Surgery – Surgically implanted vibratory hearing aid
Reexamination Certificate
1998-10-20
2001-02-20
Lacyk, John P. (Department: 3736)
Surgery
Surgically implanted vibratory hearing aid
C607S055000
Reexamination Certificate
active
06190305
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the field of devices and methods for improving hearing in hearing impaired persons and particularly to the field of implantable and external transducers for producing vibration in the middle ear.
A number of auditory system defects are known to impair or prevent hearing. To illustrate such defects, a schematic representation of part of the human auditory system is shown in FIG.
1
. The auditory system is generally comprised of an external ear AA, a middle ear JJ, and an internal ear FF. The external ear AA includes the ear canal BB and the tympanic membrane CC, and the internal ear FF includes an oval window EE and a vestibule GG which is a passageway to the cochlea (not shown). The middle ear JJ is positioned between the external ear and the middle ear, and includes an eustachian tube KK and three bones called ossicles DD. The three ossicles DD: the malleus LL, the incus MM, and the stapes HH, are positioned between and connected to the tympanic membrane CC and the oval window EE.
In a person with normal hearing, sound enters the external ear AA where it is slightly amplified by the resonant characteristics of the ear canal BB. The sound waves produce vibrations in the tympanic membrane CC, part of the external ear that is positioned at the distal end of the ear canal BB. The force of these vibrations is magnified by the ossicles DD.
Upon vibration of the ossicles DD, the oval window EE, which is part of the internal ear FF, conducts the vibrations to cochlear fluid (not shown) in the inner ear FF thereby stimulating receptor cells, or hairs, within the cochlea (not shown). Vibrations in the cochlear fluid also conduct vibrations to the round window (not shown). In response to the stimulation, the hairs generate an electrochemical signal which is delivered to the brain via one of the cranial nerves and which causes the brain to perceive sound.
The vibratory structures of the ear include the tympanic membrane, ossicles (malleus, incus, and stapes), oval window, round window, and cochlea. Each of the vibratory structures of the ear vibrates to some degree when a person with normal hearing hears sound waves. However, hearing loss in a person may be evidenced by one or more vibratory structures vibrating less than normal or not at all.
Some patients with hearing loss have ossicles that lack the resiliency necessary to increase the force of vibrations to a level that will adequately stimulate the receptor cells in the cochlea. Other patients have ossicles that are broken, and which therefore do not conduct sound vibrations to the oval window.
Prostheses for ossicular reconstruction are sometimes implanted in patients who have partially or completely broken ossicles. These prostheses are designed to fit snugly between the tympanic membrane CC and the oval window EE or stapes HH. The close fit holds the implants in place, although gelfoam is sometimes packed into the middle ear to guard against loosening. -Two basic forms are available: total ossicular replacement prostheses which are connected between the tympanic membrane CC and the oval window EE; and partial ossicular replacement prostheses which are positioned between the tympanic membrane and the stapes HH. Although these prostheses provide a mechanism by which vibrations may be conducted through the middle ear to the oval window of the inner ear, additional devices are frequently necessary to ensure that vibrations are delivered to the inner ear with sufficient force to produce high quality sound perception.
Various types of hearing aids have been developed to restore or improve hearing for the hearing impaired. With conventional hearing aids, sound is detected by a microphone, amplified using amplification circuitry, and transmitted in the form of acoustical energy by a speaker or another type of transducer into the middle ear by way of the tympanic membrane. Often the acoustical energy delivered by the speaker is detected by the microphone, causing a high-pitched feedback whistle. Moreover, the amplified sound produced by conventional hearing aids normally includes a significant amount of distortion.
Attempts have been made to eliminate the feedback and distortion problems associated with conventional hearing aid systems. These attempts have yielded devices which convert sound waves into electromagnetic fields having the same frequencies as the sound waves. A microphone detects the sound waves, which are both amplified and converted to an electrical current. A coil winding is held stationary by being attached to a nonvibrating structure within the middle ear. The current is delivered to the coil to generate an electromagnetic field. A magnet is attached to an ossicle within the middle ear so that the magnetic field of the magnet interacts with the magnetic field of the coil. The magnet vibrates in response to the interaction of the magnetic fields, causing vibration of the bones of the middle ear.
Existing electromagnetic transducers present several problems. Many are installed using complex surgical procedures which present the usual risks associated with-major surgery and which also require disarticulating (disconnecting) one or more of the bones of the middle ear. Disarticulation deprives the patient of any residual hearing he or she may have had prior to surgery, placing the patient in a worsened position if the implanted device is later found to be ineffective in improving the patient's hearing.
Existing devices also are incapable of producing vibrations in the middle ear which are substantially linear in relation to the current being conducted to the coil. Thus, the sound produced by these devices includes significant distortion because the vibrations conducted to the inner ear do not precisely correspond to the sound waves detected by the microphone.
An improved transducer is therefore needed which will ultimately produce vibrations in the cochlea that have sufficient force to stimulate hearing perception with minimal distortion.
SUMMARY OF THE INVENTION
The present invention provides a floating mass transducer that may be implanted or mounted externally for producing vibrations in vibratory structures of the ear. A floating mass transducer generally includes: a housing mountable on a vibratory structure of an ear; and a mass mechanically coupled to the housing, wherein the mass vibrates in direct response to an externally generated electric signal; whereby vibration of the mass causes inertial vibration of the housing in order to stimulate the vibratory structure of the ear.
In one embodiment, the floating mass transducer includes a magnet disposed inside the housing. The magnet generates a magnetic field and is capable of movement within the housing. A coil is also disposed within the housing but, unlike the magnet, the coil is not free to move within the housing. When an alternating current is provided to the coil, the coil generates a magnetic field that interacts with the magnetic field of the magnet, causing the magnet and coil/housing to vibrate relative-to each other. The vibration of the housing is translated into vibrations of the vibratory structure of the ear to which the housing is mounted.
In another embodiment, the floating mass transducer includes a magnet secured within the housing. A coil is also disposed within the housing but, unlike the magnet, the coil is free to move within the housing. The housing includes a flexible diaphragm or other material to which the coil is attached. When an alternating current is provided to the coil, the coil generates a magnetic field that interacts with the magnetic field of the magnet, causing the magnet/housing and coil/diaphragm to vibrate relative to each other. The vibration of the diaphragm is translated into vibrations of the vibratory structure of the ear to which the housing is mounted.
In still another embodiment, the floating mass transducer includes a bimorph piezoelectric strip disposed within the housing. The piezoelectric strip is secured at one end to the housing and may have a weig
Ball Geoffrey R.
Culp James M.
Dietz Tim
Mar Craig
Salisbury John D.
Lacyk John P.
Symphonix Devices, Inc.
Townsend and Townsend / and Crew LLP
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