U.S. patent application number 11/943093 was filed with the patent office on 2008-12-04 for therapy system.
Invention is credited to MARK RAYMOND STULTZ.
Application Number | 20080300657 11/943093 |
Document ID | / |
Family ID | 40089122 |
Filed Date | 2008-12-04 |
United States Patent
Application |
20080300657 |
Kind Code |
A1 |
STULTZ; MARK RAYMOND |
December 4, 2008 |
THERAPY SYSTEM
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. Initial values for the
parameters of a therapy program can be incremented after a
predetermined period of time by a predetermined amount to obtain a
subsequent value of the parameter and therapy can be applied using
the subsequent value. A sensor may be implanted within the patient
to determine an activity level of the patient. Weight loss of the
patient can be analyzed to determine whether the weight loss
corresponds to the activity level of the patient.
Inventors: |
STULTZ; MARK RAYMOND; (Maple
Grove, MN) |
Correspondence
Address: |
MERCHANT & GOULD PC
P.O. BOX 2903
MINNEAPOLIS
MN
55402-0903
US
|
Family ID: |
40089122 |
Appl. No.: |
11/943093 |
Filed: |
November 20, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60941118 |
May 31, 2007 |
|
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Current U.S.
Class: |
607/60 |
Current CPC
Class: |
A61N 1/36007 20130101;
A61N 1/37229 20130101; A61N 1/3752 20130101; A61N 1/3787 20130101;
A61N 1/0556 20130101; A61N 1/0558 20130101 |
Class at
Publication: |
607/60 |
International
Class: |
A61N 1/08 20060101
A61N001/08 |
Claims
1. A method for providing therapy to a patient, comprising:
selecting initial values for the parameters of a therapy program;
programming an internal component implanted within a body of the
patient to apply therapy to the patient according to the therapy
program; programming the internal component to increment the
initial value of at least one of the parameters after a
predetermined period of time by a predetermined amount to obtain a
subsequent value of the parameter; and programming the internal
component to apply therapy to the patient using the subsequent
value of the parameter after the initial value has been
incremented.
2. The method of claim 1, wherein the parameter is a parameter
selected from the group consisting of: voltage, current, pulse
width, duty cycle, frequency, and rate of change.
3. The method of claim 1, wherein selecting initial values
comprises: programming the initial values for the parameters of the
therapy program into an external component; and transmitting the
therapy program including the initial values for the parameters to
the internal component.
4. The method of claim 1, further comprising: receiving
instructions to override automatic incrementation of the parameter
at an external component; and transmitting the instructions to
override from the external component to the internal component,
wherein the internal component does not increment the initial value
of the parameter if instructions to override are received.
5. A method comprising: implanting at least one electrode within a
body of a patient including implanting the electrode adjacent an
anatomical feature of the patient to enable the electrode to
provide therapy to the anatomical feature; implanting an internal
component within the patient including communicatively coupling the
internal component to the electrode, the internal component being
programmed to generate treatment signals according to a treatment
program and to transmit the treatment signals to the electrode
according to a treatment schedule; implanting an internal antenna
within the patient including communicatively coupling the internal
antenna to the internal component, the internal antenna being
configured to send and receive RF transmissions; implanting a
sensor within the patient including communicatively coupling the
sensor to the internal component, the sensor being configured to
determine an activity level of the patient and to forward an
indication of the activity level to the internal component;
aligning an external antenna with the internal antenna sufficient
to enable RF transmission between the external antenna and the
internal antenna; receiving RF transmissions at the external
antenna from the internal antenna, the RF transmissions including
the indication of the activity level of the patient, the RF
transmissions also including an indication of whether therapy was
provided to the patient in accordance with the therapy program and
the therapy schedule; and analyzing whether weight loss of the
patient corresponds to the activity level of the patient.
6. The method of claim 6, further comprising analyzing whether the
weight loss of the patient corresponds to the therapy provided to
the patient.
Description
CROSS REFERENCE
[0001] This application claims priority to U.S. Provisional
Application Ser. No. 60/941,118, filed May 31, 2007, and entitled
"IMPLANTABLE DEVICE," the disclosure of which is hereby
incorporated by reference herein.
[0002] This application discloses and claims subject matter
disclosed in commonly assigned U.S. application Ser. Nos. ______
and (attorney docket numbers 14283.0034USU1 and 14283.0034USU3,
respectively), filed concurrently herewith and titled "Implantable
Therapy System" and "Implantable Therapy System," respectively.
U.S. application Ser. No. ______ (having attorney docket number
14283.0034USU1) names Adrianus Donders, Mark Raymond Stultz, and
Koen Jacob Weijand as inventors; and U.S. application Ser. No.
______ (having attorney docket number 14283.0034USU3) names Scott
Anthony Lambert and Adrianus Donders as inventors.
I. BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] 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 gastro-intestinal disorders
such as obesity, pancreatitis, irritable bowel syndrome 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.
[0005] 2. Description of the Prior Art
[0006] 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), inflammation, discomfort and other
disorders.
[0007] 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. As disclosed in the foregoing patent
and applications, the electrode can be placed directly on a nerve,
overlying tissue surrounding a nerve or on or in an organ near a
nerve.
[0008] 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.
[0009] In one embodiment of the electrodes a signal amplitude of
0.5 mA to 8 mA at the electrode-nerve interface has been found to
be adequate for blocking. However, depending on electrode design,
other amplitudes may suffice. Other signal parameters, as
non-limiting examples, include an adjustable pulse width (e.g., 50
.mu.sec to 500 .mu.sec), and a frequency range of (by non-limiting
example) 1000 Hz to 10,000 Hz. It must be recognized that the
frequency sets certain limitations on the available pulse width;
for example, the pulse width cannot exceed 50% of the cycle time
for a symmetrical biphasic pulse.
[0010] A typical duty cycle of therapy could consist of 5 minutes
on and 10 minutes off. These are representative only. For example,
a duty cycle could be 2 minutes on and 5 minutes off or be 30
minutes on per day. These examples are given to illustrate the wide
latitude available in selecting particular signal parameters for a
particular patient.
[0011] 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, physician and patient
controls and programming and communication with the system. These
issues and selected prior art systems for addressing these issues
will now be discussed.
II. SUMMARY OF THE INVENTION
[0012] According to a preferred 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.
[0013] According to aspects, the external component is adapted to
be configured into multiple selectable operating modes including an
operating room mode, a programming mode, and a charging mode.
[0014] For example, communicatively coupling the external component
to peripheral devices can automatically configure the external
component into one of the operating modes.
[0015] According to other aspects, the implantable component is
adapted to be configured into multiple selectable operating modes
including a training mode for simulating a therapy, and a therapy
mode for providing therapy.
[0016] According to other aspects, the implantable component may be
configured to increment therapy settings automatically by a
predetermined amount after a predetermined period of time.
III. BRIEF DESCRIPTION OF THE DRAWINGS
[0017] 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;
[0018] 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;
[0019] 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.
[0020] 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;
[0021] 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;
[0022] 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;
[0023] 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;
[0024] 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;
[0025] 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;
[0026] FIG. 8 illustrates the external coil and implanted coil of
FIG. 7 arranged in a misaligned position according to aspects of
the present disclosure;
[0027] FIG. 9 is a perspective view of a distal portion of a
bipolar therapy lead according to aspects of the present
disclosure;
[0028] FIG. 10 is a schematic representation of an electrode
placement for a blocking therapy according to aspects of the
present disclosure;
[0029] FIG. 11 is a schematic representation of a first electrode
configuration according to aspects of the present disclosure;
[0030] FIG. 12 is a schematic representation of a typical waveform
according to aspects of the present disclosure;
[0031] FIG. 13 is a schematic representation of a second electrode
configuration according to aspects of the present disclosure;
[0032] FIG. 14 is a schematic representation of a typical waveform
according to aspects of the present disclosure;
[0033] FIG. 15 is a schematic representation of a third electrode
configuration according to aspects of the present disclosure;
[0034] FIG. 16 is a schematic representation of a typical waveform
according to aspects of the present disclosure;
[0035] FIG. 17 is a schematic representation of a fourth electrode
configuration according to aspects of the present disclosure;
[0036] FIG. 18 is a schematic representation of a typical waveform
according to aspects of the present disclosure;
[0037] FIG. 19 is a graphical illustration of a treatment schedule
according to aspects of the present disclosure;
[0038] FIG. 20 is a schematic representation of a signal pulse
illustrating charge balancing according to aspects of the present
disclosure;
[0039] FIG. 21 is a schematic representation of an alternative
means of charge balancing according to aspects of the present
disclosure;
[0040] FIG. 22 is a schematic illustration of a charge balancing
system shown in a shorting state according to aspects of the
present disclosure;
[0041] FIG. 23 is the view of FIG. 22 in a non-shorting state
according to aspects of the present disclosure; and
[0042] FIG. 24 is a graphical illustration comparing waveforms in
shorting and non-shorting states according to aspects of the
present disclosure.
IV. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0043] With reference now to the various drawing figures in which
identical elements are numbered identically throughout, a
description of the preferred embodiments of the present invention
will now be described. While the invention is applicable to
treating a wide variety of gastro-intestinal disorders, the
invention will be described in preferred embodiments for the
treatment of obesity.
[0044] FIG. 1 schematically illustrates a therapy system 100 for
treating obesity or other gastro-intestinal 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.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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).
[0052] 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.
[0053] 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.
[0054] 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.
[0055] 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.
[0056] 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
[0057] a. Neuroreulator
[0058] 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.
[0059] 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.
[0060] 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.
[0061] 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.
[0062] The housing 109, 109' of the neuroregulator 104, 104' also
may contain a circuit module, such as circuit 112 (see FIG. 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.
[0063] 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.
[0064] 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.
[0065] 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 set screws 123', 123a', seals (e.g., Bal
Seals.RTM.), and/or another fastener.
[0066] 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.
[0067] 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.
[0068] 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.
[0069] 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.
[0070] The transmission of energy and data via RF/inductive
coupling is well known in the art. Further details describing
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.
[0071] 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.
[0072] 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.
[0073] 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).
[0074] 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.
[0075] 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.
[0076] 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.
[0077] 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.
[0078] 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.
[0079] The output module 161 can measures 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.
[0080] b. External Charger
[0081] 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.
[0082] 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.
[0083] 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.
[0084] 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.
[0085] 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.
[0086] 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.
[0087] 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).
[0088] 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.
[0089] 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.
[0090] 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.
[0091] 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.
[0092] 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.
[0093] 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.
[0094] 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 using the processes described in U.S.
Pat. No. 6,895,280 to Meadows issued May 17, the disclosure of
which is hereby incorporated herein by reference. In other
embodiments, however, the implanted neuroregulator 104 controls
when the battery 151 is recharged. Details pertaining to
controlling the battery recharging process can be found in U.S.
Pat. No. 3,942,535 to Schulman, issued Mar. 9, 1976; U.S. Pat. No.
4,082,097 to Mann, issued Apr. 4, 1978; U.S. Pat. No. 5,279,292 to
Baumann, issued Apr. 4, 1978; and U.S. Pat. No. 6,516,227 to
Meadows, issued Feb. 4, 2003, the disclosures of which are hereby
incorporated herein by reference. These details typically parallel
the battery manufacturer's recommendations regarding how to charge
the battery.
[0095] 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.
[0096] 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).
[0097] 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.
[0098] 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.).
[0099] 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.
[0100] 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.
[0101] 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; and a Diagnostic mode.
[0102] 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.
[0103] 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.
[0104] 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.
[0105] 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.
[0106] 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
coil 102' is connected.
[0107] 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.
[0108] 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.
[0109] 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.
[0110] 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.
[0111] 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.
[0112] 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.
[0113] 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.
[0114] c. Alignment of External and Implanted Coils
[0115] 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.
[0116] i. Positioning of External Coil
[0117] 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.
[0118] 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).
[0119] 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.
[0120] 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).
[0121] 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.
[0122] 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.
[0123] 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.
[0124] 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.
[0125] 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.
[0126] 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.
[0127] 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.
[0128] ii. Dynamic Signal Power Adiustment
[0129] 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.
[0130] 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.
[0131] 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.
[0132] 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 external
charger 101 can adjust the power level of the transmitted signal
dynamically to meet the desired target level for the implanted
neuroregulator 104.
[0133] Adjustments to the power amplification level can be made
either manually or automatically. In an embodiment, the external
charger 101 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 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.
[0134] For example, if the neuroregulator 104 indicates it is
recharging its battery 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.
[0135] The external charger 101 also may 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.
[0136] The external charger 101 also may 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.
[0137] 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. Alternatively, the
neuroregulator 104 may detune its receiving RF input circuit 157 to
reduce power and temperature.
[0138] In a preferred embodiment, the temperature of the
neuroregulator 104 should not exceed the surface temperature of the
surrounding skin by greater than about 2.degree. C. (assuming a
normal body temperature of 37.degree. C.). 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.
[0139] 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.
[0140] 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 decreases 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.
[0141] 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).
[0142] 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.
[0143] 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.
[0144] 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.
[0145] 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.
[0146] 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.
[0147] 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.
[0148] 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.
[0149] d. Implanted Leads
[0150] 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.
[0151] 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).
[0152] 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.
[0153] 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.
[0154] 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
[0155] 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).
[0156] 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.
[0157] 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).
[0158] 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.
[0159] 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.
[0160] Referring to FIGS. 11-18, the pacing 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.
[0161] a. Blocking Electrode Configuration (1)
[0162] A first blocking electrode configuration is shown in FIG.
11. 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.
[0163] 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).
[0164] b. Blocking Electrode Configuration (2)
[0165] 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. 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).
[0166] 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.
[0167] 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).
[0168] c. Blocking Electrode Configuration (3)
[0169] 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.
[0170] d. Blocking Electrode Configuration (4)
[0171] 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 PVN, AVN to provide a dual channel system. Such an
electrode arrangement routes current flow through both nerves PVN,
AVN as indicated by arrows 4.
[0172] 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.12P
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
[0173] 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).
[0174] 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.
[0175] 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.
[0176] 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
[0177] 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.
[0178] a. Treatment Schedule
[0179] 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.
[0180] 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.
[0181] 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).
[0182] 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.
[0183] 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.
[0184] b. System Operational Modes
[0185] 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.
[0186] i. Training Mode
[0187] 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.
[0188] 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.
[0189] 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.
[0190] ii. Treatment Mode
[0191] 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.
[0192] iii. Placebo Mode
[0193] This mode may be used for patients randomized to a placebo
treatment in a randomized, double-blind clinical trial. 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.
[0194] 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.
[0195] 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.
[0196] c. Treatment Therapy Settings
[0197] 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.
[0198] i. Blocking Treatment
[0199] 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.
[0200] ii. Low Frequency Mode
[0201] 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.
[0202] 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.
[0203] iii. Temporary Test Therapy Setting Mode
[0204] 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.
[0205] d. System Monitoring
[0206] The 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).
[0207] 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).
[0208] 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.
[0209] 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.
[0210] 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.
[0211] 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.).
[0212] i. Lead Impedance Measurement
[0213] 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.
[0214] These embodiments of the therapy system 100 allow the
physician to measure lead impedance on-demand. The therapy system
100 also can enables 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.
[0215] e. External Computer Interface
[0216] 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.
[0217] 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.
[0218] 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.
[0219] 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.
[0220] 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.
[0221] i. Programming Access Level
[0222] 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.
[0223] 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.
5. Charge Balancing
[0224] 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.
[0225] 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.
[0226] a. Timing Correction
[0227] 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).
[0228] 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.
[0229] 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'.
[0230] 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.
[0231] 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).
[0232] 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.
[0233] 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).
[0234] 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.
[0235] 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.
[0236] 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.
[0237] 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.
[0238] 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.
[0239] 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).
[0240] 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.
[0241] 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.
[0242] 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.
[0243] 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.
[0244] b. Shorting Correction
[0245] 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.
[0246] 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.
[0247] 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.
[0248] 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.
[0249] 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 Ds. 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.
[0250] 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 Ds of the
short is preferable not greater than about 10% of the pulse width
PW. For example, the duration Ds can range from about 10 .mu.s to
about 20 .mu.s.
6. Therapy Calibration and Safety Limits
[0251] 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.
[0252] 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).
[0253] Advantageously, calibrating the therapy system 100
significantly reduces the effect of component tolerance, drift, and
aging on the amount of current delivered. Temperature effects are
not likely to be significant since the neuroregulator 104 is at
body temperature when implanted. 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%.
[0254] 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%).
[0255] 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.
[0256] 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
[0257] 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.
[0258] 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.
[0259] 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.
[0260] 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.
[0261] 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.
[0262] 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
[0263] 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.
[0264] 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.
[0265] 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.
[0266] 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.
[0267] 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
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
[0268] 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.
[0269] 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.
[0270] 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.
[0271] 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
[0272] 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.
[0273] 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.
[0274] 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.
[0275] 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.
[0276] 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.
[0277] 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.
[0278] 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.
[0279] 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
[0280] 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.
[0281] 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.
[0282] In an embodiment, this change in activity then can be mapped
to the affects 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.
[0283] 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.
[0284] There are a variety of methods which can be used for
measuring activity level. 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).
[0285] 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.
[0286] 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.
* * * * *