U.S. patent application number 13/187979 was filed with the patent office on 2012-01-26 for vestibular implant system with internal and external motion sensors.
This patent application is currently assigned to MED-EL ELEKTROMEDIZINISCHE GERAETE GMBH. Invention is credited to Carolyn Garnham, Andreas Jager, Martin Zimmerling.
Application Number | 20120022616 13/187979 |
Document ID | / |
Family ID | 45494237 |
Filed Date | 2012-01-26 |
United States Patent
Application |
20120022616 |
Kind Code |
A1 |
Garnham; Carolyn ; et
al. |
January 26, 2012 |
Vestibular Implant System with Internal and External Motion
Sensors
Abstract
A partially implantable vestibular prosthesis system is
described which includes an external movement sensor that is
attachable to the outer skin surface of a patient's head for
generating an external movement signal which represents movement of
the patient's head. An external transmitter is in communication
with the external movement sensor and provides an electromagnetic
transmission of an implant communication signal which includes a
signal component based on the external movement signal and an
electrical power component that provides electrical power for
implanted system components. An internal movement sensor is
implantable under the skin of the patient's head for generating an
internal movement signal which represents movement of the patient's
head. And an implant processor also is implantable under the skin
and in communication with the internal movement sensor and the
external transmitter for generating an implant stimulation signal
based on one of the movement signals to electrically stimulate
target neural tissue for vestibular sensation by the patient.
Inventors: |
Garnham; Carolyn; (Matlock
Derbyshire, GB) ; Zimmerling; Martin; (Patsch,
AT) ; Jager; Andreas; (Reith bei Seefeld,
AT) |
Assignee: |
MED-EL ELEKTROMEDIZINISCHE GERAETE
GMBH
Innsbruck
AT
|
Family ID: |
45494237 |
Appl. No.: |
13/187979 |
Filed: |
July 21, 2011 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61366345 |
Jul 21, 2010 |
|
|
|
Current U.S.
Class: |
607/60 |
Current CPC
Class: |
A61B 5/6867 20130101;
A61B 2562/0219 20130101; A61N 1/375 20130101; A61B 5/6814 20130101;
A61N 1/36036 20170801; A61N 1/37211 20130101; A61B 5/11 20130101;
A61B 5/6817 20130101 |
Class at
Publication: |
607/60 |
International
Class: |
A61N 1/372 20060101
A61N001/372 |
Claims
1. A partially implantable vestibular prosthesis system comprising:
one or more external movement sensors attachable to the skin of a
patient's head for generating an external movement signal
representing movement of the patient's head; an external
transmitter in communication with the external movement sensor for
transcutaneous transmission of an implant communication signal
having an electrical power component and a signal component based
on the external movement signal; one or more internal movement
sensors implantable under the skin of the patient's head for
generating an internal movement signal representing movement of the
patient's head; and an implant processor implantable under the skin
and in communication with the internal movement sensor and the
external transmitter for generating an implant stimulation signal
based on one of the movement signals to electrically stimulate
target neural tissue for vestibular sensation by the patient.
2. A system according to claim 1, wherein the external movement
sensor is adapted to be attachable within the ear canal of the
patient's head.
3. A system according to claim 2, wherein the external movement
sensor is adapted to be magnetically attachable within the ear
canal over a corresponding implanted holding magnet which
establishes a correct position for the external movement
sensor.
4. A system according to claim 2, wherein the external movement
sensor is adapted to leave a portion of the ear canal unoccluded to
allow hearing sensation by the tympanic membrane.
5. A system according to claim 1, wherein the external movement
sensor is adapted to be magnetically attachable on the scalp of the
patient's head over a corresponding implant magnet arrangement
which establishes a correct position for the external movement
sensor.
6. A system according to claim 5, wherein the external movement
sensor includes a plurality of magnets for cooperation with a
corresponding plurality of magnets in the implant magnet
arrangement.
7. A system according to claim 6, wherein the plurality of magnets
in the external movement sensor are arranged with asymmetrical
magnetic polarities.
8. A system according to claim 6, wherein the plurality of magnets
in the external movement sensor are arranged with spatial
asymmetry.
9. A system according to claim 6, wherein the plurality of magnets
in the external movement sensor are arranged with asymmetrically
different diametrical orientations.
10. A system according to claim 6, wherein the plurality of magnets
in the external movement sensor are arranged with asymmetrically
different distances between cooperating pairs of magnets.
11. A system according to claim 6, wherein the plurality of magnets
in the external movement sensor are arranged to require orientation
of the external movement sensor so that each magnet in the external
movement sensor is cooperating with another corresponding magnet in
the implant magnet arrangement in order to have enough magnetic
attraction force to securely hold the external movement sensor.
12. A system according to claim 1, wherein the implant stimulation
signal is preferentially based on the external movement signal when
available and otherwise is based on the internal movement
signal.
13. A system according to claim 1, wherein the implant stimulation
signal is preferentially based on the internal movement signal when
the external movement signal exceeds some acceptable threshold
value.
14. A system according to claim 1, further comprising: a sensor
position sensor for generating a sensor movement signal
representing movement of the external sensor relative to the
patient's head.
15. A system according to claim 1, wherein the implant processor
includes a baseline pacing mode wherein the implant stimulation
signal is generated without reference to a movement signal.
16. A system according to claim 1, wherein the target neural tissue
includes the semicircular canals of the inner ear.
17. A system according to claim 1, wherein the target neural tissue
includes the vestibular nerve.
Description
[0001] This application claims priority from U.S. Provisional
Patent Application 61/366,345, filed Jul. 21, 2010, which is
incorporated herein by reference.
TECHNICAL FIELD
[0002] The present invention relates to implantable stimulation
systems, and more specifically to a vestibular implant system with
internal and external motion sensors.
BACKGROUND ART
[0003] A normal ear directs sounds as shown in FIG. 1 from the
outer ear pinna 101 through the generally cylindrical ear canal 110
(typically about 26 mm long and 7 mm in diameter) to vibrate the
tympanic membrane 102 (eardrum). The tympanic membrane 102 moves
the bones of the middle ear 103 (malleus, incus, and stapes) that
vibrate the cochlea 104, which in turn functions as a transducer to
generate electric pulses to the brain that are interpreted as
sounds. In addition, the inner ear also includes a balance sensing
vestibular system which involves the vestibular labyrinth 105, its
three interconnected and mutually orthogonal semi-circular canals:
the superior canal 106, posterior canal 107, and horizontal canal
108 (as well as the otolith organs, the utricle and saccule--not
shown). The canals and spaces of the vestibular labyrinth 105 are
filled with endolymph fluid which moves relative to head movements,
thereby activating hair cells that send an electrical balance
signal to the brain via the vestibular nerve 111.
[0004] In some people, the vestibular system is damaged or
impaired, causing balance problems such as unsteadiness, vertigo
and unsteady vision. Vestibular implants are currently under
development, with one of the initial challenges being the
relatively significant amount of power required by the
gyroscope/accelerometer arrays used for the movement sensors
(gyroscopes and linear accelerometers). Presently, one lower power
device is the STMicroelectronics L3G4200D, which is a three-axis
digital gyroscope that encodes all three-dimensional axes of
rotation. This device measures 4 mm square by 1 mm thick and needs
various power and signal lines to operate at the specified power
requirement of at least 6 mA at 3.6V.
[0005] For use in an implant system, the power for one or more
vestibular movement sensors can be supplied from a body worn
battery pack and transcutaneously transmitted with a head placed
coil. But the power losses for such a transcutaneous supply are
roughly a factor of two and there also is an additional risk of the
head coil falling off, power being lost, and the patient becoming
disoriented and even falling. A somewhat better solution might be
to have an implanted battery supplying power to the implanted
movement sensors, but (due to the high power requirements) this
approach is likely to require a large battery volume or very
frequent re-charging of the battery. Furthermore, failure of any of
the modules of the device would require re-implantation, with
consequent risk to hearing and residual vestibular function.
[0006] Other arrangements have also been proposed for vestibular
implant systems. For example, head-worn sensor arrays have been
proposed that would be secured by a holding band around the head,
but this approach would create an unacceptably high risk of
movement of the sensors relative to the head. Implanted sensor
arrays powered via a percutaneous plug have also been proposed, but
the serious problems with percutaneous structures are notoriously
well-known. Challa and Bhatti, A Micromachined Cupula: Toward
Biomimetic Angular Velocity Sensor Prosthesis, 33.sup.rd Mid-Winter
Research Meeting, Assn. for Research in Otolarygology, Feb. 6-10,
2010 (incorporated herein by reference) proposed a basic re-design
of the sensor array around the fluidic principle used by the
balance organ itself to reduce power requirements, but more time
and extensive reliability testing will be needed to complete the
development of such a device.
[0007] Application US2005/0267549 by Della Santina et al.
(incorporated herein by reference) teaches a combined
cochlea/vestibular stimulation system with a speech and motion
sensing processor (SMP) placed either externally or internally.
Application US2002/0104971 by Merfeld et al. (incorporated herein
by reference) teaches a motion sensing system to be worn not only
on the head but also on other body parts.
[0008] For safety reasons, it is important that the externally worn
unit including the sensor is always placed in a known, correct
orientation when driving the implant. Otherwise the sensor's
misaligned input to signal processing, and ultimately to the neural
stimulation sites, will lead to a mismatch between real and
perceived head movement. Under specific circumstances this may
cause a patient to fall and possibly result in injury. This is of
special relevance when the implant is located on the head such that
sometimes the patient can not visually observe placing the external
unit over the implant.
[0009] The correct placement of an external unit relative to an
implant is currently solved for cochlear implants and other
auditory implants by a pair of axially magnetized magnets. One
magnet is placed in the center of the implant's receiver coil. The
other magnet is placed in the center of the sender coil in the
external unit. While placing the external unit's magnet in
proximity to that of the implant, the magnetic attraction force
causes the external coil to be placed over the implant's coil in a
concentric orientation. But there is a remaining degree of freedom
in that the external unit can be turned in the radial direction a
full 360 degrees relative to the implant. Due to this degree of
radial rotation freedom, this solution is not appropriate for
placing an external sensor as part of a vestibular implant
system.
SUMMARY
[0010] Embodiments of the present invention are directed to a
partially implantable vestibular prosthesis system which includes
an external movement sensor module that is attachable to the outer
skin surface of a patient's head for generating an external
movement signal which represents movement of the patient's head. An
external transmitter is in communication with the external movement
sensor and provides an electromagnetic transmission of an implant
communication signal which includes a signal component based on the
external movement signal and an electrical power component that
provides electrical power for the implanted system components. An
additional internal movement sensor is implantable under the skin
of the patient's head for generating an internal movement signal
which represents movement of the patient's head. And an implant
processor also is implantable under the skin and in communication
with the internal movement sensor and the external transmitter for
generating an implant stimulation signal based on one or more of
the movement signals to electrically stimulate target neural tissue
such as the semicircular canals of the inner ear, the otolith
organs, and/or the vestibular nerve for augmentation or
modification of the patient's vestibular function.
[0011] In some specific embodiments, the external movement sensor
may be adapted to be attachable within the ear canal of the
patient's head. For example, the external movement sensor module
may be magnetically attachable within the ear canal over a
corresponding implanted holding magnet which establishes a correct
position for the external movement sensor. The external movement
sensor module also may be adapted to leave a portion of the ear
canal unoccluded to allow hearing sensation by the tympanic
membrane. In other embodiments, the external movement sensor module
may be magnetically attachable on the scalp of the patient's head
over a corresponding implanted holding magnet which establishes a
correct position for the external movement sensor module.
[0012] For example, the external movement sensor module may include
multiple magnets for cooperation with corresponding multiple
magnets in the implant magnet arrangement. In such an embodiments,
the magnets in the external movement sensor may be arranged with
asymmetrical magnetic polarities, with spatial asymmetry, with
asymmetrically different diametrical orientations, and/or with
asymmetrically different distances between cooperating pairs of
magnets. And the magnets in the external movement sensor may be
arranged to require orientation of the external movement sensor so
that each magnet in the external movement sensor is cooperating
with another corresponding magnet in the implant magnet arrangement
in order to have enough magnetic attraction force to securely hold
the external movement sensor.
[0013] The implant stimulation signal may be preferentially based
on the external movement signal when available, and otherwise may
be based on the internal movement signal. In addition or
alternatively, the implant stimulation signal may be preferentially
based on the internal movement signal when the external movement
signal exceeds some acceptable threshold value or when
communication between the external and internal components
transfers control. The implant processor may include a baseline
pacing mode wherein the implant stimulation signal is generated
without reference to a movement signal.
[0014] Some embodiments may also include a sensor position sensor
for generating a sensor movement signal representing movement of
the external sensor relative to the patient's head.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 shows various anatomical structures associated with
the human ear.
[0016] FIG. 2 shows one specific example of a partially implantable
vestibular prosthesis system.
[0017] FIG. 3 shows one arrangement for an implant processor for
use in embodiments of the present invention.
[0018] FIG. 4 shows some of the external components of one specific
embodiment.
[0019] FIG. 5 shows a top view of various components associated
with a scalp attached external movement sensor.
[0020] FIG. 6 shows a cross-sectional view of one specific
scalp-attachable external movement sensor arrangement using two
attachment magnets.
[0021] FIG. 7 shows an embodiment of an external movement sensor
using three attachment magnets.
[0022] FIG. 8 shows a sectorized attachment magnet for use in
embodiments of the present invention.
[0023] FIG. 9 A-D shows placement details of an embodiment of an
external movement sensor using three symmetrical attachment
magnets.
[0024] FIG. 10 A-D shows placement details of an embodiment of an
external movement sensor using three asymmetrical attachment
magnets.
DETAILED DESCRIPTION
[0025] Embodiments of the present invention are directed to a safe,
practicable and wearable partially implantable vestibular
prosthesis system which combines both internal and external
movement sensors. By making appropriate design choices, many of the
drawbacks from earlier approaches can be avoided. For example, in
some embodiments the internal implant movement sensor can be mainly
used as a backup signal source for a few hours (depending on the
battery life of the implant battery) when the main externally worn
movement sensor is unavailable or unreliable. Other embodiments may
use an implanted movement sensor as its normal main signal source,
with an external movement sensor serving as a system backup signal
source in the event of failure by the implanted movement
sensor.
[0026] FIG. 2 shows one specific example of a partially implantable
vestibular prosthesis system with an external movement sensor 208
that includes a three-axis digital gyroscope array 210 that
generates an external movement signal encoding three-dimensional
axes of rotation representing movement of the user's head. The
external movement sensor 208 is adapted to be positioned within the
ear canal 110 of the user where an attachment magnet 209 within the
external movement sensor 208 cooperates with a corresponding
implanted holding magnet 207 that is surgically implanted under the
skin of the ear canal 110.
[0027] An external movement sensor 208 that fits in the ear canal
110 also is well-suited for mild to moderately deaf patients (who
make up quite a large number of patients with vestibular problems)
and might be incorporated together with a hearing implant, or it
might be matched with hearing or a hearing aid on the other side,
and/or might include a sound channel or large vent to partially
transmit sound for patients with hearing in that ear. Locating the
external movement sensor 208 deep in the bony section of the ear
canal 110 provides a low probability of many movement artifacts and
a low risk of being displaced by normal activities. This is in
contrast to a more shallow location in the lower anterior portion
of the ear canal 110 where jaw movements may cause unacceptable
movement artifacts. An ideal location for external movement sensor
208 may be as shown in FIG. 2, fixed in place (e.g., with a
retaining magnet) adjacent to the posterior, superior portion of
the canal wall, deep in the bony section of the ear canal 110.
Adverse effects of jaw movements will be minimized using this
location and may be further minimized through use of a partially
occluding design or a flexible occluding volume.
[0028] For hearing patients, the external movement sensor 208
normally should take up as little room as possible in the ear canal
110 to allow adequate transmission of sound to the tympanic
membrane 102. It may be advantageous if the external movement
sensor 208 is adapted to leave a portion of the ear canal 110
unoccluded as shown in FIG. 2 to allow relatively normal hearing
sensation by the tympanic membrane 102.
[0029] Alternatively, the external movement sensor 208 could be
incorporated into a very deep canal fitting device such as a
Lyric-type hearing aid device which fits deeply within the ear
canal 110 nearer the tympanic membrane 102. For hearing patients,
the option of a deep canal fitting may be especially suitable if
designed to allow adequate transmission of sounds to the tympanic
membrane 102.
[0030] In another embodiment, some portion of the external movement
sensor 208 would need to be fitted snugly deep into the ear canal
110 for stability, but the external end of the ear canal 110 could
still be available for other uses such as other system components.
Additional device-related components then could be connected to the
deeply fitted part by a very flexible cable. For example, power
supply and signal processing components also could be located
within the outer portion of the ear canal 110 and be connected to
the external movement sensor 208 by a very flexible connector.
[0031] The external movement sensor 208 is connected by a connector
lead 212 to a behind-the-ear external processor 201. It is
advantageous if the connector lead 212 is very flexible so that
small movements of the outer ear 101 and/or the external processor
201 (such as for programming) do not disturb the fit and position
of the external movement sensor 208 in the ear canal 110. A
handling member 211 also projects out of the external movement
sensor 208 to aid the user's ability to remove the external
movement sensor 208, e.g., for bathing or device maintenance.
[0032] The external processor 201 in turn processes the external
movement signal to generate an implant communication signal that
includes a signal component based on the external movement signal
and an electrical power component that provides electrical power
for implanted system components (e.g. from a battery arrangement
within the external processor 201). The implant communication
signal from the external processor 201 is transmitted across the
skin by an external transmitter coil 202 to a corresponding implant
receiver coil 203. FIG. 4 shows the appearance of the external
components in another similar embodiment where an external signal
processor 403 and external battery power supply 402 hook onto the
outer ear of the user, with a flexible cable 404 connecting to an
external motion sensor arrangement in the ear canal and an external
transmitter coil 401 magnetically positioned on the scalp of the
user over a corresponding implanted receiver coil.
[0033] An implant processor 206 is implanted under the skin and
coupled to the implant receiver coil 203. The implant processor 206
contains an internal movement sensor that generates an internal
movement signal representing movement of the patient's head. The
implant processor 206 processes the implant communication signal to
extract its signal component (from the external movement sensor
208) and also has available the internal movement signal from the
internal movement sensor. From these, the implant processor 206
generates an implant stimulation signal based on one of the
movement signals to vestibular stimulator electrodes 205 that
electrically stimulate target neural tissue such as the
semicircular canals 106, 107, 108 of the vestibular labyrinth 105,
one or both otolith organs and/or the vestibular nerve 111 or
ganglion for vestibular sensation by the patient as a balance
signal.
[0034] FIG. 3 shows structural details of an implant housing 300
which includes a receiver coil 203 and an implant processor 206. A
custom ASIC 301 in the implant processor 206 provides the
processing functionality for producing the implant stimulation
signal, e.g., sequences of multiphasic pulses of varying
amplitude/duration and/or repetition frequency using bipolar or
monopolar stimulation, using single channel or multi-channel
stimulation to the vestibular stimulation electrodes 305 that are
connected to the implant housing 300. The implant processor 206 may
preferentially base the implant stimulation signal on the external
movement signal when it is available, and otherwise may use the
internal movement signal. Or in some embodiments, the implant
processor 206 may preferentially base the implant stimulation
signal on the internal movement signal when the external movement
signal exceeds some acceptable threshold value. In some
embodiments, the implant processor 206 also may include a baseline
pacing mode wherein the implant stimulation signal is generated
without reference to a movement signal. The embodiment shown in
FIG. 3 also has a separate reference electrode lead 304 that is
useful for the case of monopolar stimulation pulses. Also contained
within the implant housing 300 shown in FIG. 3 is the implant power
supply 302 (e.g., a rechargeable battery) that extracts the power
component from the received implant communications signal, and
powers the implant when the external components are not
attached.
[0035] The implant housing 300 also contains the internal movement
sensor 303, for example, a digital gyroscope array. The internal
movement sensor 303 may require less rotational sensitivity (in
terms of number of degrees per second) than the external movement
sensor, and therefore, may also need less power. Consequently, the
system power source (either in the external portion or an
implantable battery) could operate the system for a longer time
until recharging or change of batteries is required.
[0036] Embodiments are not limited to locating the external
movement sensor within the ear canal. For example, some embodiments
may be based on a button housing processor that is positioned and
stabilized on the scalp of the user in a fixed desired position
over the implanted device where the risk of being moved or falling
off is relatively low. This suggests a button housing device 600
such as the embodiment shown in FIG. 6 that contains a disposable
or rechargeable battery or battery array 601, a transmitter coil
604, one or more external movement sensor devices 602 (e.g.,
gyroscope arrays), an external signal processor 605 and a
positioning arrangement 603 (e.g., an external holding magnet that
cooperates with an implanted positioning magnet). The embodiment
shown in FIG. 6 also includes a pressure operated control switch
606 which the user can use to control operation of the button
housing device 600 and/or which can also switch an in the ear
device such as those described above. Unlike the earlier in the ear
canal arrangements, a button housing device 600 as shown in FIG. 6
requires no cable and may therefore have less chance of being
displaced in normal usage.
[0037] In button housing type embodiments, the implanted device can
usefully include a rechargeable implant battery that can provide
the implanted components with enough electrical energy for at least
some minutes of operation so that the external button housing
device 600 can be taken off for maintenance such as exchanging the
battery, or for showering, etc. In some embodiments, the battery
for the external button housing device 600 may be placed in a
separate housing which is connected by a cable to the external
button housing device 600. In some embodiments, the external button
housing device 600 may have a rechargeable battery that can be
recharged via an additional charger coil which is temporarily
placed over the device (e.g., for about one hour) either during
normal system operation or with a special recharge mode during
which time the implant uses its own batteries.
[0038] The embodiment shown in FIG. 6 is based on use of a single
external holding magnet, but other embodiments such as the one
shown in FIG. 5 may usefully include an additional secondary
retaining magnet for both implanted part and processor such as is
described in U.S. Pat. No. 6,348,070 (incorporated herein by
reference). In FIG. 5, the external device housing 501 includes the
usual main holding magnet 503 centered within an external
transmitter coil 505 which cooperates with a corresponding implant
holding magnet 508 centered within an implant receiver coil 506 in
an implant device 502 which also includes an implant processor and
(optional) movement sensors 507. Offset from the main arrangement
in the external device housing 501 is another secondary holding
magnet 504 that cooperates with a corresponding implant secondary
magnet 509 to provide an increased strength fixation of the
external device housing 501 in a desired position over the implant
device 502. The magnetic arrangement shown also reduces the
likelihood of rotation of the external device housing 501 to the
user's head.
[0039] FIG. 7 shows another embodiment of an external device 700
having a device housing 701 that includes a triangular arrangement
of three external holding magnets 702 that cooperate with a
corresponding triangular holding magnet arrangement in the
implanted device. This triangular arrangement of three external
holding magnets 702 provides a very strong and stable magnetic
fixation of the external device 700 over the implant device that
also reliably prevents rotation of the device relative to the head.
Such embodiments also provide a higher inductive link coefficient
of power since there is no magnet in the center of the transmitter
coil 704 which can absorb energy. An electronics package 705 within
the device housing 701 includes one or more external movement
sensors, a signal processor device and power supply. It may be
advantageous if the device base 703 is made of a soft material that
is bio-compatible and conforms easily to attach to the curved
surface of the user's scalp.
[0040] Introducing some form of asymmetry into the arrangement of
the external holding magnets 702 of the external device 700 can
help ensure that the external device 700 is held in a correct
position over the implant. For example, FIG. 9 A-D shows placement
details of an embodiment of an external device 700 using three
external holding magnets 702 arranged in an equilateral triangle
with an asymmetry of the magnet axial polarities (north vs. south).
In FIG. 9A, the left hand and bottom external holding magnets 702
are shown with south-north outward magnetic direction, while the
right hand external holding magnet 702 is shown with a north-south
outward magnetic direction. In FIG. 9A, the external device 700 is
correctly oriented over the implanted receiver coil 203 and implant
processor 206 to allow proper coupling of the communications signal
into the implant. FIG. 9B shows an incorrect attempt to place the
external device 700 only a single pair holding magnets are
attracting and two pairs of magnets are not magnetically engaged.
In this orientation, there will be no coupling of the
communications signal and the force holding the external device 700
next to the skin will be far weaker than normal so that the user
should be able to detect the improper engagement. FIG. 9C shows
another incorrect placement attempt where the external device 700
is properly centered over the implant receiver coil 203 to allow
coupling of the communications signal, but only one magnetic pair
is engaged with magnetic attraction and the other two pairs are
repelling--this improper orientation requires manual force to hold
the external device in position, and again, the user will know that
is wrong. FIG. 9D shows yet another type of incorrect placement
attempt of the external device 700 with two magnetic pairs
attracting and one pair not magnetically engaged--again, there will
be no coupling of the communications signal. Thus the asymmetry of
magnetic polarities ensures that the user will easily detect
whether or not the external device 700 is correctly oriented and
properly held in place.
[0041] Besides using different axial orientations of magnetic
polarities (north pole facing up vs. facing down) asymmetric
arranging of pairs of holding magnets can also be achieved in other
ways such as by:
[0042] using different diametrical orientations of holding
magnets
[0043] using different distances between any two pairs of holding
magnets
[0044] using holding magnets of low magnetic attraction force thus
requiring more than one pair being correctly placed to each other
to hold the external over the implant. For example, FIG. 10 A-D
shows placement details of an embodiment of an external movement
sensor using three external magnets 702 with identical axial
magnetic polarities arranged in an irregular triangle, i.e., with
spatial asymmetry.
[0045] FIG. 8 shows another arrangement useful for a holding magnet
in any of the above embodiments. That is, holding magnet 800 is
divided into multiple different magnetic sectors 801 such that
adjacent sectors are magnetized differently. In the example shown
in FIG. 8, the magnetic sectors 801 are in the specific form of pie
shaped segments but other specific shapes may also be useful. Again
the advantage of such an arrangement is to help avoid relative
movements or rotations of the external device relative to the head
of the patient which could generate inaccurate movement sensor
signals.
[0046] As explained above, the sensor elements in the external and
internal movement sensors might typically be digital gyroscope
arrays or digital accelerometers such as MEMS accelerometers. Small
movements such as from the user pulling out or pushing in the
external device or by unintended movement within the ear canal
(e.g., small slippage, rotation, jaw movements) can compensated for
by the location and effectiveness of the holding magnet arrangement
in restoring the correct position of the external device. Some
embodiments may also use a fail-safe sensor device for detecting
small movements either relative to the head, or to a passive
component located in the ear canal (e.g., magnet or small metal
plate), or to the implant itself. When activated by such relative
movement this fail-safe sensor device could either: [0047] (a)
Signal the implant to revert to a baseline pacing mode of operation
to which the patient is acclimatized, [0048] (b) Switch the implant
off, [0049] (c) Apply a correction signal to the implant for small
movements relative to the body which would be modify (e.g., be
subtracted from) the gyroscope-based sensor movement signal until
the relative movement became too large to correct for, and/or
[0050] (d) Excessive movement of the external movement sensor
device relative to the body would signal to the implant to
temporarily revert to its internal movement sensor device.
[0051] The sensing elements may be based on any one of several
known sensing methodologies such as electromagnetic, optical or
Hall effect sensing. For example, an electromagnetic field sensing
arrangement may sense the electric field in a search coil based on
proximity to a small implanted coil or other metal piece while a
transmitter coil generates a sensing field (like in a metal
detector or eddy current sensing).
[0052] Or a movement sensing arrangement may be based on a
transcutaneous light transmission system where a light source
(having a frequency that transmits well through body tissue and the
materials of the device) would be directed at the implanted magnet
(or a non-magnetic reflector) that would be coated with a surface
of high reflectance. Movement of the light source relative to the
magnet/reflector would change the amount of reflected light thereby
signaling movements in the device's position relative to the
implanted plate.
[0053] Or embodiments may have movement sensors using Hall Effect
sensing. During the implantation procedure, the surgeon can implant
a second small permanent sensor magnet under the skin deep in the
ear canal. Then, a two- or three-axis system of Hall Effect sensors
could detect changes in the exact position of the sensor magnet
relative to the device, and thereby the position of the gyroscope
relative to the head. In some embodiments, a single micro
three-axis sensor that works at a low enough current might be used
to make corrections to the movement signal applied to the implant.
The sensor array would be placed in a location of relatively high
field gradient, for example, to one side of the implanted
magnet.
[0054] Capacitive sensing could also provide the basis for the
movement sensor elements. The portion of the external motion sensor
inserted into the ear canal could contain a magnet to align it over
an implanted magnet, and a capacitive sensor could then be used to
indicate proximity of the device to the magnet and detect
displacement of the device (up to about 2 mm). This might be useful
as either a switch or as a measure of relative position and/or
speed/acceleration of changes in relative position.
[0055] Some embodiments may also include a magnetically activated
mechanical switch (like a magnetic reed switch) to deactivate power
to one or more system components when the ear canal device is
removed, or to switch the system to control of the (optional)
implanted movement sensors or to a backup (pacing) mode. Some
embodiments also may avoid continuous high sensor currents by using
a power control switch activated by movement relative to an
implanted magnet (e.g., using eddy current or capacitive sensing).
The movement could then be tracked by a three-axis Hall Effect (or
other) sensor arrangement so that power to monitor the relative
movements would only be needed once movement was initiated. A
similar relative movement sensing arrangement might also be useful
in other locations around the head, such as an arrangement having
magnet-based fixation somewhere external to the ear canal. Or an
inductive sensing circuit could measure the frequency of an
inductive link which changes when the external part is moved or
removed.
[0056] Some embodiments may further include a sensor position
sensor for generating a sensor movement signal representing
movement of the external sensor relative to the patient's head. The
system may use this information to modify one or more of the other
movement signals that encode head movements. For example, this may
be useful during power-up of the internal sensor as control is
transferred, or for modes using a stand-alone external sensor.
[0057] Embodiments of the present invention such as those described
above can be developed based on existing technologies and
components. Moreover, the external components such as the gyroscope
sensors can be readily accommodated. The overall system is also
robust against failure of some of the internal components. In
applications as a vestibular stimulation device only without
additional hearing functionality, the external components would not
need an opening for a microphone. As a result, the external
components can be sealed to be waterproof (or at least more water
resistant). In addition, there is design-inherent safety by
preventing implant stimulation if the external unit is not oriented
correctly on top of the implant.
[0058] Embodiments of the invention may be implemented in part in
any conventional computer programming language. For example,
preferred embodiments may be implemented in a procedural
programming language (e.g., "C") or an object oriented programming
language (e.g., "C++", Python). Alternative embodiments of the
invention may be implemented as pre-programmed hardware elements,
other related components, or as a combination of hardware and
software components.
[0059] Embodiments can be implemented in part as a computer program
product for use with a computer system. Such implementation may
include a series of computer instructions fixed either on a
tangible medium, such as a computer readable medium (e.g., a
diskette, CD-ROM, ROM, or fixed disk) or transmittable to a
computer system, via a modem or other interface device, such as a
communications adapter connected to a network over a medium. The
medium may be either a tangible medium (e.g., optical or analog
communications lines) or a medium implemented with wireless
techniques (e.g., microwave, infrared or other transmission
techniques). The series of computer instructions embodies all or
part of the functionality previously described herein with respect
to the system. Those skilled in the art should appreciate that such
computer instructions can be written in a number of programming
languages for use with many computer architectures or operating
systems. Furthermore, such instructions may be stored in any memory
device, such as semiconductor, magnetic, optical or other memory
devices, and may be transmitted using any communications
technology, such as optical, infrared, microwave, or other
transmission technologies. It is expected that such a computer
program product may be distributed as a removable medium with
accompanying printed or electronic documentation (e.g., shrink
wrapped software), preloaded with a computer system (e.g., on
system ROM or fixed disk), or distributed from a server or
electronic bulletin board over the network (e.g., the Internet or
World Wide Web).
[0060] Although various exemplary embodiments of the invention have
been disclosed, it should be apparent to those skilled in the art
that various changes and modifications can be made which will
achieve some of the advantages of the invention without departing
from the true scope of the invention.
* * * * *