U.S. patent application number 14/722345 was filed with the patent office on 2015-09-24 for electrode configuration for an implantable electroacupuncture device.
The applicant listed for this patent is Valencia Technologies Corporation. Invention is credited to David K. L. Peterson, Chuladatta H. Thenuwara.
Application Number | 20150265498 14/722345 |
Document ID | / |
Family ID | 51223762 |
Filed Date | 2015-09-24 |
United States Patent
Application |
20150265498 |
Kind Code |
A1 |
Peterson; David K. L. ; et
al. |
September 24, 2015 |
Electrode Configuration for an Implantable Electroacupuncture
Device
Abstract
An implantable electroacupuncture device (IEAD) treats a disease
or medical condition of a patient through application of
stimulation pulses applied at a specified acupoint or other target
tissue location at a very low duty cycle. In a preferred
implementation, the IEAD is an implantable, coin-sized,
self-contained, leadless device having at least two electrodes
attached to an outside surface of its housing, with at least one
electrode on the top or bottom surface of the housing functioning
as a cathode, and at least one electrode on the perimeter edge of
the housing functioning as an anode. The electrodes may be
segmented to include an array of smaller cathodic or anodic
electrodes, each of which may be selectively turned ON or OFF so as
to provide a convenient mechanism for adjusting the density of the
stimulus current flowing through the cathodic electrode surface
area.
Inventors: |
Peterson; David K. L.;
(Valencia, CA) ; Thenuwara; Chuladatta H.;
(Valencia, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Valencia Technologies Corporation |
Valencia |
CA |
US |
|
|
Family ID: |
51223762 |
Appl. No.: |
14/722345 |
Filed: |
May 27, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13776155 |
Feb 25, 2013 |
9066845 |
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14722345 |
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13598582 |
Aug 29, 2012 |
8965511 |
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13776155 |
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61606995 |
Mar 6, 2012 |
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61676275 |
Jul 26, 2012 |
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61575869 |
Aug 30, 2011 |
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Current U.S.
Class: |
607/72 ;
607/116 |
Current CPC
Class: |
A61N 1/36175 20130101;
A61N 1/36117 20130101; A61N 1/3756 20130101; A61N 1/37205 20130101;
A61H 2201/5038 20130101; A61N 1/0504 20130101; A61H 2201/5035
20130101; A61H 2201/5005 20130101; A61H 2201/5097 20130101; A61N
1/36125 20130101; A61N 1/3616 20130101; A61N 1/3782 20130101; A61N
1/3758 20130101; A61H 39/002 20130101; A61N 1/04 20130101 |
International
Class: |
A61H 39/00 20060101
A61H039/00; A61N 1/375 20060101 A61N001/375; A61N 1/05 20060101
A61N001/05 |
Claims
1. An implantable electroacupuncture (EA) device adapted to be
implanted at a specified acupoint of a patient, the
electroacupuncture device comprising: a disc-shaped housing having
a top surface, a bottom surface, and a perimeter edge connecting
the top surface to the bottom surface; at least one cathodic
electrode and at least one anodic electrode formed to reside on, or
comprise an integral part of, the surfaces of the housing, wherein
the at least one cathodic electrode is on the top or bottom surface
of the housing, and the at least one anodic electrode is on the
perimeter edge surface of the housing; stimulation circuitry
residing inside the housing and electrically coupled to the at
least one cathodic electrode and the at least one anodic electrode,
wherein the stimulation circuitry generates stimulation pulses of
electrical current that are delivered to body tissue surrounding
the housing through the at least one cathodic electrode and the at
least one anodic electrode in accordance with a prescribed
stimulation regimen; wherein the at least one cathodic electrode is
configured from a prescribed electrode material having a surface
area sufficiently large to allow a desired current density to flow
through it without causing electrode corrosion, and further wherein
the at least one cathodic electrode is positioned sufficiently far
from the at least one anodic electrode so as to prevent current
shunting to occur between the at least one cathodic electrode and
the at least one anodic electrode before the stimulation pulses of
electrical current have penetrated into the body tissue a specified
distance.
2. The EA device of claim 1, wherein the cathodic electrode
comprises a first cathodic electrode located on the top surface of
the housing and a second cathodic electrode located on the bottom
surface of the housing, and wherein the stimulation circuitry
residing inside of the housing includes switching circuitry that
selectively activates (i) only the first cathodic electrode, or
(ii) only the second cathodic electrode, or (iii) both the first
and second cathodic electrodes when the stimulation pulses are
delivered to the body tissue in accordance with the prescribed
stimulation regimen.
3. The EA device of claim 2, wherein the first and second cathodic
electrodes each comprise multiple small cathodic electrodes
distributed over the top and bottom surface areas of the housing in
accordance with a prescribed pattern.
4. The EA device of claim 3 wherein the at least one anodic
electrode comprises multiple small anodic electrodes distributed
around the perimeter edge of the housing.
5. The EA device of claim 3 wherein the stimulation circuitry
includes additional cathodic switching circuitry that selectively
energizes only a desired grouping of the first and second cathodic
electrodes, wherein the location of the body tissue receiving the
stimulation pulses may be selected by controlling which groups of
electrodes are energized and which are not energized, wherein an
energized electrode comprises an electrode that is turned ON by the
switching circuitry so that an electrical current may flow through
the electrode, and a non-energized electrode comprises an electrode
that is turned OFF by the switching circuitry so as to prevent
electrical current from flowing through the electrode.
6. The EA device of claim 1 wherein the at least one cathodic
electrode comprises a single cathodic electrode located in the
center of a bottom surface of the housing, the bottom surface
comprising that surface of the housing adapted to face towards a
target tissue location below the specified acupoint on the skin
surface of the patient.
7. The EA device of claim 6 wherein the stimulation circuitry
generates monophasic stimulation pulses having a magnitude of
between 2 to 25 ma, a pulse width of between 100 to 600 msec, and a
frequency of between 1 and 5 Hz.
8. The EA device of claim 7 wherein the housing has a diameter of
no greater than 25 mm, a thickness no greater than 3 mm, and is
adapted to be implanted at acupoint P6 at a tissue depth of between
3-6 mm.
9. The EA device of claim 8 wherein the stimulation regimen
provides a stimulation session during which stimulation pulses are
continuously generated, wherein the stimulation session has a
duration of between 10 and 60 minutes, and further wherein, after
an initialization period of no longer than two weeks, the
stimulation session is applied to the patient no more than twice a
week and no less than once every other week.
10. An implantable electroacupuncture (EA) device adapted to be
implanted at a specified acupoint of a patient, the
electroacupuncture device including: a leadless, disc-shaped,
hermetically-sealed housing having a top surface, a bottom surface,
and a perimeter edge connecting the top surface to the bottom
surface; at least one cathodic electrode and at least one anodic
electrode formed to reside on, or comprise an integral part of, the
surfaces of the housing; stimulation circuitry residing inside the
housing and electrically coupled to the at least one cathodic
electrode and the at least one anodic electrode, wherein the
stimulation circuitry generates stimulation pulses of electrical
current that are delivered to body tissue surrounding the housing
through the at least one cathodic electrode and the at least one
anodic electrode in accordance with a prescribed stimulation
regimen, wherein the stimulation regimen defines the duration and
rate at which a stimulation session is applied to the body tissue,
said stimulation regimen requiring that the stimulation session
have a duration of T3 minutes, wherein T3 is at least 10 minutes,
and a rate of occurrence of once every T4 minutes, wherein the
ratio of T3/T4 is no greater than 0.05, and wherein during each
stimulation session EA stimulation pulses having one or more
specified widths and amplitudes are generated at one or more
specified rates; and; a coin-cell type primary battery residing
inside the housing that provides the operating power for the
stimulation circuitry, wherein the primary battery has an internal
impedance that is greater than 5 ohms, and wherein the coin-cell
primary battery has sufficient capacity to power the operation of
the EA device in accordance with the prescribed stimulation regimen
for at least two years; wherein the at least one cathodic electrode
is configured from a prescribed electrode material having a surface
area sufficiently large to allow a desired current density to flow
through it without causing electrode corrosion, and further wherein
the at least one cathodic electrode is positioned sufficiently far
from the at least one anodic electrode so as to prevent current
shunting to occur between the at least one cathodic electrode and
the at least one anodic electrode before the stimulation pulses of
electrical current have penetrated into the body tissue a specified
distance.
11. The EA device of claim 10 wherein the at least one cathodic
electrode is on the top or bottom surface of the housing, and the
at least one anodic electrode is on the perimeter edge surface of
the housing.
12. The EA device of claim 11 wherein the at least one cathodic
electrode is located on a top or bottom surface of the housing and
positioned no closer than 5 mm from the closest edge of the nearest
at least one anodic electrode, wherein the total surface area of
the at least one cathodic electrode is no smaller than about 0.5
mm2.
13. The EA device of claim 12 the at least one cathodic electrode
comprises a first cathodic electrode located on a top surface of
the housing and a second cathodic electrode located on a bottom
surface of the housing, and wherein the stimulation circuitry
further includes switching circuitry that selectively activates (i)
only the first cathodic electrode, or (ii) only the second cathodic
electrode, or (iii) both the first and second cathodic electrodes
when the stimulation pulses are delivered to the body tissue in
accordance with the prescribed stimulation regimen.
14. The EA device of claim 13 wherein the at least one anodic
electrode is formed as a ring electrode residing substantially
around a perimeter edge of the housing.
15. The EA device of claim 14 wherein the first and second cathodic
electrodes each comprise multiple small cathodic electrodes
distributed over the top and bottom surface areas of the housing in
accordance with a prescribed pattern.
16. The EA device of claim 15 wherein the stimulation circuitry
includes additional cathodic switching circuitry that selectively
activates only a desired grouping of the first and second cathodic
electrodes, wherein the location of the body tissue receiving the
stimulation pulses may be selected by controlling which groups of
electrodes are activated and which are not activated, wherein an
activated electrode comprises an electrode that is turned ON by the
switching circuitry so that an electrical current may flow through
the electrode, and a non-activated electrode comprises an electrode
that is turned OFF by the switching circuitry so as to prevent
electrical current from flowing through the electrode.
17. An implantable electroacupuncture (EA) device adapted to be
implanted at a specified acupoint of a patient, the
electroacupuncture device comprising: a leadless,
hermetically-sealed disc-shaped housing; at least one cathodic
electrode and at least one anodic electrode formed in a symmetrical
pattern on the surfaces of the housing; stimulation circuitry
residing inside the housing and electrically coupled to the at
least one cathodic electrode and the at least one anodic electrode,
wherein the stimulation circuitry generates stimulation pulses of
electrical current that are delivered to body tissue surrounding
the housing through the at least one cathodic electrode and the at
least one anodic electrode in accordance with a prescribed
stimulation regimen, wherein the stimulation regimen defines the
duration and rate at which a stimulation session is applied to the
body tissue, said stimulation regimen requiring that the
stimulation session have a duration of T3 minutes, wherein T3 is at
least 10 minutes, and a rate of occurrence of once every T4
minutes, wherein the ratio of T3/T4 is no greater than 0.05; a
coin-cell type primary battery residing inside the housing that
provides the operating power for the stimulation circuitry, wherein
the primary battery has an internal impedance that is greater than
5 ohms, and wherein the coin-cell primary battery has sufficient
capacity to power the operation of the EA device in accordance with
the prescribed stimulation regimen for at least two years; wherein
the total surface area of the at least one cathodic electrode is
sufficiently large to allow a desired current density to flow
through it without causing electrode corrosion, and further wherein
the at least one cathodic electrode is positioned sufficiently far
from the at least one anodic electrode to prevent current shunting
between the at least one cathodic electrode and the at least one
anodic electrode.
18. The EA device of claim 17 wherein the at least one cathodic
electrode comprises a single cathodic electrode located in the
center of a bottom surface of the disc-shaped housing.
19. The EA device of claim 18 wherein the stimulation circuitry
generates monophasic stimulation pulses having a magnitude of
between 2 to 25 ma, a pulse width of between 100 to 600 msec, and a
frequency of between 1 and 5 Hz.
20. The EA device of claim 19 wherein the disc-shaped housing has a
diameter of no greater than 25 mm, a thickness no greater than 3
mm.
Description
RELATED APPLICATIONS
[0001] This application is a Divisional application of U.S. patent
application Ser. No. 13/776,155, filed Feb. 25, 2013, which
Application is a Continuation-in-Part (CIP) of application Ser. No.
13/598,582, filed Aug. 29, 2012, now U.S. Pat. No. 8,965,511, which
application(s) and/or patent(s), hereafter "Parent Application(s)",
are incorporated herein by reference in their entireties, including
all drawings and appendices. This application also claims the
benefit of the following previously-filed U.S. Provisional Patent
Applications, now expired, which applications are also incorporated
herein by reference:
[0002] 1. Application No. 61/606,995, filed Mar. 6, 2012, entitled
"Electrode Configuration For Implantable Electroacupuncture
Device"; and
[0003] 2. Application, No. 61/676,275, filed Jul. 26, 2012,
entitled "Radial Feed-Through Packaging for an Implantable
Electroacupuncture Device".
BACKGROUND
[0004] The present disclosure describes improvements to the
electrodes employed when using and operating a small, thin
coin-sized electroacupuncture (EA) device of the type described in
the related applications referenced above, or equivalent small,
self-contained, stimulators adapted for implantation under the
skin. More particularly, the present disclosure relates to a
preferred scheme for configuring the electrodes on the housing of
an implantable EA device.
[0005] In accordance with the teachings of the Parent Application(s
referenced above, a self-contained, coin-sized stimulator may be
implanted in a patient at or near a specified target tissue
location, e.g., one or more acupoint(s), in order to favorably
treat a condition or disease of a patient. The coin-sized
stimulator referenced in the previously-filed patent applications
is referred to as an implantable electroacupuncture device (IEAD).
Such IEAD advantageously applies electrical stimulation pulses at
very low duty cycles in accordance with a specified stimulation
regimen through electrodes that either form an integral part of the
housing of the stimulator, or are closely coupled thereto through a
very short lead. A small, thin, coin-cell type battery inside of
the IEAD case provides enough stored energy for the IEAD to carry
out its specified stimulation regimen over a period of several
years. Thus, the IEAD, once implanted, provides an unobtrusive,
needleless, long-lasting, elegant and effective mechanism for
treating certain conditions and diseases that have long been
treated by acupuncture or electroacupuncture.
[0006] The ability of the IEAD to apply its low level stimulation
through the electrodes that are attached to, carried by, or
otherwise form a part of the housing of the IEAD is, in large part,
a function of how well such electrodes are able to direct and focus
the applied stimulation to the target tissue location(s) of
interest, e.g., a designated acupoint(s), and to the tissue and
nerves associated with such target location. The present disclosure
is directed to techniques and schemes that accomplish that
goal.
[0007] It is noted that traditional acupuncture and acupressure
have been practiced in Eastern civilizations (principally in China,
but also in other Asian countries) for at least 2500 years. It is
still practiced today throughout many parts of the world, including
the United States and Europe.
[0008] Acupuncture is an alternative medicine that treats patients
by insertion and manipulation of needles in the body at selected
points. The locations where the acupuncture needles are inserted
are referred to as "acupuncture points" or simply just "acupoints".
The location of acupoints in the human body has been developed over
thousands of years of acupuncture practice, and maps showing the
location of acupoints in the human body are readily available in
acupuncture books or online, see, e.g., WHO STANDARD ACUPUNCTURE
POINT LOCATIONS IN THE WESTERN PACIFIC REGION, published by the
World Health Organization (WHO), Western Pacific Region, 2008
(updated and reprinted 2009), ISBN 978 92 9061 248 7 (hereafter
"WHO Standard Acupuncture Point Locations 2008"). This reference,
i.e., the WHO Standard Acupuncture Point Locations 2008, is
incorporated herein by reference.
[0009] In classical acupuncture treatment, once needles are
inserted at a desired acupoint location(s), the needles are
typically mechanically modulated for a short treatment time, e.g.,
30 minutes or less. The needles are then removed until the
patient's next visit to the acupuncturist, e.g., in 1-4 weeks (or
longer), when the process is repeated. Over several visits, the
patient's condition or disease is effectively treated, offering the
patient needed relief and improved health.
[0010] In electroacupuncture (EA) treatment, needles are inserted
at specified acupoints, as in classical acupuncture treatment, but
the needles, once inserted, are then connected to an external
source of electrical radio frequency (RF) energy, and electrical
stimulation signals, at a specified frequency and intensity level,
are then applied to the patient's body through the needles at the
acupoint(s), thereby also providing the patient with a measure of
needed and desired treatment for his or her condition or
disease.
[0011] While some controversy may still exist as to the precise
mechanism by which the insertion of needles into body tissue at
selected acupoint(s) achieves its beneficial results, the
successful activation of nerve fibers (whether through mechanical
modulation or electrical modulation) at the acupoint(s) is thought
by most to be a key element necessary for effective acupuncture
treatment. See, e.g., "Longhurst, Defining Meridians: A Modern
Basis of Understanding," J Acupunct Meridian Stud 2010;
3(2):67-74.
[0012] U.S. Pat. No. 6,735,475, issued to Whitehurst et al.,
discloses use of an implantable miniature neurostimulator, referred
to as a "microstimulator," that can be implanted into a desired
tissue location and used as a therapy for headache and/or facial
pain. The microstimulator has a tubular shape, with electrodes at
each end.
[0013] Other patents of Whitehurst et al. teach the use of this
small, microstimulator, placed in other body tissue locations,
including within an opening extending through the skull into the
brain, for the treatment of a wide variety of conditions, disorders
and diseases. See, e.g., U.S. Pat. No. 6,950,707 (obesity and
eating disorders); U.S. Pat. No. 7,003,352 (epilepsy by brain
stimulation); U.S. Pat. No. 7,013,177 (pain by brain stimulation);
U.S. Pat. No. 7,155,279 (movement disorders through stimulation of
Vagus nerve with both electrical stimulation and drugs); U.S. Pat.
No. 7,292,890 (Vagus nerve stimulation); U.S. Pat. No. 7,203,548
(cavernous nerve stimulation); U.S. Pat. No. 7,440,806 (diabetes by
brain stimulation); U.S. Pat. No. 7,610,100 (osteoarthritis); and
U.S. Pat. No. 7,657,316 (headache by stimulating motor cortex of
brain).
[0014] Techniques for using electrical devices, including external
EA devices, for stimulating peripheral nerves and other body
locations for treatment of various maladies are known in the art.
See, e.g., U.S. Pat. Nos. 4,535,784; 4,566,064; 5,195,517;
5,250,068; 5,251,637; 5,891,181; 6,393,324; 6,006,134; 7,171,266;
and 7,171,266. The methods and devices disclosed in these patents,
however, typically utilize (i) large implantable stimulators having
long leads that must be tunneled through tissue or blood vessels
over an extended distance to reach the desired stimulation site,
(ii) external devices that must interface with implanted electrodes
via percutaneous leads or wires passing through the skin, or (iii)
inefficient and power-consuming wireless transmission schemes. Such
devices and methods are far too invasive, and/or are ineffective
the treatment provided.
[0015] From the above, it is seen that there is a need in the art
for a less invasive device and technique for electroacupuncture
stimulation of acupoints, or other target tissue locations, that
does not require the continual use of needles inserted through the
skin, or long insulated wires implanted or inserted into blood
vessels, for the purpose of treating an illness or deficiency of a
patient.
[0016] Moreover, as will be seen from the description that follows,
the electrodes used with any implantable electroacupuncture device
must be optimally configured so that the applied stimulation
current achieves its intended purpose of acting and interacting
with nerve fibers and tissue so as to produce desired efficacious
results. The innovations described herein address that need.
SUMMARY
[0017] An implantable electroacupuncture device (IEAD) is described
herein that includes a coin-sized and -shaped housing having a top
surface, a bottom surface and a perimeter edge connecting the top
surface to the bottom surface. A preferred construction has
electrodes configured so as to reside on, or form an integral part
of, the surfaces of the housing. One preferred electrode
configuration has electrodes on the top and/or bottom surfaces
functioning as cathodes, and an electrode on the perimeter edge of
the housing functioning as an anode. The cathodic electrodes may,
in some configurations, be divided into segments, or an array of
smaller cathodic electrodes, each of which, or groups of which, may
be selectively turned ON or OFF so as to provide a convenient
mechanism for adjusting the density of the stimulus current flowing
through the cathodic electrode surface area. The anodic electrode,
which in its simplest form is a ring electrode on the perimeter
edge surface, may likewise in some configurations be divided into
segments or an array of smaller anodic electrodes spaced around the
perimeter edge. By selectively controlling the current density and
spacing between the anodic and cathodic electrodes, an optimum
stimulus current may be generated that minimizes electrode
corrosion and current shunting, yet achieves a desired range or
depth penetration of the stimulus current into the body tissue that
surrounds the EA device when the EA device is implanted in a
patient's body.
[0018] One configuration of the implantable EA device disclosed
herein may be characterized as an EA device adapted to be implanted
at a specified tissue location, e.g., at a specific acupoint of a
patient. The EA device includes (i) a housing; (ii) at least one
cathodic electrode and at least one anodic electrode formed on, or
as an integral part of, the housing; and (iii) stimulation
circuitry residing inside the housing and electrically coupled to
the at least one cathodic and at least one anodic electrodes. The
stimulation circuitry is configured, i.e., designed or programmed,
to generate stimulation pulses that are delivered to body tissue
through the at least one cathodic and at least one anodic
electrodes in accordance with a prescribed stimulation regimen. In
a preferred configuration, the at least one cathodic electrode
resides on a top and/or bottom surface of the housing and utilizes
an optimum surface area for activation, where "activation" as used
herein relates to electrically connecting the electrode (or a
prescribed portion of the electrode surface area) to the
stimulation circuitry so that the electrode is turned ON (as
opposed to being turned OFF, when the electrode is not electrically
connected to the stimulation circuitry). An "optimum surface area"
for activation comprises an electrode surface area that allows a
desired current density to flow through the electrode surface area
without causing electrode corrosion or current shunting to occur.
Electrode corrosion and current shunting are discussed in more
detail in the Detailed Description, below.
[0019] Another configuration of the invention disclosed herein may
be characterized as an IEAD adapted to be implanted at a specified
acupoint of a patient. The IEAD is coin-sized and -shaped, having a
top surface, a bottom surface, and a perimeter edge connecting the
top surface to the bottom surface. At least one cathodic electrode
and at least one anodic electrode are formed on, or comprise an
integral part of, the surfaces of the IEAD housing. Typically, the
at least one cathodic electrode is on the top or bottom surface of
the housing, and the at least one anodic electrode is on the
perimeter edge surface of the housing. Stimulation circuitry
resides inside the housing and connection means are employed that
electrically couple the at least one cathodic electrode and the at
least one anodic electrode to the stimulation circuitry. The
stimulation circuitry generates charge balanced monophasic
stimulation pulses of electrical current that are delivered to body
tissue surrounding the housing through the at least one cathodic
electrode and the at least one anodic electrode in accordance with
a prescribed stimulation regimen. The at least one cathodic
electrode has a surface area sufficiently large to allow a desired
current density to flow through it without causing electrode
corrosion. Further, the at least one cathodic electrode is
positioned sufficiently far from the at least one anodic electrode
so as to prevent current shunting to occur between the at least one
cathodic electrode and the at least one anodic electrode before the
stimulation pulses of electrical current have penetrated into the
body tissue a desired distance.
[0020] Still another configuration of the invention disclosed
herein may be characterized as a method of operating an IEAD. The
IEAD with which the method is used includes a housing having at
least two electrodes carried on, or formed as an integral part of,
the housing. Stimulation circuitry resides within the housing and
is coupled to the at least two electrodes. The stimulation
circuitry generates stimulation pulses of a prescribed frequency,
intensity and pulse width. These stimulation pulses are applied to
the at least two electrodes in accordance with a prescribed
stimulation regimen. The method of operating the EA device
includes: (i) configuring one of the at least two electrodes to be
a cathodic electrode, and placing the cathodic electrode on a top
and/or bottom portion of the housing; (ii) configuring the other of
the at least two electrodes to be an anodic electrode, and placing
the anodic electrode on a perimeter edge of the housing; and (iii)
applying monophasic electrical stimulation to the anodic and
cathodic electrodes during a stimulation session that lasts T3
minutes at a rate of once every T4 minutes, during which
stimulation session monophasic stimulation pulses having a pulse
width of T1 milliseconds (msec) are applied through the cathodic
and anodic electrodes at a rate of once every T2 msec. In
accordance with this method, the value of T1 is between 0.1 and 0.6
msec, T2 is between 200 and 1000 msec, T3 is between 10 and 60
minutes, and the ratio of T3/T4 is no greater than 0.05.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The above and other aspects, features and advantages of the
invention will be more apparent from the following more particular
description thereof, presented in conjunction with the following
drawings. These drawings illustrate various embodiments of the
principles described herein and are part of the specification. The
illustrated embodiments are merely examples and do not limit the
scope of the disclosure.
[0022] FIG. 1 is a three-dimensional sketch of human skin tissue,
including the subcutaneous tissue area below the outer layer of the
skin.
[0023] FIG. 2 shows a first embodiment of a representative
optimized electrode pair, both cathode and anode, placed on a
coin-sized stimulator housing.
[0024] FIG. 3 shows a top (or bottom) view of the cathode and anode
electrodes used with the coin-sized stimulator of FIG. 2.
[0025] FIG. 3A shows a side view of the cathode and anode
electrodes used with the stimulator of FIG. 3.
[0026] FIG. 4 shows a second embodiment of an optimized electrode
pair placed on a coin-sized stimulator housing.
[0027] FIG. 5 illustrates two ways of achieving a desired electrode
contact surface area with either a single electrode surface area,
shown on the left, or with an array of multiple smaller electrode
surface areas, shown on the right.
[0028] FIG. 5A shows a table that compares some electrode diameters
and numbers of electrodes for 316SS (SS) and Platinum (Pt) for a
current stimulus pulse having a pulse width of 0.5 milliseconds at
various amplitudes expressed in milliamps.
[0029] FIG. 6 shows concentric ring cathodic electrodes used to
keep a stimulation current of varying amplitudes focused on a
desired target acupoint.
[0030] FIG. 7 diagrammatically and functionally illustrates how the
cathodic and anodic electrodes used with a disc-shaped stimulator
may be segmented or partitioned and operated with cathodic and
anodic switching circuitry in order to better optimize the
electrode surface area, thereby helping to better control the
current density flowing through the electrodes so as to have the
stimulation current more optimally penetrate body tissue
surrounding the electrodes.
[0031] FIG. 8 is a waveform timing diagram that illustrates a
typical monophasic stimulation pulse, showing what is meant by the
terms pulse width, amplitude and frequency of stimulation, and
therefore illustrates a timing waveform diagram of representative
stimulation pulses generated during a stimulation session.
[0032] FIG. 8A shows a timing waveform diagram of multiple
stimulation sessions, and thus illustrates the waveforms of FIG. 8
on a more condensed time scale.
[0033] FIG. 9 is a perspective view of a preferred implementation
of an implantable electroacupuncture device (IEAD) made in
accordance with the teachings presented herein.
[0034] FIG. 10 illustrates the location of an exemplary target
tissue stimulation site, e.g., an acupoint, whereat the IEAD of
FIG. 9 may be implanted for the treatment of a particular disease
or condition.
[0035] FIG. 11 shows a sectional view of an IEAD implanted at a
selected target stimulation site, and illustrates the electric
field gradient lines created when an electroacupuncture (EA) pulse
is applied to the tissue through the central electrode and ring
electrode attached to the bottom surface and perimeter edge,
respectively, of the IEAD housing.
[0036] FIG. 12 shows a plan view of one surface (identified in FIG.
12 as the "Cathode Side") of the IEAD housing illustrated in FIG.
9.
[0037] FIG. 12A shows a side view of the IEAD housing illustrated
in FIG. 9.
[0038] FIG. 13 shows a plan view of the other side, indicated as
the "Skin Side," of the IEAD housing or case illustrated in FIG.
9.
[0039] FIG. 13A is a sectional view of the IEAD of FIG. 3 taken
along the line A-A of FIG. 13.
[0040] FIG. 14 is a perspective view of the IEAD housing, including
a feed-through pin, before the electronic components are placed
therein, and before being sealed with a cover plate.
[0041] FIG. 14A is a side view of the IEAD housing of FIG. 14.
[0042] FIG. 15 is a plan view of the empty IEAD housing shown in
FIG. 14.
[0043] FIG. 15A depicts a sectional view of the IEAD housing of
FIG. 15 taken along the section line A-A of FIG. 15.
[0044] FIG. 15B shows an enlarged view or detail of the portion of
FIG. 15A that is encircled with the line B.
[0045] FIG. 16 is a perspective view of an electronic assembly,
including a battery, adapted to fit inside of the empty housing of
FIG. 14 and FIG. 15.
[0046] FIGS. 16A and 16B show a plan view and side view,
respectively, of the electronic assembly shown in FIG. 16.
[0047] FIG. 17 is an exploded view of the IEAD assembly,
illustrating its constituent parts.
[0048] FIG. 17A schematically illustrates a few alternative
electrode configurations that may be used with the IEAD of FIG.
9.
[0049] FIG. 18 illustrates a functional block diagram of the
electronic circuits used within an IEAD of the type described
herein.
[0050] FIG. 19 functionally shows a basic boost converter circuit
configuration, and is used to model how the impedance of the
battery R.sub.BAT can affect its performance.
[0051] FIG. 19A illustrates a typical voltage and current waveform
for the circuit of FIG. 19 when the battery impedance R.sub.BAT is
small.
[0052] FIG. 19B shows the voltage and current waveform for the
circuit of FIG. 19 when the battery impedance R.sub.BAT is
large.
[0053] FIG. 20 shows one preferred boost converter circuit and a
functional pulse generation circuit configuration for use within
the IEAD.
[0054] FIG. 21 depicts one preferred schematic configuration for an
IEAD that utilizes a boost converter circuit U1, micro-controller
circuit U2, programmable current source U3, sensor U4 and switch
circuit U5 in order to perform the functions illustrated in the
functional diagrams of FIGS. 7, 18, 19 and 20.
[0055] FIG. 22 shows a state diagram that depicts the various
states the IEAD may assume as controlled by an external magnet.
[0056] Appendix A, submitted with Applicant's Parent
Application(s), illustrates some examples of alternate symmetrical
electrode configurations that may be used with an IEAD of the type
described herein.
[0057] Appendix B, submitted with Applicant's Parent
Application(s), illustrates a few examples of non-symmetrical
electrode configurations that may be used with an IEAD made in
accordance with the teachings herein.
[0058] Appendix C, submitted with Applicant's Parent
Application(s), shows an example of the code used in the
micro-controller IC (e.g., U2 in FIG. 21) to control the basic
operation and programming of the IEAD, e.g., to turn the IEAD
ON/OFF, adjust the amplitude of the stimulus pulse, and the like,
using only an external magnet as an external communication
element.
[0059] Appendices A, B and C are incorporated by reference
herein.
[0060] Throughout the drawings, identical reference numbers
designate similar, but not necessarily identical, elements.
DETAILED DESCRIPTION
[0061] Overview
[0062] Disclosed and claimed herein are preferred electrode
configurations for use with a coin-sized and -shaped subcutaneously
implantable electroacupuncture device (IEAD). The preferred
electrode configuration(s) is placed on, or incorporated within,
the housing of the IEAD. The IEAD is adapted to be implanted
subcutaneously through a very small incision, e.g., less than 2-3
cm in length, directly adjacent to, or at, a selected acupuncture
site (or other target nerve/tissue location). In accordance with
the teachings herein, the IEAD is subcutaneously implanted so that
its electrodes are located and anchored at a desired target tissue
stimulation site, which target site may also be referred to as an
acupuncture site, or "acupoint." The acupoint is selected based on
its known history of moderating or positively affecting a
physiological or health condition of a patient that needs
treatment. Stimulation pulses are applied by the EA device at the
selected acupoint at a very low duty cycle in accordance with a
specified stimulation regimen. This stimulation regimen is designed
to provide effective electroacupuncture (EA) or electrostimulator
(ES) treatment for a patient.
[0063] The Parent Application(s) referenced above in the first
paragraph provide a description of an IEAD, system and/or method
used to treat a particular disease or condition of a patient, e.g.,
hypertension. The present application describes in more detail a
preferred configuration or manner of constructing or forming or
orienting electrodes adapted to be used with such an IEAD. Such
electrodes are sometimes referred to in the Parent Application, for
some embodiments therein disclosed, as "needle electrodes".
However, as the description below indicates, the electrodes are not
necessarily needle-shaped, but rather typically comprise relatively
smooth surfaces that reside on or near the housing of the IEAD at
various locations and orientations.
[0064] It is a feature of the electrodes disclosed herein that when
subcutaneously placed so as to reside at or near a desired
acupoint, or other target tissue location, and when electrically
energized so as to cause a small electrical field to emanate from
the electrodes, such electrical field causes a small electrical
current to flow in the body tissue surrounding the acupoint. For an
optimally designed electrode, this electrical current, in turn,
activates as many targeted nerve fibers as possible. Such nerve
fiber activation is then able to achieve the greatest therapeutic
effect. In order to optimally achieve such desired nerve fiber
activation, with the least expenditure of energy and fewest
clinical side effects, the directionality of the nerve fibers and
proximity to the electrode is a factor that must be considered in
the electrode design.
[0065] The directionality of the nerve fibers is illustrated in
FIG. 1, which shows a three-dimensional sketch of skin tissue 100
of a human body. The skin tissue 100 illustrated in FIG. 1 includes
the outer layer of the skin, or epidermis 104, and the dermis 106.
The top surface 102 of the epidermis 104 comprises the skin layer
that is visible and exposed to the environment around the human
body. Much of the epidermis comprises dead cells impregnated with
keratin. The dermis 106 is the thick layer of living tissue that
lies beneath the epidermis. The dermis consists mainly of loose
connective tissue within which are blood capillaries, lymph
vessels, sensory nerve endings, sweat glands and their ducts, hair
follicles, sebaceous glands, and smooth muscle fibers. For purposes
of the present disclosure, the term "subcutaneously" refers broadly
to anything "beneath the skin", which in the context of this
disclosure most often means below the dermis 106. Hence,
subcutaneous tissue is loose connective tissue, often fatty,
situated under the dermis 106.
[0066] Still referring to FIG. 1, it is seen that groups of
individual nerve fibers 108 often congregate together to form a
bundle of nerve fibers 110. This bundle of nerve fibers 110 is
located beneath the dermis 106, and generally runs parallel to the
surface 102 of the skin. Some individual nerve fibers 108, near
their respective distal ends, extend away from the bundle 110 in a
direction towards the skin surface, or to some other destination.
These nerves, at or near their respective distal ends, thus
generally run orthogonal to the surface of the skin.
[0067] Thus, as illustrated in FIG. 1, the directionality of the
nerve fiber bundles 110 is parallel to the surface 102 of the skin,
while the directionality of individual nerve fibers 108 is also
predominantly parallel to the surface of the skin, with relatively
short portions of some individual nerve fibers being generally
orthogonal to the surface of the skin 102.
[0068] Cathodic stimulation preferentially activates nerve fibers
running tangential or parallel to the face of the electrode. This
is in contrast to anodic stimulation which preferentially activates
nerve fibers that run radial or perpendicular to the face of the
electrode surface. As indicated above, individual nerve fibers 108
that go to or near the skin surface 102 generally run parallel and
above the subcutaneous space 109 before curving upwards into the
dermis 106. Similarly, nerve fibers 108 in the subcutaneous space
109 run parallel to this space 109 before curving deeper into
deeper layers of tissue.
[0069] Hence, as a first aspect of electrode design for a
subcutaneously-placed implanted device, such as a small coin-sized
IEAD described herein, it is seen that the cathodic and anodic
electrode surfaces need to be optimally configured and placed.
These electrode surfaces, for the coin-sized implantable devices,
are preferably formed on, or as an integral part of, the housing of
the device. Where cathodic stimulation is used, which is common for
most implantable tissue-stimulation devices, and where the
configuration of the electrode is to be optimized to activate as
many nerves as possible at or near a specified acupoint, it is
beneficial to have a cathode electrode positioned closest to the
cutaneous layers above the device as well as to tissue layers below
the device. Any curvature of the nerves away from these
cathode-covered surfaces further reduces the threshold current
needed to activate them electrically. Exposure to anodes should
thus be limited to the edges of the device where nerve fibers are
oriented predominantly perpendicular to the electrode surface.
[0070] A second aspect for the electrode design is the proximity of
the nerve fiber relative to the size of the electrode. It is
noteworthy that activation in both the case of a cathode or an
anode depends upon the magnitude of the second spatial derivative
of the applied electric field potential along the axis of the nerve
fiber. A uniform electric field from a continuous flat plate
electrode, for example, results in a second spatial derivative of
voltage which is zero in all directions and theoretically would not
activate nerve fibers regardless of the applied current. The ideal
electrode in this respect would thus be a point source since this
maximizes the second spatial derivative of the field potential as
the nerve fiber approaches the electrode surface.
[0071] Mathematically this can be seen relatively easily for a
spherical electrode contact of radius R in a uniform volume
conductor with conductivity p. The field potential V, for a current
I at the surface of the electrode is
V = .rho. I 4 .pi. .times. 1 R . ( 1 ) ##EQU00001##
[0072] The second spatial derivative of voltage perpendicular to
the surface is
2 V r 2 = .rho. I 4 .pi. .times. 1 R 3 . ( 2 ) ##EQU00002##
[0073] Equation (2) is the activating function for a nerve aligned
radial or perpendicular to the surface of the electrode (defined as
the r direction). There is clearly a much greater activating
function magnitude for nerve fibers near the surface of the
electrode with a smaller radius electrode. The second spatial
derivative of voltage tangential to the surface is
2 V x 2 = .rho. I 4 .pi. .times. ( - 1 R 3 ) . ( 3 )
##EQU00003##
[0074] Equation (3) is the activating function for a nerve aligned
tangential or parallel to the surface of the electrode (defined as
the x direction). The sign is negative meaning that the activating
function is positive for a cathodic or negative current I. This
reflects how nerves running parallel to the electrode are optimally
depolarized by cathodic stimulation. Again, there is clearly a much
greater activating function magnitude for nerve fibers at the
surface with a smaller radius electrode.
[0075] Theoretically, smaller electrode contacts are always more
efficient at electrically activating tissue. This applies even to
non-spherical electrode contacts. In practice, however, the minimum
size of the electrode is limited by maximum current density that
can be safely injected and the available compliance voltage of the
stimulator to drive current through the smaller, and thus higher
impedance, electrode.
[0076] Turning back then to the optimal electrode configuration for
an electrical stimulation device placed at an acupuncture point (or
acupoint), it is seen that the optimal electrode configuration
takes on a form wherein: (i) small cathodes are distributed on the
upper and lower surfaces of the device parallel to the skin and
(ii) small anodes are distributed on the edges of the device which
are perpendicular to the skin. This optimal electrode configuration
is shown in FIG. 2, where a Cathode electrode 210 is formed on the
top and/or bottom surfaces of a coin-sized device housing 200
(note, the bottom of the housing is not visible in FIG. 2), while
an Anode electrode 220 is formed as a thin ring electrode around
the edge or perimeter of the housing 200.
[0077] Current shunting may occur if the distance between the anode
and cathode is too close. Current shunting applies to surface area
only in that a larger surface area of a cathode necessarily brings
the edges of the cathode closer to the anode ring. Thus, in
optimizing the electrode configuration, the size of the electrode
must be considered to prevent damage to the electrode material when
the desired current density is used (which tends to happen if the
electrode area is too small) and to prevent current shunting when
the edges of the cathode get too close to the anode ring (which
tends to happen when the electrode area is too large.
[0078] A further aspect of the electrode configuration design is
how to optimally space electrode contacts on the surface of the
housing 200 of such a device. In the simple embodiment depicted in
FIGS. 2, 3 and 3A, there are single small cathodes 210 centered on
the top and bottom of the device housing 200 with a thin ring anode
220 around the edge of the device 200. The surface area of these
electrode contacts would be the minimum for safe stimulation
without electrode corrosion and/or tissue damage. For an electrode
material such as 316 LVM stainless steel, for example, up to
0.3-0.4 microCoulombs/mm.sup.2 might be safely injected during a
stimulus pulse. (Note: a Coulomb is the basic measure of electrical
charge, and electrical current, measured in Amperes (A), is defined
as the rate at which electrical charge flows, or Coulombs per
Second.)
[0079] As further depicted in FIGS. 3 and 3A, the housing 200 is
disc-shaped (also referred to herein as "coin-shaped"), having a
diameter D1. The cathodic electrodes 210, located on the top and
bottom surfaces of the disc-shaped housing 200, have a diameter D2.
The housing 200 has a thickness of H1. Thus, the anodic electrode
220 is essentially a ring-shaped electrode having a width of about
H1, or a little less than H1, e.g., 0.2-0.4 mm less than H1, and a
diameter of D1. In one configuration, the diameter D1 of the
disc-shaped housing may be approximately 22 mm, whereas the
diameter of the cathodic electrode surface area D1 may range from
2-10 mm. The height H1, or thickness, of the disc-shaped housing
200 typically is in the range of 1.4-2.5 mm.
[0080] Should the device housing 200 have a surface area larger
than the minimum safe electrode contact area and the cathode to
anode spacing is sufficient to avoid current shunting, then a good
electrode configuration to use would be to distribute the same
electrode surface area over multiple contacts, as depicted in FIG.
4. As seen in FIG. 4, the cathode electrode 210 comprises multiple
smaller cathodic electrode contacts 212 distributed over the top
and/or bottom surface of the housing 200. (Note, again, the bottom
surface of the housing 200 is not visible in FIG. 4, but it looks
substantially identical as the top surface, which is visible in
FIG. 4.) Similarly, the anodic electrode 220 comprises multiple
smaller anodic electrode contacts 222 distributed around the
peripheral edge of the housing 200.
[0081] The electrode configuration shown in FIG. 4 advantageously
distributes the electrode activating function over more of the
surface area of the device housing 200 while preserving the ability
to use the highest current density and thus highest activating
function possible at each electrode contact.
[0082] A typical center-to-center spacing for like polarity
contacts should preferably be less than twice the individual
contact diameter in order to minimize gaps in the activation
function. Opposite polarity contacts should preferably be spaced at
least twice the individual contact diameter to minimize current
shunting. The individual contact diameter and spacing may be chosen
as needed to distribute the electrode contacts over as much of the
surface area as possible at the highest available current
density.
[0083] By way of example, if an IEAD is designed to deliver a
sequence of electrical pulses having a duration of 0.5 milliseconds
(msec) at an amplitude up to 4 milliamps (mA) (i.e. the pulse
charge delivered with each pulse is 0.5 msec.times.4 mA=2
microCoulombs), then an electrode contact surface area of 2
microCoulombs/0.3 microCoulombs/mm.sup.2=6.7 mm.sup.2 would be
required when using 316 LVM stainless steel as the electrode
material. Such electrode surface area could be realized using two
disk cathode contacts with a 2 mm diameter on the upper and lower
surface, as illustrated on the left side of FIG. 5. Alternatively,
each cathode contact could be spread out over approximately 68
contacts with a 0.25 mm diameter spaced out at 0.5 mm center to
center, as shown on right side of FIG. 5. Either electrode
configuration achieves the same total surface area, but the
configuration having approximately 68 contacts (shown on the right
side of FIG. 5) increases the area over which the activating
function can be applied for nerves close to the electrode by a
factor of roughly 4.
[0084] It should be noted that 316 LVM stainless steel (sometimes
referred to herein as just "316SS" or "316 stainless steel") may
not be the ideal electrode material if higher current amplitudes
are desired or needed. Stainless steel 316SS has a limited charge
injection capacity of about 0.3 to 0.4 .mu.C/mm.sup.2. In contrast,
platinum has a charge injection capacity of 2 to 3 .mu.C/mm.sup.2,
almost 10 times as great as 316SS. Hence, where large current
amplitudes are needed, the best electrode material would
platinum.
[0085] FIG. 5A shows a table, TABLE 1, that compares some electrode
diameters (D) and numbers of electrodes (N) for 316SS (SS) and
Platinum (Pt), for a current stimulus pulse having a pulse width
(PW) of 0.5 millisecond (ms) at various amplitudes (I), expressed
in milliamps (mA). Included in the table is the pulse charge (Q)
delivered with each pulse, expressed in microCoulombs (.mu.C). Also
included in TABLE 1 (FIG. 5A) is a color code that indicates
whether the indicated electrode size can support the charge
injection that would be required for the indicated surface area of
the electrode, current amplitude and pulse width. A "Green" color
code indicates the charge can be injected safely. A "Yellow" code
indicates a marginal condition, and a "Red" code indicates a charge
level above the accepted limit. Thus, as can be seen from TABLE 1,
with a single 4 mm diameter stainless steel electrode, the maximum
current that could be injected through the electrode would be about
5 .mu.C, or 10 mA at a 0.5 ms pulse width.
[0086] A further refinement of such a device having a cathodic
electrode configuration as shown on the right side of FIG. 5 is to
allow individual contacts 212 to be selectively turned on or off.
At any given current amplitude, this selective turning on or off
allows all active contacts to be operating at maximum current
density and thus maximum activation function magnitude. The active
contacts would be distributed across the device surface so as to
provide maximum coverage. For example, if the current amplitude
were reduced by 50%, every other contact would be turned on.
Another use of individual contact programmability would be to
adjust the activation function and focus it at specific regions
around the acupoint.
[0087] Yet a further refinement of the electrode configuration is
to have individual voltage or current sources for groups of
contacts as needed to manage different required amplitudes. For
example, the cathode(s) on the top surface of the device could be
stimulated at one amplitude while the cathode(s) on the bottom
surface of the device could be stimulated at a different
amplitude.
[0088] Still a further refinement of the electrode configuration is
to have an array of concentric cathodic ring electrodes with
increasing diameters, as shown in FIG. 6. Such a configuration
(which could be placed on both the top and bottom of the
disc-shaped housing 200, or just on one of the top or bottom
surface), allows the cathodic electrode surface area to vary with
current amplitude while maintaining the electric field centered on
the desired target acupoint.
[0089] As should be evident from the above description, the size of
the electrode should not only be selected based on the amount of
current that flows through the electrode surface, but also as a
function of the purpose for which the electrode is being used. That
is, while there is a theoretical benefit to having many small
diameter contacts to activate fibers or tissue very close to the
device, there is no benefit to having many small contacts for a
single target tissue location, such as a nerve, that is further
away. Additionally, a device intended to activate local
subcutaneous fibers is better off with electrodes on both the top
and bottom surfaces of the device. However, a device intended to a
stimulate a single target tissue location some distance from the
electrode is better off having the electrode contact only on the
bottom surface of the device so that the stimulation can be focused
at the desired stimulation site located underneath the electrode,
as described below in connection with FIG. 11.
[0090] Thus, in summary, sometimes it is best to use large surface
area electrodes, and sometimes it is best to use small surface area
electrodes. Sometimes it is best to use electrodes on both the top
and bottom surfaces of the stimulator device, and sometimes it is
best to use electrodes only on the bottom surface (where the
"bottom surface" is the surface facing the target tissue location
located more than a few millimeters away from the electrode). Much
depends on the purpose of the stimulation, and how far away the
target stimulation location is from the electrode surfaces.
[0091] FIG. 6 depicts one preferred technique to have the electrode
surface area vary with current amplitude while maintaining the
electric field centered on the acupoint, or other target location.
An inner circular electrode 260 is activated at the lowest current
amplitude. As the amplitude of the stimulation current increases,
additional ring electrodes are activated. Thus, for example, if
increasing current amplitudes of I1, I2, I3, . . . I9 are to be
used, wherein I1<I2<I3<I4 . . . <I9, then the inner
circular electrode 260 is used for the lowest amplitude stimulation
current I1. If current I2 is used, then circular electrodes 260 and
ring 262 are used. If current I3 is used, then circular electrode
260 and ring electrodes 262 and 264 are used. If current I4 is
used, then circular electrode 260 and ring electrodes 262, 264 and
268 are used. If current I5 is used, then circular electrode 260
and ring electrodes 262, 264, 268 and 270 are used. This process
continues, with one more ring electrode being added to increase the
current to the next value, until the maximum current I9 is used,
which combines circular electrode 260 and ring electrodes 262, 264,
268, 270, 272, 274, 276 and 278.
[0092] The ability to selectively use only a segment, or portion,
of the available electrode surface area in order to maximize the
current density, and thus maximize the ability to have the
stimulation current better activate stimulated tissue, is
illustrated diagrammatically and functionally in FIG. 7. As seen in
FIG. 7, the top cathode electrode 210a is shown as being segmented
into four separate cathode portions 212a, 212b, 212c and 212d. Each
of these separate segments or portions may be individually
energized (turned ON) through the functionally-illustrated Top
Cathode Switch 214a, controlled by Processor 216. The Processor 216
(which is only functionally illustrated in FIG. 6) provides all the
needed control signals for operation of the IEAD that allow it to
generate a stream of stimulation pulses (see FIGS. 8 and 8A for a
typical stimulation waveform and stimulation sad) in accordance
with a specified stimulation regimen. The stimulation regimen may
include energizing one of the four cathode electrode segments, or
all of them (or two of them, or three of them) in order to obtain
the desired density of the stimulus current that flows through the
catheter electrode 210a.
[0093] In like manner, the bottom cathode electrode 210b is shown
as being segmented into four separate cathode portions 212a, 212b,
212c and 212d. Each of these separate segments or portions may be
individually energized (turned ON) through the
functionally-illustrated Bottom Cathode Switch 214b, controlled by
Processor 216. Hence, signals from the Processor 216 may
selectively control which segments or portions of the cathode
electrode 210b are energized, thereby allowing a desired density of
the stimulus current flowing through the catheter electrode 210b to
be achieved.
[0094] The ring anodic electrode 220 may similarly be divided into
smaller portions or segments, 220a, 220b, 220c and 220d. These
segments may be individually energized by the Anode Switch 218 so
that only one segment in ON and three are OFF, two are ON and two
are OFF, three are ON and one is OFF, or all four are ON. In this
way, a desired density of the stimulus current flowing through the
anode electrode 220 may be achieved.
[0095] It is to be noted that the segmentation of the TOP and
BOTTOM Cathode electrodes 210a and 210b, as shown in FIG. 7, as
well as the segmentation of the Anode electrode 220, also shown in
FIG. 7, is intended to only be exemplary, and not limiting. That
is, while four segments for each catheter electrode are
illustrated, in practice, this could be any number of segments, or
an array of smaller cathode electrodes, as shown, e.g., in FIGS. 4
and 5, or concentric ring cathodic electrodes as shown in FIG. 6.
Similarly, while four segments or individual portions 220a, 220b,
220c and 220d of the Anode ring electrode 220 are shown, there
could be any number of anode segments employed, as shown, e.g., in
FIG. 4. The point is, both the top and bottom cathodic electrodes
210a and 210b, as well as the anodic electrode 220, may be
selectively electrically divided into smaller electrode surface
areas by controlling which segments, or portions, of the
electrode's surface area are energized (where "energized" means
electrically turned ON so that current flows through the electrode
as controlled by the processor control circuit 216). This feature
allows the current density present in the stimulus current to be
better managed, which in turn allows for better control of which
body tissue is activated by the stimulus current.
[0096] One preferred application for the IEAD disclosed herein is
for the treatment of hypertension. For this application, an IEAD is
fabricated so as to reside in a coin-sized housing having a
diameter of approximately 22-24 mm, a thickness of approximately
2.2 to 2.5 mm, which size and shape is suitable for implantation at
acupoint PC6 to a depth of between 3-5 mm. Such EA device is
configured to continuously generate a charge balanced monophasic
stimulation pulses, as diagrammatically illustrated in FIG. 8,
having a pulse amplitude A1 of between 2 to 25 mA, a pulse width
(PW), or T1, of between 0.2 to 0.6 msec (200 to 600 .mu.sec), at a
frequency of between 1 and 5 Hz (i.e., a period T2 which varies
from 200 to 1000 msec) during a stimulation session that has a
duration T3 of from 15 to 45 minutes (preferably about 30 minutes),
which stimulation session is applied no more often than a time T4,
where T4 may be, e.g., no more than twice a week and no less than
once every other week (preferably once a week).
[0097] One of the reasons that acupoint P6 is selected for the
application of electroacupuncture stimuli for the purpose of
treating hypertension is because the median nerve is also at this
location, about 5-6 mm below where the EA device is to be implanted
(2-3 mm below the skin surface). This means that not only may the
benefits for the favorable treatment of hypertension be obtained
from applying classical acupuncture or electroacupuncture at this
particular acupoint, but also the benefits for the favorable
electrostimulation of the median nerve for the treatment of
hypertension are obtained.
[0098] In order to effectively stimulate the median nerve where it
is 5-6 mm below where the stimulation device is implanted, it is
best for the anode to cathode center-to-center spacing to be at
least twice this amount, or approximately 10-12 mm. If this is not
the case, then the shunting of current between the anode and
cathode may be too great. Advantageously, this criteria is
satisfied well by having a radial ring anode electrode 220 (see,
e.g., FIGS. 2, 3, and 3A) at the edge of a 22-24 mm diameter
device.
[0099] In a specific configuration for treating, e.g., hypertension
through application of EA stimulation pulses at acupoint P6, an
IEAD is configured to generate a stimulus current having an
amplitude of 15-20 mA or so. Pulses delivered are charge balanced
monophasic passive recharge waveforms at 0.5 msec (500 .mu.sec)
delivered at up to 4 Hz (nominally 2 Hz) in 30 minute sessions once
per week. The cathode 210, as shown in FIGS. 2, 3 and 3A, has a
diameter of 2-3 mm, and is placed on the top and bottom surface of
the disc-shaped housing 200. The anode 220 comprises a ring
electrode 220 located at the perimeter of the disc-shaped housing
200.
SPECIFIC EXAMPLE
[0100] A specific example of an implantable electroacupuncture
device (IEAD) will next be described in connection with the
description of FIGS. 9-22. This description is presented only to
illustrate and describe a specific example of an IEAD. This
description is not intended to be exhaustive or to limit the
invention to any precise form disclosed. Many modifications and
variations are possible in light of the teachings presented
herein.
[0101] Advantageously, the IEAD described in connection with this
specific example comprises an implantable, self-contained, device
powered by a small, thin, coin-cell type battery having an internal
impedance of at least five ohms. While the device described is
intended for, and is described for use as, an electroacupuncture
(EA) device, or IEAD, it should be noted that it may be used for
other similar tissue stimulation applications. Moreover, while the
preferred EA device is leadless, for some applications a short lead
may be needed to correctly position the electrodes precisely at a
desired stimulation site.
[0102] In an exemplary embodiment, the EA device includes two
electrode contacts mounted on or connected to the surface of its
housing. The EA device is adapted to treat a particular disease or
health condition of a patient. In one embodiment, the electrodes of
the EA device are mounted on the surfaces of its housing and
include a central cathode electrode on one side of the housing, and
an annular anode electrode that surrounds the cathode. In another
embodiment, the anode annular electrode is a ring electrode placed
around the perimeter edge of a coin-shaped housing.
[0103] As indicated above, the preferred EA device is leadless.
This means there are no leads or electrodes at the distal end of
leads (common with most implantable electrical stimulators) that
have to be positioned and anchored at a desired stimulation site.
Also, because there are no leads, no tunneling through body tissue
or blood vessels is required in order to provide a path for the
leads to return and be connected to a tissue stimulator (also
common with most electrical stimulators).
[0104] The EA device is adapted to be implanted through a very
small incision, e.g., less than 2-3 cm in length, directly adjacent
to a selected target stimulation site, e.g., an acupuncture site
("acupoint") known to moderate or affect an identified health
condition of a patient.
[0105] The EA device is easy to implant. Also, most embodiments are
symmetrical. This means that there is no way that it can be
implanted incorrectly (unless the physician puts it in
up-side-down, which would be difficult to do given the markings on
its case). All that need be done is to cut the incision, and slide
the device in place through the incision. Once the implant pocket
has been prepared, it is as easy as sliding a coin into a slot.
Such implantation can usually be completed in less than 10 minutes
in an outpatient setting, or in a doctor's office. Only minor,
local anesthesia need be used. No major or significant
complications are envisioned for the implant procedure. The EA
device can also be easily and quickly explanted, if needed or
desired.
[0106] The EA device is self-contained. It includes a primary
battery to provide its operating power. Such primary battery has a
high impedance, greater than 5 ohms. In view of such high
impedance, the EA device includes battery control circuitry that
limits the amount of instantaneous current drawn from the primary
battery to prevent excessive voltage drops in the output voltage of
the battery. Such battery control circuitry carefully manages the
delivery of power by the EA device so as to allow the device to
perform its intended function for several years.
[0107] Once the EA device is implanted in a patient, the patient
should not even know it is there, except for a slight tingling that
may be felt when the device is delivering bursts of stimulus pulses
during a stimulation session. Also, once implanted, the patient can
just forget about it. There are no complicated user instructions
that must be followed. Just turn it on. No maintenance is needed.
Moreover, should the patient want to disable the EA device, i.e.,
turn it OFF, or change stimulus intensity, he or she can do so
using, e.g., an external magnet.
[0108] The EA device can operate for several years because it is
designed to be very efficient. Stimulation pulses applied by the EA
device at a selected target stimulation site, e.g., a specified
acupoint, are applied at a very low duty cycle in accordance with a
specified stimulation regimen. The stimulation regimen applies EA
stimulation during a stimulation session that lasts at least 10
minutes, typically 30 minutes, and rarely longer than 60 minutes.
These stimulation sessions, however, occur at a very low duty
cycle. In one preferred treatment regimen, for example, a
stimulation session having a duration of 30 minutes is applied to
the patient just once a week. The stimulation regimen, and the
selected acupoint at which the stimulation is applied, are designed
and selected to provide efficient and effective EA stimulation for
the treatment of the patient's medical condition.
[0109] The EA device is, compared to most implantable medical
devices, relatively easy to manufacture and uses few components.
This not only enhances the reliability of the device, but keeps the
manufacturing costs low, which in turn allows the device to be more
affordable to the patient.
[0110] In operation, the EA device is safe to use. There are no
horrific failure modes that could occur. Because it operates at a
very low duty cycle (i.e., it is OFF much, much more than it is
ON), it generates little heat. Even when ON, the amount of heat it
generates is not much, less than 1 mW, and is readily dissipated.
Should a component or circuit inside of the EA device fail, the
device will simply stop working. If needed, the EA device can then
be easily explanted.
[0111] A key feature included in the design of the EA device is the
use of a commercially-available battery as its primary power
source. A preferred commercially-available battery to use in the EA
device is a small, thin, disc-shaped battery, also known as a "coin
cell" battery, such as the 3 V CR1612 lithium battery available
from Panasonic, or equivalents thereof. Such coin-cell batteries
are quite common and readily available for use with most modern
hand-held electronic devices.
[0112] Coin-cell type batteries come in many sizes, and employ
various configurations and materials. However, insofar as the
inventors or Applicant are aware, such batteries have never been
used in implantable medical devices previously. This is because
their internal impedance is, or has always thought to have been,
much too high for such batteries to be of practical use within an
implantable medical device where power consumption must be
carefully monitored and managed so that the device's battery will
last as long as possible. Further, because of the high internal
impedance, dips in the battery output voltage (caused by any sudden
surge in instantaneous battery current) may occur that could
compromise the performance of the device. Additionally, the energy
requirements of other active implantable therapies are far greater
than can be provided by such coin cells without frequent
replacement.
[0113] The EA device disclosed herein advantageously employs
power-monitoring and power-managing circuits that prevent any
sudden surges in battery instantaneous current, or the resulting
drops in battery output voltage, from ever occurring, thereby
allowing a whole family of commercially-available, very thin,
high-output-impedance, relatively low capacity, small disc
batteries (or "coin cells") to be used as the EA device's primary
battery without compromising the EA device's performance. As a
result, instead of specifying that the EA device's battery must
have a high capacity, e.g., greater than 200 mAh, with an internal
impedance of, e.g., less than 5 ohms, which would either require a
thicker battery and/or preclude the use of commercially-available
coin-cell batteries, the EA device of the present invention can
readily employ a battery having a relatively low capacity, e.g.,
less than 60 mAh, and a high battery impedance, e.g., greater than
5 ohms.
[0114] Advantageously, the power-monitoring, power-managing, as
well as the pulse generation, and control circuits used within the
EA device are relatively simple in design, and may be readily
fashioned from commercially-available integrated circuits (IC's) or
application-specific integrated circuits (ASIC's), supplemented
with discrete components, as needed. In other words, the electronic
circuits employed within the EA device need not be complex nor
expensive, but are simple and inexpensive, thereby making it easier
to manufacture and to provide the device to patients at an
affordable cost.
Definitions
[0115] As used herein, "annular", "circumferential",
"circumscribing", "surrounding" or similar terms used to describe
an electrode or electrode array, or electrodes or electrode arrays,
(where the phrase "electrode or electrode array," or "electrodes or
electrode arrays," is also referred to herein as "electrode/array,"
or "electrodes/arrays," respectively) refers to an electrode/array
shape or configuration that surrounds or encompasses a point or
object, such as another electrode, without limiting the shape of
the electrode/array or electrodes/arrays to be circular or round.
In other words, an "annular" electrode/array (or a
"circumferential" electrode/array, or a "circumscribing"
electrode/array, or a "surrounding" electrode/array), as used
herein, may be many shapes, such as oval, polygonal, starry, wavy,
and the like, including round or circular.
[0116] "Nominal" or "about" when used with a mechanical dimension,
e.g., a nominal diameter of 23 mm, means that there is a tolerance
associated with that dimension of no more than plus or minus (+/-)
5%. Thus, a dimension that is nominally 23 mm means a dimension of
23 mm+/-1.15 mm (0.05.times.23 mm=1.15 mm).
[0117] "Nominal" when used to specify a battery voltage is the
voltage by which the battery is specified and sold. It is the
voltage you expect to get from the battery under typical
conditions, and it is based on the battery cell's chemistry. Most
fresh batteries will produce a voltage slightly more than their
nominal voltage. For example, a new nominal 3 volt lithium
coin-sized battery will measure more than 3.0 volts, e.g., up to
3.6 volts under the right conditions. Since temperature affects
chemical reactions, a fresh warm battery will have a greater
maximum voltage than a cold one. For example, as used herein, a
"nominal 3 volt" battery voltage is a voltage that may be as high
as 3.6 volts when the battery is brand new, but is typically
between 2.7 volts and 3.4 volts, depending upon the load applied to
the battery (i.e., how much current is being drawn from the
battery) when the measurement is made and how long the battery has
been in use.
[0118] As explained in more detail below, an important aspect of
the invention recognizes that an electroacupuncture modulation
scheme, or other tissue stimulation scheme, need not be continuous,
thereby allowing the implanted device to use a small, high density,
power source to provide such non-continuous modulation. (Here, it
should be noted that "modulation," as that phrase is used herein,
is the application of electrical stimulation pulses, at low
intensities, low frequencies and low duty cycles, to at least one
of the target stimulation sites, e.g., an acupuncture site that has
been identified as affecting a particular condition of a patient.)
As a result, the device can be very small. And, because the
electrodes typically form an integral part of the housing of the
device, the device may thus be implanted directly at (or very near
to) the desired target tissue location.
Mechanical Design
[0119] Turning to FIG. 9, a small, implantable, electroacupuncture
device (IEAD) is shown in perspective view. Such device is designed
to be used to treat a disease, deficiency, or other medical
condition of a patient. The IEAD 100 may also sometimes be referred
to as an implantable electroacupuncture stimulator (IEAS). As seen
in FIG. 9, the IEAD 100 has the appearance of a disc or coin,
having a front side 106 (which is also labeled as the "Cathode
Side"), a back side (also referred to as the "Skin Side") 102
(which skin side is not visible in FIG. 1) and an edge side
104.
[0120] As used herein, the "front" side of the IEAD 100 is the side
that is positioned so as to face the target stimulation point
(e.g., the desired acupoint) where EA stimulation is to be applied
when the IEAD is implanted. The "back" side is the side opposite
the front side and is the farthest away from the target stimulation
point when the IEAD is implanted, and is usually the side closest
to the patient's skin. The "edge" of the IEAD is the side that
connects or joins the front side to the back side. In FIG. 1, the
IEAD 100 is oriented to show the front side 102 and a portion of
the edge side 104.
[0121] It should be noted here that throughout this application,
the terms IEAD 100, IEAD housing 100, bottom case 124, can 124, or
IEAD case 124, or similar terms, are used to describe the housing
structure of the EA device. In some instances it may appear these
terms are used interchangeably. However, the context should dictate
what is meant by these terms. As the drawings illustrate,
particularly FIG. 17, there is a bottom case 124 that comprises the
"can" or "container" wherein the components of the IEAD 100 are
first placed and assembled during manufacture of the IEAD 100. When
all of the components are assembled and placed within the bottom
case 124, a cover plate 122 is welded to the bottom case 124 to
form the hermetically-sealed housing of the IEAD. The cathode
electrode 110 is attached to the outside of the bottom case 124
(which is the front side 102 of the device), and the ring anode
electrode 120 is attached, along with its insulating layer 129,
around the perimeter edge 104 of the bottom case 124. Finally, a
layer of silicone molding 125 covers the IEAD housing except for
the outside surfaces of the anode ring electrode and the cathode
electrode.
[0122] The embodiment of the IEAD 100 shown in FIG. 9 utilizes two
electrodes, a cathode electrode 110 that is centrally positioned on
the front, or "cathode," side 106 of the IEAD 100, and an anode
electrode 120. The anode electrode 120 is a ring electrode that
fits around the perimeter edge 104 of the IEAD 100. Not visible in
FIG. 9, but which is described hereinafter in connection with the
description of FIG. 17, is a layer of insulating material 129 that
electrically insulates the anode ring electrode 120 from the
perimeter edge 104 of the housing or case 124.
[0123] Not visible in FIG. 9, but a key feature of the mechanical
design of the IEAD 100, is the manner in which an electrical
connection is established between the ring electrode 120 and
electronic circuitry carried inside of the IEAD 100. This
electrical connection is established using a radial feed-through
pin that fits within a recess formed in a segment of the edge of
the case 124, as explained more fully below in connection with the
description of FIGS. 15, 15A, 15B and 17.
[0124] In contrast to the feed-through pin that establishes
electrical contact with the anode electrode, electrical connection
with the cathode electrode 110 is established simply by forming or
attaching the cathode electrode 110 to the front surface 106 of the
IEAD case 124. In order to prevent the entire case 124 from
functioning as the cathode (which is done to better control the
electric fields established between the anode and cathode
electrodes), the entire IEAD housing is covered in a layer of
silicone molding 125 (see FIG. 17), except for the outside surface
of the anode ring electrode 120 and the cathode electrode 110.
[0125] One significant advantage of this electrode configuration is
that it is symmetrical. That is, when implanted, the surgeon or
other medical personnel performing the implant procedure, need only
assure that the cathode side of the IEAD 100, which (for the
embodiment shown in FIGS. 9-17) is the front side of the device,
faces the target tissue location that is to be stimulated. In
addition, the IEAD must be implanted over the desired acupoint, or
other tissue location, that is intended to receive the
electroacupuncture (EA) stimulation. The orientation of the IEAD
100 is otherwise not important.
[0126] FIG. 10 illustrates the location of an exemplary target
stimulation acupoint, e.g. acupoint PC6 located on the patient's
wrist, whereat the IEAD of FIG. 9 may be implanted for the
treatment of a particular disease or condition of the patient,
e.g., hypertension. Such location is representative of a wide
variety of acupoints, or other target tissue locations, whereat the
IEAD of FIG. 9 could be implanted.
[0127] An implanted IEAD 100 is illustrated generally in FIG. 11,
and the manner of implanting the IEAD 100 is illustrated in FIG.
10. FIG. 11 shows a sectional view of a limb 80 of the patient
wherein an acupoint 90 (e.g., acupoint PC6) has been identified
that is to receive acupuncture treatment (in this case
electroacupuncture treatment). An incision 84 (shown in FIG. 10) is
made into the limb 80 a short distance, e.g., 10-15 mm, away from
the acupoint 90. A slot (parallel to the limb) is formed at the
incision by lifting the skin closest to the acupoint up at the
incision. As necessary, the surgeon may form a pocket under the
skin at the acupoint location. The IEAD 100, with its top side 102
being closest to the skin (and thus also referred to as the "Skin
Side"), is then slid through the slot 84 into the pocket so that
the center of the IEAD is located under the acupoint 90 on the skin
surface. This implantation process is as easy as inserting a coin
into a slot. With the IEAD 100 in place, the incision 84 is sewn or
otherwise closed, leaving the IEAD 100 under the skin 80 at the
location of the acupoint 90 where electroacupuncture (EA)
stimulation is desired (shown in FIG. 11).
[0128] In this regard, it should be noted that while the target
stimulation point is generally identified by an "acupoint," which
is typically shown in drawings and diagrams as residing on the
surface of the skin, the surface of the skin is not the actual
target stimulation point. Rather, whether such stimulation
comprises manual manipulation of a needle inserted through the skin
at the location on the skin surface identified as an "acupoint", or
whether such stimulation comprises electrical stimulation applied
through an electrical field oriented to cause stimulation current
to flow through the tissue at a prescribed depth below the acupoint
location on the skin surface, the actual target tissue point to be
stimulated is located beneath the skin at a depth d2 (see FIG. 11)
that varies depending on the particular acupoint location. When
stimulation is applied at the target tissue point, such stimulation
is effective at treating a selected condition of the patient, e.g.,
high cholesterol, because there is something in the tissue at that
location, or near that location, such as a nerve, a tendon, a
muscle, or other type of tissue, that responds to the applied
stimulation in a manner that contributes favorably to the treatment
of the condition experienced by the patient.
[0129] FIG. 11 illustrates a sectional view of the IEAD 100
implanted so as to be centrally located under the skin at the
selected acupoint 90, and over the acupoint axis line 92. Usually,
for most patients, the IEAD 100 is implanted at a depth d1 of
approximately 2-4 mm under the skin. The top (skin) side 102 of the
IEAD is nearest to the skin of the limb 80 of the patient. The
bottom (cathode) side 106 of the IEAD, which is the side on which
the central cathode electrode 110 resides, is farthest from the
skin. Because the cathode electrode 110 is centered on the bottom
of the IEAD, and because the IEAD 100 is implanted so as to be
centered under the location on the skin where the acupoint 90 is
located, the cathode 110 is also centered over the acupoint axis
line 92.
[0130] FIG. 11 further illustrates the electric field gradient
lines 88 that are created in the body tissue 86 surrounding the
acupoint 90 and the acupoint axis line 92. (Note: for purposes
herein, when reference is made to providing EA stimulation at a
specified acupoint, it is understood that the EA stimulation is
provided at a depth of approximately d2 below the location on the
skin surface where the acupoint is indicated as being located.) As
seen in FIG. 1B, the electric field gradient lines are strongest
along a line that coincides with, or is near to, the acupoint axis
line 92. It is thus seen that one of the main advantages of using a
symmetrical electrode configuration that includes a centrally
located electrode surrounded by an annular electrode is that the
precise orientation of the IEAD within its implant location is not
important. So long as one electrode is centered over the desired
target location, and the other electrode surrounds the first
electrode (e.g., as an annular electrode), a strong electric field
gradient is created that is aligned with the acupoint axis line.
This causes the EA stimulation current to flow along (or very near)
the acupoint axis line 92, and will result in the desired EA
stimulation in the tissue at a depth d2 below the acupoint location
indicated on the skin.
[0131] FIG. 12 shows a plan view of the "front" (or "cathode") side
106 of the IEAD 100. As seen in FIG. 12, the cathode electrode 110
appears as a circular electrode, centered on the front side, having
a diameter D1. The IEAD housing has a diameter D2 and an overall
thickness or width W2. For the preferred embodiment shown in these
figures, D1 is about 4 mm, D2 is about 23 mm and W2 is a little
over 2 mm (2.2 mm).
[0132] FIG. 12A shows a side view of the IEAD 100. The ring anode
electrode 120, best seen in FIG. 12A, has a width W1 of about 1.0
mm, or approximately 1/2 of the width W2 of the IEAD.
[0133] FIG. 13 shows a plan view of the "back" (or "skin") side of
the IEAD 100. As will be evident from subsequent figure
descriptions, e.g., FIGS. 15A and 15B, the back side of the IEAD
100 comprises a cover plate 122 that is welded in place once the
bottom case 124 has all of the electronic circuitry, and other
components, placed inside of the housing.
[0134] FIG. 13A is a sectional view of the IEAD 100 taken along the
line A-A of FIG. 13. Visible in this sectional view is the
feed-through pin 130, including the distal end of the feed-through
pin 130 attached to the ring anode electrode 120. Also visible in
this section view is an electronic assembly 133 on which various
electronic components are mounted, including a disc-shaped battery
132. FIG. 13A further illustrates how the cover plate 122 is
welded, or otherwise bonded, to the bottom case 124 in order to
form the hermetically-sealed IEAD housing 100.
[0135] FIG. 14 shows a perspective view of the IEAD case 124,
including the feed-through pin 130, before the electronic
components are placed therein, and before being sealed with the
"skin side" cover plate 122. The case 124 is similar to a shallow
"can" without a lid, having a short side wall around its perimeter.
Alternatively, the case 124 may be viewed as a short cylinder,
closed at one end but open at the other. (Note, in the medical
device industry the housing of an implanted device is often
referred to as a "can".) The feed-through pin 130 passes through a
segment of the wall of the case 124 that is at the bottom of a
recess 140 formed in the wall. The use of this recess 140 to hold
the feed-through pin 130 is a key feature of the invention because
it keeps the temperature-sensitive portions of the feed-through
assembly (those portions that could be damaged by excessive heat)
away from the thermal shock and residual weld stress inflicted upon
the case 124 when the cover plate 122 is welded thereto.
[0136] FIG. 14A is a side view of the IEAD case 124, and shows an
annular rim 126 formed on both sides of the case 124. The ring
anode electrode 120 fits between these rims 126 once the ring
electrode 120 is positioned around the edge of the case 124. (This
ring electrode 120 is, for most configurations, used as an anode
electrode. Hence, the ring electrode 120 may sometimes be referred
to herein as a ring anode electrode. However, it is noted that the
ring electrode could also be employed as a cathode electrode, if
desired.) A silicone insulator layer 129 (see FIG. 17) is placed
between the backside of the ring anode electrode 120 and the
perimeter edge of the case 124 where the ring anode electrode 120
is placed around the edge of the case 124.
[0137] FIG. 15 shows a plan view of the empty IEAD case 124 shown
in the perspective view of FIG. 14. An outline of the recess cavity
140 is also seen in FIG. 15, as is the feed-through pin 130. A
bottom edge of the recess cavity 140 is located a distance D5
radially inward from the edge of the case 124. In one embodiment,
the distance D5 is between about 2.0 to 2.5 mm. The feed-through
pin 130, which is just a piece of solid wire, is shown in FIG. 15
extending radially outward from the case 124 above the recess
cavity 140 and radially inward from the recess cavity towards the
center of the case 124. The length of this feed-through pin 130 is
trimmed, as needed, when a distal end (extending above the recess)
is connected (welded) to the anode ring electrode 120 (passing
through a hole in the ring electrode 120 prior to welding) and when
a proximal end of the feed-through pin 130 is connected to an
output terminal of the electronic assembly 133.
[0138] FIG. 15A depicts a sectional view of the IEAD housing 124 of
FIG. 15 taken along the section line A-A of FIG. 15. FIG. 15B shows
an enlarged view or detail of the portion of FIG. 15A that is
encircled with the line B. Referring to FIGS. 15A and 15B jointly,
it is seen that the feed-through pin 130 is embedded within an
insulator material 136, which insulating material 136 has a
diameter of D3. The feed-through pin assembly (which pin assembly
comprises the combination of the pin 130 embedded into the
insulator material 136) resides on a shoulder around an opening or
hole formed in the bottom of the recess 140 having a diameter D4.
For the embodiment shown in FIGS. 15A and 15B, the diameter D3 is
0.95-0.07 mm, where the -0.07 mm is a tolerance. (Thus, with the
tolerance considered, the diameter D3 may range from 0.88 mm to
0.95 mm) The diameter D4 is 0.80 mm with a tolerance of -0.06 mm.
(Thus, with the tolerance considered, the diameter D4 could range
from 0.74 mm to 0.80 mm).
[0139] The feed-through pin 130 is preferably made of pure platinum
99.95%. A preferred material for the insulator material 136 is Ruby
or alumina. The IEAD case 124, and the cover 122, are preferably
made from titanium. The feed-through assembly, including the
feed-through pin 130, ruby/alumina insulator 136 and the case 124
are hermetically sealed as a unit by gold brazing. Alternatively,
active metal brazing can be used. (Active metal brazing is a form
of brazing which allows metal to be joined to ceramic without
metallization.)
[0140] The hermeticity of the sealed IEAD housing is tested using a
helium leak test, as is common in the medical device industry. The
helium leak rate should not exceed 1.times.10.sup.-9 STD cc/sec at
1 atm pressure. Other tests are performed to verify the case-to-pin
resistance (which should be at least 15.times.10.sup.6 Ohms at 100
volts DC), the avoidance of dielectric breakdown or flashover
between the pin and the case 124 at 400 volts AC RMS at 60 Hz and
thermal shock.
[0141] One important advantage provided by the feed-through
assembly shown in FIGS. 14A, 15, 15A and 15B is that the
feed-through assembly made from the feed-through pin 130, the ruby
insulator 136 and the recess cavity 140 (formed in the case
material 124) may be fabricated and assembled before any other
components of the IEAD 100 are placed inside of the IEAD case 124.
This advantage greatly facilitates the manufacture of the IEAD
device.
[0142] Turning next to FIG. 16, there is shown a perspective view
of an electronic assembly 133. The electronic assembly 133 includes
a multi-layer printed circuit (pc) board 138, or equivalent
mounting structure, on which a battery 132 and various electronic
components 134 are mounted. This assembly is adapted to fit inside
of the empty bottom housing 124 of FIG. 14 and FIG. 15.
[0143] FIGS. 16A and 16B show a plan view and side view,
respectively, of the electronic assembly 133 shown in FIG. 16. The
electronic components are assembled and connected together so as to
perform the circuit functions needed for the IEAD 100 to perform
its intended functions. These circuit functions are explained in
more detail below under the sub-heading "Electrical Design".
Additional details associated with these functions may also be
found in Applicant's Parent Application(s) referenced above in the
first paragraph.
[0144] FIG. 17 shows an exploded view of the complete IEAD 100,
illustrating its main constituent parts. As seen in FIG. 17, the
IEAD 100 includes, starting on the right and going left, a cathode
electrode 110, a ring anode electrode 120, an insulating layer 129,
the bottom case 124 (the "can" portion of the IEAD housing, and
which includes the feed-through pin 130 which passes through an
opening in the bottom of the recess 140 formed as part of the case,
but wherein the feed-through pin 130 is insulated and does not make
electrical contact with the metal case 124 by the ruby or alumina
insulator 136), the electronic assembly 133 (which includes the
battery 132 and various electronic components 134 mounted on a pc
board 138) and the cover plate 122. The cover plate 122 is welded
to the edge of the bottom case 124 using laser beam welding, or
some equivalent process, as one of the final steps in the assembly
process.
[0145] Other components included in the IEAD assembly, but not
necessarily shown or identified in FIG. 17, include adhesive
patches for bonding the battery 132 to the pc board 138 of the
electronic assembly 133, and for bonding the electronic assembly
133 to the inside of the bottom of the case 124. To prevent high
temperature exposure of the battery 132 during the assembly
process, conductive epoxy is used to connect a battery terminal to
the pc board 138. Because the curing temperature of conductive
epoxy is 125.degree. C., the following process is used: (a) first
cure the conductive epoxy of a battery terminal ribbon to the pc
board without the battery, (b) then glue the battery to the pc
board using room temperature cure silicone, and (c) laser tack weld
the connecting ribbon to the battery.
[0146] Also not shown in FIG. 17 is the manner of connecting the
proximal end of the feed-through pin 130 to the pc board 138, and
connecting a pc board ground pad to the case 124. A preferred
method of making these connections is to use conductive epoxy and
conductive ribbons, although other connection methods known in the
art may also be used.
[0147] Further shown in FIG. 17 is a layer of silicon molding 125
that is used to cover all surfaces of the entire IEAD 100 except
for the anode ring electrode 120 and the circular cathode electrode
110. An overmolding process is used to accomplish this, although
overmolding using silicone LSR 70 (curing temperature of
120.degree. C.) with an injection molding process cannot be used.
Overmolding processes that may be used include: (a) molding a
silicone jacket and gluing the jacket onto the case using room
temperature cure silicone (RTV) inside of a mold, and curing at
room temperature; (b) injecting room temperature cure silicone in a
PEEK or Teflon.RTM. mold (silicone will not stick to the
Teflon.RTM. or PEEK material); or (c) dip coating the IEAD 100 in
room temperature cure silicone while masking the electrode surfaces
that are not to be coated. (Note: PEEK is a well-known
semicrystalline thermoplastic with excellent mechanical and
chemical resistance properties that are retained at high
temperatures.)
[0148] When assembled, the insulating layer 129 is positioned
underneath the ring anode electrode 120 so that the anode electrode
does not short to the case 124. The only electrical connection made
to the anode electrode 120 is through the distal tip of the
feed-through pin 130. The electrical contact with the cathode
electrode 110 is made through the case 124. However, because the
entire IEAD is coated with a layer of silicone molding 125, except
for the anode ring electrode 120 and the circular cathode electrode
110, all stimulation current generated by the IEAD 100 must flow
between the exposed surfaces of the anode and cathode.
[0149] It is noted that while the preferred configuration described
herein uses a ring anode electrode 120 placed around the edges of
the IEAD housing, and a circular cathode electrode 110 placed in
the center of the cathode side of the IEAD case 124, such an
arrangement could be reversed, i.e., the ring electrode could be
the cathode, and the circular electrode could be the anode.
[0150] Moreover, the location and shape of the electrodes may be
configured differently than is shown in the one preferred
embodiment described above in connection with the specific example
described in FIGS. 9, and 12-17. For example, the ring anode
electrode 120 need not be placed around the perimeter of the
device, but such electrode may be a flat circumferential electrode
that assumes different shapes (e.g., round or oval) that is placed
on the front or back surface of the IEAD so as to surround the
central electrode. Further, for some embodiments, the surfaces of
the anode and cathode electrodes may have convex surfaces.
[0151] It is also noted that while one preferred embodiment has
been disclosed herein that incorporates a round, or short
cylindrical-shaped housing, also referred to as a coin-shaped
housing, the invention does not require that the case 124 (which
may also be referred to as a "container"), and its associated cover
plate 122, be round. The case could just as easily be an
oval-shaped, rectangular-shaped (e.g., square with smooth corners),
polygonal-shaped (e.g., hexagon-, octagon-, pentagon-shaped),
button-shaped (with convex top or bottom for a smoother profile)
device. Any of these alternate shapes, or others, would still
permit the basic principles of the invention to be used to provide
a robust, compact, thin, case to house the electronic circuitry and
power source used by the invention; as well as to help protect a
feed-through assembly from being exposed to excessive heat during
assembly, and to allow the thin device to provide the benefits
described herein related to its manufacture, implantation and use.
For example, as long as the device remains relatively thin, e.g.,
no more than about 2-3 mm, and does not have a maximum linear
dimension greater than about 25 mm, then the device can be readily
implanted in a pocket over the tissue area where the selected
acupoint(s) is located. As long as there is a recess in the wall
around the perimeter of the case wherein the feed-through assembly
may be mounted, which recess effectively moves the wall or edge of
the case inwardly into the housing a safe thermal distance, as well
as a safe residual weld stress distance, from the perimeter wall
where a hermetically-sealed weld occurs, the principles of the
invention apply.
[0152] Further, it should be noted that while the preferred
configuration of the IEAD described herein utilizes a central
electrode on one of its surfaces that is round, having a diameter
of nominally 4 mm, such central electrode need not necessarily be
round. It could be oval shaped, polygonal-shaped, or shaped
otherwise, in which case its size is best defined by its maximum
width, which will generally be no greater than about 7 mm.
[0153] Finally, it is noted that the electrode arrangement may be
modified somewhat, and the desired attributes of the invention may
still be achieved. For example, as indicated previously, one
preferred electrode configuration for use with the invention
utilizes a symmetrical electrode configuration, e.g., an annular
electrode of a first polarity that surrounds a central electrode of
a second polarity. Such a symmetrical electrode configuration makes
the implantable electroacupuncture device (IEAD) relatively immune
to being implanted in an improper orientation relative to the body
tissue at the selected acupoint(s) that is being stimulated.
However, an electrode configuration that is not symmetrical may
still be used and many of the therapeutic effects of the invention
may still be achieved. For example, two spaced-apart electrodes on
a front surface of the housing, one of a first polarity, and a
second of a second polarity, could still, when oriented properly
with respect to a selected acupoint tissue location, provide some
desired therapeutic results.
[0154] FIG. 17A schematically illustrates a few alternative
electrode configurations that may be used with the invention. The
electrode configuration schematically shown in the upper left
corner of FIG. 17A, identified as "I", schematically illustrates
one central electrode 110 surrounded by a single round ring
electrode 120. This is one of the preferred electrode
configurations that has been described previously in connection,
e.g., with the description of FIGS. 9, 10, 11 and 17, and is
presented in FIG. 17A for reference and comparative purposes.
[0155] In the lower left corner of FIG. 17A, identified as "II", an
electrode/array configuration is schematically illustrated that has
a central electrode 310 of a first polarity surrounded by an
oval-shaped electrode array 320a of two electrodes of a second
polarity. (This oval-shaped array 320a could also be round.) When
the two electrodes (of the same polarity) in the electrode array
320a are properly aligned with the body tissue being stimulated,
e.g., aligned with a nerve underlying the desired acupoint, then
such electrode configuration can stimulate the body tissue (e.g.,
the underlying nerve) at or near the desired acupoint(s) with the
same, or almost the same, efficacy as can the electrode
configuration I (upper right corner of FIG. 17A).
[0156] Note, as has already been described above, the phrase
"electrode or electrode array," or "electrodes or electrode
arrays," may also be referred to herein as "electrode/array" or
"electrodes/arrays," respectively. For the ease of explanation,
when an electrode array is referred to herein that comprises a
plurality (two or more) of individual electrodes of the same
polarity, the individual electrodes of the same polarity within the
electrode array may also be referred to as "individual electrodes",
"segments" of the electrode array, "electrode segments", or just
"segments".
[0157] In the lower right corner of FIG. 17A, identified as "III",
an electrode configuration is schematically illustrated that has a
round central electrode/array 310b of three electrode segments of a
first polarity surrounded by an electrode array 320b of three
electrode segments of a second polarity. (These round or oval
shapes could be altered, al s desired or needed. That is, the round
central electrode/array 310b could be an oval-shaped electrode
array, and the oval-shaped electrode array 320b could be a round
electrode array.) As shown in configuration III of FIG. 17A, the
three electrode segments of the electrode array 320b are
symmetrically positioned within the array 320b, meaning that they
are positioned more or less equidistant from each other. However, a
symmetrical positioning of the electrode segments within the array
is not necessary to stimulate the body tissue at the desired
acupoint(s) with some efficacy.
[0158] In the upper right corner of FIG. 17A, identified as "IV",
an electrode/array configuration is schematically illustrated that
has a central electrode array 310c of a first polarity surrounded
by an electrode array 320c of four electrode segments of a second
polarity. The four electrode segments of the electrode array 320c
are arranged symmetrically in a round or oval-shaped array. The
four electrode segments of the electrode array 310c are likewise
arranged symmetrically in a round or oval-shaped array. While
preferred for many configurations, the use of a symmetrical
electrode/array, whether as a central electrode array 310 or as a
surrounding electrode/array 320, is not always required.
[0159] The electrode configurations I, II, III and IV shown
schematically in FIG. 17A are only representative of a few
electrode configurations that may be used with the present
invention. Further, it is to be noted that the central
electrode/array 310 need not have the same number of electrode
segments as does the surrounding electrode/array 320. Typically,
the central electrode/array 310 of a first polarity will be a
single electrode; whereas the surrounding electrode/array 320 of a
second polarity may have n individual electrode segments, where n
is an integer that can vary from 1, 2, 3, . . . n. Thus, for a
circumferential electrode array where n=4, there are four electrode
segments of the same polarity arranged in circumferential pattern
around a central electrode/array. If the circumferential electrode
array with n=4 is a symmetrical electrode array, then the four
electrode segments will be spaced apart equally in a
circumferential pattern around a central electrode/array. When n=1,
the circumferential electrode array reduces to a single
circumferential segment or a single annular electrode that
surrounds a central electrode/array.
[0160] Additionally, the polarities of the electrode/arrays may be
selected as needed. That is, while the central electrode/array 310
is typically a cathode (-), and the surrounding electrode/array 320
is typically an anode (+), these polarities may be reversed.
[0161] As has already been mentioned, the shape of the
circumferential electrode/array, whether circular, oval, or other
shape, need not necessarily be the same shape as the IEAD housing,
unless the circumferential electrode/array is attached to a
perimeter edge of the IEAD housing. The IEAD housing may be round,
or it may be oval, or it may have a polygon shape, or other shape,
as needed to suit the needs of a particular manufacturer and/or
patient.
[0162] Additional electrode configurations, both symmetrical
electrode configurations and non-symmetrical electrode
configurations, that may be used with an EA stimulation device as
described herein, are illustrated in Appendix A and Appendix B.
Electrical Design
[0163] Next, with reference to specific example presented in
connection with FIGS. 18-22, the electrical design and operation of
the circuits employed within the implantable electroacupuncture
device (IEAD) 100 will be described. Such circuits advantageously
allow a relatively inexpensive, thin, high impedance, coin-cell
type battery to be employed within the IEAD to provide its
operating power for the IEAD over a long period of time. More
details associated with the design of the electrical circuits
described herein may be found in Applicant's previously-filed
Parent Application(s).
[0164] FIG. 18 shows a functional block diagram of an IEAD 100 made
in accordance with the teachings disclosed herein. As seen in FIG.
18, the IEAD 100 uses an implantable battery 215 having a battery
voltage V.sub.BAT. In one preferred embodiment, this battery 215
comprises a lithium battery having a nominal output voltage of 3 V,
such as the CR1612 battery manufactured by Panasonic. Also included
within the IEAD 100 is a Boost Converter circuit 200, an Output
Circuit 202 and a Control Circuit 210. The battery 115, boost
converter circuit 200, output circuit 202 and control circuit 210
are all housed within an hermetically sealed housing 124.
[0165] As controlled by the control circuit 210, the output circuit
202 of the IEAD 100 generates a sequence of stimulation pulses that
are delivered to electrodes E1 and E2, through feed-through
terminals 206 and 207, respectively, in accordance with a
prescribed stimulation regimen. A coupling capacitor C.sub.C is
also employed in series with at least one of the feed-through
terminals 206 or 207 to prevent DC (direct current) current from
flowing into the patient's body tissue.
[0166] As illustrated in the timing waveform diagrams of FIGS. 8
and 8A, a typical stimulation regimen comprises a continuous stream
of stimulation pulses having a fixed amplitude, A1 (which may be
expressed in voltage or current), a fixed pulse width T1, e.g., 0.5
millisecond, and at a fixed frequency f1, e.g., 2 Hz (where the
frequency f1 is the inverse of the stimulation period T2, or
f1=1/T2), during each stimulation session. The stimulation session,
also as part of the stimulation regimen, has a duration T3, and is
generated at a very low duty cycle, e.g., for 30 minutes once each
week. The frequency of the stimulation sessions occurs once every
T4 minutes. For example, if the duration of the stimulation session
is 30 minutes, or T3=30 minutes, then T4 defines how often (or how
infrequently) a stimulation session lasting T3 minutes occurs.
Typically, the time T4 will be at least 24 hours (which is 1440
minutes), and may be as long as 20,160 minutes (2 weeks), and
typically will be on the order of 10,080 minutes (1 week). Other
stimulation regimens may also be used, e.g., using a variable
frequency for the stimulus pulse during a stimulation session
rather than a fixed frequency. Also, the rate of occurrence of the
stimulation session may be varied, e.g., particularly at startup,
so that T4 initially starts as short as, e.g., 1 day, and gradually
ramps over a period of one or two weeks to a value as long as,
e.g., 14 days.
[0167] In the specific example described here, the electrodes E1
and E2 form an integral part of the housing 124. That is, electrode
E2 may comprise a circumferential anode electrode that surrounds a
cathode electrode E1. The cathode electrode E1, for the embodiment
described here, is electrically connected to the case 124 (thereby
making the feed-through terminal 206 unnecessary).
[0168] In a second preferred embodiment, particularly well-suited
for implantable electrical stimulation devices, the anode electrode
E2 is electrically connected to the case 124 (thereby making the
feed-through terminal 207 unnecessary). The cathode electrode E1 is
electrically connected to the circumferential electrode that
surrounds the anode electrode E2. That is, the stimulation pulses
delivered to the target tissue location (i.e., to the selected
acupoint) through the electrodes E1 and E2 are, relative to a zero
volt ground (GND) reference, negative stimulation pulses, as shown
in the waveform diagram near the lower right hand corner of FIG.
18.
[0169] Thus, in the embodiment described in FIG. 18, it is seen
that during a stimulation pulse the electrode E2 functions as an
anode, or positive (+) electrode, and the electrode E1 functions as
a cathode, or negative (-) electrode.
[0170] The battery 115 provides all of the operating power needed
by the EA device 100. The battery voltage V.sub.BAT is not the
optimum voltage needed by the circuits of the EA device, including
the output circuitry, in order to efficiently generate stimulation
pulses of amplitude, e.g., -V.sub.A volts. The amplitude V.sub.A of
the stimulation pulses is typically many times greater than the
battery voltage V.sub.BAT. This means that the battery voltage must
be "boosted", or increased, in order for stimulation pulses of
amplitude V.sub.A to be generated. Such "boosting" is done using
the boost converter circuit 200. That is, it is the function of the
Boost Converter circuit 200 to take its input voltage, V.sub.BAT,
and convert it to another voltage, e.g., V.sub.OUT, which voltage
V.sub.OUT is needed by the output circuit 202 in order for the IEAD
100 to perform its intended function.
[0171] The IEAD 100 shown in FIG. 18, and packaged as described
above in connection with FIGS. 9-17, advantageously provides a tiny
self-contained, coin-sized stimulator that may be implanted in a
patient at or near a specified acupoint in order to favorably treat
a condition or disease of a patient. The coin-sized stimulator
advantageously applies electrical stimulation pulses at very low
levels and low duty cycles in accordance with specified stimulation
regimens through electrodes that form an integral part of the
housing of the stimulator. A tiny coin-cell type battery inside of
the coin-sized stimulator provides enough energy for the stimulator
to carry out its specified stimulation regimen over a period of
several years, despite the fact that the battery typically has a
relatively high battery impedance, e.g., greater than 5 ohms, and
often as high as 150 ohms, or more. Thus, the coin-sized
stimulator, once implanted, provides an unobtrusive, needleless,
long-lasting, safe, elegant and effective mechanism for treating
certain conditions and diseases that have long been treated by
acupuncture or electroacupuncture.
[0172] A boost converter integrated circuit (IC) typically draws
current from its power source in a manner that is proportional to
the difference between the actual output voltage V.sub.OUT and a
set point output voltage, or feedback signal. A representative
boost converter circuit that operates in this manner is shown in
FIG. 19. At boost converter start up, when the actual output
voltage is low compared to the set point output voltage, the
current drawn from the power source can be quite large.
Unfortunately, when batteries are used as power sources, they have
internal voltage losses (caused by the battery's internal
impedance) that are proportional to the current drawn from them.
This can result in under voltage conditions when there is a large
current demand from the boost converter at start up or at high
instantaneous output current. Current surges and the associated
under voltage conditions can lead to undesired behavior and reduced
operating life of an implanted electro-acupuncture device.
[0173] In the boost converter circuit example shown in FIG. 19, the
battery is modeled as a voltage source with a simple series
resistance. With reference to the circuit shown in FIG. 19, when
the series resistance R.sub.BAT is small (5 Ohms or less), the
boost converter input voltage V.sub.IN, output voltage V.sub.OUT
and current drawn from the battery, I.sub.BAT, typically look like
the waveform shown in FIG. 19A, where the horizontal axis is time,
and the vertical axis on the left is voltage, and the vertical axis
of the right is current.
[0174] Referring to the waveform in FIG. 19A, at boost converter
startup (10 ms), there is 70 mA of current drawn from the battery
with only -70 mV of drop in the input voltage V.sub.IN. Similarly,
the instantaneous output current demand for electro-acupuncture
pulses draws up to 40 mA from the battery with an input voltage
drop of -40 mV.
[0175] Disadvantageously, however, a battery with higher internal
impedance (e.g., 160 Ohms), cannot source more than a milliampere
or so of current without a significant drop in output voltage. This
problem is depicted in the timing waveform diagram shown in FIG.
19B. In FIG. 19B, as in FIG. 19A, the horizontal axis is time, the
left vertical axis is voltage, and the right vertical axis is
current.
[0176] As seen in FIG. 19B, as a result of the higher internal
battery impedance, the voltage at the battery terminal (V.sub.IN)
is pulled down from 2.9 V to the minimum input voltage of the boost
converter (-1.5 V) during startup and during the instantaneous
output current load associated with electro-acupuncture stimulus
pulses. The resulting drops in output voltage V.sub.OUT are not
acceptable in any type of circuit except an uncontrolled oscillator
circuit.
[0177] Also, it should be noted that although the battery used in
the boost converter circuit is modeled in FIG. 19 as a simple
series resistor, battery impedance can arise from the internal
design, battery electrode surface area and different types of
electrochemical reactions. All of these contributors to battery
impedance can cause the voltage of the battery at the battery
terminals to decrease as the current drawn from the battery
increases.
[0178] In a suitably small and thin implantable electroacupuncture
device (IEAD) of the type disclosed herein, it is desired to use a
higher impedance battery in order to assure a small and thin
device, keep costs low, and/or to have low self-discharge rates.
The battery internal impedance also typically increases as the
battery discharges. This can limit the service life of the device
even if a new battery has acceptably low internal impedance. Thus,
it is seen that for the IEAD 100 disclosed herein to reliably
perform its intended function over a long period of time, a circuit
design is needed for the boost converter circuit that can manage
the instantaneous current drawn from V.sub.IN of the battery. Such
current management is needed to prevent the battery's internal
impedance from causing V.sub.IN to drop to unacceptably low levels
as the boost converter circuit pumps up the output voltage
V.sub.OUT and when there is high instantaneous output current
demand, as occurs when stimulation pulses are generated.
[0179] To provide this needed current management, the IEAD 100
disclosed herein employs electronic circuitry as shown in FIG. 20,
or equivalents thereof. Similar to what is shown in FIG. 18, the
circuitry of FIG. 20 includes a battery, a boost converter circuit
200, an output circuit 230, and a control circuit 220. The control
circuit 220 generates a digital control signal that is used to duty
cycle the boost converter circuit 200 ON and OFF in order to limit
the instantaneous current drawn from the battery. That is, the
digital control signal pulses the boost converter ON for a short
time, but then shuts the boost converter down before a significant
current can be drawn from the battery. In conjunction with such
pulsing, an input capacitance C.sub.F is used to reduce the ripple
in the input voltage V.sub.IN. The capacitor C.sub.F supplies the
high instantaneous current for the short time that the boost
converter is ON and then recharges more slowly from the battery
during the interval that the boost converter is OFF.
[0180] A variation of the above-described use of a digital control
signal to duty cycle the boost converter circuit 200 ON and OFF is
to let the digital control be generated within the boost converter
200 itself (without having to use a separate control circuit 220).
In accordance with this variation, the boost converter circuit 200
shuts itself down whenever the battery voltage falls below a
predetermined level above that required by the remaining circuitry.
For example, the MAX8570 boost converter IC, commercially available
from Maxim, shuts down when the applied voltage falls below 2.5 V.
This is still a high enough voltage to ensure the microprocessor
and other circuitry remain operational. Thus, as soon as the input
voltage drops below 2.5 volts, the boost converter circuit shuts
down, thereby limiting the instantaneous current drawn from the
battery. When the boost converter shuts down, the instantaneous
battery current drawn from the battery is immediately reduced a
significant amount, thereby causing the input voltage to increase.
The boost converter remains shut down until the microprocessor
(e.g., the circuit U2 shown in FIG. 21, described below), and/or
other circuitry used with the boost converter, determine that it is
time to turn the boost converter back ON. Once turned ON, the boost
converter remains ON until, again, the input voltage drops to below
2.5 volts. This pattern continues, with the boost converter being
ON for a short time, and OFF for a much longer time, thereby
controlling and limiting the amount of current that can be drawn
from the battery. 2
[0181] In the circuitry shown in FIG. 20, it is noted that the
output voltage V.sub.OUT generated by the boost converter circuit
200 is set by the reference voltage V.sub.REF applied to the set
point or feedback terminal of the boost converter circuit 200. For
the configuration shown in FIG. 20, V.sub.REF is proportional to
the output voltage V.sub.OUT, as determined by the resistor
dividing network of R1 and R2.
[0182] The switches S.sub.P and S.sub.R, shown in FIG. 20 as part
of the output circuit 230, are also controlled by the control
circuit 220. These switches are selectively closed and opened to
form the EA stimulation pulses applied to the load, R.sub.LOAD.
Before a stimulus pulse occurs, switch S.sub.R is closed
sufficiently long for the circuit side of coupling capacitor
C.sub.C to be charged to the output voltage, V.sub.OUT. The tissue
side of C.sub.C is maintained at 0 volts by the cathode electrode
E2, which is maintained at ground reference. Then, for most of the
time between stimulation pulses, both switches S.sub.R and S.sub.P
are kept open, with a voltage approximately equal to the output
voltage V.sub.OUT appearing across the coupling capacitor
C.sub.C.
[0183] At the leading edge of a stimulus pulse, the switch S.sub.P
is closed, which immediately causes a negative voltage -V.sub.OUT
to appear across the load, R.sub.LOAD, causing the voltage at the
anode E1 to also drop to approximately -V.sub.OUT, thereby creating
the leading edge of the stimulus pulse. This voltage starts to
decay back to 0 volts as controlled by an RC (resistor-capacitance)
time constant that is long compared with the desired pulse width.
At the trailing edge of the pulse, before the voltage at the anode
E1 has decayed very much, the switch S.sub.P is open and the switch
S.sub.R is closed. This action causes the voltage at the anode E1
to immediately (relatively speaking) return to 0 volts, thereby
defining the trailing edge of the pulse. With the switch S.sub.R
closed, the charge on the circuit side of the coupling capacitor
C.sub.C is allowed to charge back to V.sub.OUT within a time period
controlled by a time constant set by the values of capacitor
C.sub.C and resistor R3. When the circuit side of the coupling
capacitor C.sub.C has been charged back to V.sub.OUT, then switch
S.sub.R is opened, and both switches S.sub.R and S.sub.P remain
open until the next stimulus pulse is to be generated. Then the
process repeats each time a stimulus pulse is to be applied across
the load.
[0184] Thus, it is seen that in one embodiment of the electronic
circuitry used within the IEAD 100, as shown in FIG. 20, a boost
converter circuit 200 is employed which can be shut down with a
control signal. The control signal is ideally a digital control
signal generated by a control circuit 220 (which may be realized
using a microprocessor or equivalent circuit). The control signal
is applied to the low side (ground side) of the boost converter
circuit 200 (identified as the "shutdown" terminal in FIG. 20). A
capacitor C.sub.F supplies instantaneous current for the short ON
time that the control signal enables the boost converter circuit to
operate. And, the capacitor CF is recharged from the battery during
the relatively long OFF time when the control signal disables the
boost converter circuit.
[0185] It is also seen that in a variation of the embodiment shown
in FIG. 20, a boost converter circuit 200 is used that shuts itself
down whenever the input voltage falls below a prescribed threshold,
e.g., 2.5 V. The boost converter remains shut down until other
circuitry used with the boost converter determines that it is time
to turn the boost converter back ON, e.g., whenever the feedback
signal indicates the output voltage V.sub.OUT has fallen below a
prescribed threshold, and/or whenever a prescribed period of time
has elapsed since the last stimulus pulse was generated.
[0186] One preferred circuit implementation of the embodiment of
the circuitry shown in FIG. 20 is shown in the schematic diagram
presented in FIG. 21. That is, the circuitry depicted in the
schematic diagram of FIG. 21 performs all of the functions
illustrated in connection with the functional circuitry illustrated
in FIG. 20. Additionally, the circuitry shown In FIG. 21 provides a
few other additional features not necessarily evident from the
functional diagram of FIG. 20, but which features nonetheless
contribute to the overall utility and functionality of the IEAD
circuitry shown in FIG. 21.
[0187] There are five integrated circuits (ICs) used as the main
components of the IEAD circuitry shown in FIG. 21. The IC U1 is a
boost converter circuit, and performs the function of the boost
converter circuit 200 described previously in connection with FIGS.
19 and 20.
[0188] Still referring to FIG. 21, the IC U2 is a micro-controller
IC and is used to perform the function of the control circuit 210
described previously in connection with FIG. 18, or the control
circuit 220 described previously in connection with FIG. 20. A
preferred IC for this purpose is a MS.sub.P430G24521
micro-controller chip made by Texas Instruments. This chip includes
8 KB of Flash memory. Having some memory included with the
micro-controller is important because it allows the parameters
associated with a selected stimulation regimen to be defined and
stored. One of the advantages of the IEAD described herein is that
it provides a stimulation regimen that can be defined with just 5
parameters, which five parameters are clearly evident from the
timing waveform diagrams of FIGS. 8 and 8A, and their accompanying
descriptions. This allows the programming features of the
micro-controller to be carried out in a simple and straightforward
manner.
[0189] The micro-controller U2 primarily performs the function of
generating the digital signal (when used) that shuts down the boost
converter circuit to prevent too much instantaneous current from
being drawn from the battery V.sub.BAT, or performs other functions
related to controlling and managing the power consumed within the
IEAD 100. The micro-controller U2 also controls the generation of
the stimulus pulses at the desired pulse width and frequency. It
further keeps track of the time periods associated with a
stimulation session, i.e., when a stimulation session begins and
when it ends.
[0190] The micro-controller U2 also controls the amplitude of the
stimulus pulse. This is done by adjusting the value of a current
generated by a Programmable Current Source U3. In one embodiment,
U3 is realized with a voltage controlled current source IC. In such
a voltage controlled current source, the programmed current is set
by a programmed voltage appearing across a fixed resistor R5, i.e.,
the voltage appearing at the "OUT" terminal of U3. This programmed
voltage, in turn, is set by the voltage applied to the "SET"
terminal of U3. That is, the programmed current source U3 sets the
voltage at the "OUT" terminal to be equal to the voltage applied to
the "SET" terminal. The programmed current that flows through the
resistor R5 is then set by Ohms Law to be the voltage at the "set"
terminal divided by R5. As the voltage at the "set" terminal
changes, the current flowing through resistor R5 at the "OUT"
terminal changes, and this current is essentially the same as the
current flowing through the load R.sub.LOAD. Hence, whatever
current flows through resistor R5, as set by the voltage across
resistor R5, is essentially the same current that flows through the
load R.sub.LOAD. Thus, as the micro-controller U2 sets the voltage
at the "set" terminal of U3, on the signal line labeled "AMPSET",
it controls what current flows through the load R.sub.LOAD. In no
event can the amplitude of the voltage pulse developed across the
load R.sub.LOAD exceed the voltage V.sub.OUT developed by the boost
converter less the voltage drop across the switch U5 and current
source U3.
[0191] It is important that the circuitry used in the IEAD 100,
e.g., the circuitry shown in FIG. 20 or 21, or equivalents thereof,
have some means for controlling the stimulation current that flows
through the load, R.sub.LOAD, which load may be characterized as
the patient's tissue impedance at and around the acupoint or other
target location that is being stimulated. This tissue impedance may
typically vary from between about 300 ohms to 2000 ohms. Moreover,
it not only varies from one patient to another, but it varies over
time for the same patient. Hence, there is a need to control the
current that flows through this variable load, R.sub.LOAD. One way
of accomplishing this goal is to control the stimulation current,
as opposed to the stimulation voltage, so that the same current
will flow through the tissue load regardless of changes that may
occur in the tissue impedance over time. The use of a voltage
controlled current source U3, as shown in FIG. 21, is one way to
satisfy this need.
[0192] Still referring to FIG. 21, a fourth IC U4 is connected to
the micro-controller U2. For the embodiment shown in FIG. 21, the
circuit U4 is an electromagnetic field sensor, and it allows the
presence of an externally-generated (non-implanted) electromagnetic
field to be sensed. An "electromagnetic" field, for purposes of
this application includes magnetic fields, radio frequency (RF)
fields, light fields, and the like. The electromagnetic sensor may
take many forms, such as any wireless sensing element, e.g., a
pickup coil or RF detector, a photon detector, a magnetic field
detector, and the like. When a magnetic sensor is employed as the
electromagnetic sensor U4, the magnetic field is generated using an
External Control Device (ECD) 240 that communicates wirelessly,
e.g., through the presence or absence of a magnetic field, with the
magnetic sensor U4. (A magnetic field, or other type of field if a
magnetic field is not used, is symbolically illustrated in FIG. 21
by the wavy line 242.) In its simplest form, the ECD 240 may simply
be a magnet, and modulation of the magnetic field is achieved
simply by placing or removing the magnet next to or away from the
IEAD. When other types of sensors (non-magnetic) are employed, the
ECD 240 generates the appropriate signal or field to be sensed by
the sensor that is used.
[0193] Use of the ECD 240 provides a way for the patient, or
medical personnel, to control the IEAD 100 after it has been
implanted (or before it is implanted) with some simple commands,
e.g., turn the IEAD ON, turn the IEAD OFF, increase the amplitude
of the stimulation pulses by one increment, decrease the amplitude
of the stimulation pulses by one increment, and the like. A simple
coding scheme may be used to differentiate one command from
another. For example, one coding scheme is time-based. That is, a
first command is communicated by holding a magnet near the IEAD
100, and hence near the magnetic sensor U4 contained within the
IEAD 100, for differing lengths of time. If, for example, a magnet
is held over the IEAD for at least 2 seconds, but no more than 7
seconds, a first command is communicated. If a magnet is held over
the IEAD for at least 11 seconds, but no more than 18 seconds, a
second command is communicated, and so forth. Various other coding
schemes that could be employed for this purpose are described in
Applicant's Parent Application(s), referenced above in the first
paragraph.
[0194] More sophisticated magnetic coding schemes may be used to
communicate to the micro-controller chip U2 the operating
parameters of the IEAD 100. For example, using an electromagnet
controlled by a computer, the pulse width, frequency, and amplitude
of the EA stimulation pulses used during each stimulation session
may be pre-set. Also, the frequency of the stimulation sessions can
be pre-set. Additionally, a master reset signal can be sent to the
device in order to re-set these parameters to default values. These
same operating parameters and commands may be re-sent at any time
to the IEAD 100 during its useful lifetime should changes in the
parameters be desired or needed.
[0195] Additional features associated with the use and operation of
the circuitry of FIG. 21 which are not included through operation
of the functional circuitry shown in FIG. 20, relate to the
inclusion of a Schottky diode D4 at the output terminal LX of the
boost converter circuit U1 and the inclusion of a fifth integrated
circuit (IC) U5, which circuit U5 essentially performs the same
function as the switches S.sub.R and S.sub.P shown in FIG. 20.
[0196] The Schottky diode D4 helps isolate the output voltage
V.sub.OUT generated by the boost converter circuit U1. This is
important in applications where the boost converter circuit U1 is
selected and operated to provide an output voltage V.sub.OUT that
is four or five times as great as the battery voltage, V.sub.BAT.
For example, in the embodiment for which the circuit of FIG. 21 is
designed, the output voltage V.sub.OUT is designed to be nominally
15 volts (and could be as high as 25 volts) using a battery that
has a nominal battery voltage of only 3 volts.
[0197] The inclusion of the fifth IC U5 in the circuit shown in
FIG. 21 is, as indicated, used to perform the function of a switch.
More particularly, the IC U5 shown in FIG. 21 functions as a single
pole/double throw (SPDT) switch. Numerous commercially-available
ICs may be used for this function. For example, an ADG1419 IC,
available from Analog Devices Incorporated (ADI) may be used. In
such IC U5, the terminal "D" functions as the common terminal of
the switch, and the terminals "SA" and "SB" function as the
selected output terminal of the switch. The terminals "IN" and "EN"
are control terminals to control the position of the switch. Thus,
when there is a signal present on the PULSE line, which is
connected to the "IN" terminal of U5, the SPDT switch U5 connects
the "D" terminal to the "SB" terminal, and the SPDT switch U5
effectively connects the cathode electrode E1 to the programmable
current source U3. This connection thus causes the programmed
current, set by the control voltage AMPSET applied to the SET
terminal of the programmable current source U3, to flow through
resistor R5, which in turn causes essentially the same current to
flow through the load, R.sub.LOAD, present between the electrodes
E1 and E2. When a signal is not present on the PULSE line, the SPDT
switch U5 effectively connects the cathode electrode E1 to the
resistor R6, which allows the coupling capacitors C12 and C13 to
recharge back to the voltage V.sub.OUT provided by the boost
converter circuit U2.
[0198] The schematic diagram of FIG. 21, which shows the circuit
implementation used within the IEAD 100, further includes a boost
converter circuit U1 that is modulated ON and OFF using digital
control generated within the boost converter circuit U1 itself. In
accordance with this implementation, as explained briefly
previously, the boost converter circuit 200 shuts itself down
whenever the battery voltage falls below a predetermined level
above that required by the remaining circuitry. For example, in the
embodiment shown in FIG. 21, the boost converter circuit U1 is
realized using a MAX8570 boost converter IC, commercially available
from Maxim, or equivalents thereof. This particular boost converter
IC shuts down when the applied voltage, V.sub.BAT, falls below 2.5
V. Advantageously, a battery voltage of 2.5 volts is still a high
enough voltage to ensure the microcontroller IC U2, and other
circuitry associated with the operation of the IEAD 100, remain
operational.
[0199] Thus, in operation, as soon as the battery voltage drops
below 2.5 volts, the boost converter circuit U1 shuts down, thereby
limiting the instantaneous current drawn from the battery. When the
boost converter U1 shuts down, the instantaneous battery current
drawn from the battery is immediately reduced a significant amount,
thereby causing the battery voltage V.sub.BAT to increase.
[0200] As the battery voltage V.sub.BAT increases, the boost
converter circuit U1 remains shut down until the microcontroller U2
determines that it is time to turn the boost converter back ON.
This turn ON typically occurs in one of two ways: (1) just prior to
the delivery of the next stimulus pulse, a turn ON signal may be
applied to the Shutdown ("SD") terminal, signal line 243, of the
boost converter circuit U1; or (2) as soon as the battery voltage,
V.sub.BAT, has increased a sufficient amount, as sensed at the
feedback terminal FB of the boost converter circuit U1, the
circuits within the boost converter circuit U1 are automatically
turned back ON, allowing the output voltage V.sub.OUT to build up
to a voltage level needed by the switch circuit U5 and the current
source circuit U3 to generate an output stimulus pulse of the
desired amplitude when the next PULSE signal is applied to the IN
terminal of the switch U5 by the microcontroller U2.
[0201] Once turned ON, the boost converter remains ON until, again,
the input voltage drops below 2.5 volts. This pattern continues,
with the boost converter being ON for a short time, and OFF for a
much longer time (typically, the duty cycle associated with this
ON/OFF operation of the boost converter circuit U1 is no greater
than about 0.01), thereby controlling and limiting the amount of
current that is drawn from the battery. This ON/OFF action of U1
assures that the battery voltage, V.sub.BAT, always remains
sufficiently high to permit operation of all the critical circuits
of the IEAD 100 (principally the circuits of the microcontroller
U2), except the boost converter circuit U1.
[0202] In a preferred implementation, the microcontroller circuit
U2 used in FIG. 21 comprises an MSP430G2452IRSA 16 microcontroller,
commercially available from Texas Instruments, or equivalent
microcontroller. The programmable current source circuit U3
comprises a LT3092 programmable current source commercially
available form Linear Technology, or equivalents thereof. The
sensor circuit U4 comprises an AS-M15SA-R magnetic sensor,
commercially available from Murata, or equivalents thereof. And,
the switch circuit U5 comprises an ADG1419BCPZ single pole double
throw analog switch commercially available from Analog Devices, or
equivalents thereof.
[0203] A further feature or enhancement provided by the circuit
implementation depicted in FIG. 21 relates to removing, or at least
minimizing, some undesirable leading edge transients that are seen
in the output stimulus pulses generated by the circuitry of FIG.
21. The solution to remove or mitigate the occurrence of such
leading edge transients is to insert an N-MOSFET transistor switch
Q1 at the input terminal, IN, of the programmable current source
circuit U3. This switch Q1 acts as a "cascode" stage that maintains
a more constant voltage across the current source U3 as the output
current and/or load resistance changes. Use of this N-MOSFET switch
Q1 as depicted in FIG. 21 as a cascode stage advantageously reduces
the transient leading edge of the stimulus pulse because the
capacitance looking into Q1 is much less than is seen when looking
into the current source circuit U3.
[0204] Yet an additional feature or enhancement provided by the
circuitry of FIG. 21 is to address a delay that is seen when
starting up the programmable current source circuit U3 when
programmed to provide low pulse amplitudes, (e.g., less than about
3 mA). A typical current stimulus output for the IEAD is on the
order of 15-25 mA. When a much smaller amplitude current stimulus
is used, e.g., 1.5-3 mA, the control signal that defines this
smaller amplitude pulse is significantly less than the one used to
define the more typical stimulus amplitudes of 15-25 mA. Such a
small control signal lengthens the delay between a trigger point
and the leading edge of a stimulus pulse. This problem is addressed
through use a Schottky diode D5 connected from an output port on
the microcontroller circuit U2 to the input port, IN, of the
current source circuit U3. This Schottky diode D5 is realized, for
the embodiment shown in FIG. 21, using a BAT54XV2DKR diode,
commercially available from Fairchild Semiconductor. This diode D5
is used to warm-up or "kick start" the circuit U3 when the pulse
amplitude is low. Use of the diode D5 allows the micro-controller
U2 to drive U3 directly at the start of the pulse, over the signal
line labeled "KICKER" in FIG. 21, without significantly changing
the pulse characteristics.
Use and Operation
[0205] With the implantable electroacupuncture device (IEAD) 100 in
hand, the IEAD 100 is used most effectively to treat a specified
disease or medical condition of the patent by first pre-setting
stimulation parameters that the device will use during a
stimulation session. FIG. 8 shows a timing waveform diagram
illustrating the EA stimulation parameters used by the IEAD to
generate EA stimulation pulses. As seen in FIG. 8, there are
basically four parameters associated with a stimulation session.
The time T1 defines the duration (or pulse width) of a stimulus
pulse. The time T2 defines the time between the start of one
stimulus pulse and the start of the next stimulus pulse. The time
T2 thus defines the period associated with the frequency of the
stimulus pulses. The frequency of the stimulation pulses is equal
to 1/T2. The ratio of T1/T2 is typically quite low, e.g., less than
0.01. The duration of a stimulation session is dictated or defined
by the time period T3. The amplitude of the stimulus pulses is
defined by the amplitude A1. This amplitude may be expressed in
either voltage or current.
[0206] Turning next to FIG. 8A, a timing waveform diagram is shown
that illustrates the manner in which the stimulation sessions are
administered in accordance with a preferred stimulation regimen.
FIG. 8A shows several stimulation sessions of duration T3, and how
often the stimulation sessions occur. The stimulation regimen thus
includes a time period T4 which sets the time period from the start
of one stimulation session to the start of the next stimulation
session. The time period T4 thus is the period of the stimulation
session frequency, and the stimulation session frequency is equal
to 1/T4.
[0207] In order to allow the applied stimulation to achieve its
desired effect on the body tissue at the selected target
stimulation site, an initialization period, typically no longer
than two weeks, may be employed wherein the period of the
stimulation session T4 may be varied. After the initialization
period, the stimulation sessions are regularly applied to the
patient using a fixed value of T4. For example, after the
initialization period, the stimulation sessions may be applied to
the patient no more than twice a week (i.e., T4=5,040 minutes), but
no less than once every other week (i.e., T4=20,160 minutes).
[0208] During the initialization period, the value of T4 can be
varied, in accordance with one implementation, by employing a
simple algorithm within the circuitry of the EA device changes the
value of T4 in an appropriate manner. For example, at start up, the
period T4 may be set to a minimum value, T4 (min). Then, as time
goes on, the value of T4 may be gradually increased until a desired
value of T4, T4 (final) is reached.
[0209] By way of example, during the initialization period, if T4
(min) is 1 day, and T4 (final) is 7 days, the value of T4 may vary
as follows once the stimulation sessions begin: T4=1 day for the
duration between the first and second stimulation sessions, then 2
days for the duration between the second and third stimulation
sessions, then 4 days for the duration between the third and fourth
stimulation sessions, and then finally 7 days for the duration
between all subsequent stimulation sessions after the fourth
stimulation session.
[0210] Rather than increasing the value of T4 from a minimum value
to a maximum value using a simple doubling algorithm, as described
in the previous paragraph, an enhancement is to use a table of
session durations and intervals whereby the automatic session
interval can be shorter for the first week or so. For example, a
first 30 minute stimulation session could be delivered after 1 day.
The second 30 minute session could be delivered after 2 days. The
third 30 minute session could be delivered after 4 days. Finally,
the fourth 30 minute session could be delivered for all subsequent
sessions after 7 days.
[0211] If a triggered session is delivered completely, it advances
the therapy schedule to the next table entry.
[0212] Another enhancement is that the initial set amplitude only
takes effect if the subsequent triggered session is completely
delivered. For example, should the first session be aborted by a
magnet application, the device reverts to a Shelf Mode. In this
way, the first session is always a triggered session that occurs in
the clinician setting.
[0213] The programmed values of amplitude and place in a session
table are saved in non-volatile memory when they change. This
avoids a resetting of the therapy schedule and need to reprogram
the amplitude in the event of a device reset.
[0214] By way of example, one set of parameters that could be used
to define a stimulation regimen is: [0215] T1=0.5 milliseconds
[0216] T2=500 milliseconds [0217] T3=30 minutes [0218] T4=7 days
(10,080 minutes) [0219] A1=15 volts (across 1 kOhm), or 15
milliAmperes (mA)
[0220] It is to be emphasized that the values shown above for the
stimulation regimen are representative of only one preferred
stimulation regimen that could be used.
[0221] It is also emphasized that the ranges of values presented in
the claims for the parameters used with the invention have been
selected after many months of careful research and study, and are
not arbitrary. For example, the ratio of T3/T4, which sets the duty
cycle, has been carefully selected to be very low, e.g., no more
than 0.05. Maintaining a low duty cycle of this magnitude
represents a significant change over what others have attempted in
the implantable stimulator art. Not only does a very low duty cycle
allow the battery itself to be small (coin cell size), which in
turn allows the IEAD housing to be very small, which makes the IEAD
ideally suited for being used without leads, thereby making it
relatively easy to implant the device at the desired stimulation
site (e.g., acupoint), but it also limits the frequency and
duration of stimulation sessions.
[0222] Limiting the frequency and duration of the stimulation
sessions is a key aspect of Applicant's invention because it
recognizes that some treatments, such as treating high blood
pressure, are best done slowly and methodically, over time, rather
than quickly and harshly using large doses of stimulation (or other
treatments) aimed at forcing a rapid change in the patient's
condition. Moreover, applying treatments slowly and methodically is
more in keeping with traditional acupuncture methods (which, as
indicated previously, are based on over 2500 years of experience).
In addition, this slow and methodical conditioning is consistent
with the time scale for remodeling of the central nervous system
needed to produce a sustained therapeutic effect. Thus, Applicant
has based its treatment regimen on the slow-and-methodical
approach, as opposed to the immediate-and-forced approach adopted
by many, if not most, prior art implantable electrical
stimulators.
[0223] Once the stimulation regimen has been defined and the
parameters associated with it have been pre-set into the memory of
the micro-controller circuit U2, the IEAD 100 needs to be
implanted. Implantation is usually a simple procedure, and is
described above in connection, e.g., with the description of FIGS.
10 and 11.
[0224] After implantation, the IEAD must be turned ON, and
otherwise controlled, so that the desired stimulation regimen or
stimulation paradigm may be carried out. In one preferred
embodiment, control of the IEAD after implantation, as well as any
time after the housing of the IEAD has been hermetically sealed, is
performed as shown in the state diagram of FIG. 22. Each circle
shown in FIG. 22 represents an operating "state" of the
micro-controller U2 (FIG. 21). As seen in FIG. 22, the controller
U2 only operates in one of six states: (1) a "Set Amplitude" state,
(2) a "Shelf Mode" state, (3) a "Triggered Session" state, (4) a
"Sleep" state, (5) an "OFF" state, and an (6) "Automatic Session"
state. The "Automatic Session" state is the state that
automatically carries out the stimulation regimen using the
pre-programmed parameters that define the stimulation regimen.
[0225] Shelf Mode is a low power state in which the IEAD is placed
prior to shipment. After implant, commands are made through magnet
application. Magnet application means an external magnet, typically
a small hand-held cylindrical magnet, is placed over the location
where the IEAD has been implanted. With a magnet in that location,
the magnetic sensor U4 senses the presence of the magnet and
notifies the controller U2 of the magnet's presence.
[0226] From the "Shelf Mode" state, a magnet application for 10
seconds (M.10 s) puts the IEAD in the "Set Amplitude" state. While
in the "Set Amplitude" state, the stimulation starts running by
generating pulses at zero amplitude, incrementing every five
seconds until the patient indicates that a comfortable level has
been reached. At that time, the magnet is removed to set the
amplitude.
[0227] If the magnet is removed and the amplitude is non-zero ( M
.LAMBDA. A), the device continues into the "Triggered Session" so
the patient receives the initial therapy. If the magnet is removed
during "Set Amplitude" while the amplitude is zero ( M .LAMBDA. ),
the device returns to the Shelf Mode.
[0228] The Triggered Session ends and stimulation stops after the
session time (T.sub.S) has elapsed and the device enters the
"Sleep" state. If a magnet is applied during a Triggered Session
(M), the session aborts to the "OFF" state. If the magnet remains
held on for 10 seconds (M.10 s) while in the "OFF" state, the "Set
Amplitude" state is entered with the stimulation level starting
from zero amplitude as described.
[0229] If the magnet is removed ( M) within 10 seconds while in the
OFF state, the device enters the Sleep state. From the Sleep state,
the device automatically enters the Automatic Session state when
the session interval time has expired (T.sub.I). The Automatic
Session delivers stimulation for the session time (T.sub.S) and the
device returns to the Sleep state. In this embodiment, the magnet
has no effect once the Automatic Session starts so that the full
therapy session is delivered.
[0230] While in the Sleep state, if a magnet has not been applied
in the last 30 seconds (D) and a magnet is applied for a window
between 20-25 seconds and then removed (M.20:25 s), a Triggered
Session is started. If the magnet window is missed (i.e. magnet
removed too soon or too late), the 30 second de-bounce period (D)
is started. When de-bounce is active, no magnet must be detected
for 30 seconds before a Triggered Session can be initiated.
[0231] The session interval timer runs while the device is in Sleep
state. The session interval timer is initialized when the device is
woken up from Shelf Mode and is reset after each session is
completely delivered. Thus abort of a triggered session by magnet
application will not reset the timer, the Triggered Session must be
completely delivered.
[0232] The circuitry that sets the various states shown in FIG. 22
as a function of externally-generated magnetic control commands, or
other externally-generated command signals, is the micro-controller
U2 (FIG. 21). Such processor-type circuits are programmable
circuits that operate as directed by a program. The program is
often referred to as "code", or a sequence of steps that the
processor circuit follows. The "code" can take many forms, and be
written in many different languages and formats, known to those of
skill in the art. Representative "code" for the micro-controller U2
(FIG. 14) for controlling the states of the IEAD as shown in FIG.
16 is found in Appendix C, attached hereto, and incorporated by
reference herein.
[0233] In the preceding description, various exemplary embodiments
have been described with reference to the accompanying drawings. It
will, however, be evident that various modifications and changes
may be made thereto, and additional embodiments may be implemented,
without departing from the scope of the invention as set forth in
the claims that follow. For example, certain features of one
embodiment described herein may be combined with or substituted for
features of another embodiment described herein. The description
and drawings are accordingly to be regarded in an illustrative
rather than a restrictive sense and are not intended to be
exhaustive or to limit the invention to any precise form disclosed.
Many modifications and variations are possible in light of the
above teaching. Thus, while the invention(s) herein disclosed has
been described by means of specific embodiments and applications
thereof, numerous modifications and variations could be made
thereto by those skilled in the art without departing from the
scope of the invention(s) set forth in the claims.
* * * * *