Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Ear or nose prosthesis
Reexamination Certificate
1999-07-28
2001-06-26
Isabella, David J. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Ear or nose prosthesis
Reexamination Certificate
active
06251138
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to surgical methods and prosthetic devices for ameliorating hearing loss in patients suffering from ailments of the middle ear.
Chronic otitis media (COM), a common inflammatory disease of the middle ear and mastoid, can affect 0.5 to 30% of the population (a conservative estimate of the number of people suffering from COM is over 5 million in the U.S. and over 120 million worldwide), and results in conductive hearing loss that can range in severity up to 60 dB. The main form of therapy for COM is surgical, i.e., mastoidectomy and tympanoplasty. Although tympanomastoid surgery is typically successful in controlling infection, a post-operative hearing loss of more than 20 dB persists in about 50% of patients. Such hearing loss is often significant, in the range of 40 to 60 dB. Non-aeration of the middle ear due to deposition of fibrous tissue or formation of fluid resulting from eustachian tube dysfunction is understood to be the main cause of such post-operative hearing loss.
Serous otitis media (OME) is another common disorder of the middle ear that can lead to conductive hearing loss ranging in severity up to 30-40 dB. A number of patients with OME fail to respond to medical therapy and hence require surgical intervention by way of a tympanostomy (ventilation) tube. In fact, tympanostomy tube placement is the most common operation performed in the United States, with over 1.3 million ears intubated annually. Such tubes, however, have several disadvantages that include the need for water precautions, and the potential for chronic perforations, focal tympanic membrane atrophy, formation of retraction pockets, cholesteatoma and tube extrusion.
The introduction of a small bubble of gas into the middle ear of patients with eustachian tube obstruction, in which the middle ear and mastoid are filled with serous fluid, improves the conductive hearing loss of such patients as long as the air bubble remains in the middle ear. This has led some investigators to inject air or other gases in the middle ear to improve hearing loss. Such gases, however, are short-lived in the middle ear due to absorption. Further, attempts to create long-lasting air pockets using silicone elastomers or an air-filled hollow body of silastic have failed to produce lasting benefit, presumably because of extrusion of the prosthesis and/or failure of the prosthesis to remain inflated.
U.S. Pat. No. 5,356,430 of Nadol describes a hearing prosthesis that is deemed to provide relief from hearing loss under certain conditions.
It is thus an object of the invention to provide prolonged relief from conductive hearing loss caused by ailments of the middle ear.
It is another object of the invention to provide a surgical method for ameliorating hearing loss caused by ailments of the middle ear.
SUMMARY OF THE INVENTION
The present invention attains the above and other objects by providing a middle ear prosthesis for treating hearing loss due to ailments of the middle ear. The prosthesis of the invention includes a pliant membrane of biocompatible material formed into a closed synthetic balloon configured to fit in a patient's middle ear. When implanted, the prosthesis at least partially contacts the tympanic membrane. The pliant membrane of the prosthesis is selected to be thin and substantially impermeable to water and to gases during protracted contact with body fluids. The prosthesis includes a reservoir for at least one gas within the closed balloon. The prosthesis has an acoustic impedance that is sufficiently low such that the prosthesis enhances the transfer of sound-induced motions of the tympanic membrane to the ossicles and the inner ear. Hence, the prosthesis of the invention restores tympanic membrane motion so as to enhance transfer of sound through the middle ear to the inner ear of a patient.
According to one aspect of the invention, the prosthetic balloon has an equivalent volume, defined below, that is at least approximately 70% of its physical volume. Selecting the equivalent volume of the balloon to be equal or larger than approximately 70% advantageously results in the balloon having an acoustic impedance that is low enough to effectively couple sound-induced motions of the tympanic membrane to the structures of the middle ear, such as the ossicles and the round window. This in turn enhances transmission of sound to the inner ear of the patient.
According to another aspect of the invention, the prosthesis includes a tab extending from an end of the balloon to provide a handle for manipulating the balloon in order to position it in the middle ear. The tab can include a radioopaque marker for radiographic visualization. In one preferred embodiment of the invention, the prosthetic balloon has an ovaloid shape with a generally elliptical cross section that has a major axis and a minor axis. The ovaloid balloon further has a maximum dimension between a first end and a second end along a principal axis, and with a tab extending outwardly from one of these ends.
In some preferred embodiments of the invention, the biocompatible material for forming the balloon is selected to be a homopolymer or a copolymer containing vinylidene chloride (VDC).
In accord with another aspect of the invention, the balloon contains at least one large-molecule biocompatible gas, e.g., sulfur hexafluoride (SF
6
). The balloon can also contain at least one naturally occurring atmospheric gas having a partial pressure below its normal partial pressure in the atmosphere. The total pressure of the gas within the synthetic balloon is preferably in a range of approximately 50 mm of H
2
O below the atmospheric pressure to approximately 50 mm of H
2
O above the atmospheric pressure.
In one preferred embodiment, the invention provides a middle ear prosthesis that includes a gas-filled ovaloid balloon having a length and a width that are adapted for fitting in the middle ear in contact with the tympanic membrane. The balloon is formed of a flexible film, for example a film formed of a polymer of VDC, that is substantially impervious to water and to gases such that the balloon remains inflated after implantation in the middle ear. Accordingly, the balloon maintains a reservoir of gas, thereby allowing transmission of acoustical vibrations. The film is selected to be compliant in order to respond elastically flexibly to acoustical vibrations, thereby transmitting the vibrations through normal or reconstructed ossicles.
In one preferred construction, the balloon is initially filled with a substantial portion, e.g., ten to fifty percent or more, of an unnatural, i.e., non-atmospheric, gas, preferably one to which the balloon wall is substantially impermeable, e.g., SF
6
. Nitrogen and oxygen are also present, but at lower partial pressures than in the surrounding atmosphere. After implantation of the balloon in the middle ear, the nonatmospheric gas, e.g., SF
6
, diffuses out of the balloon very slowly over time, and atmospheric gases dissolved in the middle ear fluid, e.g., nitrogen and oxygen, diffuse into the balloon at a rate slightly exceeding the rate of the loss of the non-atmospheric gas. Thus, the balloon, over the course of a few months, spontaneously self-inflates, and stays inflated over an extended time period, i.e., more than one to two years.
Another aspect of the invention relates to disposing a plurality of synthetic balloons in the middle ear, where at least one of the balloons contacts the tympanic membrane. The presence of more than one balloon in the space of the middle ear can advantageously maximize hearing restoration of a patient having an ailment of the middle ear. Each balloon is formed of a thin pliant membrane of biocompatible material that is substantially impermeable to water and to gases during protracted contact with body fluids. Each balloon has a reservoir for at least one gas, and further has an acoustic impedance that is low enough to permit sound-induced motions of the tympanic membrane, the ossicles, and the round window.
Another aspect of the
Merchant Saumil N.
Nadol, Jr. Joseph B.
Fish & Richardson PC
Isabella David J.
Massachusetts Eye & Ear Infirmary
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