U.S. patent application number 12/825089 was filed with the patent office on 2011-01-06 for implantable pulse generator for providing functional and/or therapeutic stimulation of muscles and/or nerves and/or central nervous system tissue.
This patent application is currently assigned to Medtronic Urinary Solutions, Inc.. Invention is credited to Joseph J. Mrva, Robert B. Strother, Geoffrey B. Thrope.
Application Number | 20110004269 12/825089 |
Document ID | / |
Family ID | 36941828 |
Filed Date | 2011-01-06 |
United States Patent
Application |
20110004269 |
Kind Code |
A1 |
Strother; Robert B. ; et
al. |
January 6, 2011 |
IMPLANTABLE PULSE GENERATOR FOR PROVIDING FUNCTIONAL AND/OR
THERAPEUTIC STIMULATION OF MUSCLES AND/OR NERVES AND/OR CENTRAL
NERVOUS SYSTEM TISSUE
Abstract
Improved assemblies, systems, and methods provide an implantable
pulse generator for prosthetic or therapeutic stimulation of
muscles, nerves, or central nervous system tissue, or any
combination. The implantable pulse generator is sized and
configured to be implanted subcutaneously in a tissue region. The
implantable pulse generator includes an electrically conductive
laser welded titanium case. Control circuitry is located within the
case, and includes a primary cell or rechargeable power source, a
receive coil for receiving an RF magnetic field to recharge the
rechargeable power source, and a microcontroller for control of the
implantable pulse generator. Improved assemblies, systems, and
methods also provide a stimulation system for prosthetic or
therapeutic stimulation of muscles, nerves, or central nervous
system tissue, or any combination. The stimulation system provides
at least one electrically conductive surface, a lead connected to
the electrically conductive surface, and an implantable pulse
generator electrically connected to the lead.
Inventors: |
Strother; Robert B.;
(Willoughby Hills, OH) ; Mrva; Joseph J.; (Euclid,
OH) ; Thrope; Geoffrey B.; (Shaker Heights,
OH) |
Correspondence
Address: |
SHUMAKER & SIEFFERT , P.A
1625 RADIO DRIVE , SUITE 300
WOODBURY
MN
55125
US
|
Assignee: |
Medtronic Urinary Solutions,
Inc.
|
Family ID: |
36941828 |
Appl. No.: |
12/825089 |
Filed: |
June 28, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11150535 |
Jun 10, 2005 |
7813809 |
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12825089 |
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60578742 |
Jun 10, 2004 |
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60599193 |
Aug 5, 2004 |
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60680598 |
May 13, 2005 |
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Current U.S.
Class: |
607/48 ; 607/60;
607/61 |
Current CPC
Class: |
A61B 5/0031 20130101;
A61N 1/37247 20130101; A61N 1/36003 20130101; Y10S 128/904
20130101; A61N 1/37235 20130101; A61B 5/389 20210101; Y10S 128/903
20130101; A61B 2560/0209 20130101; A61B 5/7232 20130101 |
Class at
Publication: |
607/48 ; 607/60;
607/61 |
International
Class: |
A61N 1/378 20060101
A61N001/378; A61N 1/08 20060101 A61N001/08; A61N 1/36 20060101
A61N001/36 |
Claims
1-13. (canceled)
14. A stimulation system comprising: at least one electrode; and an
implantable pulse generator including a rechargeable battery,
wherein the implantable pulse generator is configured to deliver
electrical stimulation via the at least one electrode, wherein the
implantable pulse generator comprises non-inductive wireless
telemetry circuitry and inductive wireless telemetry circuitry, the
inductive wireless telemetry circuitry comprising a power receiving
coil configured to transcutaneously receive a radio frequency
magnetic field from an external controller to recharge the
rechargeable battery, and wherein the implantable pulse generator
is configured to communicate with the external controller via the
non-inductive wireless telemetry circuitry during recharging of the
rechargeable battery.
15. The system of claim 14, wherein the non-inductive wireless
telemetry circuitry of the implantable pulse generator is
configured to receive and transmit VHF/UHF signals for programming
and interrogation of the implantable pulse generator.
16. The system of claim 15, wherein the VHF/UHF signals are defined
by a frequency in the Medical Implant Communications Service (MICS)
band between about 402 MHz and about 405 MHz.
17. The system of claim 14, wherein the implantable pulse generator
is configured to communicate with the external controller via the
non-inductive wireless telemetry circuitry to instruct the external
controller to increase or decrease the strength of the radio
frequency magnetic field during recharging of the rechargeable
battery.
18. The system of claim 14, wherein the radio frequency magnetic
field comprises a frequency between about 30 KHz and about 300
KHz.
19. The system of claim 14, wherein a thickness of a pulse
generator housing is between about 5 mm and 15 mm, a width of the
pulse generator housing is between about 45 mm and 60 mm, and a
length of the pulse generator housing is between about 45 mm and 60
mm.
20. The system of claim 14, wherein the non-inductive wireless
telemetry circuitry including a transceiver to listen for commands
from the external controller at a predetermined rate and to respond
to the commands in synchronization with when the external
controller is configured to listen for the response
21. The system of claim 14, wherein the pulse generator includes at
least three power management operating modes including an active
mode, an active and charging mode, and a dormant mode.
22. The system of claim 14, further comprising the external
controller.
23. A method comprising: recharging a rechargeable battery of an
implantable pulse generator, wherein the implantable pulse
generator comprises non-inductive wireless telemetry circuitry and
inductive wireless telemetry circuitry, the inductive wireless
telemetry circuitry comprising a power receiving coil, wherein
recharging the rechargeable battery comprises transcutaneously
receiving a radio frequency magnetic field from an external
controller via the power receiving coil of the inductive wireless
telemetry circuitry; and communicating with the external controller
via the non-inductive wireless telemetry circuitry during at least
a portion of the recharging of the rechargeable battery.
24. The method of claim 23, wherein the non-inductive wireless
telemetry circuitry of the implantable pulse generator receives and
transmits VHF/UHF signals for programming and interrogation of the
implantable pulse generator.
25. The method of claim 24, wherein the VHF/UHF signals are defined
by a frequency in the MICS (Medical Implant Communications Service)
band between about 402 MHz and about 405 MHz.
26. The method of claim 23, wherein communicating with the external
controller via the non-inductive wireless telemetry circuitry
during recharging of the rechargeable battery comprises instructing
the external controller to increase or decrease the strength of the
radio frequency magnetic field during recharging of the
rechargeable battery.
27. The method of claim 23, wherein the radio frequency magnetic
field comprises a frequency between about 30 KHz and about 300
KHz.
28. The method of claim 23, wherein a thickness of the pulse
generator housing is between about 5 mm and 15 mm, a width of the
pulse generator housing is between about 45 mm and 60 mm, and a
length of the pulse generator housing is between about 45 mm and 60
mm.
29. The method of claim 23, wherein the non-inductive wireless
telemetry circuitry includes a transceiver configured to listen for
commands from the external controller at a predetermined rate and
to respond to the commands in synchronization with when the
external controller is configured to listen for the response.
30. The method of claim 23, wherein the pulse generator includes at
least three power management operating modes including an active
mode, an active and charging mode, and a dormant mode.
31. The method of claim 23, further comprising transmitting the
radio frequency magnetic field via the external controller.
32. A neuromuscular stimulation system comprising: at least one
electrode; and means for delivering electrical stimulation via the
at least one electrode, the means for delivering electrical
stimulation including: a rechargeable battery, means for
transcutaneously receiving a radio frequency magnetic field from an
external controller to recharge the rechargeable battery, the means
for transcutaneously receiving the radio frequency magnetic field
from the external controller comprising means for transcutaneously
receiving the magnetic field via inductive wireless telemetry, and
means for communicating with the external controller via
non-inductive wireless telemetry during recharging of the
rechargeable battery.
33. The system of claim 32, wherein the means for communicating
with the external controller via non-inductive wireless telemetry
comprises means for receiving and transmitting VHF/UHF signals for
programming and interrogation of the means for delivering
electrical stimulation via the at least one electrode.
34. The system of claim 32, wherein the means for delivering
electrical stimulation via the at least one electrode is configured
to communicate with the external controller via the means for
communicating with the external controller via non-inductive
wireless telemetry to instruct the external controller to increase
or decrease the strength of the radio frequency magnetic field
during recharging of the rechargeable battery.
Description
RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application Ser. No. 60/578,742, filed Jun. 10, 2004, and
entitled "Systems and Methods for Bilateral Stimulation of Left and
Right Branches of the Dorsal Genital Nerves to Treat Dysfunctions,
Such as Urinary Incontinence," and U.S. Provisional Patent
Application Ser. No. 60/599,193, filed Aug. 5, 2004, and entitled
"Implantable Pulse Generator for Providing Functional and/or
Therapeutic Stimulation of Muscles and/or Nerves," and U.S.
Provisional Patent Application Ser. No. 60/680,598, filed May 13,
2005, and entitled "Implantable Pulse Generator for Providing
Functional and/or Therapeutic Stimulation of Muscles and/or Nerves
and/or Central Nervous System Tissue," which are incorporated
herein by reference.
FIELD OF INVENTION
[0002] This invention relates to systems and methods for providing
stimulation of central nervous system tissue, muscles, or nerves,
or combinations thereof.
BACKGROUND OF THE INVENTION
[0003] Neuromuscular stimulation (the electrical excitation of
nerves and/or muscle to directly elicit the contraction of muscles)
and neuromodulation stimulation (the electrical excitation of
nerves, often afferent nerves, to indirectly affect the stability
or performance of a physiological system) and brain stimulation
(the stimulation of cerebral or other central nervous system
tissue) can provide functional and/or therapeutic outcomes. While
existing systems and methods can provide remarkable benefits to
individuals requiring neuromuscular or neuromodulation stimulation,
many limitations and issues still remain. For example, existing
systems often can perform only a single, dedicated stimulation
function.
[0004] A variety of products and treatment methods are available
for neuromuscular stimulation and neuromodulation stimulation. As
an example, neuromodulation stimulation has been used for the
treatment of erectile dysfunction. Erectile dysfunction (ED) is
often referred to as "impotency." When a man has impotency, he
cannot get a firm erection or keep his penis erect during
intercourse. There are some common diseases such as diabetes,
Peyronie's disease, heart disease, and prostate cancer that are
associated with impotency or have treatments that may cause
impotency. And in some cases the cause may be psychological.
[0005] A wide range of options exist for the treatment of erectile
dysfunction. Treatments include everything from medications, simple
mechanical devices, psychological counseling, and surgery for both
external and implantable devices.
[0006] Both external and implantable devices are available for the
purpose of neuromodulation stimulation for the treatment of
erectile dysfunction. The operation of these devices typically
includes the use of an electrode placed either on the external
surface of the skin, an anal electrode, or a surgically implanted
electrode. Although these modalities have shown the ability to
provide a neuromodulation stimulation with positive effects, they
have received limited acceptance by patients because of their
limitations of portability, limitations of treatment regimes, and
limitations of ease of use and user control.
[0007] Implantable devices have provided an improvement in the
portability of neuromodulation stimulation devices, but there
remains the need for continued improvement. Implantable stimulators
described in the art have additional limitations in that they are
challenging to surgically implant because they are relatively
large; they require direct skin contact for programming and for
turning on and off. In addition, current implantable stimulators
are expensive; owing in part to their limited scope of usage.
[0008] These implantable devices are also limited in their ability
to provide sufficient power which limits their use in a wide range
of neuromuscular stimulation, and limits their acceptance by
patients because of the need to surgically replace the device when
batteries fail, or the need to frequently recharge a rechargeable
power supply.
[0009] More recently, small, implantable microstimulators have been
introduced that can be injected into soft tissues through a cannula
or needle. Although these small implantable stimulation devices
have a reduced physical size, their application to a wide range of
neuromuscular stimulation application is limited. Their micro size
extremely limits their ability to maintain adequate stimulation
strength for an extended period without the need for frequent
replacement, or for recharging of an internal rechargeable power
supply (battery). Additionally, their very small size limits the
tissue volumes through which stimulus currents can flow at a charge
density adequate to elicit neural excitation. This, in turn, limits
or excludes many applications.
[0010] It is time that systems and methods for providing
neuromuscular stimulation address not only specific prosthetic or
therapeutic objections, but also address the quality of life of the
individual requiring neuromuscular and neuromodulation
stimulation.
SUMMARY OF THE INVENTION
[0011] The invention provides improved assemblies, systems, and
methods for providing prosthetic or therapeutic stimulation of
central nervous system tissue, muscles, or nerves, or muscles and
nerves.
[0012] One aspect of the invention provides a stimulation assembly
sized and configured to provide prosthetic or therapeutic
stimulation of central nervous system tissue, muscles, or nerves,
or muscles and nerves. The stimulation assembly includes an
implantable pulse generator (IPG) attached to at least one lead and
one electrode. The implantable pulse generator is implanted
subcutaneously in tissue, preferably in a subcutaneous pocket
located remote from the electrode. The electrode is implanted in
electrical conductive contact (i.e., the electrode proximity to the
excitable tissue allows current flow from the electrode to excite
the tissue/nerve) with at least one functional grouping of neural
tissue, muscle, or at least one nerve, or at least one muscle and
nerve. The lead is tunneled subcutaneously in order to electrically
connect the implantable pulse generator to the electrode.
[0013] Another aspect of the invention provides improved
assemblies, systems, and methods for providing a universal device
which can be used for many specific clinical indications requiring
the application of pulse trains to muscle and/or nervous tissue for
therapeutic (treatment) or functional restoration purposes.
[0014] Most of the components of the implantable pulse generator
are desirably sized and configured so that they can accommodate
several different indications, with no or only minor change or
modification.
[0015] Technical features of the implantable pulse generator device
may include one or more of the following: a primary power source
and/or a rechargeable secondary power source for improved service
life, wireless telemetry for programming and interrogation, a
single or limited number of stimulus output stage(s) for pulse
generation that are directed to one or more output channels, a lead
connection header to provide reliable and easy connection and
replacement of the lead/electrode, a programmable microcontroller
for timing and control of the implantable pulse generator device
functions, and power management circuitry for efficient recharging
of the secondary power source, and the distribution of appropriate
voltages and currents to other circuitry, all of which are
incorporated within a small composite case for improved quality of
life and ease of implantation.
[0016] In one embodiment, the power management circuitry (through
the use of logic and algorithms implemented by the microcontroller)
communicates with an external controller outside the body through
the wireless telemetry communications link. The power management
may include operating modes configured to operate the implantable
pulse generator at its most efficient power consumption throughout
the storage and operation of the implantable pulse generator. These
modes selectively disable or shut down circuit functions that are
not needed, The modes may include, but are not limited to IPG
Active, IPG Dormant, and IPG Active and Charging.
[0017] In one embodiment, the power management circuitry may also
he generally responsible for recovery of power from a
radio-frequency (RF) magnetic field applied externally over the
implantable pulse generator, for charging and monitoring the
optional rechargeable battery. The efficient recharging of the
secondary power source (rechargeable battery) is accomplished by
adjusting the strength of the RF magnetic field generated by the
externally mounted implantable pulse generator charger in response
to the magnitude of the voltage recovered by the implantable pulse
generator and the power demands of the implantable pulse
generator's battery.
[0018] In one embodiment, the wireless telemetry may allows the
implantable pulse generator to wirelessly interact with a clinician
programmer, a clinician programmer derivative, a patient
controller, and in an alternative embodiment, an implantable pulse
generator charger, for example. The wireless telemetry allows a
clinician to transmit stimulus parameters, regimes, and other
setting to the implantable pulse generator before or after it has
been implanted. The wireless telemetry also allows the clinician to
retrieve information stored in the implantable pulse generator
about the patient's usage of the implantable pulse generator and
information about any modifications to the settings of the
implantable pulse generator made by the patient. The wireless
telemetry also allows the patient controller operated by the user
to control the implantable pulse generator, both stimulus
parameters and settings in the context of a therapeutic
application, or the real-time stimulus commands it the case of a
neural prosthetic application. In addition, the wireless telemetry
allows the operating program of the implantable pulse generator,
i.e., the embedded executable code which incorporates the
algorithms and logic for the operation of the implantable pulse
generator, to be installed or revised after the implantable pulse
generator has been assembled, tested, sterilized, and perhaps
implanted. This feature could be used to provide flexibility to the
manufacturer in the factory and perhaps to a representative of the
manufacturer in the clinical setting. In one embodiment, the
wireless telemetry allows the implantable pulse generator to
communicate with the recharger (implantable pulse generator
charger) during a battery recharge in order to adjust the
recharging parameters if necessary, which provides for an efficient
and effective recharge.
[0019] In one embodiment, the assemblies, systems and methods may
provide a clinician programmer incorporating technology based on
industry-standard hand-held computing platforms. The clinician
programmer allows the clinician or physician to set parameters in
the implantable pulse generator (IPG) relating to the treatment of
the approved indication. The clinician programmer uses the wireless
telemetry feature of the implantable pulse generator to
bi-directionally communicate to the implantable pulse generator. In
addition, additional features are contemplated based on the ability
of the clinician programmer to interact with industry standard
software and networks to provide a level of care that improves the
quality of life of the patient and would otherwise be unavailable.
Such features, using subsets of the clinician programmer software,
might include the ability of the clinician or physician to remotely
monitor and adjust parameters using the Internet or other known or
future developed networking schemes. A clinician programmer
derivative (or perhaps a feature included in the IPG charger) would
connect to the patient's computer in their home through an industry
standard network such as the Universal Serial Bus (USB), where in
turn an applet downloaded from the clinician's server would contain
the necessary code to establish a reliable transport level
connection between the implantable pulse generator and the
clinician's client software, using the clinician programmer
derivative as a bridge. Such a connection may also be established
through separately installed software. The clinician or physician
could then view relevant diagnostic information, such as the health
of the unit or its current efficacy, and then direct the patient to
take the appropriate action. Such a feature would save the
clinician, the patient and the health care system substantial time
and money by reducing the number of office visits during the life
of the implant.
[0020] Other features of the clinician programmer, based on an
industry standard platform, might include the ability to connect to
the clinician's computer system in his or hers office. Such
features may take advantage of the Conduit connection employed by
Palm OS based devices. Such a connection then would transfer
relevant patient data to the host computer or server for electronic
processing and archiving. With a feature as described here, the
clinician programmer then becomes an integral link in an electronic
chain that provides better patient service by reducing the amount
of paperwork that the physician's office needs to process on each
office visit. It also improves the reliability of the service since
it reduces the chance of mis-entered or mis-placed information,
such as the record of the parameter setting adjusted during the
visit.
[0021] Other features and advantages of the inventions are set
forth in the following specification and attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a view of a stimulation assembly that provides
electrical stimulation to central nervous system tissue, muscles
and/or nerves inside the body using a general purpose implantable
pulse generator.
[0023] FIGS. 2A and 2B are front and side views of the general
purpose implantable pulse generator shown in FIG. 1, which is
powered by a primary battery.
[0024] FIGS. 2C and 2D are front and side views of an alternative
embodiment of a general purpose implantable pulse generator shown
in FIG. 1, which is powered using a rechargeable battery.
[0025] FIG. 3 is a view showing how the geometry of the implantable
pulse generator shown in FIGS. 2A and 2B aids in its implantation
in a tissue pocket.
[0026] FIG. 4A is a view showing an alternative embodiment of the
implantable pulse generator shown in FIGS. 2C and 2D, the
alternative embodiment having a rechargeable battery and shown in
association with a transcutaneous implantable pulse generator
charger (battery recharger) including an integral charging coil
which generates the RF magnetic field, and also showing the
implantable pulse generator charger using wireless telemetry to
communicate with the implantable pulse generator.
[0027] FIG. 4B is an anatomic view showing the transcutaneous
implantable pulse generator charger (battery recharger) as shown in
FIG. 4A, including a separate, cable coupled charging coil which
generates the RF magnetic field, and also showing the implantable
pulse generator charger using wireless telemetry to communicate
with the implantable pulse generator.
[0028] FIG. 4C is a perspective view of the implantable pulse
generator charger of the type shown in FIGS. 4A and 4B, with the
charger shown docked on a recharge base with the charging base
connected to the power mains.
[0029] FIG. 5A is an anatomic view showing the implantable pulse
generator shown in FIGS. 2A and 2B in association with an external
programmer that relies upon wireless telemetry, and showing the
programmer's capability of communicating with the implantable pulse
generator up to an arm's length away from the implantable pulse
generator.
[0030] FIG. 5B is a system view of an implantable pulse generator
system incorporating a clinician programmer derivative and showing
the system's capability of communicating and transferring data over
a network, including a remote network.
[0031] FIG. 5C is a perspective graphical view of one possible type
of patient controller that may be used with the implantable pulse
generator shown in FIGS. 2A and 2B.
[0032] FIG. 6 is a block diagram of a circuit that the implantable
pulse generator shown in FIGS. 2A and 2B can incorporate.
[0033] FIG. 7 is an alternative embodiment of the block diagram
shown in FIG. 6, and shows an alternative block circuit diagram
that an implantable pulse generator having a rechargeable battery
may utilize.
[0034] FIG. 8 is a circuit diagram showing a possible circuit for
the wireless telemetry feature used with the implantable pulse
generator shown in FIGS. 2A and 2B.
[0035] FIG. 9 is a circuit diagram showing a possible circuit for
the stimulus output stage and output multiplexing features used
with the implantable pulse generator shown in FIGS. 2A and 2B.
[0036] FIG. 10 is a graphical view of a desirable biphasic stimulus
pulse output of the implantable pulse generator for use with the
system shown in FIG. 1.
[0037] FIG. 11 is a circuit diagram showing a possible circuit for
the microcontroller used with the implantable pulse generator shown
in FIGS. 2A and 2B.
[0038] FIG. 12 is a circuit diagram showing one possible option for
a power management sub-circuit where the sub-circuit includes
MOSFET isolation between the battery and charger circuit, the power
management sub-circuit being a part of the implantable pulse
generator circuit shown in FIG. 7.
[0039] FIG. 13 is a circuit diagram showing a second possible
option for a power management sub-circuit where the sub-circuit
does not include MOSFET isolation between the battery and charger
circuit, the power management sub-circuit being a part of the
implantable pulse generator circuit shown in FIG. 7.
[0040] FIG. 14 is a circuit diagram showing a possible circuit for
the VHH power supply feature used with the implantable pulse
generator shown in FIGS. 2A and 2B.
[0041] The invention may be embodied in several forms without
departing from its spirit or essential characteristics. The scope
of the invention is defined in the appended claims, rather than in
the specific description preceding them. All embodiments that fall
within the meaning and range of equivalency of the claims are
therefore intended to be embraced by the claims.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0042] The various aspects of the invention will be described in
connection with providing stimulation of central nervous system
tissue, muscles, or nerves, or muscles and nerves for prosthetic or
therapeutic purposes. That is because the features and advantages
that arise due to the invention are well suited to this purpose.
Still, it should be appreciated that the various aspects of the
invention can be applied to achieve other objectives as well.
I. Stimulation Assembly
[0043] A. System Overview
[0044] FIG. 1 shows an assembly 10 for stimulating a central
nervous system tissue, nerve, or a muscle, or a nerve and a muscle
for therapeutic (treatment) or functional restoration purposes. The
assembly includes an implantable lead 12 coupled to an implantable
pulse generator or IPG 18. The lead 12 and the implantable pulse
generator 18 are shown implanted within a tissue region T of a
human or animal body.
[0045] The distal end of the lead 12 includes at least one
electrically conductive surface, which will in shorthand be called
an electrode 16. The electrode 16 is implanted in electrical
conductive contact with at least one functional grouping of neural
tissue, muscle, or at least one nerve, or at least one muscle and
nerve. The implantable pulse generator 18 includes a connection
header 14 that desirably carries a plug-in receptacle for the lead
12. In this way, the lead 12 electrically connects the electrode 16
to the implantable pulse generator 18.
[0046] The implantable pulse generator 18 is sized and configured
to be implanted subcutaneously in tissue, desirably in a
subcutaneous pocket P, which can be remote from the electrode 16,
as FIG. 1 shows. Desirably, the implantable pulse generator 18 is
sized and configured to be implanted using a minimally invasive
surgical procedure.
[0047] The surgical procedure may be completed in a number of
steps. For example, once a local anesthesia is established, the
electrode 16 is positioned at the target site. Next, a subcutaneous
pocket P is made and sized to accept the implantable pulse
generator 18. The pocket P is formed remote from the electrode 16.
Having developed the subcutaneous pocket P for the implantable
pulse generator 18, a subcutaneous tunnel is formed for connecting
the lead 12 and electrode 16 to the implantable pulse generator 18.
The lead 12 is routed through the subcutaneous tunnel to the pocket
site P where the implantable pulse generator 18 is to be implanted.
The lead 12 is then coupled to the implantable pulse generator 18,
and both the lead 12 and implantable pulse generator 18 are placed
into the subcutaneous pocket, which is sutured closed.
[0048] As FIGS. 2A and 2B shows, the implantable pulse generator 18
includes a circuit 20 that generates electrical stimulation
waveforms. An on-board, primary battery 22 desirably provides the
power. In an alternative embodiment, the battery may be a
rechargeable battery. The implantable pulse generator 18 also
desirably includes an on-board, programmable microcontroller 24,
which carries embedded code. The code expresses pre-programmed
rules or algorithms under which the desired electrical stimulation
waveforms are generated by the circuit 20. The implantable pulse
generator 18 desirably includes an electrically conductive case 26,
which can also serve as the return electrode for the stimulus
current introduced by the lead/electrode when operated in a
monopolar configuration.
[0049] According to its programmed rules, when switched on, the
implantable pulse generator 18 generates prescribed stimulation
waveforms through the lead 12 and to the electrode 16. These
stimulation waveforms stimulate the central nervous system tissue,
muscle, nerve, or both nerve and muscle tissue that lay in
electrical conductive contact (i.e., within close proximity to the
electrode surface where the current densities are high) with the
electrode 16, in a manner that achieves the desired therapeutic
(treatment) or functional restoration result. As previously
discussed, erectile restoration is just one example of a functional
restoration result. Additional examples of desirable therapeutic
(treatment) or functional restoration indications will be described
in greater detail in section II.
[0050] The assembly 10 may also include additional operative
components, such as but not limited to, a clinician programmer, a
clinician programmer derivative, a patient controller, and an
implantable pulse generator charger, each of which will be
discussed later.
[0051] B. The Implantable Pulse Generator
[0052] Desirably, the size and configuration of the implantable
pulse generator 18 makes possible its use as a general purpose or
universal device (i.e., creating a platform technology), which can
be used for many specific clinical indications requiring the
application of pulse trains to central nervous system tissue,
muscle and/or nervous tissue for therapeutic (treatment) or
functional restoration purposes. Most of the components of the
implantable pulse generator 18 are desirably sized and configured
so that they can accommodate several different indications, without
major change or modification. Examples of components that desirably
remain unchanged for different indications include the case 26, the
battery 22, the power management circuitry 40, the microcontroller
24, much of the software (firmware) of the embedded code, and the
stimulus power supply. Thus, a new indication may require only
changes to the programming of the microcontroller 24. Most
desirably, the particular code is remotely embedded in the
microcontroller 24 after final assembly, packaging, and
sterilization of the implantable pulse generator 18.
[0053] Certain components of the implantable pulse generator 18 may
be expected to change as the indication changes; for example, due
to differences in leads and electrodes, the connection header 14
and associated receptacle(s) for the lead may be configured
differently for different indications. Other aspects of the circuit
20 may also be modified to accommodate a different indication; for
example, the stimulator output stage(s), sensor(s) and/or sensor
interface circuitry.
[0054] In this way, the implantable pulse generator 18 is well
suited for use for diverse indications. The implantable pulse
generator 18 thereby accommodates coupling to a lead 12 and an
electrode 16 implanted in diverse tissue regions, which are
targeted depending upon the therapeutic (treatment) or functional
restoration results desired. The implantable pulse generator 18
also accommodates coupling to a lead 12 and an electrode 16 having
diverse forms and configurations, again depending upon the
therapeutic or functional effects desired. For this reason, the
implantable pulse generator can be considered to be general purpose
or "universal."
1. Desirable Technical Features
[0055] The implantable pulse generator 18 can incorporate various
technical features to enhance its universality.
a. Small, Composite Case
[0056] According to one desirable technical feature, the
implantable pulse generator 18 can be sited small enough to be
implanted (or replaced) with only local anesthesia. As FIGS. 2A and
2B show, the functional elements of the implantable pulse generator
18 (e.g., circuit 20, the microcontroller 24, the battery 22, and
the connection header 14) are integrated into a small, composite
case 26. As can be seen in FIGS. 2A and 2B, the implantable pulse
generator 18 may comprise a case 26 having a small cross section,
e.g., 5 mm to 10 mm thick.times.(45 mm to 60 mm wide).times.(45 mm
to 60 mm long). The overall weight of the implantable pulse
generator 18 may be approximately twenty to thirty grams. These
dimensions make possible implantation of the case 26 with a small
incision; i.e., suitable for minimally invasive implantation.
Additionally, a larger, but similarly shaped IPG might be required
for applications with more stimulus channels (thus requiring a
large connection header) and or a larger internal battery.
[0057] FIGS. 2C and 2D illustrate an alternative embodiment of an
implantable pulse generator 68 utilizing a rechargeable battery 72.
The rechargeable implantable pulse generator 68 shares many
features of the primary cell implantable pulse generator 18. Like
structural elements are therefore assigned like numerals. As can be
seen, the case 76 defines a small cross section; e.g., (5 mm to 10
mm thick).times.(15 mm to 25 mm wide).times.(40 mm to 50 mm long).
These dimensions make possible implantation of the case 76 with a
small incision; i.e., suitable for minimally invasive
implantation.
[0058] The case 26 of the implantable pulse generator 18 is
desirably shaped with a smaller end 30 and a larger end 32. As FIG.
3 shows, this geometry allows the smaller end 30 of the case 26 to
be placed into the skin pocket P first, with the larger end 32
being pushed in last.
[0059] Desirably, the case 26 for the implantable pulse generator
18 comprises a laser welded titanium material. This construction
offers high reliability with a low manufacturing cost. The clam
shell construction has two stamped or successively drawn titanium
case halves that are laser welded around the circuit assembly and
battery 22 with feed-thrus. Typically, a molded plastic spacing
nest is used to hold the battery 22, the circuit 20, and perhaps a
power recovery (receive) coil together and secure them within the
titanium case.
[0060] The implantable pulse generator 18 shown in FIGS. 2A and 2B
includes a clam-shell case 26 having a thickness that is selected
to provide adequate mechanical strength The implantable pulse
generator 18 may be implanted at a target implant depth of not less
than five millimeters beneath the skin, and not more than fifteen
millimeters beneath the skin, although this implant depth may
change due to the particular application, or the implant depth may
change over time based on physical conditions of the patient.
[0061] In an alternative embodiment utilizing a rechargeable
battery, the thickness of the titanium for the case is selected to
provide adequate mechanical strength while balancing the greater
power absorption and shielding effects to the low to medium
frequency magnetic field 54 used to transcutaneously recharge the
implantable rechargeable battery 72 with thicker case material (the
competing factors are poor transformer action at low
frequencies--due to the very low transfer impedances at low
frequencies--and the high shielding losses at high frequencies).
The selection of the thickness ensures that the titanium case
allows adequate power coupling to recharge the secondary power
source (described below) of the rechargeable pulse generator 68 at
the target implant depth using a low frequency radio frequency (RF)
magnetic field 52 from an implantable pulse generator charger 34
mounted on the skin (see FIGS. 4A and 4B).
b. Primary Power Source
[0062] According to one desirable technical feature, the
implantable pulse generator 18 desirably possesses an internal
battery capacity sufficient to allow a service life of greater than
three years with the stimulus being a high duty cycle, e.g.,
virtually continuous, low frequency, low current stimulus pulses,
or alternatively, the stimulus being higher frequency and amplitude
stimulus pulses that are used only intermittently, e.g., a very low
duty cycle.
[0063] To achieve this feature, the primary battery 22 of the
implantable pulse generator 18 desirably comprises a primary power
source; most desirably a Lithium Ion battery 22. Given the average
quiescent operating current (estimated at 8 .mu.A plus 35 .mu.A for
a wireless telemetry receiver pulsing on twice every second) and a
seventy percent efficiency of the stimulus power supply, a 1.0
Amp-hr primary cell battery can provide a service life of less than
two years, which is too short to be clinically or commercially
viable for this indication. Therefore, the implantable pulse
generator 18 desirably incorporates a primary battery, e.g., a
Lithium Ion battery. Given representative desirable stimulation
parameters (which will be described later), a Lithium Ion battery
with a capacity of at least 30 mA-hr will operate for over three
years. Lithium Ion implant grade batteries are available from a
domestic supplier. A representative battery provides 35 mA-hr in a
package configuration that is of appropriate size and shape to fit
within the implantable pulse generator 18.
[0064] The implantable pulse generator 18 desirably incorporates
circuitry and/or programming to assure that the implantable pulse
generator 18 will suspend stimulation, and perhaps fall-back to
only very low rate telemetry, and eventually suspends all
operations when the primary battery 22 has discharged the majority
of its capacity (i.e., only a safety margin charge remains). Once
in this dormant mode, the implantable pulse generator may provide
limited communications and is in condition for replacement.
[0065] In an alternative embodiment, the rechargeable implantable
pulse generator 68 desirably possesses a rechargeable battery
capacity sufficient to allow operation with recharging not more
frequently than once per week for many or most clinical
applications. The battery 72 of the rechargeable implantable pulse
generator 68 desirably can be recharged in less than approximately
six hours with a recharging mechanism that allows the patient to
sleep in bed or carry on most normal daily activities while
recharging the battery 72 of the rechargeable implantable pulse
generator 68.
[0066] The power for recharging the battery 72 of the rechargeable
implantable pulse generator 68 is provided through the application
of a low frequency (e.g., 30 kHz to 300 KHz) RF magnetic field 52
applied by a skin or clothing mounted recharger 34 placed over the
implantable pulse generator (see FIGS. 4A and 4B). In one possible
application, it is anticipated that the user would wear the
recharger 34, including an internal magnetic coupling coil
(charging coil) 35, over the rechargeable implantable pulse
generator 58 to recharge the rechargeable implantable pulse
generator 68 (see FIG. 4A). Alternatively, the recharger 34 might
use a separate magnetic coupling coil (charging coil) 35 which is
placed and/or secured on the skin or clothing over the rechargeable
implantable pulse generator 68 and connected by cable to the
recharger 34 (circuitry and battery in a housing) that is worn on a
belt or clipped to the clothing (see FIG. 4B).
[0067] The charging coil 35 preferably includes a predetermined
construction, e.g., 200 turns of six strands of #36 enameled
magnetic wire, or the like. Additionally, the charging coil mean
diameter is preferably about 50 millimeters, although the diameter
may vary. The thickness of the charging coil 35 as measured
perpendicular to the mounting plane is to be significantly less
than the diameter, e.g., two to five millimeters, so as to allow
the coil to be embedded or laminated in a sheet to facilitate
placement on or near the skin. Such a construction will allow for
efficient power transfer and will allow the charging coil 35 to
maintain a temperature below 41 degrees Celsius.
[0068] The recharger 34 preferably includes its own internal
batteries which may be recharged from the power mains, for example.
A charging base 39 may be included to provide for convenient
docking and recharging of the system's operative components,
including the recharger and the recharger's internal batteries (see
FIG. 4C). The implantable pulse generator recharger 34 does not
need to be plugged into the power mains while in use to recharge
the rechargeable implantable pulse generator 68.
[0069] Desirably, the rechargeable implantable pulse generator 68
may be recharged while it is operating and will not increase in
temperature by more than two degrees Celsius above the surrounding
tissue during the recharging. It is desirable that the recharging
of the battery 72 requires not more than six hours, and a
recharging would be required between once per month to once per
week depending upon the power requirements of the stimulus regime
used.
c. Wireless Telemetry
[0070] According to one desirable technical feature, the system or
assembly 10 includes an implantable pulse generator 18, which
desirably incorporates wireless telemetry (rather that an
inductively coupled telemetry) for a variety of functions to be
performed within arm's reach of the patient, the functions
including receipt of programming and clinical parameters and
settings from the clinician programmer 36, communicating usage
history to the clinician programmer, providing user control of the
implantable pulse generator 18, and alternatively for controlling
the RF magnetic field 52 generated by the rechargeable implantable
pulse generator charger 34. Each implantable pulse generator may
also have a unique signature that limits communication to only the
dedicated controllers (e.g., the matched Patient Controller,
implantable pulse generator Charger, or a clinician programmer
configured for the implantable pulse generator in question).
[0071] The implantable pulse generator 18 desirably incorporates
wireless telemetry as an element of the implantable pulse generator
circuit 20 shown in FIG. 6. A circuit diagram showing a desired
configuration for the wireless telemetry feature is shown in FIG.
8. It is to be appreciated that modifications to this circuit
diagram configuration which produce the same or similar functions
as described are within the scope of the invention.
[0072] As shown in FIG. 5A, the assembly 10 desirably includes a
clinician programmer 36 that, through a wireless telemetry 38,
transfers commands, data, and programs into the implantable pulse
generator 18 and retrieves data out of the implantable pulse
generator 18. In some configurations, the clinician programmer may
communicate with more than one implantable pulse generator
implanted in the same user.
[0073] The clinician programmer 36 may incorporate a custom
programmed general purpose digital device, e.g., a custom program,
industry standard handheld computing platform or other personal
digital assistant (FDA). The clinician programmer 36 can include an
on-board microcontroller powered by a rechargeable battery. The
rechargeable battery of the clinician programmer 36 may be
recharged in the same or similar manner as described and shown for
the recharger 34, i.e., docked on a charging base 39 (see FIG. 4C);
or the custom electronics of the clinician programmer may receive
power from the connected PDA. The microcontroller carries embedded
code which may include pre-programmed rules or algorithms that
allow a clinician to remotely download program stimulus parameters
and stimulus sequences parameters into the implantable pulse
generator 18. The microcontroller of the clinician programmer 36 is
also desirably able to interrogate the implantable pulse generator
and upload usage data from the implantable pulse generator. FIG. 5A
shows one possible application where the clinician is using the
programmer 36 to interrogate the implantable pulse generator. FIG.
5B shows an alternative application where the clinician programmer,
or a clinician programmer derivative 33 intended for remote
programming applications and having the same or similar
functionality as the clinician programmer, is used to interrogate
the implantable pulse generator. As can be seen, the clinician
programmer derivative 33 is connected to a local computer, allowing
for remote interrogation via a local area network, wide area
network, or Internet connection, for example.
[0074] Using subsets of the clinician programmer software, features
of the clinician programmer 36 or clinician programmer derivative
33 might include the ability of the clinician or physician to
remotely monitor and adjust parameters using the Internet or other
known or future developed networking schemes. A clinician
programmer derivative 33 (perhaps a feature included in the
implantable pulse generator charger) would desirably connect to the
patient's computer in their home through an industry standard
network such as the Universal Serial Bus (USB), where in turn an
applet downloaded from the clinician's server would contain the
necessary code to establish a reliable transport level connection
between the implantable pulse generator 18 and the clinician's
client software, using the clinician programmer derivative 33 as a
bridge. Such a connection may also be established through
separately installed software. The clinician or physician could
then view relevant diagnostic information, such as the health of
the unit or its current settings, and then modify the stimulus
settings in the IPG or direct the patient to take the appropriate
action. Such a feature would save the clinician, the patient and
the health care system substantial time and money by reducing the
number of office visits during the life of the implant.
[0075] Other features of the clinician programmer, based on an
industry standard platform, might include the ability to connect to
the clinician's computer system in his or hers office. Such
features may take advantage of the Conduit connection employed by
Palm OS based devices. Such a connection then would transfer
relevant patient data to the host computer or sewer for electronic
processing and archiving. With a feature as described here, the
clinician programmer then becomes an integral link in an electronic
chain that provides better patient service by reducing the amount
of paperwork that the physician's office needs to process on each
office visit. It also improves the reliability of the service since
it reduces the chance of mis-entered or mis-placed information,
such as the record of the parameter setting adjusted during the
visit,
[0076] With the use of a patient controller 37 (see FIG. 5C), the
wireless link 38 allows a patient to control certain parameters of
the implantable pulse generator within a predefined limited range.
The parameters may include the operating modes/states,
increasing/decreasing or optimizing stimulus patterns, or providing
open or closed loop feedback from an external sensor or control
source. The wireless telemetry 38 also desirably allows the user to
interrogate the implantable pulse generator 18 as to the status of
its internal battery 22. The full ranges within these parameters
may be controlled, adjusted, and limited by a clinician, so the
user may not be allowed the full range of possible adjustments.
[0077] In one embodiment, the patient controller 37 is sized and
configured to couple to a key chain, as seen in FIG. 5C. It is to
be appreciated that the patient controller 37 may take on any
convenient shape, such as a ring on a finger, or a watch on a
wrist, or an attachment to a belt, for example. It may also be
desirable to combine both the functions of the implantable pulse
generator charger and the patient controller into a single external
device.
[0078] The wireless telemetry may incorporate a suitable, low power
wireless telemetry transceiver (radio) chip set that can operate in
the MICS (Medical Implant Communications Service) band (402 MHz to
405 MHz) or other VHF/UHF low power, unlicensed bands. A wireless
telemetry link not only makes the task of communicating with the
implantable pulse generator 18 easier, but it also makes the link
suitable for use in motor control applications where the user
issues a command to the implantable pulse generator to produce
muscle contractions to achieve a functional goal (e.g., to
stimulate ankle flexion to aid in the gait of an individual after a
stroke) without requiring a coil or other component taped or placed
on the skin over the implanted implantable pulse generator.
[0079] Appropriate use of power management techniques is important
to the effective use of wireless telemetry. Desirably, the
implantable pulse generator is exclusively the communications
slave, with all communications initiated by the external controller
(the communications master). The receiver chip of the implantable
pulse generator is OFF more than 99% of the time and is pulsed on
periodically to search for a command from an external controller,
including but not limited to the clinician programmer 36, the
patient controller 37, and alternatively the implantable pulse
generator charger 34. Communications protocols include appropriate
check and message acknowledgment handshaking to assure the
necessary accuracy and completeness of every message. Some
operations (such as reprogramming or changing stimulus parameters)
require rigorous message accuracy testing and acknowledgement.
Other operations, such as a single user command value in a string
of many consecutive values, might require less rigorous checking
and a more loosely coupled acknowledgement.
[0080] The timing with which the implantable pulse generator
enables its transceiver to search for RF telemetry from an external
controller is precisely controlled (using a time base established
by a quartz crystal) at a relatively low rate, e.g., the
implantable pulse generator may look for commands from the external
controller at a rate of less than one (1) Hz. This equates to a
monitoring interval of several seconds. It is to be appreciated
that the monitoring rate may vary faster or slower depending on the
application, (e.g., twice per second; i.e., every 500
milliseconds). This allows the external controller to time when the
implantable pulse generator responds to a command and then to
synchronize its commands with when the implantable pulse generator
will be listening for commands. This, in turn, allows commands
issued within a short time (seconds to minutes) of the last command
to be captured and acted upon without having to `broadcast` an idle
or pause signal for 500 milliseconds before actually issuing the
command in order to know that the implantable pulse generator will
have enabled its receiver and received the command. Similarly, the
communications sequence is configured to have the external
controller issue commands in synchronization with when the
implantable pulse generator will be listening for a command.
Similarly, the command set implemented is selected to minimize the
number of messages necessary and the length of each message
consistent with the appropriate level of error detection and
message integrity-monitoring. It is to be appreciated that the
monitoring rate may vary faster or slower depending on the
application; and may vary over time within a given application.
[0081] A suitable radio chip is used for the half duplex wireless
communications, e.g., the AMIS-52100 (AMI Semiconductor; Pocatello,
Id.). This transceiver chip is designed specifically for the MICS
and its European counter-part the ULP-AMI (Ultra Low Power-Active
Medical Implant) band. This chip set is optimized by micro-power
operation with rapid start-up, and RF `sniffing` circuitry.
[0082] In an alternative embodiment having a rechargeable battery,
the recharger 34 shown in FIGS. 4A and 4B may also use wireless
telemetry to communicate with the rechargeable implantable pulse
generator 68, so as to adjust the magnitude of the magnetic field
52 to allow optimal recharging of the rechargeable implantable
pulse generator battery 72 while minimizing unnecessary power
consumption by the recharger and power dissipation in the
rechargeable implantable pulse generator 68 (through circuit losses
and/or through absorption by the rechargeable implantable pulse
generator case 76 and construction).
d. Stimulus Output Stage
[0083] According to one desirable technical feature, the
implantable pulse generator 18 desirably uses a single stimulus
output stage (generator) that is directed to one or more output
channels (electrode surfaces) by analog switch(es) or analog
multiplexer(s). Desirably, the implantable pulse generator 18 will
deliver at least one channel of stimulation via a lead/electrode.
For applications requiring more stimulus channels, several channels
(perhaps up to four) can be generated by a single output stage. In
turn, two or more output stages could be used, each with separate
multiplexing to multiple channels, to allow an implantable pulse
generator with eight or more stimulus channels. The stimulation
desirably has a biphasic waveform (net DC current less than 10
.mu.A), amplitude of at least 8 mA, for neuromodulation
applications, or 16 mA to 20 mA for muscle stimulation
applications, and pulse durations up to 500 microseconds. The
stimulus current (amplitude) and pulse duration being programmable
on a channel to channel basis and adjustable over time based on a
clinically programmed sequence or regime or based on user (patient)
commands received via the wireless communications link.
[0084] A circuit diagram showing a desired configuration for the
stimulus output stage feature is shown in FIG. 9. It is to be
appreciated that modifications to this circuit diagram
configuration which produce the same or similar functions as
described are within the scope of the invention.
[0085] For neuromodulation/central nervous system applications, the
implantable pulse generator 18 may have the capability of applying
stimulation twenty-four hours per day. A typical stimulus regime
for such applications might have a constant stimulus phase, a no
stimulus phase, and ramping of stimulus levels between these
phases.
[0086] Desirably, the implantable pulse generator 18 includes a
single stimulus generator (with its associated DC current blocking
output capacitor) which is multiplexed to a number of output
channels; or a small number of such stimulus generators each being
multiplexed to a number of output channels. This circuit
architecture allows multiple output channels with very little
additional circuitry. A typical, biphasic stimulus pulse is shown
in FIG. 10. Note that the stimulus output stage circuitry 46 may
incorporate a mechanism to limit the recovery phase current to a
small value (perhaps 0.5 mA). Also note that the stimulus generator
(and the associated timing of control signals generated by the
microcontroller) may provide a delay (typically of the order of 100
microseconds) between the cathodic phase and the recovery phase to
limit the recovery phase diminution of the cathodic phase effective
at eliciting a neural excitation. The charge recovery phase for any
electrode (cathode) must be long enough to assure that all of the
charge delivered in the cathodic phase has been returned in the
recovery phase; i.e., greater than or equal to five time constants
are allowed for the recovery phase. This will allow the stimulus
stage to be used for the next electrode while assuring there is no
net DC current transfer to any electrode. Thus, the single stimulus
generator having this characteristic would be limited to four
channels (electrodes), each with a maximum frequency of 30 Hz to 50
Hz. This operating frequency exceeds the needs of many indications
for which the implantable pulse generator is well suited. For
applications requiring more channels (or higher composite operating
frequencies), two Or more separate output stages might each be
multiplexed to multiple (e.g., four) electrodes.
e. The Lead Connection Header
[0087] According to one desirable technical feature, the
implantable pulse generator 18 desirably includes a lead connection
header 14 for connecting the lead(s) 12 that will enable reliable
and easy replacement of the lead/electrode (see FIGS. 2A and 2B),
and includes a small antenna 54 for use with the wireless telemetry
feature.
[0088] The implantable pulse generator desirably incorporates a
connection header (top header) 14 that is easy to use, reliable,
and robust enough to allow multiple replacements of the implantable
pulse generator after many years (e.g., more than ten years) of
use. The surgical complexity of replacing an implantable pulse
generator is usually low compared to the surgical complexity of
correctly placing the implantable lead 12/electrode 16 in proximity
to the target nerve/tissue and routing the lead 12 to the
implantable pulse generator. Accordingly, the lead 12 and electrode
16 desirably has a service life of at least ten years with a
probable service life of fifteen years or more, eased on the
clinical application, the implantable pulse generator may not have
this long a service life. The implantable pulse generator service
life is largely determined by the power capacity of the Lithium Ion
battery 22, and is likely to be three to ten years, based on the
usage of the device. Desirably, the implantable pulse generator 18
has a service life of at least three years.
[0089] As described above, the implantable pulse generator
preferably will use a laser welded titanium case. As with other
active implantable medical devices using this construction, the
implantable lead(s) 12 connect to the implantable pulse generator
through a molded or cast polymeric connection header 14 (top
header). Metal-ceramic or metal-glass feed-thrus maintain the
hermetic seal of the titanium capsule while providing electrical
contact to the electrical contacts of the lead 12/electrode 16.
[0090] The standard implantable connectors may be similar in design
and construction to the low-profile IS-1 connector system (per ISO
5841-3). The IS-1 connectors have been in use since the late 1980s
and have been shown to be reliable and provide easy release and
re-connection over several implantable pulse generator replacements
during the service life of a single pacing lead. Full compatibility
with the IS-1 standard, and mating with pacemaker leads, is not a
requirement for the implantable pulse generator.
[0091] The implantable pulse generator connection system may
include a modification of the IS-1 connector system, which shrinks
the axial length dimensions while keeping the format and radial
dimensions of the IS-1. For application with more than two
electrode conductors, the top header 14 may incorporate one or more
connection receptacles each of which accommodate leads with
typically four conductors. When two or more leads are accommodated
by the header, these lead may exit the connection header in
opposite directions (i.e., from opposite sides of the header).
[0092] These connectors can be similar to the banded axial
connectors used by other multi-polar implantable pulse generators
or may follow the guidance of the draft IS-4 implantable connector
standard. The design of the implantable pulse generator housing and
header 14 preferably includes provisions for adding the additional
feed-thrus and larger headers for such indications.
[0093] The inclusion of the UHF antenna 54 for the wireless
telemetry inside the connection header (top header) 14 is necessary
as the shielding Offered by the titanium case will severely limit
(effectively eliminate) radio wave propagation through the case.
The antenna 54 connection will be made through a feed-thru similar
to that used for the electrode connections. Alternatively, the
wireless telemetry signal may be coupled inside the implantable
pulse generator onto a stimulus output channel and coupled to the
antenna 54 with passive filtering/coupling elements/methods in the
connection header 14.
f. The Microcontroller
[0094] According to one desirable technical feature, the
implantable pulse generator 18 desirably uses a standard,
commercially available micro-power, flash programmable
microcontroller 24 or processor core in an application specific
integrated circuit (ASIC). This device (or possibly more than one
such device for a computationally complex application with sensor
input processing) and other large semiconductor components may have
custom packaging such as chip-on-board, solder flip chip, or
adhesive flip chip to reduce circuit board real estate needs.
[0095] A circuit diagram showing a desired configuration for the
microcontroller 24 is shown in FIG. 11. It is to be appreciated
that modifications to this circuit diagram configuration which
produce the same or similar functions as described are within the
scope of the invention.
g. Power Management Circuitry
[0096] According to one desirable technical feature, the
implantable pulse generator 18 desirably includes efficient power
management circuitry as an element of the implantable pulse
generator circuitry 20 shown in FIG. 6. The power management
circuitry is generally responsible for the efficient distribution
of power and monitoring the battery 22, and alternatively for the
recovery of power from the RF magnetic field 52 and for charging
and monitoring the rechargeable battery 72. In addition, the
operation of the implantable pulse generator 18 can be described in
terms of having operating modes as relating to the function of the
power management circuitry. These modes may include, but are not
limited to IPG Active, IPG Dormant, and alternatively, IPG Active
and Charging. These modes will be described below in terms of the
principles of operation of the power management circuitry using
possible circuit diagrams shown in FIGS. 12 and 13. FIG. 12 shows
one possible power management sub-circuit having MOSFET isolation
between the battery 22 and the charger circuit. FIG. 13 shows
another possible power management sub-circuit diagram without
having MOSFET isolation between the battery 22 and the charger
circuit. In the circuit without the isolation MOSFET (see FIG. 13),
the leakage current of the disabled charge control integrated
circuit chip (U1) must be very low to prevent this leakage current
from discharging the battery 22 in all modes (including the Dormant
Mode). Except as noted, the description of these modes applies to
both circuits.
i. IPG Active Mode
[0097] The IPG Active mode occurs when the implantable pulse
generator 18 is operating normally. In this mode, the implantable
pulse generator may be generating stimulus outputs or it may be
waiting for the next request to generate stimulus in response to a
timed neuromodulation sequence or a telemetry command from an
external controller. In this mode, the implantable pulse generator
is active (microcontroller 24 is powered and coordinating wireless
communications and may be timing & controlling the generation
and delivery of stimulus pulses).
i (a) Principles of Operation, IPG Active Mode
[0098] In the IPG Active mode, as can be seen in FIG. 12, the lack
of DC current from VRAW means that Q5 is held off. This, in turn,
holds Q3 off and a portion of the power management circuitry is
isolated from the battery 22. In FIG. 13, the lack of DC current
from VRAW means that U1 is disabled. This, in turn, keeps the
current drain from the battery 22 to an acceptably low level,
typically less than 1 .mu.A.
ii. IPO Dormant Mode
[0099] The IPG Dormant mode occurs when the implantable pulse
generator 18 is completely disabled (powered down). In this mode,
power is not being supplied to the microcontroller 24 or other
enabled circuitry. This is the mode for the long-term storage of
the implantable pulse generator before or after implantation. The
dormant mode may only be exited by placing a pacemaker magnet (or
comparable device) over the implantable pulse generator for a
predetermined amount of time, e.g., five seconds.
[0100] In an alternative embodiment, the dormant mode may be exited
by placing the rechargeable implantable pulse generator 68 into the
Active and Charging mode by placing the implantable pulse generator
charging coil 35 of a functional implantable pulse generator
charger 34 in close proximity to the rechargeable implantable pulse
generator 68.
ii (a) Principles of Operation, IPG Dormant Mode
[0101] In the IPG Dormant mode, VBAT is not delivered to the
remainder of the implantable pulse generator circuitry because Q4
is turned off. The Dormant mode is stable because the lack of VBAT
means that VCC is also not present, and thus Q6 is not held on
through R8 and R10. Thus the battery 22 is completely isolated from
all load circuitry (the VCC power supply and the VHH power
supply).
[0102] The Dormant mode is entered through the application of a
long magnet placement over S1 (magnetic reed switch) or through the
reception of a command by the wireless telemetry. In the case of
the telemetry command, the PortD4, which is normally configured as
a microcontroller input, is configured as a logic output with a
logic low (0) value. This, in turn, discharges C8 through R12 and
turns off Q6; which, in turn, turns off Q4 and forces the
implantable pulse generator into the Dormant mode. Note that R12 is
much smaller in value than R10, thus the microcontroller 24 can
force C8 to discharge even though VCC is still present.
[0103] In FIG. 12, the lack of DC current from VRAW means that Q5
is held off. This, in turn, holds Q3 off and a portion of the power
management circuitry is isolated from the battery 22. Also, Q4 was
turned off. In FIG. 13, the lack of DC current from VRAW means that
U1 is disabled. This, in turn, keeps the current drain from the
battery 22 to an acceptably low level, typically less than 1
.mu.A.
iii. IPG Active and Charging Mode
[0104] In an alternative embodiment having a rechargeable battery,
the IPG Active and Charging mode occurs when the rechargeable
implantable pulse generator 68 is being charged. In this mode, the
rechargeable implantable pulse generator 68 is active, i.e., the
microcontroller 24 is powered and coordinating wireless
communications and may be timing and controlling the generation and
delivery of stimulus pulses. The rechargeable implantable pulse
generator 68 may be communicating with the implantable pulse
generator charger 34 concerning the magnitude of the battery
voltage and the DC voltage recovered from the RF magnetic field 52.
The charger 34 uses this data for two purposes: to provide feedback
to the user about the proximity of the charging coil 35 to the
implanted pulse generator, and to increase or decrease the strength
of the RF magnetic field 52. This, in turn, minimizes the power
losses and undesirable heating of the implantable pulse
generator.
[0105] While in the IPG Active and Charging mode, the power
management circuitry 40 serves the following primary functions:
[0106] (1) provides battery power to the rest of the rechargeable
implantable pulse generator circuitry 70,
[0107] (2) recovers power from the RF magnetic field 52 generated
by the implantable pulse generator charger 34,
[0108] (3) provides controlled charging current (from the recovered
power) to the rechargeable battery 72, and
[0109] (4) communicates with the implantable pulse generator
charger 34 via the wireless telemetry link 38 to provide feedback
to the user positioning the charging coil 35 over the rechargeable
implantable pulse generator 68, and to cause the implantable pulse
generator charger 34 to increase or decrease the strength of its RF
magnetic field 52 for optimal charging of the rechargeable
implantable pulse generator battery 72 (Lithium Ion battery).
iii (a) Principles of Operation, IPG Active and Charging Mode
[0110] iii (a) (1) RF voltage is induced in the Receive Coil by the
RF magnetic field 52 of the implantable pulse generator charger
34
[0111] iii (a) (2) Capacitor C1 is in series with the Receive Coil
and is selected to introduce a capacitive reactance that
compensates (subtracts) the inductive reactance of the Receive
Coil
[0112] iii (a) (3) D1-D2 form a full wave rectifier that converts
the AC voltage recovered by the Receive Coil into a pulsating DC
current flow iii(a)(4) This pulsating DC current is smoothed
(filtered) by C3 (this filtered DC voltage is labeled VRAW)
iii(a)(5) D4 is a zener diode that acts as a voltage limiting
device (in normal operation, D4 is not conducting significant
current)
[0113] iii (a) (6) D3 prevents the flow of current from the
rechargeable battery 72 from preventing the correct operation of
the Charge Management Circuitry once the voltage recovered from the
RF magnetic field is removed. Specifically, current flow from the
battery [through Q3 (turned ON), in the case for the circuit of
FIG. 11 ] through the body diode of Q2 would hold ON the charge
controller IC (U1). This additional current drain would be present
in all modes, including dormant, and would seriously limit battery
operating life. Additionally, this battery current pathway would
keep Q6 turned ON even if the magnetic reed switch (S1) were
closed; thus preventing the isolation of the IPG circuitry from the
battery in the dormant mode.
[0114] iii (a) (7) U1, Q2, R2, C4, C6, and C2 form the battery
charger sub-circuit [0115] U1 is a micropower, Lithium Ion
Charge
[0116] Management Controller chip implementing a constant current
phase and constant voltage phase charge regime. This chip desirably
incorporates an internal voltage reference of high accuracy
(+/-0.5%) to establish the constant voltage charge level. U1
performs the following functions: [0117] monitors the voltage drop
across a series resistor R2 (effectively the current charging the
rechargeable battery 72) to control the current delivered to the
battery through the external pass transistor Q2. U1 uses this
voltage across R2 to establish the current of the constant current
phase (typically the battery capacity divided by five hours) and
[0118] decreases the current charging the battery as required to
limit the battery voltage and effectively transition from constant
current phase to constant voltage phase as the battery voltage
approaches the terminal voltage,
[0119] iii (a) (8) U1 also includes provisions for timing the
duration of the constant current and constant voltage phases and
suspends the application of current to the rechargeable battery 72
if too much time is spent in the phase. These fault timing features
of U1 are not used in normal operation.
[0120] iii (a) (9) In this circuit, the constant voltage phase of
the battery charging sequence is timed by the microcontroller 24
and not by U1. The microcontroller monitors the battery voltage and
terminates the charging sequence (i.e., tells the implantable pulse
generator charger 34 that the rechargeable implantable pulse
generator battery 72 is fully charged) after the battery voltage
has been in the constant voltage region for greater than a fixed
time period (e.g., 15 to 20 minutes).
[0121] iii (a) (10) In FIG. 12, Q3 and Q5 are turned ON only when
the charging power is present. This effectively isolates the
charging circuit from the rechargeable battery 72 when the
externally supplied RF magnetic field 52 is not present and
providing power to charge the rechargeable battery.
[0122] iii (a) (11) In FIG. 13, U1 is always connected to the
rechargeable battery 72, and the disabled current of this chip is a
load on the rechargeable battery 72 in all modes (including the
dormant mode). This, in turn, is a more demanding requirement on
the current consumed by U1 while disabled.
[0123] iii (a) (12) F1 is a fuse that protects against
long-duration, high current component failures. In all anticipated
transient high current failures, (i.e., soft failures that cause
the circuitry to consume high current levels and thus dissipate
high power levels; but the failure initiating the high current flow
is not permanent and the circuit will resume normal function if the
circuit is removed from the power source before damage from
overheating occurs), the MAT circuitry will disconnect the
rechargeable battery 72 from the temporary high load without
blowing the fuse. The specific sequence is [0124] High current
flows into a component(s) powered by VBAT (most likely the VHH
power supply or an element powered by the VCC power supply). [0125]
The voltage drop across the fuse will (prior to the fuse blowing)
turn ON Q1 (based on the current flow through the fuse causing a
0.5V to 0.6V drop across the resistance of F1). [0126] The
collector current from Q1 will turn off Q4. [0127] VBAT drops very
quickly and, as a direct result, VCC falls. In turn, the voltage on
the PortD4 IO pin from the microcontroller voltage falls as VCC
falls, through the parasitic diodes in the microcontroller 24. This
then pulls down the voltage across C6 as it is discharged through
R12. [0128] The rechargeable implantable pulse generator 68 is now
stable in the Dormant Mode, i.e., VBAT is disconnected from the
rechargeable battery 72 by a turned OFF Q4. The only load remaining
on the battery is presented by the charging circuit and by the
analog multiplexer (switches) U3 that are used to direct an analog
voltage to the microcontroller 24 for monitoring the battery
voltage and (by subtracting the voltage after the resistance of F1)
an estimate of the current consumption of the entire circuit. A
failure of these voltage monitoring circuits is not protected by
the fuse, but resistance values limit the current flow to safe
levels even in the event of component failures. A possible source
of a transient high-current circuit failure is the SCR latchup or
supply-to-ground short failure of a semiconductor device directly
connected to VBAT or VCC.
[0129] iii (a) (13) R9 & R11 form a voltage divider to convert
VRAW (0V to 8V) into the voltage range of the microcontrollers A-D
inputs (used for closed loop control of the RF magnetic field
strength),
[0130] iii (a) (14) R8 and C9 form the usual R-C reset input
circuit for the microcontroller 24; this circuit causes a hardware
reset when the magnetic reed switch (S1) is closed by the
application of a suitable static magnetic field for a short
duration,
[0131] iii (a) (15) R10 and C8 form a much slower time constant
that allows the closure of the reed switch by the application of
the static magnetic field for a long duration to force the
rechargeable implantable pulse generator 68 into the Dormant mode
by turning OFF Q6 and thus turning OFF Q4. The use of the magnetic
reed switch for resetting the microcontroller 24 or forcing a total
implantable pulse generator shutdown (Dormant mode) may be a
desirable safety feature.
2. Representative Implantable Pulse Generator Circuitry
[0132] FIG. 6 shows an embodiment of a block diagram circuit 20 for
the primary cell implantable pulse generator 18 that takes into
account the desirable technical features discussed above. FIG. 7
shows an embodiment of a block diagram circuit 70 for the
rechargeable implantable pulse generator 68 that also takes into
account the desirable technical features discussed above.
[0133] Both the circuit 20 and the circuit 70 can be grouped into
functional blocks, which generally correspond to the association
and interconnection of the electronic components. FIGS. 6 and 7
show alternative embodiments of a block diagram that provides an
overview of a representative desirable implantable pulse generator
design. As can be seen, there may be re-use of the circuit 20, or
alternatively, portions of the circuit 20 of the primary cell
implantable pulse generator 18, with minimal modifications, e.g., a
predetermined selection of components may be included or may be
exchanged for other components, and minimal changes to the
operating firmware. Re-use of a majority of the circuitry from the
primary cell implantable pulse generator 18 and much of the
firmware from the primary cell implantable pulse generator 18
allows for a low development cost for the rechargeable implantable
pulse generator 68 having a secondary cell 72.
[0134] In FIGS. 6 and 7, seven functional blocks are shown: (1) The
Microprocessor or Microcontroller 24; (2) the Power Management
Circuit 40; (3) the VCC Power Supply 42; (4) the VHH Power Supply
44; (5) the Stimulus Output Stage(s) 46; (6) the Output
Multiplexer(s) 48; and (7) the Wireless Telemetry Circuit 50.
[0135] For each of these blocks, the associated functions, possible
key components, and circuit description are now described.
a. The Microcontroller
[0136] The Microcontroller 24 is responsible for the following
functions:
[0137] (1) The timing and sequencing of the stimulator stage and
the VHH power supply used by the stimulator stage,
[0138] (2) The sequencing and timing of power management
functions,
[0139] (3) The monitoring of the battery voltage, the stimulator
voltages produced during the generation of stimulus pulses, and the
total circuit Current consumption, VHH, and VCC.
[0140] (4) The timing, control, and interpretation of commands to
and from the wireless telemetry circuit,
[0141] (5) The logging (recording) of patient usage data as well as
clinician programmed stimulus parameters and configuration data,
and
[0142] (6) The processing of commands (data) received from the user
(patient) via the wireless link to modify the characteristics of
the stimulus being delivered.
[0143] The use of a microcontroller incorporating flash
programmable memory allows the operating program of the implantable
pulse generator as well as the stimulus parameters and settings to
be stored in non-volatile memory (data remains safely stored even
if the battery 22 becomes fully discharged; or if the implantable
pulse generator is placed in the Dormant Mode). Yet, the data
(operating program, stimulus parameters, usage history log, etc.)
can be erased and reprogrammed thousands of times during the life
of the implantable pulse generator. The software (firmware) of the
implantable pulse generator must be segmented to support the
operation of the wireless telemetry routines while the flash memory
of the microcontroller 24 is being erased and reprogrammed.
Similarly, the VCC power supply 42 must support the power
requirements of the microcontroller 24 during the flash memory
erase and program operations.
[0144] Although the microcontroller 24 may be a single component,
the firmware is developed as a number of separate modules that deal
with specific needs and hardware peripherals. The functions and
routines of these software modules are executed sequentially; but
the execution of these modules are timed and coordinated so as to
effectively function simultaneously. The microcontroller operations
that are associated directly with a given hardware functional block
are described with that block.
[0145] The Components of the Microcontroller Circuit may
include:
[0146] (1) A single chip microcontroller 24. This component may be
a member of the Texas Instruments MSP430 family of flash
programmable. micro-power, highly integrated mixed signal
microcontroller. Likely family members to be used include the
MSP430F1610, MSP430F1611, MSP430F1612, MSP430F168, and the
MSP430F169. Each of these parts has numerous internal peripherals,
and a micropower internal organization that allows unused
peripherals to be configured by minimal power dissipation, and an
instruction set that supports bursts of operation separated by
intervals of sleep where the microcontroller suspends most
functions.
[0147] (2) A miniature, quartz crystal (X1) for establishing
precise timing of the microcontroller. This may be a 32.768 KHz
quartz crystal.
[0148] (3) Miscellaneous power decoupling and analog signal
filtering capacitors.
b. Power Management Circuit
[0149] The Power Management Circuit 40 (including associated
microcontroller actions) is responsible for the following
functions:
[0150] (1) monitor the battery voltage.
[0151] (2) suspend stimulation when the battery voltage becomes
very low, and/or suspend all operation (go into the Dormant Mode)
when the battery voltage becomes critically low,
[0152] (3) communicate (through the wireless telemetry link 38)
with the external equipment the charge status of the battery
22,
[0153] (4) prevent (with single fault tolerance) the delivery of
excessive current from the battery 22,
[0154] (5) provide battery power to the rest of the circuitry of
the implantable pulse generator, i.e., VCC and VHH power
supplies,
[0155] (6) provide isolation of the Lithium Ion battery 22 from
other circuitry while in the Dormant Mode,
[0156] (7) provide a hard microprocessor reset and force entry into
the Dormant Mode in the presence of a pacemaker magnet (or
comparable device), and
[0157] (8) provide the microcontroller 24 with analog voltages with
which to measure the magnitude of the battery voltage and the
appropriate battery current flow (drain and charge).
[0158] Alternative responsibilities for the Power
[0159] Management Circuitry may include;
[0160] (1) recover power from the Receive Coil,
[0161] (2) control delivery of the Receive Coil power to recharge
the Lithium Ion secondary battery 72,
[0162] (3) monitor the battery voltage during charge and discharge
conditions,
[0163] (4) communicate (through the wireless telemetry link 38)
with the externally mounted implantable pulse generator charger 34
to increase or decrease the strength of the RF magnetic field 52
for optimal charging of the rechargeable battery 72,
[0164] (5) disable (with single fault tolerance) the delivery of
charging current to the rechargeable battery 72 in overcharge
conditions, and
[0165] (6) provide the microcontroller 24 with analog voltages with
which to measure the magnitude of the recovered power from the RP
magnetic field 52.
[0166] The Components of the Power Management Circuit may
include:
[0167] (1) Low on resistance, low threshold P channel MOSFETs with
very low off state leakage current (Q2, Q3, and Q4).
[0168] (2) Analog switches (or an analog multiplexer) U3.
[0169] (3) Logic translation N-channel MOSFETs (Q5 & Q6) with
very low off state leakage current.
[0170] Alternative components of the Power Management Circuit may
include:
[0171] (1) The Receive coil, which desirably is a multi-turn, fine
copper wire coil near the inside perimeter of the rechargeable
implantable pulse generator 68. Preferably, the receive coil
includes a predetermined construction, e.g., 300 turns of four
strands of #40 enameled magnetic wire, or the like. The maximizing
of the coil's diameter and reduction of its effective RF resistance
allows necessary power transfer at and beyond the typical implant
depth of about one centimeter.
[0172] (2) A micropower Lithium Ion battery charge management
controller IC (integrated circuit); such as the MicroChip
MCP73843-41, or the like.
c. The VCC Power Supply
[0173] The VCC Power Supply 42 is generally responsible for the
following functions:
[0174] (1) Some of the time, the VCC power supply passes the
battery voltage to the circuitry powered by VCC, such as the
microcontroller 24, stimulator output stage 46, wireless telemetry
circuitry 50, etc.
[0175] (2) At other times, the VCC power supply fractionally steps
up the voltage to about 3.3V; (other useable voltages include 3.0V,
2.7V, etc.) despite changes in the Lithium Ion battery 22 voltage.
This higher voltage is required for some operations such as
programming or erasing the flash memory in the microcontroller 24,
(i.e., in circuit programming).
[0176] The voltage converter/switch part at the center of the VCC
power supply may be a charge pump DC to DC converter. Typical
choices for this part may include the Maxim MAX1759, the Texas
Instruments TPS60204, or the Texas Instruments REG710, among
others. In an alternative embodiment having a rechargeable battery
72, the VCC power supply may include a micropower, low drop out,
linear voltage regulator; e.g., Microchip NCP1700T-3302, Maxim
Semiconductor MAX1725, or Texas Instruments TPS79730.
[0177] The characteristics of the VCC Power Supply might
include:
[0178] (1) high efficiency and low quiescent current, i.e., the
current wasted by the power supply in its normal operation. This
value should be less than a few microamperes; and
[0179] (2) drop-out voltage, i.e., the minimal difference between
the VBAT supplied to the VCC power supply and its output voltage.
This voltage may be less than about 100 mV even at the current
loads presented by the transmitter of the wireless telemetry
circuitry 50.
[0180] (3) The VCC power supply 42 may allows in-circuit
reprogramming of the implantable pulse generator firmware, or
optionally, the implantable pulse generator 18 may not use a VCC
power supply, which may not allow in-circuit reprogramming of the
implantable pulse generator firmware.
d. VHH Power supply
[0181] A circuit diagram showing a desired configuration for the
VHH power supply 44 is shown in FIG. 14. It is to be appreciated
that modifications to this circuit diagram configuration which
produce the same or similar functions as described are within the
scope of the invention.
[0182] The VHH Power Supply 44 is generally responsible for the
following functions:
[0183] (1) Provide the Stimulus Output Stage 46 and the Output
Multiplexer 48 with a programmable DC voltage between the battery
voltage and a voltage high enough to drive the required cathodic
phase current through the electrode circuit plus the voltage drops
across the stimulator stage, the output multiplexer stage, and the
output coupling capacitor. VHH is typically 12 VDC or less for
neuromodulation applications; and 25V or less for muscle
stimulation applications.
[0184] The Components of the VHH Power Supply might include:
[0185] (1) Micropower, inductor based (fly-back topology) switch
mode power supply (U10); e.g., Texas Instruments TPS61045, Texas
Instruments TPS61041, or Linear Technology LT3464 with external
voltage adjustment components.
[0186] (2) L6 is the flyback energy storage inductor.
[0187] (3) C42 & C43 form the output capacitor.
[0188] (4) R27, R28, and R29 establish the operating voltage range
for VHH given the internal DAC which is programmed via the SETVHH
logic command from the microcontroller 24.
[0189] (5) Diode D9 serves no purpose in normal operation and is
added to offer protection from over-voltage in the event of a VHH
circuit failure.
[0190] (6) The microcontroller 24 monitors VHH for detection of a
VHH power supply failure, system failures, and optimizing VHH for
the exhibited electrode circuit impedance.
e. Stimulus Output Stage
[0191] The Stimulus Output Stage(s) 46 is responsible for the
following functions;
[0192] (1) Generate the identified biphasic stimulus current with
programmable (dynamically adjustable during use) cathodic phase
amplitude, pulse width, and frequency. The recovery phase may
incorporate a maximum current limit; and there may be a delay time
(most likely a fixed delay) between the cathodic phase and the
recovery phase (see FIG. 10). Typical currents (cathodic phase) for
neuromodulation applications are 1 mA to 10 mA; and 2 mA to 20 mA
for muscle stimulation applications. For applications using nerve
cuff electrodes or other electrodes that are in very close
proximity to the excitable neural tissue, stimulus amplitudes of
less than 1 mA might be necessary. Electrode circuit impedances can
vary with the electrode and the application, but are likely to be
less than 2,000 ohms and greater than 100 ohms across a range of
electrode types.
[0193] The Components of the Stimulus Output Stage may include:
[0194] (1) The cathodic phase current through the electrode circuit
is established by a high gain (HFE) NPN transistor (Q7) with
emitter degeneration. In this configuration, the collector current
of the transistor (Q7) is defined by the base drive voltage and the
value of the emitter resistor (R24).
[0195] Two separate configurations are possible: In the first
configuration (as shown in FIG. 9), the base drive voltage is
provided by a DAC peripheral inside the microcontroller 24 and is
switched on and off by a timer peripheral inside the
microcontroller. This switching function is performed by an analog
switch (U8). In this configuration, the emitter resistor (R24) is
fixed in value and fixed to ground.
[0196] In a second alternative configuration, the base drive
voltage is a fixed voltage pulse (e.g., a logic level pulse) and
the emitter resistor is manipulated under microcontroller control.
Typical options may include resistor(s) terminated by
microcontroller IO port pins that are held or pulsed low, high, or
floating; or an external MOSFET that pulls one or more resistors
from the emitter to ground under program control. Note that the
pulse timing need only be applied to the base drive logic; the
timing of the emitter resistor manipulation is not critical.
[0197] The transistor (Q7) desirably is suitable for operation with
VHH on the collector. The cathodic phase current through the
electrode circuit is established by the voltage drop across the
emitter resistor. Diode D7, if used, provides a degree of
temperature compensation to this circuit.
[0198] (2) The microcontroller 24 (preferably including a
programmable counter/timer peripheral) generates stimulus pulse
timing to generate the cathodic and recovery phases and the
interphase delay. The microcontroller 24 also monitors the cathode
voltage to confirm the correct operation of the output coupling
capacitor, to detect system failures, and to optimize VHH for the
exhibited electrode circuit impedance; i.e., to measure the
electrode circuit impedance. Additionally, the microcontroller 24
can also monitor the pulsing voltage on the emitter resistor; this
allows the fine adjustment of low stimulus currents (cathodic phase
amplitude) through changes to the DAC value.
f. The Output Multiplexer
[0199] The Output Multiplexer 48 is responsible for the following
functions:
[0200] (1) Route the Anode and Cathode connections of the Stimulus
Output Stage 46 to the appropriate electrode based on addressing
data provided by the microcontroller 24.
[0201] (2) Allow recharge (recovery phase) current to flow from the
output coupling capacitor back through the electrode circuit with a
programmable delay between the end of the cathodic phase and the
beginning of the recovery phase (the interphase delay).
[0202] The circuit shown in FIG. 9 may be configured to provide
monopolar stimulation (using the case 26 as the return electrode)
to Electrode 1, to Electrode 2, or to both through time
multiplexing. This circuit could also be configured as a single
bipolar output channel by changing the hardwire connection between
the circuit board and the electrode; i.e., by routing the CASE
connection to Electrode 1 or Electrode 2. The use of four or more
channels per multiplexer stage (i.e., per output coupling
capacitor) is possible.
[0203] The Components of the Output Multiplexer might include:
[0204] (1) An output coupling capacitor in series with the
electrode circuit. This capacitor is desirably located such that
there is no DC across the capacitor in steady state. This capacitor
is typically charged by the current flow during the cathodic phase
to a voltage range of about 1/4th to 1/10th of the voltage across
the electrode circuit during the cathodic phase. Similarly, this
capacitor is desirably located in the circuit such that the analog
switches do not experience voltages beyond their ground of power
supply (VHH).
[0205] (2) The analog switches (U7) must have a suitably high
operating voltage, low ON resistance, and very low quiescent
current consumption while being driven from the specified logic
levels. Suitable analog switches include the Vishay/Siliconix
DG412HS, for example.
[0206] (3) Microcontroller 24 selects the electrode connections to
carry the stimulus current (and time the interphase delay) via
address lines.
[0207] (4) Other analog switches (U9) may be used to sample the
voltage of VHH, the CASE, and the selected Electrode. The switched
voltage, after the voltage divider formed by R25 and R26, is
monitored by the microcontroller 24.
g. Wireless Telemetry Circuit
[0208] The Wireless Telemetry circuit 50 is responsible for the
following functions:
[0209] (1) Provide reliable, bidirectional communications (half
duplex) with an external controller, programmer, or an optional
charger 34, for example, via a VHF-UHF RF link (likely in the 403
MHZ to 406 MHz MICS band per FCC 47 CFR Part 95 and the Ultra Low
Power--Active Medical Implant (AMI) regulations of the European
Union). This circuit will look for RP commands at precisely timed
intervals (e.g., twice a second), and this function must consume
very little power. Much less frequently this circuit will transmit
to the external controller. This function should also be as low
power as possible; but will represent a lower total energy demand
than the receiver in most of the anticipated applications. The RF
carrier is amplitude modulated (on-off keyed) with the digital
data. Serial data is generated by the microcontroller 24 already
formatted and timed. The wireless telemetry circuit 50 converts the
serial data stream into a pulsing carrier signal during the transit
process: and it converts a varying RF signal strength into a serial
data stream during the receive process.
[0210] The Components of the Wireless Telemetry Circuit might
include:
[0211] (1) a crystal controlled, micropower transceiver chip such
as the AMT Semiconductor AMIS-52100 (U6). This chip is responsible
for generating the RP carrier during transmissions and for
amplifying, receiving, and detecting (converting to a logic level)
the received RF signals. The transceiver chip must also be capable
of quickly starting and stopping operation to minimize power
consumption by keeping the chip disabled (and consuming very little
power) the majority of the time; and powering up for only as long
as required for the transmitting or receiving purpose.
[0212] (2) The transceiver chip has separate transmit and receive
ports that must be switched to a single antenna/feedthru. This
function is performed by the transmit/receive switch (U5) under
microcontroller control via the logic line XMIT. The
microcontroller 24 controls the operation of the transceiver chip
via an I.sup.2C serial communications link. The serial data to and
from the transceiver chip may be handled by a UART or a SPI
peripheral of the microcontroller. The message encoding/decoding
and error detection may be performed by a separate, dedicated
microcontroller; else this processing will be time shared with the
other tasks of the only microcontroller.
[0213] The various inductor and capacitor components (U6)
surrounding the transceiver chip and the transmit/receive switch
(U5) are impedance matching components and harmonic filtering
components, except as follows:
[0214] (1) X2, C33 and C34 are used to generate the crystal
controlled carrier, desirably tuned to the carrier frequency
divided by thirty-two,
[0215] (2) L4 and C27 form the tuned elements of a VCO (voltage
controlled oscillator) operating at twice the carrier frequency,
and
[0216] (3) R20, C29, and C30 are filter components of the PLL
(phase locked loop) filter.
II. Representative Indications
[0217] Due to their technical features, the implantable pulse
generator 18 and the alternative embodiment rechargeable
implantable pulse generator 68 as described in section I can be
used to provide beneficial results in diverse therapeutic and
functional restorations indications.
[0218] For example, in the field of urology, possible indications
for use of the implantable pulse generators 18 and 68 include the
treatment of (i) urinary and fecal incontinence; (ii)
micturition/retention; (iii) restoration of sexual function; (iv)
defecation/constipation; (v) pelvic floor muscle activity; and/or
(vi) pelvic pain.
[0219] The implantable pulse generators 18 and 68 can be used for
deep brain stimulation in the treatment of (i) Parkinson's disease;
(ii) multiple sclerosis; (iii) essential tremor; (iv) depression;
(v) eating disorders; (vi) epilepsy; and/or (vii) minimally
conscious state.
[0220] The implantable pulse generators 18 and 68 can be used for
pain management by interfering with or blocking pain signals from
reaching the brain, in the treatment of, e.g., (i) peripheral
neuropathy; and/or (ii) cancer.
[0221] The implantable pulse generators 18 and 68 can be used for
vagal nerve stimulation for control of epilepsy, depression, or
other mood/psychiatric disorders.
[0222] The implantable pulse generators 18 and 68 can be used for
the treatment of obstructive sleep apnea.
[0223] The implantable pulse generators 18 and 68 can be used for
gastric stimulation to prevent reflux or to reduce appetite or food
consumption.
[0224] The implantable pulse generators 18 and 68 can be used in
functional restorations indications such as the restoration of
motor control, to restore (i) impaired gait after stroke or spinal
cord injury (SCI); (ii) impaired hand and arm function after stroke
or SCI; (iii) respiratory disorders; (iv) swallowing disorders; (v)
sleep apnea; and/or (vi) neurotherapeutics, allowing individuals
with neurological deficits, such as stroke survivors or those with
multiple sclerosis, to recover functionally.
[0225] The foregoing is considered as illustrative only of the
principles of the invention. Furthermore, since numerous
modifications and changes will readily occur to those skilled in
the art, it is not desired to limit the invention to the exact
construction and operation shown and described. While the preferred
embodiment has been described, the details may be changed without
departing from the invention, which is defined by the claims.
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