U.S. patent application number 11/614851 was filed with the patent office on 2008-06-26 for electrically nonconductive occludent for tissue openings.
This patent application is currently assigned to Cochlear Limited. Invention is credited to Paul M. Carter.
Application Number | 20080154339 11/614851 |
Document ID | / |
Family ID | 39544023 |
Filed Date | 2008-06-26 |
United States Patent
Application |
20080154339 |
Kind Code |
A1 |
Carter; Paul M. |
June 26, 2008 |
Electrically Nonconductive Occludent For Tissue Openings
Abstract
An electrically nonconductive occludent constructed and arranged
to forcefully infill a tissue opening so as to effectively prevent
transport of electrical current, fluid and bacteria through the
tissue opening. A cochlear implant comprising: an elongate
electrode carrier member having at least one electrode disposed
thereon, wherein the carrier member is configured to traverse a
cochleostomy to position the electrodes in the cochlea; and an
electrically nonconductive occludent constructed and arranged to
circumferentially surround a portion of the carrier member
traversing the cochleostomy, and to forcefully infill cochleostomy
thereby segregating perilymphatic canals of the cochlea from
extracochlear regions.
Inventors: |
Carter; Paul M.; (West
Pennant Hills, AU) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ LLP
1875 EYE STREET, N.W., SUITE 1100
WASHINGTON
DC
20036
US
|
Assignee: |
Cochlear Limited
Lane Cove
AU
|
Family ID: |
39544023 |
Appl. No.: |
11/614851 |
Filed: |
December 21, 2006 |
Current U.S.
Class: |
607/57 ;
623/10 |
Current CPC
Class: |
A61N 1/00 20130101; A61F
11/04 20130101; A61N 1/0541 20130101; A61N 1/05 20130101; A61F 2/18
20130101 |
Class at
Publication: |
607/57 ;
623/10 |
International
Class: |
A61F 2/18 20060101
A61F002/18; A61N 1/04 20060101 A61N001/04 |
Claims
1. An electrically nonconductive occludent constructed and arranged
to forcefully infill a tissue opening so as to effectively prevent
transport of electrical current, fluid and bacteria through the
tissue opening.
2. The occludent of claim 1, wherein a component traverses the
tissue opening, and further wherein said occludent is configured to
circumferentially surround a portion of the component traversing
the tissue opening.
3. The occludent of claim 2, wherein the component is an electrode
carrier member, and further wherein said occludent is configured to
circumferentially surround said electrode carrier member thereby
segregating perilymphatic canals of the cochlea from extracochlear
regions.
4. The occludent of claim 3, wherein the electrode carrier member
is a component of a prosthetic hearing implant.
5. The occludent of claim 3, wherein the prosthetic hearing implant
comprises a cochlear implant.
6. The occludent of claim 4, wherein the tissue opening is a
cochleostomy.
7. The occludent of claim 5, wherein the cochleostomy is formed
through one of either the cochlea round window, the cochlea oval
window, the cochlea promontory, and the cochlea apical turn.
8. The occludent of claim 2, wherein the tissue opening is an
opening in a cochlea.
9. The occludent of claim 1, wherein a component traverses the
tissue opening, and further wherein said occludent has an aperture
formed therein to receive a portion of the component traversing the
tissue opening.
10. The occludent of claim 10, wherein said occludent has a
toroidal cross-sectional shape.
11. The occludent of claim 10, wherein said occludent has a
combination of one or more characteristics to enable said occludent
to forcefully consume substantially all space between the carrier
member and cochlea at the cochleostomy.
12. The occludent of claim 10, wherein said occludent is
permanently positioned on the electrode carrier member.
13. The occludent of claim 2, wherein said occludent is further
configured to slidingly receive the component.
14. The occludent of claim 11, wherein said characteristics
comprise one or more of the group consisting of shape and
durometer.
15. The occludent of claim 2, wherein said component is radially
distensible and has a accessible orifice disposed therein, and
further wherein said occludent is configured to be slidingly
adjusted within the orifice.
16. The occludent of claim 15, wherein said occludent has a surface
configuration that tapers distally.
17. The occludent of claim 15, wherein said orifice is a lumen
longitudinally disposed in the electrode carrier member.
18. The occludent of claim 17, wherein the lumen is configured to
receive a stylet, and further wherein said occludent is configured
to travel over the stylet.
19. The occludent of claim 15, wherein said occludent is
expandable, such that when expanded while located in the lumen,
said occludent causes the carrier member to radially dilate to seal
the cochleostomy.
20. The occludent of claim 1, wherein said occludent is formed from
a resilient, deformable material so that operatively it conforms
substantially to the surface of the tissue opening.
21. The occludent of claim 20, wherein said resilient, deformable
material comprises silicone.
22. The occludent of claim 20, wherein said resilient, deformable
material comprises silicone.
23. The occludent of claim 3, wherein said occludent is a truncated
cone.
24. A cochlear implant comprising: an elongate electrode carrier
member having at least one electrode disposed thereon, wherein the
carrier member is configured to traverse a cochleostomy to position
the electrodes in the cochlea; and an electrically nonconductive
occludent constructed and arranged to circumferentially surround a
portion of the carrier member traversing the cochleostomy, and to
forcefully infill cochleostomy thereby segregating perilymphatic
canals of the cochlea from extracochlear regions.
25. The cochlear implant of claim 24, wherein the cochleostomy is
formed through one of either the cochlea round window, the cochlea
oval window, the cochlea promontory, and the cochlea apical
turn.
26. The cochlear implant of claim 24, wherein said occludent has an
aperture formed therein to receive a portion of the carrier
member.
27. The cochlear implant of claim 24, wherein said occludent has a
toroidal cross-sectional shape.
28. The cochlear implant of claim 24, wherein said occludent has a
combination of one or more characteristics including shape and
durometer to enable said occludent to forcefully consume
substantially all space between the carrier member and cochlea at
the cochleostomy.
29. The cochlear implant of claim 24, wherein said occludent and
said electrode carrier member are fixedly integrated.
30. The cochlear implant of claim 24, wherein said occludent and
said electrode carrier member are unitary.
31. The cochlear implant of claim 24, wherein said occludent is
further configured to slidingly receive the component.
32. The cochlear implant of claim 27, wherein said occludent is
further configured to slidingly receive the component.
33. The cochlear implant of claim 24, wherein said carrier member
is radially distensible and has a lumen longitudinally disposed in
the electrode carrier member, and further wherein said occludent is
configured to be slidingly adjusted within the lumen.
34. The cochlear implant of claim 33, wherein said occludent has a
surface configuration that tapers distally.
35. The cochlear implant of claim 33, wherein the lumen is
configured to receive a stylet, and further wherein said occludent
is configured to travel over the stylet
36. The cochlear implant of claim 33, wherein said occludent is
expandable, such that when expanded while located in the lumen,
said occludent causes the carrier member to radially dilate to seal
the cochleostomy.
37. The cochlear implant of claim 24, wherein said occludent is
formed from a resilient, deformable material so that operatively it
conforms substantially to the surface of the tissue opening.
38. The occludent of claim 37, wherein said resilient, deformable
material comprises silicone.
39. The occludent of claim 37, wherein said resilient, deformable
material comprises silicone.
40. The occludent of claim 24, wherein said occludent is a
truncated cone.
41. A method for implanting an elongate carrier member in a cochlea
of a recipient, comprising: creating a cochleostomy; implanting the
carrier member into the cochlea; and positioning an electrically
nonconductive occludent in the cochleostomy so as to cause the
portion of the carrier member and the occludent to forcefully
infill the cochleostomy.
42. The method of claim 41, wherein said occludent is configured to
circumferentially surround a portion of the carrier member
traversing the cochleostomy.
43. The method of claim 41, wherein creating the cochleostomy
comprising: forming the cochleostomy through one of either the
cochlea round window, the cochlea oval window, the cochlea
promontory, and the cochlea apical turn.
44. The method of claim 41, wherein said occludent has an aperture
formed therein to receive a portion of said carrier member
traversing the cochleostomy, and wherein positioning the occludent
in the cochleostomy comprises: sliding said occludent over said
carrier member until at least a portion of said occludent infills
said cochleostomy.
45. The method of claim 41, wherein said occludent is permanently
positioned on the electrode carrier member, and wherein positioning
the occludent in the cochleostomy comprises: implanting said
carrier member to a depth at which at least a portion of said
occludent infills said cochleostomy.
46. The method of claim 41, wherein said carrier member is radially
distensible and has a accessible lumen longitudinally disposed
therein, wherein said occludent is configured to be slidingly
adjusted within the orifice, and further wherein positioning the
occludent in the cochleostomy comprises: sliding said occludent
through said lumen into at least a portion of said occludent infill
said cochleostomy, wherein said occludent causes the carrier member
to radially dilate to seal the cochleostomy.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from Australian Provisional
Patent Application No. 2005907188, entitled, "Improved Cochleostomy
Sealing" which was filed on Dec. 21, 2005.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention relates generally to cochlear implant
devices, and more particularly, to an electrically nonconductive
cochleostomy occludent.
[0004] 2. Related Art
[0005] Hearing loss is generally of two types, namely conductive
and sensorineural. The treatment of both of types of hearing loss
has been quite different, relying on different principles to
deliver sound signals to be perceived by the brain as sound.
Conductive hearing loss occurs when the normal mechanical pathways
for sound to reach the hair cells in the cochlea are impeded, for
example, by damage to the ossicles. In such cases, hearing loss is
often improved with the use of conventional hearing aids, which
amplify the sound so that acoustic information reaches the cochlear
hair cells. Such hearing aids utilize acoustic mechanical
stimulation, whereby the sound is amplified according to a number
of varying techniques, and delivered to the inner ear as mechanical
energy. This may be through a column of air to the eardrum, or
through direct delivery to the ossicles of the middle ear.
[0006] On the other hand, sensorineural hearing loss is due to the
absence or destruction of the cochlear hair cells which are needed
to transduce acoustic signals into auditory nerve impulses.
Individuals suffering from this type of hearing loss are unable to
derive any benefit from conventional hearing aid systems regardless
of the volume of the acoustic stimulus. This is because the natural
mechanisms for transducing sound energy into auditory nerve
impulses are either absent or damaged. In such cases, cochlear.TM.
implants (also referred to as cochlear.TM. devices, cochlear.TM.
prostheses, cochlear.TM. implant systems, and the like; simply
"cochlear implants" herein) have been developed to provide the
sensation of hearing to such individuals. In cochlear implants,
electrical stimulation is provided via stimulating electrodes
positioned as close as possible to the nerve endings of the
auditory nerve, essentially bypassing the hair cells in a normally
functioning cochlea. The application of a stimulation pattern to
the nerve endings causes impulses to be sent to the brain via the
auditory nerve, resulting in the brain perceiving the impulses as
sound.
[0007] The electrode array is inserted during an operation that
usually takes between 2-3 hours depending on the device to be
implanted. An incision is made behind the ear to expose the
temporal bone; the temporal bone consists of the squamous, the
mastoid, the tympanic, zygomatic and petrous segment. Typically,
cochlear implants require the opening of the mastoid bone which
leads to the middle ear. A shallow recess is then created to hold
the implant package in place substantially level with the bone.
Next a hole is drilled which allows the surgeon access into the
cochlea. This hole is known as a cochleostomy--the opening from the
middle ear to the perilymphatic canals of the cochlea. A
cochleostomy may be formed through the round window 141, the oval
window 110, the promontory or through the apical turn of the
cochlea. The electrode array is then gently threaded into the
shell-like structure of the cochlea and the incision closed; the
cochleostomy remains open and heals with scar tissue over the next
few days.
[0008] More recently various alternative approaches have been
proposed to cause dynamic volume displacements of the perilymph,
some of which require the implantation of an actuator that breaches
the cochlea. These procedures require a cochleostomy or equivalent
incision to provide the requisite access to the perilymphatic
canals of the cochlea.
[0009] It is conventional during surgical implantation to use a
tissue graft from the patient to provide a seal at the
cochleostomy, primarily to reduce the risk of meningitis resulting
from communication between the inner ear and the middle ear.
SUMMARY
[0010] In one aspect of the invention, an electrically
nonconductive occludent id disclosed, the occludent constructed and
arranged to forcefully infill a tissue opening so as to effectively
prevent transport of electrical current, fluid and bacteria through
the tissue opening.
[0011] In another aspect of the invention, a cochlear implant is
disclosed, the cochlear implant comprising: an elongate electrode
carrier member having at least one electrode disposed thereon,
wherein the carrier member is configured to traverse a cochleostomy
to position the electrodes in the cochlea; and an electrically
nonconductive occludent constructed and arranged to
circumferentially surround a portion of the carrier member
traversing the cochleostomy, and to forcefully infill cochleostomy
thereby segregating perilymphatic canals of the cochlea from
extracochlear regions.
[0012] In a further embodiment of the present invention, a method
for implanting an elongate carrier member in a cochlea of a
recipient is disclosed, the method comprising: creating a
cochleostomy; implanting the carrier member into the cochlea; and
positioning an electrically nonconductive occludent in the
cochleostomy so as to cause the portion of the carrier member and
the occludent to forcefully infill the cochleostomy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] An illustrative embodiment of the present invention will be
described with reference to the accompanying figures, in which:
[0014] FIG. 1 is a perspective view of an example of an implanted
cochlear implant suitable for implementing embodiments of the
present invention;
[0015] FIG. 2A is a side view of an electrode assembly in
accordance with one embodiment of the present invention;
[0016] FIG. 2B is a top view of the electrode assembly illustrated
in FIG. 2A;
[0017] FIG. 3 is a schematic diagram of the cochlea showing a
conventional intra-cochlear electrode insertion with the
cochleostomy sealed using muscle/fat tissue;
[0018] FIG. 4 is a cross-sectional view of a portion of a cochlea
showing an improved cochleostomy seal in accordance with one
embodiment of the present invention;
[0019] FIG. 5 is a perspective view of one embodiment of the
electrically nonconductive occludent of the present invention;
[0020] FIG. 6 is a perspective view of a human cochlea showing the
embodiment of the occludent illustrated in FIG. 5 implanted in a
cochleostomy, in accordance with embodiments of the present
invention; and
[0021] FIG. 7 is a cross-sectional view of an alternative
embodiment of a cochleostomy occludent of the present
invention.
DETAILED DESCRIPTION
[0022] The present invention is generally directed to an
electrically nonconductive occludent that forcefully infills and
seals a cochleostomy or other tissue opening with or without an
implantable component traversing the tissue opening. In one
application described herein, an embodiment of the electrically
nonconductive occludent is utilized to seal a cochleostomy having
an implanted electrode assembly traversing therethrough, or other
tissue opening such as the oval or round window with no such
implanted component, thereby segregating the perilymphatic canals
of the cochlea from extracochlear regions such as the middle ear.
In certain embodiments, the occludent has a toroidal
cross-sectional shape, circumferentially surrounding the implanted
component such as an electrode carrier member.
[0023] The occludent may have a combination of one or more
characteristics such as shape and durometer to partially enter the
cochleostomy and to consume substantially all space between the
carrier member and cochlea at the cochleostomy. The occludent may
be permanently positioned on the carrier member, or it may be
configured to slide over the carrier member to be positioned at the
occluding position. In alternative embodiments, the occludent is
configured to travel through the carrier member lumen to the
occluding position. Such embodiments of the occludent may be
configured to travel over the stylet used to implant the carrier
member, or may be configured to be inserted with a tool for
subsequent expansion. For example, the occludent may be a
mechanical structure that is inflated mechanically or with a
balloon.
[0024] Regardless of the method used to deploy the occludent, the
region of the radially distensible carrier member containing the
wedge dilates to consume the entire cochleostomy. Advantageously,
the present invention provides a high electrical impedance blockage
within the cochleostomy, thereby reducing the electric charge which
may travel from the electrodes to, for example, an extracochlear
reference electrode of the cochlear implant. It should be
appreciated that the present invention is operable regardless of
the relative size and location of the cochleostomy and carrier
member regardless of whether the cochleostomy is formed through
round window 141, the oval window 110, the promontory, the apical
turn of the cochlea, or at any other therapeutically beneficial
location to operatively reduce current flow through a tissue
opening and thereby improve the electrical efficiency of the
implant.
[0025] As noted, openings other than a cochleostomy may be made to
accommodate the requirements of other types of prosthetic hearing
implants. There are also circumstances that it is desirable to seal
round window 141 and/or oval window 110 due to natural conditions,
prior surgical procedure, etc. Such openings in tissue, whether
they form naturally or occur due to disease, injury or surgery, are
collectively and generally referred to herein as a tissue
opening.
[0026] The present invention may be implemented in a variety of
ways and the embodiments illustrated are to be considered only as
illustrative constructions. More particularly, the present
invention is potentially useful for purposes other than sealing a
cochleostomy created as described herein. For example, the present
invention may be applied to seal an existing orifice between the
middle ear and the inner ear such as round window 141. The present
invention may be used to seal any opening created between the
middle ear and the perilymph, whether this is intended to be used
as a conduit for a part of an implanted device, or to be sealed
completely after surgery. The term cochleostomy should accordingly
be understood for the purposes of this application in this
expansive sense. Such sealing may have further advantages, for
example reducing the chance of the recipient contracting
meningitis. It may also reduce the risk of unintended
explantation.
[0027] For the purpose of power reduction it is desirable to reduce
the amount of electrical current required to stimulate the auditory
nerve. During stimulation, as much as possible the current flowing
from the electrode within the cochlea must be directed towards the
auditory nerve. Any leakage of current through paths other through
than the auditory nerve should therefore be minimised in order to
reduce the power consumption of the implant. The present invention
accordingly allows current leakage via the cochleostomy of a
hearing implant prosthesis to be reduced. As a consequence, the
current levels used for stimulation can be decreased as the
implant's energy is used more efficiently.
[0028] Although many different stimulation approaches have been
proposed and used, in each scheme the energy for the stimulations
is provided by the implant, and conventionally this is supplied
ultimately by the batteries in the external component. Hence, the
degree to which the energy supplied by the batteries is effectively
delivered impacts upon battery life.
[0029] Embodiments of the present invention are described below in
connection with one type of stimulating medical device having an
component implantable through a tissue opening; that is, a
prosthetic hearing implant and, more specifically, a cochlear
implant. Cochlear implants use direct electrical stimulation of
auditory nerve cells to bypass absent or defective hair cells that
normally transduce acoustic vibrations into neural activity. Such
devices generally use multi-contact electrodes inserted into the
scala tympani of the cochlea so that the electrodes may
differentially activate auditory neurons that normally encode
differential pitches of sound. Such devices are also used to treat
a smaller number of patients with bilateral degeneration of the
auditory nerve. For such patients, the cochlear implant provides
stimulation of the cochlear nucleus in the brainstem. Such devices,
therefore, are commonly referred to as auditory brainstem implants
(ABIs).
[0030] Exemplary embodiments of a cochlear implant include a
Contour.TM., Freedom.TM., Nucleus.TM. or Cochlear.TM. implant sold
by Cochlear Limited, Australia. Such devices are described in U.S.
Pat. Nos. 4,532,930, 6,537,200, 6,565,503, 6,575,894, and
6,697,674, the entire contents and disclosures of which are hereby
incorporated by reference herein. It should be understood to those
of ordinary skill in the art that embodiments of the present
invention may be used in other stimulating medical devices such as
neurostimulators, cardiac pacemakers/defibrillators, etc. as well
as other medical devices which utilize an elongate carrier member
to temporarily or permanently implant, deliver or otherwise
introduce a therapeutic agent, sensor, device, etc. into a
recipient.
[0031] FIG. 1 is a cut-away view of the relevant components of
outer ear 101, middle ear 102 and inner ear 103, which are
described next below. In a fully functional ear, outer ear 101
comprises an auricle 105 and an ear canal 106. An acoustic pressure
or sound wave 107 is collected by auricle 105 and channeled into
and through ear canal 106. Disposed across the distal end of ear
cannel 106 is a tympanic membrane 104 which vibrates in response to
acoustic wave 107. This vibration is coupled to oval window, or
fenestra ovalis, 110 through three bones of middle ear 102,
collectively referred to as the ossicles 111.
[0032] Ossicles 111 comprises the malleus 112, the incus 113 and
the stapes 114. Bones 112, 113 and 114 of middle ear 102 serve to
filter and amplify acoustic wave 107, causing oval window 110 to
articulate, or vibrate. Such vibration sets up waves of fluid
motion within cochlea 115. Such fluid motion, in turn, activates
tiny hair cells (not shown) that line the inside of cochlea 115.
Activation of the hair cells causes appropriate nerve impulses to
be transferred through the spiral ganglion cells (not shown) to
auditory nerve 116 and, ultimately, to the brain where they are
perceived as sound. In some persons experiencing sensorineural
hearing loss, there is an absence or destruction of the hair cells.
Cochlear implant 120 is utilized to directly stimulate the ganglion
cells to provide a hearing sensation to such persons.
[0033] FIG. 1 also shows how cochlear implant 120 is positioned in
relation to outer ear 101, middle ear 102 and inner ear 103.
Cochlear implant 120 comprises external component assembly 122
which is directly or indirectly attached to the body of the
recipient, and an internal component assembly 124 which is
temporarily or permanently implanted in the recipient. External
assembly 122 comprises microphone 125 for detecting sound which is
provided to a behind-the-ear (BTE) speech processing unit 126 that
generates coded signals. The coded signals are provided to an
external transmitter unit 128, along with power from a power source
(not shown) such as a battery. External transmitter unit 128
comprises an external coil 130 and, preferably, a magnet (not
shown) secured directly or indirectly in external coil 130.
[0034] Internal component assembly 124 comprises an internal
receiver unit 132 having an internal coil (not shown) that
transcutaneously receives power and coded signals from external
assembly 122, and provides such signals to a stimulator unit 134.
In response to the coded signals, stimulator 134 applies
stimulation signals to cochlea 115 via an implanted electrode
assembly 140. Electrode assembly 140 enters cochlea 115 via a
cochleostomy 142, and has an array 144 of one or more electrodes
150 positioned to be substantially aligned with portions of
tonotopically-mapped cochlea 115. The delivery of stimulation
signals at various locations along cochlea 115 causes a hearing
percept representative of the received sound 107.
[0035] While cochlear implant 120 is described as having external
components, in another embodiment, the controller, including the
microphone, speech processor and power supply, may also be
implantable. In such embodiments, the controller may be contained
within a hermetically sealed housing or the housing used for
stimulator unit 134.
[0036] Electrode assembly 140 preferably assumes an optimal
electrode position in cochlea 115 upon or immediately following
implantation into the cochlea. It is also desirable that electrode
assembly 140 be configured such that the insertion process causes
minimal trauma to the sensitive structures of cochlea 115. Usually
electrode assembly 140 is pre-curved, held in a straight
configuration at least during the initial stages of the
implantation procedure, conforming to the natural shape of the
cochlea during and subsequent to implantation.
[0037] FIG. 2A is a side view of an embodiment of electrode
assembly 140, referred to herein as electrode assembly 200. FIG. 2B
is a top view of electrode assembly 200. Electrode assembly 200
comprises a carrier member 202, a stop member 204 and lead 206.
Carrier member 202 has a distal end 208 adapted to be implanted
furthest into cochlea 115, and a proximal end 210 connected to a
distal end 214 of laterally-extending stop member 204. The opposing
proximal end 216 of stop member 204 is connected to lead 206. Lead
206 physically and electrically connects electrode assembly 200
with stimulator unit 134.
[0038] When implanted in a recipient, the surface of carrier member
202 which faces the interior of cochlea 115 is referred to herein
as the medial surface 216 of carrier member 202. The opposing side
of carrier member 202, referred to herein as lateral surface 218,
faces the external wall and bony capsule (not shown) of cochlea
115. It should be understood that the terms medial surface, medial
direction, and the like, are generally used herein to refer to the
surfaces, features and directions toward the center of cochlea 115,
while the terms lateral surface, lateral direction, and the like,
are generally used herein to refer to surfaces, features and
directions toward the exterior of cochlea 115. In addition, a
longitudinal axis 250 is utilized herein to facilitate descriptions
herein.
[0039] A plurality of spaced-apart electrodes 212 are mounted on or
in carrier member 202. Electrodes 212 may be disposed in a linear
or non-linear array on or in carrier member 202, and may be
positioned to align with predetermined regions of tonotopically
mapped cochlea 115. In alternative embodiments, electrodes 212 are
implemented as described in U.S. Provisional Patent Application No.
60/748,217, 60/748,273 and 60/748,314, hereby incorporated by
reference herein.
[0040] FIG. 3 is a schematic of cochlear 115 showing a
conventional, intra-cochlear electrode insertion, where
cochleostomy 142 is sealed using a graft 302 of the recipient's
tissue, typically muscle and fat. In this illustrative example,
cochleostomy 142 is shown in an exterior wall 304 of cochlea 115,
and is situated in the space of middle ear 102. Graft 302 is
positioned around carrier member 140 over cochleostomy 142, as
shown in FIG. 3.
[0041] FIG. 4 is a cross-sectional view of a portion of a cochlea
showing an improved cochleostomy seal in accordance with one
embodiment of the present invention. In this exemplary embodiment,
a deformable electrically nonconductive occludent 400 is inserted
into cochleostomy 142 to prevent the transfer of fluids, bacteria
and electrical current through cochleostomy 142. In one particular
embodiment, occludent 400 is formed from a soft, deformable grade
of silicone elastomer. Such combination of characteristics allows
occludent 400 to elastically conform to the generally irregular
shape of cochleostomy 142.
[0042] Occludent 400 may be formed around elongate electrode
carrier member 140 so that it can slide along the carrier member.
For example, in one embodiment, occludent 400 has an aperture
suitable for slidingly receiving the implantable component that is
to be traversing through the tissue opening, here carrier member
140 traversing cochleostomy 142. In practice, the surgeon would
insert electrode carrier member 140 through cochleostomy 142 and
into cochlea 115 in a conventional manner. This process is well
understood in the art, and described in the literature, and
conventional aspects of this process will not be further described
in detail. A standard reference for such a process is described in
"Surgical Techniques for Cochlear Implants", Noel L. Cohen, Chapter
8, p 151 in "Cochlear Implants", Waltzman, S. B. and Cohen, L. L.
(1997) ISBN 0-86577-882-5, the disclosure of which is hereby
incorporated by reference.
[0043] The extent of insertion will vary significantly from
recipient to recipient, depending upon the peculiarities of the
anatomy of the recipient, the specific surgical procedure used by
the surgeon, and the precise location of cochleostomy 142. It is
expected that the most improvement in leakage reduction will be for
the basal electrodes 150, as these electrodes have the shortest
leakage path. It therefore also follows that greater improvement
may be seen in short or partial electrode arrays, for example as
used in electro-acoustic stimulation.
[0044] After carrier member 140 has been inserted as far as
desired, occludent 400 may be slid along electrode carrier member
140 to be partially inside cochlea 115 and partially outside
cochlea 115; that ins occludent 400 infills cochleostomy 142.
Because this embodiment of occludent 400 has an exterior radius
that is larger than the interior radius of cochleostomy 142, and
because occludent 400 is malleable; that is, has a low durometer,
it deforms to partially enter cochlea 115 thereby forcefully
infilling cochleostomy 142 so as to effectively prevent transport
of electrical current, fluid and bacteria through the cochleostomy.
In other words, occludent 400 fills the available space between the
walls of cochlea 115 defining cochleostomy 142 and the exterior of
carrier member 140 which passes through the cochleostomy.
Furthermore, occludent 400 sufficiently infills cochleostomy 142 so
that fluids, bacteria, etc., cannot pass through an remaining
apertures between cochlea 115 and occludent 400. Thus, occludent
400 provides a seal of electrically nonconductive, or insulating,
biocompatible material within cochleostomy 142. Occludent 400
thereby increases the impedance of the undesired current path
through cochleostomy 142 to the reference electrode (not shown) of
cochlear implant 120 located outside the inner ear 103. It should
be appreciated to those of ordinary skill in the art that as the
anatomical structures surrounding occludent 400 are partially
conductive and, as such, electric current may still leak through
this general region, but current leakage through cochleostomy 142
will be reduced.
[0045] The embodiment of occludent 400 shown in FIG. 4 is generally
toroidal in shape, as it surrounds electrode carrier member 140 and
infills cochleostomy 142 as described above. However, any other
suitable shape may be used. One such suitable shape is a truncated
cone 500, as shown in FIGS. 5 and 6. FIG. 5 is a perspective view
of an occludent 500 having a truncated cone configuration, while
FIG. 6 is a perspective view of occludent 500 inserted into
cochleostomy 142 of cochlea 115.
[0046] The end 504 of truncated cone occludent 500 which is has a
smaller diameter is dimensioned to easily pass through cochleostomy
142 to enable occludent 500 to enter cochlea 115. Conversely, the
end 508 of occludent 500 which is has a relatively greater diameter
is dimensioned to no pass through cochleostomy 142. As such,
occludent 500 forcefully infills cochleostomy 142 as it is inserted
into the cochleostomy, thereby sealing cochlea 115. In one
embodiment, body 506 of occludent 500 is also malleable to enable
the occludent to deform in response to the forced insertion of the
occludent, further insuring a forceful infilling sufficient to seal
cochleostomy 142. As shown in FIG. 6, when implanted, base 508 of
occludent 500 remains on the outside of cochleostomy 142, allowing
for easy removal should that be necessary.
[0047] As noted above with reference to the embodiment of the
electrically nonconducting occludent 400, occludent 500 may be
implemented as an integrated or unitary element of electrode
carrier member 140, or it may be a separately manufactured
component that has a channel 502 dimmensioned to slide over carrier
member 140. In either embodiment, once electrode carrier member 140
is in a suitable position and occludent 500 is in the occluding
position; that is, partially infilling cochleostomy 142, occludent
400 seals cochleostomy 142.
[0048] Occludent 500 may be formed of any suitable inert
biocompatible material that is operatively an electrical insulator.
In one embodiment, occludent 500 is preferably formed of silicone.
It should be appreciated, however, that occludent 500 may be formed
of different materials or from a combination of one or more other
material. It could be partly formed from a more stiff material,
with the outer portions being resilient in order to provide the
necessary conformable seal.
[0049] Occludent 500 may be formed from a suitable polymer putty
material in situ. It could be formed, with a slit or the like, to
allow it to be attached around the electrode carrier member 140
after insertion. Importantly, occludent 500 is formed of an
insulating material and substantially seal cochleostomy 142 so as
increase the impedance of the leakage path. If different shapes or
forms of electrode carrier member 140 are used, then the shape of
the occludent 500 will need to be adapted to suit the shape of the
implanted carrier member which traverses cochleostomy 142.
[0050] Alternatively, as shown in FIG. 7, an alternative embodiment
of the present invention, carrier member 140 is radially
distensible and has a longitudinally-extending lumen 706. In one
embodiment, lumen 706 is configured to receive a stylet as is
conventionally utilized in certain pre-curved electrode carrier
members. In an alternative embodiment, lumen 706 is configured to
interoperate with occludent 700 as described herein.
[0051] Occludent 700 is configured to be slidingly passed through
lumen 706 as shown in FIG. 7. The exterior dimensions of occludent
700 are larger than the interior dimensions of lumen 706. As such,
occludent 700 applied a force radially outward in that region of
carrier member 702 in which occludent 700 is located. Because
carrier member 702 is outwardly distensible, such force causes
carrier member 702 to dilate or expand in the region containing
occludent 700, as shown in FIG. 7. In such embodiments, advancing
occludent 700 to be partially inside cochlea 115; that is, to
infill cochleostomy 142, causes carrier member 702 to expand to
abut the perimeter of cochlea 115 that defines cochleostomy
142.
[0052] Occludent 700 may take on any form necessary. In the
embodiment shown in FIG. 7, occludent 700 is solid. Alternatively
occludent 700 may be hollow. In the embodiment shown in FIG. 7,
occludent 700 is distally tapered and has round edges. This is ti
avoid damage to in interior surfaces of carrier member 702 defining
lumen 706. it should be appreciated, however, that occludent 700
may take on other shapes in alternative embodiments.
[0053] In operation, occludent 700 is initially located near a
proximal end of electrode carrier member 702 so that it does not
interfere with the normal insertion of the carrier member. After
insertion of electrode carrier member 702, occludent 700 is slid
along lumen 706 to cochleostomy 142 where it deforms the sides of
carrier member 702 sufficiently to seal the cochleostomy 142. This
embodiment has the further advantage in that two separate
components do not abut to create a potential space, thereby
reducing the risk of infection.
[0054] It should be appreciated that tools or guide wires may be
used to facilitate the advancement of occludent 700 in lumen 706.
For example, in the example shown in FIG. 7, a guide wire 704 is
provided, and occludent 700 has an aperture for sliding receiving
the guide wire 704. Alternatively, occludent 700 may be detachably
secured to the distal end of a tool that may be advance into lumen
706.
[0055] Alternatively, occludent 700 may be formed by being moulded
as part of the electrode moulding process, at an appropriate
location along the length of electrode carrier member 702. In such
embodiments, implantation of electrode carrier member 702 is
performed until occludent 700 is positioned in cochleostomy
142.
[0056] Such an embodiment has the same advantage as the sliding
space filling plug of FIG. 7 in that it has no separate insulator
parts abutting and therefore has a reduced risk of infection. It
also has the advantage of not requiring a small device to be moved,
relative to the array, in the confined space and delicate
structures of the inner ear during implantation.
[0057] In alternative embodiment, occludent 700 may be initially of
smaller dimensions whan advanced through lumen 706, and then
expanded to a larger size to effect the radial distension of
carrier member 702 noted above. Such an expansion may be achieved
in many ways now or later developed, such as by implementing
mechanically expandable members, a material that expands in
response to the pumping of air or other fluid, the mixing of
materials, and the like.
[0058] It should also be appreciated that the occludent of the
present invention may be specifically shaped to fit an actual
aperture, for example the oval window. Alternatively, it could be
formed in situ, for example by a fast curing sealant injected
around the cochleostomy 142. Any effective artificial seal which
can be positioned as required may be used to implement the
invention.
[0059] The efficacy of implementing embodiments of the present
invention has been investigated using an animal model. Experiments
on two Guinea Pigs, with a total of three ears investigated acutely
have been performed. In these experiments, the bulla (middle ear
cavity) was exposed, a cochleostomy was drilled over the round
window and a four electrode array was inserted. Stimulation was
applied between the most apical intracochlear electrode (ICE) and a
monopolar ball electrode inserted in the temporalis muscle.
[0060] Monopolar Electrical Auditory Brainstem Response (EABR)
thresholds and the voltage waveform between the stimulus electrodes
(to deduce impedance) were measured. In the last of the three ears
investigated the voltage between the two most basal ring electrodes
was also measured during the stimulus pulse (to determine the
current flow along the cochlea at a point near the
cochleostomy).
[0061] To calibrate this measurement a known current pulse had been
previously applied between the most apical ICE and another ring
electrode (on a separate array) held by hand in the
cochleostomy.
[0062] Four different methods of sealing the cochleostomy were
used: no sealing; small piece of muscle of approx. the volume of
the cochleostomy; larger piece of muscle several times the volume
of the cochleostomy (residual muscle extending out of the
cochleostomy) and otoform paste (one ear only).
[0063] Otoform paste is a settable silicone material, used in
hearing aid fitting and similar applications, which is initially
mouldable but which then sets to a soft deformable consistency.
[0064] In every ear the EABR thresholds, the impedance and the
current flow at the cochleostomy varied depending on the plug type
used. The following table shows the four sealing methods and how
those parameters varied:
TABLE-US-00001 Plug material EABR T Impedence (Z) Cochleostomy
current Large muscle Largest lowest Largest Small muscle 2.sup.nd
largest 2.sup.nd lowest 2.sup.nd largest No seal 3.sup.rd largest
3.sup.rd lowest 3.sup.rd largest Otoform putty Smallest highest
smallest
[0065] The smallest EABR threshold (otoform putty) was about 40%
smaller than the largest threshold (large muscle). The impedance
results varied by around 20-35% from smallest to largest. The
current flow through the cochleostomy varied from 84% of total
current (large muscle) to 70% (otoform putty).
[0066] The results are consistent with a significant proportion of
the stimulus current flowing through the cochleostomy. Different
sealing arrangements appear to change the amount of current flow
through the cochleostomy and thereby change the EABR threshold. The
changes in impedance and cochleostomy current flow as measured by
the voltage on the basal two rings are consistent with this model.
These results indicate it is possible to lower thresholds by
effective sealing of the cochleostomy.
[0067] Another perspective is that any T and C decrease gained from
using the plug will manifest itself as a decrease in power
consumption of the implant and a subsequent increase in battery
life. Power consumption of the implant can be divided into two
parts--power consumed to run the implant electronics (W.sub.E) and
power consumed to deliver current to the auditory nerve (W.sub.N).
The decrease in T/C level current will manifest itself as a
proportional decrease in W.sub.N. For present implant designs the
ratio of W.sub.N to W.sub.E is about 50:50 for high rate
strategies. If, for example, it is assumed that the plug provides a
10% decrease in T/C level this would translate to about a 5%
decrease in overall implant power consumption for high rate
strategies, less for lower rate strategies. However, the most
recent tests show that the plug yields an improvement of between
20-40% decrease in T/C level, indicating at lease a 10% improvement
in power consumption.
[0068] Variations and additions are possible to the structures
described within the general scope of the present invention. For
example, embodiments of the present invention may be employed in
addition to a tissue graft type sealing approach.
[0069] Although the present invention has been principally
described with reference to a cochlear implant prosthesis, it will
be appreciated that embodiments of the present invention may
readily be applied to provide a nonconductive seal of a tissue
opening regardless of whether a carrier member 140 or other implant
prosthesis or component is positioned within the tissue opening.
Such applications in which there are electrical losses through the
tissue opening may particularly benefit from the present invention.
It should also be understood that although the description has
referred principally to a prosthetic hearing implant with an
external receiver/stimulator unit 134, embodiments of the present
invention are equally applicable to a totally implanted device.
[0070] It will also be appreciated that although this invention has
been principally used to provide sealing at the cochleostomy there
are other tissue openings between cochlea 115 and middle ear 102
that may pass similar electric current and that may also provide
similar benefit by being sealed with an embodiment of the
electrically nonconductive occludent of the present invention.
These include round window 141 and oval window 110. Embodiments of
the electrically nonconductive occludent of the present invention
which are not integrated in or unitary with a carrier member may be
inserted into these other tissue openings, providing a further
decrease in stray electrical current. It will be understood that
the present invention may also be applied to seal a cochleostomy
which is not intended to remain open, for example in some form of
totally implanted device which does not require a physical conduit
to remain out of inner ear 103.
[0071] All documents, patents, journal articles and other materials
cited in the present application are hereby incorporated by
reference.
[0072] Although the present invention has been fully described in
conjunction with several embodiments thereof with reference to the
accompanying drawings, it is to be understood that various changes
and modifications may be apparent to those skilled in the art. Such
changes and modifications are to be understood as included within
the scope of the present invention as defined by the appended
claims, unless they depart therefrom.
* * * * *