U.S. patent application number 11/035374 was filed with the patent office on 2005-06-30 for method and system for providing electrical pulses for neuromodulation of vagus nerve(s), using rechargeable implanted pulse generator.
Invention is credited to Boveja, Birinder R., Widhany, Angely.
Application Number | 20050143787 11/035374 |
Document ID | / |
Family ID | 34704997 |
Filed Date | 2005-06-30 |
United States Patent
Application |
20050143787 |
Kind Code |
A1 |
Boveja, Birinder R. ; et
al. |
June 30, 2005 |
Method and system for providing electrical pulses for
neuromodulation of vagus nerve(s), using rechargeable implanted
pulse generator
Abstract
A method and system of providing electrical pulses to vagal
nerve(s) using rechargeable implantable pulse generator for
stimulation and/or blocking to provide therapy for neurological and
neuropsychiatric disorders comprises implantable and external
components. These disorders include (but are not limited to)
epilepsy, partial complex epilepsy, generalized epilepsy, and
involuntary movement disorders such as in Parkinson's disease,
depression, bipolar depression, schizophrenia, anxiety disorders,
neurogenic/psycogenic pain, compulsive eating disorders, obesity,
obsessive compulsive disorders, dementia including Alzheimer's
disease, sleep disorders, learning difficulties, migraines and
cardiac disorders such as atrial fibrillation and congestive heart
failure (CHF). The implantable components are a lead and an
implantable pulse generator, comprising rechargeable lithium-ion or
lithium-ion polymer battery. The external components are a
programmer and an external recharger. In one embodiment, the
implanted pulse generator may also comprise stimulus-receiver
means, and a pulse generator means with rechargeable battery. The
implanted stimulus-receiver is adapted to work in conjunction with
an external stimulator. In another embodiment, the implanted pulse
generator is adapted to be rechargeable, utilizing inductive
coupling with an external recharger. Existing vagal nerve
stimulators may also be adapted to be used with rechargeable power
sources as disclosed herein. The implanted system may also use a
lead with two or more electrodes, for vagus nerve(s) modulation
with selective stimulation and/or blocking.
Inventors: |
Boveja, Birinder R.;
(Milwaukee, WI) ; Widhany, Angely; (Milwaukee,
WI) |
Correspondence
Address: |
BIRINDER R. BOVEJA & ANGELY WIDHANY
P. O. BOX 210095
MILWAUKEE
WI
53221
US
|
Family ID: |
34704997 |
Appl. No.: |
11/035374 |
Filed: |
January 13, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11035374 |
Jan 13, 2005 |
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10841995 |
May 8, 2004 |
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10841995 |
May 8, 2004 |
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10196533 |
Jul 16, 2002 |
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10196533 |
Jul 16, 2002 |
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10142298 |
May 9, 2002 |
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Current U.S.
Class: |
607/45 |
Current CPC
Class: |
A61N 1/36007 20130101;
A61N 1/40 20130101; A61N 1/36082 20130101; A61N 1/36114 20130101;
A61N 1/36071 20130101; A61N 1/3627 20130101 |
Class at
Publication: |
607/045 |
International
Class: |
A61N 001/18 |
Claims
We claim:
1. A method of providing electrical pulses with a rechargeable
implantable pulse generator for stimulation and/or blocking of
vagus nerve(s) and/or its branches or part thereof, for treating or
alleviating the symptoms for at least one of neurological,
neuropsychiatric disorders, comprising the steps of: providing said
implantable rechargeable pulse generator, comprising a
microcontroller, pulse generation circuitry, rechargeable battery,
battery recharging circuitry, and a coil; providing a lead with at
least two electrodes adapted to be in contact with said vagus
nerve(s) or its branches or part thereof, and in electrical contact
with said rechargeable implantable pulse generator; providing an
external power source to charge said rechargeable implantable pulse
generator; and providing an external programmer to program said
rechargeable implantable pulse generator.
2. A method of claim 1, wherein said neurological, neuropsychiatric
disorders comprises at least one of epilepsy, partial complex
epilepsy, generalized epilepsy, involuntary movement disorders such
as in Parkinson's disease, depression, bipolar depression,
schizophrenia, anxiety disorders, neurogenic/psycogenic pain,
compulsive eating disorders, obesity, obsessive compulsive
disorders, dementia including Alzheimer's disease, sleep disorders,
learning difficulties, migraines and cardiac disorders such as
atrial fibrillation and congestive heart failure (CHF).
3. A method of claim 1, wherein said coil is also used for
bidirectional telemetry.
4. A method of claim 1, wherein said coil used in recharging said
pulse generator is around said implantable rechargeable pulse
generator case in a silicone enclosure.
5. A method of claim 4, wherein said implantable rechargeable pulse
generator does not require magnetic shielding between said coil and
said titanium case.
6. A method of claim 1, wherein said rechargeable implanted pulse
generator further comprises one or two feedthrough(s) for unipolar
or bipolar configurations respectively.
7. A method of claim 1, wherein said implantable rechargeable pulse
generator further comprises means stimulus-receiver means such
that, said implantable rechargeable pulse generator can function in
conjunction with an external stimulator, to provide said
stimulation and/or blocking to said vagus nerve(s) and/or its
branches.
8. A method of claim 1, wherein said at least two electrodes are of
a material selected from the group consisting of platinum,
platinum/iridium alloy, platinum/iridium alloy coated with titanium
nitride, and carbon.
9. A method of claim 1, wherein said rechargeable battery comprises
at least one of lithium-ion, lithium-ion polymer batteries.
10. A method of modulating vagus nerve(s) and/or its branches or
part thereof with electrical pulses for treating or alleviating the
symptoms of neurological, or neuropsychiatric disorders, comprising
at least one of epilepsy, partial complex epilepsy, generalized
epilepsy, involuntary movement disorders such as in Parkinson's
disease, depression, bipolar depression, schizophrenia, anxiety
disorders, neurogenic/psycogenic pain, compulsive eating disorders,
obesity, obsessive compulsive disorders, dementia including
Alzheimer's disease, sleep disorders, learning difficulties,
migraines and cardiac disorders such as atrial fibrillation and
congestive heart failure (CHF), and further comprising the steps
of: providing an implantable rechargeable pulse generator, wherein
said implantable rechargeable pulse generator comprises a
stimulus-receiver means, and an implantable pulse generator means
comprising a microcontroller, pulse generation circuitry,
rechargeable battery, and battery recharging circuitry; providing a
lead with at least two electrodes adapted to be in contact with
said vagus nerve(s) or its branches or part thereof, and in
electrical contact with said implantable rechargeable pulse
generator; providing an external power source to charge
rechargeable implantable pulse generator. providing an external
programmer to program the said rechargeable implantable pulse
generator.
11. A method of claim 10, wherein said rechargeable implantable
pulse generator can function in conjunction with an external
stimulator, to provide said stimulation and/or blocking to said
vagus nerve(s) and/or its branches.
12. A method of claim 10, wherein said coil used in recharging said
pulse generator is around said implantable rechargeable pulse
generator case in a slicone enclosure.
13. A method of claim 10, wherein said rechargeable implantable
pulse generator can be recharged using an external recharger or an
external stimulator.
14. A method of claim 10, wherein said rechargeable battery
comprises at least one of lithium-ion, lithium-ion polymer
batteries.
15. A vagus nerve(s) stimulation and/or blocking system for
providing electrical pulses to vagus nerve(s) or its branches or
part thereof for treating or alleviating the symptoms for at least
one of neurological, and neuropsychiatric disorders, comprising: a
rechargeable implantable pulse generator, comprising, a
microprocessor, pulse generation circuitry, rechargeable battery,
battery recharging circuitry, and a coil; a lead with at least two
electrodes adapted to be in contact with said vagus nerve(s) or its
branches or part thereof and in electrical contact with said
implantable rechargeable pulse generator; an external power source
to charge said rechargeable implantable pulse generator; and an
external programmer to program said rechargeable implantable pulse
generator.
16. A system of claim 15, wherein said at least one of neurological
and neuropsychiatric disorders comprises at least one of epilepsy,
partial complex epilepsy, generalized epilepsy, and involuntary
movement disorders such as in Parkinson's disease, depression,
bipolar depression, schizophrenia, anxiety disorders,
neurogenic/psycogenic pain, compulsive eating disorders, obesity,
obsessive compulsive disorders, dementia including Alzheimer's
disease, sleep disorders, learning difficulties, migraines and
cardiac disorders such as atrial fibrillation and congestive heart
failure (CHF).
17. A system of claim 15, wherein said coil is used for
bidirectional telemetry, or receiving electrical pulses from said
external stimulator.
18. A system of claim 15, wherein said coil used in recharging said
pulse generator is around said rechargeable implantable pulse
generator case in a silicone enclosure.
19. A system of claim 15, wherein said rechargeable implantable
pulse generator does not require a magnetic shield between said
coil and said titanium case.
20. A system of claim 15, wherein said rechargeable implantable
rechargeable pulse generator does require a magnetic shield between
said coil and said titanium case.
21. A system of claim 15, wherein said rechargeable implanted pulse
generator further comprises one or two feedthrough(s) for unipolar
or bipolar configurations respectively.
22. A system of claim 15, wherein said implantable rechargeable
pulse generator further comprises means such that said implantable
rechargeable pulse generator can also function in conjunction with
an external stimulator, to provide said stimulation and/or blocking
to said vagus nerve(s) and/or its branches.
23. A system of claim 15, wherein said at least two electrodes are
of a material selected from the group consisting of platinum,
platinum/iridium alloy, platinum/iridium alloy coated with titanium
nitride, and carbon.
24. A system of claim 15, wherein said rechargeable battery
comprises at least one of lithium-ion, lithium-ion polymer
batteries.
25. A system for modulating the vagus nerve(s) and/or its branches
or part thereof with electrical pulses, for treating or for
alleviating the symptoms for at least one of epilepsy, partial
complex epilepsy, generalized epilepsy, involuntary movement
disorders such as in Parkinson's disease, depression, bipolar
depression, schizophrenia, anxiety disorders, neurogenic/psycogenic
pain, compulsive eating disorders, obesity, obsessive compulsive
disorders, dementia including Alzheimer's disease, sleep disorders,
learning difficulties, migraines and cardiac disorders such as
atrial fibrillation and congestive heart failure (CHF), comprising:
a rechargeable implantable pulse generator, comprising a
microprocessor, pulse generation circuitry, rechargeable battery,
and stimulus-receiver means; a lead with at least two electrodes
adapted to be in contact with said vagus nerve(s) or its branches
or part thereof and in electrical contact with said implantable
rechargeable pulse generator; an external power source to charge
implantable rechargeable pulse generator; and an external
programmer to program the said rechargeable implantable pulse
generator.
25. A system of claim 25, wherein said implantable rechargeable
pulse generator can function in conjunction with an external
stimulator, to provide said stimulation and/or blocking to said
vagus nerve(s) and/or its branches.
26. A system of claim 25, wherein said coil used in recharging said
pulse generator is around said implantable rechargeable pulse
generator case in a silicone enclosure.
27. A system of claim 25, wherein said rechargeable battery
comprises at least one of lithium-ion, lithium-ion polymer
batteries.
Description
[0001] This application is a continuation of application Ser. No.
10/841,995 filed May 8, 2004, entitled "METHOD AND SYSTEM FOR
MODULATING THE VAGUS NERVE (10.sup.th CRANIAL NERVE) WITH
ELECTRICAL PULSES USING IMPLANTED AND EXTERNAL COMPONANTS, TO
PROVIDE THERAPY FOR NEUROLOGICAL AND NEUROPSYCHIATRIC DISORDERS",
which is a continuation of application Ser. No. 10/196,533 filed
Jul. 16, 2002, which is a continuation of Ser. No. 10/142,298 filed
on May 9, 2002. The prior applications being incorporated herein in
entirety by reference, and priority is claimed from these
applications.
FIELD OF INVENTION
[0002] The present invention relates to electrical stimulation with
implanted medical device, more specifically to neuromoduation of
vagus nerve(s) with rechargeable implantable pulse generator, to
provide therapy for neurological, neuropsychiatric, and other
medical disorders.
BACKGROUND
[0003] Implantable neuromodulation systems are known in the art.
This patent application is directed to novel method and system for
increasing the useful service life of nerve stimulators which are
used for applications that can be demanding on the power source.
The implantable neurostimulation system for modulating vagus
nerve(s) is used to provide therapy for neurological,
neuropsychiatric, and other medical disorders such as obesity, and
certain cardiac disorders such as atrial fibrillation and
congestive heart failure (CHF). Vagus nerve neuromodulation systems
generally fall into two categories, RF coupled devices and
implantable pulse generators (IPG).
[0004] U.S. Pat. No. 6,205,359 (Boveja), U.S. Pat. No. 6,356,788
(Boveja), U.S. Pat. No. 6,208,902 (Boveja), U.S. Pat. No. 6,269,270
(Boveja), U.S. Pat. No. 6,611,715 (Boveja), and U.S. Pat. No.
6,668,191 (Boveja) are generally directed to neuromodulating vagus
nerve(s) with an RF coupled device. U.S. Patents, U.S. Pat. No.
4,702,254 (Zabara), U.S. Pat. No. 5,023,807 (Zabara), and U.S. Pat.
No. 4,867,164 (Zabra) are generally directed to neuromodulation of
vagus nerve, preferably using an implanted pulse generator
(IPG).
[0005] The prior art IPG devices are similar to cardiac pacemakers,
and have been adapted to deliver pulses at higher frequencies than
cardiac pacemakers. In cardiac pacing, pulses are typically
delivered at a rate of approximately one Hz (generally 50-70 beats
per min.). In contrast, pulses to vagus nerve(s) are typically
delivered at frequency of about 20-50 Hz. Electrical pulsed
neuromodulation of vagus nerve(s) can be very demanding for an
implantable power source. It would be desirable to have an
implantable pulse generator comprising a rechargeable power source,
such as rechargeable Li-ion battery or re-chargeable Li-ion polymer
battery.
[0006] This patent application discloses two embodiments of
implantable pulse generator comprising rechargeable batteries. Even
a rechargeable implanted pulse generator does not have an
indefinite life, therefore in order to enhance the service life, in
one embodiment the implanted pulse generator may comprise
stimulus-receiver means, and a pulse generator means with
rechargeable battery. The implanted pulse generator of this
embodiment is also adapted to function in conjunction with an
external stimulator. In another embodiment, the implanted pulse
generator is adapted to be rechargeable, utilizing inductive
coupling with an external recharger. Existing vagal nerve
stimulators may also be adapted to be used with rechargeable power
sources as disclosed herein.
Background of Neuromodulation
[0007] The 10.sup.th cranial nerve or the vagus nerve plays a role
in mediating afferent information from visceral organs to the
brain. The vagus nerve arises directly from the brain, but unlike
the other cranial nerves extends well beyond the head. At its
farthest extension it reaches the lower parts of the intestines.
The vagus nerve provides an easily accessible, peripheral route to
modulate central nervous system (CNS) function. Observations on the
profound effect of electrical stimulation of the vagus nerve on
central nervous system (CNS) activity extends back to the
1930's.
[0008] The present invention is primarily directed to a method and
system for selective electrical stimulation and/or blocking or
neuromodulation of vagus nerve, for providing adjunct therapy for
neurological and neuropsychiatric disorders comprises at least one
of epilepsy, partial complex epilepsy, generalized epilepsy, and
involuntary movement disorders such as in Parkinson's disease,
depression, bipolar depression, schizophrenia, anxiety disorders,
neurogenic/psycogenic pain, compulsive eating disorders, obesity,
obsessive compulsive disorders, dementia including Alzheimer's
disease, sleep disorders, learning difficulties, migraines and
cardiac disorders such as atrial fibrillation and congestive heart
failure(CHF).
[0009] In the human body there are two vagal nerves (VN), the right
VN and the left VN. Each vagus nerve is encased in the carotid
sheath along with the carotid artery and jugular vein. The
innervation of the right and left vagus nerves is different. The
innervation of the right vagus nerve is such that stimulating it
results in profound bradycardia (slowing of the heart rate). The
left vagus nerve has some innervation to the heart, but mostly
innervates the visceral organs such as the gastrointestinal tract.
It is known that stimulation of the left vagus nerve does not cause
substantial slowing of the heart rate or cause any other
significant deleterious side effects.
[0010] One of the fundamental features of the nervous system is its
ability to generate and conduct electrical impulses. Most nerves in
the human body are composed of thousands of fibers of different
sizes. This is shown schematically in FIG. 1. The different sizes
of nerve fibers, which carry signals to and from the brain, are
designated by groups A, B, and C. The vagus nerve, for example, may
have approximately 100,000 fibers of the three different types,
each carrying signals. Each axon or fiber of that nerve conducts
only in one direction, in normal circumstances. In the vagus nerve
sensory fibers outnumber parasympathetic fibers four to one.
[0011] In a cross section of peripheral nerve it is seen that the
diameter of individual fibers vary substantially, as is also shown
schematically in FIG. 2. The largest nerve fibers are approximately
20 .mu.m in diameter and are heavily myelinated (i.e., have a
myelin sheath, constituting a substance largely composed of fat),
whereas the smallest nerve fibers are less than 1 .mu.m in diameter
and are unmyelinated.
[0012] The diameters of group A and group B fibers include the
thickness of the myelin sheaths. Group A is further subdivided into
alpha, beta, gamma, and delta fibers in decreasing order of size.
There is some overlapping of the diameters of the A, B, and C
groups because physiological properties, especially in the form of
the action potential, are taken into consideration when defining
the groups. The smallest fibers (group C) are unmyelinated and have
the slowest conduction rate, whereas the myelinated fibers of group
B and group A exhibit rates of conduction that progressively
increase with diameter.
[0013] Nerve cells have membranes that are composed of lipids and
proteins (shown schematically in FIGS. 3A and 3B), and have unique
properties of excitability such that an adequate disturbance of the
cell's resting potential can trigger a sudden change in the
membrane conductance. Under resting conditions, the inside of the
nerve cell is approximately -90 mV relative to the outside. The
electrical signaling capabilities of neurons are based on ionic
concentration gradients between the intracellular and extracellular
compartments. The cell membrane is a complex of a bilayer of lipid
molecules with an assortment of protein molecules embedded in it
(FIG. 3A), separating these two compartments. Electrical balance is
provided by concentration gradients which are maintained by a
combination of selective permeability characteristics and active
pumping mechanism.
[0014] The lipid component of the membrane is a double sheet of
phospholipids, elongated molecules with polar groups at one end and
the fatty acid chains at the other. The ions that carry the
currents used for neuronal signaling are among these water-soluble
substances, so the lipid bilayer is also an insulator, across which
membrane potentials develop. In biophysical terms, the lipid
bilayer is not permeable to ions. In electrical terms, it functions
as a capacitor, able to store charges of opposite sign that are
attracted to each other but unable to cross the membrane. Embedded
in the lipid bilayer is a large assortment of proteins. These are
proteins that regulate the passage of ions into or out of the cell.
Certain membrane-spanning proteins allow selected ions to flow down
electrical or concentration gradients or by pumping them
across.
[0015] These membrane-spanning proteins consist of several subunits
surrounding a central aqueous pore (shown in FIG. 3B). Ions whose
size and charge "fit" the pore can diffuse through it, allowing
these proteins to serve as ion channels. Hence, unlike the lipid
bilayer, ion channels have an appreciable permeability (or
conductance) to at least some ions. In electrical terms, they
function as resistors, allowing a predicable amount of current flow
in response to a voltage across them.
[0016] A nerve cell can be excited by increasing the electrical
charge within the neuron, thus increasing the membrane potential
inside the nerve with respect to the surrounding extracellular
fluid. As shown in FIG. 4, stimuli 4 and 5 are subthreshold, and do
not induce a response. Stimulus 6 exceeds a threshold value and
induces an action potential (AP) which will be propagated. The
threshold stimulus intensity is defined as that value at which the
net inward current (which is largely determined by Sodium ions) is
just greater than the net outward current (which is largely carried
by Potassium ions), and is typically around -55 mV inside the nerve
cell relative to the outside (critical firing threshold). If
however, the threshold is not reached, the graded depolarization
will not generate an action potential and the signal will not be
propagated along the axon. This fundamental feature of the nervous
system i.e., its ability to generate and conduct electrical
impulses, can take the form of action potentials, which are defined
as a single electrical impulse passing down an axon. This action
potential (nerve impulse or spike) is an "all or nothing"
phenomenon, that is to say once the threshold stimulus intensity is
reached, an action potential will be generated.
[0017] FIG. 5A illustrates a segment of the surface of the membrane
of an excitable cell. Metabolic activity maintains ionic gradients
across the membrane, resulting in a high concentration of potassium
(K.sup.+) ions inside the cell and a high concentration of sodium
(Na.sup.+) ions in the extracellular environment. The net result of
the ionic gradient is a transmembrane potential that is largely
dependent on the K.sup.+ gradient. Typically in nerve cells, the
resting membrane potential (RMP) is slightly less than 90 mV, with
the outside being positive with respect to inside.
[0018] To stimulate an excitable cell, it is only necessary to
reduce the transmembrane potential by a critical amount. When the
membrane potential is reduced by an amount .DELTA.V, reaching the
critical or threshold potential (TP); Which is shown in FIG. 5B.
When the threshold potential (TP) is reached, a regenerative
process takes place: sodium ions enter the cell, potassium ions
exit the cell, and the transmembrane potential falls to zero
(depolarizes), reverses slightly, and then recovers or repolarizes
to the resting membrane potential (RMP).
[0019] For a stimulus to be effective in producing an excitation,
it must have an abrupt onset, be intense enough, and last long
enough. These facts can be drawn together by considering the
delivery of a suddenly rising cathodal constant-current stimulus of
duration d to the cell membrane as shown in FIG. 5B.
[0020] Cell membranes can be reasonably well represented by a
capacitance C, shunted by a resistance R as shown by a simplified
electrical model in diagram 5C, and shown in a more realistic
electrical model in FIG. 6, where neuronal process is divided into
unit lengths, which is represented in an electrical equivalent
circuit. Each unit length of the process is a circuit with its own
membrane resistance (r.sub.m), membrane capacitance (c.sub.m), and
axonal resistance (r.sub.a).
[0021] When the stimulation pulse is strong enough, an action
potential will be generated and propagated. As shown in FIG. 7, the
action potential is traveling from right to left. Immediately after
the spike of the action potential there is a refractory period when
the neuron is either unexcitable (absolute refractory period) or
only activated to sub-maximal responses by supra-threshold stimuli
(relative refractory period). The absolute refractory period occurs
at the time of maximal Sodium channel inactivation while the
relative refractory period occurs at a later time when most of the
Na.sup.+ channels have returned to their resting state by the
voltage activated K.sup.+ current. The refractory period has two
important implications for action potential generation and
conduction. First, action potentials can be conducted only in one
direction, away from the site of its generation, and secondly, they
can be generated only up to certain limiting frequencies.
[0022] A single electrical impulse passing down an axon is shown
schematically in FIG. 8. The top portion of the figure (A) shows
conduction over mylinated axon (fiber) and the bottom portion (B)
shows conduction over nonmylinated axon (fiber). These electrical
signals will travel along the nerve fibers.
[0023] The information in the nervous system is coded by frequency
of firing rather than the size of the action potential. This is
shown schematically in FIG. 9. The bottom portion of the figure
shows a train of action potentials.
[0024] In terms of electrical conduction, myelinated fibers conduct
faster, are typically larger, have very low stimulation thresholds,
and exhibit a particular strength-duration curve or respond to a
specific pulse width versus amplitude for stimulation, compared to
unmyelinated fibers. The A and B fibers can be stimulated with
relatively narrow pulse widths, from 50 to 200 microseconds
(.mu.s), for example. The A fiber conducts slightly faster than the
B fiber and has a slightly lower threshold. The C fibers are very
small, conduct electrical signals very slowly, and have high
stimulation thresholds typically requiring a wider pulse width
(300-1,000 .mu.s) and a higher amplitude for activation. Because of
their very slow conduction, C fibers would not be highly responsive
to rapid stimulation. Selective stimulation of only A and B fibers
is readily accomplished. The requirement of a larger and wider
pulse to stimulate the C fibers, however, makes selective
stimulation of only C fibers, to the exclusion of the A and B
fibers, virtually unachievable inasmuch as the large signal will
tend to activate the A and B fibers to some extent as well.
[0025] As shown in FIG. 10A, when the distal part of a nerve is
electrically stimulated, a compound action potential is recorded by
an electrode located more proximally. A compound action potential
contains several peaks or waves of activity that represent the
summated response of multiple fibers having similar conduction
velocities. The waves in a compound action potential represent
different types of nerve fibers that are classified into
corresponding functional categories as shown in the Table one
below,
1 TABLE 1 Conduction Fiber Fiber Velocity Diameter Type (m/sec)
(.mu.m) Myelination A Fibers Alpha 70-120 12-20 Yes Beta 40-70 5-12
Yes Gamma 10-50 3-6 Yes Delta 6-30 2-5 Yes B Fibers 5-15 <3 Yes
C Fibers 0.5-2.0 0.4-1.2 No
[0026] FIG. 10B further clarifies the differences in action
potential conduction velocities between the A.delta.-fibers and the
C-fibers. For many of the application of current patent
application, it is the slow conduction C-fibers that are stimulated
by the pulse generator.
[0027] The modulation of nerve in the periphery, as done by the
body, in response to different types of pain is illustrated
schematically in FIGS. 11 and 12. As shown schematically in FIG.
11, the electrical impulses in response to acute pain sensations
are transmitted to brain through peripheral nerve and the spinal
cord. The first-order peripheral neurons at the point of injury
transmit a signal along A-type nerve fibers to the dorsal horns of
the spinal cord. Here the second-order neurons take over, transfer
the signal to the other side of the spinal cord, and pass it
through the spinothalamic tracts to thalamus of the brain. As shown
in FIG. 12, duller and more persistent pain travel by
another-slower route using unmyelinated C-fibers. This route made
up from a chain of interconnected neurons, which run up the spinal
cord to connect with the brainstem, the thalamus and finally the
cerebral cortex. The autonomic nervous system also senses pain and
transmits signals to the brain using a similar route to that for
dull pain.
[0028] Vagus nerve stimulation with or without blocking, as
performed by the system and method of the current patent
application, is a means of directly affecting central function.
FIG. 13 shows cranial nerves have both afferent pathway 19 (inward
conducting nerve fibers which convey impulses toward the brain) and
efferent pathway 21 (outward conducting nerve fibers which convey
impulses to an effector). Vagus nerve is composed of 80% afferent
sensory fibers carrying information to the brain from the head,
neck, thorax, and abdomen. The sensory afferent cell bodies of the
vagus reside in the nodose ganglion and relay information to the
nucleus tractus solitarius (NTS).
[0029] The vagus nerve is composed of somatic and visceral
afferents and efferents. Usually, nerve stimulation activates
signals in both directions (bi-directionally). It is possible
however, through the use of special electrodes and waveforms, to
selectively stimulate a nerve in one direction only
(unidirectionally). The vast majority of vagus nerve fibers are C
fibers, and a majority are visceral afferents having cell bodies
lying in masses or ganglia in the skull.
[0030] In considering the anatomy, the vagus nerve spans from the
brain stem all the way to the splenic flexure of the colon. Not
only is the vagus the parasympathetic nerve to the thoracic and
abdominal viscera, it also the largest visceral sensory (afferent)
nerve. Sensory fibers outnumber parasympathetic fibers four to one.
In the medulla, the vagal fibers are connected to the nucleus of
the tractus solitarius (viceral sensory), and three other nuclei.
The central projections terminate largely in the nucleus of the
solitary tract, which sends fibers to various regions of the brain
(e.g., the thalamus, hypothalamus and amygdala).
[0031] As shown in FIG. 14, the vagus nerve emerges from the
medulla of the brain stem dorsal to the olive as eight to ten
rootlets. These rootlets converge into a flat cord that exits the
skull through the jugular foramen. Exiting the Jugular foramen, the
vagus nerve enlarges into a second swelling, the inferior
ganglion.
[0032] In the neck, the vagus lies in a groove between the internal
jugular vein and the internal carotid artery. It descends
vertically within the carotid sheath, giving off branches to the
pharynx, larynx, and constrictor muscles. From the root of the neck
downward, the vagus nerve takes a different path on each side of
the body to reach the cardiac, pulmonary, and esophageal plexus
(consisting of both sympathetic and parasympathetic axons). From
the esophageal plexus, right and left gastric nerves arise to
supply the abdominal viscera as far caudal as the splenic
flexure.
[0033] In the body, the vagus nerve regulates viscera, swallowing,
speech, and taste. It has sensory, motor, and parasympathetic
components. Table two below outlines the innervation and function
of these components.
2TABLE 2 Vagus Nerve Components Component fibers Structures
innervated Functions SENSORY Pharynx. larynx, General sensation
esophagus, external ear Aortic bodies, aortic arch Chemo- and
baroreception Thoracic and abdominal viscera MOTOR Soft palate,
pharynx, Speech, swallowing larynx, upper esophagus PARA- Thoracic
and abdominal Control of cardiovascular SYMPATHETIC viscera system,
respiratory and gastrointestinal tracts
[0034] On the Afferent side, visceral sensation is carried in the
visceral sensory component of the vagus nerve. As shown in FIGS.
15A and 15B, visceral sensory fibers from plexus around the
abdominal viscera converge and join with the right and left gastric
nerves of the vagus. These nerves pass upward through the
esophageal hiatus (opening) of the diaphragm to merge with the
plexus of nerves around the esophagus. Sensory fibers from plexus
around the heart and lungs also converge with the esophageal plexus
and continue up through the thorax in the right and left vagus
nerves. As shown in FIG. 15B, the central process of the nerve cell
bodies in the inferior vagal ganglion enter the medulla and descend
in the tractus solitarius to enter the caudal part of the nucleus
of the tractus solitarius. From the nucleus, bilateral connections
important in the reflex control of cardiovascular, respiratory, and
gastrointestinal functions are made with several areas of the
reticular formation and the hypothalamus.
[0035] The afferent fibers project primarily to the nucleus of the
solitary tract (shown schematically in FIGS. 16 and 17) which
extends throughout the length of the medulla oblongata. A small
number of fibers pass directly to the spinal trigeminal nucleus and
the reticular formation. As shown in FIG. 16, the nucleus of the
solitary tract has widespread projections to cerebral cortex, basal
forebrain, thalamus, hypothalamus, amygdala, hippocampus, dorsal
raphe, and cerebellum. Because of the widespread projections of the
Nucleus of the Solitary Trap, neuromodulation of the vagal afferent
nerve fibers produce alleviation of symptoms of the neurological
and neuropsychiatric disorders covered in this patent application,
such as epilepsy, depression, involuntary movement disorders
including Parkinson's disease, anxiety disorders, neurogenic pain,
psycogenic pain, obsessive compulsive disorders, migraines,
obesity, dementia including Alzheimer's disease, and the like.
PRIOR ART
[0036] U.S. Pat. Nos. 4,702,254, 4,867,164 and 5,025,807 (Zabara)
generally disclose animal research and experimentation related to
epilepsy and the like. Applicant's method of neuromodulation is
significantly different than that disclosed in Zabara '254, '164`
and '807 patents.
[0037] U.S. Pat. No. 5,299,569 (Wernicke et al.) is directed to the
use of implantable pulse generator technology for treating and
controlling neuropsychiatric disorders including schizophrenia,
depression, and borderline personality disorder.
[0038] U.S. Pat. No. 6,205,359 B1 (Boveja) and U.S. Pat. No.
6,356,788 B2 (Boveja) are directed to adjunct therapy for
neurological and neuropsychiatric disorders using an implanted
lead-receiver and an external stimulator.
[0039] U.S. Pat. No. 5,807,397 (Barreras) is directed to an
implantable stimulator with replenishable, high value capacitive
power source.
[0040] U.S. Pat. No. 5,193,539 (Schulman, et al) is generally
directed to an addressable, implantable microstimulator that is of
size and shape which is capable of being implanted by expulsion
through a hypodermic needle. In the Schulman patent, up to 256
microstimulators may be implanted within a muscle and they can be
used to stimulate in any order as each one is addressable, thereby
providing therapy for muscle paralysis.
[0041] U.S. Pat. No. 6,553,263B1 (Meadows et al.) is generally
directed to an implantable pulse generator system for spinal cord
stimulation, which includes a rechargeable battery. In the Meadows
'263 patent there is no disclosure or suggestion for combing a
stimulus-receiver module to an implantable pulse generator (IPG)
for use with an external stimulator, for providing modulating
pulses to vagal nerve(s), as in the applicant's disclosure.
[0042] U.S. Pat. No. 6,505,077 B1 (Kast et al.) is directed to
electrical connection for external recharging coil. In the Kast
'077 disclosure, a magnetic shield is required between the
externalized coil and the pulse generator case. In one embodiment
of the applicant's disclosure, the externalized coil is wrapped
around the pulse generator case, without requiring a magnetic
shield.
[0043] U.S. Pat. No. 6,622,041 B2 (Terry, Jr. et al.) is directed
to treatment of congestive heart failure and autonomic
cardiovascular drive disorders using implantable
neurostimulator.
SUMMARY OF THE INVENTION
[0044] Method and system of the current invention provides vagal
nerve(s) neuromodulation to provide therapy for at least one of
epilepsy, partial complex epilepsy, generalized epilepsy, and
involuntary movement disorders such as in Parkinson's disease,
depression, bipolar depression, schizophrenia, anxiety disorders,
neurogenic/psycogenic pain, compulsive eating disorders, obesity,
obsessive compulsive disorders, dementia including Alzheimer's
disease, sleep disorders, learning difficulties, migraines and
cardiac disorders such as atrial fibrillation and congestive heart
failure(CHF). The method and system comprises both implantable and
external components.
[0045] In one aspect of the invention, the method and system for
modulating vagal nerve(s) comprises implantable pulse generator
with rechargeable battery, and battery charging circuitry. The
charging of the implantable battery being performed by an external
charger via an inductive link.
[0046] In another aspect of the invention, one embodiment of the
implanted pulse generator comprises, a stimulus-receiver module
that can be used in conjunction with an external stimulator, and an
implanted pulse generator module with rechargeable battery.
[0047] In another aspect of the invention the implantable pulse
generator with rechargeable battery is connected to an implanted
lead with at least two electrodes for providing stimulation and/or
blocking pulses to vagal nerve(s).
[0048] In another aspect of the invention, the recharge coil is
externalized from the titanium case and is wrapped around the
titanium case in an epoxy header, thereby eliminating the need for
a magnetic shield.
[0049] In another aspect of the invention, the recharge coil is
also used for bi-directional telemetry.
[0050] In another aspect of the invention, the rechargeable battery
comprises at least one of lithium-ion, lithium-ion polymer
battery.
[0051] In another aspect of the invention, the lead comprises at
least two electrodes which are made of one from a group consisting
of platinum, platinum/iridium alloy, platinum/iridium alloy coated
with titanium nitride, and carbon.
[0052] In another aspect of the invention, the selective
stimulation and/or blocking to vagus nerve(s) may be anywhere along
the length of the nerve, for example such stimulation may be at the
cervical level or at a level near the diaphragm.
[0053] In another aspect of the invention, the stimulation and/or
blocking may be unilateral or bilateral.
[0054] In another aspect of the invention, the implanted lead body
may be made of a material selected from the group consisting of
polyurethane, silicone, and silicone with
polytetrafluoroethylene.
[0055] In yet another aspect of the invention, the implanted lead
comprises at least two electrodes selected from the group
consisting of spiral electrodes, cuff electrodes, steroid eluting
electrodes, wrap-around electrodes, and hydrogel electrodes.
[0056] Various other features, objects and advantages of the
invention will be made apparent from the following description
taken together with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0057] For the purpose of illustrating the invention, there are
shown in accompanying drawing forms which are presently preferred,
it being understood that the invention is not intended to be
limited to the precise arrangement and instrumentalities shown.
[0058] FIG. 1 is a diagram of the structure of a nerve.
[0059] FIG. 2 is a diagram showing different types of nerve
fibers.
[0060] FIGS. 3A and 3B are schematic illustrations of the
biochemical makeup of nerve cell membrane.
[0061] FIG. 4 is a figure demonstrating subthreshold and
suprathreshold stimuli.
[0062] FIGS. 5A, 5B, 5C are schematic illustrations of the
electrical properties of nerve cell membrane.
[0063] FIG. 6 is a schematic illustration of electrical circuit
model of nerve cell membrane.
[0064] FIG. 7 is an illustration of propagation of action potential
in nerve cell membrane.
[0065] FIG. 8 is an illustration showing propagation of action
potential along a myelinated axon and non-myelinated axon.
[0066] FIG. 9 is an illustration showing a train of action
potentials.
[0067] FIG. 10A is a diagram showing recordings of compound action
potentials.
[0068] FIG. 10B is a schematic diagram showing conduction of first
pain and second pain.
[0069] FIG. 11 is a schematic illustration showing mild stimulation
being carried over the large diameter A-fibers.
[0070] FIG. 12 is a schematic illustration showing painful
stimulation being carried over small diameter C-fibers
[0071] FIG. 13 is a schematic diagram of brain showing afferent and
efferent pathways.
[0072] FIG. 14 is a schematic diagram showing the vagus nerve at
the level of the nucleus of the solitary tract.
[0073] FIG. 15A is a schematic diagram showing the thoracic and
visceral innervations of the vagal nerves.
[0074] FIG. 15B is a schematic diagram of the medullary section of
the brain.
[0075] FIG. 16 is a simplified block diagram illustrating the
connections of solitary tract nucleus to other centers of the
brain.
[0076] FIG. 17 is a schematic diagram of brain showing the
relationship of the solitary tract nucleus to other centers of the
brain.
[0077] FIG. 18 is a simplified general block diagram of an
implantable pulse generator.
[0078] FIG. 19A shows the pulse train transmitted to the vagus
nerve(s).
[0079] FIG. 19B shows the ramp-up and ramp-down characteristic of
the pulse train.
[0080] FIG. 20A shows energy density of different types of
batteries.
[0081] FIG. 20B shows discharge curves for different types of
batteries.
[0082] FIG. 21 shows a block diagram of an implantable stimulator
which can be used as a stimulus-receiver or an implanted pulse
generator with rechargeable battery.
[0083] FIG. 22 is a block diagram highlighting battery charging
circuit of the implantable stimulator of FIG. 21.
[0084] FIG. 23 is a schematic diagram highlighting
stimulus-receiver portion of implanted stimulator of one
embodiment.
[0085] FIG. 24 depicts externalizing recharge and telemetry coil
from the titanium case.
[0086] FIG. 25A depicts coil around the titanium case with two
feedthroughs for a bipolar configuration.
[0087] FIG. 25B depicts coil around the titanium case with one
feedthrough for a unipolar configuration.
[0088] FIG. 25C depicts two feedthroughs for the external coil
which are common with the feedthroughs for the lead terminal.
[0089] FIG. 25D depicts one feedthrough for the external coil which
is common to the feedthrough for the lead terminal.
[0090] FIGS. 26A and 26B depict recharge coil on the titanium case
with a magnetic shield in-between.
[0091] FIG. 27 shows in block diagram form an implantable
rechargable pulse generator.
[0092] FIG. 28 depicts in block diagram form the implanted and
external components of an implanted rechargable system.
[0093] FIG. 29 depicts the alignment function of rechargable
implantable pulse generator.
[0094] FIG. 30 is a block diagram of the external recharger.
[0095] FIG. 31 depicts an implantable system with tripolar lead for
selective unidirectional blocking of vagus nerve(s) stimulation
FIG. 32 depicts selective efferent blocking in the large diameter A
and B fibers.
[0096] FIG. 33 depicts unilateral stimulation of vagus nerve at
near the diaphram level.
[0097] FIG. 34 depicts bilateral stimulation of vagus nerves with
one stimulator.
[0098] FIG. 35 is a schematic diagram of the implantable lead with
two electrodes.
[0099] FIG. 36 is a schematic diagram of the implantable lead with
three electrodes.
DETAILED DESCRIPTION OF THE INVENTION
[0100] In the method and system of this invention, electrical
pulses for stimulation and/or blocking are applied to vagus
nerve(s) for afferent neuromodulation. An implantable lead is
surgically implanted in the patient. The vagus nerve(s) is/are
surgically exposed and isolated, the electrodes on the distal end
of the lead are wrapped around the vagus nerve(s), and the proximal
end of the lead is tunneled subcutaneously. A pulse generator means
is connected to the proximal end of the lead, and surgically
implanted in a subcutaneous or submuscular pocket.
[0101] Shown in conjunction with FIG. 18, is an overall schematic
of an implantable pulse generator system to deliver electrical
pulses for modulating the vagus nerve(s) and providing therapy. The
implantable pulse generator unit 391 is a microprocessor based
device, where the entire circuitry is encased in a hermetically
sealed titanium can. As shown in the overall block diagram, the
logic & control unit 398 provides the proper timing for the
output circuitry 385 to generate electrical pulses that are
delivered to a pair of electrodes via a lead 40. Timing is provided
by oscillator 393. The pair of electrodes to which the stimulation
energy is delivered is switchable. Programming of the implantable
pulse generator (IPG) is done via an external programmer 85. Once
programmed via an external programmer 85, the implanted pulse
generator 391 provides appropriate electrical stimulation pulses to
the vagal nerve(s) 54 via the stimulating electrode pair 61,62.
[0102] Each parameter may be individually programmed and stored in
memory. The range of programmable electrical stimulation parameters
are shown in table 3 below.
3TABLE 3 Programmable electrical parameter range PARAMER RANGE
Pulse Amplitude 0.1 Volt-10 Volts Pulse width 20 .mu.S-5 mSec.
Frequency 3 Hz-300 Hz On-time 5 Secs-24 hours Off-time 5 Secs-24
hours Ramp ON/OFF
[0103] The pulses delivered to the nerve tissue for stimulation
therapy are shown graphically in FIG. 19A. As shown in FIG. 19B,
for patient comfort when the electrical stimulation is turned on,
the electrical stimulation may be ramped up and ramped down,
instead of abrupt delivery of electrical pulses.
[0104] Because of the rapidity of the pulses required for
modulating nerve tissue 54 (unlike cardiac pacing), there is a real
need for power sources that will provide an acceptable service life
under conditions of continuous delivery of high frequency pulses.
FIG. 20A shows a graph of the energy density of several commonly
used battery technologies. Lithium batteries have by far the
highest energy density of commonly available batteries. Also, a
lithium battery maintains a nearly constant voltage during
discharge. This is shown in conjunction with FIG. 20B, which is
normalized to the performance of the lithium battery. Lithium-ion
batteries also have a long cycle life, and no memory effect.
However, Lithium-ion batteries are not as tolerant to overcharging
and overdischarging. One of the most recent development in
rechargable battery technology is the Lithium-ion polymer battery.
Recently the major battery manufacturers (Sony, Panasonic, Sanyo)
have announced plans for Lithium-ion polymer battery
production.
[0105] For the practice of the current invention, two embodiments
of implantable pulse generators may be used. Both embodiments
comprise re-chargeable power sources, such as Lithium-ion polymer
battery.
[0106] In one embodiment, the implanted device comprises a
stimulus-receiver module and a pulse generator module.
Advantageously, this embodiment provides an ideal power source,
since the power source can be an external stimulator coupled with
an implanted stimulus-receiver, or the power source can be from the
implanted rechargeable battery. Shown in conjunction with FIG. 21
is a simplified overall block diagram of this embodiment. A coil
48C which is external to the titanium case may be used both as a
secondary of a stimulus-receiver, or may also be used as the
forward and back telemetry coil. The coil 48C may be externalized
at the header portion 79C of the implanted device, and may be
wrapped around the titanium can, eliminating the need for a
magnetic shield. In this case, the coil is encased in the same
material as the header 79C. Alternatively, the coil may be
positioned on the titanium case, with a magnetic shield.
[0107] In this embodiment, as disclosed in FIG. 21, the IPG
circuitry within the titanium case is used for all stimulation
pulses whether the energy source is the internal battery 740 or an
external power source. The external device serves as a source of
energy, and as a programmer that sends telemetry to the IPG. An
external stimulator and recharger may also be combined within the
same enclosure. For programming, the energy is sent as high
frequency sine waves with superimposed telemetry wave driving the
external coil 46C. The telemetry is passed through coupling
capacitor 727 to the IPG's telemetry circuit 742. For pulse
delivery using external power source, the stimulus-receiver portion
will receive the energy coupled to the implanted coil 48C and,
using the power conditioning circuit 726, rectify it to produce DC,
filter and regulate the DC, and couple it to the IPG's voltage
regulator 738 section so that the IPG can run from the externally
supplied energy rather than the implanted battery 740.
[0108] The system of this embodiment provides a power sense circuit
728 that senses the presence of external power communicated with
the power control 730, when adequate and stable power is available
from an external source. The power control circuit controls a
switch 736 that selects either implanted battery power 740 or
conditioned external power from 726. The logic and control section
732 and memory 744 includes the IPG's microcontroller,
pre-programmed instructions, and stored changeable parameters.
Using input for the telemetry circuit 742 and power control 730,
this section controls the output circuit 734 that generates the
output pulses.
[0109] Shown in conjunction with FIG. 22, this embodiment of the
invention is practiced with a rechargeable battery. This circuit is
energized when external power is available. It senses the charge
state of the battery and provides appropriate charge current to
safely recharge the battery without overcharging. Recharging
circuitry is described later.
[0110] The stimulus-receiver portion of the circuitry is shown in
conjunction with FIG. 23. Capacitor C1 (729) makes the combination
of C1 and L1 sensitive to the resonant frequency and less sensitive
to other frequencies, and energy from an external (primary) coil
46C is inductively transferred to the implanted unit via the
secondary coil 48C. The AC signal is rectified DC via diode 731,
and filtered via capacitor 733. A regulator 735 set the output
voltage and limits it to a value just above the maximum IPG cell
voltage. The output capacitor C4 (737), typically a tantalum
capacitor with a value of 100 micro-Farads or greater, stores
charge so that the circuit can supply the IPG with high values of
current for a short time duration with minimal voltage change
during a pulse while the current draw from the external source
remains relatively constant. Also shown in conjunction with FIG.
23, a capacitor C3 (727) couples signals for forward and back
telemetry.
[0111] In another embodiment, existing nerve stimulators and
cardiac pacemakers can be modified to incorporate rechargeable
batteries. Among the nerve stimulators that can be adopted with
rechargeable batteries can for example be the vagus nerve
stimulator manufactured by Cyberonics Inc. (Houston, Tex.). U.S.
Pat. No. 4,702,254 (Zabara), U.S. Pat. No. 5,023,807 (Zabara), and
U.S. Pat. No. 4,867,164 (Zabara) on Neurocybernetic Prostheses,
which can be practiced with rechargeable power source as disclosed
in the next section. These patents are incorporated herein by
reference.
[0112] As shown in conjunction with FIG. 24, in both embodiments,
the coil is externalized from the titanium case 57. The RF pulses
transmitted via coil 46 and received via subcutaneous coil 48A are
rectified via a diode bridge. These DC pulses are processed and the
resulting current applied to recharge the battery 694/740 in the
implanted pulse generator. In one embodiment the coil 48C may be
externalized at the header portion 79 of the implanted device, and
may be wrapped around the titanium can, as shown in FIGS. 25A and
25B. Shown in FIG. 25A is a bipolar configuration which requires
two feedthroughs 76,77. Advantageously, as shown in FIG. 25B
unipolar configuration may also be used which requires only one
feedthrough 75. The other end is electronically connected to the
case. In both cases, the coil is encased in the same material as
the header 79. Advantageously, as shown in conjunction with FIGS.
25C and 25D, the feedthrough for the coil can be combined with the
feedthrough for the lead terminal. This can be applied both for
bipolar and unipolar configurations.
[0113] In one embodiment, the coil may also be positioned on the
titanium case as shown in conjunction with FIGS. 26A and 26B. FIG.
26A shows a diagram of the finished implantable stimulator 391 R of
one embodiment. FIG. 26B shows the pulse generator with some of the
components used in assembly in an exploded view. These components
include a coil cover 7, the secondary coil 48 and associated
components, a magnetic shield 9, and a coil assembly carrier 11.
The coil assembly carrier 11 has at least one positioning detail 13
located between the coil assembly and the feed through for
positioning the electrical connection. The positioning detail 13
secures the electrical connection.
[0114] A schematic diagram of the implanted pulse generator (IPG
391 R), with re-chargeable battery 694, is shown in conjunction
with FIG. 27. The IPG 391 R includes logic and control circuitry
673 connected to memory circuitry 691. The operating program and
stimulation parameters are typically stored within the memory 691
via forward telemetry. Stimulation pulses are provided to the nerve
tissue 54 via output circuitry 677 controlled by the
microcontroller.
[0115] The operating power for the IPG 391 R is derived from a
rechargeable power source 694. The rechargeable power source 694
comprises a rechargeable lithium-ion or lithium-ion polymer
battery. Recharging occurs inductively from an external charger to
an implanted coil 48B underneath the skin 60. The rechargeable
battery 694 may be recharged repeatedly as needed. Additionally,
the IPG 391R is able to monitor and telemeter the status of its
rechargable battery 691 each time a communication link is
established with the external programmer 85.
[0116] Much of the circuitry included within the IPG 391 R may be
realized on a single application specific integrated circuit
(ASIC). This allows the overall size of the IPG 391 R to be quite
small, and readily housed within a suitable hermetically-sealed
case. The IPG case is preferably made from a titanium and is shaped
in a rounded case.
[0117] Shown in conjunction with FIG. 28 are the recharging
elements of the invention. The re-charging system uses a portable
external charger to couple energy into the power source of the IPG
391 R. The DC-to-AC conversion circuitry 696 of the re-charger
receives energy from a battery 672 in the re-charger. A charger
base station 680 and conventional AC power line may also be used.
The AC signals amplified via power amplifier 674 are inductively
coupled between an external coil 46B and an implanted coil 48B
located subcutaneously with the implanted pulse generator (IPG) 391
R. The AC signal received via implanted coil 48B is rectified 686
to a DC signal which is used for recharging the rechargeable
battery 694 of the IPG, through a charge controller IC 682.
Additional circuitry within the IPG 391 R includes, battery
protection IC 688 which controls a FET switch 690 to make sure that
the rechargeable battery 694 is charged at the proper rate, and is
not overcharged. The battery protection IC 688 can be an
off-the-shelf IC available from Motorola (part no. MC 33349N-3R1).
This IC monitors the voltage and current of the implanted
rechargeable battery 694 to ensure safe operation. If the battery
voltage rises above a safe maximum voltage, the battery protection
IC 688 opens charge enabling FET switches 690, and prevents further
charging. A fuse 692 acts as an additional safeguard, and
disconnects the battery 694 if the battery charging current exceeds
a safe level. As also shown in FIG. 28, charge completion detection
is achieved by a back-telemetry transmitter 684, which modulates
the secondary load by changing the full-wave rectifier into a
half-wave rectifier/voltage clamp. This modulation is in turn,
sensed by the charger as a change in the coil voltage due to the
change in the reflected impedance. When detected through a back
telemetry receiver 676, either an audible alarm is generated or a
LED is turned on.
[0118] A simplified block diagram of charge completion and
misalignment detection circuitry is shown in conjunction with FIG.
29. As shown, a switch regulator 686 operates as either a full-wave
rectifier circuit or a half-wave rectifier circuit as controlled by
a control signal (CS) generated by charging and protection
circuitry 698. The energy induced in implanted coil 48B (from
external coil 46B) passes through the switch rectifier 686 and
charging and protection circuitry 698 to the implanted rechargeable
battery 694. As the implanted battery 694 continues to be charged,
the charging and protection circuitry 698 continuously monitors the
charge current and battery voltage. When the charge current and
battery voltage reach a predetermined level, the charging and
protection circuitry 698 triggers a control signal. This control
signal causes the switch rectifier 686 to switch to half-wave
rectifier operation. When this change happens, the voltage sensed
by voltage detector 702 causes the alignment indicator 706 to be
activated. This indicator 706 may be an audible sound or a flashing
LED type of indicator.
[0119] The indicator 706 may similarly be used as a misalignment
indicator. In normal operation, when coils 46B (external) and 48B
(implanted) are properly aligned, the voltage V.sub.S sensed by
voltage detector 704 is at a minimum level because maximum energy
transfer is taking place. If and when the coils 46B and 48B become
misaligned, then less than a maximum energy transfer occurs, and
the voltage V.sub.S sensed by detection circuit 704 increases
significantly. If the voltage V.sub.S reaches a predetermined
level, alignment indicator 706 is activated via an audible speaker
and/or LEDs for visual feedback. After adjustment, when an optimum
energy transfer condition is established, causing V.sub.S to
decrease below the predetermined threshold level, the alignment
indicator 706 is turned off.
[0120] The elements of the external recharger are shown as a block
diagram in conjunction with FIG. 30. In this disclosure, the words
charger and recharger are used interchangeably. The charger base
station 680 receives its energy from a standard power outlet 714,
which is then converted to 5 volts DC by a AC-to-DC transformer
712. When the re-charger is placed in a charger base station 680,
the re-chargeable battery 672 of the re-charger is fully recharged
in a few hours and is able to recharge the battery 694 of the IPG
391 R. If the battery 672 of the external re-charger falls below a
prescribed limit of 2.5 volt DC, the battery 672 is trickle charged
until the voltage is above the prescribed limit, and then at that
point resumes a normal charging process.
[0121] As also shown in FIG. 30, a battery protection circuit 718
monitors the voltage condition, and disconnects the battery 672
through one of the FET switches 716, 720 if a fault occurs until a
normal condition returns. A fuse 724 will disconnect the battery
672 should the charging or discharging current exceed a prescribed
amount.
[0122] Since another key concept of this invention is to deliver
afferent stimulation, in one aspect efferent stimulation of
selected types of fibers may be substantially blocked, utilizing
the "greenwave" effect. In such a case, as shown in conjunction
with FIGS. 31 and 32, a tripolar lead is utilized. As depicted on
the top right portion of FIG. 31, there is a depolarization peak 10
on the vagus nerve bundle corresponding to electrode 61 (cathode)
and the two hyper-polarization peaks 8, 12 corresponding to
electrodes 62, 63 (anodes). With the microcontroller controlling
the tripolar device, the size and timing of the hyper-polarizations
8, 12 can be controlled. As was shown previously in FIGS. 2 and
10A, since the speed of conduction is different between the larger
diameter A and B fibers and the smaller diameter c-fibers, by
appropriately timing the pulses, collision blocks can be created
for conduction via the large diameter A and B fibers in the
efferent direction. This is depicted schematically in FIG. 32. A
number of blocking techniques are known in the art, such as
collision blocking, high frequency blocking, and anodal blocking.
Any of these well known blocking techniques may be used with the
practice of this invention, and are considered within the scope of
this invention.
[0123] In one aspect of the invention, the pulsed electrical
stimulation and/or blocking to the vagus nerve(s) may be provided
anywhere along the length of the vagus nerve(s). As was shown
earlier in conjunction with FIG. 31, the pulsed electrical
stimulation may be at the cervical level. Alternatively, shown in
conjunction with FIG. 33, the stimulation to the vagus nerve(s) may
be around the diaphramatic level. Either above the diaphragm or
below the diaphragm. Further, the stimulation may be unilateral or
bilateral, i.e. stimulation is to one or both vagus nerves. FIG. 34
depicts bilateral vagal nerve stimulation at around the level of
the diaphragm. Any combination of vagal nerve(s) stimulation,
either unilateral or bilateral, anywhere along the length of the
vagal nerve(s) is considered within the scope of this
invention.
[0124] Referring now to FIG. 35, the implanted lead component of
the system is similar to cardiac pacemaker leads, except for distal
portion (or electrode end) of the lead. This figure shows a pair of
electrodes 61,62 that are used for providing electrical pulses for
stimulation. Alternatively, FIG. 36 depicts a lead with tripolar
electrodes 62,61,63 for stimulation and/or blocking. The lead
terminal preferably is linear bipolar, even though it can be
bifurcated, and plug(s) into the cavity of the pulse generator
means. The lead body 59 insulation may be constructed of medical
grade silicone, silicone reinforced with polytetrafluoro-ethylene
(PTFE), or polyurethane. The electrodes 61,62 for stimulating the
vagus nerve 54 may either wrap around the nerve once or may be
spiral shaped. These stimulating electrodes may be made of pure
platinum, platinum/Iridium alloy or platinum/iridium coated with
titanium nitride. The conductor connecting the terminal to the
electrodes 61,62 is made of an alloy of nickel-cobalt. The
implanted lead design variables are also summarized in table four
below.
4TABLE 4 Lead design variables Conductor Proximal (connecting
Distal End Lead body- proximal End Lead Insulation and distal
Electrode - Electrode - Terminal Materials Lead-Coating ends)
Material Type Linear Polyurethane Antimicrobial Alloy of Pure
Spiral bipolar coating Nickel- Platinum electrode Cobalt Bifurcated
Silicone Anti- Platinum- Wrap-around Inflammatory Iridium electrode
coating (Pt/Ir) Alloy Silicone with Lubricious Pt/Ir coated Steroid
Polytetrafluoroethylene coating with Titanium eluting (PTFE)
Nitride Carbon Hydrogel electrodes Cuff electrodes
[0125] Once the lead is fabricated, coating such as anti-microbial,
anti-inflammatory, or lubricious coating may be applied to the body
of the lead.
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