U.S. patent application number 15/194143 was filed with the patent office on 2016-10-20 for safety features for use in medical devices.
The applicant listed for this patent is EnteroMedics, Inc.. Invention is credited to Al Almendinger, Stephen Ellsworth, Randy Maas, Gregory Pat Spar, Koen Jacob Weijand.
Application Number | 20160303378 15/194143 |
Document ID | / |
Family ID | 47915363 |
Filed Date | 2016-10-20 |
United States Patent
Application |
20160303378 |
Kind Code |
A1 |
Almendinger; Al ; et
al. |
October 20, 2016 |
SAFETY FEATURES FOR USE IN MEDICAL DEVICES
Abstract
A therapy system for applying an electrical signal to an
internal anatomical feature of a patient includes an implantable
component and an external component. The medical device can be
checked for safety issues by periodically initiating a sequence of
tests of an H-bridge circuit, and, during each test, monitoring a
current flow through a sensing resistor electrically connected
between a sensing connection of the H-bridge circuit and a ground.
Current flow through the sensing resistor indicates that both
series electrical switches within at least one of the two pairs of
series electrical switches are active during that test.
Inventors: |
Almendinger; Al;
(Bloomingtion, MN) ; Spar; Gregory Pat; (Big Lake,
MN) ; Weijand; Koen Jacob; (Alicante, ES) ;
Maas; Randy; (Chaska, MN) ; Ellsworth; Stephen;
(St. Paul, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EnteroMedics, Inc. |
St. Paul |
MN |
US |
|
|
Family ID: |
47915363 |
Appl. No.: |
15/194143 |
Filed: |
June 27, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13793715 |
Mar 11, 2013 |
9393420 |
|
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15194143 |
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61608949 |
Mar 9, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61N 1/37276 20130101;
A61N 1/025 20130101; A61N 1/36053 20130101; A61N 1/36125 20130101;
H02J 7/007 20130101; A61N 1/3605 20130101; A61N 1/0509 20130101;
H02J 7/0091 20130101; A61N 1/3787 20130101; A61N 1/36142 20130101;
A61N 1/0551 20130101 |
International
Class: |
A61N 1/36 20060101
A61N001/36; A61N 1/378 20060101 A61N001/378; H02J 7/00 20060101
H02J007/00; A61N 1/05 20060101 A61N001/05 |
Claims
1. A method of performing a safety check in an implantable medical
device, during which electrical signals and therapy are not
delivered to the patient, the method comprising: periodically
initiating a sequence of tests of an H-bridge circuit of an
implantable device, the implantable device comprising a H-bridge
circuit, a field-programmable gate array ("FPGA"), a
microprocessor, a current source, a voltage supply connection, a
grounding connection, a current sensing resistor, and two pairs of
series electrical switches connected in parallel between the
voltage supply connection and the grounding connection, the
sequence of tests selected to test each switch connection of the
electrical switches in the H-bridge circuit; during each test,
monitoring a current flow through a current sensing resistor
electrically connected between the current source of the H-bridge
circuit and a ground, wherein current flow through the current
sensing resistor indicates that both series electrical switches
within at least one of the two pairs of series electrical switches
are active during that test.
2. The method according to claim 1, wherein monitoring the current
flow further comprises: receiving signals indicative of a voltage
drop across the current sensing resistor by the microprocessor, the
microprocessor electrically coupled to the H-bridge circuit;
processing the signals to determine the current flow through the
sensing resistor by the microprocessor; and sending a resulting
signal to the FPGA to continue therapy or to abort therapy, the
FPGA electrically coupled to the microprocessor.
3. A method according to claim 2, further comprising controlling
the voltage of the gate inputs of the H-bridge circuit by the FPGA
based upon the resulting signal.
4. A method according to claim 2, wherein receiving signals further
comprises: receiving a signal from an analog-to-digital converter
indicative of a voltage drops across the sensing resister, wherein
the analog-to-digital converter is electrically connected to the
microprocessor, and electrically connected to the current sensing
resister.
5. The method according to claim 1, further comprising performing
the sequence of tests periodically during use of the implantable
medical device but not while therapy is being delivered.
6. The method according to claim 1, further comprising aborting use
of the implantable medical device if the current flow is above or
below predetermined limits.
7. The method according to claim 1, wherein the two pairs of series
electrical switches includes first, second, third, and fourth
electrical switches, the first and second electrical switches
connected in series to form a first pair and the third and fourth
electrical switches connected in series to form a second pair, the
first and second pairs connected in parallel with each other
between the voltage supply connection and the current source.
8. The method according to claim 7, wherein the sequence of tests
includes: activating the first and second electrical switches,
while deactivating at least the third and fourth electrical
switches; activating the third and fourth electrical switches while
deactivating at least the first and second electrical switches;
activating the first and third electrical switches while
deactivating at least the second and fourth electrical switches;
and activating the second and fourth electrical switches, while
deactivating at least the first and third electrical switches.
9. The method according to claim 7, wherein the implantable device
comprises a second H bridge circuit, the second H-bridge circuit
including a second two pairs of series electrical switches
connected in parallel between the voltage supply connection and a
second current source, the second two pairs of series electrical
switches including fifth, sixth, seventh, and eighth electrical
switches, the fifth and sixth electrical switches connected in
series to form a third pair and the seventh and eighth electrical
switches connected in series to form a fourth pair, the third and
fourth pairs connected in parallel with each other between the
voltage supply connection and the current source.
10. The method according to claim 9, wherein the sequence of tests
includes: activating the fifth and sixth electrical switches, while
deactivating the first, second, third, fourth, seventh, and eighth
electrical switches; activating the seventh and eighth electrical
switches while deactivating the first, second, third, fourth,
fifth, and sixth electrical switches; activating the fifth and
seventh electrical switches while deactivating the first, second,
third, fourth, sixth, and eighth electrical switches; and
activating the sixth and eighth electrical switches while
deactivating the first, second, third, fourth, fifth, and seventh
electrical switches.
11. A medical device configured to apply an electrical stimulus to
tissue of a patient, the medical device comprising: a first
electrical lead, including a first tip connection and a first ring
connection; a second electrical lead, including a second tip
connection and second ring connection; a voltage supply connection;
a field programmable gate array; a microprocessor electrically
connected to the field programmable gate array; a first current
source; a first grounding connection; a first sensing resistor
electrically connected to the first current source and the first
grounding connection; a digital to analog convertor electrically
connected to the microprocessor and the first current source; an
analog to digital convertor electrically connected to first sensing
resistor and the microprocessor; and a first H-bridge circuit
electrically connected to the field programmable gate array, the
voltage supply connection, and the first current source and
including first and second pairs of series electrical switches
connected in parallel, and wherein: the first tip connection is
electrically connected between the first pair of series electrical
switches of the first H-bridge circuit; the first ring connection
is electrically connected between the second pairs of series
electrical switches of the first H-bridge circuit.
12. The medical device of claim 11 further comprising a second
current source electrically connected to the digital to analog
converter; a second grounding connection, a second sensing resistor
electrically connected to the second current source and the second
grounding resistor; a second analog to digital converter
electrically connected between the second current source and the
second sensing resister; a second digital to analog converter
electrically connected to the microprocessor and the second current
source; a second H-bridge circuit electrically connected to the
field programmable gate array, the voltage supply connection, and
the second current source and including first and second pairs of
series electrical switches connected in parallel, and wherein: the
second tip connection is electrically connected between the first
of series electrical switches of the second H-bridge circuit; the
second ring connection is electrically connected between the second
pair of series electrical switches of the second H-bridge
circuit.
13. The medical device according to claim 12, wherein the
microprocessor is electrically coupled to each H-bridge circuit
through an analog-to-digital converter and a digital-to-analog
converter, wherein: the first digital-to-analog converter is
electrically connected to the first current source between the
first H-bridge circuit and the first current sensing resistor and
the second digital-to-analog converter is electrically connected to
the second current source between the second H-bridge circuit and
the second current sensing resistor; the first analog-to-digital
converter is electrically connected to the first sensing resistor;
the second analog to digital converter is electrically connected to
the second sensing resistor; and wherein the first and second
analog-to-digital converter send signals to the microprocessor
indicative of voltage drops across each of the first and second
current sensing resistors and the first and second digital to
analog convertors control the first and second current sources.
14. The medical device according to claim 11, wherein at least one
of the microprocessor and the FPGA is configured to periodically
perform a sequence of tests on the H-bridge circuit during
operation of the medical device but not while therapy is being
delivered to ensure proper operation of the device; wherein if the
sequence of tests indicate an abnormality in operation of the
H-bridge circuit, the microprocessor aborts use of the medical
device.
15. The medical device according to claim 14, wherein at least one
of the microprocessor and the FPGA is configured to perform the
sequence of tests every four seconds.
16. The medical device according to claim 11, wherein the medical
device is used for treating at least one of a plurality of
disorders of the patient selected from the group consisting of
obesity, pancreatitis, irritable bowel syndrome, diabetes,
hypertension, metabolic disease, inflammatory disorders and
combinations thereof.
17. A method of calibrating a medical device configured to deliver
electrical signals to a patient as at least a portion of a therapy,
the method comprising: detecting a positive voltage peak output
between two electrical contacts of the medical device; detecting a
negative voltage peak output by the two electrical contacts of the
medical device; comparing the positive voltage peak and the
negative voltage peak to determine at least a portion of an
impedance between the two electrical contacts; and upon detecting
that the impedance is outside a predetermined range, generating an
alarm indicating the presence of a direct current signal applied to
the tissue of the patient.
18. The method according to claim 17, further comprising: detecting
a second positive voltage output between two electrical contacts of
the medical device; detecting a second negative voltage output by
the two electrical contacts of the medical device; comparing the
second positive voltage and the second negative voltage to
determine a second portion of the impedance between the two
electrical contacts.
19. The method according to claim 18, wherein the portion of the
impedance is a capacitive portion of the impedance.
20. The method according to claim 17, wherein the predetermined
range is determined based at least on a difference between
magnitudes of the positive voltage peak and the negative voltage
peak, wherein the predetermined range is exceeded if the difference
would result in a current which exceeds about one microamp.
21. The method according to claim 17, further comprising, upon
detecting that the impedance is outside a predetermined range, and
prior to generating the alarm: decreasing an operational voltage of
the medical device; detecting a second positive voltage peak output
by the two electrical contacts of the medical device operating at
the decreased operational voltage; detecting a second negative
voltage peak output by the two electrical contacts of the medical
device operating at the decreased operational voltage; comparing
the second positive voltage peak and the second negative voltage
peak to determine a second impedance between the two electrical
contacts; upon detecting that the second impedance is outside a
second predetermined range, generating an alarm indicating the
presence of a direct current signal applied to the tissue of the
patient and halting use of the medical device.
22. The method according to claim 17, further comprising: halting
use of the medical device upon detection of the direct current
signal.
23. A medical device configured to apply an electrical stimulus to
tissue of a patient, the medical device comprising: a first
electrical lead configured to be implanted in a patient and to
introduce electrical signals at a nerve, the first electrical lead
having electrode connections including a first tip connection and a
first ring connection; a second electrical lead configured to be
implanted in a patient and to introduce electrical signals at a
nerve, the second electrical lead having electrode connections
including a second tip connection and a second ring connection; a
voltage source; at each of the first and second tip connections and
first and second ring connections, a first capacitor and a second
capacitor connected in series between the respective electrode
connection and a ground; a programmable circuit electrically
connected to locations between each of the first and second
capacitors, the programmable circuit configured to execute program
instructions which, when executed, cause the programmable circuit
to: calculate initial capacitive ratios between the first capacitor
and the second capacitor for each of the first and second tip
connections and first and second ring connections; store each of
the initial capacitive ratios in a memory associated with the
programmable circuit; prior to initiating delivery of an electrical
therapy to a patient via the first and second electrical leads,
calculating second capacitive ratios between the first capacitor
and the second capacitor for each of the first and second tip
connections and first and second ring connections; compare each of
the second capacitive ratios to the respective initial capacitive
ratios to validate the integrity of the capacitive divider
network.
24. The medical device of claim 23, wherein the programmable
circuit comprises a microprocessor, and wherein the locations
between each of the first and second capacitors are electrically
connected to general purpose I/O pins of the microprocessor.
25. The medical device of claim 24, wherein the programmable
circuit is further configured to calculate an average initial
capacitive ratio based on the initial capacitive ratios associated
with each of the first and second tip connections and first and
second ring connections.
26. The medical device of claim 24, wherein the programmable
circuit is further configured to determine if any of the initial
capacitive ratios varies from the average initial capacitive ratio
by more than a predetermined amount, and if so, halt calibration of
the output current and suspend delivery of the electrical
therapy.
27. The medical device of claim 26, wherein the predetermined
amount comprises about 10% variation from the average initial
capacitive ratio.
28. The medical device of claim 23, wherein the programmable
circuit is further configured to determine if any of the second
capacitive ratios varies from the average initial capacitive ratio
by more than a predetermined amount, and if so, halt calibration of
the output current and suspend delivery of the electrical
therapy.
29. A method of calibrating an output measurement circuit on one or
more electrical leads of an implantable medical device, each of the
one or more electrical leads having one or more electrode
connections positioned to introduce electrical signals at a portion
of the vagal nerve, the method comprising: calculating, using a
programmable circuit, initial capacitive ratios between a first
capacitor and a second capacitor connected in series between each
respective electrode connection and a ground for each of the first
and second tip connections and first and second ring connections;
storing each of the initial capacitive ratios in a memory
associated with a programmable circuit; prior to initiating
delivery of an electrical therapy to a patient via the one or more
electrical leads, calculating second capacitive ratios between the
first capacitor and the second capacitor for each of the electrode
connections; comparing each of the second capacitive ratios to the
respective initial capacitive ratios.
30. The method of claim 29, further comprising determining if any
of the initial capacitive ratios varies from the average initial
capacitive ratio by more than a predetermined amount, and if so,
halt calibration of the output current and suspend delivery of the
electrical therapy.
31. The method of claim 30, wherein the predetermined amount
comprises about 10% variation from the initial capacitive ratio for
each capacitive divider.
Description
CROSS REFERENCE
[0001] This application is a divisional of application Ser. No.
13/793,715, filed Mar. 11, 2013, which application claims the
benefit of provisional application Ser. No. 61/608,949 filed Mar.
9, 2012, which applications are incorporated herein by reference in
their entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention pertains to systems for applying electrical
signals to an anatomical feature of a patient. While many of the
disclosed concepts are applicable to a wide variety of therapies
(e.g., cardiac pacing with electrodes applied to heart tissue), the
invention is described in a preferred embodiment where the
invention pertains to the treatment of disorders such as obesity,
pancreatitis, irritable bowel syndrome, diabetes, hypertension,
metabolic disease, and inflammatory disorders. In a most preferred
embodiment, this invention pertains to the treatment of a
gastrointestinal disorder by the application of a high frequency
signal to a vagus nerve of a patient.
[0004] 2. Background
[0005] A blocking therapy can be used alone or in combination with
traditional electrical nerve stimulation in which impulses are
created for propagation along a nerve. The disorders to be treated
include, without limitation, functional gastrointestinal disorders
(FGIDs) (such as functional dyspepsia (dysmotility-like) and
irritable bowel syndrome (IBS)), gastroparesis, gastroesophageal
reflux disease (GERD), obesity, pancreatitis, diabetes,
hypertension, metabolic disease, inflammation, discomfort and other
disorders
[0006] In a blocking therapy, an electrode (or multiple electrodes)
is placed on or near a vagus nerve or nerves of a patient. By
"near", it is meant close enough that a field created by the
electrode captures the nerve. Higher frequencies (e.g., 2,500
Hz-20,000 Hz) are believed to result in more consistent neural
conduction block. Particularly, the nerve conduction block is
applied with an electrical signal selected to block the entire
cross-section of the nerve (e.g., both afferent and efferent
signals on both myelinated and non-myelinated fibers) at the site
of application of the blocking signal.
[0007] A complete system for applying a signal to a nerve may
include systems for addressing the potential for charge build-up,
assuring good communication between implanted and external
components, recharging implantable batteries, safety of the device,
physician and patient controls and programming and communication
with the system.
SUMMARY OF THE INVENTION
[0008] According to an embodiment of the present invention, a
therapy system is disclosed for applying therapy to an internal
anatomical feature of a patient. The system includes at least one
electrode for implantation within the patient and placement at the
anatomical feature (e.g., a nerve) for applying the therapy signal
to the feature upon application of a treatment signal to the
electrode. An implantable component is placed in the patient's body
beneath a skin layer and coupled to the electrode. The implantable
component includes an implanted antenna. An external component has
an external antenna for placement above the skin and adapted to be
electrically coupled to the implanted antenna across the skin
through radiofrequency transmission.
[0009] A still further aspect of the present disclosure includes a
method and system for performing a safety check in an implantable
medical device. In embodiments, a medical device configured to
conduct a safety check comprises a first electrical lead, including
a first tip connection and a first ring connection; a second
electrical lead, including a second tip connection and second ring
connection; a voltage supply connection; a field programmable gate
array; a microprocessor electrically connected to the field
programmable gate array; a first current source; a first grounding
connection; a first sensing resistor electrically connected to the
first current source and the first grounding connection; a digital
to analog convertor electrically connected to the microprocessor
and the first current source; an analog to digital convertor
electrically connected to first sensing resistor and the
microprocessor; and a first H-bridge circuit including first and
second pairs of series electrical switches connected in parallel,
and electrically connected to the field programmable gate array,
the voltage supply connection, the first current source, and the
first electrical lead; and wherein: the first tip connection is
electrically connected between the first pair of series electrical
switches of the first H-bridge circuit; the first ring connection
is electrically connected between the second pairs of series
electrical switches of the first H-bridge circuit.
[0010] In other embodiments, the medical device further comprises a
second current source electrically connected to the digital to
analog converter; a second grounding connection, a second sensing
resistor electrically connected to the second current source and
the second grounding connection; a second analog to digital
converter electrically connected between the second current source
and the microprocessor; a second digital to analog convertor
electrically connected to the microprocessor and to the second
current source; a second H-bridge circuit including first and
second pairs of series electrical switches connected in parallel,
and electrically connected to the field programmable gate array,
the voltage supply connection, the second current source and the
second electrical lead; and wherein: the second tip connection is
electrically connected between the first of series electrical
switches of the second H-bridge circuit; the second ring connection
is electrically connected between the second pair of series
electrical switches of the second H-bridge circuit.
[0011] The disclosure also provides a method of performing a safety
check in an implantable medical device, during which electrical
signals and therapy are not delivered to the patient, the method
comprising: periodically initiating a sequence of tests of an
H-bridge circuit of an implantable device, the implantable device
comprising a H-bridge circuit, a field-programmable gate array
("FPGA"), a microprocessor, a current source, a voltage supply
connection, a grounding connection, a current sensing resistor, and
two pairs of series electrical switches connected in parallel
between the voltage supply connection and the grounding connection,
the sequence of tests selected to test each switch connection of
the electrical switches in the H-bridge circuit; during each test,
monitoring a current flow through a current sensing resistor
electrically connected between the current source of the H-bridge
circuit and a ground, wherein current flow through the current
sensing resistor indicates that both series electrical switches
within at least one of the two pairs of series electrical switches
are active during that test. In other embodiments, the method
comprises receiving signals indicative of a voltage drop across the
current sensing resistor by the microprocessor, the microprocessor
electrically coupled to the H-bridge circuit; processing the
signals to determine the current flow through the sensing resistor
by the microprocessor; and sending a resulting signal to the FPGA
to continue therapy or to abort therapy, the FPGA electrically
coupled to the microprocessor. In embodiments, if the current flow
through the switches or lack thereof is abnormal (e.g. either
present when it should not be or not present when it should be),
the microprocessor will abort the therapy. In specific examples,
the medical device is utilized to treat at least one of a plurality
of gastrointestinal disorders of a patient.
[0012] In yet another aspect, a medical device is configured to
apply an electrical stimulus to tissue of a patient. The medical
device comprises, a first electrical lead, including a first tip
connection and a first ring connection; a second electrical lead,
including a second tip connection and second ring connection; a
first H-bridge circuit, a first current source, a first voltage
supply connection, a first grounding connection, and first, second,
third, and fourth electrical switches, the first and second
electrical switches connected in series to form a first pair and
the third and fourth electrical switches connected in series to
form a second pair, the first and second pairs connected in
parallel with each other between the first voltage supply
connection and the first grounding connection; a second H-bridge
circuit, a second current source, a second voltage supply
connection, a second grounding connection, and fifth, sixth,
seventh, and eighth electrical switches, the fifth and sixth
electrical switches connected in series to form a third pair and
the seventh and eighth electrical switches connected in series to
form a fourth pair, the third and fourth pairs connected in
parallel with each other between the second voltage supply
connection and the second grounding connection; a first electrical
lead including a first tip connection electrically connected
between the first and second electrical switches and a first ring
connection electrically connected between the third and fourth
electrical switches; a second electrical lead including a second
tip connection electrically connected between the fifth and sixth
electrical switches and a second ring connection electrically
connected between the seventh and eight electrical switches.
[0013] Another aspect of the disclosure provides systems and
methods for calibrating an output current. In embodiments, a
medical device comprises a first electrical lead configured to be
implanted in a patient and to introduce electrical signals at a
nerve, such as the vagal nerve, the first electrical lead having
electrode connections including a first tip connection and a first
ring connection; a second electrical lead configured to be
implanted in a patient and to introduce electrical signals at a
nerve, such as the vagal nerve, the second electrical lead having
electrode connections including a second tip connection and a
second ring connection; a voltage source; at each of the first and
second tip connections and first and second ring connections, a
first capacitor and a second capacitor connected in series between
the respective electrode connection and a ground; a programmable
circuit electrically connected to locations between each of the
first and second capacitors, the programmable circuit configured to
execute program instructions which, when executed, cause the
programmable circuit to: calculate initial capacitive ratios
between the first capacitor and the second capacitor for each of
the first and second tip connections and first and second ring
connections; store each of the initial capacitive ratios in a
memory associated with the programmable circuit; prior to
initiating delivery of an electrical therapy to a patient via the
first and second electrical leads, calculating second capacitive
ratios between the first capacitor and the second capacitor for
each of the first and second tip connections and first and second
ring connections; compare each of the second capacitive ratios to
the respective initial capacitive ratios to validate the integrity
of the capacitive divider network.
[0014] In yet another aspect of the disclosure methods and systems
are provided for charging a battery in an implantable device. In
embodiments, a medical device comprises an implantable
neuroregulator comprising a) a temperature sensor; b) a
rechargeable battery; c) a microprocessor configured to obtain a
baseline temperature of the implantable neuroregulator, to obtain a
charge level of the battery, to ascertain the type of battery, to
determine a level of charge to charge the battery, and to select
between a constant rate of charge for the battery and/or a variable
rate of charge for the battery, d) the microprocessor configured to
send a communication indicating acceptance of charge, level of
charge, a constant rate or variable rate of charge, and duration of
the charge to an external component; d) the microprocessor
configured to determine if the rate of rise of the temperature or
if the temperature exceeds a predetermined maximum as compared to
the baseline, and configured to communicate to the external charger
to stop sending charge or to change the power level of the charge
if the rate of temperature rise exceeds a predetermined maximum or
if the temperature exceeds a predetermined maximum; and ii) an
external charger configured to generate charge to charge the
battery at a level selected by the implantable neuroregulator,
configured to modify the charge level upon request by the
implantable neuroregulator, configured to deliver charge at a
constant or variable rate, and configured to stop charging upon
request by the implantable neuroregulator.
[0015] In embodiments, a method of recharging an implantable module
containing a rechargeable battery, in which the rate of rise of
temperature of the module is measured or the rise of temperature of
the module is measured over a specified time, and the charging
current is adjusted to ensure that the temperature does not
prematurely exceed the predetermined temperature limit established
by the Cenelec European Standard EN 45502-1 (August 1997, page 18,
paragraph 17.1. In other embodiments, a method comprises measuring
a baseline temperature of the implantable neuroregulator; and
selecting a constant or variable rate of charge of the battery
based on current or voltage during a selected charge session by the
implantable neuroregulator, wherein the constant or variable rate
of charge is selected to not cause an increase in temperature of
the implantable neuroregulator beyond a predetermined maximum safe
temperature over a baseline temperature.
[0016] Another aspect of the disclosure provides systems and
methods for calibrating a clock of an implantable component. In
embodiments, a medical device comprises an implantable
neuroregulator including a microprocessor, the microprocessor
including an integrated circuit and/or a crystal oscillator, a
resistive capacitor circuit clock, and a programmable circuit
configured to execute program instructions which, when executed,
cause the programmable circuit to: count an actual number of
oscillator transitions of the integrated circuit and/or crystal
oscillator during a defined period of time; compare the actual
count of oscillator transitions to an expected count of oscillator
transitions, determine if the count is out of range and calculate
an OscValue by determining the difference between that expected
count and the actual count; set an a control register to a value
that indicates the change in actual oscillator transitions during
the defined period of time; and adjust oscillation of the
integrated circuit clock based on the value in the control
register.
[0017] In other embodiments, a medical device comprises an
implantable neuroregulator including a microprocessor, the
microprocessor including a an integrated circuit and/or a crystal
oscillator, a resistive capacitor circuit clock, and a programmable
circuit configured to execute program instructions which, when
executed, cause the programmable circuit to: count the number of a
downlink carrier frequency oscillations in a set number of
resistive capacitor circuit clock cycles to determine the need to
adjust the resistive capacitor circuit clock; determine if the
actual oscillation frequency of the downlink carrier frequency is
different than the expected downlink carrier frequency oscillation;
adjust the resistive capacitor circuit clock oscillations based on
any difference between the actual downlink carrier frequency
oscillations from the expected downlink carrier frequency
oscillation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The accompanying drawings, which are incorporated in and
constitute a part of the description, illustrate several aspects of
the invention and together with the description, serve to explain
the principles of the invention. A brief description of the
drawings is as follows:
[0019] FIG. 1 is a schematic representation of a therapy system
having features that are examples of inventive aspects of the
principles of the present invention, the therapy system including a
neuroregulator and an external charger;
[0020] FIG. 2A is a plan view of an implantable neuroregulator for
use in the therapy system of FIG. 1 according to aspects of the
present disclosure;
[0021] FIG. 2B is a plan view of another implantable neuroregulator
for use in the therapy system of FIG. 1 according to aspects of the
present disclosure.
[0022] FIG. 3A is a block diagram of a representative circuit
module for the neuroregulator of FIG. 2A and FIG. 2B according to
aspects of the present disclosure;
[0023] FIG. 3B is a block diagram of another representative circuit
module for the neuroregulator of FIG. 2A and FIG. 2B according to
aspects of the present disclosure;
[0024] FIG. 4 is a block diagram of a circuit module for an
external charger for use in the therapy system of FIG. 1 according
to aspects of the present disclosure;
[0025] FIG. 5 is a plan schematic view of an example external
charger for use in the therapy system of FIG. 1 according to
aspects of the present disclosure;
[0026] FIG. 6 is a plan, schematic view of an external charger and
schematic views of a patient transmit coil and a physician transmit
coil configured to couple to the external charger according to
aspects of the present disclosure;
[0027] FIG. 7 is a side elevation, schematic view of an external
coil in a desired alignment over an implanted coil according to
aspects of the present disclosure;
[0028] FIG. 8 illustrates the external coil and implanted coil of
FIG. 7 arranged in a misaligned position according to aspects of
the present disclosure;
[0029] FIG. 9 is a perspective view of a distal portion of a
bipolar therapy lead according to aspects of the present
disclosure;
[0030] FIG. 10 is a schematic representation of an electrode
placement for a blocking therapy according to aspects of the
present disclosure;
[0031] FIG. 11 is a schematic representation of a first electrode
configuration according to aspects of the present disclosure;
[0032] FIG. 12 is a schematic representation of a typical waveform
according to aspects of the present disclosure;
[0033] FIG. 13 is a schematic representation of a second electrode
configuration according to aspects of the present disclosure;
[0034] FIG. 14 is a schematic representation of a typical waveform
according to aspects of the present disclosure;
[0035] FIG. 15 is a schematic representation of a third electrode
configuration according to aspects of the present disclosure;
[0036] FIG. 16 is a schematic representation of a typical waveform
according to aspects of the present disclosure;
[0037] FIG. 17 is a schematic representation of a fourth electrode
configuration according to aspects of the present disclosure;
[0038] FIG. 18 is a schematic representation of a typical waveform
according to aspects of the present disclosure;
[0039] FIG. 19 is a graphical illustration of a treatment schedule
according to aspects of the present disclosure;
[0040] FIG. 20 is a schematic representation of a signal pulse
illustrating charge balancing according to aspects of the present
disclosure;
[0041] FIG. 21 is a schematic representation of an alternative
means of charge balancing according to aspects of the present
disclosure;
[0042] FIG. 22 is a schematic illustration of a charge balancing
system shown in a shorting state according to aspects of the
present disclosure;
[0043] FIG. 23 is the view of FIG. 22 in a non-shorting state
according to aspects of the present disclosure; and
[0044] FIG. 24 is a graphical illustration comparing waveforms in
shorting and non-shorting states according to aspects of the
present disclosure.
[0045] FIG. 25 is a schematic representation of a medical device
configured to apply an electrical stimulus to a patient having an
H-bridge circuit according to an embodiment of the present
disclosure;
[0046] FIG. 26 is a schematic representation of dual H-bridge
circuits providing electrical connection to the pacing electrodes
of FIGS. 10-17;
[0047] FIG. 27 is a schematic diagram of a capacitive divider of an
impedance measurement device;
[0048] FIG. 28 is a graphical representation of an example voltage
output of electrical leads of a medical device;
[0049] FIG. 29 is flow chart of an example embodiment showing the
steps for conducting safety checks on an H-bridge circuit of a
medical device;
[0050] FIG. 30 is a flow chart of an example embodiment showing the
steps for conducting an impedance measurement check on a medical
device; and
[0051] FIG. 31 is a flow chart of an example embodiment showing the
steps for calibrating electrical signal output of a medical
device.
DETAILED DESCRIPTION
[0052] With reference now to the various drawing figures in which
identical elements are numbered identically throughout, a
description of the preferred embodiment of the present invention
will now be described.
[0053] FIG. 1 schematically illustrates a therapy system 100 for
treating conditions or disorder such as obesity, pancreatitis,
irritable bowel syndrome, diabetes, hypertension, metabolic
disease, and inflammatory disorders. The therapy system 100
includes a neuroregulator 104, an electrical lead arrangement 108,
and an external charger 101. The neuroregulator 104 is adapted for
implantation within a patient to be treated for obesity. As will be
more fully described herein, the neuroregulator 104 typically is
implanted just beneath a skin layer 103.
[0054] The neuroregulator 104 is configured to connect electrically
to the lead arrangement 108. In general, the lead arrangement 108
includes two or more electrical lead assemblies 106, 106a. In the
example shown, the lead arrangement 108 includes two identical
(bipolar) electrical lead assemblies 106, 106a. The neuroregulator
104 generates therapy signals and transmits the therapy signals to
the lead assemblies 106, 106a.
[0055] The lead assemblies 106, 106a up-regulate and/or
down-regulate nerves of a patient based on the therapy signals
provided by the neuroregulator 104. In an embodiment, the lead
assemblies 106, 106a include distal electrodes 212, 212a, which are
placed on one or more nerves of a patient. For example, the
electrodes 212, 212a may be individually placed on the anterior
vagal nerve AVN and posterior vagal nerve PVN, respectively, of a
patient. For example, the distal electrodes 212, 212a can be placed
just below the patient's diaphragm. In other embodiments, however,
fewer or more electrodes can be placed on or near fewer or more
nerves.
[0056] The external charger 101 includes circuitry for
communicating with the implanted neuroregulator 104. In general,
the communication is transmitted across the skin 103 along a
two-way signal path as indicated by arrows A. Example communication
signals transmitted between the external charger 101 and the
neuroregulator 104 include treatment instructions, patient data,
and other signals as will be described herein. Energy also can be
transmitted from the external charger 101 to the neuroregulator 104
as will be described herein.
[0057] In the example shown, the external charger 101 can
communicate with the implanted neuroregulator 104 via bidirectional
telemetry (e.g. via radiofrequency (RF) signals). The external
charger 101 shown in FIG. 1 includes a coil 102, which can send and
receive RF signals. A similar coil 105 can be implanted within the
patient and coupled to the neuroregulator 104. In an embodiment,
the coil 105 is integral with the neuroregulator 104. The coil 105
serves to receive and transmit signals from and to the coil 102 of
the external charger 101.
[0058] For example, the external charger 101 can encode the
information as a bit stream by amplitude modulating or frequency
modulating an RF carrier wave. The signals transmitted between the
coils 102, 105 preferably have a carrier frequency of about 6.78
MHz. For example, during an information communication phase, the
value of a parameter can be transmitted by toggling a rectification
level between half-wave rectification and no rectification. In
other embodiments, however, higher or lower carrier wave
frequencies may be used.
[0059] In an embodiment, the neuroregulator 104 communicates with
the external charger 101 using load shifting (e.g., modification of
the load induced on the external charger 101). This change in the
load can be sensed by the inductively coupled external charger 101.
In other embodiments, however, the neuroregulator 104 and external
charger 101 can communicate using other types of signals.
[0060] In an embodiment, the neuroregulator 104 receives power to
generate the therapy signals from an implantable power source 151
(see FIG. 3A), such as a battery. In a preferred embodiment, the
power source 151 is a rechargeable battery. In some embodiments,
the power source 151 can provide power to the implanted
neuroregulator 104 when the external charger 101 is not connected.
In other embodiments, the external charger 101 also can be
configured to provide for periodic recharging of the internal power
source 151 of the neuroregulator 104. In an alternative embodiment,
however, the neuroregulator 104 can entirely depend upon power
received from an external source (see FIG. 3B). For example, the
external charger 101 can transmit power to the neuroregulator 104
via the RF link (e.g., between coils 102, 105).
[0061] In some embodiments, the neuroregulator 104 initiates the
generation and transmission of therapy signals to the lead
assemblies 106, 106a. In an embodiment, the neuroregulator 104
initiates therapy when powered by the internal battery 151. In
other embodiments, however, the external charger 101 triggers the
neuroregulator 104 to begin generating therapy signals. After
receiving initiation signals from the external charger 101, the
neuroregulator 104 generates the therapy signals (e.g., pacing
signals) and transmits the therapy signals to the lead assemblies
106, 106a.
[0062] In other embodiments, the external charger 101 also can
provide the instructions according to which the therapy signals are
generated (e.g., pulse-width, amplitude, and other such
parameters). In a preferred embodiment, the external charger 101
includes memory in which several predetermined programs/therapy
schedules can be stored for transmission to the neuroregulator 104.
The external charger 101 also can enable a user to select a
program/therapy schedule stored in memory for transmission to the
neuroregulator 104. In another embodiment, the external charger 101
can provide treatment instructions with each initiation signal.
[0063] Typically, each of the programs/therapy schedules stored on
the external charger 101 can be adjusted by a physician to suit the
individual needs of the patient. For example, a computing device
(e.g., a notebook computer, a personal computer, etc.) 107 can be
communicatively connected to the external charger 101. With such a
connection established, a physician can use the computing device
107 to program therapies into the external charger 101 for either
storage or transmission to the neuroregulator 104.
[0064] The neuroregulator 104 also may include memory 152 (see
FIGS. 3A and 3B) in which treatment instructions and/or patient
data can be stored. For example, the neuroregulator 104 can store
therapy programs indicating what therapy should be delivered to the
patient. The neuroregulator 104 also can store patient data
indicating how the patient utilized the therapy system 100 and/or
reacted to the delivered therapy.
[0065] In what follows, the focus of the detailed description is
the preferred embodiment in which the neuroregulator 104 contains a
rechargeable battery 151 from which the neuroregulator 104 may draw
power (FIG. 3A).
1. System Hardware Components
[0066] a. Neuroregulator
[0067] Different embodiments of the neuroregulator 104, 104' are
illustrated schematically in FIGS. 2A and 2B, respectively. The
neuroregulator 104, 104' is configured to be implanted
subcutaneously within the body of a patient. Preferably, the
neuroregulator 104, 104' is implanted subcutaneously on the
thoracic sidewall in the area slightly anterior to the axial line
and caudal to the arm pit. In other embodiments, alternative
implantation locations may be determined by the implanting
surgeon.
[0068] The neuroregulator 104, 104' is generally sized for such
implantation in the human body. By way of non-limiting example, an
outer diameter D, D' of the neuroregulator 104, 104' is typically
less than or equal to about sixty mm and a thickness of the
neuroregulator 104, 104' is less than or equal to about fifteen mm.
In a preferred embodiment, the neuroregulator 104, 104' has a
maximum outer diameter D, D' of about fifty-five mm and a maximum
thickness of about nine mm. In one embodiment, the neuroregulator
104, 104' weighs less than about one hundred twenty grams.
[0069] Typically, the neuroregulator 104, 104' is implanted
parallel to the skin surface to maximize RF coupling efficiency
with the external charger 101. In an embodiment, to facilitate
optimal information and power transfer between the internal coil
105, 105' of the neuroregulator 104, 104' and the external coil 102
of the external charger 101, the patient can ascertain the position
of the neuroregulator 104, 104' (e.g., through palpation or with
the help of a fixed marking on the skin). In an embodiment, the
external charger 101 can facilitate coil positioning as discussed
herein with reference to FIGS. 7 and 8.
[0070] As shown in FIGS. 2A and 2B, the neuroregulator 104, 104'
generally includes a housing 109, 109' overmolded with the internal
coil 105, 105', respectively. The overmold 110, 110' of the
neuroregulator 104, 104' is formed from a bio-compatible material
that is transmissive to RF signals (i.e., or other such
communication signals). Some such bio-compatible materials are well
known in the art. For example, the overmold 110, 110' of the
neuroregulator 104, 104' may be formed from silicone rubber or
other suitable materials. The overmold 110, 110' also can include
suture tabs or holes 119, 119' to facilitate placement within the
patient's body.
[0071] The housing 109, 109' of the neuroregulator 104, 104' also
may contain a circuit module, such as circuit 112 (see FIGS. 1, 3A,
and 3B), to which the coil 105, 105' may be electrically connected
along a path 105a, 105a'. The circuit module within the housing 109
may be electrically connected to the lead assemblies 106, 106a
(FIG. 1) through conductors 114, 114a. In the example shown in FIG.
2A, the conductors 114, 114a extend out of the housing 109 through
strain reliefs 118, 118a. Such conductors 114, 114a are well known
in the art.
[0072] The conductors 114, 114a terminate at connectors 122, 122a,
which are configured to receive or otherwise connect the lead
assemblies 106, 106a (FIG. 1) to the conductors 114, 114a. By
providing connectors 122, 122a between the neuroregulator 104 and
the lead assemblies 106, 106a, the lead assemblies 106, 106a may be
implanted separately from the neuroregulator 104. Also, following
implantation, the lead assemblies 106, 106a may be left in place
while the originally implanted neuroregulator 104 is replaced by a
different neuroregulator.
[0073] As shown in FIG. 2A, the neuroregulator connectors 122, 122a
can be configured to receive connectors 126 of the lead assemblies
106, 106a. For example, the connectors 122, 122a of the
neuroregulator 104 may be configured to receive pin connectors (not
shown) of the lead assemblies 106, 106a. In another embodiment, the
connectors 122, 122a may be configured to secure to the lead
assemblies 106, 106a using set-screws 123, 123a, respectively, or
other such fasteners. In a preferred embodiment, the connectors
122, 122a are well-known IS-1 connectors. As used herein, the term
"IS-1" refers to a connector standard used by the cardiac pacing
industry, and is governed by the international standard ISO
5841-3.
[0074] In the example shown in FIG. 2B, female connectors 122',
122a' configured to receive the leads 106, 106a are molded into a
portion of the overmold 110' of the neuroregulator 104'. The leads
connectors 126 are inserted into these molded connectors 122',
122a' and secured via setscrews 123', 123a', seals (e.g., Bal
Seals.RTM.), and/or another fastener.
[0075] The circuit module 112 (see FIGS. 1, 3A, and 3B) is
generally configured to generate therapy signals and to transmit
the therapy signals to the lead assemblies 106, 106a. The circuit
module 112 also may be configured to receive power and/or data
transmissions from the external charger 101 via the internal coil
105. The internal coil 105 may be configured to send the power
received from the external charger to the circuit module 112 for
use or to the internal power source (e.g., battery) 151 of the
neuroregulator 104 to recharge the power source 151.
[0076] Block diagrams of example circuit modules 112, 112'' are
shown in FIGS. 3A, 3B, respectively. Either circuit module 112,
112'' can be utilized with any neuroregulator, such as
neuroregulators 104, 104' described above. The circuit modules 112,
112'' differ in that the circuit module 112 includes an internal
power source 151 and a charge control module 153 and the circuit
module 112'' does not. Accordingly, power for operation of the
circuit module 112'' is provided entirely by the external charger
101 via the internal coil 105. Power operation for circuit module
112 may be provided by the external charger 101 or by the internal
power source 151. Either circuit module 112, 112'' may be used with
either neuroregulator 104, 104' shown in FIGS. 2A, 2B. For ease in
understanding, the following description will focus on the circuit
module 112 shown in FIG. 3A.
[0077] The circuit module 112 includes an RF input 157 including a
rectifier 164. The rectifier 164 converts the RF power received
from the internal coil 105 into DC electric current. For example,
the RF input 157 may receive the RF power from the internal coil
105, rectify the RF power to a DC power, and transmit the DC
current to the internal power source 151 for storage. In one
embodiment, the RF input 157 and the coil 105 may be tuned such
that the natural frequency maximizes the power transferred from the
external charger 101.
[0078] In an embodiment, the RF input 157 can first transmit the
received power to a charge control module 153. The charge control
module 153 receives power from the RF input 157 and delivers the
power where needed through a power regulator 156. For example, the
RF input 157 may forward the power to the battery 151 for charging
or to circuitry for use in creating therapy signals as will be
described below. When no power is received from the coil 105, the
charge control 153 may draw power from the battery 151 and transmit
the power through the power regulator 160 for use. For example, a
central processing unit (CPU) 154 of the neuroregulator 104 may
manage the charge control module 153 to determine whether power
obtained from the coil 105 should be used to recharge the power
source 151 or whether the power should be used to produce therapy
signals. The CPU 154 also may determine when the power stored in
the power source 151 should be used to produce therapy signals.
[0079] The transmission of energy and data via RF/inductive
coupling is well known in the art. Further examples describing
general requirements of recharging a battery via an RF/inductive
coupling and controlling the proportion of energy obtained from the
battery with energy obtained via inductive coupling can be found in
the following references, all of which are hereby incorporated by
reference herein: U.S. Pat. No. 3,727,616, issued Apr. 17, 1973,
U.S. Pat. No. 4,612,934, issued Sep. 23, 1986, U.S. Pat. No.
4,793,353, issued Dec. 27, 1988, U.S. Pat. No. 5,279,292, issued
Jan. 18, 1994, and U.S. Pat. No. 5,733,313, issued Mar. 31,
1998.
[0080] In general, the internal coil 105 may be configured to pass
data transmissions between the external charger 101 and a telemetry
module 155 of the neuroregulator 104. The telemetry module 155
generally converts the modulated signals received from the external
charger 101 into data signals understandable to the CPU 154 of the
neuroregulator 104. For example, the telemetry module 155 may
demodulate an amplitude modulated carrier wave to obtain a data
signal. In one embodiment, the signals received from the internal
coil 105 are programming instructions from a physician (e.g.,
provided at the time of implant or on subsequent follow-up visits).
The telemetry module 155 also may receive signals (e.g., patient
data signals) from the CPU 154 and may send the data signals to the
internal coil 105 for transmission to the external charger 101.
[0081] The CPU 154 may store operating parameters and data signals
received at the neuroregulator 104 in an optional memory 152 of the
neuroregulator 104. Typically, the memory 152 includes non-volatile
memory. In other embodiments, the memory 152 also can store serial
numbers and/or model numbers of the leads 106; serial number, model
number, and/or firmware revision number of the external charger
101; and/or a serial number, model number, and/or firmware revision
number of the neuroregulator 104.
[0082] The CPU 154 of the neuroregulator 104 also may receive input
signals and produce output signals to control a signal generation
module 159 of the neuroregulator 104. Signal generation timing may
be communicated to the CPU 154 from the external charger 101 via
the coil 105 and the telemetry module 155. In other embodiments,
the signal generation timing may be provided to the CPU 154 from an
oscillator module (not shown). The CPU 154 also may receive
scheduling signals from a clock, such as 32 KHz real time clock
(not shown).
[0083] The CPU 154 forwards the timing signals to the signal
generation module 159 when therapy signals are to be produced. The
CPU 154 also may forward information about the configuration of the
electrode arrangement 108 to the signal generation module 159. For
example, the CPU 154 can forward information obtained from the
external charger 101 via the coil 105 and the telemetry module
155.
[0084] The signal generation module 159 provides control signals to
an output module 161 to produce therapy signals. In an embodiment,
the control signals are based at least in part on the timing
signals received from the CPU 154. The control signals also can be
based on the electrode configuration information received from the
CPU 154.
[0085] The output module 161 produces the therapy signals based on
the control signals received from the signal generation module 159.
In an embodiment, the output module 161 produces the therapy
signals by amplifying the control signals. The output module 161
then forwards the therapy signals to the lead arrangement 108.
[0086] In an embodiment, the signal generation module 159 receives
power via a first power regulator 156. The power regulator 156
regulates the voltage of the power to a predetermined voltage
appropriate for driving the signal generation module 159. For
example, the power regulator 156 can regulate the voltage to about
2.5 volts.
[0087] In an embodiment, the output module 161 receives power via a
second power regulator 160. The second power regulator 160 may
regulate the voltage of the power in response to instructions from
the CPU 154 to achieve specified constant current levels. The
second power regulator 160 also may provide the voltage necessary
to deliver constant current to the output module 161.
[0088] The output module 161 can measure the voltage of the therapy
signals being outputted to the lead arrangement 108 and reports the
measured voltage to the CPU 154. A capacitive divider 162 may be
provided to scale the voltage measurement to a level compatible
with the CPU 154. In another embodiment, the output module 161 can
measure the impedance of the lead arrangement 108 to determine
whether the leads 106, 106a are in contact with tissue. This
impedance measurement also may be reported to the CPU 154.
[0089] a. External Charger
[0090] A block diagram view of an example external charger 101 is
shown in FIG. 4. The example external charger 101 may cooperate
with any of the neuroregulators 104, 104' discussed above to
provide therapy to a patient. The external charger 101 is
configured to transmit to the neuroregulator 104 (e.g., via an RF
link) desired therapy parameters and treatment schedules and to
receive data (e.g., patient data) from the neuroregulator 104. The
external charger 101 also is configured to transmit energy to the
neuroregulator 104 to power the generation of therapy signals
and/or to recharge an internal battery 151 of the neuroregulator
104. The external charger 101 also can communicate with an external
computer 107.
[0091] In general, the external charger 101 includes power and
communications circuitry 170. The power and communications
circuitry 170 is configured to accept input from multiple sources,
to process the input at a central processing unit (CPU) 200, and to
output data and/or energy (e.g., via coil 102, socket 174, or
display 172). It will be appreciated that it is well within the
skill of one of ordinary skill in the art (having the benefit of
the teachings of the present invention) to create such circuit
components with such function.
[0092] For example, the circuit power and communications circuit
170 can be electrically connected to the external coil 102 for
inductive electrical coupling to the coil 105 of the neuroregulator
104. The power and communications circuit 170 also can be coupled
to interface components enabling input from the patient or an
external computing device (e.g., a personal computer, a laptop, a
personal digital assistant, etc.) 107. For example, the external
charger 101 can communicate with the computing device 107 via an
electrically isolated Serial port.
[0093] The external charger 101 also includes a memory or data
storage module 181 in which data received from the neuroregulator
104 (e.g., via coil 102 and socket input 176), the external
computer 107 (e.g., via socket input 174), and/or the patient (e.g.
via select input 178) can be stored. For example, the memory 181
can store one or more predetermined therapy programs and/or therapy
schedules provided from the external computer 107. The memory 181
also can store software to operate the external charger 101 (e.g.,
to connect to the external computer 107, to program external
operating parameters, to transmit data/energy to the neuroregulator
104, and/or to upgrades the operations of the CPU 200).
Alternatively, the external charger 101 can include firmware to
provide these functions. The memory 181 also can store diagnostic
information, e.g., software and hardware error conditions.
[0094] An external computer or programmer 107 may connect to the
communications circuit 170 through the first input 174. In an
embodiment, the first input 174 is a port or socket into which a
cable coupled to the external computer 107 can be plugged. In other
embodiments, however, the first input 174 may include any
connection mechanism capable of connecting the external computer
107 to the external charger 101. The external computer 107 provides
an interface between the external charger 101 and a physician
(e.g., or other medical professional) to enable the physician to
program therapies into the external charger 101, to run diagnostic
and system tests, and to retrieve data from the external charger
101.
[0095] The second input 176 permits the external charger 101 to
couple selectively to one of either an external power source 180 or
the external coil 102 (see FIG. 1). For example, the second input
176 can define a socket or port into which the power source 180 or
external coil 102 can plug. In other embodiments, however, the
second input 176 can be configured to couple to a cable or other
coupling device via any desired connection mechanism. In one
embodiment, the external charger 101 does not simultaneously
connect to both the coil 102 and the external power source 180.
Accordingly, in such an embodiment, the external power source 180
does not connect directly to the implanted neuroregulator 104.
[0096] The external power source 180 can provide power to the
external charger 101 via the second input 176 when the external
charger 101 is not coupled to the coil 102. In an embodiment, the
external power source 180 enables the external charger 101 to
process therapy programs and schedules. In another embodiment, the
external power source 180 supplies power to enable the external
charger 101 to communicate with the external computer 107 (see FIG.
1).
[0097] The external charger 101 optionally may include a battery,
capacitor, or other storage device 182 (FIG. 4) enclosed within the
external charger 101 that can supply power to the CPU 200 (e.g.,
when the external charger 101 is disconnected from the external
power source 180). The power and communications circuit 170 can
include a power regulator 192 configured to receive power from the
battery 182, to regulate the voltage, and to direct the voltage to
the CPU 200. In a preferred embodiment, the power regulator 192
sends a 2.5 volt signal to the CPU 200.
[0098] The battery 182 also can supply power to operate the
external coil 102 when the coil 102 is coupled to the external
charger 101. The battery 182 also can supply power to enable the
external charger 101 to communicate with the external computer 107
when the external power source 180 is disconnected from the
external charger 101. An indicator 190 may provide a visual or
auditory indication of the remaining power in the battery 182 to
the user.
[0099] In an embodiment, the battery 182 of the external charger
101 is rechargeable. For example, the external power source 180 may
couple to the external charger 101 to supply a voltage to the
battery 182. In such an embodiment, the external charger 101 then
can be disconnected from the external power source 180 and
connected to the external coil 102 to transmit power and/or data to
the neuroregulator 104. Further details regarding example
rechargeable systems include U.S. Pat. No. 6,516,227 to Meadows,
issued Feb. 4, 2003; U.S. Pat. No. 6,895,280 to Meadows, issued May
17, 2005; and U.S. patent application Publication No. US
2005/0107841 to Meadows May 19, 2005, the disclosures of which are
hereby incorporated herein by reference.
[0100] In an alternative embodiment, the battery 180 is a
replaceable, rechargeable battery, which is recharged external to
the external charger 101 in its own recharging stand. In yet
another embodiment, the battery 182 in the external charger 101 can
be a replaceable, non-rechargeable battery.
[0101] In use, energy from the external power source 180 flows
through the second input 176 to an energy transfer module 199 of
the power and communications circuit 170. The energy transfer
module 199 directs the energy either to the CPU 200 to power the
internal processing of the external charger 101 or to the battery
182. In an embodiment, the energy transfer module 199 first directs
the energy to a power regulator 194, which can regulate the voltage
of the energy signal before sending the energy to the battery
182.
[0102] In some embodiments, the external coil 102 of the external
charger 101 can supply energy from the battery 182 to the internal
coil 105 of the neuroregulator 104 (e.g., to recharge the internal
power source 151 (FIG. 3) of the neuroregulator 104). In such
embodiments, the energy transfer module 199 receives power from the
battery 182 via the power regulator 194. For example, the power
regulator 194 can provide a sufficient voltage to activate the
energy transfer module 199. The energy transfer module 199 also can
receive instructions from the CPU 200 regarding when to obtain
power from the battery 182 and/or when to forward power to the
external coil 102. The energy transfer module 199 delivers the
energy received from the battery 182 to the coil 102 of the
external charger 101 in accordance with the instructions provided
by the CPU 200. The energy is sent from the external coil 102 to
the internal coil 105 of the neuroregulator 104 via RF signals or
any other desired power transfer signal. In an embodiment, therapy
delivery at the neuroregulator 104 is suspended and power is
delivered from the external charger 101 during recharging of the
internal power source 151.
[0103] In some embodiments, the external charger 101 controls when
the internal battery 151 of the implanted neuroregulator 104 is
recharged. For example, the external charger 101 can determine when
to recharge the battery 151. In other embodiments, however, the
implanted neuroregulator 104 controls when the battery 151 is
recharged as described herein. In embodiments, the external charger
receives a communication from the implantable neuroregulator that
it will accept charge, the level of charge requested, and the
duration of charge. In embodiments, the external charger is
configured to deliver charge energy at a number of different
levels, for example, about 16 different levels. In embodiments, the
external charger delivers charge energy until it receives a
communication from the implantable neuroregulator to stop
charging.
[0104] As noted above, in addition to power transmissions, the
external coil 102 also can be configured to receive data from and
to transmit programming instructions to the neuroregulator 104
(e.g., via an RF link). A data transfer module 196 may receive and
transmit data and instructions between the CPU 200 and the internal
coil 105. In an embodiment, the programming instructions include
therapy schedules and parameter settings. Further examples of
instructions and data transmitted between the external coil 102 and
the implanted coil 105 are discussed in greater detail herein.
[0105] FIG. 5 shows a front view of an example external charger
101. The external charger 101 includes a housing 171 defining a
first input (e.g., socket input) 174, a second input (e.g., socket
input) 176, and a third input (e.g., select input) 178 coupled to
the communications circuit 170. In an embodiment, the housing 171
also may enclose a battery 182 configured to supply power to the
external charger 101 via the power and communications circuit 170.
Alternatively, the external charger 101 can receive power from an
external source 180 (FIG. 1).
[0106] As shown in FIG. 5, visual display 172 also is provided on
the housing 171 for presenting human readable information processed
by the communications circuit 170. In an embodiment, the visual
display 172 is a liquid crystal display (LCD) screen. In other
embodiments, however, the visual display 172 can include any
display mechanism (e.g., a light-emitting diode (LED) screen,
vacuum fluorescent display (VFD) screen, etc.). Non-limiting
examples of information that can be shown on the visual display 172
include the status of the battery 182 of the external charger 101,
the status of the battery 151 in the implanted neuroregulator 104,
coil position (as will be described), impedances between the
electrodes 212, 212a and attached tissue, and error conditions.
[0107] As shown in FIG. 5, the third input 178 of the external
charger 101 includes a selection input 178 with which the user can
interact with the external charger 101. In an embodiment, the
selection input 178 can include a button, which sequentially
selects menu options for various operations performed by the
external charger 101 when pressed successively. In other
embodiments, however, the third input 178 includes another type of
selection input (e.g., a touch screen, a toggle-switch, a
microphone for accepting voice-activated commands, etc.).
[0108] Example functions capable of selection by the user include
device reset, interrogation of battery status, interrogation of
coil position, and/or interrogation of lead/tissue impedance. In
other embodiments, a user also can select measurement of
tissue/lead impedance and/or initiation of a stomach contraction
test. Typically, the measurement and testing operations are
performed when the patient is located in an operating room,
doctor's office, or is otherwise surrounded by medical
personnel.
[0109] In another embodiment, the user can select one or more
programs and/or therapy schedules to submit to the memory 152 of
the neuroregulator 104. For example, the user can cycle through
available programs by repeatedly pressing the selection button 178
on the external charger 101. The user can indicate the user's
choice by, e.g., depressing the selector button 178 for a
predetermined period of time or pressing the selector button 178 in
quick succession within a predetermined period of time.
[0110] In use, in some embodiments, the external charger 101 may be
configured into one of multiple modes of operation. Each mode of
operation can enable the external charger 101 to perform different
functions with different limitations. In an embodiment, the
external charger 101 can be configured into five modes of
operation: an Operating Room mode; a Programming mode; a Therapy
Delivery mode; a Charging mode; a Diagnostic mode and a Maintenance
Mode.
[0111] When configured in the Operating Room mode, the external
charger 101 can be used to determine whether the implanted
neuroregulator 104 and/or the implanted lead arrangement 108 are
functioning appropriately. If any component of the therapy system
100 is not functioning as desired, then the medical personnel can
trouble-shoot the problem while still in the operation room or can
abandon the procedure, if necessary.
[0112] For example, the external charger 101 can be used to
determine whether the impedance at the electrodes 212, 212a of the
lead arrangement 108 (FIG. 1) is within a prescribed range. When
the impedance is within the prescribed range, a gastric contraction
test can be initiated to demonstrate that the electrodes 212, 212a
are appropriately positioned and can become active. If the
impedance is outside an acceptable range, the system integrity can
be checked (e.g. connections to the leads can be verified).
Additionally, the therapy electrodes 212, 212a may be repositioned
to provide better electrode-tissue contact.
[0113] In another embodiment, the external charger 101 can be used
to initiate a stomach contraction test in the operating room. The
stomach contraction test enables medical personnel to confirm the
electrodes 212, 212a of the lead arrangement 108 (FIG. 1) are in
contact with the appropriate nerves and not with some other tissue.
For example, the external charger 101 can instruct the
neuroregulator 104 to generate a signal tailored to cause the
stomach to contract if the signal reaches the appropriate
nerves.
[0114] Typically, the external charger 101 is not connected to an
external computer 107 when configured in the Operating Room mode.
In a preferred embodiment, the external charger is connected (e.g.,
via socket input 176) to a physician coil 102' (shown schematically
in FIG. 6) instead of a patient coil 102 (described above). The
physician coil 102' can differ from the patient coil 102 in one or
more respects.
[0115] For example, as shown in FIG. 6, a length L' of the
connection cable 102a' on the physician coil 102' can be longer
than a length L of the cable 102a of the patient coil 102. In one
example embodiment, the length L' of the connection cable 102a' of
the physician coil 102' can be about 300 cm and the length L of the
connection cable 102a of the patient coil 102 can be about 60 cm.
The longer length L' allows the external charger 101 to be located
outside the sterile field in the operating room when the physician
coils 102' is connected.
[0116] In another embodiment, the physician coil 102' can include
an indicator circuit to identify the coil 102' as a physician coil
to the external charger 101. For example, the physician coil 102'
can contain a small resistor 102b', which can be recognized by the
external charger 101 when the physician coil 102' is plugged into
the socket 176. When the external charger 101 detects the presence
of the indicator circuit, the external charger 101 automatically
configures itself into an Operating Room mode. This mode allows the
physician to conduct various system and patient response tests,
such as those described above, without the need for connection to a
clinician computer 107.
[0117] When configured in the Programming mode, the external
charger 101 is connected with the external computer 107 (FIG. 1)
via which the physician manages the components of the therapy
system 100. In general, the physician may select a therapy program
and a therapy schedule stored on the external computer 107 to
transfer to the external charger 101. In certain embodiments, the
external charger 101 forwards the programs and schedule to the
neuroregulator 104. In an embodiment, the external charger 101 can
be coupled to the physician coil 102' during programming. In
another embodiment, the external charger 101 can be coupled to the
patient coil 102. In addition, in different embodiments, the
external computer 107 also can assess the impedance of the
electrodes 212, 212a, initiate system and/or diagnostic tests, and
take corrective action when the external charger 101 is configured
into the Programming mode.
[0118] After the neuroregulator 104 has been implanted and the
external charger 101 and/or neuroregulator 104 have been
programmed, the external charger 101 can be configured into the
Therapy Delivery mode. When configured in the Therapy Delivery
mode, the external charger 101 communicates with and/or powers the
neuroregulator 104 as described above. Typically, the external
charger 101 is coupled to the patient coil 102 and not to the
external computer 107 when configured in the Therapy Delivery
mode.
[0119] The external charger 101 also can interact with the user via
the third input (e.g., the selector button) 178 and the display 172
to select the therapy to be provided. In an embodiment, the
external charger 101 can send instructions indicating which program
the neuroregulator 104 should follow while administering therapy.
In another embodiment, the external charger 101 sends instructions
in accordance with a selected program stored on the external
charger 101.
[0120] If the neuroregulator 104 includes an internal power source
151, then the external charger 101 can enter a Charging mode in
which the external charger 101 recharges the internal power source
151 of the neuroregulator 104 when the neuroregulator 104 is not
delivering therapy. Typically, the external charger 101 enters the
Charging mode at the request of the neuroregulator 104. In a
preferred embodiment, the neuroregulator 104 controls how much
power is sent by the external charger 101.
[0121] During follow-up visits between the patient and the
physician, the external charger 101 may be configured into a
Diagnostic mode. In this mode, the external charger 101 is coupled
to the external computer 107 to provide an interface for the
physician to obtain data stored on the external charger 101 and to
download therapy and/or software updates. In an embodiment, the
display 172 on the external charger 101 is disabled and all
information is conveyed to the physician via the external computer
107 only. The external charger 101 may be coupled to either coil
102, 102' when configured in the Diagnostic mode.
[0122] In embodiments, a maintenance mode is one in which the
neuroregulator delivers low energy electrical signals associated
with safety checks and impedance checks for a period of time of 9
hours or less. In the interest of conserving battery power, the
device may remain on but deliver the safety and impedance checks
for 30 minutes to 9 hours, 1 hour to 8 hours, 1 hour to 7 hours, 1
hour to 6 hours, 1 hour to 5 hours, 1 hour to 4 hours, 1 hour to 3
hours and 1 hour to 2 hours. In embodiments, the safety checks are
delivered at 50 Hz or less at least every 0.2.mu. and impedance
checks are delivered once every two minutes at a frequency of 1000
Hz or more. While not meant to limit the scope of the invention, it
is believed that a therapeutic effect is associated with this low
energy electrical single treatment if applied for at least 9 hours
per day and not at shorter time periods. If the patient condition
has stabilized or resolved, a health care provider may program the
device for maintenance mode, leaving open the option to initiate a
therapy program once again at a later date.
[0123] In an embodiment, the external charger 101 also can be
configured into a Shipping mode, in which the battery 182 is
disconnected from the rest of the circuitry. The Shipping mode
avoids draining the battery 182 and enhances safety. In one such
embodiment, pressing the selector button 172 causes the external
charger 101 to change from this Shipping mode into another mode,
such as the Therapy Delivery mode.
[0124] a. Alignment of External and Implanted Coils
[0125] The external charger 101 enables alignment of the relative
positions of the external and implanted coils 102, 105 and
optimization of the signal strength. Optimizing the alignment of
the coils 102, 105 and the power of the transmission signal
facilitates continuous, transcutaneous transmission of power and/or
information.
[0126] i. Positioning of External Coil
[0127] In general, the external coil 102 is adapted to be placed on
the patient's skin (e.g., by adhesives) overlying the implanted
internal coil 105. The position and orientation of the coils 102,
105 can affect signal reliability. In addition, the strength of the
transmission signals between the external coil 102 and the
implanted coil 105 also is affected by the distance between the
coils 102, 105. Implanting the neuroregulator 104 very close to the
surface of the skin 103 typically results in a large and expanded
range of signal strengths. Conversely, implanting the
neuroregulator 104 at a large distance beneath the skin 103 yields
a generally weak transmission link and a compressed range of signal
strengths.
[0128] FIG. 7 illustrates an external coil 102 appropriately
aligned with an implanted coil 105. The coil 105 is implanted
beneath the skin 103 at a preferred depth D.sub.1 (e.g., about two
centimeters to about three centimeters beneath the skin 103).
Preferably, a plane of the coil 105 extends parallel to the surface
of the skin 103. In an embodiment, each coil 102, 105 is a circular
coil surrounding a central axis X-X, Y-Y, respectively. As shown in
FIG. 7, in a preferred alignment configuration, the axes X-X, Y-Y
are collinear so that there is no lateral offset of the axes X-X,
Y-Y and the planes of the coils 102, 105 are parallel to one
another. Such an alignment configuration may be attained, e.g.,
when the external coil 102 is applied to a patient's skin 103 when
the patient is lying flat (e.g., on the patient's back).
[0129] FIG. 8 illustrates misalignment between the coils 102, 105
resulting from movement of the patient (e.g., a change in posture).
For example, when the patient sits, excess fat may cause the skin
103 to roll. This rolling may cause the spacing between the coils
102, 105 to increase to a distance D2. Also, the orientation of the
external coil 102 may change so that the axes X-X and Y-Y of the
coils 102, 105, respectively, have a lateral offset T and an
angular offset A. Such changes in spacing and orientation may be
occurring constantly throughout the day.
[0130] The relative position of the coils 102, 105 may be optimized
(e.g., for each use) when the external charger 101 senses the
transmission link is weakened (e.g., on initial power up or when
the energy transfer to the implantable neuroregulator 104 has
degraded). For example, the external charger 101 can sound an alarm
and invite the user to configure the external charger 101 into a
Locate mode. Alternatively, the user can decide independently to
enter the Locate mode (e.g., through a menu selection).
[0131] When configured in the Locate mode, the external charger 101
prompts the user to adjust the orientation of the external coil 102
to achieve an alignment (e.g., coaxial alignment) facilitating
better coil interaction. The external charger 101 also provides
feedback to the user indicating the current degree of alignment of
the coils 102, 105. Examples of such feedback include audio
signals, lit LED's, bar graphs or other textual, graphical, and/or
auditory signals provided to the user.
[0132] In general, when the external charger 101 is configured in
the Locate mode, the user sweeps the external coil 102 back and
forth across the general location of the implanted neuroregulator
104. During the sweep, the external charger 101 sends a locator
signal S.sub.1 to the implanted coil 105 (see FIG. 7). The
implanted coil 105 responds with a feedback signal S.sub.2 (FIG.
7). The external charger 101 analyzes the feedback signal S.sub.2
to determine the strength of the transmission link between the
coils 102, 105.
[0133] In an embodiment, the external charger 101 keeps track of
the strongest and weakest signals found during the sweep. The
maximum signal strength and the minimum signal strength can be
indicated to the user, e.g., via the visual display 172. These
maximum and minimum values provide the user with context for
judging the relative strength of a given signal at each location
during the sweep. In an embodiment, the relative strength of the
signal at a given position also can be displayed to the user as the
user passes the external coil 102 over the position.
[0134] For example, in one embodiment, the first signal may be
indicated initially as the maximum and minimum signal strength on
the visual display 172. As the external coil 102 is moved about,
any subsequent signals having greater signal strength replace the
maximum signal shown. The strength of any subsequent, weaker signal
also can be tracked by the external charger 101. The strength of
the weakest signal can be indicated to the user as the minimum
signal strength found. In one embodiment, if the strength of a
subsequent signal falls between the currently established values
for minimum and maximum, then an interpolated value representing
the relative strength of the signal at the respective coil position
can be displayed.
[0135] Thus the external charger 101 learns the maximum and minimum
values for signal strength pertaining to external coil positions
relative to the location of the implanted coil 105. By identifying
the context of the signal strength measurements (i.e., the maximum
and minimum signal strength found during a sweep), the external
charger 101 can provide consistent and context-sensitive
measurements of signal strength to the user regardless of the
distance of the coil 102 from the implanted coil 105. Such
measurements facilitate identification of an optimum coil
position.
[0136] After the initial placement, the external coil 102 may need
to be repositioned with respect to the implanted coil 105 to
maintain the signal integrity. The external charger 101 can monitor
whether the neuroregulator 104 is receiving signals having
sufficient signal strength. If the external charger 101 determines
the neuroregulator 104 is not receiving a sufficient signal, then
the external charger 101 may sound an alarm (e.g., auditory and/or
visual) to alert the user that coil transmission effectiveness has
been lost.
[0137] In an embodiment, after indicating the loss of transmission
effectiveness, the external charger 101 may invite the user to
configure the external charger 101 into the Locate mode to
reposition the external coil 102. Alternatively, the external
charger 101 may invite the user to modify the position of the
external coil 102 without entering the Locate mode. In an
embodiment, when the coil transmission effectiveness is
re-established, the system automatically self-corrects and resumes
therapy delivery.
[0138] ii. Dynamic Signal Power Adjustment
[0139] The amount of power received at the neuroregulator 104 can
vary due to relative movement of the coils 102, 105 after the
initial placement of the external coil 102. For example, the signal
strength may vary based on the distance between coils 102, 105, the
lateral alignment of the coils 102, 105, and/or the parallel
alignment of the coils 102, 105. In general, the greater the
distance between the coils 102, 105, the weaker the transmission
signal will be. In extreme cases, the strength of the transmission
signal may decrease sufficiently to inhibit the ability of the
neuroregulator 104 to provide therapy.
[0140] The coils 102, 105 may move relative to one another when the
patient moves (e.g., walks, stretches, etc.) to perform everyday
activities. Furthermore, even when the patient is inactive, the
external coil 102 may be placed on tissue with substantial
underlying fat layers. The surface contour of such tissue can vary
in response to changes in patient posture (e.g., sitting, standing,
or lying down). In the treatment of obesity, the distance from the
top layer of skin 103 to the implanted coil 105 can vary from
patient to patient. Moreover, the distance can be expected to vary
with time as the patient progresses with anti-obesity therapy.
[0141] In addition, the power consumption needs of the
neuroregulator 104 can change over time due to differences in
activity. For example, the neuroregulator 104 will require less
power to transmit data to the external charger 101 or to generate
therapy signals than it will need to recharge the internal battery
151.
[0142] To overcome these and other difficulties, an embodiment of
the external charger 101 can change the amplification level of the
transmission signal (e.g., of power and/or data) to facilitate
effective transmission at different distances between, and for
different relative orientations of the coils 102, 105. If the level
of power received from the external charger 101 varies, or if the
power needs of the neuroregulator 104 change, then the
neuroregulator sends a communication to the external charger 101 to
adjust the power level of the transmitted signal dynamically to
meet the desired target level for the implanted neuroregulator
104.
[0143] Adjustments to the power amplification level can be made
either manually or automatically. In an embodiment, the
neuroregulator 104 may determine a target strength of the
transmission signal (e.g., a predetermined strength selected to
provide sufficient power to the neuroregulator 104), assess the
effectiveness of the transmission signals currently being sent to
the implanted coil 105, and send a communication to the external
charger to automatically adjust the amplification levels of the
transmitted signals to enhance the effectiveness of the
transmissions between the external coil 102 and the implanted coil
105.
[0144] For example, if the neuroregulator 104 indicates its battery
151 is ready for recharging 151, then the external charger 101 may
establish a transmission link having a first power level
appropriate for the task. At the conclusion of recharging, and when
the neuroregulator 104 subsequently indicates it will begin therapy
delivery, then the external charger 101 may change the power of the
transmission link to a second power level sufficient to initiate
therapy generation and delivery.
[0145] The neuroregulator may also communicate to the external
charger 101 to increase the power level of the signal if the signal
is lost due to separation and/or misalignment of the coils. If the
external charger 101 is unable to sufficiently increase the power
level of the transmitted signal, however, then the external charger
101 may issue an alarm and/or an invitation to the user to
reposition the external coil 102 as described above.
[0146] The neuroregulator may also send a communication to the
external charger 101 to decrease the strength of the signal (i.e.,
the amount of power) being sent to the neuroregulator 104. For
example, due to safety concerns, the amount of power that can be
transmitted across skin via RF signals is limited. Receiving
excessive amounts of power could cause the neuroregulator 104 to
heat up and potentially burn the patient. In an embodiment, the
neuroregulator 104 includes a temperature sensor (not shown)
configured to monitor the temperature of the neuroregulator 104.
The neuroregulator 104 can communicate the temperature to the
external charger 101. Alternatively, the neuroregulator 104 can
issue a warning to the external charger 101 if the neuroregulator
104 becomes too warm. When the temperature of the neuroregulator
104 is too high, the external charger 101 may lower the power
transmitted to the implanted coil 105 of the neuroregulator 104 to
bring the temperature down to an acceptable level or may stop
charging. Alternatively, the neuroregulator 104 may detune its
receiving RF input circuit 157 to reduce power and temperature.
[0147] In some cases, the maximum allowable temperature of the
battery or PC board can be reached very quickly, thus truncating
the charging procedure prematurely, the implanted neuroregulator
battery then not achieving significant recharging. In an
embodiment, the rate of rise of temperature is measured, and the
charging current amplitude adjusted to achieve a lower rate of
temperature rise, to allow charging to proceed without exceeding
the temperature limit prematurely.
[0148] In embodiments, methods allow different implants that use
different battery types (with different battery chemistries and/or
voltage/charge capacities) and have different safety requirements
with regard to maximum resulting temperature due to charging, to
utilize a single device (an external charger) to safely and
effectively charge their internal batteries. This is accomplished
by having the charging control managed by the implanted device
(e.g. neuroregulator), and the charge delivery managed by the
external charger.
[0149] In embodiments, a system and method for recharging a battery
in an implantable device involves control of the duration and power
level of the charge energy by the implantable neuroregulator. In
embodiments, the implantable neuroregulator obtains a baseline
temperature of the implantable neuroregulator, typically about one
hour or more after a previous charging session. The baseline
temperature is typically around 37.degree. C. The baseline
temperature is used to determine a predetermined maximum safe
temperature, for example, no more than 2.degree. C. above the
baseline temperature. The microprocessor of the implantable
neuroregulator is configured to also measure a rate of temperature
rise over a specific period of time, typically over a charging
session. A charging session is usually at least about one hour but
may be more or less depending on patient preference and status of
the battery and temperature of the implantable component. In
embodiments, the implantable component continuously monitors the
temperature of the implant and the rate of rise of the temperature.
If the temperature of the implantable device reaches certain
defined limits, it sends a communication to the external charger to
stop charging. In embodiments, those temperatures include a
temperature about 2.degree. C. or greater than the baseline
temperature, a temperature of 45.degree. C. indicating error, and a
temperature of 16.degree. C. indicating error. In other
embodiments, the implantable neuroregulator communicates to the
external charger to stop charging if the rate of rise of the
temperature exceeds a predetermined unsafe rate, for example,
2.degree. C. rise per hour or greater.
[0150] In embodiments, the implantable neuroregulator is configured
to obtain information on the battery charge level, and the type of
battery. The implantable neuroregulator is configured to store the
battery charge curves for the type of battery employed in the
implantable device. The implantable neuroregulator is configured to
communicate to the external charger the power level for a charging
session. The power level in a typical case is selected based on the
charging curve for the type of battery and for the time of charging
session. If the battery charge level is below a predetermined level
as defined by the battery manufacturer, for example 50% or less,
the implantable neuroregulator will communicate to the external
charger to start at a very low charging power level. In
embodiments, the implantable device continuously monitors the power
level of charging and sends a communication to the external charger
to adjust the power level of the charging depending on the level of
charge in the battery, the time of the charging session, and the
temperature or rate of rise of the temperature. In embodiments, the
external charger has at least 16 different power levels for
charging.
[0151] In embodiments, charging the battery can use one of multiple
(typically two) control loop algorithms: [0152] 1. Use a regulated
(constant) charge rate chosen to allow unrestricted length of
charge interval without exceeding a maximum safe temperature rise
over a baseline temperature; or [0153] 2. Use an adaptive (variable
throughout the charge session) charge rate that is chosen to
maximize charge efficiency over a finite (fixed, but programmable)
charge interval (typically 1 hour in length) without exceeding a
maximum safe temperature rise over a baseline temperature. The
implantable neuroregulator is configured to select one or the other
control loop algorithm. In embodiments, the implantable
neuroregulator selects the regulated constant charge rate when the
battery has a charge level as defined by the battery manufacturer,
and the charging session used by the patient is typically one hour
or less. In embodiments, the variable rate of charging is utilized
when the charge level of the battery is at a lower predetermined
level of the battery manufacturer requiring a low energy charging.
The charging history of the patient can be used to determine if the
patient is charging when the battery has been depleted to less than
50% and the time of a charging session. A default algorithm can be
set at the factory or by the physician. In an embodiment, the
default is the variable charge rate.
[0154] For the above, charge rate can be based on current or
voltage delivered to the device battery. The "safe temperature
rise" is programmable based on use case scenario, typically 2
degrees C. The baseline temperature is established by the implant
prior to, or at the start of charge using temperature measurements
of the environment made by the implant, restricted to a
programmable maximum and/or minimum limit (typically 37 degrees
C.).
[0155] The control algorithm in use is chosen and managed by the
receiving implantable device. In some embodiments, the implantable
device determines it's battery condition (charge level), and based
on its charge level, battery chemistry, charge control algorithm,
and programmed charging safety parameters (baseline temperature and
max temp rise) the implantable device sends at least the following
information to the external charger: [0156] a) The implantable
device will accept application of battery charge energy [0157] b)
The level of energy to send using a multiple level scale from a
minimum level to a maximum level (typically 16 levels) [0158] c) A
duration of how long to apply the energy (typically in units of
seconds).
[0159] In embodiments, charge energy is created and delivered to
the receiving implantable device by the external charger under the
following conditions: [0160] 1. The external charger will only
deliver charge energy to the receiving implantable device if it
indicates that it will accept application of battery charge energy.
[0161] 2. The external charger will only deliver the level of
energy requested by the receiving implantable device based on a
multiple level scale from a minimum to a maximum level, programmed
into the charger (typically 16 levels). [0162] 3. The external
charger will only deliver charge energy for the duration of time
requested by the implantable device (typically in units of
milliseconds). It then stops and waits for another request from the
receiving device.
[0163] Charging is managed through means of a "charging session"
that is collaboration between the receiving device and the charging
device. In embodiments, a charging session can begin when a user
places the external charger in proximity to the implantable device
and a charging session is requested by the implantable device. A
charging session comprises a set of charging intervals, that
continue until 1) the receiving implantable device no longer will
accept application of battery charge energy, or 2) the external
charger is moved out of proximity of the implantable device for a
period of time (programmable, typically 5 minutes). If the external
charger is moved back into proximity of the implantable device
within the allowed period of time, the charging session is
continued.
[0164] In other embodiments, the methods described above can be
combined to facilitate recovery of some batteries with chemistries
that are unsafe to be charged when their battery voltages drop
below an established level.
[0165] Operational parameters, such as current, frequency, surface
area, and duty cycle, also can be limited to ensure safe operation
within the temperature limit. Further details regarding safety
concerns pertaining to transdermal power transmission can be found,
e.g., in The Cenelec European Standard, EN 45502-1 (August 1997),
page 18, paragraph 17.1, the disclosure of which is hereby
incorporated by reference herein.
[0166] In an embodiment, the external charger 101 also can decrease
the target power level based on a "split threshold" power delivery
concept. In such an embodiment, the external charger 101 initially
provides a stronger signal than necessary to the neuroregulator 104
to ensure sufficient power is available. The external charger 101
then reduces the strength of the transmissions to a level just
above the necessary signal strength when the actual requirements
have been established. This subsequent reduction in power saves
drain on the external battery 182 or power source 180.
[0167] For example, the external charger 101 can provide a low
level of power capable of sustaining basic operation of the
neuroregulator 104 when the neuroregulator 104 indicates it is not
actively providing therapy or recharging its battery 151. When the
neuroregulator 104 indicates it is about to initiate therapy,
however, the external charger 101 can increase the power level of
the transmission signal to a first threshold level, which is
comfortably in excess of the power required to provide basic
operation of the neuroregulator 104 as well as provide therapy.
When the actual power requirements for therapy delivery become
apparent, the external charger 101 may decrease the power level of
the signal to a second threshold level, which is closer to the
minimum power level required to provide basic functionality and
maintain therapy delivery.
[0168] To perform this dynamic adjustment of signal strength, the
external charger 101 analyzes a feedback signal (e.g., signal
S.sub.2 of FIG. 7) received from the implanted neuroregulator 104
indicating the amount of power required by the neuroregulator 104.
The signal S.sub.2 also may provide information to the external
charger 101 indicating the power level of the signal S.sub.1 being
received by the implanted coil 105 of the neuroregulator 104. Such
signal analysis would be within the skill of one of ordinary skill
in the art (having the benefit of the teachings of the present
invention).
[0169] In an embodiment, the external charger 101 sets the signal
power level based on a predetermined target power level for the
transmission signal S.sub.1. In response to the feedback signal
S.sub.2, the external charger 101 modifies the power level of the
transmission signal S.sub.1 to be within a tolerance range of the
target power level. In an embodiment, the external charger 101
iteratively modifies the power level of the transmission signal
S.sub.1 until the feedback signal S.sub.2 indicates the power level
is within the tolerance range.
[0170] In addition to the dynamic adjustment of transmitted signal
power described above, the neuroregulator 104 can be configured to
optimize the power received from the external charger 101 when the
neuroregulator 104 is recharging its battery 151. For example, the
neuroregulator 104 may tune (e.g., using a combination of hardware
and software) the natural resonant frequency of a recharging
circuit (not shown) to maximize the power delivered to a load
resistance for a given set of input parameters such as voltage,
current and impedance at the implanted coil 105.
[0171] Transmission of power and/or information between the
external charger 101 and the implanted neuroregulator 104 is
typically performed using a carrier frequency of 6.78 MHz. Emission
requirements of industrial, scientific and medical equipment are
governed by Federal Communications Commission requirements
described in FCC Title 47, Parts 15 and 18, and in EN 55011. The
FCC requirements in the vicinity of this frequency are more
restrictive than those of EN 55011.
[0172] A preferred method for managing the temperature and carrier
frequency of the neuroregulator 104 during the recharging process
includes passing a high power unmodulated transmission between the
external charger 101 and the implantable neuroregulator 104 for a
finite time (e.g., from about half of a minute to about five
minutes), during which time no informational communication takes
place between the external charger 101 and the implantable
neuroregulator 104 (i.e., no information is passed between the
charger 101 and the neuroregulator 104). At the conclusion of this
finite time period, the unmodulated transmission ceases.
[0173] An informational, modulated communicational transmission
then is passed at low power (e.g., within the requirements of FCC
Title 47 Part 15) during which the temperature of the implantable
neuroregulator 104 is communicated periodically to the external
charger 101. If the temperature rises within certain restrictions
(e.g., within the restrictions of The Cenelec European Standard, EN
45502-1 (August 1997), page 18, paragraph 17.1), then the
communications transmission may be terminated, and the whole cycle
may be repeated beginning with the initiation of the high power,
unmodulated, recharging transmission.
[0174] In an additional preferred embodiment, when the
informational, modulated communicational transmission is performed,
the requisite signal power is reduced by using only externally
transmitted power for the telemetered communications, and by
simultaneously using internal battery power to operate the rest of
the implanted circuitry 112 (FIGS. 3A and 3B), such as a
microcontroller and/or peripherals. In such embodiments, the
transmitted power may be less than if implant components
(microcontroller and/or peripherals) also were receiving power from
the RF transmission. Accordingly, the transmitted power may be
limited to the power required for communications at short distances
of six centimeters or less. Advantageously, such a power reduction
reduces the total power required to below FCC Part 15 limits for
telemetry communications.
[0175] During the phase in which the battery 151 of the implantable
neuromodulator 104 is being recharged by a high powered,
unmodulated transmission (e.g., under the requirements of FCC Title
47 Part 18), the temperature of the implanted neuroregulator 104
may be monitored and, if necessary, steps taken to inhibit the
temperature from exceeding certain requirements (e.g., the
requirements of The Cenelec European Standard, EN 45502-1 (August
1997), page 18, paragraph 17.1). For example, the temperature may
be reduced by terminating the high powered, unmodulated
transmission. In an alternative embodiment, the power level of the
high powered, unmodulated transmission may be reduced in later
cycles to limit the increase in temperature. In another embodiment,
a control loop is established between the temperature rise and the
power level of the unmodulated transmission to ensure the increase
in temperature always remains within the identified
requirements.
[0176] d. Implanted Leads
[0177] FIG. 9 shows an example distal end of a bipolar lead, such
as lead 106 (see FIG. 1). The lead 106 includes a lead body 210
curved to receive a nerve (e.g., a vagus nerve). The lead body 210
contains an exposed tip electrode 212 configured to contact with
the nerve received within the lead body 210. The tip electrode 212
is capable of delivering an electrical charge to nerves having a
diameter ranging from about one millimeter to about four
millimeters.
[0178] The lead body 210 also can have a suture tab 214 to attach
the lead body 210 to the patient's anatomy to stabilize the
position of the lead body 210. A first end of a flexible lead
extension 216, which encloses a conductor from the electrode 212,
couples with the lead body 210. A second, opposite end of the lead
extension 216 terminates at a pin connector (not shown) for
attachment to a connector (e.g., an IS-1 connector) 122 (shown in
FIG. 1).
[0179] The lead 106 shown in FIG. 9 also includes a ring electrode
218 surrounding the lead extension 216 at a position spaced from
the tip electrode 212. In an embodiment, the surface area of each
electrode 212, 218 is greater than or equal to about thirteen
square millimeters. A suture tab 220 may be provided for placement
of the ring electrode 218 on the patient's anatomy in general
proximity to the placement of the tip electrode 212 on the
nerve.
[0180] In an alternative embodiment, a monopolar lead (not shown)
may be implanted instead of the bipolar lead 106. Typically, the
monopolar lead is the same as the bipolar lead 106, except the
monopolar lead lacks a ring electrode 218. Such a monopolar lead is
described in commonly assigned and co-pending U.S. patent
application Ser. No. 11/205,962, to Foster et al, filed Aug. 17,
2005, the disclosure of which is hereby incorporated by
reference.
[0181] Further details pertaining to example electrode placement
and application of treatment can be found, e.g., in U.S. Pat. No.
4,979,511 to Terry, Jr., issued Dec. 25, 1990; U.S. Pat. No.
5,215,089 to Baker, Jr., issued Jun. 1, 1993; U.S. Pat. No.
5,251,634 to Weinberg, issued Oct. 12, 1993; U.S. Pat. No.
5,531,778 to Maschino et al., issued Jul. 2, 1996; and U.S. Pat.
No. 6,600,956 to Maschino et al., issued Jul. 29, 2003, the
disclosures of which are hereby incorporated by reference
herein.
2 Placement of Electrodes and Electrode Configuration Options
[0182] The electrodes can be placed on any number of nerves
including, for example, of vagus nerve, renal artery, renal nerve,
celiac plexus, a splanchnic nerve, cardiac sympathetic nerves,
spinal nerves originating between T10 to L5, glossopharyngeal
nerve, and tissue containing baroreceptors. For illustrative
purposes, placement of the electrode is described with respect to
the vagus nerve. FIG. 10 shows a posterior vagus nerve PVN and an
anterior vagus nerve AVN extending along a length of a patient's
esophagus E. The posterior nerve PVN and the anterior AVN are
generally on diametrically opposite sides of the esophagus E just
below the patient's diaphragm (not shown). A first tip electrode
212 of a lead arrangement 108 (FIG. 1) is placed on the anterior
vagus nerve AVN. A second electrode 212a of the lead arrangement
108 is placed on the posterior vagus nerve PVN. The electrodes 212,
212a are connected by leads 106, 106a to a neuroregulator 104 (FIG.
1).
[0183] At the time of placement of the leads 106, 106a, it may be
advantageous for the tip electrodes 212, 212a to be individually
energized with a stimulation signal selected to impart a neural
impulse to cause a detectable physiological response (e.g., the
generation of antropyloric waves). The absence of a physiological
response may indicate the absence of an overlying relation of the
tested electrode 212, 212a to a vagus nerve PVN, AVN. Conversely,
the presence of a physiological response may indicate an overlying
relation (e.g., correct placement) of the tested electrode 212,
212a to a vagus nerve. After determining the leads 106, 106a create
a physiologic response, the electrodes 212, 212a can be attached to
the nerves PVN, AVN.
[0184] A preferred embodiment of the leads 106, 106a for treating
obesity is shown in FIG. 10. The lead arrangement 108 includes
bipolar leads 106, 106a. The bipolar leads 106, 106a each include
one tip (i.e., or cathode) electrode 212, 212a that can be placed
directly on the nerve PVN, AVN and one ring (i.e., or anode)
electrode 218, 218a that is not placed on the nerve PVN, AVN, but
rather may be attached to another structure (e.g., the stomach). In
other embodiments, however, the lead arrangement 108 may include
monopolar leads (i.e., each lead 106, 106a having only a tip
electrode 212, 212a).
[0185] Electrical connection between the neuroregulator 104 and the
therapy leads 106, 106a is made through bipolar IS-1 compatible
lead adapters 122, 122a attached to the neuroregulator 104. If the
bipolar lead design is used, two bipolar electrode pairs--one for
the anterior vagus and one for the posterior vagus--are provided.
One bipolar lead feeds a bipolar electrode pair. If the monopolar
lead design is used, only the conductor connected to the distal tip
electrode of each bipolar IS-1 connector is used.
[0186] The therapies as previously described could be employed by
using blocking electrodes or stimulation electrodes or both in
order to down-regulate and/or up-regulate the vagus nerve. A
blocking signal down-regulates a level of vagal activity and
simulates, at least partially, a reversible vagotomy.
[0187] Referring to FIGS. 11-18, the signals to the electrodes 212,
212a can be selected to create different types of signals and
signal paths (referred to herein as "configurations"). FIGS. 11-18
illustrate four different electrode configurations.
[0188] a. Blocking Electrode Configuration (1)
[0189] A first blocking electrode configuration is shown in FIG. 11
and could be applied to any type of nerve as described herein. With
respect to the vagus nerve, this configuration creates a current
path (see arrow 1 in FIG. 11) with current flowing between the
anterior and posterior nerves AVN, PVN. The tip electrodes 212,
212a, which are located directly on the anterior and posterior
vagal nerves AVN, PVN, respectively, are electrically active. The
anodic ring electrodes 218, 218a are not energized.
[0190] A continuous waveform (e.g., the square waveform W.sub.10
shown in FIG. 12) propagates along the current path (see arrow 1)
extending across the esophagus E. Such an electrode configuration
is generally monopolar (i.e., only one location on each nerve PVN,
AVN is subject to the treatment) and could be accomplished with
monopolar leads (i.e., leads without ring electrodes 218,
218a).
[0191] b. Blocking Electrode Configuration (2)
[0192] FIG. 13 illustrates a second blocking electrode
configuration in which each of the tip electrodes 212, 212a is
associated with an anode electrode 218, 218a, respectively. With
respect to the vagus nerve, therapy signals are applied only to the
anterior vagus nerve AVN between the distal electrode 212 and the
anode electrode 218. Advantageously, current (see arrow 2 in FIG.
13) does not flow through the esophagus E, thereby decreasing the
likelihood of the patient sensing the treatment (e.g., feeling
discomfort or pain).
[0193] In general, the anode electrodes 218, 218a can be positioned
on any anatomical structure. In a preferred embodiment, the anode
electrodes 218, 218a are placed on structures in generally close
proximity (e.g., within about five centimeters) of the tip
electrodes 212, 212a. For example, the anode electrodes 218, 218a
can be placed on the same vagal nerve PVN, AVN as the anode
electrode's associated electrode 212, 212a.
[0194] In other embodiments, however, the anode electrodes 218,
218a can be placed on the stomach, the esophagus, or other
anatomical structure in the general vicinity of the electrodes 212,
212a. In an embodiment, the anode electrodes 218, 218a can be
placed on the stomach to permit monitoring of stomach contractions
(e.g., by strain receptors associated with the anode electrodes
218, 218a). The arrangement of FIG. 13 results in a pacing waveform
W.sub.11 (FIG. 14).
[0195] c Blocking Electrode Configuration (3)
[0196] FIG. 15 illustrates the same electrode configuration shown
in FIG. 13, except the signals are applied only to the posterior
vagus nerve PVN between the tip electrode 212a and the anode
electrode 218a. The corresponding current path is shown by arrow 3
in FIG. 15. In an embodiment, the example signal waveform W.sub.12
(see FIG. 16) propagating across the current path is the same as
the waveform W.sub.11 in FIG. 14. In other embodiments, however,
any desired waveform can be utilized.
[0197] d. Blocking Electrode Configuration (4)
[0198] The electrode configuration of FIG. 17 is generally the same
as the electrode configurations of FIGS. 11, 13 and 15. In FIG. 17,
however, an electrically active anode (e.g., ring electrode 218,
218a) and cathode (e.g., tip electrode 212, 212a) are associated
with each nerve to provide a dual channel system. With respect to
the vagus nerve, such an electrode arrangement routes current flow
through both nerves PVN, AVN as indicated by arrows 4.
[0199] In an embodiment, a first electrode (e.g., the tip electrode
212, 212a) is placed directly on each of the nerve trunks and a
second electrode (e.g., ring electrode 218, 218a) is located in
proximity to the first electrode. Two waveforms (e.g., an anterior
nerve waveform W.sub.12A and a posterior nerve waveform W.sub.12
shown in FIG. 18) are generated. In the example shown, the pulses
of one of the waveforms occur during no-pulse periods of the other
waveform. In such a configuration, a complete charging and
rebalancing cycle can occur on one channel before the second
channel is charged and rebalanced. Accordingly, only one channel is
electrically paced at a time. Typically, the electrodes on the
nerve are energized cathodically first.
3 Post-Operative Testing of Electrodes
[0200] After completing implantation, assembly, and positioning of
the neuroregulator 104 and the electrode arrangement 108, a
physician can determine the lead integrity by measuring the lead
impedance and assessing whether the lead impedance is within an
acceptable range. If the lead impedance is within range, the
physician can connect an external computer 107 (e.g., a clinician
computer) to the external charger 101 (see FIG. 1).
[0201] The clinician computer 107 can transmit treatment therapy
settings and treatment data to the neuroregulator 104 via the
external charger 101. The clinician computer 107 also can retrieve
data from the external charger 101 or neuroregulator 104. For
example, in one embodiment, the clinician computer 107 detects
serial numbers of the external charger 101 and neuroregulator 104
automatically. After adjustment of blocking parameters and
retrieval of data, the clinician computer 107 may be disconnected
from the external charger 101.
[0202] After the patient has adequately recovered from the surgery
(e.g., approximately fourteen days after the implantation surgery),
the physician may program initial treatment parameters into the
external charger 101. For example, the physician can couple the
clinician computer 107 to the external charger 101 and follow menu
commands on the computer 107 to upload select therapy programs to
the external charger 101. In certain embodiments, the uploaded
programs can then be transferred to the implanted neuroregulator
104.
[0203] Additionally, the physician can use the clinician computer
107 to select treatment start times for the patient. In an
embodiment, treatment start times are selected based on the
individual patient's anticipated waking and initial meal times. The
start times can be set differently for each day of the week.
Further details regarding scheduling treatment will be discussed
herein with respect to FIG. 19.
4. System Software
[0204] The external charger 101 and the neuroregulator 104 contain
software to permit use of the therapy system 100 in a variety of
treatment schedules, operational modes, system monitoring and
interfaces as will be described herein.
[0205] a Treatment Schedule
[0206] To initiate the treatment regimen, the clinician downloads a
treatment specification and a therapy schedule from an external
computer 107 to the external charger 101. In general, the treatment
specification indicates configuration values for the neuroregulator
104. For example, in the case of vagal nerve treatment for obesity,
the treatment specification may define the amplitude, frequency,
and pulse width for the electrical signals emitted by the implanted
neuroregulator 104. In another embodiment, "ramp up" time (i.e.,
the time period during which the electrical signals builds up to a
target amplitude) and "ramp down" time (i.e., the time period
during which the signals decrease from the target amplitude to
about zero) can be specified.
[0207] In general, the therapy schedule indicates an episode start
time and an episode duration for at least one day of the week. An
episode refers to the administration of therapy over a discrete
period of time. Preferably, the clinician programs an episode start
time and duration for each day of the week. In an embodiment,
multiple episodes can be scheduled within a single day. Therapy
also can be withheld for one or more days at the determination of
the clinician.
[0208] During a therapy episode, the neuroregulator 104 completes
one or more treatment cycles in which the neuroregulator 104
sequences between an "on" state and an "off" state. For the
purposes of this disclosure, a treatment cycle includes a time
period during which the neuroregulator 104 continuously emits
treatment (i.e., the "on" state) and a time period during which the
neuroregulator 104 does not emit treatment (i.e., the "off" state).
Typically, each therapy episode includes multiple treatment cycles.
The clinician can program the duration of each treatment cycle
(e.g., via the clinician computer 107).
[0209] When configured in the "on" state, the neuroregulator 104
continuously applies treatment (e.g., emits an electrical signal).
The neuroregulator 104 is cycled to an "off" state, in which no
signal is emitted by the neuroregulator 104, at intermittent
periods to mitigate the chances of triggering a compensatory
mechanism by the body. For example, if a continuous signal is
applied to a patient's nerve for a sufficient duration, the
patient's digestive system eventually can learn to operate
autonomously.
[0210] An example daily treatment schedule 1900 is schematically
shown in FIG. 19. The daily schedule 1900 includes a timeline
indicating the times during the day when the treatment is scheduled
to be applied to a patient. Duty cycle lines (dashed lines) extend
along the time periods during which treatment is scheduled. For
example, a first episode is scheduled between 8 AM and 9 AM. In
certain embodiments, the treatment schedules 1900 address other
details as well. For example, the daily schedule 1900 of FIG. 19
indicates details of the waveform (e.g., ramp-up/ramp-down
characteristics) and details of the treatment cycles.
[0211] b. System Operational Modes
[0212] The therapy system 100 can be configured into two basic
operational modes--a training mode and a treatment mode--as will be
described herein. In an embodiment, the therapy system 100 also can
be configured into a placebo mode for use in clinical trials.
[0213] i. Training Mode
[0214] The training mode is used post-operatively to train the
patient on using the therapy system 100. In this mode, electrical
signals are not delivered to the nerves for the purpose of creating
blocking action potentials. In a preferred embodiment, the
neuroregulator 104 does not generate any electrical signals. In
some embodiments, the training therapy setting can be preset by the
therapy system manufacturer and are unavailable to the treating
physician.
[0215] The training mode allows the physician to familiarize the
patient with the positioning of the external charger 101 relative
to the implanted neuroregulator 104. The physician also instructs
the patient in how to respond to the feedback parameters within the
therapy system 100. Training also can cover information and menus
which can be displayed on the external charger 101, for example:
the status of the battery 182 of the external charger 101, the
status of the battery 151 of the implanted neuroregulator 104, coil
position, lead/tissue impedances, and error conditions.
[0216] The physician also can train the patient in how to interact
with the external charger 101. In an embodiment, the patient
interacts with the external charger 101 using the selection input
button 174. For example, by successively pressing the button 174,
the patient can select one of multiple device operations, such as:
device reset, selective interrogation of battery status, and coil
position status.
[0217] ii. Treatment Mode
[0218] The treatment mode is the normal operating mode of the
neuroregulator 104 in which the neuroregulator 104 applies a
blocking signal to the nerves using blocking therapy settings. In
general, the therapy settings are specified by the physician based
on the specific needs of the patient and timing of the patient's
meals. In some embodiments, the neuroregulator 104 controls the
therapy being provided according to therapy programs and schedules
stored on the neuroregulator 104. In other embodiments, the
neuroregulator 104 follows the instructions of the external charger
101 to deliver therapy.
[0219] iii. Placebo or Maintenance Mode
[0220] This mode may be used for patients randomized to a placebo
treatment in a randomized, double-blind clinical trial or for
patients who have achieved their goals for electrical signal
therapy. In this mode, the neuroregulator 104 does not apply
therapy signals to the lead arrangement 108. Rather, in different
embodiments, therapy signals can be supplied to a dummy resistor to
drain the internal power source 151 (FIG. 3) of the neuroregulator
104.
[0221] The external charger 101 interacts with the patient and the
physician as if therapy was being applied. For example, the patient
and/or physician can view system status messages and a battery
drain rate of the external charger 101 and neuroregulator 104.
Because the external charger 101 functions as normal, the physician
and the patient are blind to the fact that no significant therapy
is being applied.
[0222] To give the patient the sensation that therapy is being
applied, current pulses may be applied to the vagal nerve trunks
during impedance measurements at the start of therapy. However, no
therapy is delivered during the remainder of the blocking cycle.
These sensations are felt by the patient and provide a misleading
indication of activity. These sensations, therefore, help in
maintaining the double blindness of the study.
[0223] In embodiments, a maintenance mode is one in which the
neuroregulator delivers low energy electrical signals associated
with safety checks and impedance checks for a period of time of 9
hours or less. In the interest of conserving battery power, the
device may remain on but deliver the safety and impedance checks
for 30 minutes to 9 hours, 1 hour to 8 hours, 1 hour to 7 hours, 1
hour to 6 hours, 1 hour to 5 hours, 1 hour to 4 hours, 1 hour to 3
hours and 1 hour to 2 hours. In embodiments, the safety checks are
delivered at 50 Hz or less at least every 0.2 .mu.s and impedance
checks are delivered once every two minutes at a frequency of 1000
Hz or more. While not meant to limit the scope of the invention, it
is believed that a therapeutic effect is associated with this low
energy electrical single treatment if applied for at least 9 hours
per day and not at shorter time periods. If the patient condition
has stabilized or resolved, a health care provider may program the
device for maintenance mode, leaving open the option to initiate a
therapy program once again at a later date.
[0224] c. Treatment Therapy Settings
[0225] The neuroregulator 104 is configured to provide therapy
signals to the electrode arrangement 108. In general, the therapy
signals can induce stimulation of the nerves, blocking of nerve
impulses, or some combination of the two.
[0226] i Blocking Treatment
[0227] During treatment, the neuroregulator 104 provides blocking
signals to the nerves of a patient. Blocking signals include high
frequency waveforms that inhibit the transmission of signals along
the nerves. In general, the physician selects and sets therapy
settings (e.g., waveform characteristics and treatment schedule)
based on meal times and a patient's eating pattern. In an
embodiment, the therapy system 100 can provide a choice of at least
three unique blocking therapy settings which can be applied as part
of a daily treatment schedule.
[0228] ii. Low Frequency Mode
[0229] The low frequency mode provides low frequency stimulating
signals along the patient's nerves to create a brief, potentially
observable, physiological response as an intra-operative screen.
Such a physiologic response could be, for example, the twitching of
a muscle or organ, such as the stomach. Alternatively, for some
nerve types, such as glossopharyngeal and/or baroreceptors a low
frequency upregulating signal is utilized.
[0230] This therapy setting may be used by the physician to confirm
correct electrode placement. The system operates in this mode for
short time periods and, typically, only when the patient is under
physician care. This mode may be accessed through the programmer
interface. In an embodiment, this mode can be enabled/disabled
(e.g., by the manufacturer) through the programming interface.
[0231] iii. Temporary Test Therapy Setting Mode
[0232] The therapy system 100 has the ability to program special
treatment/testing therapy settings to support "one-time"
physiological evaluations. Special testing therapy parameters can
be preset (e.g., by the manufacturer) to be made available for use
by the physician.
[0233] d. System Monitoring
[0234] In some embodiments, therapy system 100 facilitates
monitoring the operation of the therapy system 100 and its
components. By monitoring the operation of the therapy system 100,
faults and malfunctions can be caught early and dealt with before
becoming problematic. The therapy system 100 can record the
operation and/or the fault conditions for later analysis. The
therapy system 100 also can notify the patient and/or physician of
the system operating status and non-compliant conditions. For
example, an error message can be displayed on screen 172 (see FIG.
5) of the external charger 101 or on a display screen (not shown)
of the external computing device 107 (see FIG. 1).
[0235] Embodiments of the therapy system 100 can confirm proper
functioning of and communication between the components of the
therapy system 100. For example, the therapy system 100 can monitor
the link strength between the external charger 101 and the
neuroregulator 104. In an embodiment, immediate feedback indicating
the link strength can be provided to the patient (e.g., through the
display 172 of the external charger 101) and/or to the physician
(e.g., through the external computing device 107).
[0236] The therapy system 100 also can determine one or both of the
coils 102, 105 are broken, shorted, or disconnected. In an
embodiment, the therapy system 100 determines whether the coils
102, 105 are operational by measuring the impedance between the
coils and determining whether the measured impedance falls within
an acceptable range.
[0237] The therapy system 100 also can measure the impedance
between the electrodes 212, 212a of the lead arrangement 108 and
determine whether the impedance is out of range (e.g., due to
inadequate electrode-nerve contact, or shorted electrodes). Details
regarding the measurement of lead impedance are discussed later
herein. Impedance measurements also can be used to verify proper
lead placement, verify nerve capture, and monitor stomach
contraction during the implant procedure.
[0238] The therapy system 100 also can communicate other types of
system errors, component failures, and software malfunctions to the
patient and/or physician. For example, the therapy system 100 can
monitor the battery status (e.g., low battery, no charge, battery
disconnected, etc.) of the neuroregulator 104 and/or the external
charger 101 and warn the patient and/or physician when the battery
should be recharged and/or replaced.
[0239] The therapy system 100 can indicate an inability to deliver
a signal having the specified current (e.g., due to the impedance
being out of range or due to internal component failure) to the
lead arrangement 108 during treatment delivery. The therapy system
100 also can indicate whether the external charger 101 and/or the
neuroregulator 104 have sufficient power to transmit and/or receive
signals (e.g., based on antenna alignment, battery power,
etc.).
[0240] i. Lead Impedance Measurement
[0241] Embodiments of the therapy system 100 have the ability to
independently measure and record lead impedance values. Lead
impedance values outside a predefined range may indicate problems
or malfunctions within the therapy system 100. High impedance, for
example, could mean that the electrodes 212, 212a are not properly
coupled to the nerves of the patient. Low impedance could mean
inappropriate shorting of the electrodes 212, 212a.
[0242] These embodiments of the therapy system 100 allow the
physician to measure lead impedance on-demand. The therapy system
100 also can enable the physician to periodically measure impedance
(e.g., during the Training Mode) without initiating a blocking
therapy setting. Generally, impedance is measured and stored
separately for each channel of each electrode configuration. These
measurements may be used to establish a nominal impedance value for
each patient by calculating a moving average. The nominal impedance
and impedance tolerance range can be used for system non-compliance
monitoring, as will be described below.
[0243] ii. Device Safety Check
[0244] a. H Bridge Safety Check
[0245] As explained above, where a therapy system 100 including an
electrical circuit is utilized to apply an electrical stimulus to a
patient, it is desirable to implement safety checks to ensure
proper operation of electrical stimulators. Specifically, it is
important to protect damage to patient nerves, muscles, tissue, and
the like through methods and systems intended to increase safer
application of various stimulation therapies.
[0246] Embodiments of the present disclosure can be designed to
perform safety checks within medical devices, both prior to
operation and periodically during operation. The safety checks
disclosed herein provide continued, safe operation of such devices.
In the following paragraphs, reference is made to the accompanying
drawings that form a part hereof, and in which it is shown by way
of illustration, specific embodiments in which the invention may be
practiced. It is to be understood that other embodiments may be
utilized and structural changes may be made without departing from
the scope of the present invention. Such safety checks represent
checks that can be performed relative to circuitry included within
the system, as well as relating to the electrical signal delivered
to the patient.
[0247] In an embodiment, a safety check of the functioning of an H
bridge circuit is performed periodically but not while therapy is
being delivered. In embodiments, during a therapy cycle, the
therapy is stopped for a time interval and the function of the H
bridge is checked and then therapy is resumed in a therapy cycle.
In embodiments, that interval is about once every 4 seconds. In
embodiments, the function of the H bridge is checked to determine
if it is functioning to supply current when needed and functioning
to turn off current (e.g. that none of the switches are stuck on).
In embodiments, if any of the switches indicate that they are not
functioning, the microprocessor terminates therapy.
[0248] FIG. 25 is a schematic representation of a medical device
2000 which is configured to apply an electrical stimulus to nerves,
tissue, muscle, or the like, of a patient. The medical device 2000
can be configured to deliver any of the therapies discussed above.
In some embodiments, the medical device 2000 represents a portion
of the therapy system 100 illustrated and described above (i.e., a
portion of that therapy system delivering an electrical signal to a
patient).
[0249] In the embodiment shown, a microprocessor 2002 is
communicatively connected to an H-bridge circuit 2006 via a
field-programmable gate array ("FPGA") 2004. The microprocessor
2002 can be, for example, electrically coupled to the FPGA 2004,
which is in turn electrically connected to the H-bridge circuit
2006. The microprocessor 2002 is also directly connected to the
H-bridge circuit 2006 by way of analog-to-digital converters
("ADCs") 2010, 2012 and one or more digital to analog converters
2022. The A/D convertors can have single or multiple channels, for
example, two A/D convertors are shown here but other configurations
may be utilized depending on the number of channels in each A/D
convertor. The H-Bridge circuit is connected to current sources
2020 and 2021. The D/A Converter 2022 is controlled by the
microprocessor 2002, and provides voltage signals to the current
sources 2020 and 2021 to establish the current flowing through 2020
and 2021. A D/A convertor can be a single unit or can be multiple
D/A units, for example, a single unit with 4 different channels can
be utilized or 4 different single channel D/A convertors can be
utilized. The purpose of the A/D converters 2010 and 2012 is to
measure the voltage at the top of the current sense resistors and
verify that the programmed current is correct. The microprocessor
2002 is configured to monitor and control the activity of the
H-bridge circuit 2006. Specifically, the microprocessor 2002 is
configured to send and receive signals for directing and monitoring
activity in the H-bridge circuit 2006, including delivering a
therapy, as well as directing and monitoring tests of the circuit.
An example therapy to be delivered via the lead arrangement 108,
via the H-bridge circuit 2006 is discussed in further detail
herein.
[0250] In some embodiments, the microprocessor is electrically
coupled to each H-bridge circuit through an analog-to-digital
converter and a digital-to-analog converter, wherein: the first
digital-to-analog converter is electrically connected to a first
current source located between the first H-bridge circuit and the
first sensing resistor and a second digital-to-analog converter is
electrically connected to a second current source located between
the second H-bridge circuit and the second sensing resistor; the
first analog-to-digital converter is electrically connected to the
first current sensing resistor; the second analog-to-digital
converter is electrically connected to the second current sensing
resistor and wherein the first digital-to-analog converter and the
second digital-to-analog converters receive signals from the
microprocessor to control the first and second current sources and
the first analog-to-digital converter and the second
analog-to-digital converter send signals to the microprocessor
indicative of voltage drops across each of the first and second
sensing resistors.
[0251] In some embodiments, microprocessor 2002 corresponds to CPU
154 of FIGS. 3A-3B; in such embodiments, the microprocessor 2002
can execute instructions stored in the memory 152 for monitoring
and managing signal levels at the lead arrangement 108.
[0252] In some embodiments, the H-bridge circuit 2006 provides an
interface to electrodes, such as the lead arrangement 108. The
H-bridge circuit 2006 provides a structure by which various signals
can be delivered to a vagus nerve of a patient. Specifically, the
H-bridge circuit 2006 controls the amount of electrical stimulation
applied at the electrodes by controlling the output voltage (i.e.,
potential difference) between those electrodes. To do this, the
H-bridge circuit 2006 controls the flow of electricity though one
or both of the lead(s) by selectively activating and deactivating
electrical switches (not shown) in the H-bridge circuit 2006, so
that the output voltage between the lead(s), or across contacts of
a particular lead, maintain a waveform-shape. For example, the
H-bridge circuit 2006 can correspond to or be included in the
output module 161 of FIGS. 3A-3B.
[0253] In one possible embodiment, the H-bridge circuit 2006
includes dual H-bridge circuits (See FIG. 26), each separately
coupled to the high voltage source 2008. Additional details of the
H-bridge circuit 2006 are discussed below.
[0254] In the embodiment shown, a high voltage source 2008 is
electrically coupled to the H-bridge circuit 2006 to drive the
device 2000. The high voltage source 2008 can be, in various
embodiments, an adjustable voltage source configured to deliver a
desired voltage (and associated current) for use in delivering a
therapy to a patient, for example through use in connection with
the H-bridge circuit 2006. In some embodiments, the high voltage
source 2008 is programmable or otherwise adjustable by the
microprocessor and/or FPGA. For example, in some embodiments, the
high voltage source 2008 corresponds to the power source 161 and
associated charge control module 153, and power regulator modules
156, 160, of FIGS. 3A-3B, such that the high voltage source 2008
receives feedback from the processor 2002 (e.g., the CPU 154), and
delivers an adjustable signal to the H-bridge circuit 2006 (e.g.,
the output module 161). In some embodiments, the high voltage
source includes a 12 volt battery and associated circuitry useable
to control and/or adjust output voltage; in alternative
embodiments, other voltage levels or types of voltage sources could
be used.
[0255] Due to the sensitive nature of therapy delivery using the
device 2000, the device can be configured to perform tests to
ensure safe operation of the H-bridge circuit 2006 and associated
electrodes, as well as many other features of the device 2000. For
example, in some instances, the switches in the H-bridge circuit
2006 may fail to activate or deactivate as required, thereby
creating one or more types of malfunction effects. For example, a
DC offset could be generated, which can adversely affect the
electrical stimulation applied to the patient. In certain
instances, moderate to severe damage to a patient's nerves, tissue,
muscle, or the like may occur as a result of such DC offset. To
ensure that the switches are activating and deactivating as
intended, the device 2000 periodically performs an H-bridge safety
check prior to and during therapy of a patient, details of which
are discussed below.
[0256] In some embodiments, the microprocessor 2002 is configured
to periodically perform a sequence of tests on the H-bridge circuit
2006 during operation of the device 2000 to ensure proper operation
of the H-bridge circuit 2006 but not while therapy is being
delivered to the patient. In one embodiment, the sequence of tests
occurs once every four seconds; in alternative embodiments, the
microprocessor 2002 can be programmed to perform H-bridge tests at
various times, such as prior to delivery of a therapy, every 30
seconds, or upon receiving a signal from remote from the device
2000 (e.g., from a remote system, or based on an interrupt from the
FPGA 2004). In alternative embodiments, testing time intervals may
vary depending on the circumstances surrounding use of the medical
device.
[0257] According to some embodiments the microprocessor 2002 is
configured to receive signals indicative of a voltage drop across
each of a first sensing resistor 2014 and a second sensing resistor
2016 (FIG. 25). Both sensing resistors 2014, 2016 are electrically
connected between the H-bridge circuit 2006 and a ground 2018.
Further, the microprocessor 2002 is configured to generate signals
indicative of current flow through each of the sensing resistors
2014, 2016. Upon generation of signals indicating current flow
above or below a predetermined threshold current (or otherwise
outside of an expected threshold current), the microprocessor 2002
aborts use of the device 2000. The microprocessor 2002 may
accomplish sending and receiving of signals either independently or
through the interconnectivity of the ADCs 2010, 2012.
[0258] In embodiments, receiving signals further comprise receiving
a signal from an analog-to-digital converter; the analog-to-digital
converter is electrically connected between the sensing resistor
and the ground; and wherein, the digital-to-analog converter and
the analog-to-digital converter are electrically connected between
the H-bridge circuit and the microprocessor. In embodiments, the
microprocessor sends a signal to the one or more digital to analog
converters to control the current source.
[0259] In some embodiments, the FPGA 2004 is configured to drive
control inputs provided to the H-bridge circuit 2006, and
accordingly to manage delivery of voltage to the lead arrangement
108. As such, in some embodiments the FPGA 2004 can perform one or
more functions described above as associated with the signal
generation module 159 (FIG. 3B). Specifically, the FPGA 2004 is
configured to receive the signals sent by the microprocessor 2002,
indicating a particular state of the H-bridge 2006 (e.g., as
determined from a current detected through each of the sensing
resistors 2014, 2016), and a current state or signal to deliver to
the H-bridge. In response to the signals, the FPGA 2004 generates a
set of control outputs that are connected to various switches in
the H-bridge 2006 (as illustrated, for example, in FIG. 26) that
control the current flow from the high voltage source 2008 and
through the H-bridge circuit 2006. Further, the FPGA 2004 may be
configured to, in connection with the microprocessor 2002, drive
H-bridge inputs to perform intermittent testing of the H-bridge
circuit 2006 through a sequence of tests. Based upon these tests,
the microprocessor may abort use of the device 2000 if the tests
indicate current flow above or below a predetermined threshold
current.
[0260] Referring now to FIG. 26, a schematic representation is
shown of one embodiment of a system 2100 including H-bridge
circuitry 2101. The H-bridge circuitry 2101 includes a first
H-bridge circuit 2132 and a second H-bridge circuit 2134, which are
electrically coupled to a high voltage source 2102. More
specifically, circuitry 2101 is one embodiment of the H-bridge
circuit 2106 of the device 2000 illustrated in FIG. 25;
analogously, high voltage source 2102 is an example embodiment of
the high voltage source 2008 of FIG. 25, and as such, an embodiment
of the power source 151, charge control module 153, and power
regulator modules 156, 160 of FIGS. 3A-3B. As in FIG. 25, the
H-Bridge circuit is connected to current sources 2020 and 2021. The
D/A Converter 2022 is controlled by the microprocessor 2002, and
provides voltage signals to the current sources 2020 and 2021 to
establish the current flowing through 2020 and 2021. Additionally,
the first H-bridge circuit 2132 and second H-bridge circuit 2134
are electrically connected to a ground by sensing resistors 2112,
2122, analogously to resistors 2014, 2016 of FIG. 25.
[0261] As shown in system 2100, dual H-bridge circuits 2132, 2134
are illustrated which include first and second electrical leads
2136, 2138. Each H-bridge circuit 2132, 2134 includes connections
to the high voltage source 2102, sensing resistors 2112, 2122, and
two pairs of series electrical switches connected in parallel
between the voltage supply connections and sensing resistors 2112,
2122. In certain embodiments, the leads 2136, 2138 are connected to
tissues, muscles, nerves, or the like of a patient and are utilized
to apply an electrical stimulation thereupon. The H-bridge circuits
2132, 2134 control flow of electricity to the leads 2136, 2138 by
reversing the flow of electricity through the leads 2136, 2138,
thereby, creating a steady waveform-shaped output voltage between
the leads 2136, 2138.
[0262] More specifically, the first electrical lead 2136 forms a
first electrode, and includes a first tip connection 2124 and a
first ring connection 2126. The second electrical lead 2138 forms a
second electrode, and includes a second tip connection 2128 and a
second ring connection 2130. In embodiments, at least one of the
first and second tip and ring connections include a pad and hook
shaped arrangement. Such tip and ring connections can, in some
embodiments, correspond to the anterior and posterior tip and ring
connections described above in connection with FIGS. 10-17. In
certain embodiments of the present invention, the first lead 2136
is an anterior lead and the second lead 2138 is a posterior lead.
Thus, the first lead 2136 is connected to the anterior trunk of the
patient's vagal nerve, while the second lead 2138 is connected to
the posterior trunk of the patient's vagal nerve. In alternative
embodiments, this arrangement may be reversed such that the first
lead is a posterior lead and the second lead is an anterior
lead.
[0263] To ensure appropriate electrical stimulation, the first
H-bridge circuit 2132 controls electrical flow of the first lead
2136, and the second H-bridge circuit 2134 controls electrical flow
of the second lead 2138. In particular, each of the tip and ring
connections 2124-2130 can be tied either to a high voltage or to
ground by activating a switch to electrically connect the
respective tip and/or ring to the high voltage source 2102 or to a
ground. In particular, the first tip connection 2124 is tied to the
high voltage source 2102 by a first switch 2104 and to ground by a
second switch 2106. The first ring connection 2126 is tied to the
high voltage source 2102 by a third switch 2108 and to ground by a
fourth switch 2110. Similarly, the second tip connection 2128 is
tied to the high voltage source 2102 by a fifth switch 2114 and to
ground by a sixth switch 2116. The second ring connection 2130 is
tied to the high voltage source 2102 by a seventh switch 2118 and
to ground by a eighth switch 2120.
[0264] In general, in this embodiment, differential signals can be
applied from the first tip connection 2124 to the first ring
connection 2126, and from the second tip connection 2128 to the
second ring connection 2130. As such, signals are applied at local
areas, the exact location depending upon placement of the first
and/or second electrodes. In some embodiments, a ninth switch 2123
connects across the H-bridge circuits 2132, 2134, for example from
the first tip connection 2124 to the second ring connection 2130,
or otherwise across the circuits. The ninth switch 2123 allows a
further control input to activate a differential tip-to-tip or
ring-to-ring activation configuration, allowing for activation of
only a portion of the overall circuitry, as described in some of
the configurations described above. In various embodiments, the
electrical switches 2104, 2106, 2108, 2110, 2114, 2116, 2118, 2120,
2123 may be transistors, such as, a field-effect transistor,
bipolar junction transistor, or any other similarly functioning
electrical switch.
[0265] During the course of controlling the electrical flow to the
leads 2136, 2138, one or more of electrical switches 2104, 2106,
2108, 2110, 2114, 2116, 2118, 2120, 2123 may fail to activate or
deactivate, thereby creating a potential DC offset which could
damage the patient's nerve, muscle, tissue, or the like. In an
effort to protect against potential DC offset difficulties, the
device 2000 performs periodic safety checks on the H-bridge
circuits 2132, 2134. During each test, the device 2000 monitors a
current flow through the sensing resistors 2112, 2122, wherein the
current flow indicates that various switches are operational within
the H-bridge circuits 2132, 2134. More specifically, the H-bridge
safety check is performed by individually turning on each vertical
leg and each horizontal leg of the H-bridge circuits 2132, 2134 and
determining current flow through the sensing resistors 2112, 2122,
for example by receiving at the microprocessor 2002 a voltage
reading (via A/D converters 2010, 2012, on either side of each
resistor.
[0266] For example, in one embodiment of the testing sequence, the
first and second switches 2104, 2106 are activated. At this point,
the current flow through the sensing resistor 2112 is determined.
Because activation of switches 2104, 2106 closes a circuit between
the high voltage source 2102 and the sensing resistor 2112, the
voltage drop over the resistor will be nearly a full voltage drop
from the high voltage source 2102 to ground, and the current will
equivalently be high. Next, the first and second switches 2104,
2106 are deactivated, and the third and fourth switches 2108, 2110
are activated. Again, the current flow through the sensing resistor
2112 is measured, and the same result is expected. Thereafter, the
third and fourth switches 2108, 2110 are deactivated, and the fifth
and sixth switches 2114, 2116 are activated and the current flow
through the sensing resistor 2122 is determined. Finally, the fifth
and sixth switches 2114, 2116 are deactivated, and the seventh and
eighth switches 2118, 2120 are activated. Once again, the current
flow through the sensing resistor 2122 is measured. At this point,
the seventh and eighth switches 2118, 2120 are deactivated. If the
current flow measurements are outside an expected current flow
range at any time during the testing sequence, this indicates that
one or more of the switches cannot activate, and therefore a
connection between the voltages source 2102 and the ground may fail
(resulting in a lower than expected current across one of the
resistors 2112, 2122). In this case, the device 2000 (and in
particular the microprocessor 202) alarms an error and therapy is
aborted.
[0267] In another embodiment of the testing sequence, the above
series of tests is followed by a second series of tests.
Specifically, the first and third switches 2104, 2108 are
activated, with switches 2106, 2110 maintained as deactivated.
Next, the current flow through sensing resistor 2112 is determined.
In this case, minimal current flow through the resistor 2112 is
expected, because no direct path to voltage source 2102 should be
available. Then, the first and third switches 2104, 2108 are
deactivated, and the second and fourth switches 2106, 2110 are
activated. Again, the current flow through the sensing resistor
2112 is measured. Next, the second and fourth switches 2106, 2110
are deactivated, and the fifth and seventh switches 2114, 2118 are
activated. The current flow through the sensing resistor 2122 is
then determined. Finally, the fifth and seventh switches 2114, 2118
are deactivated, and the sixth and eighth switches 2116, 2120 are
activated. Next, the current through the sensing resistor 2122 is
calculated. Again, if the current flow measurements are outside an
expected current flow range (in this case, unexpectedly high) at
any time during the testing sequences, the device 2000, and in
particular the microprocessor 2002, alarms and therapy is aborted.
In yet another embodiment, the second series of tests is not
preceded by the first series of tests.
[0268] b. Voltage Output Safety Check
[0269] In another embodiment, a medical device comprises a first
electrical lead comprising a first tip connection and a first ring
connection; a second electrical lead comprising a second tip
connection and a second ring connection; and an impedance
measurement device configured to monitor an output voltage applied
to the nerve to detect a direct current offset. In embodiments, the
use of the medical device is halted if a direct current is
detected. In embodiments, the impedance measurement device is
configured to monitor the output voltage for symmetry between
positive and negative voltages applied to the nerve. In other
embodiments, the impedance measurement device monitors a cumulative
additive effect of the output voltage over a predetermined
period.
[0270] In some embodiments, the impedance measurement device
includes a programmable circuit electrically connected to the first
and second electrical leads and configured to execute program
instructions, which, when executed, cause the impedance measurement
device to detect a first positive voltage peak applied across
electrical connections of one or both first and second electrical
leads; to detect a first negative voltage peak applied across
electrical connections of one or both first and second electrical
leads; compare the first positive voltage peak and the first
negative voltage peak to determine at least a portion of an
impedance; and upon detecting that the impedance is outside a
predetermined range, generate an alarm indicating the presence of a
direct current signal applied to the nerve. In some cases, the
first positive voltage peak and the first negative voltage peak are
applied across the first tip connection and the second tip
connection.
[0271] In yet other embodiments, the programmable circuit is
further configured to cause the impedance measurement device to
detect a second positive voltage peak applied across electrical
connections of one or both first and second electrical leads; to
detect a second negative voltage peak applied across electrical
connections of one or both first and second electrical leads;
compare the second positive voltage peak and the second negative
voltage peak to determine at least a portion of an impedance; and
upon detecting that the impedance is outside a predetermined range,
generate an alarm indicating the presence of a direct current
signal applied to the nerve.
[0272] In some embodiments, the system 2100 also includes
capacitive dividers 2140, 2142, 2144, 2146. In the current
embodiment, the capacitive dividers 2140, 2142, 2144, 2146 are
positioned on each ring and tip connection of the H-bridge
circuits, and are used by the device as a part of an impedance
measurement device useable to calculate portions of the impedance
of the circuitry.
[0273] An example of such a capacitive divider circuit is
illustrated in FIG. 26, described in further detail below. The
capacitive dividers 2140, 2142, 2144, and 2146 are configured to
monitor an output voltage between various connections of the
H-bridge circuits to determine a portion of an impedance between
those connections. For example, in one embodiment, the capacitive
dividers 2140, 2142 monitor an output voltage between the first tip
connection 2124 and the first ring connection 2126. In an
alternative embodiment, the capacitive dividers 2140, 2144 monitor
an output voltage between the first tip connection 2124 and the
second tip connection 2128 and/or the first ring connection 2126
and the second ring connection 2130. Varying combinations of
capacitive dividers 2140, 2142, 2144, 2146 may be used depending on
which of the connections 2124, 2126, 2128, 2130 are being used by
the device to apply an electrical stimulus. If the determined
impedance is outside a predetermined range, the device generates an
alarm indicating the presence of a direct current signal applied to
the patient.
[0274] In still some further embodiments, additional tests can be
performed using different combinations of switches, including
switch 2123, useable for alternative tip-to-tip configurations.
Various testing arrangements relative to the H-bridge are discussed
below in connection with FIG. 29.
[0275] Now referring to FIG. 27, a schematic diagram of a
capacitive divider 2200 is illustrated, according to an example
embodiment of the present disclosure. The capacitive divider 2200
is useable within an overall device, such as those described
herein, as an embodiment of the capacitive dividers 2140, 2142,
2144, 2146 of FIG. 26, and can represent the capacitive divider
module 162 of FIGS. 3A-3B. The capacitive divider 2200 can be used,
for example, to allow a microprocessor to monitor a state of a
particular electrode connection at one of the leads of an
implantable medical device, without directing current onto the
lead. This can be used, for example, to calibrate the electrodes to
ensure consistent voltage levels delivered by each electrode,
despite possible manufacturing tolerances in capacitors used in
such a system.
[0276] As illustrated, the capacitive divider 2200 includes first
and second capacitors 2204, 2206 electrically connected in series
between an electrode connection of a lead of the implantable
medical device and a ground 2208. The capacitive divider 2200 can
be used to monitor for possible DC offset effects present in the
medical device. For example, in some embodiments, the capacitive
divider 2200 can be used to detect peak positive and negative
voltages generated by the device (e.g., as illustrated in waveform
2300, discussed below), to determine uniformity of positive and
negative signal generation. Non-uniform positive and negative
signals (or signal duration) can result in an overall DC offset
across a patient's tissue, which, over time, can potentially have
detrimental effects to the patient.
[0277] Furthermore, due to manufacturing variances in capacitive
values among various capacitors, a voltage output received at the
microprocessor from the capacitive divider may vary among devices,
despite the fact that the same voltage value may be present at the
electrode. In some embodiments, the capacitive divider therefore
generates a voltage measurement that can be passed to the
microprocessor, to calculate a capacitive ratio, based on the
voltage observed by the microprocessor and the known voltage output
from a high voltage source. The capacitive ratio can be used to
ensure that the correct (and consistent) current level is delivered
to the lead arrangement 108, for example by allowing the
microprocessor to adjust the output of the high voltage source. For
continued monitoring, the microprocessor is configured to calculate
an initial ratio of capacitances and periodically calculate a
second ratio of capacitances based on the first and second
capacitors 2204, 2206. The microprocessor then compares the second
ratio to the first ratio to calibrate a voltage or current output
by the medical device.
[0278] In various embodiments of the devices discussed herein, the
capacitors 2204, 2206 can have a number of different values,
depending upon the particular electrical characteristics of the
therapy to be delivered, as well. For example, in some embodiments,
capacitor 2204 can be a 47 pF capacitor, and capacitor 2206 can be
a 220 pF capacitor. It is understood that additional capacitance,
such as a parasitic capacitance present in the circuit, may be
present as well. Furthermore, the capacitors, due to manufacturing
variances, may depart from desired or expected values, either
initially or over time. For example, the voltage exposed to the
microprocessor may vary among the various tip and ring connections,
and may vary over time as capacitors fail. In some embodiments of
the medical device disclosed herein, a capacitive calibration
process can be integrated into operation of the device, to control
current flow across tip and ring connections and to guard against
capacitor failure. An example of such a test is discussed below in
connection with FIG. 31.
[0279] Now referring to FIG. 28, a graph illustrating an ideal
output voltage waveform 2300 produced between two electrical
contacts of a medical device is shown. In various embodiments, the
waveform 2300 can represent a therapy applied from a tip connection
to a ring connection at one or both electrodes of a medical device,
such as are illustrated above in connection with FIGS. 25-26.
Alternatively, the waveform 2300 can be applied in a tip-to-tip
arrangement across two electrodes.
[0280] In preferred embodiments, the waveform is symmetric, as
shown. In the embodiment shown, each symmetric positive and
negative signal portion of the waveform includes first and second
peaks, e.g., A1 and B1, or A2 and B2, respectively. These peaks
represent voltage difference variations between tip and ring
connections, respectively. For example, the A1 and B1 peaks can
represent connection of a tip connection to a ground (at A1), and
subsequent connection of the ring connection to a positive voltage
(at B1), thereby creating a negative potential from tip to ring.
The A2 and B2 peaks can, correspondingly, represent connection of
the tip connection to a positive voltage (at A2), and subsequent
connection of the ring connection to ground (at B2).
[0281] To attempt to maintain symmetry between positive and
negative signal portions of a pulse, the magnitudes of peaks A1 and
A2, B1 and B2, and areas C1 and C2 are approximately equal,
respectively. In some embodiments, the waveform 2300 as illustrated
is executed at a 5 kHz frequency, with each pulse width being
approximately 90 microseconds long. In alternative embodiments, the
waveform can be executed at a 2.5 kHz frequency, effectively
doubling the distance between adjacent sets of positive and
negative pulses. Furthermore, in some embodiments, the current
delivered using the therapy can be approximately 1-8 milliamps. In
one example embodiment, a 4 milliamp signal is delivered, within 5%
of a known value. Still other variations to the waveform are
possible as well. In general, changes in symmetry among the various
peaks and areas defined by the waveform 2300 can, due to greater
positive or negative current time (i.e., areas C1 and C2), result
in an overall DC current passing between the two electrodes or
tip/ring arrangements, depending upon the specific configuration
used. As such, it is desirable to limit such DC current, for
example to less than one microamp.
[0282] c. Clock Accuracy Adjustment Circuit
[0283] Another aspect of the disclosure provides a clock accuracy
adjustment circuit. Implantable neuroregulators include a
microprocessor as exemplified in FIG. 3A-3B and as identified as
CPU 154. Activities of the microprocessor are synchronized by a
clock signal. Typically, quartz piezo-electric oscillators are used
to generate clock signals for microprocessors. In some instances
Resistor-Capacitor (RC) circuits are used to generate clock signals
for microprocessors. Quartz oscillators are generally more accurate
than RC circuit because RC Circuits may drift over time. Drift may
cause a therapy to be applied at the wrong time, or a therapy to be
applied incorrectly. Quartz oscillators consume more power than RC
circuits. These types of oscillators cannot be used in a low-power
system intended to have a long-lasting battery. The battery's life
can be extended by minimizing the power consumption of the medical
device.
[0284] In embodiments, to help minimize the power consumption of
the medical device, an RC circuit generates the clock signal
instead of a quartz oscillator. Because the RC circuit is less
accurate than a quartz oscillator, the RC circuit needs to be
fine-tuned in order to ensure that the RC circuit generates a clock
signal at an appropriate frequency. Tuning the RC circuit is
necessary to get optimum communications performance and to get
accurate delay timing. In an embodiment, a method for adjusting RC
Circuit accuracy involves usage of integrated circuit and/or
crystal oscillator for resynchronization of RC Circuit.
[0285] In embodiments, a method for tuning an RC circuit clock
comprises activating an integrated circuit and/or crystal
oscillator, initiating instructions in the microprocessor to count
an actual number of oscillator transitions of the integrated
circuit and/or crystal oscillator during a defined period of time;
comparing the actual count of oscillator transitions to an expected
count of oscillator transitions, determining if the count is out of
range and calculating an OscValue by determining the difference
between that expected count and the actual count; setting an a
control register to a value that indicates the change in actual
oscillator transitions during the defined period of time; and
adjusting oscillation of the RC circuit clock based on the value in
the control register. In embodiments, the integrated circuit is a
real time clock such as a real time clock having a frequency of 32
KHz. In other embodiments, any type of crystal oscillator can be
utilized. In embodiments, the crystal oscillator and/or integrated
circuit are activated for a defined period of time and then turned
off in order to conserve power. In embodiments, the RC circuit
clock signal has a frequency of about 8 MHz. In embodiments, the
count of oscillator transitions occurs during one or more defined
time periods of at least 4 msec intervals. In embodiments, the RC
circuit clock adjustment is scheduled at least once daily. In other
embodiments, the RC circuit is tuned at least once daily and at any
time the device is powered up.
[0286] In an embodiment, a system comprises a neuroregulator
comprising a microprocessor comprising a RC circuit; and an
integrated circuit and/or crystal oscillator that functions as a
real time clock. In embodiments, the microprocessor contains
instructions for implementing a method for tuning a RC circuit as
described above. The microprocessor comprises an activate module to
activate the integrated circuit and/or crystal oscillator for a
period of time and then to deactivate the integrated circuit and/or
crystal oscillator after tuning is completed. The microprocessor
further comprises a counting module to count the actual oscillator
transitions of the integrated circuit and/or crystal oscillator
over a defined period of time; a compare module to determine if the
count is out of range and calculating an OscValue by determining
the difference between that expected count and the actual count;
and an adjustment module to set a control register to a value that
indicates the change in actual oscillator transitions during the
defined period of time and to adjust oscillation of the RC circuit
based on the value in the control register. An example of a control
register is an OSCTUNE register.
[0287] In other embodiments, a method of tuning an RC circuit
involves a downlink carrier frequency. In an embodiment, a method
comprises counting the number of carrier frequency oscillations in
a set number of RC clock cycles to determine the need to adjust the
RC clock; determining if the actual oscillation frequency of the
carrier frequency is different than the expected carrier frequency
oscillation; adjusting the RC clock oscillations based on any
difference between the actual carrier frequency oscillations from
the expected carrier frequency oscillation. In embodiments the RC
circuit clock signal has a frequency of about 8 MHz. In
embodiments, the downlink carrier frequency is the carrier
frequency of a data signal communicated from an external device to
the neuroregulator. In embodiments, the downlink carrier frequency
is about 19.2 MHz. In embodiments, the count of oscillator
transitions during a defined time periods of at least 4 msec
intervals. In embodiments, the RC circuit clock adjustment is
scheduled at least once daily. In other embodiments, the RC circuit
is tuned at least once daily and/or at any time the neuroregulator
receives a downlink carrier signal. In embodiments, a
microprocessor comprises a counting module to count the number of
carrier frequency oscillations in a set number of RC clock cycles,
a compare module to determine if the actual oscillation frequency
of the carrier frequency is different than the expected carrier
frequency oscillation, and an adjustment module to adjusting the RC
clock oscillations based on any difference between the actual
carrier frequency oscillations from the expected carrier frequency
oscillation.
[0288] In other embodiments, a method of tuning an RC circuit
involves bit mapping. In an embodiment, a method comprises
determining bit timing in a set number of RC clock cycles to
determine the need to adjust the RC clock; determining if the bit
timing is different than the expected bit timing; adjusting the RC
clock oscillations based on any difference between the actual bit
timing from the expected bit timing. In embodiments the RC circuit
clock signal has a frequency of about 8 MHz. In embodiments, the
bit timing is determined by using bit edges to detect signals (e.g.
sending alternating 1's and 0's or other pattern). In embodiments,
the bit timing is measured during a defined time periods of at
least 4 msec intervals. In embodiments, the RC circuit clock
adjustment is scheduled at least once daily. In other embodiments,
the RC circuit is tuned at least once daily and/or at any time the
neuroregulator receives a downlink carrier signal.
5 External Computer Interface
[0289] Programmer software, with which the physician can program
treatment configurations and schedules, resides on and is
compatible with an external computing device 107 (FIG. 1) that
communicates with the external charger 101. In general, application
software for the computing device 107 is capable of generating
treatment programs stored in a commonly accepted data file format
upon demand.
[0290] The programming interface of the computing device 107 is
designed to enable the physician to interact with the components of
the therapy system 100. For example, the programming interface can
enable the physician to modify the operational modes (e.g.,
training mode, treatment mode) of the external charger 101. The
programming interface also can facilitate downloading treatment
parameters to the external charger 101. The programming interface
enables the physician to alter the treatment parameters of the
neuroregulator 104, and to schedule treatment episodes via the
external charger 101.
[0291] The programming interface also enables the physician to
conduct intra-operative testing amongst the components of the
therapy system 100. For example, the physician can initiate a lead
impedance test via the programming interface. The physician also
can program temporary treatment settings for special physiologic
testing. The programming interface also can facilitate conducting
diagnostic stimulation at follow-up visits between the patient and
the physician.
[0292] The programming interface of the computing device 107 also
enables the physician to access patient data (e.g., treatments
delivered and noted physiological effects of the treatment). For
example, the programming interface can enable the physician to
access and analyze patient data recorded by the therapy system 100
(e.g., stored in the memory 152 of the neuroregulator 104 and/or
the memory 181 of the external charger 101). The physician also can
upload the patient data to the external computing device 107 for
storage and analysis.
[0293] The programming interface also can enable the physician to
view system operation information such as non-compliant conditions,
system faults, and other operational information (e.g., lead
impedance) of the therapy system 100. This operational data also
can be uploaded to the external computing device 107 for storage
and analysis.
[0294] i. Programming Access Level
[0295] In certain embodiments, the programming interface defines at
least two levels of access, one for the physician and one for the
system manufacturer. The programming interface can provide
different types of information to a requestor depending on what
level of access the requestor has. For example, the programming
interface may enable the system manufacturer to program system
settings (e.g., default values for treatment parameters, acceptable
ranges for treatment parameters and/or system settings, system
tolerances, etc.) that cannot be adjusted by the physician.
[0296] In an embodiment, a user with a high level of access can
select, for each system setting, the level of access required
before the programming interface will enable a user to modify the
system setting. For example, the system manufacturer may wish to
prevent treating physicians from modifying default treatment
settings. It will be appreciated that generating software
implementing the above-described features of the programming
interface is within the skill of one of ordinary skill in the art
having the benefits of the teachings of the present
application.
6. Charge Balancing
[0297] Nerves may be damaged when exposed to direct current (e.g.,
net current from electrical stimulation) over extended periods of
time. Such damage may result from very small net currents acting
over a long time, e.g. microamperes of current over minutes. For
example, direct current can be caused by a voltage buildup at the
electrodes 212, 212a (FIG. 1) due to inherent differences in
electrode component values.
[0298] Charge-balancing advantageously mitigates (and may
eliminate) damage to the nerve due to charge build-up during
treatment. However, conventional processes for achieving a
current/charge balance to within (for example) 1 .mu.A in a current
of about 6 mA place inordinate requirements on the implantable
device of providing consistent power at a consistent frequency.
Below are descriptions of two processes for balancing charge, a
timing process and a shorting process, that do not require such
inordinate consistency.
[0299] i. Timing Correction
[0300] Referring to FIGS. 20-24, charge or current on the patient's
nerves can be balanced by applying a correction to a pulse-width PW
of a treatment signal pulse 2000 over a number of cycles (see FIG.
20). A cycle refers to a single iteration of the pulse. The
correction includes adding or subtracting a "timer tick" to the
pulse-width PW of at least one phase of the treatment signal pulse
2000 to increase or decrease the pulse-width for a period of time.
In an embodiment, an example timer tick can equate to the minimum
resolution of the applied clock frequency (e.g., about 560
nanoseconds).
[0301] Typically, the treatment signal pulse 2000 is a bi-phasic
(e.g., having a negative phase and a positive phase) pulse signal
having a pulse-width PW. In general, the negative charge provided
by the first phase of the signal pulse 2000 is balanced by the
positive charge provided by the second phase of the signal pulse
2000. One or more timer ticks can be added to one or both phases of
the pulse 2000 to correct a charge imbalance.
[0302] In the example shown in FIG. 20, the first phase of the
signal pulse 2000 has a first pulse-width PW1 and the second phase
of the signal pulse 2000 has a second pulse-width PW2. One or more
timer ticks can be added to the pulse-width PW1, PW2 of one or both
phases of the signal pulse 2000. For example, the pulse-width PW1
of the first phase can be increased by two timer ticks to a
pulse-width of PW1'. Alternatively, the pulse-width PW2 of the
second phase can be decreased by two timer tick to a pulse-width of
PW2'.
[0303] To determine the number of timer ticks to add or subtract
from each pulse-width, the neuroregulator 104 periodically can
measure the voltage of the signal applied to each lead electrode
212, 212a of lead arrangement 108. The combination of charge
buildup sensing and pulse width control creates a feedback loop to
minimize the resulting voltage offset. Advantageously, this sense
and control process is effective in the presence of physiologic
variations, circuit tolerances, differences in electrode size, and
temperature changes.
[0304] For example, as shown in FIGS. 3A and 3B, the electrodes of
each lead (e.g., the tip electrodes 212, 212a in contact with the
anterior and posterior vagal nerves AVN, PVN, respectively) are
coupled to the CPU 154 of the neuroregulator 104 via a capacitive
divider 162. The CPU 154 provides timed instructions to the output
module 161 for controlling the voltage measurements V.sub.A,
V.sub.B of the signals applied by the electrodes 212, 212a (FIG.
1).
[0305] Between pulses, the microprocessor CPU 154 can zero the
capacitive divider 162, release the capacitive divider 162 at a
predetermined time relative to the signal cycle, and measure the
voltages V.sub.A, V.sub.B of the electrodes 212, 212a. For example,
the CPU 154 can zero the capacitive divider 162, release the
capacitive divider 162 approximately ten microseconds into a
negative phase of the pulse, and measure the voltages V.sub.A,
V.sub.B (see FIG. 20). The CPU 154 can subsequently measure the
voltages V.sub.A, V.sub.B at approximately 10 microseconds into a
positive phase of the pulse. If the voltage measurement V.sub.A of
the electrode 212 is greater than the voltage measurement V.sub.B
of the second electrode 212a, then the CPU 154 delivers
instructions to decrease the pulse width (e.g., by about 560
nanoseconds) of the negative phase of the pulse of the
next/subsequent cycle.
[0306] The above process may be repeated at a sampling frequency
(e.g., typically about 40 Hz). Gradually, the number of pulse width
corrective increments ("timer ticks") applied to the signal can be
adjusted. For example, the pulse width PW1 of the positive phase of
the pulse can be increased or decreased every sample period until
the voltage measurement V.sub.A of the first electrode 212 is less
than the voltage measurement V.sub.B of the second electrode 212a.
In such a case, the pulse width PW2 of the negative pulse then can
be increased to achieve balance. When the maximum pulse width PW2
of the negative phase of the pulse is reached, then the pulse width
PW1 of the positive phase of the biphasic pulse may be decreased to
maintain balance. In a preferred embodiment, the corrective
increment is applied to a series of signals until the net offset
current is well below a target current (e.g., about 1 .mu.A).
[0307] In an embodiment, the amplitudes of the positive and
negative phases of the pulse are compared very early in the cycle,
and a relatively large correction is initially applied to the pulse
width of the signal. Subsequently, the balancing correction is
refined by changing the pulse width by only the one or two ticks as
described above.
[0308] Advantageously, the charge-balancing goal can be achieved
over a number of these cycles using the above described processes
without requiring a high clock frequency. Because the charge
buildup tends to be a slow process, correcting the charge buildup
can be done less frequently than delivering therapy signals. For
example, in an embodiment, therapy signals can be delivered at
about 5 kHz and correction pulses can be delivered at about 40
Hertz.
[0309] FIG. 21 illustrates an example application of charge
balancing through timing corrections. FIG. 21 illustrates a
blocking waveform 222 (e.g., a biphasic, symmetric current
waveform), which results in a voltage waveform 224 at the
electrode-tissue interface. The voltage waveform 224 includes an
exponential voltage component 226 which reflects the fact that the
electrode-tissue interface has capacitive elements, resulting in
charging and discharging of this capacitance.
[0310] In one cycle of the current waveform 222, the charge applied
to the electrode-tissue interface is balanced when the voltages
V.sub.C and V.sub.D are equal. Accordingly, in such a case, the net
potential of the electrode-tissue interface is zero. As described
above, however, there are a number of reasons why, in practice,
voltages V.sub.C and V.sub.D may not be equal, resulting in a
charge imbalance.
[0311] Typically, in practical operation, the voltage values of
V.sub.C and V.sub.D are measured periodically (e.g., about every 25
milliseconds). If the voltage V.sub.C is greater than the voltage
V.sub.D then the pulse width 228 of the first phase of the current
waveform 222 is reduced by one "timer tick," and applied for about
1 millisecond. At the end of subsequent measurement periods (e.g.,
about every 25 milliseconds), the values of voltages V.sub.C and
V.sub.D are measured again. When the voltage V.sub.C is greater
than the voltage V.sub.D the pulse width 228 of the first phase is
reduced by an additional timer tick. The current waveform 222
having the phase with the reduced pulse-width 228 is applied for an
additional 1 millisecond.
[0312] When the value of the voltage V.sub.C is eventually less
than the value of the voltage V.sub.D, then the pulse width 228 of
the first phase can be increased by one timer tick for 1
millisecond for each measurement period. In this situation, it may
be that the maximum pulse width (as determined by the applied
frequency of the therapy) 228, is reached while the voltage V.sub.C
is still less than the voltage V.sub.D. If this occurs, then the
pulse width 230 of the second phase of the current pulse 222 is
decreased one timer tick at a time, as described above, until
equilibrium is established (i.e., V.sub.C=V.sub.D).
[0313] Additionally, in the methods represented by FIGS. 20 and 21,
the microprocessor CPU 154 can short out the electrodes 212, 212a
at the beginning, midpoint and/or end of the biphasic, square-wave,
current pulse, as described in more detail herein. Over a series of
such sampling cycles, it has been demonstrated that the net offset
current is well below the design goal of 1 .mu.A.
[0314] During a feedback cycle, software stored in the
microprocessor CPU 154 can initiate a therapy shut down if the
sensed voltage offset exceeds safe values. This is an advantageous
feature in actual use, where electrode configurations and other
parameters could vary.
[0315] By using a combination of both hardware (i.e., electrode
shorting) and closed-loop software techniques, the average charge
imbalance may be lower than with either method individually.
[0316] At the end of therapy delivery, it is useful to have the
hardware briefly drain any residual charge. Subsequently, the
circuitry may be made safe until the next therapy delivery and the
software loop turned off.
[0317] ii. Shorting Correction
[0318] Some processing for achieving charge balance have involved
the use of biphasic pulses in which, for example, the negative
charge provided by the first part of the waveform is balanced by
the positive charge provided by the second part of the waveform.
Further details describing the use of electrode shorting to achieve
charge balancing can be found in U.S. Pat. No. 4,498,478 to
Bourgeois, issued Feb. 12, 1985; U.S. Pat. No. 4,592,359 to
Galbraith, issued Jun. 3, 1986; and U.S. Pat. No. 5,755,747 to Daly
et al, issued May 26, 1998, the disclosures of which are hereby
incorporated by reference herein.
[0319] FIGS. 22-24 illustrate a preferred charge balancing process.
FIGS. 22 and 23 schematically illustrate an implanted circuit 112
of a neuroregulator 104 connected to nerve electrodes 212, 212a.
The circuit 112 has components schematically illustrated as a
switch 150 for selectively creating an electrical short between the
electrodes 212, 212a. In FIG. 22, the switch 150 is arranged in a
short state to create an electrical short between electrodes 212,
212a. In FIG. 23, the switch 150 is arranged in a non-short state
with no short being created between the electrodes 212, 212a.
[0320] FIG. 24 schematically illustrates signal waveforms W.sub.1,
W.sub.2, W.sub.1A, W.sub.2A produced at the electrodes 212, 212a
under various conditions of operation of the switch 150. The
waveforms W.sub.1 and W.sub.2 show the signals produced at
electrodes 212, 212a, respectively, when the switch 150 is arranged
in the non-short state. Each waveform W.sub.1 and W.sub.2 has a
negative pulse and a positive pulse of equal pulse width PW. The
waveforms W.sub.1, W.sub.2 are out of phase so that the negative
pulses of the waveform W.sub.1 occur during the positive pulses of
the waveform W.sub.2.
[0321] It will be appreciated, these waveforms are illustrative
only. Any other waveform (e.g., the time offset waveform W.sub.12A
of FIG. 18 could be used). In addition, while the short is shown
between electrodes 212, 212a, the short alternatively or
additionally could be created between cathode and anode pairs 212,
218 and 212a, 218a, previously described.
[0322] In the example shown, the switch 150 is operated to create a
short between electrodes 212, 212a at the start of each pulse and
for a duration D.sub.S. The waveforms at electrodes 212, 212a
resulting from such shorting are shown in FIG. 24 as W.sub.1A,
W.sub.2A. As a result of the short, any charge build-up at an
electrode (e.g., electrode 212) is distributed to the oppositely
charged electrode (e.g., electrode 212a). The pulse width PW of
each pulse is reduced to a pulse width PW.sub.A. Advantageously,
repeating this process throughout the therapy maintains any net
charge build-up below tolerable levels.
[0323] The example given shows the short state occurring at the
beginning of each signal pulse. This is illustrative only. The
short state can occur at the beginning, end or any intermediate
time of a signal pulse. Furthermore, the short state need not be
applied to every pulse, but rather can occur intermittently
throughout the pulse cycles or even during time delays between
pulses. When applied during a pulse cycle, the duration D.sub.s of
the short is preferable not greater than about 10% of the pulse
width PW. For example, the duration D.sub.s can range from about 10
.mu.s to about 20 .mu.s.
[0324] iii. Therapy Calibration, Safety Limits and Safety
Checks
[0325] The design of the neuroregulator 104 (FIG. 3) includes a
capacitive divider 162 and an output module 161 to measure the
voltage present at the lead arrangement 108 (e.g., the tip
electrodes 212, 212a and/or ring electrodes 218 and 218a of both
anterior and posterior leads 106, 106a). The output module 161 can
measure the current flow through the electrodes arranged in any of
the four electrode configurations (see FIGS. 11, 13, 15, and 17). A
programmable current source (not shown) can enable a physician to
select how current is delivered through the electrodes 212, 212a,
218, and 218a to the nerve.
[0326] Before therapy is delivered, the physician can calibrate the
neuroregulator 104 to ensure the desired current can be delivered
to the nerves. For example, this calibration can be accomplished by
connecting the programmable current source from a power source to
ground and adjusting the current to the desired level. Current does
not flow through the leads 106 during this calibration procedure.
If the desired current cannot be delivered, or if the DC voltage
offset is greater than a programmed limit, then the therapy can be
terminated (e.g., such conditions trigger a flag or error
alert).
[0327] Advantageously, calibrating the therapy system 100
significantly reduces the effect of component tolerance, drift, and
aging on the amount of current delivered. In addition, the
capacitive divider 162 can be calibrated before therapy is
delivered. Advantageously, calibrating the divider 162 can enhance
the accuracy of the safety checks from a 20% worst case value to
approximately 2%.
[0328] During therapy, the current between the active electrodes is
measured during each signal pulse to ensure that the delivered
current is within the programmed tolerance (e.g., +/- about
5%).
[0329] Additionally, in order to determine the state of charge
balance, the therapy system 100 can determine a peak-to-peak
voltage quantity for each signal pulse. The peak-to-peak voltage
quantity is divided by two and compared to the peak voltage
measurement of each phase of the waveform. If the deviation exceeds
a predetermined value, the therapy can be shut down.
[0330] Referring now to FIGS. 29-31, various test methods that can
be employed within a system 100, and in particular a medical device
2000 as illustrated in FIGS. 25-28 are illustrated. In general, the
test methods discussed herein represent algorithms that can be
performed, either in whole or part, by a processing unit (e.g., CPU
or other programmable circuit) periodically to ensure continued
accurate and safe operation of the device/system. FIG. 29 describes
an example method of performing safety checks of the H-bridge
leading to the lead arrangement 108, while FIG. 30 describes an
example method for monitoring impedance, and therefore detecting
any potentially harmful DC offset effects occurring in the
delivered therapy. FIG. 31 illustrates an example method for
implementing a capacitive divider and thereby adjusting output
current to the lead arrangement 108
[0331] Now referring to FIG. 29, a flow chart of an embodiment of
the present disclosure showing a method 2400 for conducting safety
checks on an H-bridge circuit of a medical device is illustrated.
The method 2400 generally revolves around testing activation of the
various switches available in an H-bridge circuit, such as the
circuits 2132, 2134 of FIG. 26.
[0332] The method 2400 involves periodically initiating a sequence
of tests of an H-bridge circuit (step 2402). This can occur, for
example, prior to initiating operation of the device 2000, or
periodically during operation or delivery of a therapy. The method
2400 involves, at that predetermined or periodic time for testing
the circuit, transmitting a set of control signals input to
switches in an H-bridge circuit (step 2404), for example, driving
such signals from a microprocessor and/or FPGA, such as those
illustrated in FIG. 25.
[0333] The method 2400 further includes, during each test (i.e.,
while certain switch inputs are set), monitoring a current flow
across a sensing resistor electrically connected between a sensing
connection of the H-bridge circuit and a ground (step 2406) but
while not therapy is being delivered. In embodiments, in a therapy
cycle therapy delivery signals are stopped, an H bridge safety
check is conducted, and then therapy is resumed. A current flow
through the sensing resistor indicates that both series switches,
within at least one of the two pairs of series switches are active
during that test, while absence of current indicates that at least
one of the series switches is non-functional, as explained above
with respect to FIG. 26. A current assessment operation determines
whether a detected current flow is outside of an expected range of
acceptable currents (operation 2408). If the current flow is
outside of an expected range (e.g., a high current during the first
type of status checks discussed above, or a low current during the
second type of status checks discussed above), the system enters an
alarm state (step 2410), and halts operation to prevent
unintentional injury to the patient. If the current flow is within
the predetermined range of acceptable current for the given test,
operation either returns to reset the test inputs for testing a
next subsequent combination of switches (step 2404), or the test
completes (at end step 2412).
[0334] Overall, the sequence of tests is configured to test each
switch connection of two pairs of series switches connected in
parallel between a voltage supply and the sensing connection. In
one embodiment, the method illustrated in FIG. 29 can be
implemented by the circuitry shown in FIGS. 25-26. For example, the
microprocessor 2002, configured to send and receive signals
indicative of activity in the H-bridge circuit 2006 may
periodically perform the sequence of tests on the H-bridge circuit
2006 during operation of the device 2000 to ensure proper operation
of the H-bridge circuit 2006. In such embodiments, the FPGA 2004,
configured to receive the signals sent by the microprocessor 2002
regarding a desired state, may control the current flow through the
H-bridge circuit 2006 by setting the various switches included in
the H-bridge circuit 2006. To accomplish this, the FPGA 2004 may
control the voltage of the gate inputs of the H-bridge circuit
based upon the signals sent by the microprocessor 2002. In either
example, if the current flow through the sensing resistors 2014,
2016 is above a predetermined threshold current, either the
microprocessor 2002 halts and/or aborts use of the medical device
2000, and in some embodiments, triggers an alarm.
[0335] In some embodiments, the sequence of tests can be executed
either prior to operation, or periodically during operation of the
device 2000. For example, in some embodiments, a sequence of tests
of H-bridge circuitry can be executed approximately every four
seconds during operation of the device. Other periods, or scheduled
tests, could be used as well.
[0336] Now referring to FIG. 30, a method 2500 for conducting
impedance measurement checks on a medical device is shown. The
method 2500 can be executed by a device such as device 2000 of FIG.
25, and can be performed, for example, continually during delivery
of a therapy. In particular, the impedance checks provided by the
present disclosure can utilize capacitive dividers, such as those
illustrated in FIGS. 26-27, for measuring impedance of a circuit,
for example to determine the existence of a DC offset in a
delivered electrical signal delivered as a therapy to a patient. A
greater than expected DC offset, signifying less than adequate
current flow through one or both of the electrical contacts, can
affect the electrical simulation applied by the electrical contacts
onto a patient.
[0337] In the embodiment shown, after initiation (step 2502), the
method 2500 includes detecting a first voltage peak output between
two electrical contacts of a medical device (step 2504). After this
step, the process continues by detecting a second voltage peak
output by the two electrical contacts of the device (step 2506).
This second voltage peak output, based on the waveforms used in the
therapy, has a magnitude approximately equal to but opposite in
polarity from the first voltage peak output. These peaks can be,
for example, the maximum peaks of the positive and negative
portions of the waveform, such as points B1, B2 of FIG. 28. The
difference between these peaks represents the DC offset of the
circuit. By comparing the two voltage peaks, in particular by
comparing the magnitudes of those peaks, at least a portion of an
impedance (i.e., a capacitive portion) between the two electrical
contacts is determined (step 2508). The impedance is then compared
to a predetermine impedance range, such as a minimum or maximum
acceptable impedance. If it is found that the determined impedance
is outside a predetermined impedance range (step 2510), an alarm is
generated indicating the presence of a direct current signal
applied to the tissue of a patient (step 2512). However, if the
determined impedance is within the predetermined range, the process
will either begin again to confirm the impedance of the same
electrical contacts, begin again to determine the impedance of two
different electrical contacts (or the same two electrical contacts
during delivery of a different therapy cycle; returning to step
2504) or end (step 2514). In some embodiments, this comparison can
determine whether the DC offset exceeds 1 microamp; however, in
alternative embodiments, other DC offsets may be deemed
acceptable.
[0338] Referring to FIG. 30 generally, it is noted that in some
embodiments, an improper DC offset can be calculated by determining
the height difference between peaks A1/A2 and B1/B2, respectively,
as illustrated in FIG. 27. In one embodiment, an impedance
measurement device is used to calculate these height differences
and ensure that the medical device is operational before each
application of an electrical stimulus. In some embodiments, it is
desirable to ensure that magnitudes of the peaks (e.g., comparing
A1 to A2, and comparing B1 to B2) are within approximately 400 mV.
However, in alternative embodiments, other thresholds could be
used. In any event, to maintain a desired level of symmetry, peaks
should be compared, as well as the duration of each pulse (e.g.,
the width of pulses C1, C2).
[0339] In varying embodiments, the method 2500 may include several
other steps. For example, the process may begin again to detect a
second positive and negative output voltage to determine a second
portion of the impedance between the same electrical contacts.
Further, in calculating the impedance, an electrical current of
about 3 mA may be used. However, in alternative embodiments, this
value may either be increased or decreased depending on various
factors including the function of the medical device and the amount
of electrical stimulus desired.
[0340] In still other embodiments, the process 2500 may include
intermediary steps between detecting that the impedance is outside
a predetermined range (step 2510) and generating the alarm (step
2512). For example, for purposes of accuracy, the process may
include decreasing an operational voltage of the medical device and
then detecting a second positive and negative voltage output by the
same two electrical contacts of the medical device operating at the
decreased operational voltage. After comparing the second voltage
peaks to determine a second impedance, the second impedance may be
compared to a predetermined range. If at this point the second
impedance is determined to be outside the predetermined range, the
process may include generating the alarm and halting use of the
medical device. However, if the impedance or second impedance is
determined to be within the predetermined range, the process may
include restarting the medical device.
[0341] In one embodiment, the process 2500 illustrated in FIG. 30,
can be implemented by a medical device, embodiments of which are
shown in FIGS. 25-26. Specifically, the medical device of FIGS.
25-27 can be calibrated such that the voltage output between any
two electrical connections 2124, 2126, 2128, 2130 produces the
ideal waveform 2300, seen in FIG. 28. To do this, an impedance
measurement device, such as capacitive dividers 2140, 2142, 2144,
2146 connected to a microprocessor, detect a negative and a
positive voltage peak output between any two electrical connections
2124, 2126, 2128, 2130. By comparing the negative and positive
voltage peaks, the impedance measurement device determines at least
a portion of an impedance between the chosen connections, and
ensures that the portion of the impedance is within a predetermined
range of acceptable impedance values. In this way, the impedance
measurement device confirms that the electrical stimulus applied to
a vagal nerve of a patient is within a safe and appropriate range.
If the portion of the impedance is not within the predetermined
range, the impedance measurement device may trigger an alarm and/or
halt usage of the medical device.
[0342] In varying embodiments of the present disclosure, the
portion of the determined impedance may be the resistive portion or
the capacitive portion of the impedance. Further, the sequence of
tests conducted to ensure that impedance measurements conform to
predetermined standards can occur at any time prior to application
of electrical stimulus, for example in four second intervals, as
programmed into the impedance measurement device, or as directed by
the operator of the medical device. For instance, a programmable
circuit, configured to execute program instructions, may be
electrically coupled to the first and second electrical leads of
the medical device. The programmable circuit, for example, the
microprocessor 2002, can cause an impedance measurement device to
perform the steps discussed above. In alternative embodiments, the
programmable circuit may be an FPGA, such as FPGA 2004, or any
other programmable circuitry capable to drive the operation of an
impedance measurement device.
[0343] Referring now to FIG. 31, a flow chart of an example method
2600 showing the steps for calibrating electrical signal output of
a medical device is illustrated. The method 2600 is useable in
association with any of a variety of embodiments of the medical
device, such as those illustrated in FIGS. 25-27. In particular,
the method 800 provides for calibration of an output voltage by
monitoring capacitor values in a capacitive divider.
[0344] The method 2600 is initiated (step 2602) upon initial
operation of an implantable medical device, for example upon
manufacturing of the device. The method 2600 includes calculating
initial ratios between the capacitors in the capacitive divider for
each electrode connection (i.e., each of the first and second tip
and ring connections of FIG. 26, above) (step 2604). The initial
ratios are calculated, for example, by using a known high voltage
value from the a high voltage source, and detecting a voltage
between two capacitors of the capacitor divider (e.g., as connected
to a general purpose I/O pin of a microprocessor, as discussed
above in connection with FIG. 27). This allows the initial ratios
to be tested without applying a current through the electrode,
because some or all of the H-bridge switches can remain
disconnected during calibration. The method 2600 further includes
storing the initial ratios in a memory, such as a memory associated
with the microprocessor or FPGA of the medical device, for later
reference (step 2606).
[0345] In some embodiments, calculation and storage of capacitive
ratios can further include calculating and storing an average ratio
for all of the capacitive dividers present within the device. If
one or more of the capacitive ratios then diverges from that
average number, either initially prior to use or after the device
is implanted and a therapy is about to be delivered, it can be
assumed that some malfunction occurred within the medical device
(e.g., one or more of the capacitors failed).
[0346] In the embodiment shown, prior to actual delivery of a
therapy, the method 2600 includes a second calculation of
capacitive ratios for each of the electrode connections, or at
least those used to deliver the therapy (step 2608). Those second
ratios can then be compared to initial ratios prior to delivery of
a therapy, to ensure that the correct current level is delivered
(step 2610). If the second ratios are approximately the same as the
initial ratios (i.e., they vary by less than a predetermined
percentage, such as 5%), a therapy can be delivered (step 2612). If
the ratios are off by some predetermined amount, a further
assessment can be made, to determine whether any of the ratios
diverges from an overall average of the capacitive ratios (step
2614). This comparison can be, for example, to the initial average
determined and stored in steps 2604-2606, or to a current average
of second ratios.
[0347] If one or more of the second ratios diverges from the
overall average of ratios by at least a predetermined amount, an
alarm is generated and operation of the medical device is halted
(step 2616). The predetermined threshold can be set based on a
number of parameters, for example based on a level of adjustability
provided by the microprocessor or based on an expected threshold
that would indicate failure of one or more of the capacitors in a
capacitive divider. In some embodiments, the predetermined
threshold is set at about 15% difference from the overall average
capacitive divider ratio.
[0348] If none of the second ratios diverges from the overall
average of ratios by greater than that preset, threshold amount,
rather than halting operation, the microprocessor will calibrate
outputs to the FPGA and/or voltage source to adjust the output
current to be delivered on the electrode connections (step 2618),
thereby providing a consistent output current for each electrode
connection and across all electrode connections. Once the
capacitive ratios are recalibrated, a therapy could be delivered
(step 2612). Operation can terminate upon completion of the therapy
(step 2620), or operation can loop back for recalibration and
delivery of subsequent therapies during operation of the
device.
[0349] Referring to FIGS. 29-31 overall, it is noted that, in
addition to the steps/operations as shown can be performed in
varying order, and also additional steps or operations could be
performed. For example, an assessment operation for each of the
initial ratios could be performed, analogous to step 2614.
Additionally, in some other embodiments, status checks such as the
recalibration procedure illustrated in FIG. 31 could be performed
periodically rather than prior to each therapy delivery, for
example every x minutes/seconds, or every x therapy deliveries.
[0350] In addition, relative to FIGS. 29-31 overall, it is noted
that some of the logical operations of the various embodiments of
the disclosure can be implemented as: (1) a sequence of computer
implemented steps, operations, or procedures running on a
programmable circuit within a computer, and/or (2) a sequence of
computer implemented steps, operations, or procedures running on a
programmable circuit within a directory system, database, or
compiler.
[0351] In addition to the methods of FIGS. 29-31, the normal
shutdown of the output module 161 shorts the electrodes together
and connects them to ground through one of the current sources.
Normally, this is a desirable and safe condition. However, certain
failures could cause current to flow after shutdown, resulting in
damage to the nerve. To eliminate this problem, an additional check
can be made after normal shutdown has been completed. If current
flow is detected, the leads are disconnected from each other
(allowed to float) and the current sources are programmed to zero
current.
7. Auto-Increment Therapy Delivery
[0352] For blocking therapy to be effective, energy delivery may
need to be increased beyond the level that a patient perceives as
acceptable at the initiation of therapy. The power of the therapy
signals can be increased in small increments to enable the patient
to acclimate to the more powerful therapy signals.
[0353] For example, the current of the therapy signal can be
increased in steps of about 1 mA at weekly follow-up visits. Over
time, patients may willingly accept multiple increments of 1
mA/week through periodic follow-up visits and programming sessions.
For example, an initial setting of 3 mA may rise to at least 6 mA
as a result of such follow-up sessions.
[0354] In certain embodiments of the therapy system 100, energy
(i.e., power) delivery can be incrementally increased or decreased
automatically over a pre-determined period of time. Advantageously,
this automatic incremental increase can mitigate the need for
frequent doctor office visits. This flexibility is especially
convenient for patients who are located remote from the implanting
bariatric center.
[0355] In an embodiment, the therapy system 100 automatically
increases the current of the therapy signal by, for example, 0.25
mA every other day, cumulatively achieving the 1 mA/week
incremental increase. In another embodiment, the therapy system 100
increases the current by about 0.125 mA per day. Initial studies
have demonstrated such increment levels as acceptable.
[0356] The patient can retain the ability to turn therapy off at
any time and return to the physician for re-evaluation.
Alternatively, the patient can revert to previously acceptable
therapy delivery levels (e.g., the therapy level of the previous
day). For example, the patient can interact with the external
charger 101 to issue such an instruction.
[0357] The physician can choose whether to activate the
auto-increment therapy capability. The physician also can specify
the date and/or time of therapy initiation and therapy parameters
(e.g., including the starting and ending therapy parameters). The
physician also may specify safety limits or tolerances for the
therapy parameters. Additionally, the physician can specify the
rate at which the therapy parameters are incremented over various
time periods (e.g., about 0.5 mA/day for the first 7 days, then
0.125 mA/day over the following 24 days).
8. Predetermined Programs
[0358] One or more therapy programs can be stored in the memory of
the external computer 107. The therapy programs include
predetermined parameters and therapy delivery schedules. For
example, each therapy program can specify an output voltage, a
frequency, a pulse width, ramp-up rates, ramp-down rates, and an
on-off cycle period. In an embodiment, the ramp-up rates and
ramp-down rates can be individually and separately programmed.
[0359] In use, the physician may select any one of these therapy
programs and transmit the selected therapy program to the implanted
neuroregulator 104 (e.g., via the external charger 101) for storage
in the memory of the neuroregulator 104. The stored therapy program
then can control the parameters of the therapy signal delivered to
the patient via the neuroregulator 104.
[0360] Typically, the parameter settings of the predetermined
programs are set at the factory, prior to shipment. However, each
of these parameters can be adjusted over a certain range, by the
physician, using the computer 100 to produce selectable,
customized, predetermined therapy programs. Using these selectable,
customized therapy programs, the physician can manage the patient's
care in an appropriate manner.
[0361] For example, when patients require more varied therapies,
the neuroregulator 104 can store a therapy program including one or
more combinations of multiple therapy modes sequenced throughout
the day.
[0362] For example, referring to electrode configuration shown in
FIG. 10, a single therapy program can include instructions to apply
a blocking signal between electrode tips 212 (anterior vagal nerve)
and 212a (posterior vagal nerve) from 8 a.m. to noon at 6 mA and 5
kHz; alternating between applying a blocking signal to posterior
tip 212a to ring 218a and applying a blocking signal to anterior
tip 212 to ring 218 from noon to 2 p.m. at 3 mA and 2.5 kHz; and
applying a blocking signal from electrode tip 212 to electrode tip
212a from 2 p.m. from 2 p.m. to midnight at 6 mA and 5 kHz.
9. Operation Logs
[0363] In general, the neuroregulator 104 can have a time base to
facilitate the delivery of therapy according to the treatment
schedule. To determine this time base, the neuroregulator 104 can
maintain one or more operating logs indicating the operations of
the therapy system 100.
[0364] For example, the neuroregulator 104 maintains a
time-and-date-stamped delivery log of the actual delivery of
therapy. For example, the delivery log can include the time and
date of initiation of each therapy episode, the time and date of
completion of the therapy episode, the therapy parameters
associated with the therapy episode. Both scheduled therapy and
automatically-initiated therapy can be logged. The delivery log
also can include a parameter to indicate whether the therapy
episode was scheduled or automatically initiated.
[0365] Additionally, the neuroregulator 104 can maintain a
time-and-date-stamped error log of all conditions that interfered
with the delivery of therapy. For example, the error log can record
all impedances measured, temperatures measured by the on-board
temperature sensor, each instance in which the battery was charged
by the external charger 101, each instance in which the battery
reached its low-charge threshold, and each instance in which the
battery reached its depleted threshold.
[0366] The delivery log and the error log are readable by the
external computer 107 (e.g., a clinician programmer). In an
embodiment, the delivery log and the error log each can accommodate
up to about 3 months of data.
10 Detection of Food Passage Through the Esophagus
[0367] Neural blocking therapy can affect the rate at which the
stomach empties and the level of intestinal motility. When applying
neural blocking therapy for obesity control, it is desirable to
determine the approximate times at which the patient ingests food
(i.e., mealtimes) and the approximate quantity of food being
consumed at each meal. Advantageously, with this information, the
duty cycle of the therapy system 100 can be synchronized with the
mealtimes. Additionally, the nature of the therapy can be adjusted
in accordance with the quantity of food being consumed. For
example, food detection is described in U.S. Pat. No. 5,263,480 to
Wernicke et al, issued Nov. 23, 1993, the disclosure of which is
hereby incorporated herein by reference.
[0368] In certain embodiments of the therapy system 100, the
anterior and posterior vagal nerve electrodes 212, 212a can be
positioned on the esophagus E adjacent to the junction between the
esophagus E and the stomach. An impedance measurement between the
anterior and posterior vagal nerve electrodes 212, 212a provides a
measure of the presence of food in the esophagus E between the
electrodes 212, 212a (e.g., see FIG. 11). The time integration of
this impedance value provides a measure of the quantity of food
consumed.
[0369] The impedance value between the electrodes 212, 212a can be
measured by passing a low amplitude, sinusoidal signal (e.g.,
having a frequency of about 500-1000 Hz) between the electrodes
212, 212a. In an alternative embodiment, the impedance can be
measured by passing the signal between the ring electrodes 218,
218a. In other embodiments, the dual bipolar lead/electrode
configuration can operate as a quadripolar array.
[0370] In a quadripolar electrode array, two pairs of electrodes
are typically secured in generally the same plane and normal to the
length of the esophagus E. In such a configuration, a small signal
applied across one pair of the electrodes (e.g., tip electrode 212,
ring electrode 218) can be detected across the other pair (e.g.,
tip electrode 212a, ring electrode 218a). In general, changes in
relative amplitude of the detected signal are proportional to
changes in resistance of the signal path.
[0371] The impedance of the signal changes when food progresses
down the esophagus E. This impedance change causes the amplitude of
the detected signal to change, thereby providing an indication of
the fact that food has passed, and giving an indication of the
quantity of food. While a bipolar electrode pair may be used for
both signal application and sensing across the esophagus E, it has
the disadvantage of some interference as a result of polarization
potentials.
[0372] More generally, this technology can be used to detect
changes in the nature of the fluid within a vessel or lumen of the
body. Such technology can be utilized in multiple applications. For
example, this impedance measurement technology can be used to
detect the presence of liquid/food in the distal esophagus to
ascertain the presence of esophageal reflux. In another embodiment,
this impedance measurement technology can be used in diagnosing
eating abnormalities, such as bulimia.
[0373] In one embodiment, the time history of the transesophageal
impedance measurement is recorded in the memory of the implanted
module (e.g., in an operating log), for later telemetry to the
external module, for review and analysis by the physician. With
this information, the physician can preferentially choose the
operating parameters of the system to best suit the eating habits
of an individual patient.
[0374] In an alternative embodiment, the output of the
transesophageal impedance measurement becomes a control input into
CPU 154 of circuit 112 in neuroregulator 104 (FIG. 3). The therapy
signal output of the neuroregulator 104 can be timed automatically
to correspond to the timing and quantity of food consumed via a
suitable algorithm.
11. Activity Monitoring System
[0375] The weight reduction resulting from the application of
therapy described in this patent application is expected to produce
an increased feeling of well-being in the patient, and possibly an
increase in the amount of activity in which the patient is
comfortable becoming involved.
[0376] In certain embodiments, the therapy system 100 monitors the
activity of the patient. Generally, the therapy system 100 records
the change in activity over the course of treatment. The therapy is
applied to accomplish a goal (e.g., obesity reduction), and the
activity level as a consequence of achieving the goal (e.g., weight
loss) is then measured.
[0377] In an embodiment, this change in activity then can be mapped
to the effects of the treatment. This mapping of the change in
activity to the results of treatment can be personally advantageous
to patients as well as advantageous to the medical community. For
example, knowledge of the likely change, both in weight and in
activity level, could be useful information for patients who are
contemplating the implant and associated therapy.
[0378] In addition, such mapping would advantageously provide
documented evidence of the positive effect of the weight control
system to reimbursement groups. Additionally, from a
medical/scientific perspective, it is known that weight loss is
generally related to caloric intake, activity level, and metabolic
rate. Increased quantification in the area of activity level would
aid in developing a robust relationship among these factors.
[0379] There are a variety of methods which can be used for
measuring activity level.
[0380] Some of these models have been used as the basis for
determining the preferred rate of implantable pacemakers and
defibrillators. For example, a sensor of movement or acceleration
(e.g., a gyroscope-based sensor), can provide an instantaneous
measurement of activity level. Suitable hardware, software, and/or
algorithm systems can then derive from these measurements the
activity level averaged over a period of time (e.g., a 24 hr
period).
[0381] An accelerometer also can be used to track patient activity.
Other examples of activity sensing options include tracking the
respiratory rate of the patient, by monitoring bio-impedance
measurements (e.g., intrathoracic impedance), measuring a minute
volume of, e.g., a compendium of respiratory rate and tidal volume,
and monitoring blood pH, blood oxygen level, and blood pressure. In
each case, the instantaneous value of the measurement can be
integrated over a suitable time period.
[0382] Referring now to the present disclosure generally, the
various program modules and operational steps can be implemented as
routines, programs, components, data structures, and other types of
structures that may perform particular tasks or that may implement
particular abstract data types. Embodiments of the present
disclosure can be implemented as a computer process (method), a
computing system, or as an article of manufacture, such as a
computer program product or computer readable media. The computer
program product may be a computer storage media readable by a
computer system and encoding a computer program of instructions for
executing a computer process. Accordingly, embodiments of the
present disclosure may be embodied in hardware and/or in software
(including firmware, resident software, micro-code, etc.), within
various computing systems, such as the microprocessor, FPGA, or
other memory or logical devices such as those illustrated in FIG.
25, or other processing units and/or programmable circuits
discussed herein. In other words, embodiments of the present
disclosure may take the form of a computer program product on a
computer-usable or computer-readable storage medium having
computer-usable or computer-readable program code embodied in the
medium for use by or in connection with an instruction execution
system. A computer-usable or computer-readable medium may be any
medium that can contain or store the program for use by or in
connection with the instruction execution system, apparatus, or
device, but generally excludes propagated signals.
[0383] With the foregoing detailed description of the present
invention, it has been shown how the objects of the invention have
been attained in a preferred manner. Modifications and equivalents
of disclosed concepts such as those which might readily occur to
one skilled in the art are intended to be included in the scope of
the claims which are appended hereto. Any publications referred to
herein are hereby incorporated by reference.
* * * * *