Surgery – Diagnostic testing – Ear or testing by auditory stimulus
Reexamination Certificate
2001-04-23
2002-12-10
Walberg, Teresa (Department: 3742)
Surgery
Diagnostic testing
Ear or testing by auditory stimulus
C600S310000, C600S359000, C073S655000, C073S657000, C356S340000
Reexamination Certificate
active
06491644
ABSTRACT:
The invention relates to an implantable sound receptor for hearing aids, in particular for implantable hearing aids.
The majority of the known hearing aids is unsuitable for implantation. In principle, such hearing aids employ converters that are able to convert sound waves into electric signals. Such converters are known in the form of microphones and require appropriate membranes whose vibrations can be transformed into electric signals. The sensitivity of such microphones is largely influenced by the site of attachment and, above all, the size of the membrane. Acoustic vibrations can be picked up by pressure-sensitive membranes as is usually the case with microphone structures, or they can be detected by vibrometers receiving vibrations as acceleration signals or even as expansion measuring signals at deformations of vibrating structural components.
In U.S. Pat. No. 5,531,787, accelerometers in the form of piezo-resistive vibration sensors have been proposed. Alternatively, capacitive acceleration sensors are known to scan sound vibrations. Such miniaturized sensors have already been proposed for implantation in the region of the middle ear, whereby acoustic pressure waves generated in the region of the middle ear are scanned in the form of mechanical vibrations. In principle, such microphone structures are, however, relatively insensitive, because precise tuning to the acoustic impedance between the sensor and the tympanic cavity of the middle ear is not readily feasible.
Also other references such as, for instance, U.S. Pat. No. 3,557,775 have described microphones which may be implanted under the skin to receive audio signals, transmission being effected into the middle ear. Such arrangements, too, in terms of sensitivity are subjected to a number of not readily controllable foreign influences such as, for instance, the thickness of the skin and an unforeseeable formation of scar tissue and granulation tissue during the healing process, so that the sensitivity at the frequencies that are important to hearing will be attenuated in a variable and uncontrolled manner.
In principle, sounds that are heard are generated by sound waves, the pitch of a tone increasing with increasing frequency and the loudness increasing with increasing amplitude. In addition to tones and sounds, which constitute tonal mixtures, also a plurality of tones irregularly sounding simultaneously and having different frequencies and pitches are generated, which are heard as noises. By the natural hearing process, those sound waves are distinguished which are conducted from the auricle to the external auditory, thus causing the tympanic membrane to vibrate. The tympanic membrane is grown together with the hammer shank, whereby further transmission is effected via the auditory ossicles through the base of the stapes to the perilymphatic liquid, which causes the organ of Corti to vibrate. The excitation of the hair cells in the organ of Corti cause the generation of nerve impulses which are conducted by the auditory nerve into the brain, where they will be distinguished consciously.
The tympanic membrane functions as a pressure receiver and has a diameter of about 1 cm. If microphones having such large membranes are to be used to receive sound waves, such microphones will hardly be suitable for implantation, since the space required therefor is not available in the region of the ear.
Impaired hearing may have various causes. In a considerable number of hearing defects, the mechanical part of the vibration transmission from the tympanic membrane via the auditory ossicles to the liquid in the
scala vestibuli
is intact. It has, therefore, been already proposed to connect a vibration sensor directly with the membrane or the auditory ossicles in order to accordingly convert into electric signals, and amplify, the vibrations brought about by sound. Such an intervention has the drawback that, on the one hand, relatively high operating expenditures are involved in the arrangement of such sensors and, on the other hand, every mechanical influence of vibrating parts and, in particular, the damping of such vibrating parts, considerably influences the vibration behavior of those parts such that correct signals as are generated during the natural hearing process will not be obtained in that case, either. In principle, the miniaturization of microphones results in a decrease of sensitivity, this being not least due to the missing tuning of the acoustic impedance between microphone and ambient air. Even if this effect can be improved by implanting the microphone under the skin, this will lead to an alteration of the scannable frequency range with, in particular, higher frequencies being more strongly attenuated. Also other mechanical sound wave receptors such as, for instance, tubes filled with fluids, lead to an attenuation due to the viscosity of the used fluid, whereby rigid acoustic couplers, in general, are unsuitable for implantation.
The invention aims to provide a small-structured implantable sound receptor which avoids the drawbacks of the known sound receptors while maintaining the acoustic sensitivity on a constantly high level over the entire frequency range that is essential to hearing, i.e., from about 100 Hz to more than 10 kHz. The invention, furthermore, aims to keep the structural dimensions so small as to enable its implantation in the middle ear and/or the adjacent mastoid antrum. The surgical intervention preferably is to be reversible, whereby no substantial deterioration of the previously existing audition is to occur at a functional failure of the sound receptor. In a restrictive manner, an operative interruption of the sound transmission chain may, however, be required as a function of the employed actuator and its point of application, in order to avoid feedbacks. In addition to these demands set on an implantable sound receptor, also the energy consumption of the sound receptor and of a consecutive evaluation circuit is, of course, to be kept so low as to enable a total implantation due to miniaturization.
To solve this object, the implantable sound receptor for implantable hearing aids according to the invention essentially consists in that the sound sensor is designed as an optical sensor for vibration and distance measurements and is arranged within the ear at a distance from the surface of a sound transmission part capable of being excited to acoustic vibrations. Due to the fact that, as opposed to the hitherto applied physical principles of sound receptors for hearing aids, contactless scanning by means of an optical scanner has been proposed, it is actually feasible to measure the vibrations that are physiologically transmitted by the tympanic membrane and the auditory ossicles. The contactless configuration prevents undesired side effects of an attenuation of such vibrating auditory ossicles and the tympanic membrane and enables the unhampered use of the relatively large vibration pickup surface of the tympanic membrane for measuring, so that a considerably higher sensitivity can actually be attained than would be feasible with accordingly smaller membranes. Due to the fact that the optical sensor is arranged or arrangeable within the ear at a distance from the surface of a vibration transmission part capable of being excited to vibrations, it is ensured that any attenuation of the vibrations of such vibration transmission parts capable of being excited to vibrations will be reliably excluded and the use of optical sensors will allow the use of extremely small-structured sensors.
By optical sensors, sensors that do not necessarily use visible light are to be understood in this context. For optical sensors, electromagnetic waves in a relatively wide frequency range that goes beyond the spectrum of visible light may be used. As transmitters, laser diodes may, in particular, be used both in the infrared and ultraviolet ranges of radiation and in the visible range, as long as the vibrating surface to be measured is sufficiently reflective in the range of the irradiated wavelength. Optica
Detter Helmut
Pavelka Robert
Tomic Milos
Vujanic Aleksandar
Chapman and Cutler
Fuqua Shawntina T.
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