U.S. patent application number 14/024620 was filed with the patent office on 2014-01-09 for apparatus and methods using acoustic telemetry for intrabody communications.
This patent application is currently assigned to Remon Medical Technologies, LTD.. The applicant listed for this patent is Remon Medical Technologies, LTD.. Invention is credited to Eyal Doron, Abraham Penner.
Application Number | 20140012342 14/024620 |
Document ID | / |
Family ID | 33131405 |
Filed Date | 2014-01-09 |
United States Patent
Application |
20140012342 |
Kind Code |
A1 |
Penner; Abraham ; et
al. |
January 9, 2014 |
APPARATUS AND METHODS USING ACOUSTIC TELEMETRY FOR INTRABODY
COMMUNICATIONS
Abstract
Systems and methods provide intrabody communication using
acoustic telemetry. The system includes a first or control implant
including a first acoustic transducer, and a second implant
including a switch and a second acoustic transducer coupled to the
switch. The second acoustic transducer receives acoustic signals
from the first acoustic transducer for closing the switch to
activate the second implant. The second implant may include a
therapeutic device for providing therapy to the patient. For
example, the second implant may provide pacing therapy,
defibrillation therapy, pain control stimulation, or
neuro-stimulation.
Inventors: |
Penner; Abraham; (Tel-Aviv,
IL) ; Doron; Eyal; (Kiriat-Yam, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Remon Medical Technologies, LTD. |
Caesarea |
|
IL |
|
|
Assignee: |
Remon Medical Technologies,
LTD.
Caesarea
IL
|
Family ID: |
33131405 |
Appl. No.: |
14/024620 |
Filed: |
September 11, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11680529 |
Feb 28, 2007 |
8540631 |
|
|
14024620 |
|
|
|
|
10413428 |
Apr 14, 2003 |
7198603 |
|
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11680529 |
|
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Current U.S.
Class: |
607/7 ; 607/32;
607/46; 607/60 |
Current CPC
Class: |
A61B 5/0028 20130101;
A61B 5/0215 20130101; A61B 5/0031 20130101; A61M 5/1723 20130101;
A61B 5/4839 20130101; A61N 1/37217 20130101; A61M 5/14276 20130101;
A61M 2205/3507 20130101; A61B 2560/0257 20130101; A61B 5/0008
20130101; A61B 5/031 20130101; A61N 1/37288 20130101; A61N 1/378
20130101; A61B 5/026 20130101; A61B 2017/00026 20130101; A61B
5/14539 20130101; A61B 5/14532 20130101; A61B 2560/0214
20130101 |
Class at
Publication: |
607/7 ; 607/32;
607/60; 607/46 |
International
Class: |
A61N 1/372 20060101
A61N001/372 |
Claims
1. A system for communicating within a patient's body, comprising:
at least one implantable medical device configured to provide
pacing therapy, wherein the at least one implantable medical device
is adapted to be placed within a body of a patient, the at least
one implantable medical device including an electrical energy
source, electrical circuitry configured to control an operation of
the at least one implantable medical device, and an acoustic
transducer, wherein the at least one implantable medical device
further includes an acoustic switch that is configured to allow an
electrical current to flow from the electrical energy source to the
electrical circuitry in response to receiving an acoustic signal,
thereby activating the at least one implantable medical device; and
a control implant adapted to be implanted in the patient, the
control implant including an acoustic transducer configured for
acoustic communication with the at least one implantable medical
device.
2. The system of claim 1, wherein the electrical energy source
comprises an energy exchanger.
3. The system of claim 1, wherein the electrical energy source
comprises a battery.
4. The system of claim 1, wherein the electrical energy source
comprises a capacitor.
5. The system of claim 1, wherein the at least one implantable
medical device is coupled to a fixation element adapted to secure
the medical device within the patient's body.
6. The system of claim 5, wherein the fixation element is a
stent.
7. A system for communicating within a patient's body, comprising:
at least one implantable medical device comprising at least one
therapeutic device, wherein the at least one implantable medical
device is adapted to be placed within a body of a patient, the at
least one implantable medical device including an electrical energy
source, electrical circuitry configured to control an operation of
the at least one implantable medical device, and an acoustic
transducer, wherein the at least one implantable medical device
further includes an acoustic switch that is configured to allow an
electrical current to flow from the electrical energy source to the
electrical circuitry in response to receiving an acoustic signal,
thereby activating the at least one implantable medical device; and
a control implant adapted to be implanted in the patient, the
control implant including an acoustic transducer configured for
acoustic communication with the at least one implantable medical
device.
8. The system of claim 7, wherein the at least one therapeutic
device is configured to provide pacing therapy.
9. The system of claim 7, wherein the at least one therapeutic
device is configured to provide at least one of atrial
defibrillation therapy, pain relief stimulation, and
neuro-stimulation.
10. A system for communicating within a patient's body, comprising:
at least one implantable medical device adapted to be placed within
a body of a patient, the at least one implantable medical device
including an electrical energy source, electrical circuitry
configured to control an operation of the at least one implantable
medical device, and an acoustic transducer, wherein the at least
one implantable medical device further includes an acoustic switch
that is configured to allow an electrical current to flow from the
electrical energy source to the electrical circuitry in response to
receiving an acoustic signal, thereby activating the at least one
implantable medical device; and a control implant adapted to be
implanted in the patient, the control implant including an acoustic
transducer configured for acoustic communication with the at least
one implantable medical device.
11. The system of claim 10, wherein the at least one implantable
medical device includes at least one therapeutic device.
12. The system of claim 11, wherein the at least one therapeutic
device is configured to provide pacing therapy.
13. The system of claim 11, wherein the at least one therapeutic
device is configured to provide atrial defibrillation therapy.
14. The system of claim 11, wherein the at least one therapeutic
device is configured to provide pain relief stimulation.
15. The system of claim 11, wherein the at least one therapeutic
device is configured to provide neuro-stimulation.
16. The system of claim 10, wherein the electrical energy source
comprises an energy exchanger.
17. The system of claim 10, wherein the electrical energy source
comprises a battery.
18. The system of claim 10, wherein the electrical energy source
comprises a capacitor.
19. The system of claim 10, wherein the at least one implantable
medical device is coupled to a fixation element adapted to secure
the medical device within the patient's body.
20. The system of claim 19, wherein the fixation element is a
stent.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of co-pending U.S.
application Ser. No. 11/680,529, filed on Feb. 28, 2007, which is a
continuation of U.S. application Ser. No. 10/413,428, filed on Apr.
14, 2003, now U.S. Pat. No. 7,198,603.
TECHNICAL FIELD
[0002] The present invention relates generally to devices for
implantation within a patient's body, and more particularly to
systems and methods for communication within a patient's body using
acoustic telemetry, e.g., using one implant within a body to
activate, deactivate, and/or otherwise control one or more
additional implants located within the body that monitor
physiological conditions and/or provide therapeutic functions.
BACKGROUND
[0003] Devices are known that may be implanted within a patient's
body to monitor one or more physiological conditions and/or to
provide therapeutic functions. For example, sensors or transducers
may be located deep within the body for monitoring a variety of
properties, such as temperature, pressure, strain, fluid flow,
chemical properties, electrical properties, magnetic properties,
and the like. In addition, devices may be implanted that perform
one or more therapeutic functions, such as drug delivery,
defibrillation, electrical stimulation, and the like.
[0004] Often it is desirable to control or otherwise communicate
with such devices once they are implanted within a patient, for
example, to obtain data, and/or to activate or deactivate the
implanted device. An implant may include wire leads that extend
from the implant to an exterior surface of the patient, thereby
allowing an external controller or other device to be directly
coupled to the implant. Alternatively, the implant may be remotely
controlled or communicated with using an external induction device.
For example, an external radio frequency (RF) transmitter may be
used to communicate with the implant. In addition, RF devices have
been suggested that may be implanted within a patient's body to
communicate with another implant at another location within the
patient's body.
[0005] RF energy, however, may only penetrate a few millimeters
within a body, because of the body's dielectric nature, and
therefore may not be able to communicate effectively with an
implant that is located deep within the body. RF devices may also
require substantial electrical power, because the devices generally
consume electrical energy even when in a dormant state. In
addition, although an RF transmitter may be able to induce a
current within an implant, the implant's receiving antenna,
generally a low impedance coil, may generate a voltage that is too
low to provide a reliable switching mechanism.
[0006] In a further alternative, magnetic energy may be used to
control or otherwise communicate with an implant, since a body
generally does not attenuate magnetic fields. The presence of
external magnetic fields encountered by the patient during normal
activity, however, may expose the patient to the risk of false
positives, i.e., accidental activation or deactivation of the
implant. Furthermore, external electromagnetic systems may be
cumbersome and may not be able to effectively transfer coded
information to an implant.
[0007] Accordingly, it is believed that apparatus and methods for
communicating with implants using acoustic telemetry would be
useful.
SUMMARY
[0008] The present invention is generally directed to implants that
may be surgically or otherwise located within a body for monitoring
one or more physiological parameters and/or for performing one or
more therapeutic functions. More particularly, the present
invention is directed to systems and methods for communicating
between implants within a patient's body using acoustic telemetry,
e.g., using one implant within the body to activate, deactivate,
and/or otherwise control another implant located within the body.
One or both of the implants may monitor physiological conditions
and/or provide therapeutic functions. Implants in accordance with
the present invention may be used for various diagnostic and/or
therapeutic functions, e.g., atrial defibrillation, pacing, pain
relief stimulation, neuro-stimulation, drug release, activation of
a light source for photodynamic therapy, monitoring of a radiation
dose including ionizing, magnetic or acoustic radiation, monitoring
of flow in a bypass graft, producing cell oxygenation and membrane
electroportation, and measurement of various physiological
parameters including heart chamber pressure, infraction
temperature, intracranial pressure, electrical impedance, position,
orthopedic implant strain/displacement, or pH.
[0009] In a accordance with a first aspect of the present
invention, a system is provided for communication within a
patient's body that includes a first implant, also called a control
implant and a second implant, also called a dormant implant.
Optionally, the system may include one or more additional implants,
e.g., one or more additional dormant implants, and/or the system
may include a therapeutic device for treating the patient.
[0010] Generally, the first implant includes a first acoustic
transducer for transmitting acoustic signals. The first implant may
include other components, e.g., a processor, controller, and/or
other electrical circuitry, memory, an energy source (e.g., a
nonrechargeable or rechargeable battery and/or capacitor), one or
more sensors, and/or a therapeutic device. The second implant
generally includes an electrical circuit configured for performing
one or more commands when the implant is activated; a switch
coupled to the electrical circuit; and a second acoustic transducer
coupled to the switch, the acoustic transducer configured for
receiving one or more acoustic signals from the first acoustic
transducer for closing the switch to activate the second
implant.
[0011] Preferably, the switch is configured such that the switch is
closed only when the second acoustic transducer receives a first
acoustic excitation signal followed by a second acoustic excitation
signal, the first and second acoustic excitation signals being
separated by a predetermined delay. This or other signal
configurations may be used, e.g., when it is desired to activate
one of a plurality of available dormant implants controlled by the
first implant.
[0012] In a first preferred embodiment, the second implant may
include a sensor coupled to the electrical circuit, the sensor
configured for measuring a physiological parameter within the body
when the second implant is activated. The second acoustic
transducer may be configured for transmitting a signal including
physiological data related to the measured physiological parameter
to the first acoustic transducer.
[0013] For example, the first implant may include a controller
coupled to a pacemaker, and the second implant may include a
pressure sensor for measuring pressure in the patient's heart. The
second implant may be configured to transmit acoustic signals to
the first implant, the acoustic signals including the measured
pressure within the patient's heart. The controller may be
configured for extracting the measured pressure from the acoustic
signals and controlling the pacemaker at least partially based upon
the measured pressure.
[0014] In another example, the first implant may include a
controller coupled to an insulin pump, and the second implant may
include a glucose sensor for measuring blood sugar concentration
within the patient's body. The second implant may be configured to
transmit acoustic signals to the first implant, the acoustic
signals including measured blood sugar concentration within the
patient's body. The controller may be configured for extracting the
measured blood sugar concentration from the acoustic signals and
controlling the insulin pump at least partially based upon the
measured blood sugar concentration.
[0015] In yet another example, the second implant may include a
sensor for measuring a physiological parameter within the patient's
body. The second implant may be configured to transmit acoustic
signals to the first implant, the acoustic signals including data
related to the measured physiological parameter. The first implant
may include memory for storing the data related to the measured
physiological parameter, and a transmitter for transmitting the
data to a device located outside the patient's body.
[0016] In accordance with another aspect of the present invention,
a method is provided for communicating between first and second
implants implanted at different locations within a patient's body,
the second implant including an acoustic switch coupled to an
electrical circuit. An acoustic activation signal may be
transmitted from the first implant towards the second implant; and
the acoustic switch may be closed in response to the acoustic
activation signal, whereupon the second implant becomes
activated.
[0017] Once activated, the second implant may measure a
physiological parameter within the body, e.g., blood pressure
within a chamber or other vessel of the patient's heart, or in a
peripheral vessel, such as the aorta, renal, or iliac artery.
Alternatively, the second implant may measure blood sugar
concentration. The second implant may transmit an acoustic signal
including data related to the physiological parameter from the
second implant towards the first implant.
[0018] The first implant may store the data related to the
physiological parameter in memory of the first implant, e.g., along
with a time stamp identifying when the parameter was measured for
later retrieval. For example, an external device outside the
patient's body may interrogate the first implant, whereupon the
first implant may transmit one or more acoustic or electromagnetic
signals including the data related to the physiological parameter.
In addition or alternatively, the first implant may control a
therapeutic device, e.g., an insulin pump, pacemaker, and the like,
at least partially based upon the data related to the physiological
parameter.
[0019] In accordance with yet another aspect of the present
invention, a method is provided for monitoring a physiological
parameter within a patient's body. One or more acoustic signals are
transmitted from a control implant implanted within the body to
activate a dormant implant located at a location within the body. A
physiological parameter is measured at the location with the
dormant implant, and one or more acoustic signals are transmitted
from the dormant implant to the control implant, the one or more
acoustic signals including the physiological parameter data
measured by the dormant implant.
[0020] In one embodiment, the control implant may store the data in
memory. Optionally, the control implant may activate a plurality of
dormant implants located within the body, whereupon each of the
dormant implants may measure a physiological parameter and transmit
one or more acoustic signals to the control implant, the one or
more acoustic signals including physiological parameter data
measured by each respective dormant implant. Subsequently, the
control implant may be interrogated using an external device
disposed outside the body, whereupon the control implant may
transmit data including the physiological parameter data (from one
or more dormant implants if multiple dormant implants are present)
to the external device, e.g., using acoustic or RF telemetry.
[0021] For example, the dormant implant(s) may measure pressure,
e.g., within the patient's aorta, a renal or iliac artery, and the
like. The pressure data may be transmitted by the control implant
to an external device such that the data may be used by a
healthcare professional to monitor a condition of the patient.
[0022] In another embodiment, the patient's heart may be
electrically stimulated based at least in part upon the pressure
data measured by the dormant implant. For example, the dormant
implant may be implanted within a chamber of the heart or a
pulmonary artery. The control implant may be included in a
pacemaker or coupled to a pacemaker for controlling the pacing
provided by the pacemaker.
[0023] In yet another embodiment, the dormant implant may measure
blood sugar concentration at a location within the patient's body,
and transmit one or more acoustic signals to the control implant,
the one or more acoustic signals including blood sugar
concentration data measured by the dormant implant. Insulin may be
delivered into the body based at least in part upon the blood sugar
concentration measured by the dormant implant, e.g., using an
insulin pump coupled to the control implant or including the
implant therein.
[0024] Thus, the systems and methods of the present invention may
facilitate intrabody communication between two implants using
acoustic telemetry, where one of the implants may serve as a master
implant, controlling the operation of the second (or additional)
implant. The first implant, via an acoustic command, may switch the
second passive implant to an active status, whereupon it may
perform a series of predefined activities including therapeutic
and/or diagnostic functions. At any stage of its operation, the
second implant may communicate with the first implant, i.e.,
transmitting and/or receiving information. For example, the second
implant may activate drugs using photodynamic therapy or ultrasonic
activation or control opening of a drug reservoir.
[0025] Via the communication bus, the second implant may receive
commands, e.g., related to dosing or other parameters that may be
preprogrammed, externally controlled, or provide feedback from a
sensor that monitor some relevant physiological parameter. A sensor
may be included in either implant or in a third implant, e.g., in
communication with the first implant. Alternatively, the second
implant may serve as a sensor for some physiological or physical
parameter, including pressure, blood coagulation, acidity level
(pH), temperature, flow, impedance, glucose, potassium, calcium,
light attenuation, acceleration, oxygen saturation, drug
concentrations, and the like.
[0026] Other objects and features of the present invention will
become apparent from consideration of the following description
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The invention is herein described, by way of example only,
with reference to the accompanying drawings, wherein:
[0028] FIG. 1 is a block diagram, showing an exemplary embodiment
of a system including two implants that may communicate with one
another using acoustic telemetry, in accordance with the present
invention.
[0029] FIG. 2A is a top view of a first embodiment of a control
implant, in accordance with the present invention.
[0030] FIG. 2B is a cross-section of the control implant of FIG.
2A.
[0031] FIG. 3 is a top view of another embodiment of a control
implant, in accordance with the present invention.
[0032] FIG. 4 is a flow diagram, showing an exemplary sequence of
communications between master and slave implants, in accordance
with the present invention.
[0033] FIG. 5 is a cross-section of a body, showing a system for
monitoring blood pressure within the body.
[0034] FIG. 6 is a cross-section of a body, showing a closed loop
system for delivering insulin within the body.
DETAILED DESCRIPTION
[0035] Turning to the drawings, FIG. 1 shows a first preferred
embodiment of a system 10 for intrabody communication between two
or more implants implanted within a patient's body (not shown).
Generally, the system 10 includes a first implant 12 (also called
the control or master implant), and a second implant 32 (also
called the dormant or slave implant). Optionally, the system 10 may
include additional implants (not shown), e.g., one or more
additional dormant or slave implants, similar to the second implant
32, with which the control implant 12 may communicate, as described
below.
I. Control Implant
[0036] The control implant 12 may include a plurality of
components, e.g., electrical circuitry 14, an acoustic transducer
16, and/or an energy source 18, provided within a box or casing 20.
The casing 20, e.g., formed from titanium and the like, may be
substantially sealed, and preferably hermetically sealed to
substantially isolate the components of the control implant 12 from
outside the casing 20. The casing 20 may include one or more
regions, e.g., one or more side panels, that facilitate acoustic
energy passing through the casing 20, i.e., to and/or from the
acoustic transducer 16. For example a panel 20a overlying the
acoustic transducer 16 may be a relatively thin wall of titanium or
other material, e.g., having a thickness of about one half
millimeter (0.5 mm) or less, that may allow acoustic waves to pass
substantially therethrough. Additional information on possible ways
to construct any of the implants discussed herein may be found in
co-pending application Ser. No. 09/888,272, filed Jun. 21, 2001,
the disclosure of which is expressly incorporated herein by
reference.
[0037] The electrical circuitry 14 may be coupled to the energy
source 18 such that at least some component(s) of the electrical
circuitry 14 may remain active at all times, although,
alternatively, all or part of the electrical circuitry 14 may be
periodically dormant and/or selectively activated. The electrical
circuitry 14 may include one or more controllers for controlling
components of the control implant 12, timer circuitry (e.g., a
clock or counter), an oscillator or other circuitry for driving the
first acoustic transducer 16, and/or a processor for generating
electrical signals being transmitted by and/or analyzing electrical
signals received by the first acoustic transducer 16 (not
shown).
[0038] In addition, the control implant 12 may include memory 22,
e.g., volatile or non-volatile memory, including flash memory or
ferroelectric memory. The memory 22 may store information, e.g.,
data received from one or more sensors (not shown) of the control
implant 12 and/or the dormant implant 32, and/or commands for use
internally or for controlling the dormant implant 32. Optionally,
the control implant 12 may include a transmitter and/or receiver 24
for communicating with external devices (not shown), e.g., a radio
frequency ("RF") or acoustic transmitter and/or receiver. The
circuitry 14 of the control implant 12 may include one or more
micro-controllers, digital signal processors ("DSPs"), Field
Programmable Gate Arrays ("FPGAs"), other programmable devices,
and/or any other hardware components or software modules that may
be required for processing, analyzing, and/or storing data and/or
for controlling operation of the control implant 12 and/or dormant
implant(s) 32.
[0039] Optionally, the control implant 12 may include an acoustic
switch (not shown) for activating and/or deactivated the control
implant 12 during use. In addition or alternatively, the control
implant 12 may include one or more sensors (not shown) for
measuring or otherwise monitoring one or more physiological
parameters, similar to the dormant implant 32, as described further
below. In addition or alternative, the control implant 12 may
include an actuator (not shown) for actuating a therapeutic and/or
diagnostic device coupled to the control implant 12. Examples of
implants including acoustic switches, sensors, and/or actuators are
disclosed in co-pending application Ser. No. 10/152,091, filed May
20, 2002, Ser. No. 09/989,912, filed Nov. 19, 2001, Ser. No.
09/888,272, filed Jun. 21, 2001, and Ser. No. 09/690,615, filed
Oct. 16, 2000. The disclosures of these references and any others
cited therein are expressly incorporated by reference herein.
[0040] The acoustic transducer 16 generally includes one or more
piezoelectric elements (not shown) configured for transmitting one
or more acoustic signals, e.g., including an activation or
deactivation command, such that the acoustic signal(s) may reach
the dormant implant 32. In addition, the acoustic transducer 16 may
include one or more piezoelectric elements (also not shown) for
receiving one or more acoustic signals, e.g., from the dormant
implant(s) 32 and/or from an external device (not shown). It will
be appreciated by those skilled in the art that the same or
different piezoelectric elements may be used for transmitting and
receiving acoustic signals.
[0041] The acoustic transducer 16 may transmit acoustic waves or
signals intended to reach one or more dormant implants 32. For
example, the acoustic signals may include one or more activation
signals to activate one or more dormant implants, one or more
deactivation signals, and/or commands to program or otherwise
instruct the dormant implant(s), e.g., to follow or modify a
sequence of operations performed by the dormant implant(s). In
addition, the acoustic transducer 16 may be used to communicate
with an external device, e.g., a controller or recorder (not
shown), and/or to act as an energy exchanger, i.e., to receive
acoustic or electromagnetic energy from an external charger that
may be used to recharge the control implant 12.
[0042] An exemplary embodiment of a control implant 12 is shown in
FIGS. 2A and 2B that includes an acoustic transducer 16 integrated
within a hermetically sealed casing 20. Another embodiment of a
control implant 112 is shown in FIG. 3 in which the acoustic
transducer 116 is a piezoelectric ceramic cylinder provided at the
tip of a lead 126. This configuration may facilitate integrating
the control implant 112 into an existing medical implant with
minimal modifications, e.g., a pacemaker, because the acoustic
transducer 116 may be attached to an outer surface of the casing
120 containing the components of the implant 112.
[0043] A. Exemplary Interrogation Energy Requirements
[0044] The following description illustrates exemplary energy
consumption parameters, and, consequently, exemplary power
requirements for an energy source, such as a battery, for a control
implant, such as the control implant 12 shown in FIGS. 1, 2A, and
2B. Acoustic energy exchangers or transducers may currently achieve
a sensitivity of about 2 V/kPa. An acoustic switch, which may be
used to activate the implant, may operate by closing a MOSFET
switch, which may require about a half volt (0.5 V) in silicon
piezoelectric elements. The minimal acoustic level required to
close the acoustic switch is therefore between about two hundred
fifty and five hundred Pascals (250-500 Pa). Assuming a distance
between transmitter and receiver (e.g., the distance between the
acoustic transducers of control and dormant implants implanted
within a patient's body) of about ten centimeters (10 cm), the
acoustic power yielding five hundred Pascals (500 Pa @ 10 cm) is
therefore: P=4.pi.R.sup.2p.sup.2/(.rho.c)=21 mW (1)
[0045] where ".rho." and "c" are the density and sound velocity of
water, respectively, "R" is the distance and "p" is the desired
acoustic pressure. Assuming an electro-acoustic conversion
efficiency of twenty percent (20%), this equation would provide an
instantaneous electrical power requirement of about one hundred
milliwatts (100 mW).
[0046] It may be possible to close the switch using only a single
acoustic oscillation. However, this may not be practical, as it may
require an extremely wideband transducer and matching network. A
more realistic estimate may be a pulse length of between about five
and ten (5-10) oscillations. A ten (10) oscillation pulse at forty
kilohertz (40 kHz) is about two hundred fifty microseconds
(250.mu.sec) long. Thus, the energy expended in such a pulse would
be: E=250.times.10.sup.-6.times.0.1=25.mu.J. (2)
[0047] A typical interrogation would consist of between one and
four pulses. Thus, for one interrogation per hour, the energy drain
would be: P=25.times.10.sup.-6.times.4/3600=0.028.mu.W. (3)
[0048] In addition, the power requirements of the receiver should
be considered. An amplifier of the required sensitivity may take
about ten milliWatts (10 mW) of power. If it is powered for one
second every hour, this translates to a mean power drain of about
2.8.mu.W. This may be lowered by a factor of at least two to ten
(2-10) by using more aggressive power management, e.g. by powering
down the amplifier between words and/or focusing on specific
segments of the pressure waveform such as the diastole. This power
requirement may be substantially larger than the power taken by the
transmission itself. Thus, the power drain of the interrogation
circuits may be on the order of about one microwatt (1.mu.W).
[0049] B. Exemplary Transmitter/Receiver Element (Acoustic
Transducer)
[0050] The acoustic transducer of a control implant ("the
interrogating transducer") may be constructed in many ways. One
example is a piezoelectric ceramic cylinder, identified in FIG. 3
as acoustic transducer 116. Such a product is sold by Physik
Instrumente (PI) GmbH & Co. KG of Karlsruhe, Germany, and
identified as PIC181 PZT. The cylinder inflates and contracts under
the influence of an applied alternating voltage. This changes its
volume and transmits an acoustic signal into any surrounding fluid
as a simple (i.e., monopole) source.
[0051] The equation relating the acoustic output of a monopole
source with its mechanical vibrations is:
p=sho.c/(2.lamda.R).times.differential.V/.differential.t (4)
[0052] where ".lamda." is the acoustic wavelength and "V" is the
element volume. To get the required acoustic level of 500 Pa @ 10
cm at 40 kHz, a volume change of about 2.5.times.10.sup.-6
m.sup.3/sec is needed, or a volume change amplitude of about
10.sup.-11 m.sup.3.
[0053] Assume, for example, that the transmitter is a ceramic
cylinder having a length of about ten millimeters (L=10 mm) and
radius of about two and a half millimeters (a=2.5 mm), with
electrodes on its inner and outer surfaces. Applying a voltage
causes the material to expand equally in the tangential and axial
directions, since the ceramic material is isotropic. The total
volume change is then given by: dV=dV/da da+dV/dL dL=3V S (5)
[0054] where "S" is the strain. To obtain a volume change of
10.sup.-11 m.sup.3, a strain must be induced of about
4.times.10.sup.-6. For the PIC181 PZT from PI, the piezoelectric
strain constant is 120.times.10.sup.-12 m/m/V/m. Thus, to obtain a
strain of 4.times.10.sup.-6, an electrical field of about 33,000
V/m should be applied, or an amplitude of about thirty three volts
(33 V) for a wall thickness of about one millimeter (1 mm).
[0055] The battery to provide this energy may be one of a variety
of types, such as those used in other active implantable devices,
such as defibrillators, pacemakers, nerve stimulators, and the
like. For example, the battery may be Lithium polymer, Lithium
iodide, Lithium ion, and/or nickel metal. Assuming that the
acoustic transducer may be used to activate the dormant implant
every hour, the average power will be about one microwatt (1.mu.W),
which is less than the power used by conventional pacemakers.
II. Dormant Implant
[0056] Returning to FIG. 1, an exemplary embodiment of a second or
dormant implant 32 is shown. Generally, similar to the control
implant 12, the dormant implant 32 may include a plurality of
components, e.g., electrical circuitry 34, an acoustic switch 42,
and/or an energy source 38, contained within a casing 40. The
casing 40, e.g., formed from titanium and the like, may be
hermetically or otherwise sealed to substantially isolate the
components of the dormant implant 312 from outside the casing 40.
The casing 40 may include one or more regions that facilitate
acoustic energy passing through the casing 40. For example, a panel
40a overlying the acoustic transducer 36 may be a relatively thin
membrane of titanium or other material, e.g., having a thickness of
about fifty micrometers (50.mu.m) or less, that may allow acoustic
waves to pass therethrough.
[0057] The acoustic switch 42 is coupled to the electrical
circuitry 34 and the energy source 38, and may be activated upon
acoustic excitation by an external acoustic energy source, e.g.,
from the control implant 12, to allow current flow from the energy
source 38 to the electrical circuitry 34. In a preferred
embodiment, the acoustic switch 42 includes an energy exchanger,
i.e., an acoustic transducer 36, and a switch circuit 44. Exemplary
switch circuits and acoustic switches that may be used with
implants of the present invention are disclosed in co-pending
application Ser. Nos. 10/152,091, 09/989,912, 09/888,272, and
09/690,615, incorporated by reference above. Basically, an acoustic
transmission from the control implant 12 may vibrate the acoustic
transducer 36 of the dormant implant 32, forming a voltage pulse
that is conveyed to the switch circuit 44. When the voltage exceeds
a predetermined threshold, e.g., about a half volt (0.5 V), the
switch circuit 44 may close, and current may flow from the energy
source 38, thereby activating the implant 32.
[0058] The energy source 38 may include any of a variety of
devices, such as an energy exchanger, a battery, and/or a capacitor
(not shown). Preferably, the energy source 38 is a battery capable
of storing electrical energy substantially indefinitely, e.g., for
as long as the acoustic switch 42 remains open, i.e., when the
dormant implant 32 is in a "sleep" mode. In addition, the energy
source 38 may be capable of being charged from an external source,
e.g., inductively, using acoustic energy received by the acoustic
transducer 36, as will be appreciated by those skilled in the
art.
[0059] In another embodiment, the energy source 38 may include both
a capacitor and a primary, non-rechargeable battery, although,
alternatively, the energy source 38 may include a secondary,
rechargeable battery and/or capacitor that may be energized before
activation or use of the dormant implant 32. For example, the
energy source 38 may include a Lithium thin film battery, such as
those available from Oak Ridge Micro-energy Inc. of Salt Lake City,
Utah, Infinite Power Supply of Denver, Colo., or Cymber Corporation
of Elk River, Minn. Alternatively, the energy source 38 may include
a standard coin type manganese lithium rechargeable battery, such
as those available from Matsushita Battery Industrial Co., Ltd.
(MBI) of Osaka, Japan.
[0060] Optionally, the dormant implant 32 may include other
components for carrying out a variety of monitoring, diagnostic,
and/or therapeutic functions. For example, the electrical circuit
34 may include a control circuit, memory, a biosensor, an actuator,
and/or a transmitter (none of which are shown), as explained in
more detail below. The dormant implant 32 may be configured for
providing one or more therapeutic functions, for example, to
activate and/or control a therapeutic device implanted within a
patient's body, such as an atrial defibrillator, a pacemaker, a
pain relief stimulator, a neuro-stimulator, a drug delivery device
(e.g., an insulin pump), and/or a light source used for
photodynamic therapy. Alternatively, the implant 32 may be used to
monitor a radiation dose including ionizing, magnetic and/or
acoustic radiation, to monitor flow in a bypass graft, to produce
cell oxygenation and membrane electroporation, and the like. In
addition or alternatively, the implant 32 may include one or more
sensors for measuring one or more physiological parameters within
the patient's body, such as pressure, temperature, electrical
impedance, position, strain, fluid flow, pH, and the like.
[0061] For example, the implant 32 may include a biosensor
including one or more sensors capable of measuring physiological
parameters, such as those described above. U.S. Pat. No. 4,793,825
issued to Benjamin et al. and U.S. Pat. No. 5,833,603 issued to
Kovacs et al., which disclose exemplary embodiments of biosensors
that may be included in an implant, in accordance with the present
invention. The disclosure of these references and any others cited
therein are expressly incorporated herein by reference. The
biosensor may generate a signal proportional to a physiological
parameter that may be processed and/or relayed by the electrical
circuitry 34 to the acoustic transducer 36, which, in turn, may
generate a transmission signal to be received by the control
implant 12.
[0062] In addition or alternatively, the implant 32 may include an
actuator (not shown) that may be coupled to a therapeutic device
(also not shown) provided in or otherwise coupled to the implant
32, such as a light source, a nerve stimulator, a defibrillator, or
a valve communicating with an implanted drug reservoir (in the
implant or otherwise implanted within the body in association with
the implant). For example, the actuator may be a light source for
photo-dynamic therapy, such as that disclosed in U.S. Pat. No.
5,800,478 issued to Chen et al., the disclosure of which is
expressly incorporated herein by reference.
[0063] Thus, the second implant 32 may remain in a dormant state
and become active upon receiving an acoustic signal that may induce
a voltage high enough to close the acoustic switch 42. In the
dormant state, the second implant 32 may consume substantially
little or no energy, thereby allowing it to remain within the body
substantially indefinitely.
[0064] Once activated, the acoustic transducer 36 may convert the
acoustic signals received, e.g., from the control implant 12, into
one or more electrical signals, which may be processed by the
electrical circuitry 34 or otherwise used to control operation of
the dormant implant 32. The acoustic transducer 36 may also be used
to charge the energy source 38, e.g., a rechargeable battery and/or
capacitor. Similar to the control implant 12 described above, the
acoustic transducer 36 may include one or more piezoelectric
elements that may be used to receive acoustic signals, to transmit
acoustic signals, or both.
[0065] FIG. 4 shows an exemplary sequence of operations that may be
performed by a system, such as the system 10 shown in FIG. 1.
Initially, the control implant 12 and second implant 32 may be
implanted within the patient's body at different locations, with
the second implant 32 being in a passive or "sleep" mode. At step
60, the acoustic transducer 16 of the control implant 12 may
transmit one or more acoustic signals, including an activation
command, that may be received by the acoustic transducer 36 of the
second implant 32. If the acoustic signal(s) satisfy the threshold
requirements of the acoustic switch 42, the switch 44 may be
closed, thereby activating the second implant 32.
[0066] For example, the acoustic switch 42 may only be activated
when it receives a specific sequence of acoustic signals, e.g., an
initiation pulse followed after a predetermined delay by a
confirmation pulse. Such a sequence may prevent false
activation/deactivation and/or may be used to activate only one of
multiple dormant implants (not shown), e.g., by assigning different
threshold parameters to each of the dormant implants. Using a
confirmation signal may be particularly important for certain
applications, for example, to prevent unintentional release of
drugs by a drug delivery implant. In addition, the initiation
signal and/or confirmation signals may be unique, i.e., configured
to activate a single selected dormant implant 132, e.g., if
multiple dormant implants 32 are implanted within the patient's
body 90.
[0067] Once the second implant 32 is activated, the acoustic
transducer 36 may convert the acoustic signal(s) into one or more
electrical signals, and the electrical circuitry 34 of the second
implant 32 may analyze the electrical signal(s). For example, the
electrical circuitry 34 may extract one or more commands from the
signal(s), and then control the implant 32 to complete the
command(s). Alternatively, the second implant 32 may be
preprogrammed, and may automatically perform a predetermined
sequence of operations once activated. This may involve activating
one or more sensors to obtain physiological data related to the
patient, and/or actuating a therapeutic and/or diagnostic device
(not shown) coupled to the second implant 32.
[0068] At step 70, the acoustic transducer 36 of the second implant
32 may transmit one or more acoustic signals including data back to
the control implant 12. This may involve associating physiological
data obtained from one or more sensors with respective time stamps,
and converting the data to signals that may be transmitted by the
acoustic transducer 36. In addition, the acoustic signal(s) may
include operating parameters of the second implant 32 and/or a
device (not shown) coupled to the second implant 32. The acoustic
transducer 16 of the control implant 12 may receive the acoustic
signal(s) and convert the acoustic signal(s) into one or more
electrical signals from which the electrical circuitry 14 of the
control implant 12 may extract physiological data or other
information generated by the second implant 32. The control implant
12 may store the data, e.g., for later retrieval and/or
transmission to an external recorder and/or controller. In
addition, the control implant 12 may use the data to control
another implant (not shown) that may be coupled directly, e.g., via
one or more leads, or indirectly, e.g., via acoustic telemetry, to
the control implant 12. For example, the control implant 12 may
interrogate the second implant 32 to obtain data related to
physiological parameters of the patient, and then control another
implanted device, e.g., a pacemaker or insulin pump, to operate in
a particular manner.
[0069] If the second implant 32 is configured to operate
continuously and/or indefinitely, at step 80, the control implant
12 may transmit one or more acoustic signals to deactivate the
second implant 32 after it has obtained sufficient data. Similar to
the activation signal(s) described, the deactivation signal(s) may
include an initiation pulse followed by a confirmation pulse or
other sequences necessary to ensure the appropriate implant
responds appropriately. Once the deactivation signal is received by
the second implant 32, the switch 44 may open, returning the second
implant 32 to its sleep mode. Alternatively, the implant 132 may
include a timer (not shown), such that the switch 44 remains closed
only for a predetermined time, e.g., monitoring pressure
continuously or intermittently when activated, whereupon the switch
44 may automatically open, returning the implant 132 to its sleep
mode.
III. Exemplary Embodiments
[0070] A. Measuring Physiological Pressure
[0071] In one embodiment, a dormant implant, such as the implant 32
shown in FIG. 1, may be used to monitor physiological pressure at a
location within a patient's body where the dormant implant 32 is
implanted. For such an application, the dormant implant 32 may
include a pressure sensor (not shown) coupled to the electrical
circuitry 34. The pressure sensor may be contained within the
implant 32, i.e., with an active sensor probe exposed to pressure
within the patient's body, although, alternatively, the pressure
sensor may be coupled to the implant 32, e.g., by one or more leads
(in either case, this pressure sensor may be referred to herein as
the "internal pressure sensor").
[0072] Because the internal pressure sensor may measure absolute
pressure, it may be necessary to determine the patient's
physiological pressure, i.e., a gauge pressure, within the
patient's body from this absolute pressure measured. To accomplish
this, the patient may carry an "external" pressure sensor (not
shown) for measuring ambient barometric pressure. The external
pressure sensor may assign and/or store a time stamp with any
barometric pressure measured, e.g., uniquely identifying a time,
date, and the like when the barometric pressure was measured. The
sensor may include a timer and/or memory to facilitate time
stamping the barometric pressure data. Alternatively, the dormant
implant 32 and/or the control implant 12 may assign a time stamp to
barometric pressure data obtained from the external pressure
sensor.
[0073] For example, the external pressure sensor may be secured to
an exterior of the patient's skin, e.g., on a patch adhered to the
patient's skin, a belt, or otherwise carried such that it is
exposed to ambient pressure outside the patient's body. The control
implant 12 and/or the dormant implant 32 may be coupled to the
external sensor, e.g., directly via one or more leads, or
indirectly, e.g., via a wireless transmitter/receiver, such as an
acoustic or RF transducer. The control implant 12 or the dormant
implant 32 may assign a time stamp to the barometric pressure data,
e.g., using their internal clock(s) and/or may store the barometric
pressure data and associated time stamp locally in memory.
[0074] The dormant implant 32 may be used to measure absolute
internal pressure data using the internal pressure sensor. The
dormant implant 32 may assign a time stamp to any internal pressure
data, and transmit the time stamp to the control implant 12 along
with the associated internal pressure data. The control implant 12
may then subtract the barometric pressure (obtained from the
external sensor) from the absolute pressure (obtained from the
internal sensor) having the same time stamp to yield the desired
physiological pressure at the time identified by the time stamp.
The control implant 12 may then store any of the data, e.g.,
physiological pressure data and/or the other data, locally in
memory for later use, and/or may use the data to monitor and/or
change treatment parameters related to the patient.
[0075] In another embodiment, a barometric pressure sensor (not
shown) may be implanted in the patient's body, e.g., subdermally
near the control implant 12. The sub-dermal sensor may be coupled
to the control implant 12, e.g., directly (via one or more leads,
or via a pressure lumen of a catheter configured to transfer
pressure) or indirectly (via acoustic telemetry or other wireless
communications link), similar to the external sensor described
above. Alternatively, if the control implant 12 is implanted
subdermally or otherwise close to the skin, a barometric pressure
sensor may be included within the control implant 12, e.g., beneath
a pressure sensitive area of the casing 20 of the control implant
12. Although a subdermal pressure sensor may not provide a precise
measure of barometric pressure, it may provide a sufficiently
accurate estimate of barometric pressure to allow the physiological
pressure to be reasonably estimated. Other apparatus and methods
for obtaining barometric pressure data, e.g., using a location
finder, are disclosed in co-pending application Ser. No.
10/152,091, filed May 20, 2002, and entitled "Barometric Pressure
Correction Based on Remote Sources of Information," and U.S. Pat.
No. 6,234,973 issued to Meador et al. The disclosures of these
references and any others cited therein are expressly incorporated
by reference herein.
[0076] In a preferred embodiment, the system 10 may be used to
monitor pressure within a patient's cardiovascular system. For
example, one of the implants, i.e., the control implant 12 or the
dormant implant 32, may be incorporated into and/or coupled to
other diagnostic and/or therapeutic devices implanted within the
patient's cardiovascular system, e.g., a pacemaker. The other
implant may be implanted relatively close to the surface of the
patient's body, e.g., subdermally. For example, the control implant
12 may be located subdermally, while the dormant implant 32 may be
implanted deeper within the patient's body, e.g., within a blood
vessel or adjacent to the patient's heart. For a deeply implanted
dormant implant 32, it is preferred that the energy source 38 be a
battery having sufficient power to allow the dormant implant 32 to
operate intermittently for an extended period of time without
requiring recharging or exchange. The acoustic switch 42 may allow
the implant 32 to remain dormant, i.e., using little or no
electrical energy, for extended periods of time until activated by
the control implant 12, thereby minimizing its energy consumption
and extending its useful life.
[0077] To illustrate the energy requirements of a dormant implant,
the energy consumption of a dormant acoustic implant (such as those
disclosed in the applications incorporated by reference above),
when activated, may be about five microamperes (I.about.5.mu.A).
The minimal required operation time may be as low as about one (1)
second. Assuming three (3) seconds for sampling a few heartbeats
(t=3 seconds), and assuming that about ten (10) pressure samples
per day may be desired, the total sampling duration, T, over a year
would be about three hours (T=3.times.10.times.365=10.sup.4
seconds.about.3 hours). This would result in the amount of power
being consumed during a year of such pressure measurements to be
about fifteen microampere hours (P.sub.sampling=15.mu.A Hr).
[0078] The leakage current through a properly functioning acoustic
switch should be smaller than about one nanoampere (1 nA). Assuming
one nanoampere (1 nA) leakage rate, the leakage over a year will be
about nine microampere hours (P.sub.leakage=1 nA.times.8760
Hr=8.7.mu.A Hr). Thus, the total power consumed by a dormant
implant, including desired activation time and leakage would be
about twenty four microampere hours (24.mu.A Hr).
[0079] Batteries are available that may be incorporated into an
implant while maintaining the overall implant size not larger than
eight millimeters long, two millimeters wide, and 0.3 millimeters
thick (8 mm.times.2 mm.times.0.3 mm,
Length.times.Width.times.Thickness). For example, a thin film
lithium battery to accommodate this size may have a capacity of
about two hundred microampere hours per square centimeter per
fifteen micrometer thickness (200.mu.A Hr cm.sup.-2/15.mu.m) thick
cell. Assuming ten (10) layers of cells, the overall capacity of
such a battery would be about two thousand (2,000).mu.A Hr
cm.sub.-2. For a battery cell area of about 0.8 cm.times.0.2 cm,
the overall capacity of the battery (assuming fifty percent (50%)
cathode efficiency) would be about one hundred sixty microampere
hours (P.sub.battery=0.8.times.0.2.times.1000=160.mu.A Hr).
[0080] This suggests that, given the assumption that ten (10)
pressure samples are taken per day, the battery life would be more
than six years. If the battery is rechargeable, e.g., using
acoustic energy transformed using an energy exchanger, such as the
acoustic transducer 36 described above (and disclosed in U.S. Pat.
No. 6,140,740, the disclosure of which is expressly incorporated
herein by reference), this life may be extended further.
[0081] Turning to FIG. 5, an exemplary embodiment of a system 110
is shown that includes a control implant 112 and a plurality of
dormant implants 132 for monitoring hypertension within a patient
90. Although two dormant implants 132 are shown, it will be
appreciated that one or more implants 132 may be used, depending
upon the number of points from which pressure is desired to be
measured. The control implant 112 and/or dormant implant(s) 132 may
be constructed similar to any of the embodiments described
above.
[0082] Hypertension is one of the most widespread diseases in the
modern world, affecting an estimated fifty million people in the
United States alone, and with about one million new cases being
diagnosed annually. It is often devoid of symptoms and as many as
one third of patients are unaware of their illness. Nevertheless,
hypertension is strongly associated with a high risk for stroke,
chronic heart failure ("CHF"), myocardial infarction ("MI"), renal
failure, and other health problems, and may have a causal
relationship with many of these diseases. Direct mortality from
hypertension was attributed to about forty two thousand (42,000) in
the United States in 1997, and it was a contributing factor in
about two hundred ten thousand (210,000) additional deaths.
[0083] Blood pressure (BP) regulation is based on a complex
neuro-hormonal balance, involving a wide variety of systemic and
local regulating hormones and substances that regulate cardiac
function, systemic resistance, and renal function. Feedback may be
provided by groups of baroreceptors located in the cardiac atrium
and in the carotid arteries. Hypertension is defined as a systolic
pressure above about one hundred forty millimeters of Mercury (140
mm Hg) and/or a diastolic pressure above about ninety millimeters
of mercury (90 mm Hg). Between about ninety and ninety five percent
(90-95%) of hypertension is primary. Hypertension is often
diagnosed serendipitously during routine BP measurements, but may
also produce symptoms such as dizziness, headaches, or vision
disturbances. Of the about fifty million Americans estimated to
have hypertension, about thirty two percent (32%) are unaware of
their condition, about fifteen percent (15%) have mild hypertension
and are not medicated, about twenty seven percent (27%) are
medicated and their BP is well controlled, while about twenty six
percent (26%) are medicated without achieving proper control of the
BP.
[0084] Treating hypertension is a complex task, and may address
several points in the regulation of BP. However, the task is often
difficult, and half the patients being treated for hypertension may
not achieve proper control of their BP. The lack of control
contributes significantly to associated morbidity and mortality,
imposing a high cost on the health care system and society at
large.
[0085] To monitor and/or treat hypertension, a patient's BP may be
measured periodically, e.g., generally during office visits with a
physician. In some cases, this may be supplemented by home
measurements by the patient. However, whether these infrequent
measurements are done, the therapy and the measure for the success
of the therapy are based on sporadic, random measurements.
Monitoring using a BP Holter device, a twenty four (24) hour BP
recording device, may be employed to produce a more comprehensive
picture of the disease in uncontrolled patients. The device,
however, is uncomfortable, cumbersome, and expensive to use, and
its clinical application has been limited since it cannot be used
on a chronic base.
[0086] In contrast, the system 110 of FIG. 5 may allow a patient's
BP to be measured frequently over an extended period of time. As
shown, each dormant implant 132 may be implanted in an artery, such
as the iliac artery 92 or the aorta 94 (which may be more easily
accessed, due to their size, with minimal convenience, and/or which
may be more easily protected). Within the artery, the dormant
implant(s) 132 may monitor the patient's BP periodically, e.g., at
a frequency programmed by the patient's physician. For example, the
control implant 112 may be programmed at time of implantation to
periodically interrogate each dormant implant 132, e.g., several
times a day. Alternatively, the control implant 112 may be
programmed periodically using an external device (not shown). In
this alternative, the control implant 112 may include a receiver,
which may be the same acoustic transducer used to transmit acoustic
signals to and/or receive acoustic signals from the dormant
implant(s) 132. Alternatively, the control implant 112 may include
a separate receiver, e.g., a RF or acoustic transmitter/receiver,
that may communicate with external devices.
[0087] Each dormant implant 132 may be no larger than about nine
millimeters in length by two millimeters in width, by one
millimeter in thickness (9 mm.times.2 mm.times.1 mm,
L.times.W.times.T). The dormant implant(s) 132 may be implanted
endoluminally, for example, using a catheter or sheath, e.g., about
seven French (7 Fr.) or smaller, that may be introduced
percutaneously into a peripheral artery, e.g., a femoral artery,
and advanced to the implantation site using conventional
methods.
[0088] In one embodiment, the implant 132 may be secured within the
artery using a scaffolding structure or other fixture, similar to a
stent, to which the implant 132 may be secured. Exemplary
structures that may be used to carry and/or deliver a dormant
implant are disclosed in U.S. Pat. No. 6,442,413 or published PCT
application No. WO 99/34,731. The disclosures of these references
and any others cited therein are expressly incorporated herein by
reference. Alternatively, a dormant implant may be attached to a
graft structure for detecting endoleaks within an aneurysm, such as
those disclosed in co-pending application Ser. No. 09/522,724,
filed Mar. 10, 2000, the disclosure of which is expressly
incorporated herein by reference. The implant 132 may be implanted
in a dedicated procedure, may be implanted in conjunction with
another procedure, e.g., a catheterization procedure, such as
coronary catheterization or a peripheral intervention, or may be
sutured in a vessel in conjunction of another open or minimally
invasive surgical or endoscopic procedure, such as coronary
bypass.
[0089] The control implant 112 may be implanted at a different
location than the implantation site(s) of the pressure sensing
implant(s), for example, at a sub-dermal location within the
patient's abdomen. The location may be accessed via a small
superficial incision, e.g., about two centimeters (2 cm) long, to
create a pocket within which the control implant 112 may be
received.
[0090] Once implanted, the control implant 112 may periodically
interrogate the dormant implant(s) 132, which may then acquire BP
data and transfer the data back to the control implant 132,
whereupon the control implant 112 may store the data (preferably
along with associated time stamps) within its memory. Optionally,
in addition to BP measurements, the system may also acquire and
store data related to the patient's exertion, e.g., to correlate
the patient's BP to his/her level of exertion at the time. For
example, a silicon one accelerometer sensor (not shown) may be
provided in the control implant or otherwise carried by the patient
to monitor the patient's level of physical activity. In addition or
alternatively, the system may determine the patient's posture at
the time of obtaining BP data for calculating an orthostatic
correction factor.
[0091] Occasionally, e.g., at regularly scheduled time, the control
implant 112 may be interrogated, e.g., in a clinic, hospital, or
other health care facility to receive the BP (and other associated)
data to monitor the patient's condition and/or modify their
treatment. To obtain the data, an external controller and/or
recorder may be provided, similar to that disclosed in the
applications incorporated by reference above. The recorder may be
placed in contact with the patient's skin, e.g., in close proximity
to the control implant 112, and the control implant 112 may be
instructed to transmit the BP data, e.g., using acoustic telemetry
and the acoustic transducer 116, or using another communication
link, e.g., RF telemetry.
[0092] Alternatively, a home-based patient monitor, e.g., a
controller and/or recorder (not shown), may be used that may
interrogate the control implant 112 transfer the BP data, e.g.,
over telephone, internet, or other telecommunications systems, to a
health care facility for evaluation. Optionally, the external
controller may be used to change the frequency and/or other
parameters of the activities performed by the control implant 112
and/or dormant implants 132. For example, the external controller
may transmit new parameters to the control implant 112, which may
store them for future activity and/or relay them to any dormant
implants 132 with which it communicates.
[0093] The BP data transmitted by the control implant 112 may
include full pressure patterns or simply one or more desired
parameters, such as systolic, diastolic, and/or mean blood
pressure. The collected data may give a comprehensive picture of
the patient's disease and its management, may optimize drug
treatment of the patient, and/or may allow efficient treatment for
currently uncontrolled patients. It may also reduce the frequency
of office visits and hospitalizations, thereby reduce the cost of
treating the patient.
[0094] B. Heart Pressure Monitoring
[0095] In another embodiment, the systems and methods of the
present invention may be used for monitoring pressure with heart
chambers and/or great vessels within a patient's heart. The data
obtained may be used to provide physiological feedback to a device,
e.g., for a pacing implant, such as a pacemaker or bi-ventricle
pacer, in order to optimize the performance to the device.
[0096] For example, a bi-ventricular pacemaker (not shown) may
control a delay between the contractions of different chambers of a
patient's heart, e.g., to optimize the pumping efficiency of the
heart. A dormant transducer may act as a telemetric pressure
sensor, transmitting pressure data from a vessel, e.g., pulmonary
artery, left atrium, or left ventricle, to the bi-ventricular
pacemaker for providing feedback to the pacemaker. A dormant
implant may also be used to measure pressure and transfer pressure
data to improve the performance of a defibrillator.
[0097] An implantable cardioverter defibrillator (ICD) is a device
that may be implanted in the chest to monitor for and, if
necessary, correct episodes of rapid heartbeat. If the heartbeat
gets too fast (ventricular tachycardia), the ICD may stimulate the
heart electrically to restore a normal rhythm (antitachycardia
pacing). In cases where the heartbeat is so rapid that the person
may die (ventricular fibrillation), the ICD may also give an
electric shock (defibrillation) to "reset" the heartbeat.
[0098] To facilitate deciding what mode for the ICD to use, systems
and methods in accordance with the present invention may be used to
monitor pressure within the heart chambers in order to
differentiate between conditions, e.g., whether a patient is
experiencing atrial fibrillation or ventricular fibrillation. For
example, a system similar to those described above may be provided
that includes one or more dormant implants implanted in the left
ventricle, the left atrium, and/or the pulmonary artery of the
patient. A control implant may be implanted subcutaneously, e.g.,
by creating a small superficial incision, e.g., about two or three
centimeters (2-3 cm) long, in the chest within which the control
implant may be inserted, whereupon a few sutures may be used to
close the incision. The control implant may be coupled to an ICD,
e.g., directly or indirectly, similar to the embodiments described
above. Alternatively, the components of the control implant may be
incorporated into an ICD.
[0099] During use, the control implant may activate one or more
dormant implants that may measure pressure in the respective
cardiac region(s), and transmit the information to the control
implant. This may involve activating multiple dormant implants
alternately, sequentially, and/or simultaneously, receiving
pressure data and storing the data in memory of the control
implant, similar to the embodiments described previously. A health
care profession and/or the patient may periodically download the
pressure data using an external device communicating using acoustic
or RF telemetry, also similar to the embodiments described above.
The readings may enable the physician to make a decision about the
adequacy of the medical treatment the patient receives, and make
the appropriate corrections, if required, e.g., by reprogramming
the patient's ICD, control implant, and/or dormant implant(s). This
in turn, may ensure better patient treatment, better use of the
medical resources, and reduce the need for hospitalization.
[0100] Alternatively, the system may allow an ICD to automatically
determine whether merely to stimulate or to defibrillate, since
these two types of fibrillation require different treatments. One
or more dormant implants may be provided within different chambers
of the patient's heart, e.g., for monitoring pressure therein. A
control implant may be provided outside the heart, e.g., coupled to
or provided within a pacemaker, that may selectively or
periodically interrogate the dormant implant(s) to obtain pressure
data. The data may then allow the control implant and/or pacemaker
to determine the appropriate response to the patient's
condition.
[0101] Alternatively, the systems and methods of the present
invention may be used to provide hemodynamic feedback for a
congestive heart failure (CHF) patient. Hemodynamic information,
and more specifically pressure information, may be used to improve
treating CHF patients. CHF is a complex chronic and progressive
disease, in which the capacity of the heart to pump is compromised,
and the ability of the patient to perform physical activity is
reduced. The body employs a variety of compensatory mechanisms to
offset the pumping failure, which becomes symptomatic when their
compensatory capacity is exceeded. The overall prognosis for
patients diagnosed with heart failure is one of a gradual
deterioration of cardiac function, eventually leading to death.
[0102] Managing CHF is a complex task, and involves balancing
several drugs, which may interact with each other and/or trigger
further compensatory responses. Thus, treating CHF is an art of
balancing the hemodynamic status of the patient in a state of
compensation in order to slow progression of the disease. The
delicate balance of compensation may be easily upset, resulting in
decompensation crises. Current monitoring techniques may not
prevent these episodes, which account for about one million
hospitalizations every year in the United States, totaling about
six and a half million hospital days a year.
[0103] C. Providing a Feedback Loop for Insulin Dosing
[0104] Diabetes is the sixth leading cause of death in the United
States and is rapidly increasing in prevalence. For millions of
diabetics who cannot be treated by dietary changes alone,
successful control of their disease depends upon adequately
monitoring and treating blood sugar levels with insulin. To do so,
diabetics must repeatedly stick their fingers with needles and
submit blood samples to a blood sugar or glucose test. Depending
upon the result, they must then inject themselves with a dose of
insulin to bring their glucose back to an acceptable level. Failure
to maintain the appropriate blood sugar level may lead to serious
complications involving multiple body organs and progression of
cardiovascular and kidney disease, vision impairment, and/or
peripheral vascular disease.
[0105] Even with these incentives to maintain appropriate glucose
control, many patients consider the endless cycle of finger-sticks
and insulin injections to be burdensome. In addition, for maximum
effectiveness, insulin should be administered as closely as
possible to the time when it is needed. This time, however, may
occur at an inconvenient moment, e.g., in the middle of a meal or
in a social environment where there may be stigma associated with
syringes or other devices used to deliver insulin. Thus, a diabetic
may often compromise proper glucose control for convenience, social
conformity, and/or quality of life. Too often, these actions lead
to less than optimal blood sugar control, diminished outcomes for
diabetics, and increased hospitalization costs.
[0106] Even a model diabetic patient who does not miss a blood
sugar measurement or insulin injection, however, cannot monitor
glucose with the level of precision obtained by the body's natural
insulin producer, the pancreas. For diabetics, the most important
function of the pancreas is to produce the hormone insulin. A
properly functioning pancreas continuously monitors blood sugar
levels and responds by releasing insulin to assist the body in
using its glucose. Although it is possible to transplant a human
pancreas, the rejection rate is high and there are limited numbers
of donors available. Thus, much attention is focused on finding an
"artificial pancreas" alternative.
[0107] Artificial pancreas research attempts to produce a pump-like
device that may continuously monitor glucose levels and immediately
respond by delivering precise insulin doses needed at any given
moment, just as the human pancreas does naturally. Insulin pumps
are already available, for example, from companies such as Mini Med
(CA). There are currently two types of insulin pumps available, a
fully implanted pump that is implanted within a patient's abdomen,
and an external pump that injects insulin through a needle
subcutaneously. Exemplary insulin pumps are disclosed in U.S. Pat.
Nos. 4,373,527 and 4,573,994, and in published European Patent
Application No. EP 300,552, the disclosures of which are expressly
incorporated herein by reference.
[0108] Turning to FIG. 6, a system 410 is shown that includes a
control implant 412 and a glucose sensor 432 that may be implanted
within a patient's body 90 to provide feedback to an insulin pump
450. As explained above, the insulin pump 450 may be fully
implanted within the body 90 or may be external the body 90 with a
needle (not shown) extending from the pump into the patient's body.
If the insulin pump 450 is implanted, the control implant 412 may
be coupled directly to the insulin pump 450, e.g., via one or more
leads, or indirectly, e.g., via wireless telemetry. Alternatively,
the components of the control implant 412 may be incorporated
directly into the insulin pump 450, which may then be implanted at
a desired location within the patient's body.
[0109] The control implant 412 may include one or more components,
similar to the control implants described above, e.g., an acoustic
transducer, electrical circuitry, memory, and/or an energy source
(not shown). The glucose sensor 432 may be a dormant implant
similar to the embodiments described previously, including an
acoustic switch, an acoustic transducer, an energy source,
electrical circuitry, and/or a sensor for measuring blood sugar
concentration (not shown). The glucose sensor 432 may be implanted
at any location allowing it to measure the patient's glucose
concentration. Preferably, because the service life of a glucose
sensor may be relatively short, e.g., currently only days (and
possibly lasting weeks or months in the future), the glucose sensor
432 may be implanted subcutaneously, e.g., within the patient's
abdomen, or at another location that may be accessed relatively
easily. Thus, all or part of the glucose sensor 432 may be
replaced, after its service life has expired, with a new glucose
sensor (not shown) that may continue to provide feedback to the
control implant 432 and/or insulin pump 450.
[0110] Thus, the system 410 may provide a closed loop, allowing
frequent feedback to control a rate of insulin delivered by the
insulin pump 450, and thereby preventing substantial fluctuations
of the patient's blood sugar concentration. An acoustic transducer
(not shown) of the control implant 412 may periodically interrogate
the glucose sensor 432, whereupon the glucose sensor 432 may
measure the patient's blood sugar concentration and transmit data
back to the control implant 412 via its acoustic transducer (also
not shown). The control implant 412 may control the rate of insulin
delivery by the pump 450 in response to the data obtained from the
glucose sensor 432. Because of the dormant state of the glucose
sensor 432, relatively low amounts of energy may be consumed by the
glucose sensor 432, which may extend the life of the components of
the system 410 substantially, as compared to systems using other
modes of communication, such as RF telemetry. Thus, acoustic
telemetry may provide a more efficient and convenient method for
transferring blood sugar concentration data from the glucose sensor
432 to the insulin pump 450 via the control implant 412.
[0111] It will be appreciated that the above descriptions are
intended only to serve as examples, and that many other embodiments
are possible within the spirit and the scope of the present
invention.
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