phase is about 1:1 to about
1:5..].
.[.9. The method as set forth in claim 8, wherein said second
amplitude is greater than said first amplitude..].
.[.10. The method as set forth in claim 8, wherein said second
duration is less than said first duration..].
.[.11. The method as set forth in claim 8, wherein said pulses of
said waveform are delivered at a rate of between about 5 kilohertz
(kHz) and 10 kilohertz (kHz) inclusive..].
.[.12. The method as set forth in claim 8, wherein at least one of
said first and second amplitude are increased over time to block
conduction of said action potential in progressively smaller nerve
fibers..].
.[.13. The method as set forth in claim 8, further comprising:
monitoring at least one of electroneurogram (ENG) activity and
electromyogram (EMG) activity of the animal of which said nerve is
a part; and, using said at least one of said electroneurogram and
electromyogram activity to derive said waveform..].
.[.14. The method as set forth in claim 8, wherein said first phase
is cathodic and the second phase is anodic..].
.Iadd.15. A method, comprising: generating a steady state
electrical waveform, where the steady state electrical waveform has
a first phase having a first polarity, a first duration, and a
first amplitude, the first phase being a cathodic, depolarizing
phase configured to depolarize a nerve, where the steady state
electrical waveform has a second phase having a second polarity, a
second duration, and a second amplitude, the second phase being an
anodic, repolarizing phase configured to repolarize the nerve,
where the ratio of the first amplitude to the second amplitude is
1:1 to 1:5, where each of the first phase and the second phase has
a frequency in the range of 5 kiloHertz (KHz) up to 10 KHz, and
applying an electric current to the nerve in an animal according to
the steady state waveform, where applying the electric current
comprises: selectively, repetitively, alternately applying the
first phase of the steady state electrical waveform to the nerve
and then applying the second phase of the steady state electrical
waveform to the nerve for a period of time sufficient to arrest
signal transmission through the nerve, and arresting signal
transmission in progressively smaller nerve fibers in the nerve by
altering, over time, at least one of the first amplitude and the
second amplitude. .Iaddend.
.Iadd.16. The method of claim 15, where the first amplitude is
about 0 milliamps to 1 milliamps. .Iaddend.
.Iadd.17. A method, comprising: selectively blocking conduction of
an action potential in a nerve in an animal by selectively,
repetitively delivering a series of bi-phasic pulses to the nerve,
where a member of the series of the bi-phasic pulses has a first
phase and a second phase, the first phase having a first polarity,
a first duration, and a first amplitude, the first phase being a
cathodic, depolarizing phase, the second phase having a second
polarity, a second duration, and a second amplitude, the second
phase being an anodic, repolarizing phase, each of the first phase
and the second phase being delivered at a frequency in the range of
at least 5 KHz up to 10 KHz, where the ratio of the first amplitude
to the second amplitude is 1:1 to 1:5, and selectively blocking
conduction of action potentials in progressively smaller nerve
fibers in the nerve by altering, over a period of time, one or more
of the first amplitude and the second amplitude. .Iaddend.
.Iadd.18. The method of claim 17, where the first duration is
greater than the second duration. .Iaddend.
.Iadd.19. The method of claim 17, comprising: acquiring, from the
animal, one or more of, electroneurogram (ENG) data, and
electromyogram (EMG) data; and configuring the electrical waveform
as a function of one or more of, the ENG data, and the EMG data.
.Iaddend.
.Iadd.20. The method of claim 17, where selectively blocking
conduction of the action potential down regulates neural activity
in the animal. .Iaddend.
.Iadd.21. The method of claim 20, comprising down regulating neural
activity in an amount sufficient to treat a disease or condition.
.Iaddend.
.Iadd.22. The method of claim 21, the disease or condition being
one of, neuroma, spasticity, and muscle spasms. .Iaddend.
.Iadd.23. A method, comprising: selectively blocking conduction of
an action potential in a nerve in an animal by selectively,
repetitively delivering a series of bi-phasic pulses to the nerve,
where a member of the series of the bi-phasic pulses has a first
phase and a second phase, the first phase having a first polarity,
a first duration, and a first amplitude, the first phase being a
cathodic, depolarizing phase, the second phase having a second
polarity, a second duration, and a second amplitude, the second
phase being an anodic, repolarizing phase, each of the first phase
and the second phase being delivered at a frequency in the range of
at least 5 KHz up to 10 KHz, where the ratio of the first amplitude
to the second amplitude is 1:1 to 1:5, and where the first duration
is greater than the second duration. .Iaddend.
Description
FIELD OF THE INVENTION
This invention relates to systems and methods for selectively
blocking nerve activity in animals, including humans, e.g., to
reduce the incidence or intensity of muscle spasms, treat
spacticity, or for pain reduction.
BACKGROUND OF THE INVENTION
Spinal cord injury can lead to uncontrolled muscle spasms.
Spasticity can also occur as a result of stroke, cerebral palsy and
multiple sclerosis. Peripheral nerve injury can cause pain, such as
neuroma pain.
Various nerve blocking techniques have been proposed or tried to
treat spasms, spacticity, and pain. They have met with varying
degree of success. Problems have been encountered, such as damage
and destruction to the nerve, and the inability to achieve a
differentiation of nerve blocking effects among large and small
nerve fibers in a whole nerve.
SUMMARY OF THE INVENTION
The invention provides systems and methods for blocking nerve
impulses using an implanted electrode located near, on, or in a
nerve region. A specific waveform is used that causes the nerve
membrane to become incapable of transmitting an action potential.
The effect is immediately and completely reversible. The waveform
has a low amplitude and can be charge balanced, with a high
likelihood of being safe to the nerve for chronic conditions. It is
possible to selectively block larger (motor) nerve fibers within a
mixed nerve, while allowing sensory information to travel through
unaffected nerve fibers.
The applications for a complete non-destructive nerve block are
many. A partial or complete block of motor fiber activity can be
used for the reduction of spasms in spinal cord injury, and for the
reduction of spasticity in stroke, cerebral palsy and multiple
sclerosis. A complete block of sensory input, including pain
information, can be used as a method for pain reduction in
peripheral nerve injury, such as neuroma pain. A partial or
complete block of motor fiber activity could also be used in the
treatment of Tourette's Syndrome.
Other features and advantages of the inventions are set forth in
the following specification and attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is block diagram of a system that serves to generate a
waveform that stimulates a targeted nerve region to cause either a
partial or complete block of motor nerve fiber activity;
FIG. 2 is block diagram of an alternative embodiment of a system
that serves to generate a waveform that stimulates a targeted nerve
region to cause either a partial or complete block of motor nerve
fiber activity;
FIG. 3 is an enlarged view of a pulse controller that can be used
in association with the system shown in FIG. 1 or FIG. 2, the pulse
controller including a microprocessor that generates the desired
stimulation waveform;
FIG. 4 is a graph showing the shape of the stimulation waveform
that embodies features of the invention, which is constant current
and delivered through .[.at.]. .Iadd.an .Iaddend.electrode near the
nerve and comprises a depolarizing cathodic pulse for blocking
nerve conduction immediately followed by an anodic pulse;
FIG. 5 is a diagram depicting the presumed action of the voltage
controlled sodium ion gates during propagation of an action
potential along a nerve. The top trace shows the transmembrane
potential and the bottom trace shows the activity of the sodium
gates during the same time period. The action potential begins when
the m gates, which have a fast response time, open completely. The
h gates, which respond more slowly, begin to close, which begins to
restore the transmembrane potential. As the potential decreases,
the m gates close and the h gates return to their resting position
(partially open);
FIG. 6 is a diagram showing the action of the depolarizing waveform
shown in FIG. 4, which is also shown in FIG. 6 below the upper
graph, on the nerve membrane dynamics. The first cathodic, pulse
causes the h gate to close and the m gate to open slightly. The
anodic phase, which is shorter in duration, causes the m gate to
return to the fully open state, but the h gate, because it responds
more slowly, does not return completely to its resting value. As
subsequent pulses are delivered, the h gate progressively closes,
which causes the membrane to become inactivated. When the h gate is
sufficiently closed, the nerve membrane can no longer conduct an
action potential; and
FIG. 7 is a diagram depicting the progressive block of two
different nerve fiber diameters, the larger fiber responding to the
lower amplitude depolarizing pulse (shown in the lower half of the
diagram). The h gate is closed by this waveform and the large nerve
fiber becomes inactive. The stimulus amplitude can then be
increased so that inactivation of the smaller fiber can take
place.
The invention may be embodied in several forms without departing
from its spirit or essential characteristics. The scope of the
invention is defined in the appended claims, rather than in the
specific description preceding them. All embodiments that
.[.fail.]. .Iadd.fall .Iaddend.within the meaning and range of
equivalency of the claims are therefore intended to be embraced by
the claims.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The various aspects of the invention will be described in
connection with providing nerve stimulation to cause the blocking
of the transmission of action potentials along a nerve. That is
because the features and advantages that arise due to the invention
are well suited to this purpose. Still, it should be appreciated
that the various aspects of the invention can be applied to achieve
other objectives as well.
I. System Overview
FIG. 1 shows a system 10 that makes possible the stimulation of a
targeted nerve region N to cause either a partial or complete block
of motor nerve fiber activity, which is non-destructive and
immediately reversible. In use, the system 10 generates and
distributes specific electrical stimulus waveforms to one or more
targeted nerve regions N. The stimulation causes a blocking of the
transmission of action potentials in the targeted nerve region N.
The stimulation can be achieved by application of the waveforms
near, on, or in .Iadd.a .Iaddend.nerve region, using, e.g.,
.[.using.]. a nerve cuff electrode, .[.or.]. a nerve hook
electrode, .[.or.]. an intramuscular electrode, or a surface
electrode on a muscle or on the skin near a nerve region.
The system 10 comprises basic functional components including (i) a
control signal source 12; (ii) a pulse controller 14; (iii) a pulse
transmitter 16; (iv) a receiver/stimulator 18; (v) one or more
electrical leads 20; and (vi) one or more electrodes 22.
As assembled and arranged in FIG. 1, the control signal source 12
functions to generate an output, typically in response to some
volitional action by a patient, e.g., by a remote control switching
device, reed switch, or push buttons on the controller 14 itself.
Alternatively, the control signal source 12 can comprise
myoelectric surface electrodes applied to a skin surface, that,
e.g., would detect an impeding spasm based upon preestablished
criteria, and automatically generate an output without a volitional
act by a patient.
In response to the output, the pulse controller 14 functions
according to preprogrammed rules or algorithms, to generate a
prescribed electrical stimulus waveform, which is shown in FIG.
4.
The pulse transmitter 18 functions to transmit the prescribed
electrical stimulus waveform, as well as an electrical operating
potential, to the receiver/stimulator 18. The receiver/stimulator
18 functions to distribute the waveform, through the leads 20 to
the one or more electrodes 22. The one or more electrodes 22 store
electrical energy from the electrical operating potential and
function to apply the electrical signal waveform to the targeted
nerve region, causing the desired inhibition of activity in the
nerve fibers.
The basic functional components can be constructed and arranged in
various ways. In a representative implementation, some of the
components, e.g., the control signal source 12, the pulse
controller 14, and the pulse transmitter 16 comprise external units
manipulated outside the body. In this implementation, the other
components, e.g., the receiver/stimulator 18, the leads 20, and the
electrodes 22 comprise, implanted units placed under the skin
within the body. In this arrangement, the pulse transmitter 16 can
take the form of a transmitting coil, which is secured to a skin
surface over the receiver/stimulator 18, e.g., by tape. The pulse
transmitter 16 transmits the waveform and power through the skin to
the receiver/stimulator 18 in the form of radio frequency carrier
waves. Because the implanted receiver/stimulator 18 receives power
from the external pulse controller 14 through the external pulse
transmitter 16, the implanted receiver/stimulator 18 requires no
dedicated battery power source, and therefore has no finite
lifetime.
A representative example of this implementation (used to accomplish
functional electrical stimulation to perform a prosthetic
finger-grasp function) can be found is in Peckham et al U.S. Pat.
No. 5,167,229, which is incorporated herein by reference. A
representative commercial implementation can also be found in the
FREEHAND.TM. System, sold by NeuroControl Corporation. (Cleveland,
Ohio).
In an alternative arrangement (see FIG. 2), the leads 20 can be
percutaneously installed and be coupled to an external
interconnection block 24 taped to the skin. In this arrangement,
the pulse transmitter 16 is directly coupled by a cable assembly 26
(see FIG. 3, also) to the interconnection block 24. In this
arrangement, there is no need for a pulse transmitter 16 and
receiver/stimulator 18. A representative commercial example of this
implementation (used to achieve neuromuscular stimulation to
therapeutically treat shoulder subluxation and pain due to stroke)
can be found in the StIM.TM. System, sold by NeuroControl
Corporation (Cleveland, Ohio).
II. The Pulse Controller
The pulse controller 14 is desirably housed in a compact,
lightweight, hand held housing 28 (see FIG. 3). The controller 14
desirably houses a microprocessor 30. Desirably, the microprocessor
30 carries imbedded code, which expresses the pre-programmed rules
or algorithms under which the desired electrical stimulation
waveform is generated in response to input from the external
control source 12. The imbedded code can also include
pre-programmed rules or algorithms that govern operation of a
display and keypad on the controller 14 to create a user interface
32.
A. The Desired Electrical Stimulation Waveform
The waveform 34 that embodies features of the invention is shown in
FIG. 4. A stimulus provided by this waveform 34 is delivered to a
nerve N through the electrodes 22 located on or around the nerve N.
The waveform 34, when applied, places the nerve fiber membrane into
a state in which it is unable to conduct action potentials.
The specific electrical stimulus waveform 34 that can be applied to
cause a blocking of the transmission of action potentials along the
nerve has two phases 36 and 38 (see FIG. 4).
The first phase 36 produces subthreshold depolarization of the
nerve membrane through a low amplitude cathodic pulse. The first
phase 36 can be a shaped cathodic pulse with a duration of 0.1 to
1000 millisecond and a variable amplitude between 0 and 1 milliamp.
The shape of the pulse 36 can vary. It can, e.g., be a typical
square pulse, or possess a ramped shape. The pulse, or the rising
or falling edges of the pulse, can present various linear,
exponential, hyperbolic, or quasi-trapezoidal shapes.
The second phase 38 immediately follows the first pulse 36 with an
anodic current. The second anodic phase 38 has a higher amplitude
and shorter duration than the first pulse 36. The second pulse 38
can balance the charge of the first phase 36; that is, the total
charge in the second phase 38 can be equal but opposite to the
first phase 36, with the second phase having a higher amplitude and
shorter duration. However, the second pulse 38 need not balance the
charge of the first pulse 36. The ratio of the absolute value of
the amplitudes of the second phase 38 compared to the first phase
36 can be, e.g., 1.0 to 5.0. Because of the short duration of the
anodic phase 38, the nerve membrane does not completely recover to
the non-polarized state.
This biphasic pulse is repeated continuously to produce the
blocking stimulus waveform. The pulse rate will vary depending on
the duration of each phase, but will be in range of 0.5 Hz up to,
10 KHz. When this stimulus waveform 34 is delivered at the
appropriate rate, typically about 5 kHz, the nerve membrane is
rendered incapable of transmitting an action potential. This type
of conduction block is immediately reversible by ceasing the
application of the waveform.
Larger nerve fibers have a lower threshold for membrane
depolarization, and are therefore blocked at low stimulus
amplitudes. As a result, it is possible to block only the largest
nerve fibers in a whole nerve, while allowing conduction in the
smaller fibers. At higher stimulus amplitudes, all sizes of fibers
can be blocked completely.
The physiological basis on which the waveform 34 is believed to
work can be described .[...]. using the values of the sodium gating
parameters, as shown in FIG. 5. The unique ability of the nerve
axon to transmit signals is due to the presence of voltage
controlled ion channels. The function of the sodium ion channels
are influenced by two gates. One gate responds quickly to voltage
changes, and is frequently termed the "m" gate. The other gate
responds more slowly to voltage changes, and is termed the "h"
gate. When the nerve is in, the rest condition, the m gates are
almost completely closed, while the h gates are partially opened.
When an action potential propagates along the axon, the m gates
open rapidly, resulting in a rapid depolarization of the nerve
membrane. The h gates respond by slowly closing. The membrane
begins to repolarize, and the m gates begin to close rapidly. At
the end of action potential generation, the m gates have returned
to their initial state and the nerve membrane is slightly more
polarized than at rest. The h gates return more slowly to their
resting values, producing a period of reduced excitability which is
referred to as the refractory period. The same series of events can
be initiated by an externally applied cathodic (depolarizing)
stimulus pulse. This is the basis for electrical stimulation of
nerves.
The waveform 34 of the invention makes use of the different
relative responses of the two types of sodium ion channel gates.
The first phase 36 of the waveform 34 is a subthreshold
depolarizing pulse. The nerve membrane response is shown in FIG. 6.
The h gates begin to slowly close during the first phase, while the
m gates respond by opening only slightly. As long as the initial
phase is maintained below the activation threshold for the nerve,
the m gates will exhibit only a small response. If the depolarizing
pulse 36 is maintained for long periods of time, the h gates will
eventually close to the point that the membrane is no longer able
to transmit an action potential.
The second phase 38 of the waveform 34 is a hyperpolarizing pulse
of shorter duration than the initial depolarizing pulse. The effect
of this pulse 38 is to cause the m gates to close completely and
the h gates begin to slowly open. However, since this phase 38 is
shorter than the first phase 36, the h gates do not return to their
resting levels by the end of the phase 38. A second pulse of the
waveform 34 of the same shape is then delivered to the nerve. The
depolarization of the first phase 36 results in further closing of
the h gates, with slight opening of the m gates. Some opening of
the h gates again occurs with the second hyperpolarizing phase 38
of the pulse, but recovery back to the initial value does not
occur. With subsequent pulses, the h gate progressively nears
complete closing, while the m gate varies slightly between fully
closed and slightly open. Due to the dynamics of the h gate, it
will not fully close, but will continue to oscillate with each
pulse near the fully closed condition. With both the m gate and the
h gate nearly closed, the nerve membrane is now incapable of
conducting action potentials. The nerve is effectively blocked.
This block can be maintained indefinitely by continuously
delivering these pulses to the nerve. The block is quickly
reversible when the stimulation is stopped. The h and m gates will
return to their resting values within a few milliseconds, and the
nerve will again be able to transmit action potentials.
Larger nerve fibers will have a lower threshold for subthreshold
depolarizing block. Therefore, when the blocking waveform is
delivered to a whole nerve, only the largest nerve fibers will be
blocked. This provides a means of selective block, allowing a block
of motor activation without affecting sensory information, which
travels along the smaller nerves.
In order to generate a block of smaller nerve fibers in a large
nerve, the amplitude of the waveform can be increased. As the
amplitude is increased, the first phase of the waveform may produce
a stimulated action potential in the larger nerves. However,
because of the nerve membrane dynamics, it is possible to gradually
increase the stimulus amplitude over time with each successive
pulse, until even the smallest nerve fibers are blocked. This, is
shown in FIG. 7. Very low amplitude pulses are used to put the
membrane of the largest nerve fibers into an unexcitable state over
the course of a few pulses. Once these largest fibers are at a
steady state, they will not be activated even by very large
cathodic pulses. At this point, the blocking stimulus amplitude can
be increased so that it produces the closed h and m gate response
in the smaller nerve fibers. The amplitude can be progressively
increased until all nerve fibers are blocked. This progressive
increase can occur rather quickly, probably within a few hundred
milliseconds. This mechanism also serves to underscore the
possibility of selective blocking of fibers of largest size using
this waveform.
EXAMPLE 1
Neuroma Pain
A system 10 such as shown in FIG. 1 can be used to block neuroma
pain association with an amputated arm of leg. In this arrangement,
one or more electrodes 22 are secured on, in, or near the neuroma.
The pulse controller 14 can comprise a handheld, battery powered
stimulator having an on-board microprocessor. The microprocessor is
programed by a clinician to generate a continuous waveform that
embodies features of the invention, having the desired amplitude,
duration, and shape to block nerve impulses, in the region of the
neuroma. The pulse controller 14 can be coupled to the electrode,
e.g., by percutaneous leads, with one channel dedicated to, each
electrode used. A control signal source 12 could comprise an on-off
button on the stimulator, to allow the individual to suspend or
continue the continuous application of the waveform, to block the
neuroma pain. No other special control functions would be
required.
EXAMPLE 2
Muscle Spasms Due to Spinal Cord Injury, Cerebral Palsy, or
Tourett's Syndrome
A system 10 like that shown in FIG. 1 can be used to block muscle
spasms due to, e.g., a spinal cord injury, cerebral palsy, or
tourett's syndrome. In this arrangement, one or more electrodes 22
are secured on, in, or near the nerve or nerves affecting the
muscle spasms. As in Example 1, the pulse controller 14 can
comprise a handheld, battery powered stimulator having an on-board
microprocessor. The microprocessor is programed by a clinician to
generate a continuous waveform that embodies features of the
invention, having the desired amplitude, duration, and shape to
block nerve impulses in the region of the muscle spasms. As in
Example 1, the pulse controller 14 can be coupled to the electrode,
e.g., by percutaneous leads, with one channel dedicated to each
electrode used. A control signal source 12 could comprise an on-off
button on the stimulator, to allow the individual to suspend or
continue the continuous application of the waveform, to block the
muscle spasms. Thus, for example, the individual could turn the
stimulator off during sleep, or during a period where muscle
function is otherwise desired. The selective stimulation-off
feature also allows the individual to perform muscle functions
necessary to maintain muscle tone. In this arrangement, no other
special control functions would be required.
Alternatively, the control signal source 12 could comprise an
electrode to sense electroneurogram (ENG) activity in the region
where muscle spasms occur. The electrode could comprise the
stimulation electrode itself, or a separate ENG sensing electrode.
The electrode detects ENG activity of a predetermined level above
normal activity (e.g., normal ENG activity X10), identifying a
spasm episode. In this arrangement, the microprocessor is programed
to commence generation of the desired waveform when the above
normal ENG activity is sensed. The microprocessor is programmed to
continue to generate the waveform for a prescribed period of time
(e.g., 1 minute) to block the spasm, and then cease waveform
generation until another spasm episode is detected. In this
arrangement, the stimulator can also include a manual on-off
button, to suspend operation of the stumulator in response to input
from the sensing electrode.
EXAMPLE 3
Block Uncoordinated Finger Flexure Spasms Due to Multiple Sclerosis
or Stroke
A system 10 like that shown in FIG. 1 can be used to block finger
flexure spasms due to, e.g., a multiple sclerosis or stroke. In
this arrangement, one or more epimysial and intramuscular
electrodes 22 are appropriately implanted by a surgeon in the
patient's arm. The implanted electrodes 22 are positioned by the
surgeon by conventional surgical techniques to block conduction of
impulses to finger flexure muscles. As in Example 1, the pulse
controller 14 can comprise a handheld, battery powered stimulator
having an on-board microprocessor. The microprocessor is programed
by a clinician to generate a continuous waveform that embodies
features of the invention, having the desired amplitude, duration,
and shape to provide a low level block of nerve impulses to the
finger flexure muscles. A control signal source 12 could comprise
an on-off button on the stimulator, to allow the individual to
select the continuous application of the waveform, e.g., while the
individual is opening or closing their hand.
Alternatively, the control signal source 12 could comprise an
electrode to sense electromyogram (EMG) activity in the finger
flexor muscles. The electrode detects EMG activity during
stimulated activation of the finger extensor muscles. If this
activity exceeds a preset level (e.g. 30% maximum contraction
level), the microprocessor is programmed to commence generation of
the desired waveform to block some or all of the finger flexor
muscle activity. The microprocessor can be programmed to deliver a
block proportional to the level of EMG activity, or to deliver a
block for a prescribed period of time, or to deliver a block as
determined through a combination of parameters (e.g., EMG activity
from multiple muscles in the arm).
In another alternative embodiment, the control signal source 12 can
comprise comprises a mechanical joy stick-type control device,
which senses movement of a body region, e.g., the shoulder.
Movement of the body region in one prescribed way causes the
microprocessor to commence generation of the desired waveform.
Movement of the body region in another prescribed way causes the
microprocessor to cease generation of the desired waveform.
In either alternative arrangements, the stimulator can also include
a manual on-off button, to suspend operation of the stumulator in
response to the external inputs.
Various features of the invention are set forth in the following
claims.
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