U.S. patent application number 15/173404 was filed with the patent office on 2016-09-29 for implantable stimulation device, stimulation system and method for data communication.
This patent application is currently assigned to BIOTRONIK SE & CO. KG. The applicant listed for this patent is BIOTRONIK SE & CO. KG. Invention is credited to Marcelo BARU, J. Christopher MOULDER.
Application Number | 20160279430 15/173404 |
Document ID | / |
Family ID | 50000831 |
Filed Date | 2016-09-29 |
United States Patent
Application |
20160279430 |
Kind Code |
A1 |
BARU; Marcelo ; et
al. |
September 29, 2016 |
IMPLANTABLE STIMULATION DEVICE, STIMULATION SYSTEM AND METHOD FOR
DATA COMMUNICATION
Abstract
An implantable stimulation device including a stimulation module
and a data communication module. The stimulation device includes
electrodes to delivery stimulation pulses, a voltage source, a
DC-blocking capacitor and autoshort switch. The voltage source is
connected to the electrodes via stimulation-pulse-switch(s) that
controls delivery pacing pulses. The DC-blocking capacitor is
connected with the voltage source and an electrode. The autoshort
switch allows discharging of the DC-blocking capacitor via the
electrodes when closed. The data communication module includes a
data transmission control module connected to the autoshort switch
and/or the at least one stimulation-pulse-switch, to alternatingly
open and close the autoshort switch or the at least one
stimulation-pulse-switch respectively, during an autoshort period
following the delivery of a stimulation pulse or during a
stimulation pulse period, respectively, to modulate an autoshort
pulse or a stimulation pulse peak amplitude, respectively.
Inventors: |
BARU; Marcelo; (Tualatin,
OR) ; MOULDER; J. Christopher; (Portland,
OR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BIOTRONIK SE & CO. KG |
Berlin |
|
DE |
|
|
Assignee: |
BIOTRONIK SE & CO. KG
Berlin
DE
|
Family ID: |
50000831 |
Appl. No.: |
15/173404 |
Filed: |
June 3, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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14176027 |
Feb 7, 2014 |
9375581 |
|
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15173404 |
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61761707 |
Feb 7, 2013 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61N 1/3727 20130101;
A61N 1/37217 20130101; A61N 1/37276 20130101; A61N 1/3708 20130101;
A61N 1/378 20130101 |
International
Class: |
A61N 1/372 20060101
A61N001/372; A61N 1/37 20060101 A61N001/37 |
Claims
1. A method of communicating data from an implantable stimulation
device, said method comprising: altering a local electric field in
a body using an implantable stimulation device, by modulating one
of an autoshort pulse or a stimulation pulse amplitude delivered by
the implantable stimulation device; wherein said implantable
stimulation device comprises at least one stimulation module; at
least two electrodes configured to allow delivery of stimulation
pulses; and, at least one data communication module; wherein said
at least one stimulation module comprises a voltage source, wherein
said voltage source is configured to connect to the at least two
electrodes via at least one stimulation-pulse-switch that is
configured to control delivery of a pacing pulse, at least one
DC-blocking capacitor connected in series with the voltage source
and the at least two electrodes, and an autoshort switch configured
to allow discharging of the at least one DC-blocking capacitor via
the at least two electrodes when the autoshort switch is closed;
wherein said at least one data communication module comprises at
least one data transmission control module connected to the
autoshort switch; and, sensing the change of the local electric
field caused by the modulation of one of the autoshort pulse or the
stimulation pulse amplitude, respectively, using an external device
comprising at least two cutaneous electrodes; wherein the external
device further comprises at least one sensor module configured to
sense one or more of alterations of body impedance and the local
electric field generated by the implantable stimulation device.
2. The method according to claim 1, wherein the step of altering
the local electric field using the implantable stimulation device
comprises alternatingly opening and closing the autoshort switch or
the stimulation-pulse-switch, respectively, during an autoshort
period following the delivery of a stimulation pulse or during a
stimulation pulse period, respectively, to modulate an autoshort
pulse or a stimulation pulse amplitude, respectively using said at
least one data communication module.
3. The method according to claim 1, wherein an oscillatory electric
field is imposed to the body using the external device comprising
at least two cutaneous electrodes.
4. The method according to claim 3, wherein the step of sensing the
change of a local electric field comprises sensing a current or
voltage over the at least two cutaneous electrodes and integrating
a sensed voltage or current over a number of cycles of the
oscillatory electric field, wherein said number of cycles
correspond to a frequency division factor of a frequency divider of
the implantable stimulation device.
5. The method according to claim 3, further comprising sensing the
oscillatory electric field that is imposed to the body using the
implantable stimulation device.
6. The method according to claim 1, wherein said at least one data
communication module is controlled to modulate one or more of a
stimulation pulse amplitude or an autoshort pulse to a
code-representing data, and wherein said code-representing data is
transmitted from the implantable stimulation device to the external
device.
7. The method according to claim 1, wherein the modulating of the
stimulation pulse amplitude comprises amplitude changes without a
return to a baseline amplitude.
8. The method according to claim 1, further comprising modulating
balancing of residual charge from said pacing pulse during an
autoshort period following the delivery of the stimulation pulse to
effect communication.
9. The method according to claim 8, wherein the residual charges
that are modulated create a change in the local electrical field
around the implantable stimulation device that cause voltage
changes, and wherein the external device is configured to sense
said voltage changes.
10. The method according to claim 1, wherein said external device
further comprises a receiving lock-in amplifier, and further
comprising modulating a charge present following the delivery of
the stimulation pulse to cause the local electric field to change
within a frequency range of the receiving lock-in amplifier, and
wherein the change of the local electrical field causes
communication.
11. The method according to claim 1, wherein said external device
is configured to impart an oscillatory electric field on the body
to create a carrier for said implantable stimulation device used to
transmit data.
12. The method according to claim 11, further comprising sensing
said oscillatory electric field by said implantable stimulation
device and activating data communication by said implantable
stimulation device upon sensing said oscillatory electric
field.
13. The method according to claim 1, wherein the at least one data
communication module is connected to the at least two electrodes
and is further configured to sense an oscillatory electric field
imposed on body tissue surrounding the implantable stimulation
device.
14. The method according to claim 1, wherein the data communication
module further comprises a phase-locked loop (PLL) and a frequency
divider, wherein the phase-locked loop is configured to lock in a
frequency of the oscillatory electric field imposed on body tissue
surrounding the implantable stimulation device, and wherein the
frequency divider is configured to connect to the phase-locked loop
and divide a frequency signal put out by the phase-locked loop
Description
[0001] This application is a divisional application of U.S. patent
application Ser. No. 14/176,027, filed on 7 Feb. 2014, which claims
the benefit of U.S. Provisional Patent Application 61/761,707,
filed on 7 Feb. 2013, and U.S. Provisional Patent Application
61/906,902, filed on 21 Nov. 2013, the specifications of which are
hereby incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] Embodiments of the invention generally relate to implantable
medical devices and more particularly to communication techniques
to transmit data from the implanted medical device to an external
programmer.
[0004] 2. Description of the Related Art
[0005] Typically, implantable medical devices, in particular
implantable stimulation devices, such as implantable therapy and/or
monitoring devices including pacemakers, cardioverters and
defibrillators or the like, may include data communication means to
transmit data from the implantable stimulation device to an
external device, such as a device external to the body, or vice
versa.
[0006] Generally, a system for data communication with an
implantable stimulation device thus may include an implantable
stimulation device and an external device such as a programmer.
[0007] A typical implantable stimulation device includes a battery,
a monitoring and/or therapy control unit, and in some cases one or
more therapy units such as stimulation modules, and a memory for
storing control program and/or data sensed by the implantable
stimulation device. If the implantable stimulation device is a
pacemaker or an implantable cardioverter/defibrillator (ICD),
generally, the therapy units include stimulation (pacing) units for
generating and delivering electric stimulation pulses to a
patient's heart tissue (myocardium). Often, sensing units for
sensing cardiac activity are provided. Sensing units may often
process electrical signals that represent electrical potentials
that may be picked up via electrodes, e.g., in the heart.
[0008] In order to transmit data acquired by the implantable
stimulation device to an external device or to other implanted
devices, generally, a telemetry unit may be provided. Typically,
the telemetry unit may allow a bidirectional data communication,
that is, the telemetry unit may transmit and receive data
wirelessly.
[0009] Limited battery capacity of an implantable stimulation
device often calls for energy-efficient data communication. An
implantable stimulation device with limited battery power typically
requires a low-power communication scheme in order to program it
and to download acquired data. With extremely low-power
communication, generally, more data can be transmitted more
often.
[0010] Typically, the implantable stimulation device must source
all of the energy required for transmitting data in all of the
communication solutions disclosed in prior art. Pulses generated
for data transmission generally use either current or voltage to
create an electric field that is sensed at the receiver. Thus, the
receiver often passively decodes the communication and the
transmitter often uses sufficient energy to enable the receiver to
sense the signal. This arrangement is often detrimental to
extremely low-power devices, such as intracardiac leadless
pacemakers (iLP). The available energy for these devices is
generally extremely limited making high-energy pulses problematic.
Typically, the pulses for data transmission must generally be
sub-threshold because clinical complications could occur if
communication caused capturing of surrounding tissue, e.g.
myocardium of the heart. To reduce the possibility of capturing the
heart, generally, very short transmission windows must be used to
limit communication during times when the heart is refractory to
stimulation. These reduced communication times often precipitate
the use of high-data transmission rates that subsequently require
higher clock rates for the implantable device. The higher clock
rates generally complicate design and increase power
consumption.
[0011] Typical communication schemes utilize sub-threshold pulses
to galvanically transmit data to another device. When
supra-threshold pulses are used, generally, the data is encoded
within the pulse itself. The information in either case is often
transmitted by pulses that are received and decoded. Typically, the
electric field generated by the pulses is detected at the receiver,
where all of the energy required for transmission is generated at
the transmitter.
[0012] United States Patent Publication 2012/0078322 to Molin et
al., entitled "Apparatus And Methods For Wireless Communication Via
Electrical Pulses Conducted By The Interstitial Tissue Of The Body
For An Active Implantable Medical Device", discloses the use of
biphasic pulses to maintain charge balancing while
communicating.
[0013] U.S. Pat. No. 8,412,352 to Griswold et al., entitled
"Communication Dipole For Implantable Medical Device", discloses a
device where the fixation mechanism is also connected to the
communications module. The module of Griswold et al. uses electric
pulses to communicate with another device.
[0014] U.S. Pat. No. 7,945,333 to Jacobson, entitled "Programmer
For Biostimulator System", discloses the combination of a
programmer and an implantable device that communicate using encoded
pulses. According to Jacobson, these pulses are described as
modulated pacing pulses. Thus, if the data is encoded on pacing
pulses then supra-threshold pulses are used.
[0015] Other typical communication schemes used for data
communication by a telemetry unit involve either RF or magnetic
communication. RF frequencies of .about.400 or .about.900 MHz or
magnetic coupling in the 100s of kHz range generally require
several mA of current to transmit and receive data. Such high
current requirements are typically out of reach of devices with
battery capacities of at most a few hundred mAh.
[0016] In addition, typical RF schemes require large antennas and
magnetic coupling requires large transmit and receive coils for
communication. Generally, the space available in an iLP
(intracardiac leadless pacer), for instance, would not allow such
large coils or antennas. iLPs are often designed to be placed
within a heart chamber as opposite to conventional pacemakers,
where the pacemaker itself is placed outside the heart and
electrode leads extend from the pacemaker into the heart.
[0017] U.S. Pat. No. 6,704,602 to Berg et al., entitled "Implanted
Medical Device/External Medical Instrument Communication Utilizing
Surface Electrodes", discloses a medical device communication
system using sub-threshold pulses for electrical communication with
external devices. The medical device communication system of Berg
et al. includes an implantable medical device and external devices.
The external devices may be connected to the skin of a body with a
plurality of electrodes. The implantable medical device includes
stimulation electrodes, surface electrodes in contact with tissue
of a patient, and a can including a pulse generation circuit. The
reference also discloses an electrode switching circuit coupled to
the pulse generation circuit and serves to deliver electrical
stimulation pulses to the stimulation electrodes as therapy to a
patient. Furthermore, Berg et al. discloses wherein the electrode
switching circuit also serves to deliver subthreshold pulses to the
surface electrodes of the can in a predetermined pattern of
modulations constituting an encoded data signal that propagates as
a signal transmission through the patient tissue. According to Berg
et al., the plurality of electrodes connected to the external
device serve to receive the sub-threshold pulses and allow the
external device to detect the encoded data signal.
[0018] For example, United States Patent Publication 2012/0109236
to Jacobson et al., entitled "Leadless Cardiac Pacemaker With
Conducted Communication", discloses a system for pacing a heart of
a human including a leadless pacemaker in a hermetic housing with
at least two electrodes and at least one external device with at
least two skin electrodes. The electrodes of Jacobson et al. appear
to deliver energy to stimulate a heart and to transfer information
to or from the skin electrodes of the external devices. The
information in Jacobson et al. is preferably encoded in
sub-threshold pulses delivered by the electrodes and generated by a
pulse generator in the housing of the leadless pacemaker. According
to Jacobson et al., the hermetic housing of the leadless pacemaker
may further comprise a controller configured to communicate with
the external devices by transferring information through the
electrodes. Jacobson et al. also discloses wherein the controller
may be configured to communicate with the external devices outside
of a refractory period or pacing pulse.
[0019] In view of the above, there is a need for a communication
scheme with an implantable device that does not employ RF or
magnetic coupling.
BRIEF SUMMARY OF THE INVENTION
[0020] One or more embodiments of the invention are related to an
alternative implantable stimulation device and an alternative data
communication system and method that minimizes battery drain from
the implantable stimulation device's battery.
[0021] At least one embodiment of the invention may include an
implantable stimulation device, which includes at least one
stimulation module and at least one data communication module. In
one or more embodiments, the at least one stimulation module may
include or may be connected to at least two electrodes that may
allow delivery of stimulation pulses. By way of at least one
embodiment, the at least one stimulation module may include one or
more of: [0022] a voltage source that may be connected to the at
least two electrodes via at least one stimulation-pulse-switch that
may control delivery of a pacing pulse, [0023] a DC-blocking
capacitor that may be connected in series with the voltage source
and one of the at least two electrodes, and [0024] an autoshort
switch that may allow discharging of the DC-blocking capacitor via
the at least two electrodes when the autoshort switch is
closed.
[0025] According to one or more embodiments, the at least one data
communication module may include at least one data transmission
control module that may be connected to the autoshort switch and/or
to the stimulation-pulse-switch. In at least one embodiment, the at
least one data transmission control module may alternatingly open
and close the autoshort switch during an autoshort period following
the delivery of a stimulation pulse to thus modulate a autoshort
pulse. In at least one embodiment, the at least one data
transmission control module may alternatingly open and close the at
least one stimulation-pulse-switch during the delivery of a
stimulation pulse or during a stimulation pulse period to thus
modulate a stimulation pulse.
[0026] In one or more embodiments the voltage source may include a
capacitor that may be charged prior to delivery of a stimulation
pulse for pacing a human heart. A blocking capacitor, in at least
one embodiment, may be provided to block delivery of DC-voltage to
the tissue to be stimulated.
[0027] One or more embodiments of the invention may allow an
implantable stimulation device with limited battery supply the
ability to transmit increased amount of data while using reduced
power. In at least one embodiment, data transmission may be
achieved by modulating a local electric field generated by the
implantable stimulation device and read by the receiver. Continuous
medium rate data transmission, in at least one embodiment, may be
achieved while using reduced battery power.
[0028] By way of one or more embodiments, the at least one data
communication module may sense an oscillatory electric field
imposed on body tissue surrounding the implantable stimulation
device when the implantable stimulation device is in its implanted
state. Thus, in at least one embodiment, it is possible to
synchronize switching of the autoshort switch and/or the
stimulation-pulse-switch with the oscillatory electric field
imposed on the body tissue surrounding or encompassing the
implantable stimulation device. The synchronization may be phase
synchronized. In one or more embodiments, data communication of the
implantable medical device is activated upon sensing an oscillatory
electric field.
[0029] To implement synchronizing, according to one or more
embodiments of the invention, the data communication module may
include a phase-locked loop (PLL) and a frequency divider, wherein
the PLL may lock in a frequency of an oscillatory electric field
imposed on body tissue surrounding the implantable stimulation
device when the implantable stimulation device is in its implanted
state. The frequency divider, in at least one embodiment, may be
connected to the PLL and may divide a frequency signal put out by
the PLL. Thus, in one or more embodiments of the invention, the
implantable stimulation device may generate a code that may
represent data to be transmitted from the implantable stimulation
device to an external device. In one or more embodiments, a clock
for such code may be provided and may be a fraction of the
frequency of the oscillatory electric field imposed on the body
tissue surrounding the implantable stimulation device. The clock
frequency, in at least one embodiment, may be in a range of 0.1 to
50 kHz, such as a range of 1 to 20 kHz, more preferably in a range
of 7 to 9 kHz, and most preferably the clock frequency is 8
kHz.
[0030] According to at least one embodiment, the data communication
module may be connected to the at least two electrodes and may
sense an oscillatory electric field imposed on body tissue via the
at least two electrodes. The data communication module, in at least
one embodiment, may include a band-pass filter, wherein the
band-pass filter may filter a signal fed to the phase-locked
loop.
[0031] One or more embodiments of the invention may include a data
communication system including an implantable stimulation device as
described above and an external device that may include or may be
connected to at least two cutaneous electrodes. The external
device, in at least one embodiment, may include at least one
external field generating module that may generate an oscillatory
electric field to be transcutaneously imposed on the body via the
at least two cutaneous electrodes. In one or more embodiments, the
external device may include at least one sensor module that may
sense alterations of body impedance and/or a local electric field
generated by the implantable stimulation device when the
implantable stimulation device is in its implanted state.
[0032] By way of one or more embodiments, the external device may
include one or more of a lock-in amplifier, an AM demodulator that
may demodulate amplitude-modulated signals, and an
analog-to-digital converter, wherein the analog-to-digital
converter may be connected to the AM demodulator and the lock-in
amplifier, and wherein the analog-to-digital converter may put out
a signal that represents a signal transmitted by the implantable
stimulation device.
[0033] In at least one embodiment of the invention, the implantable
device may include a hermetically sealed housing. The hermetically
sealed implantable device with a hermetically sealed housing, in at
least one embodiment, may be a medical therapy and/or a monitoring
device.
[0034] According to one or more embodiments of the invention, a
method of communicating data from an implantable stimulation device
to an external device may be provided, wherein the method may
include one or more of: [0035] altering a local electric field in
the body using the implantable stimulation device, by modulating an
autoshort pulse or a stimulation pulse amplitude that may be
delivered by the implantable stimulation device, and, [0036]
sensing the change of the local electric field caused by the
modulation of the autoshort pulse and/or a stimulation pulse
amplitude, respectively, using an external device that includes or
may be connected to at least two cutaneous electrodes.
[0037] Additionally, in at least one embodiment, the method may
include, before the step of altering a local electric field, one or
more of the steps of: [0038] imposing an oscillatory electric field
in body tissue encompassing an implantable stimulation device using
an external device comprising at least two cutaneous electrodes,
and, [0039] sensing the imposed oscillatory electric field using
the implantable stimulation device.
[0040] In one or more embodiments, the step of altering the local
electric field using the implantable stimulation device may be
performed using at least two electrodes that may be connected to,
operatively connected to, or may be part of the implantable
stimulation device, and at least one data transmission control
module that may be connected to, or operatively connected to, the
at least two electrodes. In at least one embodiment, the at least
one data transmission control module may be controlled to modulate
a stimulation pulse amplitude and/or an autoshort pulse to a
code-representing data that may be transmitted from the implantable
stimulation device to the external device. In at least one
embodiment, the modulating may cause a detectable change of a local
electric field.
[0041] Preferably, in one or more embodiments, the modulation of a
stimulation pulse amplitude may include amplitude changes without
return to a baseline amplitude.
[0042] According to at least one embodiment of the invention, a
transceiver may be utilized that may impart an electric field
across the implantable stimulation device. At least one embodiment
of the invention may include a lock-in amplifier that may detect
changes in the local field around the implantable device, and an
implantable device that may use charge to alter the local electric
field.
[0043] During an autoshort period following delivery of a
stimulation pulse, by way of one or more embodiments, the
implantable device may use the residual charge from the pacing
pulse and may modulate the balancing of such charge to effect
communication. In this case, in at least one embodiment, the
residual charges may form the local electric field that may be
altered to effect communication. In at least one embodiment, if
communication may be required during the delivery of a stimulation
pulse, fast modulation of the stimulation-pulse peak amplitude
without return to baseline may effect communication instead. In
this case, in one or more embodiments, the stimulation pulse may
form the local electric field that may be altered to effect
communication.
[0044] According to one or more embodiments, amplifying the local
impedance or electric field change around the implantable
stimulation device may increase the signal-to-noise ratio and may
make communication more reliable. Also, in at least one embodiment,
allowing communication while pacing may increase the allowable
communication time for data communication.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] The above and other aspects, features and advantages of at
least one embodiment of the invention will be more apparent from
the following more particular description thereof, presented in
conjunction with the following drawings wherein:
[0046] FIG. 1: is a representation of a communication system,
including an implantable stimulation device in its implanted state
and an external device, according to at least one embodiment of the
invention.
[0047] FIG. 2: is a more abstract representation of the system
depicted in FIG. 1, according to at least one embodiment of the
invention.
[0048] FIG. 3: is a stimulation pulse showing modulation of the
autoshort period, according to at least one embodiment of the
invention.
[0049] FIG. 4: is a schematic representation of a pacing circuit
for data transmission during the autoshort period, according to at
least one embodiment of the invention.
[0050] FIG. 5: is a stimulation pulse showing modulation of the
peak amplitude without return to baseline, according to at least
one embodiment of the invention.
[0051] FIG. 6: is a schematic representation of a pacing circuit
for data transmission during a stimulation pulse, according to at
least one embodiment of the invention.
[0052] FIG. 7: is a representation of an embodiment of an
implantable stimulation device showing elements that allow
synchronization of the switching with an imposed oscillatory
electric field, according to at least one embodiment of the
invention.
[0053] FIG. 8: is a more detailed representation of an external
device showing those elements, according to at least one embodiment
of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0054] The following description is of the best mode presently
contemplated for carrying out at least one embodiment of the
invention. This description is not to be taken in a limiting sense,
but is made merely for the purpose of describing the general
principles of the invention. The scope of the invention should be
determined with reference to the claims.
[0055] FIG. 1 shows a representation of a communication system,
including an implantable stimulation device in its implanted state
and an external device, according to at least one embodiment of the
invention. As shown in FIG. 1, at least one embodiment of the
invention includes an implantable pacemaker such as an implantable
stimulation device 10, a programmer/communication device such as
external device 12, and at least two cutaneous electrodes 14 placed
on either side of the heart. In at least one embodiment, the
external device 12 may detect changes of a local electric field in
the body. In particular, in one or more embodiments, the external
device 12 may detect changes of a local electric field in the body
caused by a stimulation pulse and/or autoshort pulse. The external
device 12, in at least one embodiment, may induce an oscillating
electric field through the at least two cutaneous electrodes 14
between 50 kHz to 1 MHz, preferably between 300 to 500 kHz, at a
specific voltage or current. In at least one embodiment, the
stimulation device 10 implanted in the heart may be located between
the at least two cutaneous electrodes 14; as shown in FIG. 2.
[0056] FIG. 2 is a more abstract representation of the system
depicted in FIG. 1, according to at least one embodiment of the
invention. In one or more embodiments, the implantable stimulation
device 10 includes a battery 50 with limited capacity. Optionally,
in at least one embodiment, to multiply the voltage V.sub.bat of
battery 50 to generate a voltage needed for a stimulation pulse, a
voltage multiplier 52 may be provided. By way of at least one
embodiment, a stimulation pulse capacitor 54 may be provided that
may be charged when connected to voltage multiplier 52 or battery
50. To enable charging of the stimulation pulse capacitor 54, in
one or more embodiments, a charging control switch 56 may be
provided. In at least one embodiment, the stimulation pulse
capacitor 54 may be charged when charging control switch 56 may be
closed.
[0057] According to one or more embodiments of the invention, to
deliver the charge from stimulation pulse capacitor 54 to
electrodes 18 and to thus deliver a stimulation pulse, a
stimulation-pulse-switch 58 may be provided. In at least one
embodiment, when the charging control switch 56 is opened and the
stimulation-pulse-switch 58 is closed, current may flow to
electrodes 18 via a blocking capacitor C.sub.block 60. Via
stimulation-pulse-switch 58, in one or more embodiments, the
duration of a stimulation pulse period may be controlled. In at
least one embodiment, the stimulation pulse period may last as long
as stimulation-pulse-switch 58 is closed.
[0058] By way of one or more embodiments, after delivery of a
stimulation pulse when the stimulation-pulse-switch 58 is opened,
charge remaining on blocking capacitor 60 may be discharged via
autoshort switch 62 and electrodes 18. Thus, in at least one
embodiment, an autoshort pulse may be generated that may dissipate
charge on the blocking capacitor remaining from the stimulation
pulse. As such, in one or more embodiments, the autoshort pulse may
be controlled by autoshort switch 62.
[0059] According to at least one embodiment, autoshort switch 62
may be controlled by at least one data communication module (not
shown in FIG. 2). According to at least one embodiment, at least
one data communication module may comprise at least one data
transmission control module that may control autoshort switch
62.
[0060] By way of one or more embodiments, utilizing the charge
present on the blocking capacitor 60 after delivery of a
stimulation pulse may effect an observable change of an electric
field that may be used for data transmission. Often, after delivery
of a stimulation pulse, the residual charge on the blocking
capacitor 60 may be removed by shorting the stimulation electrodes
18 together (autoshort). The voltage left on the capacitor 60 after
delivery of a stimulation pulse, for example, may not be
stimulating voltage, rather, it is unused. As such, it is a
by-product of pacing and detrimental to leads and tissue.
Therefore, in at least one embodiment, it may be removed to prevent
for example electrode corrosion and therefore autoshort switch 62
may be provided. By modulating the shorting process to encode data,
in at least one embodiment, a detectable data transmission signal
may be produced. In at least one embodiment, the modulation may
include any suitable modulation and coding, for example amplitude
modulation (AM) or amplitude modulation that is binary phase shift
keying encoded (AM-BP SK).
[0061] By way of one or more embodiments, the modulated residual
charge may create a large change in the local field around the
implantable stimulation device 10 that may cause large voltage
changes as sensed by the external device 12. The external device
12, in at least one embodiment, may impart an oscillatory electric
field on the body that may create a carrier for the implanted
device to use for transmission. In one or more embodiments, the
implantable medical device activates data communication upon
sensing an oscillatory electric field. In one or more embodiments,
modulating the charge present after delivery of a stimulation pulse
may cause the local field to change within the frequency range of a
receiving lock-in amplifier of the external device 12. A
synchronization of the modulation to the frequency of the
externally imparted electric field, in at least one embodiment, may
improve signal-to-noise ratio. In at least one embodiment, the
change in the field produced by the external device 12, which
includes a receiver, may cause communication. This communication,
in one or more embodiments, may be termed pseudo-passive because
charge may be used to change the local field, whereas passive may
only use a switch.
[0062] In at least one embodiment, this method may be extended for
use with stimulation pulses. Fast modulation of stimulation-pulse
peak amplitudes, without return to baseline, in one or more
embodiments, may be achieved using a circuit that may include one
or more of a blocking capacitor C.sub.block 60, a rectifier diode
bridge 64, and four switches 58.1, 58.2, 58.3 and 58.4, as shown in
FIG. 6 and discussed further below. In at least one embodiment, one
or more of the switches 58.1, 58.2, 58.3 and 58.4 may allow
bi-directional current flow through the blocking capacitor
C.sub.block 60, and such current may be unidirectionally delivered
to tissue via the rectifier diode bridge 64. The blocking capacitor
C.sub.block 60, in one or more embodiments, may charge and
discharge within the delivery of a stimulation pulse and may be
sized to provide the desired modulation of the peak amplitude of
the stimulation pulse. This approach, in at least one embodiment,
may result in a smaller blocking capacitor C.sub.block 60 which may
be an advantage for volume-constrained applications such an iLP. In
at least one embodiment modulation of stimulation pulse amplitude
is controlled such, that an average peak amplitude is
maintained.
[0063] According to one or more embodiments, passive charge
balancing of a pacing pulse may involve the connection of on or
more analog switches that may allow discharging of the blocking
capacitor C.sub.block 60 through tissue, returning charge for
neutrality purposes. FIG. 4 shows a schematic representation of a
pacing circuit for data transmission during the autoshort period,
according to at least one embodiment of the invention. In such a
circuit, in at least one embodiment, capacitor C.sub.res 54 may be
charged via switch S.sub.res 56 to a multiple N of the battery
voltage V.sub.bat 50 (N can be 1). In at least one embodiment,
AC-coupled stimulation, via capacitor C.sub.block 60, may occur by
opening switch S.sub.res 56 and closing switch S.sub.pace 58,
connecting capacitor C.sub.res 54 in series with C.sub.block 60 and
tissue (represented by Z) between electrodes 18. In one or more
embodiments, capacitor C.sub.block 60 may then charge during the
delivery of the stimulation pulse and such charge may flow in the
opposite direction following the stimulation pulse (opening of
switch S.sub.pace 58) to allow for charge-balanced stimulation. In
at least one embodiment, this may be achieved by closing switch
S.sub.dis 62 for a finite time that may depend on the
Re(Z).times.C.sub.block time constant.
[0064] By way of one or more embodiments, fast
connection/disconnection of switch S.sub.dis 62 causes interruption
of the balancing autoshort pulse, which in turn creates voltage
glitches between the electrodes 18. Such glitches, in at least one
embodiment, may be detected using a lock-in amplifier, as disclosed
in FIG. 8 and discussed further below.
[0065] FIG. 3 illustrates a stimulation pulse showing modulation of
the autoshort period, according to at least one embodiment of the
invention. As shown in FIG. 3, in at least one embodiment,
transmission during the balancing phase may be divided into
different sections. In one or more embodiments, each section may be
selected according to a maximum .DELTA.V discharge of the blocking
capacitor that may allow decoding the glitches within a section
using the same integration time for the receiving lock-in
amplifier. Consecutive transmission sections, in at least one
embodiment, may have increasing integration times until charge
balancing completes. In at least one embodiment, transition from
one section to the next may be achieved by simple start and stop
bits in the link layer.
[0066] According to one or more embodiments, the implantable
stimulation device 10 may measure the lead impedance and may
compare such value against those in a non-volatile table stored in
the device's memory to support determination of each section's
modulating frequency. In at least one embodiment, this information
may be transmitted to the external receiver during synchronization,
or extracted by such, to determine the corresponding integration
times that may be used.
[0067] FIG. 5 is a stimulation pulse showing modulation of the peak
amplitude without return to baseline, according to at least one
embodiment of the invention. According to at least one embodiment,
FIG. 5 shows modulation of the stimulation-pulse peak amplitude
instead, for data transmission during delivery of a stimulation
pulse. Such modulation, in at least one embodiment, may be achieved
with the circuit shown in FIG. 6.
[0068] FIG. 6 is a schematic representation of a pacing circuit for
data transmission during a stimulation pulse, according to at least
one embodiment of the invention. As shown in FIG. 6, similar to the
circuit diagram shown in FIG. 4, capacitor C.sub.res 54 may be
charged to a multiple N of the battery voltage V.sub.bat. To cause
delivery of a stimulation pulse, in at least one embodiment, switch
S.sub.res 56 may be opened and switches 58.1, 58.2, 58.3 and 58.4
may be opened and closed in an H-bridge type of configuration. For
example, in one or more embodiments, during the high-phase of
.PHI..sub.A, switches 58.1 and 58.2 may be closed simultaneously
which may allow diodes D1 and D2 to conduct flowing current from
the first electrode 18.1 to the second electrode 18.2. In one or
more embodiments, C.sub.block may then charge in the direction of
diode D2 and switch 58.2, reducing (approximately linearly) the
voltage across Z. The former, in at least one embodiment, may be
dimensioned to provide the desired amplitude/timing modulation
shown in FIG. 5 (for a range of Re(Z)).
[0069] According to one or more embodiments, in the opposite phase,
i.e. high .PHI..sub.B and low .PHI..sub.A, switches 58.1 and 58.2
may be opened and switches 58.3 and 58.4 may be closed. The
accumulated voltage on C.sub.block 60, in at least one embodiment,
will instantaneously add to the stimulation pulse peak voltage,
making the transitions shown in the zoom of FIG. 5. In at least one
embodiment, current flows through switch 58.3 to capacitor
C.sub.block 60 to diode D3 to diode D4 to switch 58.4, thus
discharging C.sub.block 60.
[0070] In at least one embodiment, diodes D1, D2, D3 and D4 shown
in FIG. 6 may be replaced by switching elements for high efficiency
implementation.
[0071] In one or more embodiments, combination of the schematized
circuits of FIG. 4 and FIG. 6 may be provided to achieve data
transmission during both the stimulation pulse period and the
autoshort period.
[0072] FIG. 7 is a representation of an embodiment of an
implantable stimulation device showing elements that allow
synchronization of the switching with an imposed oscillatory
electric field, according to at least one embodiment of the
invention. As shown in FIG. 7, the implantable stimulation device
10 may include at least two electrodes 18 that may contact body
tissue surrounding the implantable stimulation device 10 in its
implanted state, wherein the at least two electrodes 18 may be
implantable electrodes. By way of at least one embodiment, switch
62 and switches 58.1, 58.2, 58.3 and 58.4, respectively, may be
represented by single switch 16 as shown in FIG. 7.
[0073] In one or more embodiments, the at least two electrodes 18
of the implantable stimulation device 10 may be arranged on the
external surface of a hermetically sealed housing 28 encapsulating
the implantable stimulation device 10. According to at least one
embodiment, parts of the housing 28 itself may form the at least
two electrodes 18. In one or more embodiments, the at least two
electrodes 18 may also be formed by a tip electrode 18 that may be
located at a tip of the implantable stimulation device 10, and a
ring electrode that may be located on the circumference of the
implantable stimulation device 10 (not shown).
[0074] In order to control switching of the switch or switches
represented by switch 16, in at least one embodiment, the
implantable stimulation device 10 may include a frequency divider
20 that may be connected to a sine-to-square converting comparator
22 that in turn may be connected to a phase-locked loop (PLL) 24.
In one or more embodiments, phase-locked loop 24 may be connected
to the at least two electrodes 18 via a band-pass filter 26. In at
least one embodiment, phase-locked loop 24 and frequency divider 20
may be part of a switch control of implantable stimulation device
10.
[0075] In one or more embodiments, the field induced between the
cutaneous electrodes 14 may be sensed by the implantable
stimulation device 10. In at least one embodiment, the implantable
stimulation device 10 may lock in the frequency of the electric
field using the phase-locked loop 24. Once the implantable
stimulation device 10 may be locked on to the frequency of the
external device's induced field, in one or more embodiments, it may
activate the switch 16 between the at least two electrodes 18 that
may be in the field in synch with the frequency of the electric
field, as shown in FIG. 2 and FIG. 4.
[0076] In at least one embodiment of the invention, the implantable
stimulation device 10 may receive the imposed oscillatory electric
signal as input signal that may be detected via the at least two
electrodes 18. Thus, in one or more embodiments, the implantable
stimulation device 10 may have an input sine signal that may be
detected as an alternating voltage across electrodes 18 or across a
resistor. This input sine signal, in one or more embodiments, may
be band-pass filtered by band-pass filter 26. A representation of
such a band-pass filtered signal is shown in representation (a) of
FIG. 7.
[0077] In at least one embodiment, the band-pass filtered input
sine signal is fed to the phase-locked loop (PLL) 24 that locks in
the frequency of the input sine signal. PLL 24, in one or more
embodiments, may put out a synchronized sine signal to a comparator
22 that may convert the sine signal, depicted by representation (a)
of FIG. 7, to a square signal depicted by representation (b) of
FIG. 7. The square signal thus generated, in at least one
embodiment, may be fed to frequency divider 20 that may generate a
clock signal for switching the switch 16. In one or more
embodiments, the clock signal thus generated may have a frequency
corresponding to a fraction of the frequency of the oscillatory
electric field wherein the fraction may be determined by a
frequency division factor applied by frequency divider 20. The
clock signal frequency, in at least one embodiment, may be in a
range of 0.1 to 50 kHz, such as a range of 1 to 20 kHz, more
preferably in a range of 7 to 9 kHz, most preferably the clock
signal frequency is 8 kHz.
[0078] According to one or more embodiments, the actual switching
of the switch or switches represented by switch 16 may further
depend on data that may be transmitted from the implantable
stimulation device 10 to the external device 12. The data to be
transmitted, in at least one embodiment, may be coded and the code
may determine the actual sequence of switching of the switch or
switches represented by switch 16.
[0079] In at least one embodiment, frequency divider 20 may be a
flip-flop counter.
[0080] In one or more embodiments, the change of an electrical
field caused by switching the switch 62 and/or switches 58.1, 58.2,
58.3 and 58.4 represented by switch 16 may be sensed by external
device 12.
[0081] In at least one embodiment of the invention, data
transmission from the implantable stimulation device 10 to the
external device 12 may be summarized as follows: generate a local
electric field in the body by discharging a capacitor to the body
tissue, switch on/off the switch or switches represented by switch
16 in implantable device 10 to cause changes of the body electric
field and detect change by external device 12.
[0082] In at least one embodiment of the invention, data
transmission from the implantable stimulation device 10 to the
external device 12 may be summarized as follows: apply signal
(oscillatory electric field), propagate in body, switch on/off the
switch or switches represented by switch 16 in implantable device
10 to cause changes of the body electric field and detect change by
external device 12.
[0083] In one or more embodiments, the switch control of the
implantable stimulation device 10 may receive an input sine signal
by detecting a voltage across electrodes 18. The switch control of
the implantable stimulation device 10, according to at least one
embodiment of the invention, may include one or more of a band-pass
filter 26, a phase-locked loop 24 that may lock in the frequency of
the input sine signal, a comparator 22 that may convert the sine
signal to a square signal, and a flip-flop counter that may act as
a frequency divider 20 that may control the at least one switch 16.
Switch 16, in at least one embodiment, may have a small
on-resistance.
[0084] In one or more embodiments, the changes of the electric
field caused by the implantable stimulation device 10, as shown in
FIG. 4 and FIG. 6, may be detected by the external device 12. FIG.
8 is a more detailed representation of an external device showing
those elements, according to at least one embodiment of the
invention. As shown in FIG. 8, the external device 12 may include a
lock-in amplifier 30 that may generate an output signal (depicted
as representation (c) of FIG. 8) that may represent the signal that
may be transmitted by implantable stimulation device 10 by way of
electric field changes. Lock-in amplifier 30, in at least one
embodiment, may use the signal imposed on a body by means of
cutaneous electrodes 14 as a reference signal. For this purpose, in
at least one embodiment, a network of resistors 32 may be provided
that may cause a voltage drop representing the signal (the
oscillatory electric field) imposed on a body via cutaneous
electrodes 14.
[0085] In one or more embodiments, this signal may be amplified by
pre-amplifier 34 of lock-in amplifier 30.
[0086] By way of one or more embodiments, the amplified signal
sensed via at least one sensing module 43, i.e. at least two
cutaneous electrodes 14 and the resistor network 32, may be fed to
an AM demodulator that may include a phase-sensitive detector 36,
and may further be fed to a low-pass filter 38, as depicted in FIG.
8. The amplified input signal sensed via cutaneous electrodes 14
and the resistor network 32, in at least one embodiment, may be
represented as signal (a) of FIG. 8. The output signal of the
phase-sensitive detector 36, in at least one embodiment, may be
depicted as signal (b) of FIG. 8. In one or more embodiments, the
low-pass filtered output signal of lock-in amplifier 30 may be
depicted in FIG. 8 as signal (c). In at least one embodiment,
signal (c) may correspond to the signal generated by implantable
stimulation device 10 and may represent data to be transmitted from
implantable stimulation device 10 to external device 12. In at
least one embodiment, this signal may be analog-to-digital
converted and stored. In one or more embodiments, block 40 in FIG.
8 may include one or more of an analog-to-digital converter (ADC)
41, a memory for data storage and a display of external device
12.
[0087] According to at least one embodiment, for the detection of
electric field changes of the body caused by the implantable
stimulation device 10, the external device 12 may include a lock-in
amplifier 30 that may use the input as a reference signal,
including an AM demodulator which in turn may include a precision
rectifier and a low-pass filter 38. The low-pass filtered signal,
in at least one embodiment, may be fed to an analog-to-digital
converter 41.
[0088] In one or more embodiments, the communication from
implantable stimulation device 10 to external device 12 may be
understood as follows.
[0089] In at least one embodiment, as the implantable stimulation
device 10 alternatively shorts and opens the switch 62 or switches
58.1, 58.2, 58.3 and 58.4 represented by switch 16, the electric
field between the external device electrodes 14 may be slightly
changed or modulated. In one or more embodiments, the external
device 12 may sense the change of the electric field by measuring
how much voltage or current may be imparted on the electrodes 14
that may create the oscillator electric field between the external
device electrodes 14.
[0090] In at least one embodiment, the external device 12 may
implement detection using a lock-in amplifier 30 that may be
synchronized to the electric field frequency and phase. As the
implantable stimulation device 10 modulates the electric field
between the external device electrodes 14, in one or more
embodiments, the external device 12 may integrate the changing
current or voltage. In at least one embodiment, the integration may
allow a very small change in sourced voltage or current that may be
detected using amplitude modulation.
[0091] In one or more embodiments, communication may occur at
approximately 1/10 to 1/100th of the modulation frequency of the
imposed oscillatory electric field. In at least one embodiment,
this may allow for .about.10-100 cycles of the electric field to be
integrated that may determine the imparted current or voltage.
[0092] By way of one or more embodiments, a communication from
external device 12 to implantable stimulation device 10 may be done
as follows:
[0093] In at least one embodiment, the imposed oscillatory electric
field may include a fundamental frequency that the implantable
stimulation device 10 may use to lock onto. The fundamental
frequency, in one or more embodiments, may also be used as a
carrier frequency to send modulated data to the implantable
stimulation device 10. According to at least one embodiment, the
external device 12 may modulate data, using frequency modulation or
amplitude modulation, on top of the carrier imparted electric
field. The implantable stimulation device 10, in at least one
embodiment, may decode the modulated data sensed through the
electrodes 18.
[0094] One or more embodiments of the invention may not require the
implantable stimulation device 10 to actively transmit data using
its own power in the case of impedance modulation embodiment.
Rather, in at least one embodiment, the implantable stimulation
device 10 may modulate a field imparted on it by an external device
12. In one or more embodiments, the resulting drain on the
implantable stimulation device's battery may be negligible. Because
of the reduced power consumption, in at least one embodiment, it
may be possible to transmit more data to the external device
12.
[0095] In one or more embodiments, modulating a local electric
field as described above may allow for improved data communication
than data communication provided by causing pure impedance changes
(passive). In at least one embodiment, the changes in the local
electric field may produce much larger changes in the sensed
voltage at the receiver than pure impedance changes between
electrodes of the implantable device. Because of the large sensed
difference, in at least one embodiment, a shortened integration
time may be possible. In one or more embodiments, by shortening the
integration time of the lock-in amplifier, higher data rates may be
achieved.
[0096] Further, in at least one embodiment of the invention,
utilizing this method may enable post-stimulation-pulse
transmission of data.
[0097] It will be apparent to those skilled in the art that
numerous modifications and variations of the described examples and
embodiments are possible in light of the above teaching. The
disclosed examples and embodiments are presented for purposes of
illustration only. Other alternate embodiments may include some or
all of the features disclosed herein. Therefore, it is the intent
to cover all such modifications and alternate embodiments as may
come within the true scope of this invention.
* * * * *