U.S. patent application number 14/338695 was filed with the patent office on 2015-01-29 for systems and methods of providing modulation therapy without patient-perception of stimulation.
The applicant listed for this patent is Boston Scientific Neuromodulation Corporation. Invention is credited to Tamara C. Baynham, Jordi Parramon.
Application Number | 20150032181 14/338695 |
Document ID | / |
Family ID | 51303112 |
Filed Date | 2015-01-29 |
United States Patent
Application |
20150032181 |
Kind Code |
A1 |
Baynham; Tamara C. ; et
al. |
January 29, 2015 |
SYSTEMS AND METHODS OF PROVIDING MODULATION THERAPY WITHOUT
PATIENT-PERCEPTION OF STIMULATION
Abstract
A neuromodulation system and method of providing sub-threshold
modulation therapy. Electrical modulation energy is delivered to a
target tissue site of the patient at a programmed intensity value,
thereby providing therapy to a patient without perception of
stimulation. In response to an event, electrical modulation energy
is delivered at incrementally increasing intensity values. At least
one evoked compound action potential (eCAP) is sensed in a
population of neurons at the target tissue site of the patient in
response to the delivery of the electrical modulation energy at the
incrementally increasing intensity values. One of the incrementally
increased intensity values is selected based on the sensed eCAP(s).
A decreased intensity value is automatically computed as a function
of the selected intensity value. Electrical modulation energy is
delivered to the target tissue site of the patient at the computed
intensity value, thereby providing sub-threshold therapy to the
patient.
Inventors: |
Baynham; Tamara C.;
(Valencia, CA) ; Parramon; Jordi; (Valencia,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Boston Scientific Neuromodulation Corporation |
Valencia |
CA |
US |
|
|
Family ID: |
51303112 |
Appl. No.: |
14/338695 |
Filed: |
July 23, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61858730 |
Jul 26, 2013 |
|
|
|
Current U.S.
Class: |
607/46 ;
607/59 |
Current CPC
Class: |
A61N 1/3615 20130101;
A61N 1/36071 20130101; A61N 1/36139 20130101 |
Class at
Publication: |
607/46 ;
607/59 |
International
Class: |
A61N 1/36 20060101
A61N001/36 |
Claims
1. A method of providing therapy to a patient, comprising:
delivering electrical modulation energy to a target tissue site of
the patient at a programmed intensity value, thereby providing
therapy to the patient without perception of stimulation;
delivering, in response to an event, electrical modulation energy
at a series of incrementally increasing intensity values relative
to the programmed intensity value; sensing at least one evoked
compound action potential (eCAP) in a population of neurons at the
target tissue site of the patient in response to the delivery of
the electrical modulation energy at the series of incrementally
increasing intensity values; selecting one of the series of
incrementally increased intensity values based on the at least one
sensed eCAP; automatically computing a decreased intensity value as
a function of the selected intensity value; and delivering
electrical modulation energy to the target tissue site of the
patient at the computed intensity value.
2. The method of claim 1, wherein the perception of stimulation is
a perception of paresthesia.
3. The method of claim 1, wherein the programmed intensity value is
a programmed amplitude value, and the incrementally increasing
intensity values are incrementally increasing amplitude values.
4. The method of claim 1, wherein the programmed intensity value is
a programmed pulse width value, and the incrementally increasing
intensity values are incrementally increasing pulse width
values.
5. The method of claim 1, wherein the selected intensity value
corresponds to the intensity value of the delivered electrical
modulation energy in response to which a first one of the at least
one eCAP is sensed.
6. The method of claim 1, further comprising: comparing a
characteristic of each of the at least one sensed eCAP to a
corresponding characteristic of a reference eCAP indicative of a
perception threshold; and selecting one of the series of
incrementally increased intensity values based on the
comparison.
7. The method of claim 6, wherein the characteristic of the each
sensed eCAP is at least one of peak delay, width, amplitude, and
waveform morphology.
8. The method of claim 6, wherein the reference eCAP is stored, the
at least one sensed eCAP comprises two or more eCAPs respectively
sensed in response to the delivery of the electrical modulation
energy at two or more of the intensity values, the method further
comprising: obtaining the characteristic from the stored reference
eCAP; and determining one of the two or more sensed eCAPs having
the characteristic that best matches the characteristic of the
reference eCAP, wherein the intensity value of the delivered
electrical modulation energy in response to which the determined
eCAP is sensed is selected.
9. The method of claim 6, wherein the characteristic of the
reference eCAP is a stored threshold value, the at least one sensed
eCAP comprises one or more eCAPs respectively sensed in response to
the delivery of the electrical modulation energy at each of two or
more of the intensity values, the method further comprising
determining a function of the one or more sensed eCAPs having the
characteristic that equals or exceeds the stored threshold value,
wherein the intensity value of the delivered electrical modulation
energy in response to which the determined one or more eCAPs is
sensed is selected.
10. The method of claim 6, further comprising: storing a list of
reference eCAPs characteristics, each of which is indicative of a
perception threshold when the patient is engaged in a particular
physical activity and/or posture; identifying a physical activity
and/or posture in which the patient is currently engaged; and
selecting, from the list of reference eCAP characteristics, the
reference eCAP characteristic corresponding to the identified
physical activity and/or posture, wherein the selected reference
eCAP characteristic is the reference eCAP characteristic to which
the characteristic of each of the at least one sensed eCAP is
compared.
11. The method of claim 1, wherein the event is one of an
identified physical activity and/or posture, a user-initiated
signal, a signal indicating migration of an electrode from which
the electrical modulation energy is delivered, and a predetermined
periodically recurring signal.
12. The method of claim 1, wherein the computed intensity value is
a percentage of the selected intensity value.
13. The method of claim 12, wherein the percentage is in the range
of 30%-70%.
14. The method of claim 12, wherein the percentage is in the range
of 40%-60%.
15. The method of claim 12, wherein the percentage is in the range
of 10%-90%.
16. The method of claim 1, wherein the computed function is a
difference between the selected intensity value and a constant.
17. The method of claim 1, wherein both the electrical modulation
energy delivered at the programmed intensity and the electrical
energy delivered at the series of incrementally increasing
intensity values comprise electrical pulse trains, and each of the
programmed intensity value, incrementally increased intensity
value, and computed intensity value is a pulse intensity value.
18. The method of claim 1, wherein the patient suffers from chronic
pain in a body region, and the perception of threshold comprises
paresthesia perceived by the patient in the body region.
19. A neuromodulation system, comprising: a plurality of electrical
terminals respectively configured for being electrically coupled to
a plurality of electrodes implanted within a target tissue site;
modulation output circuitry coupled to the plurality of electrical
terminals for delivering electrical modulation energy to the target
tissue site of the patient at a programmed intensity value, thereby
providing therapy to the patient without perception of stimulation;
monitoring circuitry coupled to the plurality of electrical
terminals; and control/processing circuitry configured for:
directing, in response to an event, the modulation output circuitry
to deliver electrical modulation energy at a series of
incrementally increasing intensity values relative to the
programmed intensity value; prompting the modulation output
circuitry to evoke at least one compound action potential (CAP) in
a populations of neurons in the target tissue site of the patient
in response to the delivery of the electrical modulation energy at
the series of incrementally increasing intensity values; prompting
the monitoring circuitry to sense the at least one evoked CAP
(eCAP); selecting one of the series of incrementally increased
intensity values based on the at least one sensed eCAP;
automatically computing a decreased value as a function of the
selected intensity value; and directing the modulation output
circuitry to deliver electrical modulation energy to the target
tissue site of the patient at the computed intensity value.
20. The neuromodulation system of claim 19, wherein the perception
of stimulation is a perception of paresthesia.
Description
CLAIM OF PRIORITY
[0001] This application claims the benefit of priority under 35
U.S.C. .sctn.119(e) of U.S. Provisional Patent Application Ser. No.
61/858,730, filed on Jul. 26, 2013, which is herein incorporated by
reference in its entirety.
FIELD OF THE INVENTION
[0002] The present inventions relate to tissue modulation systems,
and more particularly, to programmable neuromodulation systems.
BACKGROUND
[0003] Implantable neuromodulation 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 have
been applied to restore some functionality to paralyzed extremities
in spinal cord injury patients.
[0004] Each of these implantable neuromodulation systems typically
includes at least one neuromodulation lead implanted at the desired
modulation site and an Implantable Pulse Generator (IPG) implanted
remotely from the modulation site, but coupled either directly to
the neuromodulation lead(s), or indirectly to the neuromodulation
leads) via one or more lead extensions. Thus, electrical pulses can
be delivered from the neuromodulator to the electrodes carried by
the neuromodulation leads) to stimulate or activate a volume of
tissue in accordance with a set of modulation parameters and
provide the desired efficacious therapy to the patient. The
neuromodulation system may further comprise a handheld remote
control (RC) to remotely instruct the neuromodulator to generate
electrical modulation pulses in accordance with selected modulation
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.
[0005] Electrical modulation energy may be delivered from the
neuromodulation device to the electrodes in the form of an
electrical pulsed waveform. Thus, electrical modulation energy may
be controllably delivered to the electrodes to modulate neural
tissue. The configuration of electrodes used to deliver electrical
pulses to the targeted tissue constitutes an electrode
configuration, with the electrodes capable of being selectively
programmed to act as anodes (positive), cathodes (negative), or
left off (zero). In other words, an electrode configuration
represents the polarity being positive, negative, or zero. Other
parameters that may be controlled or varied include the amplitude,
width, and rate of the electrical pulses provided through the
electrode array. Each electrode configuration, along with the
electrical pulse parameters, can be referred to as a "modulation
parameter set."
[0006] With some neuromodulation systems, and in particular, those
with independently controlled current or voltage sources, the
distribution of the current to the electrodes (including the case
of the neuromodulation device, which may act as an electrode) may
be varied such that the current is supplied via numerous different
electrode configurations. In different configurations, the
electrodes may provide current or voltage in different relative
percentages of positive and negative current or voltage to create
different electrical current distributions fractionalized electrode
configurations).
[0007] As briefly discussed above, an external control device can
be used to instruct the neuromodulation device to generate
electrical pulses in accordance with the selected modulation
parameters. Typically, the modulation parameters programmed into
the neuromodulation device can be adjusted by manipulating controls
on the external control device to modify the electrical modulation
energy delivered by the neuromodulation device system to the
patient. Thus, in accordance with the modulation parameters
programmed by the external control device, electrical pulses can be
delivered from the neuromodulation device to the electrode(s) to
modulate a volume of tissue in accordance with the set of
modulation parameters and provide the desired efficacious therapy
to the patient. The best modulation parameter set will typically be
one that delivers electrical energy to the volume of tissue that
must be modulate in order to provide the therapeutic benefit (e.g.,
treatment of pain), while minimizing the volume of non-target
tissue that is modulated.
[0008] However, the number of electrodes available combined with
the ability to generate a variety of complex electrical pulses,
presents a huge selection of modulation parameter sets to the
clinician or patient. For example, if the neuromodulation system to
be programmed has an array of sixteen electrodes, millions of
modulation parameter sets may be available for programming into the
neuromodulation system. Today, neuromodulation system ay have up to
thirty-two electrodes, thereby exponentially increasing the number
of modulation parameters sets available for programming.
[0009] To facilitate such selection, the clinician generally
programs the neuromodulation device through a computerized
programming system. This programming system can be a self-contained
hardware/software system, or can be defined predominantly by
software running on a standard personal computer (PC). The PC or
custom hardware may actively control the characteristics of the
electrical pulses generated by the neuromodulation device to allow
the optimum modulation parameters to be determined based on patient
feedback or other means and to subsequently program the
neuromodulation device with the optimum modulation parameter set or
sets. The computerized programming system may be operated by a
clinician attending the patient in several scenarios.
[0010] For example, in order to achieve an effective result from
conventional SCS, the lead or leads must be placed in a location,
such that the electrical modulation (and in this case, electrical
modulation) will cause paresthesia. The paresthesia induced by the
electrical modulation and perceived by the patient should be
located in approximately the same place in the patient's body as
the pain that is the target of treatment. If a lead is not
correctly positioned, it is possible that the patient will receive
little or no benefit from an implanted SCS system. Thus, correct
lead placement can mean the difference between effective and
ineffective pain therapy. When leads are implanted within the
patient, the computerized programming system, in the context of an
operating room (OR) mapping procedure, may be used to instruct the
neuromodulation device to apply electrical modulation to test
placement of the leads and/or electrodes, thereby assuring that the
leads and/or electrodes are implanted in effective locations within
the patient.
[0011] Once the leads are correctly positioned, a fitting
procedure, which may be referred to as a navigation session, may be
performed using the computerized programming system to program the
external control device, and if applicable the neuromodulation
device, with a set of modulation parameters that best addresses the
painful site. Thus, the navigation session may be used to pinpoint
the volume of activation (VOA) or areas correlating to the pain.
Such programming ability is particularly advantageous for targeting
the tissue during implantation, or after implantation should the
leads gradually or unexpectedly move that would otherwise relocate
the modulation energy away from the target site. By reprogramming
the neuromodulation device (typically by independently varying the
modulation energy on the electrodes), the volume of activation
(VOA) can often be moved back to the effective pain site without
having to re-operate on the patient in order to reposition the lead
and its electrode array. When adjusting the volume of activation
(VOA) relative to the tissue, it is desirable to make small changes
in the proportions of current, so that changes in the spatial
recruitment of nerve fibers will be perceived by the patient as
being smooth and continuous and to have incremental targeting
capability.
[0012] Although alternative or artifactual sensations are usually
tolerated relative to the sensation of pain, patients sometimes
report these sensations to be uncomfortable, and therefore, they
can be considered an adverse side-effect to neuromodulation therapy
in some cases. Because the perception of paresthesia has been used
as an indicator that the applied electrical energy is, in fact,
alleviating the pain experienced by the patient, the amplitude of
the applied electrical energy is generally adjusted to a level that
causes the perception of paresthesia. It has been shown, however,
that the delivery of sub-threshold electrical energy (e.g.,
high-rate pulsed electrical energy and/or low pulse width
electrical energy) can be effective in providing neuromodulation
therapy for chronic pain without causing paresthesia.
[0013] However, because there is a lack of paresthesia that may
otherwise indicate that the activated electrodes are properly
located relative to the targeted tissue site, it is difficult to
immediately determine if the delivered sub-threshold
neuromodulation therapy is optimized in terms of both providing
efficacious therapy and minimizing energy consumption. Furthermore,
if the implanted neuromodulation lead(s) migrate relative to the
target tissue site to be modulated, it is possible that the
sub-threshold neuromodulation may fall outside of the effective
therapeutic range (either below the therapeutic range if the
coupling efficiency between the neuromodulation lead(s) and target
tissue site decreases, resulting in a lack of efficacious therapy,
or above the therapeutic range if the coupling efficiency between
the neuromodulation lead(s) and the target tissue site increases,
resulting in the perception of paresthesia or inefficient energy
consumption). Similarly, a change in the patient's physical
activity and/or posture may also cause the neuromodulation lead(s)
to migrate relative to the target tissue, and/or alternatively
impede optimal treatment contact to the target tissue, consequently
rendering the sub-threshold neuromodulation therapy
inefficacious.
[0014] There, thus, remains a need to provide a neuromodulation
system that is capable of compensating for the migration of
neuromodulation lead(s) and/or a change in physical activity and/or
posture during sub-threshold neuromodulation therapy.
SUMMARY OF THE INVENTION
[0015] In accordance with a first aspect of the present inventions,
a method of providing therapy to a patient is provided. The method
comprises delivering electrical modulation energy to a target
tissue site of the patient at a programmed intensity value (e.g.,
an amplitude value or a pulse width value), thereby providing
therapy to the patient without the perception of paresthesia,
delivering, in response to an event, electrical modulation energy
at a series of incrementally increasing intensity values relative
to the programmed intensity value, sensing at least one evoked
compound action potential (eCAP) in a population of neurons at the
target tissue site of the patient in response to the delivery of
the electrical modulation energy at the series of incrementally
increasing intensity values of the electrical modulation energy,
selecting one of the series of incrementally increased intensity
values based on the at least one sensed eCAP, automatically
computing a decreased intensity value as a function of the selected
intensity value and delivering electrical modulation energy to the
target tissue site of the patient at the computed intensity
value.
[0016] In one method, the selected intensity value may correspond
to the intensity value of the delivered electrical modulation
energy in response to which a first one of the at least eCAP is
sensed.
[0017] The method may also include comparing a characteristic of
each of the at least one sensed eCAP to a corresponding
characteristic of a reference eCAP that is indicative of a
perception threshold and selecting one of the series of
incrementally increased intensity values based on the comparison.
The characteristic of the each sensed eCAP may be at least one a
peak delay, width, amplitude and waveform morphology.
[0018] When the sensed eCAP comprises two or more eCAPs
respectively sensed in response to the delivery of the electrical
modulation energy at two or more of the intensity values, the
method may also include obtaining the characteristic from a stored
reference eCAP, determining one of the two or more sensed eCAPs
having the characteristic that best matches the characteristic of
the reference eCAP.
[0019] The characteristic of the reference eCAP may be a stored
threshold value. When the at least one sensed eCAP comprises one or
more eCAPs respectively sensed in response to the delivery of the
electrical modulation energy at each of two or more of the
intensity values, the method may also comprise determining a
function of the one or more sensed eCAPs having the characteristic
that equals or exceeds the threshold value.
[0020] The method may also include storing a list of reference
eCAPs characteristics, each of which is indicative of a perception
threshold when the patient is engaged in a particular physical
activity and/or posture, identifying a physical activity and/or
posture in which the patient is currently engaged, and selecting,
from the list of reference eCAP characteristics, the reference eCAP
characteristic corresponding to the identified physical activity
and/or posture, and comparing the characteristic of each of the at
least one sensed eCAP to the selected reference eCAP.
[0021] The event may be an identified physical activity and/or
posture, a user-initiated signal, a signal indicating migration of
an electrode from which the electrical modulation energy is
delivered, and a predetermined periodically recurring signal. The
user-initiated signal may be generated by an external control
device in some methods.
[0022] The computed function may be percentage of the selected
intensity value. The percentage may be in the range of 10%-90%,
40%-60%, or 30%-70%. In another method, the computed function may
be a difference between the selected intensity value and a
constant.
[0023] In accordance with a second aspect of the present
inventions, a neuromodulation system for use with a patient is
provided. The neuromodulation system comprises a plurality of
electrical terminals configured to be respectively coupled to a
plurality of electrodes implanted within a target tissue site,
modulation output circuitry coupled to the plurality of electrical
terminals to deliver electrical modulation energy to the target
tissue site of the patient at a programmed intensity value, thereby
providing therapy to the patient without the perception of
paresthesia, monitoring circuitry coupled to the plurality of
electrical terminals, control/processing circuitry configured to
direct, in response to an event, the modulation output circuitry to
deliver electrical modulation energy at a series of incrementally
increasing intensity values relative to the programmed intensity
value, prompt the modulation output circuitry to evoke at least one
compound action potential (CAP) in a population of neurons in the
target tissue site of the patient in response to the delivery of
the electrical modulation energy at the series of incrementally
increased intensity values, prompt the monitoring circuitry to
sense the at least one evoked CAP (eCAP), select one of the series
of incrementally increased intensity values based on the at least
one sensed eCAP, automatically compute a decreased value as a
function of the selected intensity value, and direct the modulation
output circuitry to deliver electrical modulation energy to the
target tissue site of the patient at the computed intensity
value.
[0024] In one embodiment, the selected intensity value corresponds
to the intensity value of the delivered electrical modulation
energy in response to which a first one of the at least one eCAP is
sensed.
[0025] In another embodiment, the neuromodulation system further
comprises a memory configured to store at least one characteristic
of a reference eCAP indicative of a perception threshold. The
controller/processing circuitry may be further configured to
compare a characteristic of each of the at least one sensed eCAP to
a corresponding characteristic of a reference eCAP, and select one
of the series of incrementally increased intensity values based on
the comparison. The characteristic of the each sensed eCAP may be
at least one a peak delay, width, amplitude and waveform
morphology.
[0026] When the sensed eCAP comprises two or more eCAPs
respectively sensed in response to the delivery of the electrical
modulation energy at two or more of the intensity values, the
control/processing circuitry may be further configured to obtain
the characteristic from a stored reference eCAP, determine one of
the two or more sensed eCAPs having the characteristic that best
matches the characteristic of the reference eCAP, and select the
intensity value of the delivered electrical modulation energy in
response to which the determined eCAP is sensed.
[0027] When the at least one sensed eCAP comprises one or more
eCAPs respectively sensed in response to the delivery of the
electrical modulation energy at each of two or more of the
intensity values, the control/processing circuitry may be further
configured to determine a function of the one or more sensed eCAPs
having the characteristic that equals or exceeds the threshold
value and select the intensity value of the delivered electrical
modulation energy in response to which the determined one or more
eCAPs is sensed.
[0028] In another embodiment, the memory may be further configured
to store a list of reference eCAP characteristics, each of which is
indicative of a perception threshold when the patient is engaged in
a particular physical activity and/or posture. The
control/processing circuitry may be further configured to identify
a physical activity and/or posture in which the patient is
currently engaged, and select, from the list of reference eCAP
characteristics, the reference eCAP characteristic corresponding to
the identified physical activity and/or posture, and compare the
characteristic of each of the at least one sensed eCAP to the
selected reference eCAP.
[0029] 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
[0030] 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:
[0031] FIG. 1 is a plan view of a Spinal Cord Modulation (SCM)
system constructed in accordance with one embodiment of the present
inventions;
[0032] FIG. 2 is a profile view of an implantable pulse generator
(IPG) used in the SCM system of FIG. 1;
[0033] FIG. 3 is a plan view of the SCM system of FIG. 1 in use
with a patient;
[0034] FIG. 4 is a block diagram of the internal components of the
IPG of FIG. 2; and
[0035] FIG. 5 is a flow diagram illustrating one method performed
by the IPG of FIG. 2 to compute a suitable amplitude for
sub-threshold modulation therapy.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0036] The description that follows relates to a spinal cord
modulation (SCM) system. However, it is to be understood that the
while the invention lends itself well to applications in SCM, 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.
[0037] Turning first to FIG. 1, an exemplary SCM system 10
generally includes a plurality (in this case, two) of implantable
neuromodulation leads 12, an implantable pulse generator (IPG) 14,
an external remote controller RC 16, a clinician's programmer (CP)
18, an external trial modulator (ETM) 20, and an external charger
22.
[0038] The IPG 14 is physically connected via one or more
percutaneous lead extensions 24 to the neuromodulation leads 12,
which carry a plurality of electrodes 26 arranged in an array. In
the illustrated embodiment, the neuromodulation leads 12 are
percutaneous leads, and to this end, the electrodes 26 are arranged
in-line along the neuromodulation leads 12. The number of
neuromodulation leads 12 illustrated is two, although any suitable
number of neuromodulation leads 12 can be provided, including only
one. Alternatively, a surgical paddle lead in can be used in place
of one or more of the percutaneous leads. As will be described in
further detail below, the IPG 14 includes pulse generation
circuitry that delivers electrical modulation 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
modulation parameters.
[0039] The ETM 20 may also be physically connected via the
percutaneous lead extensions 28 and external cable 30 to the
neuromodulation leads 12. The ETM 20, which has similar pulse
generation circuitry as the IPG 14, also delivers electrical
modulation energy in the form of a pulse electrical waveform to the
electrode array 26 accordance with a set of modulation parameters.
The major difference between the ETM 20 and the IPG 14 is that the
ETM 20 is a non-implantable device that is used on a trial basis
after the neuromodulation leads 12 have been implanted and prior to
implantation of the IPG 14, to test the responsiveness of the
modulation that is to be provided. Thus, any functions described
herein with respect to the IPG 14 can likewise be performed with
respect to the ETM 20. For purposes of brevity, the details of the
ETM 20 will not be described herein.
[0040] The RC 16 may be used to telemetrically control the ETM 20
via a bi-directional RF communications link 32. Once the IPG 14 and
neuromodulation 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 modulation parameter
sets. The IPG 14 may also be operated to modify the programmed
modulation parameters to actively control the characteristics of
the electrical modulation energy output by the IPG 14. As will be
described in further detail below, the CP 18 provides clinician
detailed modulation parameters for programming the IPG 14 and ETM
20 in the operating room and in follow-up sessions.
[0041] The CP 18 may perform this function by indirectly
communicating with the IPG 14 or ETM 20, through the RC 16, via an
IR communications link 36. Alternatively, the CP 18 may directly
communicate with the IPG 14 or ETM 20 via an RF communications link
(not shown). The clinician detailed modulation parameters provided
by the CP 18 are also used to program the RC 16, so that the
modulation 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).
[0042] The external charger 22 is a portable device used to
transcutaneously charge the IPG 14 via an inductive link 38. Once
the IPG 14 has been programmed, and its power source has been
charged by the external charger 22 or otherwise replenished, the
IPG 14 may function as programmed without the RC 16 or CP 18 being
present.
[0043] For purposes of brevity, the details of the RC 16, CP 18,
ETM 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.
[0044] Referring now to FIG. 2, the external features of exemplary
neuromodulation leads 12 and the IPG 14 will be briefly described.
One of the neuromodulation leads 12(1) has eight electrodes 26
(labeled E1-E8), and the other neuromodulation lead 12(2) has eight
electrodes 26 (labeled E9-E16). Of course, the number and shape of
the leads and the electrodes may vary based on the intended
application of the neuromodulation system. Further details
describing the construction and method of manufacturing
percutaneous neuromodulation leads are disclosed in U.S. Pat. No.
8,019,439, entitled "Lead Assembly and Method of Making Same," and
U.S. Pat. No. 7,650,184, entitled "Cylindrical Multi-Contact
Electrode Lead for Neural Stimulation and Method of Making Same,"
which are expressly incorporated herein by reference. In some
embodiments, a surgical paddle lead can be utilized, the details of
which are disclosed in U.S. Patent Publication. No. 2007/0150036
A1, entitled "Stimulator Leads and Methods for Lead Fabrication and
2012/0059446 A1 entitled Collapsible/Expandable Tubular Electrode
Leads," which is expressly incorporated herein by reference.
[0045] The IPG 14 comprises an outer case 40 for housing the
electronic and other components (described in further detail
below), and a connector 42 to which the proximal ends of the
neuromodulation leads 12 mate in a manner that electrically couples
the electrodes 26 to the electronics within the outer case 40. The
outer case 40 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 40
may serve as an electrode.
[0046] The IPG 14 includes a pulse generation circuitry that
provides electrical modulation energy to the electrodes 26 in
accordance with a set of modulation parameters. Such parameters may
include electrode combinations, which define the electrodes that
are activated as anodes (positive), cathodes (negative), and turned
off (zero). The modulation parameters may further include pulse
amplitude (measured in milliamps or volts depending on whether the
IPG 14 supplies constant current or constant voltage to the
electrodes), pulse width (measured in microseconds), pulse rate
(measured in pulses per second), duty cycle (pulse width divided by
cycle duration), burst rate (measured as the modulation energy on
duration X and modulation energy off duration Y), and pulse
shape.
[0047] With respect to the pulse patterns provided during operation
of the system 10, electrodes that are selected to transmit or
receive electrical energy are referred to herein as"activated,"
while electrodes that are not selected to transmit or receive
electrical energy are referred to herein as "non-activated."
Electrical energy delivery will occur between two (or more)
electrodes, one of which may be the IPG outer case 40. Electrical
energy may be transmitted to the tissue in a monopolar or
multipolar (for example, bipolar, tripolar and similar
configurations) fashion or by any other means available.
[0048] The IPG 14 may be operated in either a super-threshold
delivery mode or a sub-threshold delivery mode. While in the
super-threshold delivery mode, the IPG 14 is configured for
delivering electrical modulation energy that provides
super-threshold therapy to the patient (in this case, causes the
patient to perceive paresthesia). For example, an exemplary
super-threshold pulse train may be delivered at a relatively high
pulse amplitude (e.g., 5 ma), a relatively low pulse rate (e.g.,
less than 1500 Hz, preferably less than 500 Hz), and a relatively
high pulse width (e.g., greater than 100 .mu.s, preferably greater
than 200 .mu.s).
[0049] While in the sub-threshold delivery mode, the IPG 14 is
configured for delivering electrical modulation energy that
provides sub-threshold therapy to the patient (in this case, does
not cause the patient to perceive paresthesia). For example, an
exemplary sub-threshold pulse train may be delivered at a
relatively low pulse amplitude (e.g., 2.5 ma), a relatively high
pulse rate (e.g., greater than 1500 Hz, preferably greater than
2500 Hz), and a relatively low pulse width (e.g., less than 100
.mu.s, preferably less than 50 .mu.s).
[0050] As shown in FIG. 3, the neuromodulation leads 12 are
implanted within the spinal column 46 of a patient 48. The
preferred placement of the neuromodulation leads 12 is adjacent,
i.e., resting near, or upon the dura, adjacent to the spinal cord
area to be stimulated. The neuromodulation leads 12 will be located
in a vertebral position that depends upon the location and
distribution of the chronic pain. For example, if the chronic pain
is in the lower back or legs, the neuromodulation leads 12 may be
located in the mid- to low-thoracic region (e.g., at the T9-12
vertebral levels). Due to the lack of space near the location where
the neuromodulation leads 12 exits the spinal column 46, 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.
[0051] More significant to the present inventions, because
sub-threshold therapy does not produce paresthesia, it is important
to continuously monitor the sub-threshold modulation energy to
ensure that the patient is receiving optimal treatment. To this
end, the IPG 14 is configured to automatically initiate calibration
of sub-threshold therapy that may have fallen outside of the
therapeutic range. The goal of the calibration process is to
determine a perception threshold, and then compute a decreased
intensity value as a function of the perception threshold to be
used in sub-threshold modulation therapy.
[0052] In the illustrated embodiment, initiation of the calibration
process may be triggered by a particular event, such as, e.g., a
user actuation of a control element located on the RC 16 or CP, a
sensor signal indicating that one or more of the neuromodulation
leads 12 has migrated relative to a target site in the patient, a
sensor signal indicating that the patient's physical activity
and/or posture has changed relative to a previous physical activity
and/or posture, or a periodically recurring signal generated in
response to an elapsed time, a time of day, day of the week,
etc.
[0053] Once the sub-threshold calibration is initiated, the SCM
system 10 delivers the modulation output energy to the electrodes
26 at incrementally increasing intensity values, such as amplitude
values (e.g., amplitude at a 0.1 mA step size). Preferably, if the
amplitude values are incrementally increased, the other modulation
parameters, such as the electrode combination, pulse rate, and
pulse width are not altered during the incremental increase of the
amplitude. Thus, the only modulation parameter of the sub-threshold
modulation program that is altered is the pulse amplitude. In the
instance in which the intensity value is pulse width (e.g., at a 10
.mu.s step size), the only modulation parameter of the
sub-threshold modulation program that is altered in pulse
width.
[0054] In response to the delivered electrical modulation energy at
the incrementally increasing intensity values, at least one
compound action potential (CAP) is evoked by the modulation of
neural tissue at the target tissue site. An evoked CAP (eCAP) is
the simultaneous evoking of action potentials traveling down a
population of neurons. Thus, the total magnitude of the eCAP is
proportional to the number of neurons that are carrying action
potentials, and therefore, may function as a clinical measurement
as to the intensity level (i.e., strength of the conveyed
electrical modulation energy), which is both the dose of therapy
that is used to decrease the pain in the patient, and the
physiological signal that causes the patient to perceive either
comfortable paresthesia, painful overstimulation, or lack of
stimulation. Significantly, the eCAP(s) (which in some cases, may
only be one eCAP, and in other cases may be several eCAPs) are used
as indicators of the perception threshold of the patient. To this
end, the SCM system 10 senses and measures these eCAP(s), the
characteristics of which may be used to ultimately determine a
suitable intensity for sub-threshold modulation therapy, as will be
described in further detail below.
[0055] To determine the perception threshold, the SCM system 10
evaluates the measured eCAP(s) and selects intensity value
corresponding to at least one of the measured eCAP(s) as the
perception threshold.
[0056] In one embodiment, the SCM system 10 may automatically
select the amplitude value at which a first eCAP is sensed as the
perception threshold. For example, when the amplitude of the
delivered electrical modulation energy is incrementally increased,
the first eCAP may be sensed at 5.1 mA. Thus, the SCM system 10 may
select the amplitude value corresponding to 5.1 mA as the
perception threshold.
[0057] Alternatively, the SCM system 10 may automatically select
the amplitude value based on a comparison between the measured
eCAPs and a reference eCAP indicative of the perception threshold.
The reference eCAP, which may be determined empirically, captures
the characteristics of an eCAP at the amplitude of the delivered
electrical modulation energy at which the patient felt paresthesia
(the perception threshold). This reference eCAP (or a
characteristic or characteristics of the reference eCAP) may then
be used to compare the eCAP(s) (or characteristics of the eCAPs)
measured in response to the delivery of the electrical modulation
energy during the calibration process. The characteristics of the
eCAP may include, e.g., amplitude, peak delay, width, as well as
waveform morphology.
[0058] For example, in one technique, the SCM system 10 may compare
a waveform morphology of the measured eCAP to the waveform
morphology of the reference eCAP to select the eCAP whose waveform
morphology most closely resembles that of the reference eCAP. Thus,
the amplitude of the delivered energy that resulted in the eCAP
that most closely resembles the reference eCAP is determined to be
the perception threshold.
[0059] In another technique, the SCM system 10 may store a
particular characteristic of the reference eCAP as a threshold
value to be used in determining the perception threshold. In this
case, the SCM system 10 may compare a value of a selected
characteristic of the measured eCAP to the stored threshold value.
In one example, the threshold value may simply be the amplitude of
the reference eCAP. In such a case, when the amplitude of a
measured eCAP is equal to or greater than the threshold value, the
amplitude of the delivered energy that resulted in that measured
eCAP is determined to be the perception threshold. In another
example, the threshold value may be the peak delay of the reference
eCAP, such that when the peak delay of a measured eCAP is equal to
or greater than the threshold value, the amplitude of the delivered
energy that resulted in that measured eCAP is determined to be the
perception threshold. In yet another example, the threshold value
may be width of the reference eCAP, such that when the width of a
measured eCAP is equal to or greater than the threshold value, the
amplitude of the delivered energy that resulted in that measured
eCAP is determined to be the perception threshold.
[0060] Although the previous examples have been focused on
comparing a characteristic of a single eCAP to the reference eCAP,
it should be appreciated that a function of characteristic(s) of
multiple eCAP measurements may be compared to the reference eCAP.
That is, because multiple eCAPs may be measured in response to the
corresponding pulses in the electrical pulse train delivered at a
specific amplitude value, a function (e.g., an average) of a
characteristic of these eCAPs may be compared to the reference
eCAP. This can be particularly useful in increasing the
signal-to-noise ratio. For example, assume that an electrical pulse
train comprises ten pulses in response to which ten eCAP
measurements are respectively made. When the amplitude of the
electrical pulse train is high enough, or close to that of the
perception threshold, ten eCAPs may be measured in response to the
ten pulses. Any one of these measured eCAPs will thus be truly
indicative of the perception threshold. When the amplitude of the
electrical pulse train is at a lower level, however, only one CAP
may be evoked in response to the ten pulses and the other nine of
the eCAP measurements may be zero. This one measured eCAP will thus
not be indicative of the perception threshold.
[0061] To avoid such anomalies that may be caused by noise and/or
system errors, an average of all the eCAP measurements at a
particular amplitude value may render more accurate results than
using individual eCAP measurements. It should be appreciated that
the signal-to-noise ratio is reduced when a higher number of eCAP
measured are used for comparison, bringing the average of the eCAP
measurements closer to the true indication of whether or not the
perception threshold has been reached. Thus, to increase the
signal-to-noise ratio, the average of the eCAP measurements for
each amplitude value of the delivered electrical pulse train may be
compared to the reference eCAP. For example, if the average of all
the eCAP measurements made in response to an electrical pulse train
of a particular amplitude value equal or exceed the threshold
value, that amplitude value is determined to be the perception
threshold.
[0062] Although in the previous embodiments, only one reference
eCAP is described as being stored, multiple reference eCAPs from
which one reference eCAP can be selected for comparison can be
stored. For example, in one embodiment, the SCM system 10 may store
a list of reference eCAPs associated with a set of patient
activities and/or postures. The perception threshold and
corresponding reference eCAP may be different when the patient is
walking as compared to when the patient is lying down, or sitting.
These reference eCAPs, which are indicative of perception
thresholds when the patient is engaged in a particular activity
and/or posture, may be determined empirically and recorded. For
example, each physical activity and/or posture may be characterized
in the laboratory for each individual patient to generate a
personalized look-up table that correlates the physical activity
and/or posture with a reference eCAP. The SCM system 10 is
configured to identify the physical activity and/or posture of the
patient, as will be described below, and select the appropriate
reference eCAP for comparison with the measured eCAP(s).
[0063] There may be many ways to identify the physical activity
and/or posture of the patient. In one technique, the patient's
physical activity and/or posture may be tracked and identified by
measuring electrical parameter data (i.e., interelectrode impedance
and/or measured field potentials) and performing time-varying
analysis on the measured electrical parameter data, as disclosed in
U.S. Patent Publication. No. 2008/0188909 A1, entitled
"Neurostimulation system and method for measuring patient
activity," which is expressly incorporated herein by reference. In
another technique, the patient's physical activity and/or posture
may be tracked and identified using an orientation sensitive device
that is implanted in the IPG 14, as described in U.S. patent
application Ser. No. 13/446,191, entitled "Sensing Device For
Indicating Posture of a Patient Implanted With a Neurostimulation
Device," which is expressly incorporated herein by reference. In
still another technique, the patient's physical activity and/or
posture may be tracked and identified by measuring characteristic
impedance waveform morphologies, as described in U.S. Pat. No.
7,317,948, which is expressly incorporated herein by reference.
[0064] It should be appreciated that the physical activity and/or
posture of the patient may be identified regardless of the nature
of the event that triggers the calibration process. Thus, the
calibration process may be initiated by an event independent from
the identification of the physical activity and/or posture, in
which case, the physical activity and/or posture is identified only
to determine the reference eCAP for comparison with the measured
eCAPs. However, the event itself may be identification of a
triggering physical activity and/or posture, in which case, the
calibration process is initiated by it in addition to helping
determine the reference eCAP. For example, the SCM system 10 might
detect that the patient is engaged in a triggering physical
activity (e.g., running) and initiate the calibration process. In
this case, the SCM system 10 is similarly configured to select the
reference eCAP associated with the identified triggering physical
activity and/or posture and compare the selected reference eCAP
with the measured eCAP(s) to determine the perception threshold.
Constantly calibrating the SCM system 10 whenever the patient
changes his posture or physical activity may prove to be rather
inefficient. Accordingly, the SCM system 10 may be provided with a
predetermined list of triggering physical activities, such that the
SCM system 10 only initiates the calibration process when a
triggering physical activity and/or posture is identified. For
example, only physical strenuous activities like running, lifting
weights, etc., may trigger calibration.
[0065] Once the perception threshold has been determined, the SCM
system 10 automatically computes a decreased amplitude for
sub-threshold modulation as a function of the perception threshold.
The function of the selected amplitude value is designed to ensure
that the modulation energy subsequently delivered to the patient at
the computed amplitude value falls within the sub-threshold therapy
range. For example, the computed function may be a percentage
(preferably in the range of 30%-70%, and more preferably in the
range of 40%-60%) of the last incrementally increased amplitude
value. As another example, the computed function may be a
difference between the last incrementally increased amplitude value
and a constant (e.g., 1 mA). The SCM system 10 is also configured
for modifying the sub-threshold modulation program stored in the
IPG 14, such that the modulation energy is delivered to the
electrodes 26 in accordance with the modified modulation program at
the computed amplitude value.
[0066] Turning next to FIG. 4, one exemplary embodiment of the IPG
14 will now be described. The IPG 14 includes modulation output
circuitry 50 configured for generating electrical modulation energy
in accordance with an electrical pulse train having a programmed
pulse amplitude, pulse rate, pulse width, duty cycle, burst rate,
and shape under control of control logic 52 over data bus 54. The
pulse rate and the duration of stimulation may be controlled by
analog circuitry, or digital timer logic circuitry 56 controlling
the analog circuitry, and which may have a suitable resolution,
e.g., 10 .mu.s. The modulation energy generated by the modulation
output circuitry 50 is output via capacitors C1-C16 to electrical
terminals 58 respectively corresponding to electrodes E1-E16.
[0067] The modulation output circuitry 50 may either include
independently controlled current sources for providing modulation
pulses of a specified and known amperage to or from the electrical
terminals 58, or independently controlled voltage sources for
providing modulation pulses of a specified and known voltage at the
electrical terminals 58 or to multiplexed current or voltage
sources that are then connected to the electrical terminals 58. The
operation of this modulation output circuitry 50, including
alternative embodiments of suitable output circuitry for performing
the same function of generating modulation pulses of a prescribed
amplitude and width, is described more fully in U.S. Pat. Nos.
6,516,227 and 6,993,384, which are expressly incorporated herein by
reference. Thus, it can be appreciated that the modulation output
circuitry 50 is capable of delivering electrical energy to the
electrodes 26 via the electrical terminals 58 at a series of
incrementally increasing amplitude values when the calibration
process is initiated, and for the purpose of evoking CAPs in the
neural tissue in response to the series of incrementally increasing
amplitude values and/or for delivering sub-threshold modulation
therapy based on the perception threshold determined through the
process of calibration.
[0068] The modulation output circuitry 50 may either include
independently controlled current sources for providing stimulation
pulses of a specified and known amperage to or from the electrical
terminals 58, or independently controlled voltage sources for
providing stimulation pulses of a specified and known voltage at
the electrical terminals 58 or to multiplexed current or voltage
sources that are then connected to the electrical terminals 58. The
operation of this modulation output circuitry 50, including
alternative embodiments of suitable output circuitry for performing
the same function of generating stimulation pulses of a prescribed
amplitude and width, is described more fully in U.S. Pat. Nos.
6,516,227 and 6,993,384, which are expressly incorporated herein by
reference.
[0069] Thus, it can be appreciated that the modulation output
circuitry 50 is capable of delivering electrical energy to the
electrodes 26 via the electrical terminals 58 for the purpose of
providing therapy to the patient and/or evoking CAPs in the neural
tissue during the calibration process described above.
[0070] The IPG 14 also includes 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. Notably, the electrodes 26 fit
snugly within the epidural space of the spinal column, and because
the tissue is conductive, electrical measurements can be taken from
the electrodes 26 in order to determine the coupling efficiency
between the respective electrode 26 and the tissue and/or to
facilitate fault detection with respect to the connection between
the electrodes 26 and the modulation output circuitry 60 of the IPG
14.
[0071] More significant to the present inventions, the monitoring
circuitry 60 is configured to measure characteristic(s) of the CAPs
evoked in response to the stimulation of neural tissue via the
modulation output circuitry 50 during the calibration process. The
evoked potential measurement technique may be performed by
generating an electrical field at one of the electrodes 26, which
is strong enough to depolarize the neurons adjacent the stimulating
electrode beyond a threshold level, thereby inducing the firing of
an eCAP that propagates along the neural fibers. Such stimulation
is preferably supra-threshold, but not uncomfortable. A suitable
stimulation pulse for this purpose is, for example, 4 mA for 200
.mu.s. While a selected one of the electrodes 26 is activated to
generate the electrical field, a selected one or ones of the
electrodes 26 (different from the activated electrode) is operated
to record a measurable deviation in the voltage caused by the
evoked potential due to the stimulation pulse at the stimulating
electrode. To the extent that other physiological information is
acquired for the purpose of triggering the modulation parameter
adjustment process, the monitoring circuitry 60 may be coupled to
various sensors. If the physiological measurements are electrical,
the sensors may be one or more of the electrodes 26. For other
types of non-electrical physiological information, however,
separate sensors may be used for appropriate measurements.
[0072] The IPG 14 further includes a control/processing circuitry
in the form of a microcontroller (.mu.C) 64 (or a processor) 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
includes memory 70 and oscillator and clock circuit 72 coupled to
the microcontroller 64.
[0073] Further, 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 modulation parameters. In controlling the
operation of the IPG 14, the microcontroller 64 is able to
individually generate electrical energy at the electrodes 26 using
the modulation 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, pulse amplitude,
pulse rate, pulse width, and pulse duty cycle through which the
electrical energy is provided. Further, the microcontroller 64
initiates the calibration process in response to the event.
[0074] The microcontroller 64 is also configured for initiating and
performing the calibration process, including directing the
modulation output circuitry 50 to deliver the electrical energy at
increasing amplitude levels, directing the monitoring circuitry 60
to sense any eCAPs in response to the delivered electrical energy,
determining the perception threshold of the patient in response to
the sensing of the eCAPs, and computing a decreased amplitude
suitable for sub-threshold modulation therapy based on the
perception threshold.
[0075] The memory 70 may store various data (e.g. modulation
parameters, reference eCAPs, threshold values, etc.) and a series
of instructions to be executed by the microcontroller 64. The
microcontroller 64, in combination with the memory 70 and
oscillator and clock circuit 72, thus include 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 control/processing functions may be carried out
by a suitable state machine.
[0076] The IPG 14 further includes an alternating current (AC)
receiving coil 74 for receiving programming data (e.g., the
operating program and/or modulation 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.
[0077] The IPG further includes a 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 modulation 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.
[0078] Notably, if the RC 16, or alternatively the CP 18, is used
to perform the automated modulation parameter adjustment technique,
the measured eCAPs can be transmitted from the IPG 14 to the RC 16
or CP 18 via the back telemetry circuitry 78 and coil 80. The RC 16
or the CP 18 may perform the necessary routine to adjust the
modulation parameters and transmit the adjusted set of modulation
parameters to the IPG 14 so that the IPG 14 can generate the
electrical modulation energy in accordance with the adjusted set of
modulation parameters.
[0079] The IPG 14 further includes 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., include 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, an external charger (not shown), 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.
[0080] 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. Pat. No. 7,539,538, 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 the IPG
14, 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 ell 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.
[0081] Turning now to FIG. 5 an exemplary method 300 of using eCAPs
to automatically compute a decreased amplitude suitable for
sub-threshold modulation therapy will be described. First, the SCM
system 10 delivers electrical modulation energy to a target tissue
of the patient in accordance with the sub-threshold modulation
program stored within the SCM system 10, thereby providing therapy
to the patient without the perception of paresthesia (step 302).
Next, a calibration triggering event occurs (step 304). As
previously discussed, such triggering event can be an identified
triggering physical activity and/or posture, a user-initiated
signal, a signal indicating electrode-migration or a predetermined
periodically recurring signal. Next, the SCM system 10 identifies
the patient's physical activity and/or posture if it has not
already been identified as a triggering event (step 306). Based on
the patient/s physical activity and/or posture, the SCM system 10
selects, from the stored list of reference eCAPs, the reference
eCAP corresponding to the identified physical activity and/or
posture (step 308).
[0082] Next, the SCM system 10 delivers an electrical pulse train
of a specified amplitude (which may initially be the programmed
amplitude at which the electrical pulse train was delivered to
provide the sub-threshold therapy), in response to which eCAP
measurements are made for at least one pulse of the delivered
electrical pulse train (step 310). To increase the signal-to-noise
ratio, an eCAP measurement may be made after each pulse. Next, the
SCM system 10 compares the eCAP measurement(s) to the selected
reference eCAP corresponding to the identified physical activity
and/or posture (step 312). As previously discussed, a
characteristic (e.g., amplitude, peak delay, width, morphology) of
an eCAP measurement or function of multiple eCAP measurements may
be compared to the same characteristic of the reference eCAP.
[0083] If the eCAP comparison reveals that the perception threshold
of the patient has not been reached (step 314), the SCM system 10
increases the amplitude of the delivered electrical energy by a
step size (step 316), and returns to making eCAP measurements) in
response to the delivered electrical energy at the increased
amplitude (step 310). If the eCAP comparison reveals that the
perception threshold of the patient has been reached (step 314),
the SCM system 10 computes a decreased amplitude value as a
function of the amplitude value indicative of the perception
threshold (step 318). As described above, such function can be,
e.g., a percentage of the determined perception threshold or a
difference between the determined perception threshold and a
constant. The SCM system 10 then modifies the sub-threshold
modulation program with the computed amplitude value (step 320) and
returns to step 302 to direct the IPG 14 to deliver electrical
modulation energy in accordance with a modified sub-threshold
modulation program, thereby providing therapy to the patient
without the perception of paresthesia.
[0084] Thus, it can be appreciated that the sub-threshold
calibration technique ensures that any intended sub-threshold
therapy remains within an efficacious and energy efficient
therapeutic window that may otherwise fall outside of this window
due to environmental changes, such as lead migration or changes in
patient's physical activity and/or posture. Although the
sub-threshold calibration technique has been described with respect
to sub-threshold therapy designed to treat chronic pain, it should
be appreciated that this calibration technique can be utilized to
calibrate any sub-threshold therapy provided to treat a patient
with any disorder where the perception of paresthesia may be
indicative of efficacious treatment of the disorder. Furthermore,
although the sub-threshold calibration technique has been described
as being performed in the IPG 14, it should be appreciated that
this technique could be performed in the CP 18, or even the RC
16.
[0085] It should also be appreciated that although the
sub-threshold calibration technique has been described with the
adjustment of the amplitude of the electrical modulation energy, it
should be appreciated that other modulation parameters that affect
the intensity of the electrical modulation energy can be varied.
For example, instead of incrementally increasing amplitude values
relative to a programmed amplitude value while maintaining the
pulse width value and pulse rate value the same, and computing a
decreased amplitude value as a function of one of the increased
amplitude values, pulse width values may be incrementally increased
relative to a programmed pulse width value while maintaining the
amplitude value and pulse rate value the same, and computing a
decreased pulse width value as a function of one of the increased
pulse width value. The significance is that a parameter that
directly effects the intensity of the electrical modulation energy
in a controllable and predictable fashion is used to calibrate the
sub-threshold therapy.
[0086] 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.
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