U.S. patent application number 15/084362 was filed with the patent office on 2016-07-21 for implantable electroacupuncture device and method.
The applicant listed for this patent is Valencia Technologies Corporation. Invention is credited to Jeffrey H. Greiner, Stacy O. Greiner, David K. L. Peterson, Chuladatta Thenuwara.
Application Number | 20160206507 15/084362 |
Document ID | / |
Family ID | 51223742 |
Filed Date | 2016-07-21 |
United States Patent
Application |
20160206507 |
Kind Code |
A1 |
Greiner; Jeffrey H. ; et
al. |
July 21, 2016 |
Implantable Electroacupuncture Device and Method
Abstract
An electroacupuncture device includes 1) a housing configured to
be implanted beneath a skin surface of the patient at an acupoint
within the patient, 2) a central electrode centrally located on a
first surface of the housing, 3) an annular electrode that
surrounds the central electrode on the first surface of the
housing, the annular electrode being spaced apart from the central
electrode, and 4) pulse generation circuitry located within the
housing, wherein the pulse generation circuitry generates
stimulation sessions at a duty cycle that is less than 0.05 and
applies the stimulation sessions at the acupoint by way of the
central electrode and the annular electrode in accordance with the
duty cycle.
Inventors: |
Greiner; Jeffrey H.;
(Valencia, CA) ; Peterson; David K. L.; (Valencia,
CA) ; Thenuwara; Chuladatta; (Castaic, CA) ;
Greiner; Stacy O.; (Valencia, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Valencia Technologies Corporation |
Valencia |
CA |
US |
|
|
Family ID: |
51223742 |
Appl. No.: |
15/084362 |
Filed: |
March 29, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13796314 |
Mar 12, 2013 |
9327134 |
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15084362 |
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13598582 |
Aug 29, 2012 |
8965511 |
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13796314 |
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13622653 |
Sep 19, 2012 |
8996125 |
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13598582 |
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13630522 |
Sep 28, 2012 |
9173811 |
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13622653 |
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61609875 |
Mar 12, 2012 |
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61672257 |
Jul 16, 2012 |
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61672661 |
Jul 17, 2012 |
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61673254 |
Jul 19, 2012 |
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61674691 |
Jul 23, 2012 |
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61676275 |
Jul 26, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61N 1/36096 20130101;
H01L 2224/48091 20130101; A61N 1/36107 20130101; A61N 1/3758
20130101; A61N 1/36067 20130101; A61N 1/3782 20130101; A61N 1/36114
20130101; A61H 39/002 20130101; A61N 1/36175 20130101; Y10T
29/49002 20150115; A61N 1/37205 20130101; A61N 1/3756 20130101;
H01L 2924/00014 20130101; A61N 1/36117 20130101; H01L 2224/48091
20130101; A61N 1/36125 20130101 |
International
Class: |
A61H 39/00 20060101
A61H039/00; A61N 1/372 20060101 A61N001/372; A61N 1/375 20060101
A61N001/375; A61N 1/36 20060101 A61N001/36 |
Claims
1. An electroacupuncture device for treating a medical condition of
a patient, comprising: a housing configured to be implanted beneath
a skin surface of the patient at an acupoint within the patient; a
central electrode of a first polarity and centrally located on a
first surface of the housing; an annular electrode of a second
polarity and that surrounds the central electrode on the first
surface of the housing, the annular electrode being spaced apart
from the central electrode; and pulse generation circuitry located
within the housing and electrically coupled to the annular and
central electrodes, wherein the pulse generation circuitry
generates stimulation sessions at a duty cycle that is less than
0.05, and applies the stimulation sessions at the acupoint by way
of the central electrode and the annular electrode in accordance
with the duty cycle, wherein each stimulation session included in
the stimulation sessions comprises a series of stimulation pulses,
the duty cycle is a ratio of T3 to T4, and each stimulation session
included in the stimulation sessions has a duration of T3 minutes
and occurs at a rate of once every T4 minutes.
2. The electroacupuncture device of claim 1, wherein the acupoint
comprises at least one of acupoints BL14, BL23, BL52, EXHN1, EXHN3,
GB34, GV4, GV20, HT5, HT7, KI6, LI4, LI11, LR3, LR8, LU2, LU7, PC5,
PC6, PC7, SP4, SP6, SP9, ST36, ST37, and ST40.
3. The electroacupuncture device of claim 1, wherein the medical
condition comprises at least one of hypertension, cardiovascular
disease, depression, bipolar disorder, anxiety, obesity,
dyslipidemia, Parkinson's disease, essential tremor, and erectile
dysfunction.
4. The electroacupuncture device of claim 1, wherein T3 is at least
10 minutes and less than 60 minutes, and wherein T4 is at least
1440 minutes.
5. The electroacupuncture device of claim 1, further comprising: a
sensor that receives, from a device external to the
electroacupuncture device, a control command configured to control
the electroacupuncture device.
6. The electroacupuncture device of claim 5, wherein: the control
command sets the times T3 and T4 to appropriate values configured
to treat the medical condition; and the pulse generation circuitry
generates the stimulation sessions in accordance with the control
command.
7. The electroacupuncture device of claim 1, wherein the housing is
coin-sized and coin-shaped.
8. The electroacupuncture device of claim 1, wherein the annular
electrode is located on the first surface of the housing.
9. The electroacupuncture device of claim 1, wherein the annular
electrode comprises a ring electrode located around a perimeter
edge of the housing.
10. The electroacupuncture device of claim 1, further comprising a
primary battery contained within the housing and that provides
operating power for the pulse generation circuitry, the primary
battery having a nominal output voltage of 3 volts and an internal
impedance greater than 5 ohms.
11. The electroacupuncture device of claim 10, wherein the pulse
generation circuitry comprises: a boost converter circuit that
boosts the nominal voltage of the primary battery to an output
voltage VOUT that is at least three times the nominal battery
voltage; a control circuit for selectively turning the boost
converter circuit OFF and ON to limit the amount of current that is
drawn from the primary battery; and an output circuit powered by
VOUT and that generates the stimulation pulses.
12. The electroacupuncture device of claim 11, wherein the pulse
generation circuitry further is configured to create a reverse
trapezoidal stimulation pulse waveshape for the stimulation
pulses.
13. A method of treating a medical condition of a patient,
comprising: generating, by an electroacupuncture device implanted
beneath a skin surface of the patient at an acupoint within the
patient, stimulation sessions at a duty cycle that is less than
0.05, wherein each stimulation session included in the stimulation
sessions comprises a series of stimulation pulses, the duty cycle
is a ratio of T3 to T4, each stimulation session included in the
stimulation sessions has a duration of T3 minutes and occurs at a
rate of once every T4 minutes, and the electroacupuncture device
comprises a central electrode of a first polarity centrally located
on a first surface of a housing of the electroacupuncture device
and an annular electrode of a second polarity and that is spaced
apart from the central electrode; and applying, by the
electroacupuncture device, the stimulation sessions at the acupoint
by way of the central electrode and the annular electrode in
accordance with the duty cycle.
14. The method of claim 13, wherein the acupoint comprises at least
one of acupoints BL14, BL23, BL52, EXHN1, EXHN3, GB34, GV4, GV20,
HT5, HT7, KI6, LI4, LI11, LR3, LR8, LU2, LU7, PC5, PC6, PC7, SP4,
SP6, SP9, ST36, ST37, and ST40.
15. The method of claim 13, wherein the medical condition comprises
at least one of hypertension, cardiovascular disease, depression,
bipolar disorder, anxiety, obesity, dyslipidemia, Parkinson's
disease, essential tremor, and erectile dysfunction.
16. The method of claim 13, further comprising receiving, by the
electroacupuncture device from a device external to the
electroacupuncture device, a control command configured to control
the electroacupuncture device.
17. The method of claim 16, wherein: the control command sets the
times T3 and T4 to appropriate values configured to treat the
medical condition; and the generating of the stimulation sessions
is performed in accordance with the control command.
18. The method of claim 13, wherein the housing is coin-sized and
coin-shaped.
19. The method of claim 13, wherein the annular electrode is
located on the first surface of the housing.
20. The method of claim 13, wherein the annular electrode comprises
a ring electrode located around a perimeter edge of the housing.
Description
RELATED APPLICATIONS
[0001] The present application is a continuation application of
U.S. patent application Ser. No. 13/796,314, filed Mar. 12, 2013,
which application is a continuation-in-part (CIP) application of
U.S. application Ser. No. 13/598,582, filed Aug. 29, 2012; U.S.
patent application Ser. No. 13/622,653, filed Sep. 19, 2012; and
U.S. patent application Ser. No. 13/630,522, filed Sep. 28, 2012.
U.S. application Ser. No. 13/796,314 also claims priority under 35
U.S.C. .sctn.119(e) to U.S. Provisional Patent Application No.
61/609,875, filed Mar. 12, 2012; U.S. Provisional Patent
Application No. 61/672,257, filed Jul. 16, 2012; U.S. Provisional
Patent Application No. 61/672,661, filed Jul. 17, 2012; U.S.
Provisional Patent Application No. 61/673,254, filed Jul. 19, 2012;
U.S. Provisional Patent Application No. 61/674,691, filed Jul. 23,
2012; and U.S. Provisional Patent Application No. 61/676,275, filed
Jul. 26, 2012. All of these applications are incorporated herein by
reference in their respective entireties
BACKGROUND INFORMATION
[0002] Acupuncture has 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. A good
summary of the history of acupuncture, and its potential
applications may be found in Cheung, et al., "The Mechanism of
Acupuncture Therapy and Clinical Case Studies", (Taylor &
Francis, publisher) (2001) ISBN 0-415-27254-8, hereafter referred
to as "Cheung, Mechanism of Acupuncture, 2001." The Forward, as
well as Chapters 1-3, 5, 7, 8, 12 and 13 of Cheung, Mechanism of
Acupuncture, 2001, are incorporated herein by reference.
[0003] Despite the practice in Eastern countries for over 2500
years, it was not until President Richard Nixon visited China (in
1972) that acupuncture began to be accepted in the West, such as
the United States and Europe. One of the reporters who accompanied
Nixon during his visit to China, James Reston, from the New York
Times, received acupuncture in China for post-operative pain after
undergoing an emergency appendectomy under standard anesthesia.
Reston experienced pain relief from the acupuncture and wrote about
it in The New York Times. In 1973 the American Internal Revenue
Service allowed acupuncture to be deducted as a medical expense.
Following Nixon's visit to China, and as immigrants began flowing
from China to Western countries, the demand for acupuncture
increased steadily. Today, acupuncture therapy is viewed by many as
a viable alternative form of medical treatment, alongside Western
therapies. Moreover, acupuncture treatment is now covered, at least
in part, by most insurance carriers. Further, payment for
acupuncture services consumes a not insignificant portion of
healthcare expenditures in the U.S. and Europe. See, generally,
Cheung, Mechanism of Acupuncture, 2001, vii.
[0004] Acupuncture is an alternative medicine that treats patients
by insertion and manipulation of needles in the body at selected
points. See, Novak, Patricia D. et al (1995). Dorland's Pocket
Medical Dictionary (25th ed.), Philadelphia: (W.B. Saunders
Publisher), ISBN 0-7216-5738-9. The locations where the acupuncture
needles are inserted are referred to herein 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. For
example, see, "Acupuncture Points Map," found online at:
http://www.acupuncturehealing.org/acupuncture-points-map.html.
Acupoints are typically identified by various letter/number
combinations, e.g., L6, S37. The maps that show the location of the
acupoints may also identify what condition, illness or deficiency
the particular acupoint affects when manipulation of needles
inserted at the acupoint is undertaken.
[0005] References to the acupoints in the literature are not always
consistent with respect to the format of the letter/number
combination. Some acupoints are identified by a name only, e.g.,
Tongli. The same acupoint may be identified by others by the name
followed with a letter/number combination placed in parenthesis,
e.g., Tongli (HT5). Alternatively, the acupoint may be identified
by its letter/number combination followed by its name, e.g., HT5
(Tongli). The first letter typically refers to a body organ, or
meridian, or other tissue location associated with, or affected by,
that acupoint. However, usually only the letter is used in
referring to the acupoint, but not always. Thus, for example, the
acupoint BL23 is the same as acupoint Bladder 23 which is the same
as BL-23 which is the same as BL 23 which is the same as Shenshu.
For purposes of this patent application, unless specifically stated
otherwise, all references to acupoints that use the same name, or
the same first letter and the same number, and regardless of slight
differences in second letters and formatting, are intended to refer
to the same acupoint.
[0006] An excellent reference book that identifies most all of the
traditional acupoints within the human body is 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"). For
the convenience of the reader, the Table of Contents, Forward (page
v-vi) and General Guidelines for Acupuncture Point Locations (pages
1-21), as well as pages 26, 29, 35, 39, 64, 66, 71-72, 74, 84-85,
106, 111, 125, 138, 154-155, 188, 197, 199, 205, 213 (which
illustrate with particularity the location of selected acupoints
referenced herein), are submitted herewith as Appendix D. The
entire book, WHO Standard Acupuncture Point Locations 2008, is
incorporated herein by reference.
[0007] While many in the scientific and medical community are
highly critical of the historical roots upon which acupuncture has
developed, (e.g., claiming that the existence of meridians, qi, yin
and yang, and the like have no scientific basis), see, e.g.,
http://en.wikipedia.org/wiki/Acupuncture, few can refute the vast
amount of successful clinical and other data, accumulated over
centuries of acupuncture practice, that shows needle manipulation
applied at certain acupoints is quite effective.
[0008] The World Health Organization and the United States'
National Institutes of Health (NIH) have stated that acupuncture
can be effective in the treatment of neurological conditions and
pain. Reports from the USA's National Center for Complementary and
Alternative Medicine (NCCAM), the American Medical Association
(AMA) and various USA government reports have studied and commented
on the efficacy of acupuncture. There is general agreement that
acupuncture is safe when administered by well-trained practitioners
using sterile needles, but not on its efficacy as a medical
procedure.
[0009] An early critic of acupuncture, Felix Mann, who was the
author of the first comprehensive English language acupuncture
textbook Acupuncture: The Ancient Chinese Art of Healing, stated
that "The traditional acupuncture points are no more real than the
black spots a drunkard sees in front of his eyes." Mann compared
the meridians to the meridians of longitude used in geography--an
imaginary human construct. Mann, Felix (2000). Reinventing
acupuncture: a new concept of ancient medicine. Oxford:
Butterworth-Heinemann. pp. 14; 31. ISBN 0-7506-4857-0. Mann
attempted to combine his medical knowledge with that of Chinese
theory. In spite of his protestations about the theory, however, he
apparently believed there must be something to it, because he was
fascinated by it and trained many people in the West with the parts
of it he borrowed. He also wrote many books on this subject. His
legacy is that there is now a college in London and a system of
needling that is known as "Medical Acupuncture". Today this college
trains doctors and Western medical professionals only.
[0010] For purposes of this patent application, the arguments for
and against acupuncture are interesting, but not that relevant.
What is important is that a body of literature exists that
identifies several acupoints within the human body that, rightly or
wrongly, have been identified as having an influence on, or are
otherwise somehow related to, the treatment of various
physiological conditions, deficiencies or illnesses. With respect
to these acupoints, the facts speak for themselves. Either these
points do or do not affect the conditions, deficiencies or
illnesses with which they have been linked. The problem lies in
trying to ascertain what is fact from what is fiction. This problem
is made more difficult when conducting research on this topic
because the insertion of needles, and the manipulation of the
needles once inserted, is more of an art than a science, and
results from such research become highly subjective. What is needed
is a much more regimented approach for doing acupuncture
research.
[0011] It should also be noted that other medical research, not
associated with acupuncture research, has over the years identified
nerves and other locations throughout a patient's body where the
application of electrical stimulation produces a beneficial effect
for the patient. Indeed, the entire field of neurostimulation deals
with identifying locations in the body where electrical stimulation
can be applied in order to provide a therapeutic effect for a
patient. For purposes of this patent application, such known
locations within the body are treated essentially the same as
acupoints--they provide a "target" location where electrical
stimulation may be applied to achieve a beneficial result, whether
that beneficial result is to treat erectile dysfunction, reduce
cholesterol or triglyceride levels, to treat cardiovascular
disease, to treat mental illness, or to address some other issue
associated with a disease or condition of the patient.
[0012] Returning to the discussion regarding acupuncture, some have
proposed applying moderate electrical stimulation at selected
acupuncture points through needles that have been inserted at those
points. See, e.g., http://en.wikipedia.org/wiki/Electroacupuncture.
Such electrical stimulation is known as electroacupuncture (EA).
According to Acupuncture Today, a trade journal for acupuncturists:
"Electroacupuncture is quite similar to traditional acupuncture in
that the same points are stimulated during treatment. As with
traditional acupuncture, needles are inserted on specific points
along the body. The needles are then attached to a device that
generates continuous electric pulses using small clips. These
devices are used to adjust the frequency and intensity of the
impulse being delivered, depending on the condition being treated.
Electroacupuncture uses two needles at a time so that the impulses
can pass from one needle to the other. Several pairs of needles can
be stimulated simultaneously, usually for no more than 30 minutes
at a time." "Acupuncture Today: Electroacupuncture". 2004-02-01
(retrieved on-line 2006-08-09 at
http://www.acupuncturetoday.com/abc/electroacupuncture.php).
[0013] U.S. Pat. No. 7,203,548, 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 cavernous nerve
stimulation. The microstimulator has a tubular shape, with
electrodes at each end.
[0014] 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. 6,735,745
(headache and/or facial pain); 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). The microstimulator patents either require electronics and
battery in a coil on the outside of the body or a coil on the
outside that enables the recharging of a rechargeable battery. The
use of an outside coil, complex electronics, and the tubular shape
of the microstimulator have all limited the commercial feasibility
of the microstimulator device and applications described in the
Whitehurst patents.
[0015] 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 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 still far too invasive, or are ineffective,
and thus are subject to the same limitations and concerns, as are
the previously described electrical stimulation devices.
[0016] 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 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 erectile dysfunction.
SUMMARY
[0017] One characterization of the invention described herein is
that of an Implantable ElectroAcupuncture Device (IEAD) adapted to
treat a specified medical condition of a patient through
application of stimulation pulses applied substantially at or near
a specified target tissue location. Such IEAD includes: (a) a small
IEAD housing having an electrode configuration thereon that
includes at least two electrodes/arrays, the longest liner
dimension of the small IEAD housing being no greater than about 25
mm, and the shortest linear dimension, measured orthogonal to the
longest linear dimension, is no greater than about 2.5 mm, wherein
at least one of the at least two electrodes/arrays comprises a
central electrode/array located substantially in the center of a
first surface of the IEAD housing, and wherein at least another of
the at least two electrodes/arrays comprises a circumferential
electrode/array located substantially around and at least 5 mm
distant from the center of the central electrode/array, wherein the
first surface (106) of the IEAD housing when implanted is adapted
to face inwardly into the patient's tissue at or near the specified
target tissue location; (b) pulse generation located within the
IEAD housing and electrically coupled to the at least two
electrodes/arrays, wherein the pulse generation circuitry is
adapted to deliver stimulation pulses to the patient's body tissue
at or near the target tissue location in accordance with a
specified stimulation regimen, the stimulation regimen defining a
duration (T3) and rate (1/T4) at which a stimulation session is
applied to the patient, the stimulation regimen requiring that the
stimulation session have a duration of T3 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
stimulation pulses having one or more specified widths (T1) and
amplitudes (A1) are generated at one or more specified rates
(1/T2); (c) a primary battery contained within the IEAD housing and
electrically coupled to the pulse generation circuitry that
provides operating power for the pulse generation circuitry, the
primary battery having a nominal output voltage of 3 volts, and an
internal impedance greater than 5 ohms; and (d) a sensor contained
within the IEAD housing responsive to operating commands wirelessly
communicated to the IEAD from a non-implanted location, said
operating commands allowing limited external control of the
IEAD.
[0018] The specified medical condition, in accordance with some
embodiments of the invention, includes at least one of (1)
hypertension, (2) cardiovascular disease, (3) depression, (4)
bipolar disorder, (5) Anxiety, (6) obesity, (7) dyslipidemia, (8)
Parkinson's disease, (9) Essential tremor, or (10) erectile
dysfunction. Moreover, in other embodiments of the invention where
at least one of the specified medical conditions is used, the
specified target tissue location comprises at least one acupoint
selected from the group of acupoints comprising: BL14, BL23, BL52,
EXHN1, EXHN3, GB34, GV4, GV20, HT5, HT7, KI6, LI4, LI11, LR3, LR8,
LU2, LU7, PC5, PC6, PC7, SP4, SP6, SP9, ST36, ST37, and ST40.
[0019] In accordance with another embodiment, the invention
described herein may be characterized as a an implantable
electroacupuncture device (IEAD) adapted to generate and apply
electrical stimulus pulses to a target tissue location of a patient
when the IEAD is implanted at or near a target tissue location.
This embodiment of the invention includes: (a) an hermetically
sealed case having a linear dimension in first plane no greater
than about 25 mm, and a linear dimension in a second plane
orthogonal to the first plane no greater than about 2.5 mm; (b) at
least anodic electrode and at least one cathodic electrode secured
to an outside surface of the hermetically sealed case, the
separation between the point where the cathodic electrode is
closest to the anodic electrode being at least 5 mm; (c) electronic
circuitry housed within the hermetically sealed case that causes
electrical stimulus pulses to be generated and applied to the at
least one cathodic electrode and the at least one anodic electrode
in accordance with a prescribed stimulation regime: (d) means for
electrically connecting the electronic circuitry on the inside of
the hermetically sealed case to the at least two electrodes on the
outside of the hermetically sealed case; and (e) a primary battery
on the inside of the hermetically sealed case connected to the
electronic circuitry that provides operating power for the
electronic circuitry, the primary battery having a nominal output
voltage of V.sub.BAT volts, where V.sub.BAT ranges from as low 2.2
volts to as high as 3.6 volts. The primary battery has an internal
impedance greater than 5 ohms. Additionally, the electronic
circuitry includes power management circuitry that limits the
amount of instantaneous current that can be drawn from the battery.
Further, the electronic circuitry is able to control the generation
of the electrical stimulus pulses so that the stimulus pulses are
applied only during a stimulation session having a duration of T3
minutes, and wherein the time interval between stimulation sessions
is T4 minutes, and wherein the ratio of T3/T4 is maintained at a
value that is no greater than 0.05.
[0020] The invention herein described may also be characterized as
a method for operating an implantable electroacupuncture device
(IEAD) powered only by a thin, coin-cell type battery having an
internal impedance greater than 5 ohms, over a period of at least 2
years, during which time the IEAD is adapted to generate stimulus
pulses during a stimulation session in accordance with a prescribed
stimulation regimen. Such method includes the steps of: (a)
powering pulse generation circuitry within the IEAD with the
coin-cell type battery; (b) limiting the the duration of
stimulation sessions during which stimulus pulses are generated to
a time period that has a duty cycle of less than 0.05, where the
duty cycle is the ratio of T3 to T4, where T3 is the duration of
the stimulation session, and where T4 is the time interval between
stimulation sessions; (c) boosting the battery voltage from the
coin-cell type battery using a boost converter circuit by a factor
of at least 4 in order to provide sufficient operating power to
generate current stimulus pulses of up to 25 mA during a
stimulation session; and (d) limiting the instantaneous current
that can be drawn from the coin-cell type battery to prevent the
battery voltage, V.sub.BAT, from dropping below safe operating
levels.
[0021] Additionally, the invention described herein may be
characterized as a method of assembling an implantable
electroacupuncture device (IEAD) for use in treating a specified
medical condition of a patient. The IEAD is assembled so as to
reside in a round, thin, hermetically-sealed, coin-sized housing.
An important feature of the coin-size housing, and the method of
assembly associated therewith, is that the method electrically and
thermally isolates a feed-through pin assembly radially passing
through a wall of the coin-sized housing from the high temperatures
associated with welding the housing closed to hermetically seal its
contents. Such method of assembling includes the steps of: [0022]
a. forming a coin-sized housing having a bottom case and a top
cover plate, the top cover plate being adapted to fit over the
bottom case, the bottom case being substantially round and having a
diameter D2 that is nominally 23 mm and a perimeter side wall
extending all the way around the perimeter of the bottom case, the
perimeter side wall having a height W2, wherein the ratio of W2 to
D2 is no greater than about 0.13; [0023] b. forming a recess in one
segment of the side wall, the recess extending radially inwardly
from the side wall to a depth D3, and the recess having an opening
in a bottom wall portion thereof; [0024] c. hermetically sealing a
feed-through assembly in the opening in the bottom of the recess,
the feed-through assembly having a feed-through pin that passes
through the opening without contacting the edges of the opening, a
distal end of the pin extending radially outward beyond the side
wall of the bottom case, and a proximal end of the feed-through pin
extending radially inward toward the center of the bottom case,
whereby the feed-through pin assembly is hermetically bonded to the
opening in the side wall at a location in the bottom of the recess
that is a distance D3 from the perimeter side wall, thereby
thermally isolating the feed-through assembly from the high
temperatures that occur at the perimeter side wall when the cover
plate is welded to the edge of the perimeter side wall; [0025] d.
attaching a central electrode to the thin, coin-sized housing at a
central location on the bottom outside surface of the feed-through
housing; [0026] e. inserting an electronic circuit assembly,
including a battery, inside of the bottom case, and connecting the
proximal end of the feed-though pin to an output terminal of the
electronic circuit assembly, and electrically connecting the bottom
case to a reference terminal of the battery; [0027] f. baking out
the assembly to remove moisture, back filling with a mixture of
He/Ar inert gas, and then welding the top cover plate to the edges
of the side wall of the bottom case, thereby hermetically sealing
the electronic circuit assembly, including the battery, inside of
the thin, coin-sized IEAD housing; [0028] g. leak testing the
welded assembly to assure a desired level of hermeticity has been
achieved; [0029] h. placing an insulating layer of non-conductive
material around the perimeter edge of the thin coin-sized housing,
then placing a circumscribing electrode over the insulating layer
of non-conductive material, and then electrically connecting the
distal end of the feed-through pin to the circumscribing electrode;
and [0030] i. covering all external surface areas of the thin,
coin-sized housing with a layer of non-conductive material except
for the circumscribing electrode around the perimeter of the
coin-sized housing and the central electrode centrally located on
the bottom surface of the thin-coin-sized housing.7
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] 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.
[0032] FIG. 1 is a perspective view of an Implantable
Electroacupuncture Device (IEAD) made in accordance with the
teachings presented herein.
[0033] FIG. 1A illustrates the location of an exemplary acupoint
(target stimulation site) on a limb of a patient, and illustrates
one way in which an implantable electroacupuncture device (IEAD) of
the type disclosed herein may be implanted at the target
stimulation site for the purpose of providing electroacupuncture
(EA) stimulation at that site.
[0034] FIG. 1B shows a sectional view of an IEAD implanted at a
selected target stimulation site, and illustrates the electric
field gradient lines created when electroacupuncture (EA)
stimulation pulses are applied to the tissue through electrodes
attached to the surface of the IEAD housing.
[0035] FIG. 2 shows a plan view of one surface, indicated as the
"Cathode Side," of the IEAD housing illustrated in FIG. 1.
[0036] FIG. 2A shows a side view of the IEAD housing illustrated in
FIG. 1.
[0037] FIG. 3 shows a plan view of the other side, indicated as the
"Skin Side," of the IEAD housing or case illustrated in FIG. 1.
[0038] FIG. 3A is a sectional view of the IEAD of FIG. 3 taken
along the line A-A of FIG. 3.
[0039] FIG. 4 is a perspective view of the IEAD housing, including
a radial feed-through pin, before the electronic components are
placed therein, and before being sealed with a cover plate.
[0040] FIG. 4A is a side view of the IEAD housing of FIG. 4.
[0041] FIG. 5 is a plan view of the empty IEAD housing shown in
FIG. 4.
[0042] FIG. 5A depicts a sectional view of the IEAD housing of FIG.
5 taken along the section line A-A of FIG. 5.
[0043] FIG. 5B shows an enlarged view or detail of the portion of
FIG. 5A that is encircled with the line B.
[0044] FIG. 6 is a perspective view of an electronic assembly,
including a battery, adapted to fit inside of the empty housing of
FIG. 4 and FIG. 5.
[0045] FIGS. 6A and 6B show a plan view and side view,
respectively, of the electronic assembly shown in FIG. 6.
[0046] FIG. 7 is an exploded view of the IEAD assembly,
illustrating its constituent parts.
[0047] FIG. 7A schematically illustrates a few alternative
electrode configurations that may be used with the IEAD.
[0048] FIG. 8A illustrates a functional block diagram of the
electronic circuits used within an IEAD of the type disclosed
herein.
[0049] FIG. 8B shows a functional block diagram of a basic boost
converter circuit configuration, and is used to model how the
impedance of the battery R.sub.BAT can affect its performance.
[0050] FIG. 9A illustrates a typical voltage and current waveform
for the circuits of FIGS. 8A and 8B when the battery impedance
R.sub.BAT is small.
[0051] FIG. 9B shows the voltage and current waveforms for the
circuits of FIGS. 8A and 8B when the battery impedance R.sub.BAT is
large.
[0052] FIG. 10 shows a functional diagram of one preferred boost
converter circuit and pulse generation circuit for use within the
IEAD.
[0053] FIG. 11 shows an alternate functional diagram of a boost
converter circuit and pulse generation circuit for use within the
IEAD.
[0054] FIG. 12 shows a refinement of the functional circuit
configurations of FIG. 11.
[0055] FIG. 13A shows one preferred schematic configuration for use
within an IEAD that implements the functional circuits shown in
FIG. 10.
[0056] FIG. 13B shows current and voltage waveforms associated with
the operation of the circuits shown in FIG. 13A.
[0057] FIG. 14 illustrates another preferred schematic
configuration for an IEAD similar to that shown in FIG. 13A, but
which uses an alternate output circuitry configuration for
generating the stimulus pulses.
[0058] FIG. 14A depicts yet a further preferred schematic
configuration for an IEAD similar to that shown in FIG. 13A or FIG.
14, but which includes additional enhancements and circuit
features.
[0059] FIGS. 14B and 14C show timing waveform diagrams that
illustrate the operation of the circuit of FIG. 14 before (FIG.
14B) and after (FIG. 14C) the addition of a cascode stage to the
IEAD circuitry that removes some undesirable transients from the
leading edge of the stimulus pulse.
[0060] FIGS. 14D and 14E illustrate timing waveform diagrams that
show the operation of the circuit of FIG. 14 before (FIG. 14D) and
after (FIG. 14E) the addition of circuitry that addresses a delay
when starting the current regulator U3 for low amplitude stimulus
pulses.
[0061] FIG. 15 shows a reverse trapezoidal waveform of the type
that is generated by the pulse generation circuitry of the IEAD,
and further illustrates one approach for achieving the desired
reverse trapezoidal waveform shape.
[0062] FIG. 15A shows a timing waveform diagram of representative
EA stimulation pulses generated by the IEAD during a stimulation
session in accordance with a specified stimulation regimen.
[0063] FIG. 15B shows a timing waveform diagram of multiple
stimulation sessions, and illustrates the waveforms on a more
condensed time scale.
[0064] FIG. 15C shows another preferred schematic configuration for
an IEAD similar to that shown in FIGS. 13A, 14 and 14A, which
includes all the additional enhancements included in the circuit of
FIG. 14A, and further includes a real time clock (RTC) module to
better facilitate and manage chronotherapeutic applications of the
stimulation regimen.
[0065] FIG. 16 shows a state diagram that depicts the various
states the IEAD circuitry may assume as controlled by an external
magnet.
[0066] FIG. 17 illustrates various exemplary acupoints on a
patient's body.
[0067] FIG. 17A shows a sectional view of a first way that an IEAD
may be implanted at a selected target stimulation site when there
is a bone or other skeletal structure that prevents the IEAD from
being implanted very deep below the skin.
[0068] FIG. 17B shows a sectional view of a second way that an IEAD
may be implanted at a selected target stimulation site when there
is a bone or other skeletal structure that prevents the IEAD from
being implanted very deep below the skin.
[0069] FIG. 18 is a table that summarizes various acupoints or
other target tissue locations that may be stimulated with
stimulation pulses provided by an IEAD implanted at or near the
target tissue locations in order to treat or provide therapy for
the conditions indicated.
[0070] Appendix A, submitted with one or more of Applicant's parent
applications, illustrates some examples of alternate symmetrical
electrode configurations that may be used with an IEAD of the type
described herein.
[0071] Appendix B, also submitted with one or more of Applicant's
parent applications, illustrates a few examples of non-symmetrical
electrode configurations that may be used with an IEAD made in
accordance with the teachings herein.
[0072] Appendix C, also submitted with one or more of Applicant's
parent applications, shows an example of the code used in a
micro-controller IC 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.
[0073] Appendix D, also submitted with one or more of Applicant's
parent applications, contains selected pages from the WHO Standard
Acupuncture Point Locations 2008 reference book.
[0074] Appendices A, B, C and D are incorporated by reference
herein, and comprise a part of the specification of this patent
application.
[0075] Throughout the drawings and appendices, identical reference
numbers designate similar, but not necessarily identical,
elements.
DETAILED DESCRIPTION
Overview
[0076] Disclosed and claimed herein is an implantable,
self-contained, leadless electroacupuncture (EA) device having at
least two electrode contacts mounted on the surface of its housing.
The EA device disclosed herein, which is also referred to as an
implantable electroacupuncture device (IEAD), is adapted to treat
various medical conditions, deficiencies and illnesses of a patient
when implanted at selected target tissue locations, e.g.,
acupoints, and when the IEAD is activated to provide EA stimulation
at those target locations in accordance with a specified
stimulation regimen. Ideally, the IEAD is coin-shaped and -sized,
making it easy to implant.
[0077] In one preferred embodiment, the electrodes on the surface
of the EA device include a central cathode electrode on a bottom
side of the housing, and an annular anode electrode that surrounds
the cathode. In another preferred embodiment, the annular anode
electrode is a ring electrode placed around the perimeter edge of
the coin-shaped housing.
[0078] The 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).
[0079] 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 affect or influence a particular medical
condition or illness of a patient that needs to receive
treatment.
[0080] 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). Once an incision has been made and an implant pocket has
been prepared by skilled medical personnel, implantation of the
IEAD is almost as easy as sliding a coin into a slot. Such
implantation can usually be completed in less than 10 minutes in an
outpatient setting, using only local anesthesia. When done
properly, no major or significant complications should occur during
or after the implant procedure. The EA device can also be easily
and quickly explanted, if needed.
[0081] The EA device is self-contained. It includes a primary
battery to provide its operating power. It includes all of the
circuitry it needs, in addition to the battery, to allow it to
perform its intended function for several years. Once implanted,
the patient will not even know it is there, except for a slight
tingling that may be felt when the device is delivering 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.
[0082] 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, through its electrodes formed on its case 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 that is being treated.
[0083] 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. One key feature included in the
mechanical design of the EA device is the use of a radial
feed-through assembly to connect the electrical circuitry inside of
its housing to one of the electrodes on the outside of the housing.
The design of this radial feed-through pin assembly greatly
simplifies the manufacturing process. The process places the
temperature sensitive hermetic bonds used in the assembly--the bond
between a pin and an insulator and the bond between the insulator
and the case wall--away from the perimeter of the housing as the
housing is hermetically sealed at the perimeter with a high
temperature laser welding process, thus preserving the integrity of
the hermetic bonds that are part of the feed-through assembly.
[0084] 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.
[0085] Another key feature included in the design of the EA device
is the use of a commercially-available battery as its primary power
source. Small, thin, disc-shaped batteries, also known as "coin
cells," are quite common and readily available for use with most
modern electronic devices. Such batteries come in many sizes, and
use 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, and so that dips in the battery output
voltage (caused by any sudden surge in instantaneous battery
current) do not occur that could compromise the performance of the
device. Furthermore, the energy requirements of other active
implantable therapies are far greater than can be provided by such
coin cells without frequent replacement.
[0086] 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.
[0087] Moreover, 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 it to patients at an affordable
cost.
DEFINITIONS
[0088] 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.
"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). "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.
[0089] As explained in more detail below, an important aspect of
the invention recognizes that an electroacupunture modulation
scheme need not be continuous, thereby allowing the implanted EA
device to use a small, high density, power source to provide such
non-continuous EA modulation. (Here, it should be noted that "EA
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 the patient. As a result, the
EA device can be very small. And, because the electrodes form an
integral part of the housing of the EA device, the EA device may
thus be implanted directly at (or very near to) the desired target
tissue location, e.g., the target stimulation site, such as the
target acupoint.
[0090] In summary, the basic approach of EA stimulation disclosed
herein includes: (1) identify an acupoint(s) or other target
stimulation site that may be used to treat or mediate the
particular illness, condition or deficiency that has manifest
itself in the patient, e.g., erectile dysfunction; (2) implant an
EA device, made as described herein, so that its electrodes are
located to be near or on the identified acupoint(s) or other target
stimulation site; (3) apply EA modulation, having a low intensity,
low frequency, and low duty cycle through the electrode(s) of the
EA device so that electrical stimulation pulses flow through the
tissue at the target stimulation site following a prescribed
stimulation regimen over several weeks or months or years. At any
time during this EA stimulation regimen, the patient's illness,
condition or deficiency may be evaluated and, as necessary, the
parameters of the EA modulation applied during the EA stimulation
regimen may be adjusted or "tweaked" in order to improve the
results obtained from the EA modulation.
Conditions Treated
[0091] The IEAD disclosed herein may be used to treat many
different medical conditions of a patient, including, inter alia,
(1) hypertension, (2) cardiovascular disease, (3) depression, (4)
bipolar disorder, (5) Anxiety, (6) obesity, (7) dyslipidemia, (8)
Parkinson's disease, (9) Essential tremor, and (10) erectile
dysfunction (ED). For each of these ten enumerated conditions,
Applicant has performed extensive research in the acupuncture art
to determine which acupoints are likely to be the best candidates
for being modulated (i.e., stimulated with electroacupuncture
pulses) in order to treat and/or provide some meaningful relief
relative to symptoms of these conditions. This research is
documented in some of Applicant's previously-filed patent
applications, which other patent applications can be located by
searching in the records of the U.S. Patent Office for patent
applications of Valencia Technologies Corporation, of Valencia,
Calif. As a result of this research, Applicant has identified at
least one acupoint for each of the above-identified ten enumerated
conditions/diseases, which at least one acupoint
represents--insofar as the inventors are presently aware--the best
candidate(s) for where EA stimulation from an IEAD of the type
described herein should be applied for successful treatment of the
condition/disease. Some overlap exists between the identified
acupoints, i.e., in some instances the same acupoint(s) may be
stimulated to treat multiple conditions. The results of this
research are summarized in Table 1, shown in FIG. 18.
[0092] As seen in Table 1 (FIG. 18), the ten conditions are listed
in the left column. The acupoint(s) that represents, based on
Applicant's research, the best candidate(s) for applying electrical
stimulation pulses in order to treat the indicated condition,
is/are listed in the column of Table 1 labeled "Acupoints (Target
Tissue Locations)". The nomenclature used in the reference book WHO
Standard Acupuncture Point Locations 2008 is used to identify most
of these acupoints. Moreover, selected pages from the WHO Standard
Acupuncture Point Locations 2008 reference book that show detailed
diagrams of where the identified acupoint(s) is/are located on the
human body are included in Appendix D, submitted herewith. Finally,
in the six columns on the right of Table 1, the stimulation
parameters thought by the inventors at the present time to provide
the most effective stimulation regimen for the identified
acupoint(s) are set forth. The meaning of these parameters will
become apparent from the description below under the heading
"Locations Stimulated and Stimulation Paradigms/Regimens," as well
as the description of the IEAD presented below in connection with
the description of, e.g., FIGS. 8A, 10, 14A, 15A and 15B.
[0093] It should be noted that the ten conditions enumerated in
Table 1 (FIG. 18) are only exemplary of a small set of conditions
of what Applicant believes may eventually be a much larger set of
conditions that can be treated by using an IEAD as described herein
to apply electrical stimulation to selected target tissue locations
throughout a patient's body. That is, the list of 10 conditions
presented above, and shown in Table 1, is an "open" list, not a
"closed" list. It is hoped that use of this device--the IEAD
described herein--, or equivalents thereof, will prove to be a
useful tool not only to provide needed treatment and relief for
patients suffering from any of these enumerated conditions, but
will also promote additional research that will identify many more
conditions and associated target tissue locations whereat EA
stimulation can be successfully applied.
[0094] In this regard, it should further be emphasized that "EA
stimulation" or "EA modulation", as those terms are used herein, is
not intended to limit the resulting electrical stimulation pulses
to be applied at a specified acupoint. Rather, for purposes herein,
"EA stimulation" or "EA modulation" is electrical stimulation that
is applied to whatever target tissue stimulation point has been
selected in a manner consistent with the teachings herein, i.e., at
a very low duty cycle. This low duty cycle (less than 0.05) means
using stimulation sessions that have a duration of 10-60 minutes,
and where the stimulation sessions are applied no more than once a
day, but usually only once a week or once every other week.
Further, "EA stimulation" or "EA modulation" means, most of the
time, using stimulation pulses during a stimulation session that
are at a low frequency (e.g., 1 Hz to 15 Hz), low intensity (less
than 25 mA amplitude), and narrow pulse width (e.g., from 0.1 to 2
m). Finally, "EA stimulation" or "EA modulation" means applying the
electrical stimulation through electrodes that are either attached
directly to the case of the EA device, or coupled to the EA device,
i.e., the IEAD, through a very short lead. In other words, there
are no needles inserted through the skin to reach the target
stimulation site, as occurs in traditional acupuncture, or
traditional electroacupuncture. Rather, everything associated with
the applied EA stimulation is done with a device, and its
electrodes, that is implanted.
Locations Stimulated and Stimulation Paradigms/Regimens
[0095] As indicated above, Applicant has identified the acupoints
(or other target tissue locations) listed in Table 1 (FIG. 18) as
most responsible in acupuncture studies and most ideal for
application of its technological approach to treat the conditions
indicated. A description of the acupoints listed in Table 1 can be
found in the reference book: WHO Standard Acupuncture Point
Locations 2008, previously incorporated herein by reference. See,
also, Appendix D, submitted herewith, and incorporated herein by
reference, which contains selected pages from this reference
book.
[0096] The stimulation parameters associated with the EA
stimulation that should be applied to at least one of the indicated
acupoints or other target tissue locations for treatment of the
specified condition are also shown or listed in Table 1. In
general, these parameters are typical of low-frequency
electroacupuncture. That is, the EA stimulation should be applied
at a low frequency, low intensity, and narrow pulse width. The
pulse width of the stimulation pulse is defined as a time T1. The
time interval between the start of one stimulation pulse and the
start of the next stimulation pulse is a time T2. The frequency, or
rate of occurrence of the stimulation pulses is thus 1/T2,
expressed in units of pulses/sec, or Hz. The ratio of T1/T2 should
be no greater than about 0.03, and is usually less than 0.01, thus
assuring a narrow stimulation pulse width. The intensity, or
amplitude, of the stimulation pulses (measured in either voltage or
current, i.e., units of volts or milliAmps, or mA) is defined as
A1. If the stimulation session has a duration of T3 minutes, and
the stimulation sessions occur only once every T4 minutes (which
may be expressed in units of minutes, hours, days or weeks, but
care must be exercised when determining the duty cycle, or T3/T4,
to ensure that the same units are used for both T3 and T4), then
the duty cycle is T3/T4, and, in accordance with the operation
restrictions of Applicant's IEAD, should be (must be) no greater
than 0.05 in order to preserve the stored power of the small
battery carried inside of the IEAD, and allowing the IEAD to
operate for several years.
[0097] In summary, it is to be emphasized that the duration and
rate of occurrence of the EA stimulation pulses applied by the IEAD
described herein are not arbitrary nor chosen haphazardly or by
guesswork. Rather these parameters have been chosen after a careful
examination of the reports of successful manual acupuncture
studies.
[0098] As can be seen from Table 1 (FIG. 18), the duration T3 of
the stimulation sessions for the ten conditions listed in Table 1
varies from as short as ten minutes to as long as about 70 minutes;
the interval between stimulation sessions T4 varies from as short
as 1/2 day to as long as 14 days. The stimulus pulses during a
stimulation session have a pulse width T1 that is, in some
instances, as short as 0.1 milliseconds (ms) and, in other
instances, as long as 2 ms. The period between application of
stimulus pulses varies from as short as 67 milliseconds (ms),
corresponding to a rate of about 15 Hz, to as long as 1 second,
corresponding to a rate of 1 Hz. The amplitude A1 of the stimulus
pulses varies from as low as 1 mA to as much as 25 mA. The
parameters T1, T2, T3, T4 and A1 define the stimulation paradigm or
regimen that is applied by the IEAD at a selected target tissue
location.
[0099] A representative pulse width of the stimulus pulse T1 is 0.5
ms. A representative period T2 for the stimulus pulse rate is 500
ms=0.5 seconds (rate=1/0.5=2 Hz). A representative duration of a
stimulation session T3 is thirty minutes, and a representative rate
of occurrence of the stimulation session T4 is once every week.
(Note: duty cycle T3/T4=30 min/10,080 min=0.003.) A representative
amplitude A1 of the stimulus pulse is, e.g., 15 mA, but can be set
as high as 25 mA.
Mechanical Design
[0100] A perspective view of one preferred embodiment of an
implantable electroacupuncture device (IEAD) 100 that may be used
for the purposes described herein is shown in FIG. 1. The IEAD 100
is also sometimes referred to as an implantable electroacupuncture
stimulator (IEAS). As seen in FIG. 1, the IEAD 100 has the
appearance of a disc or coin, having a front side 106, a back side
102 (not visible in FIG. 1) and an edge side 104.
[0101] 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 front side 106 may also be referred
to herein as the "cathode side" 106. The "back" side 102 is the
side opposite the front side and is the side farthest away from the
target stimulation point when the IEAD is implanted. The "back"
side 102 may also be referred to herein as the "skin" side 102
because most of the time it is the side closest to the skin when
the IEAD is implanted (but, as explained below in connection with
FIG. 17B, not always). 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 106 and a portion of
the edge side 104.
[0102] Many of the features associated with the mechanical design
of the IEAD 100 shown in FIG. 1 are the subject of Applicant's
co-pending U.S. patent application Ser. No. 13/777,901, filed Feb.
28, 2013, entitled "Radial Feed Through Packaging for an
Implantable Electroacupuncture Device," Docket No. VT11-001-06,
which application is incorporated here by reference.
[0103] 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. 7, 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 106 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.
[0104] The embodiment of the IEAD 100 shown in FIG. 1 utilizes two
electrodes, a cathode electrode 110 that is centrally positioned on
the front 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. 1, but
which is described hereinafter in connection with the description
of FIG. 7, 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.
[0105] Not visible in FIG. 1, 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. 5, 5A, 5B and 7.
[0106] 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. 7), except for the outside surface
of the anode ring electrode 120 and the cathode electrode 110.
[0107] The advantage of using a central cathode electrode and a
ring anode electrode is described in Applicant's co-pending U.S.
patent application Ser. No. 13/776,155, filed Feb. 25, 2013,
entitled "Electrode Configuration for an Implantable
Electroacupuncture Device," (Docket No. VT11-001-05), which
application is incorporated herein by reference. 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. 1-7) 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.
[0108] Turning next to FIG. 17, a representation of a human patient
is depicted showing the location of several acupoints on the
patient's body. As the reference book WHO Standard Acupuncture
Point Locations 2008 teaches, and as is known in the art, the
acupoints shown in FIG. 17 represent only a very small number of
the total number of acupoints that have been identified on the
human body. Any of these acupoints (those shown and not shown in
FIG. 17), as well as other target tissue locations, such as nerves
or muscle fibers, could be designated as the target stimulation
point for use by the IDEA described herein.
[0109] For example, FIG. 1A illustrates the location of an
exemplary target stimulation point 90, e.g. a point on a limb 80 of
the patient, whereat the IEAD of FIG. 1 may be implanted for the
treatment of a particular disease or condition of the patient. Such
location is representative of a wide variety of acupoints, or other
target tissue locations, where the IEAD of FIG. 1 could be
implanted.
[0110] An implanted IEAD 100 is illustrated generally in FIGS. 1A
and 1B. Shown in FIG. 1B is a sectional view of the limb 80, or
other body tissue, of the patient wherein a target tissue location
90 has been identified that is to receive electroacupuncture (EA)
treatment using the IEAD 100. An incision 84 (shown in FIG. 1A) is
made into the limb 80 a short distance, e.g., 10-15 mm, away from
the target tissue location 90. A slot (e.g., parallel to the limb
or tissue) 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 carefully slid through the
slot 84 into the pocket so that the center of the IEAD is located
under the point 90 on the skin surface. This implantation process
can be as easy as inserting a coin into a slot. With the IEAD 100
in place, the incision is sewn or otherwise closed, leaving the
IEAD 100 under the skin 80 at the location of the target point 90
where electroacupuncture (EA) stimulation is desired.
[0111] 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 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 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.
[0112] FIG. 1B illustrates a sectional view of the IEAD 100
implanted so as to be centrally located under the skin at the
selected target stimulation point 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 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 target point 90
is located, the cathode 110 is also centered over the acupoint axis
line 92.
[0113] FIG. 1B 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 target point
location indicated on the skin.
[0114] As can be seen from FIG. 17, some acupoints may be located
on the head of the patient, e.g., acupoints GV20, or in other
tissue locations where the patient's skull bone, or other skeletal
structure, prevent implanting the IEAD 100 very deep below the
skin. This situation is illustrated schematically in FIGS. 17A and
17B. As seen in these figures, a bone 89, e.g., the skull bone, is
right under the skin 80, with not much tissue separating the two.
These two figures assume that the actual desired target stimulation
point is a nerve 87 (or some other tissue formation) between the
underneath side of the skin 80 and the top surface of the bone 89.
Hence, the challenge is to implant the IEAD 100 in a manner that
provides effective EA stimulation at the desired target stimulation
site, e.g., at the nerve 87 (or other tissue formation) that
resides beneath the acupoint 90. FIGS. 17A and 17B illustrate
alternative methods for achieving this goal.
[0115] Shown in FIG. 17A is one alternative for implanting the IEAD
100 at an acupoint 90 located on the surface of the skin 80 above
the bone 89, where the actual target stimulation point is a nerve
87, or some other tissue formation, that is located between the
bone 89 and the underneath side of the skin 80. As shown in FIG.
17A, the IEAD 100 is implanted right under the skin with its front
surface 106 facing down towards the target tissue location 87. This
allows the electric fields (illustrated by the electric field
gradient lines 88) generated by the IEAD 100 when EA stimulation
pulses are to be generated to be most heavily concentrated at the
target tissue stimulation site 87. These electric field gradient
lines 88 are established between the two electrodes 110 and 120 of
the IEAD. For the embodiment shown here, these two electrodes
comprise a ring electrode 120, positioned around the perimeter edge
of the IEAD housing, and a central electrode 110, positioned in the
center of the front surface 102 of the IEAD housing. These gradient
lines 88 are most concentrated right below the central electrode,
which is where the target tissue location 87 resides. Hence, the
magnitude of the electrical stimulation current will also be most
concentrated at the target tissue location 87, which is the desired
result.
[0116] FIG. 17B shows another alternative for implanting the IEAD
100 at the acupoint 90 located on the surface of the skin 80 above
the bone 89, where the actual target stimulation point is a nerve
87, or some other tissue formation, that is located between the
bone 89 and the underneath side of the skin 80. As shown in FIG.
17B, the IEAD 100 is implanted in a pocket 81 formed in the bone 89
at a location underneath the acupoint 90. In this instance, and as
the elements are oriented in FIG. 17B, the front surface 106 of the
IEAD 100 faces upwards towards the target tissue location 87. As
with the implant configuration shown in FIG. 17A, this
configuration also allows the electric fields (illustrated by the
electric field gradient lines 88) that are generated by the IEAD
100 when EA stimulation pulses are generated to be most heavily
concentrated at the target tissue stimulation site 87.
[0117] There are advantages and disadvantages associated with each
of the two alternative implantation configurations shown in FIGS.
17A and 17B. Generally, the implantation procedure used to achieve
the configuration shown in FIG. 17A is a simpler procedure with
less risk. That is, all that need to be done by the surgeon to
implant that EA device 100 as shown in FIG. 17A is to make an
incision 82 in the skin 80 a short distance, e.g., 10-15 mm, away
from the acupoint 90. This incision should be made parallel to the
nerve 87 so as to minimize the risk of cutting the nerve 87. A slot
is then formed at the incision by lifting the skin closest to the
acupoint up at the incision and by carefully sliding the IEAD 100,
with its front side 102 facing the skull, into the slot so that the
center of the IEAD is located under the acupoint 90. Care is taken
to assure that the nerve 87 resides below the front surface of the
IEAD 100 as the IEAD is slid into position.
[0118] In contrast, if the implant configuration shown in FIG. 17B
is to be used, then the implant procedure is somewhat more
complicated with somewhat more risk. That is, to achieve the
implant configuration shown in FIG. 17B, a sufficiently large
incision must be made in the skin at the acupoint 90 to enable the
skin 80 to be peeled or lifted away to expose the surface of the
bone so that the cavity 81 may be formed in the bone. While doing
this, care must be exercised to hold the nerve 87 (or other
sensitive tissue areas) away from the cutting tools used to form
the cavity 81. Once the cavity 81 is formed, the IEAD 100 is laid
in the cavity, with its front surface 102 facing upward, the nerve
87 (and other sensitive tissue areas) are carefully repositioned
above the IEAD 100, and the skin is sewn or clamped to allow the
incision to heal. In this unique situation, where a cavity is
formed in the bone to hold the IEAD 100, the back side 102 of the
IEAD 100 (which sometimes is called the "skin" side), is actually
farthest away from the skin surface.
[0119] However, while the surgical procedure and attendant risks
may be more complicated when the configuration of FIG. 17B is
employed, the final results of the configuration of FIG. 17B may be
more aesthetically pleasing to the patient than are achieved with
the configuration of FIG. 17A. That is, given the shallow space
between the skin and the bone at an acupoint above the bone, the
implant configuration of FIG. 17A will likely result in a small
hump or bump at the implant site.
[0120] Insofar as Applicant is aware at the present time, of the
two implant configurations shown in FIGS. 17A and 17B, there is no
theoretical performance advantage that one implant configuration
provides over the other. That is, both implant configurations
should perform equally well insofar as providing EA stimulation
pulses at the desired target tissue location 87 is concerned.
[0121] Thus, which implant configuration is used will, in large
part, be dictated by individual differences in patient anatomy,
patient preference, and surgeon preferences and skill levels.
[0122] From the above, it is seen that one of the main advantages
of using a symmetrical electrode configuration that includes a
centrally located electrode surrounded by an annular electrode, as
is used in the embodiment described in connection with FIGS. 1-7,
is that the precise orientation of the IEAD 100 within its implant
location is not important. So long as one electrode faces and 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
desired target tissue location. This causes the EA stimulation
current to flow at (or very near to) the target tissue location
87.
[0123] FIG. 2 shows a plan view of the "cathode" (or "front") side
106 of the IEAD 100. As seen in FIG. 2, 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).
[0124] FIG. 2A shows a side view of the IEAD 100. The ring anode
electrode 120, best seen in FIG. 2B, has a width W1 of about 1.0
mm, or approximately 1/2 of the width W2 of the IEAD.
[0125] FIG. 3 shows a plan view of the "back" (or "skin") side 102
of the IEAD 100. As will be evident from subsequent figure
descriptions, e.g., FIGS. 5A and 5B, the back side 102 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.
[0126] FIG. 3A is a sectional view of the IEAD 100 of FIG. 1 taken
along the line A-A of FIG. 3. 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. 3A 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.
[0127] FIG. 4 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 a
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.
[0128] FIG. 4A 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. 7) 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.
[0129] FIG. 5 shows a plan view of the empty IEAD case 124 shown in
the perspective view of FIG. 4. An outline of the recess cavity 140
is also seen in FIG. 5, 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. 5
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.
[0130] FIG. 5A depicts a sectional view of the IEAD housing 124 of
FIG. 5 taken along the section line A-A of FIG. 5. FIG. 5B shows an
enlarged view or detail of the portion of FIG. 5A that is encircled
with the line B. Referring to FIGS. 5A and 5B 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. 5A and 5B, 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.)
[0131] 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.)
[0132] 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.
[0133] One important advantage provided by the feed-through
assembly shown in FIGS. 4A, 5, 5A and 5B 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.
[0134] Additional details associated with the radial feed-through
pin 130, and its use within an electronic package, such as the IEAD
100 described herein, may be found in Applicant's co-pending U.S.
patent application Ser. No. 13/777,901, filed Feb. 26, 2013,
entitled "Radial Feed Through Packaging for an Implantable
Electroacupuncture Device," Docket No. VT11-001-06, which
application was previously incorporated herein by reference.
[0135] Turning next to FIG. 6, 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. 4 and FIG. 5.
[0136] FIGS. 6A and 6B show a plan view and side view,
respectively, of the electronic assembly 133 shown in FIG. 6. 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 many of the co-pending patent applications referenced
herein.
[0137] FIG. 7 shows an exploded view of the complete IEAD 100,
illustrating its main constituent parts. As seen in FIG. 7, 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 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.
[0138] Other components included in the IEAD assembly, but not
necessarily shown or identified in FIG. 7, 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.
[0139] Also not shown in FIG. 7 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.
[0140] Further shown in FIG. 7 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 over-molding process is used to accomplish this, although
over-molding using silicone LSR 70 (curing temperature of
120.degree. C.) with an injection molding process cannot be used.
Over-molding 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.)
[0141] 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.
[0142] 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.
[0143] 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 FIGS. 1, and 2-7. 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.
[0144] 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
acupuoint(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.
[0145] 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.
[0146] 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.
[0147] FIG. 7A 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. 7A, identified as "I", schematically illustrates one
central electrode 110 surrounded by a single 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. 1-7, and is presented in FIG. 7A for reference and
comparative purposes.
[0148] In the lower left corner of FIG. 7A, 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. (The oval-shaped electrode array 320a could also be other
shapes, e.g., 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.
7A).
[0149] 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".
[0150] In the lower right corner of FIG. 7A, identified as "III",
en electrode configuration is schematically illustrated that has a
central electrode/array 310b of three electrode segments of a first
polarity surrounded by an oval-shaped electrode array 320b of three
electrode segments of a second polarity. (This oval-shaped array
320b could also be other shapes, e.g., round.) As shown in
configuration III of FIG. 7A, the three electrode segments of the
electrode array 320b are positioned more or less equidistant from
each other, although a true equidistant positioning, especially
relative to the central electrode array 310b, is not readily
achieved with 3 electrodes placed in an oval-shaped array. 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.
[0151] In the upper right corner of FIG. 7A, 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.
[0152] The electrode configurations I, II, III and IV shown
schematically in FIG. 7A 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.
[0153] 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.
[0154] It should be noted that 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.
[0155] For a more thorough description of the electrode materials
best suited for the cathode electrode 110 and the anode electrode
120, as well as the surface area required for these electrodes, see
Applicant's co-pending U.S. patent application Ser. No. 13/776,155,
filed Feb. 25, 2013, "Electrode Configuration for an Implantable
Electroacupuncture Device," Docket No. VT11-001-05, previously
incorporated hereby by reference.
[0156] 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
[0157] Next, with reference to FIGS. 8A-16, the electrical design
and operation of the circuits employed within the IEAD 100 will be
described. Additional details regarding the electrical design and
operation of the IEAD may be gleaned from Applicant's co-pending
U.S. patent application Ser. No. 13/769,699, filed Feb. 18, 2013,
entitled "Circuits and Methods for Using a High Impedance, Thin,
Coin-cell Type Battery in an Implantable Electroacupuncture
Device," Docket No. VT11-001-04, which application is incorporated
herein by reference.
[0158] FIG. 8A shows a functional block diagram of an implantable
electroacupuncture device (IEAD) 100 made in accordance with the
teachings disclosed herein. As seen in FIG. 8A, the IEAD 100 uses
an implantable battery 215 having a battery voltage V.sub.BAT. 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.
[0159] 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 Cc 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.
[0160] As explained more fully below in connection with the
description of FIGS. 15A and 15B, and as can also be seen from the
waveform 219 shown in the lower right corner of FIG. 8A, the
prescribed stimulation regimen typically comprises a continuous
stream of stimulation pulses having a fixed amplitude, e.g.,
V.sub.A volts (also referred to as an amplitude A1), a fixed pulse
width, e.g., 0.5 millisecond, and at a fixed frequency, e.g., 2 Hz,
during each stimulation session. The stimulation session, also as
part of the stimulation regimen, is generated at a very low duty
cycle, e.g., for 30 minutes once each 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 from as short as, e.g., 1 day, to as long as, e.g.,
14 days.
[0161] 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).
[0162] 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.
8A.
[0163] Thus, in the embodiment described in FIG. 8A, 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.
[0164] 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.
[0165] The IEAD 100 shown in FIG. 8A, and packaged as described
above in connection with FIGS. 1-7, 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 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.
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.
[0166] 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. 8B. 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.
[0167] In the boost converter circuit example shown in FIG. 8B, the
battery is modeled as a voltage source with a simple series
resistance. With reference to the circuit shown in FIG. 8A, 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. 9A, where the horizontal axis is time,
and the vertical axis on the left is voltage, and the vertical axis
of the right is current.
[0168] Referring to the waveform in FIG. 9A, at boost converter
startup (10 ms), there is 70 mA of current drawn from the battery
with only .about.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 .about.40 mV.
[0169] 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.
9B. In FIG. 9B, as in FIG. 9A, the horizontal axis is time, the
left vertical axis is voltage, and the right vertical axis is
current.
[0170] As seen in FIG. 9B, 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 (.about.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.
[0171] Also, it should be noted that although the battery used in
the boost converter circuit is modeled in FIG. 8B 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.
[0172] 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 EA stimulation pulses are generated.
[0173] To provide this needed current management, the IEAD 100
disclosed herein employs electronic circuitry as shown in FIG. 10,
or equivalents thereof. Similar to what is shown in FIG. 8A, the
circuitry of FIG. 10 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.
[0174] In the circuitry shown in FIG. 10, 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. 10, V.sub.REF is proportional to
the output voltage V.sub.OUT, as determined by the resistor
dividing network of R1 and R2.
[0175] The switches S.sub.P and S.sub.R, shown in FIG. 10 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.
[0176] 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.
[0177] Thus, it is seen that in one embodiment of the electronic
circuitry used within the IEAD 100, as shown in FIG. 10, 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. 10). A
capacitor CF supplies instantaneous current for the short ON time
that the control signal enables the boost converter circuit to
operate. And, the capacitor C.sub.F is recharged from the battery
during the relatively long OFF time when the control signal
disables the boost converter circuit.
[0178] An alternate embodiment of the electronic circuitry that may
be used within the IEAD 100 is shown in FIG. 11. This circuit is in
most respects the same as the circuitry shown in FIG. 10. However,
in this alternate embodiment shown in FIG. 11, the boost converter
circuit 200 does not have a specific shut down input control.
Rather, as seen in FIG. 11, the boost converter circuit is shut
down by applying a control voltage to the feedback input of the
boost converter circuit 200 that is higher than V.sub.REF. When
this happens, i.e., when the control voltage applied to the
feedback input is greater than V.sub.REF, the boost converter will
stop switching and draws little or no current from the battery. The
value of V.sub.REF is typically a low enough voltage, such as a 1.2
V band-gap voltage, that a low level digital control signal can be
used to disable the boost converter circuit. To enable the boost
converter circuit, the control signal can be set to go to a high
impedance, which effectively returns the node at the V.sub.REF
terminal to the voltage set by the resistor divider network formed
from R1 and R2. Alternatively the control signal can be set to go
to a voltage less than V.sub.REF.
[0179] A low level digital control signal that performs this
function of enabling (turning ON) or disabling (turning OFF) the
boost converter circuit is depicted in FIG. 11 as being generated
at the output of a control circuit 220. The signal line on which
this control signal is present connects the output of the control
circuit 220 with the V.sub.REF node connected to the feedback input
of the boost converter circuit. This control signal, as suggested
by the waveform shown in FIG. 11, varies from a voltage greater
than V.sub.REF, thereby disabling or turning OFF the boost
converter circuit, to a voltage less than V.sub.REF, thereby
enabling or turning the boost converter circuit ON.
[0180] A refinement to the alternate embodiment shown in FIG. 11 is
to use the control signal to drive the low side of R2 as shown in
FIG. 12. That is, as shown in FIG. 12, the boost converter circuit
200 is shut down when the control signal is greater than V.sub.REF
and runs when the control signal is less than V.sub.REF. A digital
control signal can be used to perform this function by switching
between ground and a voltage greater than V.sub.REF. This has the
additional possibility of delta-sigma modulation control of
V.sub.OUT if a measurement of the actual V.sub.OUT is available for
feedback, e.g., using a signal line 222, to the controller.
[0181] One preferred embodiment of the circuitry used in an
implantable electroacupuncture device (IEAD) 100 that employs a
digital control signal as taught herein is shown in the schematic
diagram shown in FIG. 13A. In FIG. 13A, there are basically four
integrated circuits (ICs) used as the main components. The IC U1 is
a boost converter circuit, and performs the function of the boost
converter circuit 200 described previously in connection with FIGS.
8B, 10, 11 and 12.
[0182] The IC U2 is a micro-controller IC and is used to perform
the function of the control circuit 220 described previously in
connection with FIGS. 10, 11 and 12. A preferred IC for this
purpose is a MSP430G2452I 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, as taught below in connection
with FIGS. 15A and 15B. This allows the programming features of the
micro-controller to be carried out in a simple and straightforward
manner.
[0183] The micro-controller U2 primarily performs the function of
generating the digital signal that shuts down the boost converter
to prevent too much instantaneous current from being drawn from the
battery V.sub.BAT. 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.
[0184] 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 pulled through the closed switch M1, which is essentially
the same 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 drops across the
switches and current source.
[0185] The switches SR and SP described previously in connection
with FIGS. 10, 11 and 12 are realized with transistor switches M1,
M2, M3, M4, M5 and M6, each of which is controlled directly or
indirectly by control signals generated by the micro-controller
circuit U2. For the embodiment shown in FIG. 13A, these switches
are controlled by two signals, one appearing on signal line 234,
labeled PULSE, and the other appearing on signal line 236, labeled
RCHG (which is an abbreviation for "recharge"). For the circuit
configuration shown in FIG. 13A, the RCHG signal on signal line 236
is always the inverse of the PULSE signal appearing on signal line
234. This type of control does not allow both switch M1 and switch
M2 to be open or closed at the same time. Rather, switch M1 is
closed when switch M2 is open, and switch M2 is closed, when switch
M1 is open. When switch M1 is closed, and switch M2 is open, the
stimulus pulse appears across the load, R.sub.LOAD, with the
current flowing through the load, R.sub.LOAD, being essentially
equal to the current flowing through resistor R5. When the switch
M1 is open, and switch M2 is closed, no stimulus pulse appears
across the load, and the coupling capacitors C5 and C6 are
recharged through the closed switch M2 and resistor R6 to the
voltage V.sub.OUT in anticipation of the next stimulus pulse.
[0186] The circuitry shown in FIG. 13A is only exemplary of one
type of circuit that may be used to control the pulse width,
amplitude, frequency, and duty cycle of stimulation pulses applied
to the load, R.sub.LOAD. Any type of circuit, or control, that
allows stimulation pulses of a desired magnitude (measured in terms
of pulse width, frequency and amplitude, where the amplitude may be
measured in current or voltage) to be applied through the
electrodes to the patient at the specified acupoint at a desired
duty cycle (stimulation session duration and frequency) may be
used. However, for the circuitry to perform its intended function
over a long period of time, e.g., years, using only a small energy
source, e.g., a small coin-sized battery having a high battery
impedance and a relatively low capacity, the circuitry must be
properly managed and controlled to prevent excessive current draw
from the battery.
[0187] It is also important that the circuitry used in the IEAD
100, e.g., the circuitry shown in FIG. 10, 11, 12, 13A, 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 being stimulated. This tissue impedance, as
shown in FIGS. 11 and 12, 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. 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. 13A, is one
way to satisfy this need.
[0188] Still referring to FIG. 13A, a fourth IC U4 is connected to
the micro-controller U2. For the embodiment shown in FIG. 13A, the
IC 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. 13A
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.
[0189] 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.
[0190] Another coding scheme that could be used is a sequence-based
coding scheme. That is, application of 3 magnetic pulses may be
used to signal one external command, if the sequence is repeated 3
times. A sequence of 2 magnetic pulses, repeated twice, may be used
to signal another external command. A sequence of one magnetic
pulse, followed by a sequence of two magnetic pulses, followed by a
sequence of three magnetic pulses, may be used to signal yet
another external command.
[0191] Other simple coding schemes may also be used, such as the
letters AA, RR, HO, BT, KS using international Morse code. That is,
the Morse code symbols for the letter "A" are dot dash, where a dot
is a short magnetic pulse, and a dash is a long magnetic pulse.
Thus, to send the letter A to the IEAD 100 using an external
magnet, the user would hold the magnet over the area where the IEAD
100 is implanted for a short period of time, e.g., one second or
less, followed by holding the magnet over the IEAD for a long
period of time, e.g., more than one second.
[0192] 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.
[0193] The current and voltage waveforms associated with the
operation of the IEAD circuitry of FIG. 13A are shown in FIG. 13B.
In FIG. 13B, the horizontal axis is time, the left vertical axis is
voltage, and the right vertical axis is current. The battery in
this example has 160 Ohms of internal impedance.
[0194] Referring to FIGS. 13A and 13B, during startup, the boost
converter ON time is approximately 30 microseconds applied every
7.8 milliseconds. This is sufficient to ramp the output voltage
V.sub.OUT up to over 10 V within 2 seconds while drawing no more
than about 1 mA from the battery and inducing only 150 mV of input
voltage ripple.
[0195] The electroacupuncture (EA) simulation pulses resulting from
operation of the circuit of FIG. 13A have a width of 0.5
milliseconds and increase in amplitude from approximately 1 mA in
the first pulse to approximately 15 mA in the last pulse. The
instantaneous current drawn from the battery is less than 2 mA for
the EA pulses and the drop in battery voltage is less than
approximately 300 mV. The boost converter is enabled (turned ON)
only during the instantaneous output current surges associated with
the 0.5 milliseconds wide EA pulses.
[0196] Another preferred embodiment of the circuitry used in an
implantable electroacupuncture device (IEAD) 100 that employs a
digital control signal as taught herein is shown in the schematic
diagram of FIG. 14. The circuit shown in FIG. 14 is, in most
respects, very similar to the circuit described previously in
connection with FIG. 13A. What is new in FIG. 14 is the inclusion
of a Schottky diode D4 at the output terminal of the boost
convertor U1 and the inclusion of a fifth integrated circuit (IC)
U5 that essentially performs the same function as the switches
M1-M6 shown in FIG. 13A.
[0197] 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. 14 is
designed, the output voltage V.sub.OUT is designed to be nominally
15 volts using a battery that has a nominal battery voltage of only
3 volts. (In contrast, the embodiment shown in FIG. 13A is designed
to provide an output voltage that is nominally 10-12 volts, using a
battery having a nominal output voltage of 3 volts.)
[0198] The inclusion of the fifth IC U5 in the circuit shown in
FIG. 14 is, as indicated, used to perform the function of a switch.
The other ICs shown in FIG. 14, U1 (boost converter), U2
(micro-controller), U3 (voltage controlled programmable current
source) and U4 (electromagnetic sensor) are basically the same as
the IC's U1, U2, U3 and U4 described previously in connection with
FIG. 13A.
[0199] The IC U5 shown in FIG. 14 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.
[0200] Yet another preferred embodiment of the circuitry used in an
implantable electroacupuncture device (IEAD) 100 that employs an
ON-OFF approach to duty-cycle modulate the boost converter as a
tool for limiting the amount of instantaneous battery current drawn
from the high impedance battery 215 is shown in the schematic
diagram of FIG. 14A. The circuit shown in FIG. 14A is, in most
respects, very similar to, or the same as, the circuit described
previously in connection with FIG. 14 or FIG. 13A, and that
description will not be repeated here. What is new in FIG. 14A are
the addition of elements and features that address additional
issues associated with the operation of an IEAD 100.
[0201] One feature included in the circuitry of FIG. 14A, which is
described briefly above in connection with the description of FIG.
10, is that the boost converter circuit U1 is modulated ON and OFF
using digital control generated within the boost converter circuit
U1 itself. 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, in the embodiment shown in FIG. 14A, 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 high enough to ensure the
microcontroller IC U2, and other circuitry associated with the
operation of the IEAD 100, remain operational.
[0202] 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.
[0203] 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.
[0204] 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.
[0205] In a preferred implementation, the microcontroller circuit
U2 used in FIG. 14A comprises an MSP430G2452IRSA 16
micro-controller, commercially available from Texas Instruments, or
equivalent microcontroller The 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.
[0206] Another feature or enhancement provided by the circuit
implementation depicted in FIG. 14A 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. 14. 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. The gate (G) terminal of
the switch Q1 is driven by the battery voltage, V.sub.BAT, which
means the voltage at the source terminal (S) of switch Q1, which is
connected to the IN terminal of the current source U3, is limited
to roughly V.sub.BAT-V.sub.GS, where V.sub.GS is the threshold
voltage across the gate (G)-source (S) terminals of Q1.
[0207] Use of this N-MOSFET switch Q1 as depicted in FIG. 14A
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 because of the
Miller effect. That is, there is considerable loop gain in the
operation of the U3 current source circuit to servo the current.
This loop gain directly scales the input capacitance so that there
is a much larger leading edge spike on the pulse. This in turn
causes a 30 to 40 microsecond transient at the leading edge of the
current pulse as the current source U3 recovers current
regulation.
[0208] An example of this leading edge transient is illustrated in
the timing waveform diagram of FIG. 14B. In FIG. 14B (as well as in
FIGS. 14C, 14D and 14E, which all show similar timing waveform
diagrams), the horizontal axis is time and the vertical axis is
voltage, which (assuming a resistive load of 600 ohms) may readily
be converted to current, as has been done in these figures. The
stimulus pulse begins at a trigger location near the left edge of
the waveform, labeled TRIG. As seen in FIG. 14B, immediately after
the trigger point, which should mark the beginning or leading edge
of the stimulus pulse, an initial spike 251 occurs that has a
magnitude on the order of twice the amplitude of the stimulus
pulse. This spike 251 shoots down (as the waveform is oriented in
the figures) and then shoots back up, and eventually, after a delay
of t1 microseconds, becomes the leading edge of the pulse. The
delay t1 is about 30-40 microseconds, which means that the leading
edge of the stimulus pulse is delayed 30-40 microseconds. Having a
leading edge delay of this magnitude is not a desirable result.
[0209] Next, with the cascode stage (comprising the switch Q1)
connected to the input terminal, IN, of the current source U3, the
stimulus pulse is again illustrated. Because the cascode stage
significantly reduces the input capacitance looking into the drain
(D) terminal of the switch Q1, the leading edge transient is
significantly reduced, as illustrated in the timing waveform
diagram of FIG. 14C. As seen in FIG. 14C, the leading edge
transient has all but disappeared, and the delay t1 between the
trigger point and the leading edge of the stimulus pulse is
negligible.
[0210] Another feature or enhancement provided by the circuitry of
FIG. 14A is to address a delay that is seen when starting up the
programmable current source U3 at 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, t.sub.D, between
the trigger point, TRIG, and the leading edge 253 of the stimulus
pulse. FIG. 14D illustrates this long delay, t.sub.D, which is on
the order of 200 microseconds.
[0211] The address the problem illustrated in the waveform diagram
of FIG. 14D, a Schottky diode D5 is connected in the circuit of
FIG. 14A from an output port on the microcontroller circuit U2 to
the input port, IN, of the current source circuit U3. In a
preferred implementation of the circuit of FIG. 14A, this Schottky
diode D5 is realized using a BAT54XV2DKR diode, commercially
available from Fairchild Semiconductor. This diode is used to
warm-up or "kick start" the circuit U3 when the pulse amplitude is
low so that there is less of a delay, t.sub.D, before current is
regulated at the start of the pulse. Since the cascode stage Q1
keeps the drop across U3 low, U3 can be driven directly from the
microcontroller U2 at the start of the pulse without significantly
changing the pulse characteristics (e.g., amplitude or timing) in
such a way that the delay, t.sub.D, before current is regulated at
the start of the pulse can be reduced.
[0212] FIG. 14E illustrates the timing waveform diagram achieved
using the circuit of FIG. 14A with the diode D5 inserted so as to
allow the microcontroller U2 to directly drive, or "kick start",
the current source circuit U3 at the start of the pulse. As seen in
FIG. 14E, the delay, t.sub.D, realized with the "kick start" has
been significantly reduced from what it was without the "kick
start" (as shown in FIG. 14D), e.g., from about 200 microseconds to
about 40 microseconds, or less. Thus, this "kick start" feature
shortens the undesired delay, t.sub.D, by at least a factor of
about 5.
[0213] An additional feature provided by the circuitry of FIG. 14A
addresses a concern regarding EMI (electromagnetic interference).
EMI can occur, for example, during electrocautery and/or external
defibrillation. Should any of the circuit elements used within the
IEAD 100, such as the analog switch U5, have a transient voltage
exceeding approximately 0.3 V appear on its pins (which transient
voltage could easily occur if the IEAD is subjected to uncontrolled
EMI), then the IC could be damaged. To prevent such possible EMI
damage, the output voltage pulse, appearing on the signal line
labeled V.sub.PULSE, is clamped to ground through the forward bias
direction of the diode D3. In contrast, in the circuits shown in
FIGS. 13A and 14, there are two zenor diodes, D2 and D3, connected
back to back, to limit the voltage appearing on the V.sub.PULSE
line to voltages no greater than the zenor diode voltage in either
direction. As seen in FIG. 14A, diode D2 has been replaced with a
short, thereby clamping the voltage that can appear on the output
voltage line--the signal line where V.sub.PULSE appears--in one
polarity direction to no greater than the forward voltage drop
across the diode D3.
[0214] As is evident from the waveforms depicted in FIGS. 14B, 14C,
14D and 14E, the basic current stimulus waveform is not a square
wave, with a "flat top", (or, in the case of a negative current
waveform, with a "flat bottom") as depicted in most simplified
waveform diagrams (see, e.g., FIG. 15A). Rather, the current
stimulus waveforms shown in FIGS. 14B, 14C, 14D and 14E have what
the inventors refer to as a reverse trapezoidal shape. That is, the
current waveforms start at a first value, at the leading edge of
the pulse, and gradually ramp to a second, larger, value at the
trailing edge of the pulse (i.e., the current increases during the
pulse). For a negative-going pulse, as is shown in these figures,
the ramp slopes downward, but this corresponds to the amplitude of
the pulse getting larger.
[0215] This pulse shape--a reverse trapezoidal shape--for the
current stimulus pulse is by design. That is, the inventors want
the current to increase during the pulse because such shape is
believed to be more selective for the recruitment of smaller fiber
diameter tissue and nerves, and thus has the potential to be more
effective in achieving its intended goal of activating desired
tissue at the target tissue location.
[0216] The reverse trapezoidal stimulus pulse shape is illustrated
in more detail in FIG. 15, as is one manner for achieving it. Shown
on the right side of FIG. 15 is a sketch of reverse trapezoidal
pulse. (Note, it is referred to as a "reverse trapezoidal" pulse
because the current, or waveform, gets larger or increases during
the pulse. This is in contrast to a conventional voltage regulated
pulse, which is "trapezoidal", but in the other direction, i.e.,
the current decreases during the pulse.) As seen in FIG. 15, the
reverse trapezoidal pulse has a duration T1, but the magnitude
(amplitude) of the current during the pulse increases from a first
value at the leading edge of the pulse to a second value at the
trailing edge of the pulse. The increase in current from the
leading edge of the pulse to the trailing edge is a value A.sub.P.
The average amplitude of the pulse during the pulse time T1 is a
value A1, which is typically measured at a time T.sub.M, which is
about in the middle of the pulse. That is, T.sub.M=1/2T1.
[0217] Also shown in FIG. 15, on the left side, is the circuitry
that is used to create the reverse trapezoidal waveform. This
circuitry is part of the circuitry shown, e.g., in FIG. 14A, and
includes a capacitor C1 in parallel with a large resistor R8 (270
K.OMEGA.) connected to the "set" terminal of the programmable
current source U3. The "AMPSET" signal, generated by the
micro-controller circuit U2 to set the amplitude A1 of the current
stimulus pulse to be generated, is applied to the "set" terminal of
U3. When enabled by the AMPSET signal, the capacitor C1 starts to
charge up during the pulse at a rate of approximately 10 .mu.A
(which comes from the "set" pin of U3, i.e., from the circuitry
inside of U3). For C1=0.1 microfarads, this turns out to be 100
mV/ms, or 50 mV for a pulse having a pulse duration or width (T1)
of 0.5 ms. Since the pulse current is approximately equal to
V.sub.SET/R5, the pulse current will increase by 50 mV/R5. Or,
where R5 is 22 ohms, this increase in current turns out to be 50
mV/22=2.27 mA at the end of the 0.5 ms pulse. This increase is
essentially fixed regardless of the programmed pulse amplitude.
[0218] While the circuitry described above performs the intended
function of causing the current stimulus pulse to have a reverse
trapezoidal shape in a simple and straightforward manner, it should
be noted that there are other circuits and techniques that could
also be used to achieve this same result. Moreover, it would be
possible to directly control the shape of the V.sub.SET signal
during the pulse duration in order to create any desired stimulus
pulse shape.
[0219] As shown in embodiment of the IEAD shown in FIG. 14A, the
stimulation circuitry uses a micro-controller integrated circuit
(IC) U2 which generates all of the operating control signals needed
to guide other circuits, including the Boost Converter circuit IC
U1, to generate the desired stream of stimulation pulses. These
other circuits include a programmable current source IC U3, an
analog switch U5, and a magnetic sensor U4. As can be seen in FIG.
14A, the micro-controller circuit U2 is driven by a clock circuit
that includes a crystal oscillator to provide a very stable
frequency reference. However, when the stimulus pulses are not
being generated--which is most of the time given the very low duty
cycle of operation, e.g., T3/T4 is less than 0.05--the
micro-controller U2 is able to go into a very low power sleep
state, thereby conserving power.
[0220] In order for the present invention to provide accurate
chronotherapeutics (i.e., the delivery of stimulation sessions
having very precise stimulation parameters at very precise times),
it would be desirable to use a crystal time base. In the existing
micro-controller U2 design, however, the crystal clock circuit does
not provide an accurate time base; rather, all it provides is a
steady or stable clock signal that can be counted using simple
counter circuits. A crystal time base, on the other hand, could
accurately perform all the functions of a rather sophisticated stop
watch, including keeping track of multiple time bases.
[0221] A crystal time base (operating all the time--which it would
need to do to provide accurate chronotherapeutics) would roughly
double the battery current between therapy sessions, thereby taking
the nominal longevity of the implantable electroacupuncture device
(IEAD) down roughly from 3 years to 2 years.
[0222] Reducing the longevity of the IEAD by a factor of 1/3 is not
viewed as an acceptable tradeoff to provide accurate
chronotherapeutics. Hence, what is needed is a design, or alternate
approach, whereby an accurate time base could be provided without
sacrificing a significant loss in longevity of the IEAD.
[0223] One way to accomplish this desired result is to add another
small IC to the circuits of the IEAD that functions as a real time
clock (RTC). Such RTC may be realized from a very small device
(3.2.times.1.5 mm) that runs on 360 nanoAmps (nA) of current. Such
device, referred to as a Real Time Clock Module is commercially
available from Micro Crystal AG, of Grenchen, Switzerland, as part
number RV-4162-C7.
[0224] A schematic diagram of an IEAD design that uses such an RTC
Module to replace the crystal time base presently used with the
micro-controller U2 is shown in FIG. 15C. In most respects, the
circuit shown in FIG. 15C is the same as the circuit shown in FIG.
14A. The one key difference between the IEAD circuit of FIG. 15A
and the IEAD circuit of FIG. 14A, is the insertion of a RTC module
U6. As seen in FIG. 15C, the RTC module U6 is connected to the
micro-controller circuit U2 and replaces the previously-used
external crystal oscillator. The RTC module U6 is able to be set to
wake up the micro-controller circuit U2 when needed, and/or put the
micro-controller U2 in a shut-down (sleep) state when not needed.
Advantageously, the shut down mode is even a lower power state than
is achieved with the sleep state controlled by the previously-used
external crystal oscillator.
[0225] From the above description, it is seen that an implantable
IEAD 100 is provided that uses a digital control signal to
duty-cycle limit the instantaneous current drawn from the battery
by a boost converter. Three different exemplary functional
configurations (FIGS. 10, 11 and 12) are taught for achieving this
desired result, and four exemplary circuit designs, or
implementations, have been presented that may be used to realize
the desired configurations (FIGS. 13A, 14, 14A and 15C). One
implementation (FIG. 15C), in addition to including all the
enhancements added to the base implementation circuit of FIG. 13A
(to address, e.g., problems of slow starts, delays, and needed
circuit isolation, and to add improvements such as better
switching, reverse trapezoidal stimulation wave shapes and EMI
protection), teaches the use of a real time clock module to provide
a crystal time base to facilitate the use of chronotherapeutics.
One configuration (FIG. 12) teaches the additional capability to
delta-sigma modulate the boost converter output voltage.
[0226] Delta-sigma modulation is well described in the art.
Basically, it is a method for encoding analog signals into digital
signals or higher-resolution digital signals into lower-resolution
digital signals. The conversion is done using error feedback, where
the difference between the two signals is measured and used to
improve the conversion. The low-resolution signal typically changes
more quickly than the high-resolution signal and it can be filtered
to recover the high resolution signal with little or no loss of
fidelity. Delta-sigma modulation has found increasing use in modern
electronic components such as converters, frequency synthesizers,
switched-mode power supplies and motor controllers. See, e.g.,
Wikipedia, Delta-sigma modulation.
Use and Operation
[0227] With the implantable electroacupuncture device (IEAD) 100 in
hand, the IEAD 100 may be 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. FIGS. 15A and 15B show timing waveform
diagrams illustrating the EA stimulation parameters used by the
IEAD to generate EA stimulation pulses. As seen in FIG. 15A, 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, but may, in some instances, be as much as 0.03. The
duration of a stimulation session is dictated or defined by the
time period T3. The amplitude of the stimulation pulses is defined
by the amplitude A1. This amplitude may be expressed in either
voltage or current.
[0228] FIG. 15B illustrates the manner in which the stimulation
sessions are administered in accordance with a specified
stimulation regimen. FIG. 15B 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. T4 thus is the period of the
stimulation session frequency, and the stimulation session
frequency is equal to 1/T4.
[0229] In order to allow the applied stimulation to achieve its
desired effect on the body tissue at the selected target
stimulation site, the period of the stimulation session T4 may be
varied when the stimulation sessions are first applied. This can be
achieved by employing a simple algorithm within the circuitry of
the EA device that 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.
[0230] By way of example, 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.
[0231] 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 that
defines session durations and intervals whereby the automatic
session interval can be shorter for the first week or so. For
example, T3 is 30 minutes, the first 30 minute 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 4.sup.th 30 minute session
could be delivered for all subsequent sessions after 7 days.
[0232] If a triggered session is delivered completely, it advances
the therapy schedule to the next table entry.
[0233] Another enhancement is that the initial set amplitude only
takes effect if the subsequent triggered session is completely
delivered. If the first session is 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.
[0234] Finally, the amplitude and place in the 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.
[0235] By way of example, one preferred set of parameters that
could be used to define a stimulation regimen is as follows: [0236]
T1=0.5 milliseconds [0237] T2=500 milliseconds [0238] T3=30 minutes
[0239] T4=7 days (10,080 minutes) [0240] A1=15 volts (across 1
K.OMEGA.), or 15 milliAmps (mA)
[0241] An example of typical ranges for each parameter, for
treating a particular condition or disease, is as follows: [0242]
T1=0.1 to 2.0 milliseconds (ms) [0243] T2=67 to 1000 ms (15 Hz to 1
Hz) [0244] T3=20 to 60 minutes [0245] T4=1,440 to 10,080 minutes (1
day to 1 week) [0246] A1=1 to 15 mA
[0247] It is to be emphasized that the values shown above for the
stimulation regimen and ranges of stimulation parameters for use
within the stimulation regimen are only exemplary. Other
stimulation regimens that could be used, and the ranges of values
that could be used for each of these parameters, are as defined in
the claims.
[0248] 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 at the desired stimulation site (e.g.,
acupoint), but it also limits the frequency and duration of
stimulation sessions.
[0249] Limiting the frequency and duration of the stimulation
sessions is a key aspect of Applicant's invention because it
recognizes that some treatments 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.
[0250] 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.
1A and 1B.
[0251] 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
anytime after the housing of the IEAD has been hermetically sealed,
is performed as shown in the state diagram of FIG. 16. Each circle
shown in FIG. 16 represents an operating "state" of the
micro-controller U2 (FIGS. 13A, 14, 14A of 15C). As seen in FIG.
16, 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.
[0252] 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.
[0253] 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.
[0254] 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.
[0255] 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.
[0256] 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.
[0257] 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.
[0258] 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.
[0259] The circuitry that sets the various states shown in FIG. 16
as a function of externally-generated magnetic control commands, or
other externally-generated command signals, is the micro-controller
U2 (FIG. 14), the processor U2 (FIG. 13A), or the control circuit
220 (FIGS. 10, 11 and 12). 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. 14A) for controlling the states of the IEAD as shown in
FIG. 16 is found in Appendix C, attached hereto, and incorporated
by reference herein.
[0260] In the preceding description, various exemplary embodiments
have been described with reference to the accompanying drawings and
appendices. 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 teachings. 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.
* * * * *
References