Surgery – Surgically implanted vibratory hearing aid
Reexamination Certificate
1999-10-29
2003-10-07
Lacyk, John P. (Department: 3736)
Surgery
Surgically implanted vibratory hearing aid
C381S312000
Reexamination Certificate
active
06629922
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to devices and methods for improving hearing, particularly in the field of hearing aids. The invention is an output actuator that is a component of a class of hearing devices known as surgically implantable hearing aids. This invention relates to both fully implanted and partially implanted hearing aids. More particularly, methods and devices are disclosed to provide an actuator for directly driving the inner-ear fluid, or the middle-ear bones referred to as the ossicular chain, resulting in the sensation of hearing.
BACKGROUND OF THE INVENTION
Over 26 million people in the United States suffer from some type of hearing loss. A large portion of this population can regain the ability to hear or at least improve their diminished hearing with the use of a hearing aid. Yet, many people choose not to use a hearing aid for such reasons as social stigma, the discomfort associated with a device in the ear canal, the unnatural, hollow sound and/or plugged up sensation that some hearing aid users report (commonly referred to as the occlusion effect), and noise caused by feedback of the device. Surgically implantable hearing aids address all of these concerns and could increase the frequency of use by those individuals previously reluctant to use hearing aids. A detailed discussion on the usefulness and benefit of implantable hearing aids is found in U.S. Pat. No. 5,772,575 to Lesinski et al.
Like most natural processes of the body, the ability to hear is made possible by an intricate process involving many steps. The mechanical portion of this intricate process takes place in the outer ear, middle ear, and the inner ear. The outer ear, the auricle, collects sound waves and leads these waves into the middle ear. The middle ear couples the sound waves in the air-filled ear canal to fluid of the inner-ear (perilymph). The middle ear, containing the eardrum (tympanic membrane) and three tiny bones (malleus, incus and stapes), is an interface between the low impedance of air and high impedance of inner ear fluid. Pressure induced vibrations of the tympanic membrane ultimately induce a proportional motion of the stapes, the smallest of the three auditory ossicles in the middle ear. This motion is the output of the middle-ear. The stapes transmits this motion to the inner ear. In the inner ear, this motion produces a large pressure in the scala vestibuli, a perilymphatic channel on one side of the cochlear duct, in comparison with the scala tympani, a perilymphatic channel on the other side of the cochlear duct separated from the tympanic cavity by the round window membrane. The pressure difference between the two scalae in turn causes a traveling wave to move apically on the basilar membrane. The motion of the basilar membrane causes the cilium of receptor cells, also known as the inner hair cells (IHC) to move, which in turn causes firing of the auditory nerve. This process produces the sensation of hearing.
The ability to hear and the sensitivity at which one is able to hear is diminished by two basic types of ear pathologies that are commonly referred to as i) conductive hearing loss, and ii) sensory-neural hearing loss. Conductive hearing loss may be traced to either a pathological condition of the middle ear or the middle-ear cavity, or impairment (i.e., blockage) of canal or the outer ear. This type of hearing loss is routinely repaired by otologic surgeons. On the other hand sensory-neural hearing loss is due to a pathological condition of the inner ear and is nearly impossible to repair via surgery.
Different pathological conditions of the inner-ear can lead to sensory-neural impairment. See, for example, Killion, M. C. (1997) “SNR Loss: I can hear what people say but I can't understand them,”
The Hearing Review
4(12)8-14 (1997). First, there is the loss of outer hair cells (OHC), normally organized in three to four rows along the length of the basilar membrane. In this condition there is a decrease in basilar membrane motion and consequently there is a reduction in movement of the receptor cells. Most researchers agree that loss of OHC results in an increase in threshold to tonal stimuli. That is, the loss of OHC appears to reduce an individual's ability to hear quiet or low volume sounds. The loss of inner hair cells (IHC) or their cilium (hair bundles) is another disease state of the inner ear. It is believed that IHC provide all of the auditory information to the brain. Thus, in this pathological state, there is a decrease in the number of auditory nerve fibers that send neural impulses to the more central portion of the auditory system. As a result, as seen with loss of OHC, the loss of IHC results in an increase in threshold to tones. In addition, it has been speculated that loss of IHC also causes a loss of clarity of hearing. In other words, it is thought that loss of IHC results in an effective increase in internal noise and thus requires a greater signal-to-noise ratio (SNR) than patients with no IHC pathology (Killion, 1997). In this type of hearing loss there is a reduction in an individual's ability to understand speech (i.e., the signal) in the presence of background sound (i.e., the noise). By itself, any hearing aid can address the threshold issue and will improve an individual's ability to hear quiet or low volume sounds. Yet, not all hearing aids will address the signal-to-noise ratio issue—i.e., most hearing aids fail to improve one's ability to hear speech in the presence of background noise.
Two commonly found causes of sensory-neural hearing loss are presbyacusis and noise induced hearing loss. Presbyacusis is the loss of ability to perceive or discriminate sounds. This loss of high frequency hearing increases with age. Hearing is also compromised by an individual's exposure to loud sounds. For example, without hearing protection, sounds from machinery, excessive live or recorded music, gun shots, etc. cause sensory-neural hearing loss. The extent of damage depends upon the intensity, frequency, content, and duration.
Individuals having a high degree of sensory-neural hearing impairment, but who still have some residual hearing capability, can achieve normal pure-tone thresholds if the motion of the stapes is amplified. In other words, exaggerating the motion of the stapes permits a hearing impaired individual to hear sounds that were previously too soft to hear. Alternatively, driving the cochlear fluid by other means (e.g., at a location other than the stapes), and at an amplified level, also improves the ability of the hearing impaired to hear sound. Basically, the location of where cochlear fluid is put into motion does not matter. This phenomena is known as “paradoxical motion” and was described by the Nobel laureate Von Bekesey (1960). It is this “paradoxical motion” that is the basis for bone-conduction hearing which is routinely measured in audiology clinics.
Several individuals have proposed methods for directly driving cochlear-fluid. See, e.g., Yanagihara, N., Gyo, K., Suzuki, J., and Akara, H. (1983). “Perception of sound through direct oscillation of the stapes using a piezoelectric ceramic bimorph,”
Ann Otol Rhinol Laryngol
92:223; Yanagihara, N., Suzuki, J., Gyo, K., Syono, H., and Ikeda, H. (1984). “Development of an implantable hearing aid using a piezoelectric vibrator of bimorph design: State of the art,”
Ann Otol Rhinol Laryngol.
; and Suzuki et al., Middle Ear Implant for Humans,
Acia Otolaryngol
(Sockh) (1985) 99:313-317. The entirety of the above references is hereby incorporated by reference. These documents describe output transducers for use in implantable hearing aids. These hearing aids rely upon a piezo bimorph. A bimorph consists of two piezo materials bonded together, sometimes having a metallic sheet (a shim) sandwiched between the piezo materials. The bimorph causes bending deformation as each piezo material produces extension or contraction under an electric field. The bonding of the two materials allows for a magnification of the displacem
Perkins Rodney C.
Puria Sunil
Lacyk John P.
Soundport Corporation
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