U.S. patent application number 15/264409 was filed with the patent office on 2017-01-05 for field augmented current steering using voltage sources.
The applicant listed for this patent is Boston Scientific Neuromodulation Corporation. Invention is credited to David K.L. Peterson.
Application Number | 20170001009 15/264409 |
Document ID | / |
Family ID | 47997874 |
Filed Date | 2017-01-05 |
United States Patent
Application |
20170001009 |
Kind Code |
A1 |
Peterson; David K.L. |
January 5, 2017 |
FIELD AUGMENTED CURRENT STEERING USING VOLTAGE SOURCES
Abstract
A neurostimulation comprises a plurality of electrical terminals
configured for being respectively coupled to an array of
electrodes, at least three configurable sources respectively
coupled to at least three of the electrical terminals, and control
circuitry configured for programming each of the at least three
configurable sources to be either a current source or a voltage
source. A method of providing neurostimulation therapy to a patient
using an array of electrodes implanted adjacent neural tissue of
the patient, comprises conveying electrical stimulation energy
between a first one the electrodes and a second one of the
electrodes, thereby creating an electrical field potential within
the neural tissue, regulating a first current flowing through the
first electrode, and regulating a first voltage at a third
different one of the electrodes, thereby modifying a shape of the
electrical field potential within the neural tissue.
Inventors: |
Peterson; David K.L.;
(Valencia, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Boston Scientific Neuromodulation Corporation |
Valencia |
CA |
US |
|
|
Family ID: |
47997874 |
Appl. No.: |
15/264409 |
Filed: |
September 13, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13794359 |
Mar 11, 2013 |
9446239 |
|
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15264409 |
|
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|
61611951 |
Mar 16, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61N 1/36125 20130101;
A61N 1/36071 20130101; A61N 1/36182 20130101; A61N 1/0551
20130101 |
International
Class: |
A61N 1/36 20060101
A61N001/36; A61N 1/05 20060101 A61N001/05 |
Claims
1. (canceled)
2. A neurostimulation system, comprising: at least one lead to
provide an array of electrodes; a plurality of electrical terminals
configured to be electrically connected to the array of electrodes
via the at least one lead; independent sources including
independent current sources and independent voltage sources; and
control circuitry configured to connect the independent sources to
select ones of the plurality of electrodes to both regulate current
flow to provide an electric field with a shape and regulate voltage
to further shape the electric field.
3. The neurostimulation system of claim 2, wherein each of the
independent sources include a current source and a voltage source,
and each of the independent sources are capable of being programmed
to operate as the current source and being capable of being
programmed to operate as the voltage source.
4. The neurostimulation system of claim 3, wherein the control
circuitry is configured to program at least one of the independent
sources to operate as a current source and to connect the current
source to at least one electrode in the array of electrodes to
generate a current distribution in neural tissue and program at
least one other independent source to operate as a voltage source
and to connect the voltage source to at least one other electrode
in the array of electrodes to shape the current distribution.
5. The neurostimulation system of claim 4, further comprising
monitoring circuitry configured for measuring compliance voltages
on electrical terminals to which the positive and negative current
sources are coupled, and the control circuitry is configured for
assigning a voltage value to the voltage source that is between the
compliance voltages on the electrical terminals.
6. The neurostimulation system of claim 4, wherein the control
circuitry is further configured for selecting stimulation magnitude
values for the current source and the voltage source.
7. The neurostimulation system of claim 2, wherein the control
circuitry is configured for programming one of the independent
sources as a positive current source, one of the independent
sources as a negative current source, and one of the independent
sources as a voltage source.
8. The neurostimulation system of claim 2, wherein the independent
sources comprise at least four independent sources.
9. The neurostimulation system of claim 2, wherein the independent
sources comprise five independent sources, wherein the system is
configured to program three of the five independent sources as
current sources and to connect them to the plurality of electrodes
to provide a current-regulated rostro-caudal anode guarded tripole,
and the system is configured to program two of the five independent
sources as voltage sources and to connect them to the plurality of
electrodes to provide two voltage-regulated media-lateral flanking
electrodes.
10. A neurostimulation system, comprising: at least one lead to
provide an array of electrodes; a plurality of electrical terminals
configured to be electrically connected to the array of electrodes
via the at least one lead; independent sources including
independent current sources and independent voltage sources; and
control circuitry configured to connect the independent sources to
select ones of the plurality of electrodes to provide a
current-regulated tripole to provide an electric field with a shape
and voltage regulated flanking electrodes to further shape the
electric field.
11. The neurostimulation system of claim 10, wherein each of the
independent sources include a current source and a voltage source,
and each of the independent sources are capable of being programmed
to operate as the current source and being capable of being
programmed to operate as the voltage source.
12. The neurostimulation system of claim 11, wherein the control
circuitry is configured to program at least one of the independent
sources to operate as a current source and to connect the current
source to at least one electrode in the tripole to generate a
current distribution in neural tissue and program at least one
other independent source to operate as a voltage source and to
connect the voltage source to at least one flanking electrode
separate from the tripole to shape the current distribution.
13. The neurostimulation system of claim 12, further comprising
monitoring circuitry configured for measuring compliance voltages
on the at least one flanking electrode separate from the tripole,
and wherein the control circuitry is configured to assign a voltage
value to the voltage source that is between the compliance voltages
on the electrical terminals.
14. The neurostimulation system of claim 10, wherein the control
circuitry is configured to provide and shape the field to stimulate
targeted spinal cord tissue and avoid non-targeted spinal cord
tissue.
15. A method comprising: applying an electric field to stimulate
targeted tissue and avoid non-targeted tissue, including creating
the electric field with a shape using a current-regulated tripole,
and further shaping the electric field using voltage-regulated
flanking electrodes.
16. The method of claim 15, further comprising delivering a current
from at least one flanking electrode of the tripole to a central
electrode of the tripole.
17. The method of claim 16, further comprising applying a voltage
to at least one flanking electrode separate from the tripole.
18. The method of claim 17, wherein the voltage applied to at least
one flanking electrode separate from the tripole is between
compliance voltages on the flanking electrode of the tripole and
the central electrode of the tripole.
19. The method of claim 15, further comprising coupling a
programmable current source to the at least one flanking electrode
of the tripole and the central electrode of the tripole and
programming the current source to deliver the current from the at
least one flanking electrode of the tripole to the central
electrode of the tripole.
20. The method of claim 16, further comprising coupling a
programmable voltage source to the at least one flanking electrode
separate from the tripole and programming the voltage source to
deliver the voltage to the at least one flanking electrode separate
from the tripole.
21. The method of claim 14, wherein the targeted tissue includes
spinal cord tissue and the non-targeted tissue includes other
spinal cord tissue.
Description
RELATED APPLICATION DATA
[0001] The present application is a continuation of U.S.
application Ser. No. 13/794,359, filed Mar. 11, 2013, which claims
the benefit under 35 U.S.C. .sctn.119 to U.S. provisional patent
application Ser. No. 61/611,951, filed Mar. 16, 2012. The foregoing
applications are hereby incorporated by reference into the present
application in their entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to tissue stimulation
systems.
BACKGROUND OF THE INVENTION
[0003] Implantable neurostimulation systems have proven therapeutic
in a wide variety of diseases and disorders. Pacemakers and
Implantable Cardiac Defibrillators (ICDs) have proven highly
effective in the treatment of a number of cardiac conditions (e.g.,
arrhythmias). Spinal Cord Stimulation (SCS) systems have long been
accepted as a therapeutic modality for the treatment of chronic
pain syndromes, and the application of tissue stimulation has begun
to expand to additional applications such as angina pectoralis and
incontinence. Deep Brain Stimulation (DBS) has also been applied
therapeutically for well over a decade for the treatment of
refractory chronic pain syndromes, and DBS has also recently been
applied in additional areas such as movement disorders and
epilepsy. Further, in recent investigations Peripheral Nerve
Stimulation (PNS) systems have demonstrated efficacy in the
treatment of chronic pain syndromes and incontinence, and a number
of additional applications are currently under investigation.
Furthermore, Functional Electrical Stimulation (FES) systems such
as the Freehand system by NeuroControl (Cleveland, Ohio) have been
applied to restore some functionality to paralyzed extremities in
spinal cord injury patients.
[0004] Each of these implantable neurostimulation systems typically
includes an electrode lead implanted at the desired stimulation
site and an implantable pulse generator (IPG) implanted remotely
from the stimulation site, but coupled either directly to the
electrode lead or indirectly to the electrode lead via a lead
extension. Thus, electrical pulses can be delivered from the
neurostimulator to the stimulation electrode(s) to stimulate or
activate a volume of tissue in accordance with a set of stimulation
parameters and provide the desired efficacious therapy to the
patient. A typical stimulation parameter set may include the
electrodes that are sourcing (anodes) or returning (cathodes) the
stimulation current at any given time, as well as the amplitude,
duration, rate, and burst rate of the stimulation pulses.
[0005] The neurostimulation system may further comprise a handheld
remote control (RC) to remotely instruct the neurostimulator to
generate electrical stimulation pulses in accordance with selected
stimulation parameters. The RC may, itself, be programmed by a
technician attending the patient, for example, by using a
Clinician's Programmer (CP), which typically includes a general
purpose computer, such as a laptop, with a programming software
package installed thereon.
[0006] Electrical stimulation energy may be delivered from the
neurostimulator to the electrodes using one or more
current-controlled sources for providing stimulation pulses of a
specified and known current (i.e., current regulated output
pulses), or one or more voltage-controlled sources for providing
stimulation pulses of a specified and known voltage (i.e., voltage
regulated output pulses). The circuitry of the neurostimulator may
also include voltage converters, power regulators, output coupling
capacitors, and other elements as needed to produce constant
voltage or constant current stimulus pulses.
[0007] Single source current regulated and voltage regulated
neurostimulators are highly limited in their ability to shape the
current distribution and electric field around the electrode array
used to activate excitable tissue. In essence, the electric field
is determined by the electrode array geometry and the impedance
profile of the surrounding tissue.
[0008] Multiple independent current source neurostimulators were
developed to address this limitation. These neurostimulator types
can be used to more precisely control the current distribution in
tissue, and thus more selectively activate excitable tissue. This
augments the capability inherent in the electrode array geometry
and limits the influence of the surrounding impedance profile. In
one technique particularly useful for SCS, three electrodes are
rostro-caudally arranged along the spinal cord of the patient, with
the center electrode configured as a cathode, and the top and
bottom flanking electrodes configured as anodes, thereby focusing
the stimulation energy at the spinal cord tissue adjacent the
center electrode. The shape of the electric field produced by
multiple independent current source neurostimulators, however, is
still limited to what can be achieved by superposition of current
sources in a conductive medium. In addition, current sources are
less capable of controlling the electric field potential, which is
determined by tissue impedance. Multiple independent voltage source
neurostimulators, in principle, can be used to more precisely
control the electric field; however, the currents delivered by the
voltage sources change with impedance.
[0009] Conventional battery-operated neurostimulators typically
apply stimulation pulses to the tissue that are referenced to an
internal circuit voltage in the neurostimulator, with a relatively
low impedance connection being located between one or more
stimulation electrodes and internal circuitry. This relatively low
impedance effectively clamps the voltage on these stimulation
electrodes to the internal circuit voltage, as described in U.S.
patent application Ser. No. 12/821,043, entitled "Symmetrical
Output Neurostimulation Device," which is expressly incorporate
herein by reference."
[0010] Because the voltage at the unregulated side of the electrode
will be clamped to the voltage of the internal circuitry, and
because the stimulation output circuitry may be unbalanced in that
some components in the circuitry (coupling capacitors, protection
circuits, etc.) may be present on the cathode side of the circuit
but not the anode side of the circuit, or vice versa, the output
stimulation circuitry between the cathode and the anode will be
asymmetrical, such that the cathode and the anode will be
asymmetrically referenced to the internal circuit. For example, a
shift in voltage in the output stimulation circuit results in
asymmetrical voltage shifts between the anodes and cathodes, as
described in U.S. patent application Ser. No. 12/821,043. The
asymmetry between anodes and cathodes in the output stimulation
circuitry may be associated with undesired side effects during
stimulation that lead to reduced patient comfort. In particular,
parasitic coupling of the common mode signal to the implantable
device can give rise to an additional stimulation signal that is
superimposed on the differential stimulation signal.
[0011] In addition to the problem of asymmetry in the output
stimulation circuit, referencing the voltage at the cathodes and
anodes to an internal circuit may require excessive voltage levels
at the cathodes and anodes in order to maintain the desired voltage
potential therebetween. For example, if the desired voltage
potential between a cathode and an anode is 5V, and if the internal
voltage is 20V, the voltage at the anode would have to be 25V and
the voltage at the cathode would have to be 20V. The increased
voltage at the electrodes will increase the voltage relative to the
tissue, which may cause problems such as unwanted stimulation and
even electro-chemical reactions resulting in corrosion of the
electrodes.
[0012] There, thus, remains a need for an improved method and
system for conveying stimulation to tissue in a controlled
manner.
SUMMARY OF THE INVENTION
[0013] In accordance with a first aspect of the present inventions,
a neurostimulation system comprises a plurality of electrical
terminals configured for being respectively coupled to an array of
electrodes, at least three configurable sources respectively
coupled to at least three of the electrical terminals, and control
circuitry configured for programming each of the at least three
configurable sources to be either as a current source or a voltage
source. The control circuitry may further be configured selecting
stimulation magnitude values for the at least three configurable
sources. In an optional embodiment, the control circuitry may be
configured for programming one of the at least three configurable
sources as a positive current source, one of the at least three
configurable sources as a negative current source, and one of the
at least three configurable sources as a voltage source. The
neurostimulation system may comprise monitoring circuitry
configured for measuring compliance voltages on electrical
terminals to which the positive and negative current sources are
coupled, in which case, the control circuitry may be configured for
assigning a voltage value to the voltage source that is between the
compliance voltages on the electrical terminals. The
neurostimulation system may further comprise a housing containing
the plurality of electrical terminals and at least three
configurable sources.
[0014] In accordance with a second aspect of the present
inventions, a method of providing neurostimulation therapy to a
patient using an array of electrodes implanted adjacent neural
tissue (e.g., spinal cord tissue) of the patient is provided. The
method comprises conveying electrical stimulation energy between a
first one the electrodes and a second one of the electrodes,
thereby creating an electrical field potential within the neural
tissue, and regulating a first current flowing through the first
electrode. The method further comprises regulating a first voltage
at a third different one of the electrodes, thereby modifying a
shape of the electrical field potential within the neural
tissue.
[0015] An optional method further comprises regulating a second
current through the second electrode, in which case, the first
electrode may be an anode and the second electrode may be a
cathode. The optional method may further comprise regulating a
third current flowing through a fourth one of the electrodes, in
which case, the fourth electrode may be an anode, and the cathode
may be physically located between the anodes. The optional method
may further comprise regulating a second voltage at a fourth one of
the electrodes, in which case, the first and second electrodes may
be physically located between the third and fourth electrodes. The
first and second voltages may be the same. The first voltage may be
between compliance voltages on the respective first and second
electrodes.
[0016] Another optional method further comprises programming a
programmable current source coupled to the first electrode to set
the first current to a first value, and programming a programmable
voltage course coupled to the second electrode to set the first
voltage to a first value. A first configurable source may be
coupled to the first electrode, a second configurable source may be
coupled to the third electrode, and each of the first and second
configurable sources can either be configured as a current source
or a voltage source, in which case, the method may further comprise
configuring the first source as a current source, and configuring
the second source as a voltage source.
[0017] Other and further aspects and features of the invention will
be evident from reading the following detailed description of the
preferred embodiments, which are intended to illustrate, not limit,
the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The drawings illustrate the design and utility of preferred
embodiments of the present invention, in which similar elements are
referred to by common reference numerals. In order to better
appreciate how the above-recited and other advantages and objects
of the present inventions are obtained, a more particular
description of the present inventions briefly described above will
be rendered by reference to specific embodiments thereof, which are
illustrated in the accompanying drawings. Understanding that these
drawings depict only typical embodiments of the invention and are
not therefore to be considered limiting of its scope, the invention
will be described and explained with additional specificity and
detail through the use of the accompanying drawings in which:
[0019] FIG. 1 is a plan view of a Spinal Cord Stimulation (SCS)
system constructed in accordance with one embodiment of the present
inventions;
[0020] FIG. 2 is a plan view of the SCS system of FIG. 1 in use
within a patient;
[0021] FIG. 3 is a plan view of an implantable pulse generator
(IPG) and three percutaneous stimulation leads used in the SCS
system of FIG. 1;
[0022] FIG. 4 is a plan view of an implantable pulse generator
(IPG) and a surgical paddle lead used in the SCS system of FIG.
2;
[0023] FIG. 5 is a block diagram of the internal components of the
IPG of FIG. 5;
[0024] FIG. 6 is a block diagram of programmable hybrid
voltage/current sources contained in the stimulation output
circuitry of FIG. 5;
[0025] FIG. 7 is a plan view of current regulated and voltage
regulated electrodes in accordance one preferred technique of
delivering stimulation energy to the patient using the SCS system
of FIG. 1; and
[0026] FIG. 8 is a diagram illustrating one preferred technique for
voltage clamping current-regulated electrodes using
voltage-regulated electrodes.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0027] The description that follows relates to a spinal cord
stimulation (SCS) system. However, it is to be understood that the
while the invention lends itself well to applications in SCS, the
invention, in its broadest aspects, may not be so limited. Rather,
the invention may be used with any type of implantable electrical
circuitry used to stimulate tissue. For example, the present
invention may be used as part of a pacemaker, a defibrillator, a
cochlear stimulator, a retinal stimulator, a stimulator configured
to produce coordinated limb movement, a cortical stimulator, a deep
brain stimulator, peripheral nerve stimulator, microstimulator, or
in any other neural stimulator configured to treat urinary
incontinence, sleep apnea, shoulder sublaxation, headache, etc.
[0028] Turning first to FIG. 1, an exemplary spinal cord
stimulation (SCS) system 10 generally includes one or more (in this
case, three) implantable stimulation leads 12, a pulse generating
device in the form of an implantable pulse generator (IPG) 14, an
external control device in the form of a remote controller RC 16, a
clinician's programmer (CP) 18, an external trial stimulator (ETS)
20, and an external charger 22.
[0029] The IPG 14 is physically connected via one or more lead
extensions 24 to the stimulation leads 12, which carry a plurality
of electrodes 26 arranged in an array. The stimulation leads 12 are
illustrated as percutaneous leads in FIG. 1, although as will be
described in further detail below, a surgical paddle lead can be
used in place of the percutaneous leads. As will also be described
in further detail below, the IPG 14 includes pulse generation
circuitry that delivers electrical stimulation energy in the form
of a pulsed electrical waveform (i.e., a temporal series of
electrical pulses) to the electrode array 26 in accordance with a
set of stimulation parameters.
[0030] The ETS 20 may also be physically connected via the
percutaneous lead extensions 28 and external cable 30 to the
stimulation leads 12. The ETS 20, which has similar pulse
generation circuitry as the IPG 14, also delivers electrical
stimulation energy in the form of a pulse electrical waveform to
the electrode array 26 accordance with a set of stimulation
parameters. The major difference between the ETS 20 and the IPG 14
is that the ETS 20 is a non-implantable device that is used on a
trial basis after the stimulation leads 12 have been implanted and
prior to implantation of the IPG 14, to test the responsiveness of
the stimulation that is to be provided. Thus, any functions
described herein with respect to the IPG 14 can likewise be
performed with respect to the ETS 20.
[0031] The RC 16 may be used to telemetrically control the ETS 20
via a bi-directional RF communications link 32. Once the IPG 14 and
stimulation leads 12 are implanted, the RC 16 may be used to
telemetrically control the IPG 14 via a bi-directional RF
communications link 34. Such control allows the IPG 14 to be turned
on or off and to be programmed with different stimulation parameter
sets. The IPG 14 may also be operated to modify the programmed
stimulation parameters to actively control the characteristics of
the electrical stimulation energy output by the IPG 14. As will be
described in further detail below, the CP 18 provides clinician
detailed stimulation parameters for programming the IPG 14 and ETS
20 in the operating room and in follow-up sessions.
[0032] The CP 18 may perform this function by indirectly
communicating with the IPG 14 or ETS 20, through the RC 16, via an
IR communications link 36. Alternatively, the CP 18 may directly
communicate with the IPG 14 or ETS 20 via an RF communications link
(not shown). The clinician detailed stimulation parameters provided
by the CP 18 are also used to program the RC 16, so that the
stimulation parameters can be subsequently modified by operation of
the RC 16 in a stand-alone mode (i.e., without the assistance of
the CP 18).
[0033] For purposes of brevity, the details of the RC 16, CP 18,
ETS 20, and external charger 22 will not be described herein.
Details of exemplary embodiments of these devices are disclosed in
U.S. Pat. No. 6,895,280, which is expressly incorporated herein by
reference.
[0034] As shown in FIG. 2, the stimulation leads 12 are implanted
within the spinal column 42 of a patient 40. The preferred
placement of the electrode leads 12 is adjacent, i.e., resting
near, the spinal cord area to be stimulated. Due to the lack of
space near the location where the electrode leads 12 exit the
spinal column 42, the IPG 14 is generally implanted in a
surgically-made pocket either in the abdomen or above the buttocks.
The IPG 14 may, of course, also be implanted in other locations of
the patient's body. The lead extensions 24 facilitate locating the
IPG 14 away from the exit point of the electrode leads 12. As there
shown, the CP 18 communicates with the IPG 14 via the RC 16.
[0035] Referring now to FIG. 3, the external features of the
stimulation leads 12 and the IPG 14 will be briefly described. Each
of the stimulation leads 12 has eight electrodes 26 (respectively
labeled E1-E8, E9-E16, and E17-E24). The actual number and shape of
leads and electrodes will, of course, vary according to the
intended application. Further details describing the construction
and method of manufacturing percutaneous stimulation leads are
disclosed in U.S. patent application Ser. No. 11/689,918, entitled
"Lead Assembly and Method of Making Same," and U.S. patent
application Ser. No. 11/565,547, entitled "Cylindrical
Multi-Contact Electrode Lead for Neural Stimulation and Method of
Making Same," the disclosures of which are expressly incorporated
herein by reference.
[0036] Alternatively, as illustrated in FIG. 4, the stimulation
lead 12 takes the form of a surgical paddle lead on which
electrodes 26 are arranged in a two-dimensional array in three
columns (respectively labeled E1-E5, E6-E10, and E11-E15) along the
axis of the stimulation lead 12. In the illustrated embodiment,
five rows of electrodes 26 are provided, although any number of
rows of electrodes can be used. Each row of the electrodes 26 is
arranged in a line transversely to the axis of the lead 12. The
actual number of leads and electrodes will, of course, vary
according to the intended application. Further details regarding
the construction and method of manufacture of surgical paddle leads
are disclosed in U.S. patent application Ser. No. 11/319,291,
entitled "Stimulator Leads and Methods for Lead Fabrication," the
disclosure of which is expressly incorporated herein by
reference.
[0037] In each of the embodiments illustrated in FIGS. 3 and 4, the
IPG 14 comprises an outer case 44 for housing the electronic and
other components (described in further detail below). The outer
case 44 is composed of an electrically conductive, biocompatible
material, such as titanium, and forms a hermetically sealed
compartment wherein the internal electronics are protected from the
body tissue and fluids. In some cases, the outer case 44 may serve
as an electrode. The IPG 14 further comprises a connector 46 to
which the proximal ends of the stimulation leads 12 mate in a
manner that electrically couples the electrodes 26 to the internal
electronics (described in further detail below) within the outer
case 44. To this end, the connector 46 includes one or more ports
(three ports 48 or three percutaneous leads or one port for the
surgical paddle lead) for receiving the proximal end(s) of the
stimulation lead(s) 12. In the case where the lead extensions 24
are used, the port(s) 48 may instead receive the proximal ends of
such lead extensions 24.
[0038] The IPG 14 includes pulse generation circuitry that provides
electrical conditioning and stimulation energy in the form of a
pulsed electrical waveform to the electrode array 26 in accordance
with a set of stimulation parameters programmed into the IPG 14.
Such stimulation parameters may comprise electrode combinations,
which define the electrodes that are activated as anodes
(positive), cathodes (negative), and turned off (zero), percentage
of stimulation energy assigned to each electrode (fractionalized
electrode configurations), and electrical pulse parameters, which
define the pulse amplitude (measured in milliamps or volts
depending on whether the IPG 14 supplies constant current or
constant voltage to the electrode array 26), pulse width (measured
in microseconds), pulse rate (measured in pulses per second), and
burst rate (measured as the stimulation on duration X and
stimulation off duration Y).
[0039] Electrical stimulation will occur between two (or more)
activated electrodes, one of which may be the IPG case 44.
Simulation energy may be transmitted to the tissue in a monopolar
or multipolar (e.g., bipolar, tripolar, etc.) fashion. Monopolar
stimulation occurs when a selected one of the lead electrodes 26 is
activated along with the case 44 of the IPG 14, so that stimulation
energy is transmitted between the selected electrode 26 and the
case 44. Bipolar stimulation occurs when two of the lead electrodes
26 are activated as anode and cathode, so that stimulation energy
is transmitted between the selected electrodes 26. For example, an
electrode on one lead 12 may be activated as an anode at the same
time that an electrode on the same lead or another lead 12 is
activated as a cathode. Tripolar stimulation occurs when three of
15 the lead electrodes 26 are activated, two as anodes and the
remaining one as a cathode, or two as cathodes and the remaining
one as an anode. For example, two electrodes on one lead 12 may be
activated as anodes at the same time that an electrode on another
lead 12 is activated as a cathode.
[0040] The stimulation energy may be delivered between electrodes
as monophasic electrical energy or multiphasic electrical energy.
Monophasic electrical energy includes a series of pulses that are
either all positive (anodic) or all negative (cathodic).
Multiphasic electrical energy includes a series of pulses that
alternate between positive and negative. For example, multiphasic
electrical energy may include a series of biphasic pulses, with
each biphasic pulse including a cathodic (negative) stimulation
pulse and an anodic (positive) recharge pulse that is generated
after the stimulation pulse to prevent direct current charge
transfer through the tissue, thereby avoiding electrode degradation
and cell trauma. That is, charge is conveyed through the
electrode-tissue interface via current at an electrode during a
stimulation period (the length of the stimulation pulse), and then
pulled back off the electrode-tissue interface via an oppositely
polarized current at the same electrode during a recharge period
(the length of the recharge pulse).
[0041] Turning next to FIG. 5, the main internal components of the
IPG 14 will now be described. The IPG 14 includes stimulation
output circuitry 50 configured for generating electrical
stimulation energy in accordance with a defined pulsed waveform
having a specified pulse amplitude, pulse rate, pulse width, pulse
shape, and burst rate under control of control logic 52 over data
bus 54. Control of the pulse rate and pulse width of the electrical
waveform is facilitated by timer logic circuitry 56, which may have
a suitable resolution, e.g., 10 .mu.s. The stimulation energy
generated by the stimulation output circuitry 50 is output via
capacitors C1-Cn to electrical terminals 58 corresponding to the
electrodes 26.
[0042] As illustrated in FIG. 6, the stimulation output circuitry
50 comprises a plurality of configurable hybrid current/voltage
sources 100 for providing stimulation pulses of either a specified
and known amperage to or from the electrodes 26 or a specified and
known voltage at the electrodes 26. In this manner, each of the
electrodes 26 can be operated in either a current source mode or a
voltage source mode. In the illustrated embodiment, each of the
hybrid sources 100 is dedicated to an electrical terminal 58, and
thus, the particular electrode 26 coupled to the electrical
terminal 58. Thus, the number of hybrid sources 100 will be equal
to the number of electrical terminals 58, and thus the number of
electrodes 26.
[0043] Alternatively, the number of hybrid sources 100 may be less
than the number of electrical terminals 58, and thus less than the
number of electrodes 26, in which case, a low impedance switch
matrix (not shown) can be coupled between the hybrid sources 100
and the electrical terminals 58, so that any of the hybrid sources
100 may be coupled to the electrical terminals 58, and thus
electrodes 26, to be activated. In any event, the number of hybrid
sources 100 equals at least three, and preferably at least five, in
order to form an electrode configuration comprising a current
regulated rostro-caudal anode guarded tripole and two voltage
regulated medio-lateral flanking electrodes, as will be described
in further detail below.
[0044] Each of the hybrid sources 100 comprises a programmable
voltage source 102 and a current source pair 104. The voltage
source 102 can be programmed to have a positive voltage or a
negative voltage. One current source 104a of each pair 104
functions as a positive (+) current source, while the other current
source 104b of each pair 104 functions as a negative (-) current
source. The outputs of the programmable voltage source 102, and the
outputs of the positive current source 104a and the negative
current source 104b of each pair 104 are connected to a common node
106. The common node 106 is coupled to the respective one of the
electrodes E1-En via the electrical terminals 78. Hence, it is seen
that each of the n programmable electrical terminals 78 can be
programmed to have a positive voltage, a negative voltage, a
positive (sourcing current), a negative (sinking current), or off
(no current) polarity. A compliance voltage VH is supplied to each
of the hybrid sources 100. The magnitude of the compliance voltage
VH will depend on whether the respective hybrid source 100 is
programmed as a voltage source, a positive current source, or a
negative current source.
[0045] Referring back to FIG. 5, the IPG 14 further comprises
monitoring circuitry 60 for monitoring the status of various nodes
or other points 62 throughout the IPG 14, e.g., power supply
voltages, temperature, battery voltage, and the like. The
monitoring circuitry 60 is also configured for measuring electrical
parameter data (e.g., electrode impedance and/or electrode field
potential). The IPG 14 further comprises processing circuitry in
the form of a microcontroller (.mu.C) 64 that controls the control
logic 52 over data bus 66, and obtains status data from the
monitoring circuitry 60 via data bus 68. The IPG 14 additionally
controls the timer logic 56. The IPG 14 further comprises memory 70
and oscillator and clock circuit 72 coupled to the microcontroller
64. The microcontroller 64, in combination with the memory 70 and
oscillator and clock circuit 72, thus comprise a microprocessor
system that carries out a program function in accordance with a
suitable program stored in the memory 70. Alternatively, for some
applications, the function provided by the microprocessor system
may be carried out by a suitable state machine.
[0046] Thus, the microcontroller 64 generates the necessary control
and status signals, which allow the microcontroller 64 to control
the operation of the IPG 14 in accordance with a selected operating
program and stimulation parameters. In controlling the operation of
the IPG 14, the microcontroller 64 is able to individually generate
stimulus pulses at the electrodes 26 using the stimulation output
circuitry 50, in combination with the control logic 52 and timer
logic 56, thereby allowing each electrode 26 to be paired or
grouped with other electrodes 26, including the monopolar case
electrode, to control the polarity, amplitude, rate, pulse width
and channel through which the current stimulus pulses are
provided.
[0047] More specific to the present invention, the microcontroller
64 is capable of programming each of the hybrid sources 100 as
either a voltage source or a current source and to further assign
the desired stimulation value for the programmed source. In one
technique described in further detail below, the microcontroller 64
can program one of the hybrid sources 100 as a positive current
source 104a, one of the hybrid sources as a negative current source
104b, and one of the hybrid sources 100 as a voltage source 102. In
this case, the monitoring circuitry 60 can measure the compliance
voltages on the electrical terminals 78 to which the positive and
negative current sources 102 are respectively coupled, and
microcontroller 64 is configured for assigning a voltage value to
the voltage source 102 that is between the compliance voltages on
the electrical terminals 78. In essence, the microcontroller 64
ensures that the voltage output by the voltage source 102 falls
within the compliance voltage window of the respective current
sources 104, which would otherwise operate as current sources 104
if the output voltage of the voltage source 102 falls outside of
the compliance voltage window.
[0048] The IPG 14 further comprises an alternating current (AC)
receiving coil 74 for receiving programming data (e.g., the
operating program and/or stimulation parameters) from the RC 16
and/or CP 18 in an appropriate modulated carrier signal, and
charging and forward telemetry circuitry 76 for demodulating the
carrier signal it receives through the AC receiving coil 74 to
recover the programming data, which programming data is then stored
within the memory 70, or within other memory elements (not shown)
distributed throughout the IPG 14.
[0049] The IPG 14 further comprises back telemetry circuitry 78 and
an alternating current (AC) transmission coil 80 for sending
informational data sensed through the monitoring circuitry 60 to
the RC 16 and/or CP 18. The back telemetry features of the IPG 14
also allow its status to be checked. For example, when the RC 16
and/or CP 18 initiates a programming session with the IPG 14, the
capacity of the battery is telemetered, so that the RC 16 and/or CP
18 can calculate the estimated time to recharge. Any changes made
to the current stimulus parameters are confirmed through back
telemetry, thereby assuring that such changes have been correctly
received and implemented within the implant system. Moreover, upon
interrogation by the RC 16 and/or CP 18, all programmable settings
stored within the IPG 14 may be uploaded to the RC 16 and/or CP
18.
[0050] The IPG 14 further comprises a rechargeable power source 82
and power circuits 84 for providing the operating power to the IPG
14. The rechargeable power source 82 may, e.g., comprise a
lithium-ion or lithium-ion polymer battery. The rechargeable
battery 82 provides an unregulated voltage to the power circuits
84. The power circuits 84, in turn, generate the various voltages
86, some of which are regulated and some of which are not, as
needed by the various circuits located within the IPG 14. The
rechargeable power source 82 is recharged using rectified AC power
(or DC power converted from AC power through other means, e.g.,
efficient AC-to-DC converter circuits, also known as "inverter
circuits") received by the AC receiving coil 74. To recharge the
power source 82, the external charger 22 (shown in FIG. 1), which
generates the AC magnetic field, is placed against, or otherwise
adjacent, to the patient's skin over the implanted IPG 14. The AC
magnetic field emitted by the external charger induces AC currents
in the AC receiving coil 74. The charging and forward telemetry
circuitry 76 rectifies the AC current to produce DC current, which
is used to charge the power source 82. While the AC receiving coil
74 is described as being used for both wirelessly receiving
communications (e.g., programming and control data) and charging
energy from the external device, it should be appreciated that the
AC receiving coil 74 can be arranged as a dedicated charging coil,
while another coil, such as coil 80, can be used for bi-directional
telemetry.
[0051] Additional details concerning the above-described and other
IPGs may be found in U.S. Pat. No. 6,516,227, U.S. Patent
Publication No. 2003/0139781, and U.S. patent application Ser. No.
11/138,632, entitled "Low Power Loss Current Digital-to-Analog
Converter Used in an Implantable Pulse Generator," which are
expressly incorporated herein by reference. It should be noted that
rather than an IPG, the system 10 may alternatively utilize an
implantable receiver-stimulator (not shown) connected to leads 12.
In this case, the power source, e.g., a battery, for powering the
implanted receiver, as well as control circuitry to command the
receiver-stimulator, will be contained in an external controller
inductively coupled to the receiver-stimulator via an
electromagnetic link. Data/power signals are transcutaneously
coupled from a cable-connected transmission coil placed over the
implanted receiver-stimulator. The implanted receiver-stimulator
receives the signal and generates the stimulation in accordance
with the control signals.
[0052] It should be noted that rather than an IPG, the SCS system
10 may alternatively utilize an implantable receiver-stimulator
(not shown) connected to the stimulation leads 12. In this case,
the power source, e.g., a battery, for powering the implanted
receiver, as well as control circuitry to command the
receiver-stimulator, will be contained in an external controller
inductively coupled to the receiver-stimulator via an
electromagnetic link. Data/power signals are transcutaneously
coupled from a cable-connected transmission coil placed over the
implanted receiver-stimulator. The implanted receiver-stimulator
receives the signal and generates the stimulation energy and
background energy in accordance with the control signals.
[0053] Having described the structure and function of the SCS
system 100, one technique for operating the system 100 to provide
therapy to the patient, and in particular, to configure the hybrid
sources 100 in a novel manner will now be described. Although the
technique described below does not require the use of a hybrid
multiple independent current and voltage controlled stimulator
output topology, the use of the hybrid sources 100 can be used in a
variety of neurostimulator applications to gain better control of
the current distribution and electric field than can be provided by
dedicated independent current sources and independent voltage
sources alone.
[0054] In general, electrical stimulation energy is conveyed
between at least two electrodes, thereby creating an electric field
within the neural tissue is a conventional manner. The hybrid
sources 100 coupled to these electrodes are configured as current
sources, such that the electrical current flowing through these
electrodes is current regulated. In this manner, the current
distribution in the tissue targeted for stimulation can be more
precisely controlled, thereby more selectively activated the
tissue. A first voltage can be regulated at another one of the
electrodes, thereby modifying a shape of the electrical field
potential within the neural tissue.
[0055] For example, as briefly discussed above, and as illustrated
in FIG. 7, the hybrid sources 100 can be configured to form an
electrode configuration comprising a current regulated
rostro-caudal anode guarded tripole and two voltage regulated
medio-lateral flanking electrodes; that is, the hybrid source 100
coupled to the center electrode E.sub.C is configured as a negative
current source, such that this electrode is activated as a cathode,
the hybrid sources 100 respectively coupled to the vertically
flanking upper and lower electrodes E.sub.U, E.sub.L are configured
as positive current sources, such that these electrodes are
activated as anodes, and the hybrid sources 100 respectively
coupled to the horizontally flanking electrodes E.sub.L, E.sub.R
are configured as voltage sources. In the exemplary embodiment, the
center electrode E.sub.C sinks a current regulated value of -4 mA,
each of the vertically flanking electrodes E.sub.U, E.sub.L source
a current regulated value of +2 mA, and each of the horizontally
flanking electrodes E.sub.L, E.sub.R has a voltage regulated value
of +2V. The current-regulated rostro-caudal tripole can be used to
stimulate dorsal column (DC) nerve fibers within the spinal cord of
the patient, while the voltage-regulated pair of electrodes can be
used to suppress stimulation of the dorsal root (DR) nerve
fibers.
[0056] Notably, as discussed above, it is important that each of
the voltage values at horizontally flanking electrodes E.sub.L,
E.sub.R, when reference to the ground of the IPG 14, fall within
the compliance voltage window of the current regulated tripole;
that is, the voltage values at the horizontally flanking electrodes
E.sub.L, E.sub.R are regulated, such that they are between the
minimum compliance voltage at the pertinent electrode of the
current-regulated tripole and the maximum compliance voltage at the
pertinent electrode of the current-regulated tripole. In this
manner, the programmed current sources that regulate the current at
the tripole will continue to operate as current sources. In the
exemplary case illustrated in FIG. 7, the vertically flanking
electrodes E.sup.U, E.sub.L that source +2 mA are at a voltage
potential that is greater than +2V, and the center electrode
E.sub.C that sinks -4 mA is at a voltage potential that is less
than +2V.
[0057] Furthermore, the current values of the tripole (i.e.,
electrodes E.sub.C, E.sub.L, E.sub.R) preferably sum to zero (e.g.,
+2 mA+2 mA-4 mA=0 as shown in FIG. 7), and the respective voltage
values at the horizontally flanking electrodes E.sub.L, E.sub.R are
the same (2V=2V as shown in FIG. 7). In this scenario, no net
current flows through the electrodes associated with the voltages
sources (in this case, the horizontally flanking electrodes
E.sub.L, E.sub.R), although the voltage potentials at these
electrodes influence the current distribution in the tissue created
by the current-regulated tripole. In the cases where the current
values of the current-regulated electrodes do not sum to zero or
the voltage potentials at the voltage regulated electrodes are not
equal, the electrical current will flow through the voltage
regulated electrodes in accordance with the electric field and the
surrounding impedance profile.
[0058] In addition to providing the capability of reshaping the
electric field generated by the current-regulated electrodes, the
voltage-regulated electrodes provides the ability to adjust the
voltage to which the current-regulated electrodes are clamped, as
opposed to the case where the voltage of the current-regulated
electrodes would be clamped to the output circuitry of the IPG 14.
For example, as illustrated in FIG. 8, the minimum and maximum
compliance voltages at two current regulated electrodes can be
adjusted up or down by adjusting the clamping voltage of the
voltage-regulated electrodes. In the embodiment illustrated in FIG.
8, a 5V difference between the current-regulated electrodes is
required to generate the required regulated current flow. The
voltage at the voltage-regulated electrodes may be adjusted upward
to increase the respective voltages at the current-regulated
electrodes, or adjusted downward to decrease the respective
voltages at the current-regulated electrodes.
[0059] Although particular embodiments of the present inventions
have been shown and described, it will be understood that it is not
intended to limit the present inventions to the preferred
embodiments, and it will be obvious to those skilled in the art
that various changes and modifications may be made without
departing from the spirit and scope of the present inventions.
Thus, the present inventions are intended to cover alternatives,
modifications, and equivalents, which may be included within the
spirit and scope of the present inventions as defined by the
claims.
* * * * *