U.S. patent application number 16/520630 was filed with the patent office on 2019-12-12 for devices and methods for non-invasive electrical stimulation and their use for vagal nerve stimulation.
The applicant listed for this patent is ElectroCore, Inc.. Invention is credited to Joseph P. Errico, John T. Raffle, Bruce J. Simon.
Application Number | 20190374771 16/520630 |
Document ID | / |
Family ID | 51865347 |
Filed Date | 2019-12-12 |
United States Patent
Application |
20190374771 |
Kind Code |
A1 |
Simon; Bruce J. ; et
al. |
December 12, 2019 |
DEVICES AND METHODS FOR NON-INVASIVE ELECTRICAL STIMULATION AND
THEIR USE FOR VAGAL NERVE STIMULATION
Abstract
A non-invasive electrical stimulation device shapes an elongated
electric field of effect that can be oriented parallel to a long
nerve, such as a vagus nerve in a patient's neck, producing a
desired physiological response in the patient. The stimulator
comprises a source of electrical power, at least one electrode and
a continuous electrically conducting medium in which the
electrode(s) are in contact. The stimulation device is configured
to produce a peak pulse voltage that is sufficient to produce a
physiologically effective electric field in the vicinity of a
target nerve, but not to substantially stimulate other nerves and
muscles that lie between the vicinity of the target nerve and
patient's skin. Current is passed through the electrodes in bursts
of preferably five sinusoidal pulses, wherein each pulse within a
burst has a duration of preferably 200 microseconds, and bursts
repeat at preferably at 15-50 bursts per second.
Inventors: |
Simon; Bruce J.; (Mountain
Lakes, NJ) ; Errico; Joseph P.; (Warren, NJ) ;
Raffle; John T.; (Austin, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ElectroCore, Inc. |
Basking Ridge |
NJ |
US |
|
|
Family ID: |
51865347 |
Appl. No.: |
16/520630 |
Filed: |
July 24, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15149406 |
May 9, 2016 |
10363415 |
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16520630 |
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14337930 |
Jul 22, 2014 |
9333347 |
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15149406 |
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13075746 |
Mar 30, 2011 |
8874205 |
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14337930 |
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12964050 |
Dec 9, 2010 |
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13075746 |
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12859568 |
Aug 19, 2010 |
9037247 |
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12964050 |
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61451259 |
Mar 10, 2011 |
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61415469 |
Nov 19, 2010 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61N 1/36053 20130101;
A61N 1/0472 20130101; A61N 1/0456 20130101; A61N 1/36034 20170801;
A61N 1/36014 20130101; A61N 2/006 20130101; A61N 1/40 20130101 |
International
Class: |
A61N 1/36 20060101
A61N001/36; A61N 1/04 20060101 A61N001/04; A61N 2/00 20060101
A61N002/00 |
Claims
1. A method comprising: positioning a contact surface of a housing
in contact with an outer skin surface of a body of a patient;
generating an electrical impulse within the housing, wherein the
electrical impulse comprises bursts of pulses with each of the
bursts having a frequency from about 1 Hz to about 100 Hz and with
each of the pulses generated from a signal that is not modulated by
another signal; and conducting the electrical impulse from the
contact surface through the outer skin surface to a target region
in the patient such that an electrical field is generated in the
target region and the electrical field modulates a nerve in the
target region.
2. The method of claim 1, wherein the conducting comprises spacing
an electrode within the housing from the outer skin surface.
3. The method of claim 1, wherein the conducting comprises
conducting the electrical impulse from inside the housing and
through the contact surface to the outer skin surface.
4. The method of claim 1, wherein each of the pulses has a duration
of about 100 microseconds to about 400 microseconds.
5. The method of claim 1, wherein each of the pulses has a duration
of about 200 microseconds.
6. The method of claim 1, wherein the target region is a first
target region and further comprising: constraining the electrical
impulse from modulating a nerve at a second target region between
the outer skin surface and the first target region.
7. The method of claim 6, wherein the constraining comprises
positioning an electrically conductive medium around a portion of
an electrode within the housing such that a direction of a
generated electric field is constrained within the electrically
conductive medium.
8. The method of claim 6, wherein the constraining comprises
positioning an electrical insulator around a portion of an
electrode within the housing such that a component of a generated
electric field substantially normal to a surface of the electrical
insulator is about zero.
9. The method of claim 1, wherein the generating comprises
generating the electric field within the housing with a power
supply contained within the housing.
10. The method of claim 1, wherein the generating comprises
generating a magnetic field within the housing, wherein the
magnetic field is sufficient to induce the electric field at the
target region.
11. The method of claim 1, wherein the target region includes a
vagus nerve.
12. The method of claim 1, wherein the positioning comprises
positioning the contact surface in contact with a neck of the
patient.
13. The method of claim 7, wherein the electrically conductive
medium comprises an electrically conductive gel.
14. The method of claim 1, wherein the electric field has a
gradient of greater than about 2 V/m/mm.
15. The method of claim 1, wherein the electrical field has an
amplitude equal to or greater than about 10 V/m and equal to or
less than about 600 V/m.
16. The method of claim 1, wherein the nerve is modulated to treat
at least one of a disorder of the patient or a condition of the
patient, wherein at least one of the disorder or the condition
includes at least one of primary headache, allergic rhinitis,
Alzheimer's disease, postoperative cognitive dysfunction,
rheumatoid arthritis, bronchoconstriction, Parkinson's disease,
dementia, multiple sclerosis, neurodegenerative disease,
depression, epilepsy, gastroparesis, or an auto-immune disease or
disorder.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Divisional of U.S. Non-Provisional
application Ser. No. 15/149,406 filed 9 May 2016; which is a
Divisional of U.S. Non-Provisional application Ser. No. 14/337,930
filed 22 Jul. 2014 now U.S. Pat. No. 9,333,347 issued 10 May 2016;
which is a Continuation of U.S. Non-Provisional application Ser.
No. 13/075,746 filed 30 Mar. 2011 now U.S. Pat. No. 8,874,205
issued 28 Oct. 2015, which (i) claims the benefit of priority to
U.S. Provisional Application Ser. No. 61/451,259 filed 10 March
2011, and (ii) is a Continuation in Part of U.S. Non-Provisional
application Ser. No. 12/964,050 filed 9 Dec. 2010, which (i) claims
the benefit of priority to U.S. Provisional Application Ser. No.
61/415,469 filed 19 Nov. 2010, and (ii) is a Continuation in Part
of U.S. Non-Provisional application Ser. No. 12/859,568 filed 19
Aug. 2010 now U.S. Pat. No. 9,037,247 issued 19 May 2015; each of
which is fully incorporated by reference herein for all
purposes.
BACKGROUND OF THE INVENTION
[0002] The field of the present invention relates to the delivery
of energy impulses (and/or fields) to bodily tissues for
therapeutic purposes. It relates more specifically to the use of
non-invasive devices and methods, particularly transcutaneous
electrical nerve stimulation devices, as well as methods of
treating patients using energy that is delivered by such devices.
The disclosed methods and devices may be used to stimulate the
vagus nerve of a patient to treat many conditions, such as:
headaches such as migraine headaches, tension headaches, sinus
headaches, cluster headaches and the like, allergic rhinitis,
post-operative ileus, dysfunction associated with TNF-alpha in
Alzheimer's disease, postoperative cognitive dysfunction,
postoperative delirium, rheumatoid arthritis, asthmatic
bronchoconstriction, urinary incontinence and/or overactive
bladder, and sphincter of Oddi dysfunction, as well as
neurodegenerative diseases more generally, including essential
tremor, Alzheimer's disease and its precursor mild cognitive
impairment (MCI), Parkinson's disease (including Parkinson's
disease dementia) and multiple sclerosis.
[0003] Treatments for various infirmities sometime require the
destruction of otherwise healthy tissue in order to produce a
beneficial effect. Malfunctioning tissue is identified and then
lesioned or otherwise compromised in order to produce a beneficial
outcome, rather than attempting to repair the tissue to its normal
functionality. A variety of techniques and mechanisms have been
designed to produce focused lesions directly in target nerve
tissue, but collateral damage is inevitable.
[0004] Other treatments for malfunctioning tissue can be medicinal
in nature, but in many cases the patients become dependent upon
artificially synthesized chemicals. In many cases, these medicinal
approaches have side effects that are either unknown or quite
significant. Unfortunately, the beneficial outcomes of surgery and
medicines are often realized at the cost of function of other
tissues, or risks of side effects.
[0005] The use of electrical stimulation for treatment of medical
conditions has been well known in the art for nearly two thousand
years. It has been recognized that electrical stimulation of the
brain and/or the peripheral nervous system and/or direct
stimulation of the malfunctioning tissue holds significant promise
for the treatment of many ailments, because such stimulation is
generally a wholly reversible and non-destructive treatment.
[0006] Nerve stimulation is thought to be accomplished directly or
indirectly by depolarizing a nerve membrane, causing the discharge
of an action potential; or by hyperpolarization of a nerve
membrane, preventing the discharge of an action potential. Such
stimulation may occur after electrical energy, or also other forms
of energy, are transmitted to the vicinity of a nerve [F. RATTAY.
The basic mechanism for the electrical stimulation of the nervous
system. Neuroscience 89 (2, 1999):335-346; Thomas HEIMBURG and
Andrew D. Jackson. On soliton propagation in biomembranes and
nerves. PNAS 102 (28, 2005): 9790-9795]. Nerve stimulation may be
measured directly as an increase, decrease, or modulation of the
activity of nerve fibers, or it may be inferred from the
physiological effects that follow the transmission of energy to the
nerve fibers.
[0007] One of the most successful applications of modern
understanding of the electrophysiological relationship between
muscle and nerves is the cardiac pacemaker. Although origins of the
cardiac pacemaker extend back into the 1800's, it was not until
1950 that the first practical, albeit external and bulky, pacemaker
was developed. The first truly functional, wearable pacemaker
appeared in 1957, and in 1960, the first fully implantable
pacemaker was developed.
[0008] Around this time, it was also found that electrical leads
could be connected to the heart through veins, which eliminated the
need to open the chest cavity and attach the lead to the heart
wall. In 1975 the introduction of the lithium-iodide battery
prolonged the battery life of a pacemaker from a few months to more
than a decade. The modern pacemaker can treat a variety of
different signaling pathologies in the cardiac muscle, and can
serve as a defibrillator as well (see U.S. Pat. No. 6,738,667 to
DENO, et al., the disclosure of which is incorporated herein by
reference).
[0009] Another application of electrical stimulation of nerves has
been the treatment of radiating pain in the lower extremities by
stimulating the sacral nerve roots at the bottom of the spinal cord
(see U.S. Pat. No. 6,871,099 to WHITEHURST, et al., the disclosure
of which is incorporated herein by reference).
[0010] Electrical stimulation of the brain with implanted
electrodes has also been approved for use in the treatment of
various conditions, including movement disorders such as essential
tremor and Parkinson's disease. The principle underlying these
approaches involves disruption and modulation of hyperactive
neuronal circuit transmission at specific sites in the brain.
Unlike potentially dangerous lesioning procedures in which aberrant
portions of the brain are physically destroyed, electrical
stimulation is achieved by implanting electrodes at these sites.
The electrodes are used first to sense aberrant electrical signals
and then to send electrical pulses to locally disrupt pathological
neuronal transmission, driving it back into the normal range of
activity. These electrical stimulation procedures, while invasive,
are generally conducted with the patient conscious and a
participant in the surgery.
[0011] However, brain stimulation, and deep brain stimulation in
particular, is not without some drawbacks. The procedure requires
penetrating the skull, and inserting an electrode into brain matter
using a catheter-shaped lead, or the like. While monitoring the
patient's condition (such as tremor activity, etc.), the position
of the electrode is adjusted to achieve significant therapeutic
potential. Next, adjustments are made to the electrical stimulus
signals, such as frequency, periodicity, voltage, current, etc.,
again to achieve therapeutic results. The electrode is then
permanently implanted, and wires are directed from the electrode to
the site of a surgically implanted pacemaker. The pacemaker
provides the electrical stimulus signals to the electrode to
maintain the therapeutic effect. While the therapeutic results of
deep brain stimulation are promising, significant complications may
arise from the implantation procedure, including stroke induced by
damage to surrounding tissues and the neuro-vasculature.
[0012] Most of the above-mentioned applications of electrical
stimulation involve the surgical implantation of electrodes within
a patient. In contrast, for embodiments of the present invention,
the disclosed devices and medical procedures stimulate nerves by
transmitting energy to nerves and tissue non-invasively. They may
offer the patient an alternative that does not involve surgery. A
medical procedure is defined as being non-invasive when no break in
the skin (or other surface of the body, such as a wound bed) is
created through use of the method, and when there is no contact
with an internal body cavity beyond a body orifice (e.g, beyond the
mouth or beyond the external auditory meatus of the ear). Such
non-invasive procedures are distinguished from invasive procedures
(including minimally invasive procedures) in that invasive
procedures do involve inserting a substance or device into or
through the skin or into an internal body cavity beyond a body
orifice. For example, transcutaneous electrical nerve stimulation
(TENS) is non-invasive because it involves attaching electrodes to
the surface of the skin (or using a form-fitting conductive
garment) without breaking the skin. In contrast, percutaneous
electrical stimulation of a nerve is minimally invasive because it
involves the introduction of an electrode under the skin, via
needle-puncture of the skin (see commonly assigned co-pending US
Patent Application 2010/0241188, entitled Percutaneous Electrical
Treatment of Tissue to ERRICO et al, which is hereby incorporated
by reference in its entirety).
[0013] Potential advantages of non-invasive medical methods and
devices relative to comparable invasive procedures are as follows.
The patient may be more psychologically prepared to experience a
procedure that is non-invasive and may therefore be more
cooperative, resulting in a better outcome. Non-invasive procedures
may avoid damage of biological tissues, such as that due to
bleeding, infection, skin or internal organ injury, blood vessel
injury, and vein or lung blood clotting. Non-invasive procedures
generally present fewer problems with biocompatibility. In cases
involving the attachment of electrodes, non-invasive methods have
less of a tendency for breakage of leads, and the electrodes can be
easily repositioned if necessary. Non-invasive methods are
sometimes painless or only minimally painful and may be performed
without the need for even local anesthesia. Less training may be
required for use of non-invasive procedures by medical
professionals. In view of the reduced risk ordinarily associated
with non-invasive procedures, some such procedures may be suitable
for use by the patient or family members at home or by
first-responders at home or at a workplace, and the cost of
non-invasive procedures may be reduced relative to comparable
invasive procedures.
[0014] Electrodes that are applied non-invasively to the surface of
the body have a long history, including electrodes that were used
to stimulate underlying nerves [L. A. GEDDES. Historical Evolution
of Circuit Models for the Electrode-Electrolyte Interface. Annals
of Biomedical Engineering 25 (1997):1-14]. However, electrical
stimulation of nerves in general fell into disfavor in middle of
the twentieth century, until the "gate theory of pain" was
introduced by Melzack and Wall in 1965. This theory, along with
advances in electronics, reawakened interest in the use of
implanted electrodes to stimulate nerves, initially to control
pain. Screening procedures were then developed to determine
suitable candidates for electrode implantation, which involved
first determining whether the patient responded when stimulated
with electrodes applied to the surface of the body in the vicinity
of the possible implant. It was subsequently found that the surface
stimulation often controlled pain so well that there was no need to
implant a stimulating electrode [Charles Burton and Donald D.
Maurer. Pain Suppression by Transcutaneous Electronic Stimulation.
IEEE Transactions on Biomedical Engineering BME-21(2, 1974):
81-88]. Such non-invasive transcutaneous electrical nerve
stimulation (TENS) was then developed for treating different types
of pain, including pain in a joint or lower back, cancer pain,
post-operative pain, post-traumatic pain, and pain associated with
labor and delivery [Steven E. ABRAM. Transcutaneous Electrical
Nerve Stimulation. pp 1-10 in: Joel B. Myklebust, ed. Neural
stimulation (Volume 2). Boca Raton, Fla. CRC Press 1985; WALSH D M,
Lowe A S, McCormack K. Willer J-C, Baxter G D, Allen J M.
Transcutaneous electrical nerve stimulation: effect on peripheral
nerve conduction, mechanical pain threshold, and tactile threshold
in humans. Arch Phys Med Rehabil 79(1998):1051-1058; J A CAMPBELL.
A critical appraisal of the electrical output characteristics of
ten transcutaneous nerve stimulators. Clin. phys. Physiol. Meas.
3(2,1982): 141-150; Patents U.S. Pat. No. 3,817,254, entitled
Transcutaneous stimulator and stimulation method, to Maurer; U.S.
Pat. No. 4,324,253, entitled Transcutaneous pain control and/or
muscle stimulating apparatus, to Greene et al; U.S. Pat. No.
4,503,863, entitled Method and apparatus for transcutaneous
electrical stimulation, to Katims; U.S. Pat. No. 5,052,391,
entitled High frequency high intensity transcutaneous electrical
nerve stimulator and method of treatment, to Silberstone et al;
U.S. Pat. No. 6,351,674, entitled Method for inducing
electroanesthesia using high frequency, high intensity
transcutaneous electrical nerve stimulation, to Silverstone].
[0015] As TENS was being developed to treat pain, non-invasive
electrical stimulation using surface electrodes was simultaneously
developed for additional therapeutic or diagnostic purposes, which
are known collectively as electrotherapy. Neuromuscular electrical
stimulation (NMES) stimulates normally innervated muscle in an
effort to augment strength and endurance of normal (e.g., athletic)
or damaged (e.g., spastic) muscle. Functional electrical
stimulation (FES) is used to activate nerves innervating muscle
affected by paralysis resulting from spinal cord injury, head
injury, stroke and other neurological disorders, or muscle affected
by foot drop and gait disorders. FES is also used to stimulate
muscle as an orthotic substitute, e.g., replace a brace or support
in scoliosis management. Another application of surface electrical
stimulation is chest-to-back stimulation of tissue, such as
emergency defibrillation and cardiac pacing. Surface electrical
stimulation has also been used to repair tissue, by increasing
circulation through vasodilation, by controlling edema, by healing
wounds, and by inducing bone growth. Surface electrical stimulation
is also used for iontophoresis, in which electrical currents drive
electrically charged drugs or other ions into the skin, usually to
treat inflammation and pain, arthritis, wounds or scars.
Stimulation with surface electrodes is also used to evoke a
response for diagnostic purposes, for example in peripheral nerve
stimulation (PNS) that evaluates the ability of motor and sensory
nerves to conduct and produce reflexes. Surface electrical
stimulation is also used in electroconvulsive therapy to treat
psychiatric disorders; electroanesthesia, for example, to prevent
pain from dental procedures; and electrotactile speech processing
to convert sound into tactile sensation for the hearing impaired.
All of the above-mentioned applications of surface electrode
stimulation are intended not to damage the patient, but if higher
currents are used with special electrodes, electrosurgery may be
performed as a means to cut, coagulate, desiccate, or fulgurate
tissue [Mark R. Prausnitz. The effects of electric current applied
to skin: A review for transdermal drug delivery. Advanced Drug
Delivery Reviews 18 (1996) 395-425].
[0016] Despite its attractiveness, non-invasive electrical
stimulation of a nerve is not always possible or practical. This is
primarily because the current state of the art may not be able to
stimulate a deep nerve selectively or without producing excessive
pain, since the stimulation may unintentionally stimulate nerves
other than the nerve of interest, including nerves that cause pain.
For this reason, forms of electrical stimulation other than TENS
may be best suited for the treatment of particular types of pain
[Paul F. WHITE, Shitong Li and Jen W. Chiu. Electroanalgesia: Its
Role in Acute and Chronic Pain Management. Anesth Analg
92(2001):505-13].
[0017] For some other electrotherapeutic applications, it has also
been difficult to perform non-invasive stimulation of a nerve, in
lieu of stimulating that nerve invasively. The therapies most
relevant to the present invention involve electrical stimulation of
the vagus nerve in the neck, in order to treat epilepsy,
depression, and other medical conditions. For these therapies, the
left vagus nerve is ordinarily stimulated at a location within the
neck by first surgically implanting an electrode there, then
connecting the electrode to an electrical stimulator [Patent
numbers U.S. Pat. No. 4,702,254 entitled Neurocybernetic
prosthesis, to ZABARA; U.S. Pat. No. 6,341,236 entitled Vagal nerve
stimulation techniques for treatment of epileptic seizures, to
OSORIO et al and U.S. Pat. No. 5,299,569 entitled Treatment of
neuropsychiatric disorders by nerve stimulation, to WERNICKE et al;
G. C. ALBERT, C. M. Cook, F. S. Prato, A. W. Thomas. Deep brain
stimulation, vagal nerve stimulation and transcranial stimulation:
An overview of stimulation parameters and neurotransmitter release.
Neuroscience and Biobehavioral Reviews 33 (2009) 1042-1060; GROVES
D A, Brown V J Vagal nerve stimulation: a review of its
applications and potential mechanisms that mediate its clinical
effects. Neurosci Biobehav Rev (2005) 29:493-500; Reese TERRY, Jr.
Vagus nerve stimulation: a proven therapy for treatment of epilepsy
strives to improve efficacy and expand applications. Conf Proc IEEE
Eng Med Biol Soc. 2009; 2009:4631-4634; Timothy B. MAPSTONE. Vagus
nerve stimulation: current concepts. Neurosurg Focus 25
(3,2008):E9, pp. 1-4].
[0018] When it is desired to avoid the surgical implantation of an
electrode, vagal nerve stimulation (VNS) may be performed less
invasively by positioning one or more electrodes in the esophagus,
trachea, or jugular vein, but with one electrode positioned on the
surface of the body [Patent No. U.S. Pat. No. 7,340,299, entitled
Methods of indirectly stimulating the vagus nerve to achieve
controlled asystole, to PUSKAS; and U.S. Pat. No. 7,869,884,
entitled Non-surgical device and methods for trans-esophageal vagus
nerve stimulation, to SCOTT et al]. Despite their advantage as
being non-surgical, such methods nevertheless exhibit other
disadvantages associated with invasive procedures.
[0019] In other patents, non-invasive VNS is disclosed, but at a
location other than in the neck [e.g., U.S. Pat. No. 4,865,048,
entitled Method and apparatus for drug free neurostimulation, to
ECKERSON; U.S. Pat. No. 6,609,025 entitled Treatment of obesity by
bilateral sub-diaphragmatic nerve stimulation to BARRETT et al;
U.S. Pat. No. 5,458,625, entitled Transcutaneous nerve stimulation
device and method for using same, to KENDALL; U.S. Pat. No.
7,386,347, entitled Electric stimulator for alpha-wave derivation,
to Chung et al.; U.S. Pat. No. 7,797,042, entitled Device for
applying a transcutaneous stimulus or for transcutaneous measuring
of a parameter, to Dietrich et al.; patent application
US2010/0057154, entitled Device and Method for the Transdermal
Stimulation of a Nerve of the Human Body, to Dietrich et al;
US2006/0122675, entitled Stimulator for auricular branch of vagus
nerve, to Libbus et al; US2008/0288016, entitled Systems and
Methods for Stimulating Neural Targets, to Amurthur et al].
However, because such non-invasive VNS occurs at a location other
than the neck, it is not directly comparable to invasive VNS in the
neck, for which therapeutic results are well-documented. Among
other patents and patent applications, non-invasive VNS is
sometimes mentioned along with invasive VNS methods, but without
addressing the problem of unintentional stimulation of nerves other
than the vagus nerve, particularly nerves that cause pain [e.g.,
US20080208266, entitled System and Method for Treating Nausea and
Vomiting by Vagus Nerve Stimulation, to LESSER et al]. Other
patents are vague as to how non-invasive electrical stimulation in
the vicinity of the vagus nerve in the neck is to be accomplished
[e.g., U.S. Pat. No. 7,499,747, entitled External baroreflex
activation, to KIEVAL et al].
[0020] In view of the foregoing background, there is a long-felt
but unsolved need to stimulate the vagus nerve electrically in the
neck, totally non-invasively, selectively, and essentially without
producing pain. As compared with what would have been experienced
by a patient undergoing non-invasive stimulation with conventional
TENS methods, the vagal nerve stimulator should produce relatively
little pain for a given depth of stimulus penetration. Or
conversely, for a given amount of pain or discomfort on the part of
the patient (e.g., the threshold at which such discomfort or pain
begins), an objective of some embodiments of the present invention
is to achieve a greater depth of penetration of the stimulus under
the skin. Furthermore, an objective of some embodiments of the
present invention is to mitigate significant stimulation of other
nerves and muscle that lie near the vagus nerve in the neck, but
nevertheless to stimulate the vagus nerve to achieve therapeutic
results.
SUMMARY OF THE INVENTION
[0021] In one aspect of the invention, devices and methods are
described to produce therapeutic effects in a patient by utilizing
an energy source that transmits energy non-invasively to nervous
tissue. In certain embodiments, the disclosed devices can transmit
energy to, or in close proximity to, a vagus nerve in the neck of
the patient, in order to temporarily stimulate, block and/or
modulate electrophysiological signals in that nerve. The methods
that are disclosed herein comprise stimulating the vagus nerve with
particular stimulation waveform parameters, preferably using the
nerve stimulator devices that are also described herein.
[0022] In one aspect of the invention, a novel stimulator device is
used to modulate electrical activity of a vagus nerve or other
nerves or tissue. The stimulator comprises a source of electrical
power and one or more electrodes that are configured to stimulate a
deep nerve relative to the nerve axis. The device also comprises
continuous electrically conducting media within which the
electrode(s) are in contact. The conducting media provides
electrically communication between the electrode(s) and the
patient's tissue such that the electrode(s) are not in direct
contact with the tissue. The conducting medium preferably has a
shape that conforms to the contour of a target body surface of a
patient when the medium is applied to the target body surface
[0023] For the present medical applications, the device is
ordinarily applied to the patient's neck. In a preferred embodiment
of the invention, the stimulator comprises two electrodes that lie
side-by-side within separate stimulator heads, wherein the
electrodes are separated by electrically insulating material. Each
electrode and the patient's skin are in continuous contact with an
electrically conducting medium that extends from the skin to the
electrode. The conducting media for different electrodes are also
separated by electrically insulating material.
[0024] The source of power supplies a pulse of electric charge to
the electrode(s), such that the electrode(s) produce an electric
current and/or an electric field within the patient. The stimulator
is configured to induce a peak pulse voltage sufficient to produce
an electric field in the vicinity of a nerve such as a vagus nerve,
to cause the nerve to depolarize and reach a threshold for action
potential propagation. By way of example, the threshold electric
field for stimulation of the nerve may be about 8 V/m at about 1000
Hz. For example, the device may produce an electric field within
the patient from about 10 to about 600 V/m and an electrical field
gradient of greater than about 2 V/m/mm.
[0025] Current passing through an electrode may be from about 0 to
about 40 mA, with voltage across the electrodes from about 0 to
about 30 volts. The current is passed through the electrodes in
bursts of pulses. There may be from about 2 to about 20 pulses per
burst, preferably from about 4 to about 10 pulses and more
preferably about five pulses. Each pulse within a burst has a
duration from about 20 to about 1000 microseconds, preferably from
about 100 to about 400 microseconds and more preferably about 200
microseconds. A burst followed by a silent inter-burst interval
repeats from about 1 to about 5000 bursts per second (bps),
preferably from about 15 to about 50 bps. The preferred shape of
each pulse is a full sinusoidal wave. The preferred stimulator
shapes an elongated electric field of effect that can be oriented
parallel to a long nerve, such as a vagus nerve in the patient's
neck. By selecting a suitable waveform to stimulate the nerve,
along with suitable parameters such as current, voltage, pulse
width, pulses per burst, inter-burst interval, etc., the stimulator
produces a correspondingly selective physiological response in an
individual patient. Such a suitable waveform and parameters are
simultaneously selected to avoid substantially stimulating nerves
and tissue other than the target nerve, particularly avoiding the
stimulation of nerves that produce pain.
[0026] Teachings of the present invention demonstrate how the
disclosed non-invasive stimulators may be positioned and used
against body surfaces, particularly at a location on the patient's
neck under which a vagus nerve is situated. Those teachings also
describe the production of certain beneficial, therapeutic effects
in a patient. However, it should be understood that application of
the methods and devices is not limited to the examples that are
given.
[0027] The novel systems, devices and methods for treating
conditions using the disclosed stimulator or other non-invasive
stimulation devices are more completely described in the following
detailed description of the invention, with reference to the
drawings provided herewith, and in claims appended hereto. Other
aspects, features, advantages, etc. will become apparent to one
skilled in the art when the description of the invention herein is
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] For the purposes of illustrating the various aspects of the
invention, there are shown in the drawings forms that are presently
preferred, it being understood, however, that the invention is not
limited by or to the precise data, methodologies, arrangements and
instrumentalities shown, but rather only by the claims.
[0029] FIG. 1 is a schematic view of a nerve or tissue modulating
device according to the present invention, which supplies
controlled pulses of electrical current to electrodes that are
continuously in contact with a volume filled with electrically
conducting material.
[0030] FIG. 2A illustrates an exemplary electrical voltage/current
profile for a blocking and/or modulating impulses that are applied
to a portion or portions of a nerve, in accordance with an
embodiment of the present invention.
[0031] FIG. 2B illustrates a single burst of pulses for an
electrical impulse according to the present invention.
[0032] FIG. 2C illustrates an ON/OFF pattern for a pair of bursts
of pulses according to the present invention.
[0033] FIG. 3A is a perspective view of a dual-electrode stimulator
according to an embodiment of the present invention.
[0034] FIG. 3B is a cut-a-way view of the dual-electrode stimulator
of FIG. 3A, illustrating the stimulator's electrodes and electronic
components.
[0035] FIG. 4A is an exploded view of one embodiment of the head of
the dual-electrode stimulator that is shown in FIG. 3A.
[0036] FIG. 4B is a cross-sectional view of the head of FIG.
4A;
[0037] FIG. 4C is an exploded view of an alternative embodiment of
a head for the dual-electrode stimulator shown in FIG. 3A.
[0038] FIG. 4D is a cross-sectional view of the head of FIG.
4C.
[0039] FIG. 5A is a perspective view of the top of an alternate
embodiment of a dual-electrode stimulator according to the present
invention.
[0040] FIG. 5B is a perspective view of the bottom of the
dual-electrode stimulator of FIG. 5A.
[0041] FIG. 5C is a cross-sectional view of the dual-electrode
stimulator of FIG. 5A.
[0042] FIG. 6 illustrates an approximate position of a housing of
the dual-electrode stimulator according one embodiment of the
present invention, when the electrodes used to stimulate the vagus
nerve in the neck of a patient.
[0043] FIG. 7 illustrates the housing of the dual-electrode
stimulator according one embodiment of the present invention, as
the electrodes are positioned to stimulate the vagus nerve in a
patient's neck via electrically conducting gel (or some other
conducting material), which is applied to the surface of the neck
in the vicinity of the identified anatomical structures.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0044] In the present invention, energy is transmitted
non-invasively to a patient. The invention is particularly useful
for producing applied electrical impulses that interact with the
signals of one or more nerves to achieve a therapeutic result. In
particular, the present disclosure describes devices and methods to
stimulate a vagus nerve non-invasively at a location on the
patient's neck.
[0045] There is a long-felt but unsolved need to stimulate the
vagus nerve electrically in the neck, totally non-invasively,
selectively, and essentially without producing pain. As described
below, this is evidenced by the failure of others to solve the
problem that is solved by the present invention, such that
investigators abandoned the attempt to non-invasively stimulate
electrically in the neck, in favor of stimulating the vagus nerve
at other anatomical locations, or in favor of stimulating the vagus
nerve non-electrically. Japanese patent application JP2009233024A
with a filing date of Mar. 26, 2008, entitled Vagus Nerve
Stimulation System, to Fukui YOSHIHITO, is concerned with
stimulation of the vagus nerve on the surface of the neck to
control heart rate, rather than epilepsy, depression, or other
infirmities that vagal nerve stimulation (VNS) is ordinarily
intended to treat. Nevertheless, the approach that is taken by
Yoshihito illustrates the difficulties encountered with
non-invasive electrical stimulation the vagus nerve. Yoshihito
notes that because electrical stimulation on the surface of the
neck may co-stimulate the phrenic nerve that is involved with the
control of respiration, the patient hiccups and does not breathe
normally, resulting in "a patient sense of incongruity and
displeasure." Yoshihito's proposed solution to the problem is to
modulate the timing and intensity of the electrical stimulation at
the neck as a function of the respiratory phase, in such a way that
the undesirable respiratory effects are minimized. Thus,
Yoshihito's approach is to compensate for non-selective nerve
stimulation, rather than find a way to stimulate the vagus nerve
selectively. However, such compensatory modulation might also
prevent the stimulation from achieving a beneficial effect in
treating epilepsy, depression, and other infirmities that are
ordinarily treated with VNS. Furthermore, Yoshihito does not
address the problem of pain in the vicinity of the stimulation
electrodes. Similar issues could conceivably arise in connection
with possible co-stimulation of the carotid sinus nerve [Ingrid J.
M. Scheffers, Abraham A. Kroon, Peter W. de Leeuw. Carotid
Baroreflex Activation: Past, Present, and Future. Curr Hypertens
Rep 12(2010):61-66]. Side effects due to co-activation of muscle
that is controlled by the vagus nerve itself may also occur, which
exemplify another type of non-selective stimulation [M Tosato, K
Yoshida, E Toft and J J Struijk. Quasi-trapezoidal pulses to
selectively block the activation of intrinsic laryngeal muscles
during vagal nerve stimulation. J. Neural Eng. 4 (2007):
205-212].
[0046] One circumvention of the problem that the present invention
solves is to non-invasively stimulate the vagus nerve at an
anatomical location other than the neck, where the nerve lies
closer to the skin. A preferred alternate location is in or around
the ear (tragus, meatus and/or concha) although other locations
have been proposed [Manuel L. KARELL. TENS in the Treatment of
Heroin Dependency. The Western Journal of Medicine 125 (5,
1976):397-398; Enrique C. G. VENTUREYRA. Transcutaneous vagus nerve
stimulation for partial onset seizure therapy. A new concept.
Child's Nery Syst 16 (2000):101-102; T. KRAUS, K. Hosl, O. Kiess,
A. Schanze, J. Kornhuber, C. Forster. BOLD fMRI deactivation of
limbic and temporal brain structures and mood enhancing effect by
transcutaneous vagus nerve stimulation. J Neural Transm 114 (2007):
1485-1493; POLAK T, Markulin F, Ehlis A C, Langer J B, Ringel T M,
Fallgatter A J. Far field potentials from brain stem after
transcutaneous vagus nerve stimulation: optimization of stimulation
and recording parameters. J Neural Transm 116 (10,2009):1237-1242;
Patent U.S. Pat. No. 5,458,625, entitled Transcutaneous nerve
stimulation device and method for using same, to KENDALL; U.S. Pat.
No. 7,797,042, entitled Device for applying a transcutaneous
stimulus or for transcutaneous measuring of a parameter, to
Dietrich et al.; patent application US2010/0057154, entitled Device
and Method for the Transdermal Stimulation of a Nerve of the Human
Body, to Dietrich et al; See also the non-invasive methods and
devices that Applicant disclosed in commonly assigned co-pending
U.S. patent application Ser. No. 12/859,568, entitled Non-invasive
Treatment of Bronchial Constriction, to SIMON]. However, it is not
certain that stimulation in this minor branch of the vagus nerve
will have the same effect as stimulation of a main vagus nerve in
the neck, where VNS electrodes are ordinarily implanted, and for
which VNS therapeutic procedures produce well-documented
results.
[0047] Another circumvention of the problem is to substitute
electrical stimulation of the vagus nerve in the neck with some
other form of stimulation. For example, mechanical stimulation of
the vagus nerve on the neck has been proposed as an alternative to
electrical stimulation [Jared M. HUSTON, Margot Gallowitsch-Puerta,
Mahendar Ochani, Kanta Ochani, Renqi Yuan, Mauricio Rosas-Ballina,
Mala Ashok, Richard S. Goldstein, Sangeeta Chavan, Valentin A.
Pavlov, Christine N. Metz, Huan Yang, Christopher J. Czura, Haichao
Wang, Kevin J. Tracey. Transcutaneous vagus nerve stimulation
reduces serum high mobility group box 1 levels and improves
survival in murine sepsis Crit Care Med 35 (12,2007):2762-2768;
Artur BAUHOFER and Alexander Torossian. Mechanical vagus nerve
stimulation--A new adjunct in sepsis prophylaxis and treatment?
Crit Care Med 35 (12,2007):2868-2869; Hendrik SCHMIDT, Ursula
Muller-Werdan, Karl Werdan. Assessment of vagal activity during
transcutaneous vagus nerve stimulation in mice. Crit Care Med 36
(6,2008):1990; see also the non-invasive methods and devices that
Applicant disclosed in commonly assigned co-pending U.S. patent
application Ser. No. 12/859,568, entitled Non-invasive Treatment of
Bronchial Constriction, to SIMON]. However, such mechanical VNS has
only been performed in animal models, and there is no evidence that
such mechanical VNS would be functionally equivalent to electrical
VNS.
[0048] Another circumvention of the problem is to use magnetic
rather than purely electrical stimulation of the vagus nerve in the
neck [Q. AZIZ et al. Magnetic Stimulation of Efferent Neural
Pathways to the Human Oesophagus. Gut 33: S53-S70 (Poster Session
F218) (1992); AZIZ, Q., J. C. Rothwell, J. Barlow, A. Hobson, S.
Alani, J. Bancewicz, and D. G. Thompson. Esophageal myoelectric
responses to magnetic stimulation of the human cortex and the
extracranial vagus nerve. Am. J. Physiol. 267 (Gastrointest. Liver
Physiol. 30): G827-G835, 1994; Shaheen HAMDY, Qasim Aziz, John C.
Rothwell, Anthony Hobson, Josephine Barlow, and David G. Thompson.
Cranial nerve modulation of human cortical swallowing motor
pathways. Am. J. Physiol. 272 (Gastrointest. Liver Physiol. 35):
G802-G808, 1997; Shaheen HAM DY, John C. Rothwell, Qasim Aziz,
Krishna D. Singh, and David G. Thompson. Long-term reorganization
of human motor cortex driven by short-term sensory stimulation.
Nature Neuroscience 1 (issue 1, May 1998):64-68; A. SHAFIK.
Functional magnetic stimulation of the vagus nerve enhances colonic
transit time in healthy volunteers. Tech Coloproctol (1999)
3:123-12; see also the non-invasive methods and devices that
Applicant disclosed in co-pending U.S. patent application Ser. No.
12/859,568 entitled Non-invasive Treatment of Bronchial
Constriction, to SIMON, as well as co-pending U.S. patent
application Ser. No. 12/964,050, entitled Magnetic Stimulation
Devices and Methods of Therapy, to SIMON et al]. Magnetic
stimulation might functionally approximate electrical stimulation.
However, magnetic stimulation has the disadvantage that it
ordinarily requires complex and expensive equipment, and the
duration of stimulation may be limited by overheating of the
magnetic stimulator. Furthermore, in some cases, magnetic
stimulation in the neck might also inadvertently stimulate nerves
other than the vagus nerve, such as the phrenic nerve [SIMILOWSKI,
T., B. Fleury, S. Launois, H. P. Cathala, P. Bouche, and J. P.
Derenne. Cervical magnetic stimulation: a new painless method for
bilateral phrenic nerve stimulation in conscious humans. J. Appl.
Physiol. 67(4): 1311-1318, 1989; Gerrard F. RAFFERTY, Anne
Greenough, Terezia Manczur, Michael I. Polkey, M. Lou Harris, Nigel
D. Heaton, Mohamed Rela, and John Moxham. Magnetic phrenic nerve
stimulation to assess diaphragm function in children following
liver transplantation. Pediatr Crit Care Med 2001, 2:122-126; W.
D-C. MAN, J. Moxham, and M. I. Polkey. Magnetic stimulation for the
measurement of respiratory and skeletal muscle function. Eur Respir
J 2004; 24: 846-860]. Furthermore, magnetic stimulation may also
stimulate nerves that cause pain. Other stimulators that make use
of magnetic fields might also be used, but they too are complex and
expensive and may share other disadvantages with more conventional
magnetic stimulators [Patent U.S. Pat. No. 7,699,768, entitled
Device and method for non-invasive, localized neural stimulation
utilizing hall effect phenomenon, to Kishawi et al].
[0049] Transcutaneous electrical stimulation (as well as magnetic
stimulation) can be unpleasant or painful, in the experience of
patients that undergo such procedures. The quality of sensation
caused by stimulation depends strongly on current and frequency,
such that currents barely greater than the perception threshold
generally cause painless sensations described as tingle, itch,
vibration, buzz, touch, pressure, or pinch, but higher currents can
cause sharp or burning pain. As the depth of penetration of the
stimulus under the skin is increased (e.g., to deeper nerves such
as the vagus nerve), any pain will generally begin or increase.
Strategies to reduce the pain include: use of anesthetics placed on
or injected into the skin near the stimulation and placement of
foam pads on the skin at the site of stimulation [Jeffrey J.
BORCKARDT, Arthur R. Smith, Kelby Hutcheson, Kevin Johnson, Ziad
Nahas, Berry Anderson, M. Bret Schneider, Scott T. Reeves, and Mark
S. George. Reducing Pain and Unpleasantness During Repetitive
Transcranial Magnetic Stimulation. Journal of ECT 2006;
22:259-264], use of nerve blockades [V. HAKKINEN, H. Eskola, A.
Yli-Hankala, T. Nurmikko and S. Kolehmainen. Which structures are
sensitive to painful transcranial stimulation? Electromyogr. clin.
Neurophysiol. 1995, 35:377-383], the use of very short stimulation
pulses [V. SUIHKO. Modelling the response of scalp sensory
receptors to transcranial electrical stimulation. Med. Biol. Eng.
Comput., 2002, 40, 395-401], decreasing current density by
increasing electrode size [Kristof VERHOEVEN and J. Gert van Dijk.
Decreasing pain in electrical nerve stimulation. Clinical
Neurophysiology 117 (2006) 972-978], using a high impedance
electrode [N. SHA, L. P. J. Kenney, B. W. Heller, A. T. Barker, D.
Howard and W. Wang. The effect of the impedance of a thin hydrogel
electrode on sensation during functional electrical stimulation.
Medical Engineering & Physics 30 (2008): 739-746] and providing
patients with the amount of information that suits their
personalities [Anthony DELITTO, Michael J Strube, Arthur D Shulman,
Scott D Minor. A Study of Discomfort with Electrical Stimulation.
Phys. Ther. 1992; 72:410-424]. Patent U.S. Pat. No. 7,614,996,
entitled Reducing discomfort caused by electrical stimulation, to
RIEHL discloses the application of a secondary stimulus to
counteract what would otherwise be an uncomfortable primary
stimulus.
[0050] Additional considerations related to pain resulting from the
stimulation are as follows. When stimulation is repeated over the
course of multiple sessions, patients may adapt to the pain and
exhibit progressively less discomfort. Patients may be
heterogeneous with respect to their threshold for pain caused by
stimulation, including heterogeneity related to gender and age.
Electrical properties of an individual's skin vary from day to day
and may be affected by cleaning, abrasion, and the application of
various electrode gels and pastes. Skin properties may also be
affected by the stimulation itself, as a function of the duration
of stimulation, the recovery time between stimulation sessions, the
transdermal voltage, the current density, and the power density.
The application of multiple electrical pulses can result in
different perception or pain thresholds and levels of sensation,
depending on the spacing and rate at which pulses are applied. The
separation distance between two electrodes determines whether
sensations from the electrodes are separate, overlap, or merge. The
limit for tolerable sensation is sometimes said to correspond to a
current density of 0.5 mA/cm.sup.2, but in reality the functional
relationship between pain and current density is very complicated.
Maximum local current density may be more important in producing
pain than average current density, and local current density
generally varies under an electrode, e.g., with greater current
densities along edges of the electrode or at "hot spots."
Furthermore, pain thresholds can have a thermal and/or
electrochemical component, as well as a current density component.
Pulse frequency plays a significant role in the perception of pain,
with muscle contraction being involved at some frequencies and not
others, and with the spatial extent of the pain sensation also
being a function of frequency. The sensation is also a function of
the waveform (square-wave, sinusoidal, trapezoidal, etc.),
especially if pulses are less than a millisecond in duration [Mark
R. PRAUSNITZ. The effects of electric current applied to skin: A
review for transdermal drug delivery. Advanced Drug Delivery
Reviews 18 (1996): 395-425].
[0051] Considering that there are so many variables that may
influence the likelihood of pain during non-invasive electrical
stimulation (detailed stimulus waveform, frequency, current
density, electrode type and geometry, skin preparation, etc.),
considering that these same variables can be simultaneously
selected in order to independently produce a desired therapeutic
outcome by vagal nerve stimulation, and considering that one also
wishes to selectively stimulate the vagus nerve (e.g, avoid
stimulating the phrenic nerve), it is understandable that prior to
the present disclosure, no one has described devices and methods
for stimulating the vagus nerve electrically in the neck, totally
non-invasively, selectively, and without causing substantial
pain.
[0052] Applicant discovered the disclosed devices and methods in
the course of experimentation with a magnetic stimulation device
that was disclosed in Applicant's commonly assigned co-pending U.S.
patent application Ser. No. 12/964,050, entitled Magnetic
Stimulation Devices and Methods of Therapy, to SIMON et al. Thus,
combined elements in the invention do not merely perform the
function that the elements perform separately (viz., perform
therapeutic VNS, minimize stimulation pain, or stimulate the vagus
nerve selectively), and one of ordinary skill in the art would not
have combined the claimed elements by known methods because the
archetypal magnetic stimulator was known only to Applicant. That
stimulator used a magnetic coil, embedded in a safe and practical
conducting medium that was in direct contact with
arbitrarily-oriented patient skin, which had not been described in
its closest art [Rafael CARBUNARU and Dominique M. Durand. Toroidal
coil models for transcutaneous magnetic stimulation of nerves. IEEE
Transactions on Biomedical Engineering 48 (4, 2001): 434-441;
Rafael Carbunaru FAIERSTEIN, Coil Designs for Localized and
Efficient Magnetic Stimulation of the Nervous System. Ph.D.
Dissertation, Department of Biomedical Engineering, Case Western
Reserve, May, 1999. (UMI Microform Number: 9940153, UMI Company,
Ann Arbor Mich.)]. Such a design, which is adapted herein for use
with surface electrodes, makes it possible to shape the electric
field that is used to selectively stimulate a deep nerve such as a
vagus nerve in the neck. Furthermore, the design produces
significantly less pain or discomfort (if any) to a patient than
stimulator devices that are currently known in the art. Conversely,
for a given amount of pain or discomfort on the part of the patient
(e.g., the threshold at which such discomfort or pain begins), the
design achieves a greater depth of penetration of the stimulus
under the skin.
[0053] FIG. 1 is a schematic diagram of a nerve
stimulating/modulating device 300 for delivering impulses of energy
to nerves for the treatment of medical conditions. As shown, device
300 may include an impulse generator 310; a power source 320
coupled to the impulse generator 310; a control unit 330 in
communication with the impulse generator 310 and coupled to the
power source 320; and electrodes 340 coupled via wires 345 to
impulse generator 310.
[0054] Although a pair of electrodes 340 is shown in FIG. 1, in
practice the electrode(s) may comprises a single electrode with a
large surface area, or a plurality of distinct electrode elements,
each of which is connected in series or in parallel to the impulse
generator 310. Thus, the electrodes 340 that are shown in FIG. 1
represent all electrodes of the device collectively.
[0055] The item labeled in FIG. 1 as 350 is a volume, contiguous
with an electrode 340, that is filled with electrically conducting
medium. As shown in the preferred embodiment, the medium is also
deformable such that it is form-fitting when applied to the surface
of the body. Thus, the sinuousness or curvature shown at the outer
surface of the electrically conducting medium 350 corresponds also
to sinuousness or curvature on the surface of the body, against
which the conducting medium 350 is applied, so as to make the
medium and body surface contiguous. As described below in
connection with a preferred embodiment, the volume 350 is
electrically connected to the patient at a target skin surface in
order to shape the current density passed through an electrode 340
that is needed to accomplish stimulation of the patient's nerve or
tissue. As also described below in connection with exemplary
embodiments of the invention, the conducting medium in which the
electrode 340 is embedded need not completely surround an
electrode.
[0056] The control unit 330 controls the impulse generator 310 to
generate a signal for each of the device's electrodes. The signals
are selected to be suitable for amelioration of a particular
medical condition, when the signals are applied non-invasively to a
target nerve or tissue via the electrodes 340. It is noted that
nerve stimulating/modulating device 300 may be referred to by its
function as a pulse generator. Patent application publications
US2005/0075701 and US2005/0075702, both to SHAFER, both of which
are incorporated herein by reference, relating to stimulation of
neurons of the sympathetic nervous system to attenuate an immune
response, contain descriptions of pulse generators that may be
applicable to the present invention. By way of example, a pulse
generator 300 is also commercially available, such as Agilent
33522A Function/Arbitrary Waveform Generator, Agilent Technologies,
Inc., 5301 Stevens Creek Blvd Santa Clara Calif. 95051.
[0057] The control unit 330 may also comprise a general purpose
computer, comprising one or more CPU, computer memories for the
storage of executable computer programs (including the system's
operating system) and the storage and retrieval of data, disk
storage devices, communication devices (such as serial and USB
ports) for accepting external signals from the system's keyboard
and computer mouse as well as any externally supplied physiological
signals, analog-to-digital converters for digitizing externally
supplied analog signals, communication devices for the transmission
and receipt of data to and from external devices such as printers
and modems that comprise part of the system, hardware for
generating the display of information on monitors that comprise
part of the system, and busses to interconnect the above-mentioned
components. Thus, the user may operate the system by typing
instructions for the control unit 330 at a device such as a
keyboard and view the results on a device such as the system's
computer monitor, or direct the results to a printer, modem, and/or
storage disk. Control of the system may be based upon feedback
measured from externally supplied physiological or environmental
signals. Alternatively, the control unit 330 may have a compact and
simple structure, for example, wherein the user may operate the
system using only an on/off switch and power control wheel or
knob.
[0058] Parameters for the nerve or tissue stimulation include power
level, frequency and train duration (or pulse number). The
stimulation characteristics of each pulse, such as depth of
penetration, strength and selectivity, depend on the rise time and
peak electrical energy transferred to the electrodes, as well as
the spatial distribution of the electric field that is produced by
the electrodes. The rise time and peak energy are governed by the
electrical characteristics of the stimulator and electrodes, as
well as by the anatomy of the region of current flow within the
patient. In one embodiment of the invention, pulse parameters are
set in such as way as to account for the detailed anatomy
surrounding the nerve that is being stimulated [Bartosz SAWICKI,
Robert Szmurto, Przemystaw Ptonecki, Jacek Starzy ski, Stanistaw
Wincenciak, Andrzej Rysz. Mathematical Modelling of Vagus Nerve
Stimulation. pp. 92-97 in: Krawczyk, A. Electromagnetic Field,
Health and Environment: Proceedings of EHE'07. Amsterdam, 105
Press, 2008]. Pulses may be monophasic, biphasic or polyphasic.
Embodiments of the invention include those that are fixed
frequency, where each pulse in a train has the same inter-stimulus
interval, and those that have modulated frequency, where the
intervals between each pulse in a train can be varied.
[0059] FIG. 2A illustrates an exemplary electrical voltage/current
profile for a stimulating, blocking and/or modulating impulse
applied to a portion or portions of selected nerves in accordance
with an embodiment of the present invention. For the preferred
embodiment, the voltage and current refer to those that are
non-invasively produced within the patient by the electrodes. As
shown, a suitable electrical voltage/current profile 400 for the
blocking and/or modulating impulse 410 to the portion or portions
of a nerve may be achieved using pulse generator 310. In a
preferred embodiment, the pulse generator 310 may be implemented
using a power source 320 and a control unit 330 having, for
instance, a processor, a clock, a memory, etc., to produce a pulse
train 420 to the electrodes 340 that deliver the stimulating,
blocking and/or modulating impulse 410 to the nerve. Nerve
stimulating/modulating device 300 may be externally powered and/or
recharged may have its own power source 320. The parameters of the
modulation signal 400, such as the frequency, amplitude, duty
cycle, pulse width, pulse shape, etc., are preferably programmable.
An external communication device may modify the pulse generator
programming to improve treatment.
[0060] In addition, or as an alternative to the devices to
implement the modulation unit for producing the electrical
voltage/current profile of the stimulating, blocking and/or
modulating impulse to the electrodes, the device disclosed in
patent publication No. US2005/0216062 (the entire disclosure of
which is incorporated herein by reference) may be employed. That
patent publication discloses a multifunctional electrical
stimulation (ES) system adapted to yield output signals for
effecting electromagnetic or other forms of electrical stimulation
for a broad spectrum of different biological and biomedical
applications, which produce an electric field pulse in order to
non-invasively stimulate nerves. The system includes an ES signal
stage having a selector coupled to a plurality of different signal
generators, each producing a signal having a distinct shape, such
as a sine wave, a square or a saw-tooth wave, or simple or complex
pulse, the parameters of which are adjustable in regard to
amplitude, duration, repetition rate and other variables. Examples
of the signals that may be generated by such a system are described
in a publication by LIBOFF [A.R. LIBOFF. Signal shapes in
electromagnetic therapies: a primer. pp. 17-37 in:
Bioelectromagnetic Medicine (Paul J. Rosch and Marko S. Markov,
eds.). New York: Marcel Dekker (2004)]. The signal from the
selected generator in the ES stage is fed to at least one output
stage where it is processed to produce a high or low voltage or
current output of a desired polarity whereby the output stage is
capable of yielding an electrical stimulation signal appropriate
for its intended application. Also included in the system is a
measuring stage which measures and displays the electrical
stimulation signal operating on the substance being treated as well
as the outputs of various sensors which sense conditions prevailing
in this substance whereby the user of the system can manually
adjust it or have it automatically adjusted by feedback to provide
an electrical stimulation signal of whatever type the user wishes,
who can then observe the effect of this signal on a substance being
treated.
[0061] The stimulating, blocking and/or modulating impulse signal
410 preferably has a frequency, an amplitude, a duty cycle, a pulse
width, a pulse shape, etc. selected to influence the therapeutic
result, namely, stimulating, blocking and/or modulating some or all
of the transmission of the selected nerve. For example, the
frequency may be about 1 Hz or greater, such as between about 15 Hz
to 50 Hz, more preferably around 25 Hz. The modulation signal may
have a pulse width selected to influence the therapeutic result,
such as about 20 microseconds or greater, such as about 20
microseconds to about 1000 microseconds. For example, the electric
field induced by the device within tissue in the vicinity of a
nerve is 10 to 600 V/m, preferably around 300 V/m. The gradient of
the electric field may be greater than 2 V/m/mm. More generally,
the stimulation device produces an electric field in the vicinity
of the nerve that is sufficient to cause the nerve to depolarize
and reach a threshold for action potential propagation, which is
approximately 8 V/m at 1000 Hz.
[0062] An objective of some embodiments of the disclosed stimulator
is to provide both nerve fiber selectivity and spatial selectivity.
Spatial selectivity may be achieved in part through the design of
the electrode configuration, and nerve fiber selectivity may be
achieved in part through the design of the stimulus waveform, but
designs for the two types of selectivity are intertwined. This is
because, for example, a waveform may selectively stimulate only one
of two nerves whether they lie close to one another or not,
obviating the need to focus the stimulating signal onto only one of
the nerves [GRILL W and Mortimer J T. Stimulus waveforms for
selective neural stimulation. IEEE Eng. Med. Biol. 14 (1995):
375-385].
[0063] To date, the selection of stimulation waveform parameters
for vagal nerve stimulation (VNS) has been highly empirical, in
which the parameters are varied about some initially successful set
of parameters, in an effort to find an improved set of parameters
for each patient. A more efficient approach to selecting
stimulation parameters might be to select a stimulation waveform
that mimics electrical activity in the regions of the brain that
one is attempting stimulate indirectly, in an effort to entrain the
naturally occurring electrical waveform, as suggested in patent
number U.S. Pat. No. 6,234,953, entitled Electrotherapy device
using low frequency magnetic pulses, to THOMAS et al. and
application number US20090299435, entitled Systems and methods for
enhancing or affecting neural stimulation efficiency and/or
efficacy, to GLINER et al. One may also vary stimulation parameters
iteratively, in search of an optimal setting [Patent U.S. Pat. No.
7,869,885, entitled Threshold optimization for tissue stimulation
therapy, to Begnaud , et al]. However, some VNS stimulation
waveforms, such as those described herein, are discovered by trial
and error, and then deliberately improved upon.
[0064] Invasive vagal nerve stimulation typically uses square wave
pulse signals. In some embodiments, the typical waveform parameter
values for VNS therapy for epilepsy and depression are: a current
between 1 and 2 mA, a frequency of between 20 and 30 Hz, a pulse
width of 250-500 microseconds, and a duty cycle of 10% (signal ON
time of 30 s, and a signal OFF time to 5 min). Output current is
gradually increased from 0.25 mA to the maximum tolerable level
(maximum, 3.5 mA), with typical therapeutic settings ranging from
1.0 to 1.5 mA. Greater output current is associated with increased
side effects, including voice alteration, cough, a feeling of
throat tightening, and dyspnea. Frequency is typically 20 Hz in
depression and 30 Hz in epilepsy. The therapy is adjusted in a
gradual, systematic fashion to individualize therapy for each
patient. To treat migraine headaches, typical VNS parameters are a
current of 0.25 to 1 mA, a frequency of 30 Hz, a pulse width of 500
microseconds, and an `ON` time of 30 s every 5 min. To treat
migrane plus epilepsy, typical parameters are 1.75 mA, a frequency
of 20 Hz, a pulse width of 250 microseconds, and `ON` time of 7 s
followed by an `OFF` time of 12 s. To treat mild to moderate
Alzheimer's disease, typical VNS waveform parameters are: a current
of 0.25 to 0.5 mA, a frequency of 20 Hz, a pulse width of 500
microseconds, and an `ON` time of 30 s every 5 min. [ANDREWS, A.
J., 2003. Neuromodulation. I. Techniques-deep brain stimulation,
vagus nerve stimulation, and transcranial magnetic stimulation.
Ann. N.Y. Acad. Sci. 993, 1-13; LABINER, D. M., Ahern, G. L., 2007.
Vagus nerve stimulation therapy in depression and epilepsy:
therapeutic parameter settings. Acta. Neurol. Scand. 115, 23-33; G.
C. ALBERT, C. M. Cook, F. S. Prato, A. W. Thomas. Deep brain
stimulation, vagal nerve stimulation and transcranial stimulation:
An overview of stimulation parameters and neurotransmitter release.
Neuroscience and Biobehavioral Reviews 33 (2009) 1042-1060].
Applicant found that these square waveforms are not ideal for
non-invasive VNS stimulation as they produce excessive pain.
[0065] Prepulses and similar waveform modifications have been
suggested as means to improve selectivity of vagus and other nerve
stimulation waveforms, but Applicant did not find them ideal
[Aleksandra VUCKOVIC, Marco Tosato and Johannes J Struijk. A
comparative study of three techniques for diameter selective fiber
activation in the vagal nerve: anodal block, depolarizing prepulses
and slowly rising pulses. J. Neural Eng. 5 (2008): 275-286;
Aleksandra VUCKOVIC, Nico J. M. Rijkhoff, and Johannes J.
Struijk.Different Pulse Shapes to Obtain Small Fiber Selective
Activation by Anodal Blocking--A Simulation Study. IEEE
Transactions on Biomedical Engineering 51 (5,2004):698-706;
Kristian HENNINGS. Selective Electrical Stimulation of Peripheral
Nerve Fibers: Accommodation Based Methods. Ph.D. Thesis, Center for
Sensory-Motor Interaction, Aalborg University, Aalborg, Denmark,
2004].
[0066] Applicant also found that stimulation waveforms consisting
of bursts of square pulses are not ideal for non-invasive VNS
stimulation [M. I. JOHNSON, C. H. Ashton, D. R. Bousfield and J. W.
Thompson. Analgesic effects of different pulse patterns of
transcutaneous electrical nerve stimulation on cold-induced pain in
normal subjects. Journal of Psychosomatic Research 35 (2/3,
1991):313-321; Patent U.S. Pat. No. 7,734,340, entitled Stimulation
design for neuromodulation, to De Ridder]. However, bursts of
sinusoidal pulses are a preferred stimulation waveform, as shown in
FIG. 2B and 2C. As seen there, individual sinusoidal pulses have a
period of .tau., and a burst consists of N such pulses. This is
followed by a period with no signal (the inter-burst period). The
pattern of a burst plus followed by silent inter-burst period
repeats itself with a period of T. For example, the sinusoidal
period .tau. may be between about 50 us to about 1 ms, preferably
between about 100 us to 400 us, and more preferably about 200
microseconds; the number of pulses per burst (N) maybe be between
about 2 to 20 pulses, preferably about 4 to 10 pulses and more
preferably 5 pulses; and the whole pattern of burst followed by
silent inter-burst period may have a period (T) of about 1 to 100
Hz, preferably about 10 to 35 Hz and more preferably about 25 Hz or
40000 microseconds (a much smaller value of T is shown in FIG. 2C
to make the bursts discernable). Applicant is unaware of such a
waveform having been used with vagal nerve stimulation, but a
similar waveform has been used to stimulate muscle as a means of
increasing muscle strength in elite athletes. However, for the
muscle strengthening application, the currents used (200 mA) may be
very painful and two orders of magnitude larger than what is
disclosed herein for VNS. Furthermore, the signal used for muscle
strengthening may be other than sinusoidal (e.g., triangular), and
the parameters .tau., N, and T may also be dissimilar from the
values exemplified above [A. DELITTO, M. Brown, M. J. Strube, S. J.
Rose, and R. C. Lehman. Electrical stimulation of the quadriceps
femoris in an elite weight lifter: a single subject experiment. Int
J Sports Med 10 (1989):187-191; Alex R WARD, Nataliya Shkuratova.
Russian Electrical Stimulation: The Early Experiments. Physical
Therapy 82 (10,2002): 1019-1030; Yocheved LAUFER and Michal Elboim.
Effect of Burst Frequency and Duration of Kilohertz-Frequency
Alternating Currents and of Low-Frequency Pulsed Currents on
Strength of Contraction, Muscle Fatigue, and Perceived Discomfort.
Physical Therapy 88 (10,2008):1167-1176; Alex R WARD. Electrical
Stimulation Using Kilohertz-Frequency Alternating Current. Physical
Therapy 89 (2,2009):181-190; J. PETROFSKY, M. Laymon, M. Prowse, S.
Gunda, and J. Batt. The transfer of current through skin and muscle
during electrical stimulation with sine, square, Russian and
interferential waveforms. Journal of Medical Engineering and
Technology 33 (2,2009): 170-181]. By way of example, the electric
field shown in FIGS. 2B and 2C may have an Emax value of 17 V/m,
which is sufficient to stimulate the vagus nerve but is
significantly lower than the threshold needed to stimulate
surrounding muscle.
[0067] In order to compare the stimulator that is disclosed herein
with existing electrodes and stimulators used for non-invasive
electrical stimulation, it is useful to first summarize the
relevant physics of electric fields and currents that are produced
by the electrodes. According to Maxwell's equation (Ampere's law
with Maxwell correction): .gradient..times.B=J+
(.differential.E/.differential.t), where B is the magnetic field, J
is the electrical current density, E is the electric field, E is
the permittivity, and t is time [Richard P. FEYNMAN, Robert B.
Leighton, and Matthew Sands. The Feynman Lectures on Physics.
Volume II. Addison-Wesley Publ. Co. (Reading Mass, 1964), page
15-15].
[0068] According to Faraday's law,
.gradient..times.E=-.differential.B/.differential.t. However, for
present purposes, changes in the magnetic field B may be ignored,
so .gradient..times.E=0, and E may therefore be obtained from the
gradient of a scalar potential .PHI.: E=-.gradient..PHI.. In
general, the scalar potential .PHI. and the electric field E are
functions of position (r) and time (t).
[0069] The electrical current density J is also a function of
position (r) and time (t), and it is determined by the electric
field and conductivity as follows, where the conductivity .sigma.
is generally a tensor and a function of position (r):
J=.sigma.E=-.sigma..gradient..PHI.
[0070] Because .gradient..gradient..times.B=0, Ampere's law with
Maxwell's correction may be written as:
.gradient.J+.gradient..PHI.(.differential.E/.differential.t)=0. If
the current flows in material that is essentially unpolarizable
(i.e., is presumed not to be a dielectric so that =0), substitution
of the expression for J into the above expression for Ampere's law
gives -.gradient.(.sigma..gradient..PHI.)=0, which is a form of
Laplace's equation. If the conductivity of material in the device
(or patient) is itself a function of the electric field or
potential, then the equation becomes non-linear, which could
exhibit multiple solutions, frequency multiplication, and other
such non-linear behavior. The equation has been solved analytically
for special electrode configurations, but for more general
electrode configurations, it can be solved numerically [Petrus J.
CILLIERS. Analysis of the current density distribution due to
surface electrode stimulation of the human body. Ph.D.
Dissertation, Ohio State University, 1988. (UMI Microform Number:
8820270, UMI Company, Ann Arbor Mich.); Martin REICHEL, Teresa
Breyer, Winfried Mayr, and Frank Rattay. Simulation of the
Three-Dimensional Electrical Field in the Course of Functional
Electrical Stimulation. Artificial Organs 26 (3,2002):252-255;
Cameron C. McINTYRE and Warren M. Grill. Finite Element Analysis of
the Current-Density and Electric Field Generated by Metal
Microelectrodes. Annals of Biomedical Engineering 29 (2001):
227-235; A. PATRICIU, T. P. DeMonte, M. L. G. Joy, J. J. Struijk.
Investigation of current densities produced by surface electrodes
using finite element modeling and current density imaging.
Proceedings of the 23rd Annual EM BS International Conference, Oct.
25-28, 2001, Istanbul, Turkey: 2403-2406; Yong H U, X B Xie, L Y
Pang, X H Li K D K Luk. Current Density Distribution Under Surface
Electrode on Posterior Tibial Nerve Electrical Stimulation.
Proceedings of the 2005 IEEE Engineering in Medicine and Biology
27th Annual Conference Shanghai, China, Sep. 1-4, 2005: 3650-3652].
The equation has also been solved numerically in order to compare
different electrode shapes and numbers [Abhishek DATTA, Maged
Elwassif, Fortunato Battaglia and Marom Bikson. Transcranial
current stimulation focality using disc and ring electrode
configurations: FEM analysis. J. Neural Eng. 5 (2008) 163-174; Jay
T. RUBENSTEIN, Francis A. Spelman, Mani Soma and Michael F.
Suesserman. Current Density Profiles of Surface Mounted and
Recessed Electrodes for Neural Prostheses. IEEE Transactions on
Biomedical Engineering BME-34 (11,1987): 864-875; David A.
KSIENSKI. A Minimum Profile Uniform Current Density Electrode. IEEE
Transactions on Biomedical Engineering 39 (7,1992): 682-692;
Andreas KUHN, Thierry Keller, Silvestro Micera, Manfred Morari.
Array electrode design for transcutaneous electrical stimulation: A
simulation study. Medical Engineering & Physics 31 (2009)
945-951]. The calculated electrical fields may be confirmed using
measurements using a phantom [A. M. SAGI_DOLEV, D. Prutchi and R.
H. Nathan. Three-dimensional current density distribution under
surface stimulation electrodes. Med. and Biol. Eng. and Comput.
33(1995): 403-408].
[0071] If capacitive effects cannot be ignored, an additional term
involving the time-derivative of the gradient of the potential
appears in the more general expression, as obtained by substituting
the expressions for J and E into the divergence of Ampere's law
with Maxwell's correction:
-.gradient.-(.sigma..gradient..PHI.)-.gradient.(
.gradient..PHI.(.differential..PHI./.differential.t))=0
[0072] The permittivity is a function of position (r) and is
generally a tensor. It may result from properties of the body and
may also be a property of the electrode design [L. A. GEDDES, M.
Hinds and K. S. Foster. Stimulation with capacitor electrodes. Med.
and Biol. Eng. and Comput. 25(1987):359-360]. As a consequence of
such a term, the waveform of the electrical potential at points
within the body will generally be altered relative to the waveform
of the voltage signal(s) applied to the electrode(s). Furthermore,
if the permittivity of a material in the device itself (or patient)
is a function of the electric field or potential, then the equation
becomes non-linear, which could exhibit multiple solutions,
frequency multiplication, and other such non-linear behavior. This
time-dependent equation has been solved numerically [KUHN A, Keller
T. A 3D transient model for transcutaneous functional electrical
stimulation. Proc. 10th Annual Conference of the International FES
Society July 2005--Montreal, Canada: pp. 1-3; Andreas KUHN, Thierry
Keller, Marc Lawrence, Manfred Morari. A model for transcutaneous
current stimulation: simulations and experiments. Med Biol Eng
Comput 47(2009):279-289; N. FILIPOVIC, M. Nedeljkovic, A. Peulic.
Finite Element Modeling of a Transient Functional Electrical
Stimulation. Journal of the Serbian Society for Computational
Mechanics 1 (1, 2007):154-163; Todd A. KUIKEN, Nikolay S. Stoykov,
Milica Popovic, Madeleine Lowery and Allen Taflove. Finite Element
Modeling of Electromagnetic Signal Propagation in a Phantom Arm.
IEEE Transactions on Neural Systems and Rehabilitation Engineering
9 (4,2001): 346-354].
[0073] In any case, Dirichlet (D) boundary conditions define
voltage sources, and Neumann (N) boundary conditions describe the
behavior of the electric field at the crossover boundary from skin
to air, as follows:
N : .differential..PHI./.differential.n=.sigma.(r) and D :
.PHI.=V(t)
where n denotes the outward pointing normal vector, i.e., the
vector orthogonal to the boundary curve; and V(t) denotes the
voltage applied to an electrode. Thus, no conduction current can
flow across an air/conductor interface, so according to the
interfacial boundary conditions, the component of any current
normal to the an air/conductor interface should be zero. In
constructing the above differential equation for .PHI. as a
function of time, the divergence of J is taken, which satisfies the
continuity equation:
.gradient.J=-.differential..rho./.differential.t, where .rho. is
the charge density. Conservation of charge requires that sides of
this equation equal zero everywhere except at the surface of the
electrode where charge is impressed upon the system (injected or
received).
[0074] It is an objective of some embodiments of the present
invention to shape an elongated electric field of effect that can
be oriented parallel to a long nerve such as the vagus nerve in the
neck. The term "shape an electric field" as used herein means to
create an electric field or its gradient that is generally not
radially symmetric at a given depth of stimulation in the patient,
especially a field that is characterized as being elongated or
finger-like, and especially also a field in which the magnitude of
the field in some direction may exhibit more than one spatial
maximum (i.e. may be bimodal or multimodal) such that the tissue
between the maxima may contain an area across which current flow is
restricted. Shaping of the electric field refers both to the
circumscribing of regions within which there is a significant
electric field and to configuring the directions of the electric
field within those regions. Our invention does so by configuring
elements that are present within the equations that were summarized
above, comprising (but not limited to) the following exemplary
configurations that may be used alone or in combination.
[0075] First, different contours or shapes of the electrodes affect
.gradient.J. For example, charge is impressed upon the system
(injected or received) differently if an electrode is curved versus
flat, or if there are more than two electrodes in the system.
[0076] Second, values of the voltage V(t) in the above boundary
condition is manipulated to shape the electric field. For example,
if the device contains two pairs of electrodes that are
perpendicular or at a variable angle with respect to one another,
the waveform of the voltage across one pair of electrodes may be
different than the waveform of the voltage across the second pair,
so that the superimposed electric fields that they produce may
exhibit beat frequencies, as has been attempted with
electrode-based stimulators [Patent U.S. Pat. No. 5,512,057,
entitled Interferential stimulator for applying localized
stimulation, to REISS et al.], and acoustic stimulators [Patent No.
U.S. Pat. No. 5,903,516, entitled Acoustic force generator for
detection, imaging and information transmission using the beat
signal of multiple intersecting sonic beams, to GREENLEAF et
al].
[0077] Third, the scalar potential .PHI. in the above equation a
.differential..PHI./.differential.n=.sigma.(r) may be manipulated
to shape the electric field. For example, this is accomplished by
changing the boundaries of conductor/air (or non-conductor)
interfaces, thereby creating different boundary conditions. For
example, the conducting material may pass through conducting
apertures in an insulated mesh before contacting the patient's
skin, creating thereby an array of electric field maxima. As
another example, an electrode may be disposed at the end of a long
tube that is filled with conducting material, or the electrode may
be situated at the bottom of a curved cup that is filled with
conducting material. In those cases the dimensions of the tube or
cup would affect the resulting electric fields and currents.
[0078] Fourth, the conductivity .sigma. (in the equation
J=.sigma.E) may be varied spatially within the device by using two
or more different conducting materials that are in contact with one
another, for given boundary conditions. The conductivity may also
be varied by constructing some conducting material from a
semiconductor, which allows for adjustment of the conductivity in
space and in time by exposure of the semiconductor to agents to
which they are sensitive, such as electric fields, light at
particular wavelengths, temperature, or some other environmental
variable over which the user of the device has control. For the
special case in which the semiconductor's conductivity may be made
to approach zero, that would approximate the imposition of an
interfacial boundary condition as described in the previous
paragraph.
[0079] Fifth, a dielectric material having a high permittivity ,
such as Mylar, neoprene, titanium dioxide, or strontium titanate,
may be used in the device, for example, in order to permit
capacitative electrical coupling to the patient's skin. Changing
the permittivity in conjunction along with changing the waveform
V(t) would especially affect operation of the device, because the
permittivity appears in a term that is a function of the
time-derivative of the electric potential: .gradient.(
.gradient.(.differential..PHI./.differential.t)).
[0080] In configurations of the present invention, an electrode is
situated in a container that is filled with conducting material. In
one embodiment, the container contains holes so that the conducting
material (e.g., a conducting gel) can make physical contact with
the patient's skin through the holes. For example, the conducting
medium 350 in FIG. 1 may comprise a chamber surrounding the
electrode, filled with a conductive gel that has the approximate
viscosity and mechanical consistency of gel deodorant (e.g., Right
Guard Clear Gel from Dial Corporation, 15501 N. Dial Boulevard,
Scottsdale Ariz. 85260, one composition of which comprises aluminum
chlorohydrate, sorbitol, propylene glycol, polydimethylsiloxanes
Silicon oil, cyclomethicone, ethanol/SD Alcohol 40, dimethicone
copolyol, aluminum zirconium tetrachlorohydrex gly, and water). The
gel, which is less viscous than conventional electrode gel, is
maintained in the chamber with a mesh of openings at the end where
the device is to contact the patient's skin. The gel does not leak
out, and it can be dispensed with a simple screw driven piston.
[0081] In another embodiment, the container itself is made of a
conducting elastomer (e.g., dry carbon-filled silicone elastomer),
and electrical contact with the patient is through the elastomer
itself, possibly through an additional outside coating of
conducting material. In some embodiments of the invention, the
conducting medium may be a balloon filled with a conducting gel or
conducting powders, or the balloon may be constructed extensively
from deformable conducting elastomers. The balloon conforms to the
skin surface, removing any air, thus allowing for high impedance
matching and conduction of large electric fields in to the
tissue.
[0082] Agar can also be used as part of the conducting medium, but
it is not preferred, because agar degrades in time, is not ideal to
use against skin, and presents difficulties with cleaning the
patient. Rather than using agar as the conducting medium, an
electrode can instead be in contact with in a conducting solution
such as 1-10% NaCl that also contacts an electrically conducting
interface to the human tissue. Such an interface is useful as it
allows current to flow from the electrode into the tissue and
supports the conducting medium, wherein the device can be
completely sealed. Thus, the interface is material, interposed
between the conducting medium and patient's skin, that allows the
conducting medium (e.g., saline solution) to slowly leak through
it, allowing current to flow to the skin. Several interfaces are
disclosed as follows.
[0083] One interface comprises conducting material that is
hydrophilic, such as Tecophlic from The Lubrizol Corporation, 29400
Lakeland Boulevard, Wickliffe, Ohio 44092. It absorbs from 10-100%
of its weight in water, making it highly electrically conductive,
while allowing only minimal bulk fluid flow.
[0084] Another material that may be used as an interface is a
hydrogel, such as that used on standard EEG, EKG and TENS
electrodes [Rylie A GREEN, Sungchul Baek, Laura A Poole-Warren and
Penny J Martens. Conducting polymer-hydrogels for medical electrode
applications. Sci. Technol. Adv. Mater. 11 (2010) 014107 (13pp)].
For example it may be the following hypoallergenic, bacteriostatic
electrode gel: SIGNAGEL Electrode Gel from Parker Laboratories,
Inc., 286 Eldridge Rd., Fairfield N.J. 07004. Another example is
the KM10T hydrogel from Katecho Inc., 4020 Gannett Ave., Des Moines
Iowa 50321.
[0085] A third type of interface may be made from a very thin
material with a high dielectric constant, such as those used to
make capacitors. For example, Mylar can be made in submicron
thicknesses and has a dielectric constant of about 3. Thus, at
stimulation frequencies of several kilohertz or greater, the Mylar
will capacitively couple the signal through it because it will have
an impedance comparable to that of the skin itself. Thus, it will
isolate the electrode and conducting solution in from the tissue,
yet allow current to pass.
[0086] The stimulator 340 in FIG. 1 shows two equivalent
electrodes, side-by-side, wherein electrical current would pass
through the two electrodes in opposite directions. Thus, the
current will flow from one electrode, through the tissue and back
through the other electrode, completing the circuit within the
electrodes' conducting media that are separated from one another.
An advantage of using two equivalent electrodes in this
configuration is that this design will increase the magnitude of
the electric field gradient between them, which is important for
exciting long, straight axons such as the vagus nerve in the neck
and other deep peripheral nerves.
[0087] A preferred embodiment of the stimulator is shown in FIG.
3A. A cross-sectional view of the stimulator along its long axis is
shown in FIG. 3B. As shown, the stimulator (30) comprises two heads
(31) and a body (32) that joins them. Each head (31) contains a
stimulating electrode. The body of the stimulator (32) contains the
electronic components and battery (not shown) that are used to
generate the signals that drive the electrodes, which are located
behind the insulating board (33) that is shown in FIG. 3B. However,
in other embodiments of the invention, the electronic components
that generate the signals that are applied to the electrodes may be
separate, but connected to the electrode head (31) using wires.
Furthermore, other embodiments of the invention may contain a
single such head or more than two heads.
[0088] Heads of the stimulator (31) are applied to a surface of the
patient's body, during which time the stimulator may be held in
place by straps or frames (not shown), or the stimulator may be
held against the patient's body by hand. In either case, the level
of stimulation power may be adjusted with a wheel (34) that also
serves as an on/off switch. A light (35) is illuminated when power
is being supplied to the stimulator. A cap (36) is provided to
cover each of the stimulator heads (31), to protect the device when
not in use, to avoid accidental stimulation, and to prevent
material within the head from leaking or drying. Thus, in this
embodiment of the invention, mechanical and electronic components
of the stimulator (impulse generator, control unit, and power
source) are compact, portable, and simple to operate. A cap (36) is
provided to cover each of the stimulator heads (31), to protect the
device when not in use, to avoid accidental stimulation, and to
prevent material within the head from leaking or drying. However,
for embodiments of the stimulator head in which the head is covered
with Mykir or some other high-dielectric material that can
capacitively couple the signal to the skin, the Mylar may
completely seal the gel within the stimulator head, thereby
preventing exposure of the gel to the outside. In that case, there
would be no gel evaporation. Then, the cap (36) would be less
advantageous because the head can be cleaned between stimulation
sessions (e.g., with isopropyl alcohol) with no chance of
contaminating the internal gel.
[0089] Construction of the stimulator head is shown in more detail
in FIG. 4. In the embodiment shown in FIGS. 4A and 4B, the
stimulator head contains an aperture screen, but in the embodiment
shown in FIGS. 4C and 4D, there is no aperture screen. Referring
now to the exploded view shown in FIG. 4A, the electrode head is
assembled from a snap-on cap (41) that serves as a tambour for a
conducting membrane (42), an aperture screen (43), the head-cup
(44), the electrode which is also a screw (45), and a lead-mounting
screw (46) that is inserted into the electrode (45). The electrode
(45) seen in each stimulator head has the shape of a screw that is
flattened on its tip. Pointing of the tip would make the electrode
more of a point source, such that the above-mentioned equations for
the electrical potential may have a solution corresponding more
closely to a far-field approximation. Rounding of the electrode
surface or making the surface with another shape will likewise
affect the boundary conditions. Completed assembly of the
stimulator head is shown in FIG. 4B, which also shows how the head
is attached to the body of the stimulator (47).
[0090] As examples, the conducting membrane (42) may be a sheet of
Tecophlic material from Lubrizol Corporation, 29400 Lakeland
Boulevard, Wickliffe, Ohio 44092. The apertures may be open, or
they may be plugged with conducting material, for example, KM10T
hydrogel from Katecho Inc., 4020 Gannett Ave., Des Moines Iowa
50321. If the apertures are so-plugged, the conducting membrane
(42) becomes optional. The head-cup (44) is filled with conducting
material, for example, SIGNAGEL Electrode Gel from Parker
Laboratories, Inc., 286 Eldridge Rd., Fairfield N.J. 07004. The
snap-on cap (41), aperture screen (43), head-cup (44) and body of
the stimulator are made of a non-conducting material, such as
acrylonitrile butadiene styrene. The depth of the head-cup from its
top surface to the electrode may be between one and six
centimeters. The head-cup may have a different curvature than what
is shown in FIG. 4, or it may be tubular or conical or have some
other inner surface geometry that will affect the Neumann boundary
conditions.
[0091] The stimulator is preferably configured such that the
distribution of current passing into the patient's tissue is
substantially uniform to minimize high current densities that would
potentially cause pain to the patient. In one exemplary embodiment,
the electrode(s) are preferably spaced from the conducting membrane
42 by a distance of about 0.25 to 4 times the diameter of the
conducting membrane 42. Thus, if the diameter of the conducting
membrane 42 is 1 inch then the electrode should be between 0.25 and
4 inches from the conducting membrane, preferably about 0.5 to 2
inches. In addition, in order to reach a nerve at a depth d, the
electrode diameter should be between 0.2 and 2 d, preferable about
1 d and the spacing (from center to center) should be between 1.5 d
and 3 d, preferable about 2 d. The conducting medium preferably has
a conductivity that is high enough to allow current flow
therethrough, but low enough to minimize a non-uniform distribution
of current passing through the conducting membrane 42 into the
patient's tissue.
[0092] The alternate embodiment of the stimulator head that is
shown in FIG. 4C also contains a snap-on cap (41), a conducting
membrane (42), the head-cup (44), the electrode which is also a
screw (45), and a lead-mounting screw (46) that is inserted into
the electrode (45). This alternate embodiment differs from the
embodiment shown in FIGS. 4A and 4B in regard to the mechanical
support that is provided to the conducting membrane (42). Whereas
the aperture screen had provided mechanical support to the membrane
in the other embodiment, in the alternate embodiment a reinforcing
ring (40) is provided to the membrane. That reinforcement ring
rests on non-conducting struts (49) that are placed in the head-cup
(44), and a non-conducting strut-ring (48) is placed within notches
in the struts (49) to hold the struts in place. An advantage of the
alternate embodiment is that without apertures, current flow is
less restricted through the conducting membrane (42). Furthermore,
although the struts and strut-ring are made of non-conducting
material in this alternate embodiment, the design may be adapted to
position additional electrode or other conducting elements within
the head-cup for other more specialized configurations of the
stimulator head, the inclusion of which will influence the electric
fields that are generated by the device. Completed assembly of the
alternate stimulator head is shown in FIG. 4D, without showing
attachment to the body of the stimulator, and without showing the
insertion of the lead-mounting screw (46). In fact, it is also
possible to insert a lead under the head of the electrode (45), and
many other methods of attaching the electrode to the
signal-generating electronics of the stimulator are known in the
art.
[0093] Another embodiment of the stimulator is shown in FIG. 5,
showing a device in which electrically conducting material is
dispensed from the device to the patient's skin. FIGS. 5A and 5B
respectively provide top and bottom views of the outer surface of
the electrical stimulator 50. FIG. 5C provides a bottom view of the
stimulator 50, after sectioning along its long axis to reveal the
inside of the stimulator.
[0094] FIGS. 5A and 5C show a mesh 51 with openings that permit a
conducting gel to pass from inside of the stimulator to the surface
of the patient's skin at the position of nerve or tissue
stimulation. Thus, the mesh with openings 51 is the part of the
stimulator that is applied to the skin of the patient, through
which conducting material may be dispensed. In any given
stimulator, the distance between the two mesh openings 51 in FIG.
5A is constant, but it is understood that different stimulators may
be built with different inter-mesh distances, in order to
accommodate the anatomy and physiology of individual patients.
Alternatively, the inter-mesh distance may be made variable as in
the eyepieces of a pair of binoculars. A covering cap (not shown)
is also provided to fit snugly over the top of the stimulator
housing and the mesh openings 51, in order to keep the housing's
conducting medium from leaking or drying when the device is not in
use.
[0095] FIGS. 5B and 5C show the bottom of the self-contained
stimulator 50. An on/off switch 52 is attached through a port 54,
and a power-level controller 53 is attached through another port
54. The switch is connected to a battery power source (320 in FIG.
1), and the power-level controller is attached to the control unit
(330 in FIG. 1) of the device. The power source battery and
power-level controller, as well as the impulse generator (310 in
FIG. 1) are located (but not shown) in the rear compartment 55 of
the housing of the stimulator 50.
[0096] Individual wires (not shown) connect the impulse generator
(310 in FIG. 1) to the stimulator's electrodes 56. The two
electrodes 56 are shown here to be elliptical metal discs situated
between the head compartment 57 and rear compartment 55 of the
stimulator 50. A partition 58 separates each of the two head
compartments 57 from one another and from the single rear
compartment 55. Each partition 58 also holds its corresponding
electrode in place. However, each electrode 56 may be removed to
add electrically conducting gel (350 in FIG. 1) to each head
compartment 57. Each partition 58 may also slide towards the head
of the device in order to dispense conducting gel through the mesh
apertures 51. The position of each partition 58 therefore
determines the distance 59 between its electrode 56 and mesh
openings 51, which is variable in order to obtain the optimally
uniform current density through the mesh openings 51. The outside
housing of the stimulator 50, as well as each head compartment 57
housing and its partition 58, are made of electrically insulating
material, such as acrylonitrile butadiene styrene, so that the two
head compartments are electrically insulated from one another.
[0097] In the preferred embodiments, electrodes are made of a
metal, such as stainless steel. However, in other embodiments, the
electrodes may have many other sizes and shapes, and they may be
made of other materials [Thierry KELLER and Andreas Kuhn.
Electrodes for transcutaneous (surface) electrical stimulation.
Journal of Automatic Control, University of Belgrade, 18
(2,2008):35-45; G. M. LYONS, G. E. Leane, M. Clarke-Moloney, J. V.
O'Brien, P. A. Grace. An investigation of the effect of electrode
size and electrode location on comfort during stimulation of the
gastrocnemius muscle. Medical Engineering & Physics 26 (2004)
873-878; Bonnie J. FORRESTER and Jerrold S. Petrofsky. Effect of
Electrode Size, Shape, and Placement During Electrical Stimulation.
The Journal of Applied Research 4, (2, 2004): 346-354; Gad ALON,
Gideon Kantor and Henry S. Ho. Effects of Electrode Size on Basic
Excitatory Responses and on Selected Stimulus Parameters. Journal
of Orthopaedic and Sports Physical Therapy. 20(1,1994):29-35].
[0098] For example, there may be more than two electrodes; the
electrodes may comprise multiple concentric rings; and the
electrodes may be disc-shaped or have a non-planar geometry. They
may be made of other metals or resistive materials such as
silicon-rubber impregnated with carbon that have different
conductive properties [Stuart F. COGAN. Neural Stimulation and
Recording Electrodes. Annu. Rev. Biomed. Eng. 2008. 10:275-309;
Michael F. NOLAN. Conductive differences in electrodes used with
transcutaneous electrical nerve stimulation devices. Physical
Therapy 71 (1991):746-751].
[0099] Although the electrode may consist of arrays of conducting
material, the embodiments shown in FIGS. 3 to 5 avoid the
complexity and expense of array or grid electrodes [Ana
POPOVIC-BIJELIC, Goran Bijelic, Nikola Jorgovanovic, Dubravka
Bojanic, Mirjana B. Popovic, and Dejan B. Popovic. Multi-Field
Surface Electrode for Selective Electrical Stimulation. Artificial
Organs 29 (6,2005):448-452; Dejan B. POPOVIC and Mirjana B.
Popovic. Automatic determination of the optimal shape of a surface
electrode: Selective stimulation. Journal of Neuroscience Methods
178 (2009) 174-181; Thierry KELLER, Marc Lawrence, Andreas Kuhn,
and Manfred Morari. New Multi-Channel Transcutaneous Electrical
Stimulation Technology for Rehabilitation. Proceedings of the 28th
IEEE EMBS Annual International Conference New York City, USA, Aug.
30-Sep. 3, 2006 (WeC14.5): 194-197]. This is because the designs
shown in FIGS. 3 to 5 provide a uniform surface current density,
which would otherwise be a potential advantage of electrode arrays,
and which is a trait that is not shared by most electrode designs
[Kenneth R. BRENNEN. The Characterization of Transcutaneous
Stimulating Electrodes. IEEE Transactions on Biomedical Engineering
BME-23 (4, 1976): 337-340; Andrei PATRICIU, Ken Yoshida, Johannes
J. Struijk, Tim P. DeMonte, Michael L. G. Joy, and Hans
Stodkilde-Jorgensen. Current Density Imaging and Electrically
Induced Skin Burns Under Surface Electrodes. IEEE Transactions on
Biomedical Engineering 52 (12,2005): 2024-2031; R. H. GEUZE. Two
methods for homogeneous field defibrillation and stimulation. Med.
and Biol. Eng. and Comput. 21 (1983), 518-520; J. PETROFSKY, E.
Schwab, M. Cuneo, J. George, J. Kim, A. Almalty, D. Lawson, E.
Johnson and W. Remigo. Current distribution under electrodes in
relation to stimulation current and skin blood flow: are modern
electrodes really providing the current distribution during
stimulation we believe they are? Journal of Medical Engineering and
Technology 30 (6,2006): 368-381; Russell G. MAUS, Erin M. McDonald,
and R. Mark Wightman. Imaging of Nonuniform Current Density at
Microelectrodes by Electrogenerated Chemiluminescence. Anal. Chem.
71 (1999): 4944-4950]. In fact, patients found the design shown in
FIGS. 3 to 5 to be less painful in a direct comparison with a
commercially available grid-pattern electrode [UltraStim
grid-pattern electrode, Axelggard Manufacturing Company , 520
Industrial Way, Fallbrook Calif., 2011].
[0100] The stimulator designs shown in FIGS. 3 to 5 situate the
electrode remotely from the surface of the skin within a chamber,
with conducting material placed in the chamber between the skin and
electrode. Such a chamber design had been used prior to the
availability of flexible, flat, disposable electrodes [Patent U.S.
Pat. No. 3,659,614, entitled Adjustable headband carrying
electrodes for electrically stimulating the facial and mandibular
nerves, to Jankelson; U.S. Pat. No. 3,590,810, entitled Biomedical
body electode, to Kopecky; U.S. Pat. No. 3,279,468, entitled
Electrotherapeutic facial mask apparatus, to Le Vine; U.S. Pat. No.
6,757,556, entitled Electrode sensor, to Gopinathan et al; U.S.
Pat. No. 4,383,529, entitled Iontophoretic electrode device, method
and gel insert, to Webster; U.S. Pat. No. 4220159, entitled
Electrode, to Francis et al. U.S. Pat. No. 3862633, U.S. Pat. No.
4,182,346, and U.S. Pat. No. 3,973,557, entitled Electrode, to
Allison et al; U.S. Pat. No. 4,215,696, entitled Biomedical
electrode with pressurized skin contact , to Bremer et al; and U.S.
Pat. No. 4,166,457, entitled Fluid self-sealing bioelectrode, to
Jacobsen et al.] The stimulator designs shown in FIGS. 3 to 5 are
also self-contained units, housing the electrodes, signal
electronics, and power supply. Portable stimulators are also known
in the art, for example, patent U.S. Pat. No. 7,171,266, entitled
Electro-acupuncture device with stimulation electrode assembly, to
Gruzdowich]. One of the novelties or the present invention is that
two or more remote electrodes are configured for placement relative
to the axis of a deep, long nerve, such that the stimulator along
with a correspondingly suitable stimulation waveform shapes the
electric field, producing a selective physiological response by
stimulating that nerve, but avoiding substantial stimulation of
nerves and tissue other than the target nerve, particularly
avoiding the stimulation of nerves that produce pain.
[0101] Examples in the remaining disclosure will be directed to
methods for using the disclosed electrical stimulation devices for
treating a patient. These applications involve stimulating the
patient in and around the patient's neck. However, it will be
appreciated that the systems and methods of the present invention
might be applied equally well to other nerves of the body,
including but not limited to parasympathetic nerves, sympathetic
nerves, and spinal or cranial nerves. As examples, the disclosed
devices may used to treat particular medical conditions, by
substituting the devices disclosed herein for the stimulators
disclosed in the following patent applications.
[0102] Applicant's commonly assigned co-pending patent application,
Ser. No. 12/964,050, entitled Magnetic Stimulation Devices and
Methods of Therapy, disclosed methods for using the device to treat
such conditions as post-operative ileus, dysfunction associated
with TNF-alpha in Alzheimer's disease, postoperative cognitive
dysfunction, rheumatoid arthritis, bronchoconstriction, urinary
incontinence and/or overactive bladder, and sphincter of Oddi
dysfunction.
[0103] Another commonly assigned co-pending application, Ser. No.
13/005,005, entitled Non-invasive Treatment of Neurodegenerative
Diseases, disclosed methods and devices for treating
neurodegenerative diseases more generally, including essential
tremor, Alzheimer's disease and its precursor mild cognitive
impairment (MCI), Parkinson's disease (including Parkinson's
disease dementia) and multiple sclerosis, as well as postoperative
cognitive dysfunction and postoperative delirium. The devices and
methods may also be used to treat conditions that were not
disclosed in those patent applications, such as allergic rhinitis,
headaches, particularly tension headaches, cluster headaches, sinus
headaches and migraine headaches [Alberto Proietti CECCHINI, Eliana
Mea, Vincenzo Tullo, Marcella Curone, Angelo Franzini, Giovanni
Broggi, Mario Savino,Gennaro Bussone, Massimo Leone. Vagus nerve
stimulation in drug-resistant daily chronic migraine with
depression: preliminary data. Neurol Sci (2009) 30 (Suppl
1):S101-S104].
[0104] Selected nerve fibers are stimulated in different
embodiments of methods that make use of the disclosed electrical
stimulation devices, including stimulation of the vagus nerve at a
location in the patient's neck. At that location, the vagus nerve
is situated within the carotid sheath, near the carotid artery and
the interior jugular vein. The carotid sheath is located at the
lateral boundary of the retopharyngeal space on each side of the
neck and deep to the sternocleidomastoid muscle. The left vagus
nerve is sometimes selected for stimulation because stimulation of
the right vagus nerve may produce undesired effects on the heart,
but depending on the application, the right vagus nerve or both
right and left vagus nerves may be stimulated instead.
[0105] The three major structures within the carotid sheath are the
common carotid artery, the internal jugular vein and the vagus
nerve. The carotid artery lies medial to the internal jugular vein,
and the vagus nerve is situated posteriorly between the two
vessels. Typically, the location of the carotid sheath or interior
jugular vein in a patient (and therefore the location of the vagus
nerve) will be ascertained in any manner known in the art, e.g., by
feel or ultrasound imaging. Proceeding from the skin of the neck
above the sternocleidomastoid muscle to the vagus nerve, a line may
pass successively through the sternocleidomastoid muscle, the
carotid sheath and the internal jugular vein, unless the position
on the skin is immediately to either side of the external jugular
vein. In the latter case, the line may pass successively through
only the sternocleidomastoid muscle and the carotid sheath before
encountering the vagus nerve, missing the interior jugular vein.
Accordingly, a point on the neck adjacent to the external jugular
vein might be preferred for non-invasive stimulation of the vagus
nerve. The magnetic stimulator coil may be centered on such a
point, at the level of about the fifth to sixth cervical
vertebra.
[0106] FIG. 6 illustrates use of the devices shown in FIGS. 3 to 5
to stimulate the vagus nerve at that location in the neck, in which
the stimulator device 50 in FIG. 5 is shown to be applied to the
target location on the patient's neck as described above. For
reference, locations of the following vertebrae are also shown:
first cervical vertebra 71, the fifth cervical vertebra 75, the
sixth cervical vertebra 76, and the seventh cervical vertebra
77.
[0107] FIG. 7 provides a more detailed view of use of the
electrical stimulator, when positioned to stimulate the vagus nerve
at the neck location that is indicated in FIG. 6. As shown, the
stimulator 50 in FIG. 5 touches the neck indirectly, by making
electrical contact through conducting gel 29 (or other conducting
material) which may be is dispensed through mesh openings
(identified as 51 in FIG. 5) of the stimulator or applied as an
electrode gel or paste. The layer of conducting gel 29 in FIG. 7 is
shown to connect the device to the patient's skin, but it is
understood that the actual location of the gel layer(s) may be
generally determined by the location of mesh 51 shown in FIG. 5.
Furthermore, it is understood that for other embodiments of the
invention, the conductive head of the device may not necessitate
the use of additional conductive material being applied to the
skin. The vagus nerve 60 is identified in FIG. 7, along with the
carotid sheath 61 that is identified there in bold peripheral
outline. The carotid sheath encloses not only the vagus nerve, but
also the internal jugular vein 62 and the common carotid artery 63.
Features that may be identified near the surface of the neck
include the external jugular vein 64 and the sternocleidomastoid
muscle 65. Additional organs in the vicinity of the vagus nerve
include the trachea 66, thyroid gland 67, esophagus 68, scalenus
anterior muscle 69, and scalenus medius muscle 70. The sixth
cervical vertebra 76 is also shown in FIG. 7, with bony structure
indicated by hatching marks.
[0108] If it is desired to maintain a constant intensity of
stimulation in the vicinity of the vagus nerve (or any other nerve
or tissue that is being stimulated), methods may also be employed
to modulate the power of the stimulator in order to compensate for
patient motion or other mechanisms that would otherwise give rise
to variability in the intensity of stimulation. In the case of
stimulation of the vagus nerve, such variability may be
attributable to the patient's breathing, which may involve
contraction and associated change in geometry of the
sternocleidomastoid muscle that is situated close to the vagus
nerve (identified as 65 in FIG. 7). Methods for compensating for
motion and other confounding factors were disclosed by the present
applicant in commonly assigned co-pending application Ser. No.
12/859,568, entitled Non-Invasive Treatment of Bronchial
Constriction, to SIMON, which is hereby incorporated by
reference.
[0109] Methods of treating a patient comprise stimulating the vagus
nerve as indicated in FIGS. 6 and 7, using the electrical
stimulation devices that are disclosed herein. The position and
angular orientation of the device are adjusted about that location
until the patient perceives stimulation when current is passed
through the stimulator electrodes. The applied current is increased
gradually, first to a level wherein the patient feels sensation
from the stimulation. The power is then increased, but is set to a
level that is less than one at which the patient first indicates
any discomfort. Straps, harnesses, or frames are used to maintain
the stimulator in position (not shown in FIG. 6 or 7). The
stimulator signal may have a frequency and other parameters that
are selected to produce a therapeutic result in the patient.
Stimulation parameters for each patient are adjusted on an
individualized basis. Ordinarily, the amplitude of the stimulation
signal is set to the maximum that is comfortable for the patient,
and then the other stimulation parameters are adjusted.
[0110] In other embodiments of the invention, pairing of vagus
nerve stimulation may be with a time-varying sensory stimulation.
The paired sensory stimulation may be bright light, sound, tactile
stimulation, or electrical stimulation of the tongue to simulate
odor/taste, e.g., pulsating with the same frequency as the vagus
nerve electrical stimulation. The rationale for paired sensory
stimulation is the same as simultaneous, paired stimulation of both
left and right vagus nerves, namely, that the pair of signals
interacting with one another in the brain may result in the
formation of larger and more coherent neural ensembles than the
neural ensembles associated with the individual signals, thereby
enhancing the therapeutic effect. For example, the hypothalamus is
well known to be responsive to the presence of bright light, so
exposing the patient to bright light that is fluctuating with the
same stimulation frequency as the vagus nerve (or a multiple of
that frequency) may be performed in an attempt to enhance the role
of the hypothalamus in producing the desired therapeutic effect.
Such paired stimulation does not rely upon neuronal plasticity and
is in that sense different from other reports of paired stimulation
[Navzer D. ENGINEER, Jonathan R. Riley, Jonathan D. Seale, Will A.
Vrana, Jai A. Shetake, Sindhu P. Sudanagunta, Michael S. Borland
and Michael P. Kilgard. Reversing pathological neural activity
using targeted plasticity. Nature (2011): published online
doi:10.1038/nature09656].
[0111] Although the invention herein has been described with
reference to particular embodiments, it is to be understood that
these embodiments are merely illustrative of the principles and
applications of the present invention. It is therefore to be
understood that numerous modifications may be made to the
illustrative embodiments and that other arrangements may be devised
without departing from the spirit and scope of the present
invention as defined by the appended claims.
* * * * *