Contactless transducer stimulation and sensing of ossicular chain

An implantable hearing aid system for the middle ear utilizes pairs of permanent magnets to engage transducers with auditory elements in a middle ear. At least one transducer is supported within the middle ear cavity by a support. A transducer is magnetically-engaged with a malleus in one embodiment and another transducer is magnetically-engaged with a stapes in other embodiments. When using two contactless transducers, a permanent magnet is attached to each transducer. A permanent magnet is also attached to the malleus and to the stapes. The permanent magnet on each transducer is situated such that its polarity acts in repulsion to the permanent magnet on the adjacent auditory element.

FIELD OF THE INVENTION 
This invention relates to mounting implantable hearing system transducers 
within the middle ear. 
BACKGROUND 
In an implantable hearing aid system, transducers within the middle ear 
engage an auditory element and transduce from electrical signals into 
mechanical vibrations, and vice versa. Middle ear hearing aid systems are 
not as susceptible to mechanical feedback as other types of systems. Such 
implantable hearing aid systems are more comfortable for the patient than 
other types of hearing aids, such as those placed directly in the external 
auditory canal. 
Transducers which contact an auditory element, such as one of the elements 
of the ossicular chain, require reliable disposition within the middle 
ear. Some disposition methods mechanically affix transducers directly to 
elements of the ossicular chain, e.g. mechanical fasteners, such as 
screws; metal hooks or bands; a constant force alone; or adhesives mount 
the transducer to an auditory element. Each of these methods has 
associated problems with affixation. There is a need for improving the 
disposition of transducers in an implantable hearing aid system. 
SUMMARY OF THE INVENTION 
An implantable hearing system for the middle ear utilizes pairs of 
permanent magnets to engage transducers with auditory elements in a middle 
ear. The two transducers are supported within the middle ear cavity by a 
support. A transducer is magnetically-engaged with a malleus and another 
transducer is magnetically-engaged with a stapes. However, it is not 
necessary to support both sensing and stimulating transducers within the 
middle ear using this invention. This invention is particularly 
advantageous for supporting sensing transducers, but driving transducers 
could be supported as well. 
A permanent magnet is attached to each transducer. A permanent magnet is 
also attached to the malleus and to the stapes. The permanent magnet on 
each transducer is situated such that its polarity acts in repulsion to 
the permanent magnet on the adjacent auditory element. Alternatively, an 
implantable hearing aid may use just one of the magnet-magnet devices. The 
other driver/sensor (input or output) may then use traditional attachment 
means. In further embodiments, each transducer is encased in a 
biocompatible transducer case. By encasing the transducer in a case, 
acoustic feedback is decreased as compared with non-encased transducers. 
Preferably, the transducer is a piezoelectric transducer, which exhibits a 
higher efficiency than other types of transducers that can be used with 
the invention. After the transducer support and permanent magnets are 
implanted and physiologically adapted in the middle ear, a constant force 
is applied at all times.

DETAILED DESCRIPTION 
This invention provides a mount for engaging a transducer with an auditory 
element in the middle ear for use in an implantable hearing aid (IHA) 
system or other implantable hearing system, such as a cochlear implant 
with middle ear vibration sensing. The invention utilizes permanent 
magnets to engage the transducer with the auditory element. The invention 
is particularly applicable to both partial middle ear implantable (P-MEI) 
or total middle ear implantable (T-MEI) hearing aid systems. A P-MEI or 
T-MEI hearing aid system assists the human auditory system in converting 
acoustic energy contained within sound waves into electrochemical signals 
delivered to the brain and interpreted as sound. FIG. 1A illustrates 
generally the use of the invention in a human auditory system. Sound waves 
are directed into an external auditory canal 20 by an outer ear (pinna) 
25. The frequency characteristics of the sound waves are slightly modified 
by the resonant characteristics of the external auditory canal 20. These 
sound waves impinge upon the tympanic membrane (eardrum) 30, interposed at 
the terminus of the external auditory canal, between it and the tympanic 
cavity (middle ear) 35. Variations in the sound waves produce tympanic 
vibrations. The mechanical energy of the tympanic vibrations is 
communicated to the inner ear, comprising cochlea 60, vestibule 61, and 
semicircular canals 62, by a sequence of articulating bones located in the 
middle ear 35. This sequence of articulating bones is referred to 
generally as the ossicular chain. Thus, the tympanic membrane 30 and 
ossicular chain transform acoustic energy in the external auditory canal 
20 to mechanical energy at the cochlea 60. 
The ossicular chain includes three primary components: a malleus 40, an 
incus (not shown), and a stapes 50. The malleus 40 includes manubrium and 
head portions. The manubrium of the malleus 40 attaches to the tympanic 
membrane 30. The head of the malleus 40 articulates with one end of the 
incus. The incus normally couples mechanical energy from the vibrating 
malleus 40 to the stapes 50. The stapes 50 includes a capitulum portion, 
comprising a head and a neck, connected to a footplate portion by means of 
a support crus comprising two crura. The stapes 50 is disposed in and 
against a membrane-covered opening on the cochlea 60. This 
membrane-covered opening between the cochlea 60 and middle ear 35 is 
referred to as the oval window 55. Oval window 55 is considered part of 
cochlea 60 in this patent application. The incus articulates the capitulum 
of the stapes 50 to complete the mechanical transmission path. 
Normally, prior to implantation of the invention, tympanic vibrations are 
mechanically conducted through the malleus 40, incus, and stapes 50, to 
the oval window 55. Vibrations at the oval window 55 are conducted into 
the fluid-filled cochlea 60. These mechanical vibrations generate fluidic 
motion, thereby transmitting hydraulic energy within the cochlea 60. 
Pressures generated in the cochlea 60 by fluidic motion are accommodated 
by a second membrane-covered opening on the cochlea 60. This second 
membrane-covered opening between the cochlea 60 and middle ear 35 is 
referred to as the round window 65. Round window 65 is considered part of 
cochlea 60 in this patent application. Receptor cells in the cochlea 60 
translate the fluidic motion into neural impulses which are transmitted to 
the brain and perceived as sound. However, various disorders of the 
tympanic membrane 30, ossicular chain, and/or cochlea 60 can disrupt or 
impair normal hearing. 
Hearing loss due to damage in the cochlea is referred to as sensorineural 
hearing loss. Hearing loss due to an inability to conduct mechanical 
vibrations through the middle ear is referred to as conductive hearing 
loss. Some patients have an ossicular chain lacking sufficient resiliency 
to transmit mechanical vibrations between the tympanic membrane 30 and the 
oval window 55. As a result, fluidic motion in the cochlea 60 is 
attenuated. Thus, receptor cells in the cochlea 60 do not receive adequate 
mechanical stimulation. Damaged elements of ossicular chain may also 
interrupt transmission of mechanical vibrations between the tympanic 
membrane 30 and the oval window 55. 
Various techniques have been developed to remedy hearing loss resulting 
from conductive or sensorineural hearing disorder. For example, 
tympanoplasty is used to surgically reconstruct the tympanic membrane 30 
and establish ossicular continuity from the tympanic membrane 30 to the 
oval window 55. Various passive mechanical prostheses and implantation 
techniques have been developed in connection with reconstructive surgery 
of the middle ear 35 for patients with damaged ossicles. Two basic forms 
of prosthesis are available: total ossicular replacement prostheses 
(TORP), which is connected between the tympanic membrane 30 and the oval 
window 55; and partial ossicular replacement prostheses (PORP), which is 
positioned between the tympanic membrane 30 and the stapes 50. 
Various types of hearing aids have been developed to compensate for hearing 
disorders. A conventional "air conduction" hearing aid is sometimes used 
to overcome hearing loss due to sensorineural cochlear damage or mild 
conductive impediments to the ossicular chain. Conventional hearing aids 
utilize a microphone, which transduces sound into an electrical signal. 
Amplification circuitry amplifies the electrical signal. A speaker 
transduces the amplified electrical signal into acoustic energy 
transmitted to the tympanic membrane 30. However, some of the transmitted 
acoustic energy is typically detected by the microphone, resulting in a 
feedback signal which degrades sound quality. Conventional hearing aids 
also often suffer from a significant amount of signal distortion. 
Implantable hearing aid systems have also been developed, utilizing various 
approaches to compensate for hearing disorders. For example, cochlear 
implant techniques implement an inner ear hearing aid system. Cochlear 
implants electrically stimulate auditory nerve fibers within the cochlea 
60. A typical cochlear implant system includes an external microphone, an 
external signal processor, and an external transmitter, as well as an 
implanted receiver and an implanted single channel or multichannel probe. 
A single channel probe has one electrode. A multichannel probe has an 
array of several electrodes. In the more advanced multichannel cochlear 
implant, a signal processor converts speech signals transduced by the 
microphone into a series of sequential electrical pulses of different 
frequency bands within a speech frequency spectrum. Electrical pulses 
corresponding to low frequency sounds are delivered to electrodes that are 
more apical in the cochlea 60. Electrical pulses corresponding to high 
frequency sounds are delivered to electrodes that are more basal in the 
cochlea 60. The nerve fibers stimulated by the electrodes of the cochlear 
implant probe transmit neural impulses to the brain, where these neural 
impulses are interpreted as sound. 
Other inner ear hearing aid systems have been developed to aid patients 
without an intact tympanic membrane 30, upon which "air conduction" 
hearing aids depend. For example, temporal bone conduction hearing aid 
systems produce mechanical vibrations that are coupled to the cochlea 60 
via a temporal bone in the skull. In such temporal bone conduction hearing 
aid systems, a vibrating element can be implemented percutaneously or 
subcutaneously. 
A particularly interesting class of hearing aid systems includes those 
which are configured for disposition principally within the middle ear 35 
space. In middle ear implantable (MEI) hearing aids, an 
electrical-to-mechanical output transducer couples mechanical vibrations 
to the ossicular chain, which is optionally interrupted to allow coupling 
of the mechanical vibrations to the ossicular chain. Both electromagnetic 
and piezoelectric output transducers have been used to effect the 
mechanical vibrations upon the ossicular chain. 
One example of a partial middle ear implantable (P-MEI) hearing aid system 
having an electromagnetic output transducer comprises: an external 
microphone transducing sound into electrical signals; external 
amplification and modulation circuitry; and an external radio frequency 
(RF) transmitter for transdermal RF communication of an electrical signal. 
An implanted receiver detects and rectifies the transmitted signal, 
driving an implanted coil in constant current mode. A resulting magnetic 
field from the implanted drive coil vibrates an implanted magnet that is 
permanently affixed only to the incus. Such electromagnetic output 
transducers have relatively high power consumption, which limits their 
usefulness in total middle ear implantable (T-MEI) hearing aid systems. 
A piezoelectric output transducer is also capable of effecting mechanical 
vibrations to the ossicular chain. An example of such a device is 
disclosed in U.S. Pat. No. 4,729,366, issued to D. W. Schaefer on Mar. 8, 
1988. In the '366 patent, a mechanical-to-electrical piezoelectric input 
transducer is associated with the malleus 40, transducing mechanical 
energy into an electrical signal, which is amplified and further 
processed. A resulting electrical signal is provided to an 
electrical-to-mechanical piezoelectric output transducer that generates a 
mechanical vibration coupled to an element of the ossicular chain or to 
the oval window 55 or round window 65. In the '366 patent, the ossicular 
chain is interrupted by removal of the incus. Removal of the incus 
prevents the mechanical vibrations delivered by the piezoelectric output 
transducer from mechanically feeding back to the piezoelectric input 
transducer. 
Piezoelectric output transducers have several advantages over 
electromagnetic output transducers. The smaller size or volume of the 
piezoelectric output transducer advantageously eases implantation into the 
middle ear 35. The lower power consumption of the piezoelectric output 
transducer is particularly attractive for T-MEI hearing aid systems, which 
include a limited longevity implanted battery as a power source. 
For implantation of hearing aid components, an access hole 85 is created in 
a region of the temporal bone known as the mastoid 80. An incision is made 
in the skin covering the mastoid 80, and an underlying access hole 85 is 
created through the mastoid 80 allowing external access to the middle ear 
35. The access hole 85 is located approximately posterior and superior to 
the external auditory canal 20. By placing the access hole 85 in this 
region, transducers 90 and 95 can be placed on approximately the same 
planar level as the auditory elements 40 and 50, which they respectively 
engage. The electronics unit 100 of the IHA is separately implanted. This 
eases implantation and repair or adjustment to the electronics unit 100 of 
the IHA. Repairs, such as changing a battery in the electronics unit 100 
of the IHA, are easily made without removing other system components. 
A sensing transducer 90 is magnetically-engaged with the malleus 40 on one 
side of the middle ear cavity 35. On the other side of the middle ear 
cavity 35, a stimulating transducer 95 is magnetically-engaged with the 
stapes 50. The two transducers 90 and 95 are positioned within the middle 
ear cavity 35 by a support 120. The support 120 couples the two 
transducers 90 and 95 together and positions the transducers 90 and 95 
within the middle ear 35 in a stable manner. For example, the support 120 
is coupled to the mastoid bone 80 in one embodiment. It is preferable, but 
not necessary, for the support 120 to be adjustable in both the 
longitudinal and radial positions. The most preferred support 120 is 
described in co-pending U.S. patent application, entitled, "One Piece 
Input/Output Transducer Bracket," application Ser. No. 08695,099, filed on 
Aug. 7, 1996. 
A first permanent magnet 110 is affixed to each transducer 90, 95, facing 
the respective auditory element 40, 50 which it engages. A second 
permanent magnet 105 is attached to the malleus 40 (preferably the body 
portion) and to the stapes 50 (preferably the head portion), such that it 
is magnetically-repulsed, opposite from the first permanent magnet 110. 
The permanent magnets 105 and 110 are attached to the transducers 90 and 
95, respectively, and to the auditory elements 40 and 50, respectively, by 
a mechanical method or a biocompatible adhesive, or any other affixing 
method well known to one skilled in the art. In the preferred embodiment, 
a biocompatible adhesive is used. Biocompatible adhesives comprise 
ultra-violetcured epoxies, two-part epoxies, silicone adhesives, dental 
adhesives, acrylic methacrylate, and urethane methacrylate. 
The permanent magnet 110 on each transducer 90, 95 is situated such that 
its polarity acts in repulsion to the permanent magnet 105 on the adjacent 
auditory element 40, 50. Either negative poles of both permanent magnets 
105 and 110 are situated adjacent to each other, or positive poles of both 
permanent magnets 105 and 110 are situated adjacent to each other. 
Preferably, each transducer 90, 95 is a piezoelectric transducer, which is 
more efficient than electromagnetic transducers, for example. However, 
other types of transducers 90, 95 can be used in this invention. After the 
transducer support 120 and permanent magnets 105 and 110 are implanted and 
physiologically adapted in the middle ear 35, a constant force is applied 
against the auditory element 40, 50 at all times, preferably approximately 
10 dynes. Thus, permanent magnets 105 and 110 need to be selected and 
placed within the middle ear 35 according to the desired force against the 
auditory element 40, 50. 
Vibrations from the malleus 40 are sensed by the movement in the permanent 
magnet 110, which is affixed to the sensing transducer 90. The distance 
between the two permanent magnets, which magnetically engage the sensing 
transducer 90 with the malleus 40, will be approximately constant, due to 
the force of magnetic repulsion. Thus, movement in the second permanent 
magnet 105 resulting from auditory vibrations effects movement in the 
first permanent magnet 110 affixed to the piezoelectric transducer 90. 
Such movement sends a signal to the electronics unit 100 of the IHA 
system, where it is amplified. The amplified signal is then sent to the 
stimulating transducer 95, where it stimulates the stapes 50. 
Finally, it is preferred that each of the permanent magnets 105 and 110 be 
encompassed in an individual biocompatible material case 130 and 135, 
respectively, as shown in FIG. 1B. Piezoelectric transducers are often 
very brittle, making surgery very difficult. By placing the transducer 90, 
95 in a biocompatible case 130, 135, piezoelectric transducers are more 
resistant to breaking during implantation. Furthermore, acoustic feedback 
is decreased when using such encased transducers 90, 95. The first 
permanent magnet 110 and the transducer 90, 95, to which it is affixed, 
are encompassed in the same case 135. Examples of biocompatible materials 
include titanium, stainless steel, certain ceramics (ex. alumina), certain 
polymers (ex. polycarbonates), and other materials well known to one 
skilled in the art. 
In all embodiments, the type of permanent magnets 105 and 110 used in this 
invention is not critical, as long as it provides a sufficient repulsive 
magnetic force to create a compressive force against the ossicular chain 
element 40, 50. Several different types of magnets provide such a force. 
For example, samarium-cobalt (SmCo.sub.5) and neodymium-iron-boron (NdFeB) 
magnets work well. The magnets 105 and 110 should be coated with a 
biocompatible material prior to their placement within the middle ear 35. 
In further embodiments, a flexible and/or conformable material is preformed 
on the contact surface of the magnet 105, which is affixed to the 
ossicular chain element 40, 50. A flexible material, such as low-durometer 
silicone, is advantageous to use because it would hold the magnet 105 in 
place on the ossicular chain by conforming to the shape of the ossicular 
chain element 40, 50, and creating friction between the material and the 
ossicular chain element 40, 50. A conformable material is advantageous to 
use because it would also conform to the shape of the ossicular chain 
element 40, 50, and create friction between the material and the ossicular 
chain element 40, 50. Certain types of material can also solidify after 
implantation, adding further stability to the ossicular attachment. 
However, the flexible and/or conformable material should always be 
biocompatible. 
Both sensing and stimulating transducers 90 and 95, respectively, do not 
need to be of the contactless type described in this invention. 
Alternatively, as shown in FIGS. 1C and 1D, only the sensing transducer 90 
engages the malleus 40. The stimulating transducer (not shown) is any 
conventional transducer. The contactless transducer 90 described in this 
invention is preferably used for a sensing transducer 90, but can be used 
for a stimulating transducer alone in further embodiments.