Abstract:
A system for enhancing a patient&#39;s hearing using electrically driven sound transducer, i.e., a speaker, implanted in the patient&#39;s middle ear cavity. More particularly, the speaker is implanted in the middle ear cavity inward of the tympanic membrane and oriented to direct sound energy toward the ossicles or the round window. In a first arrangement, the speaker functions to vibrate the ossicles and thus, via the oval window, actuate the perilymph in the cochlea. In an alternative arrangement, the speaker functions to actuate the cochlea via sound injected into the round window.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application 60/212,307 filed Jun. 17, 2000. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to a system and method for enhancing hearing in patients suffering from sensorineural hearing deficiencies and more particularly to a system including an electrically driven speaker implanted adjacent the middle ear cavity. 
     BACKGROUND OF THE INVENTION 
     The prior art is replete with descriptions of various devices and techniques for enhancing hearing in patients suffering from sensorineural hearing deficiencies. 
     As an example, U.S. Pat. No. 5,913,815 contains an extensive description of the background of hearing aids and cites a multiplicity of prior patents and publications. For example, the &#39;815 patent discusses that “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.” 
     The &#39;815 patent also mentions that “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.” 
     In order to mitigate the aforementioned and other shortcomings of earlier devices and techniques, various efforts have been directed toward surgically implanting devices which produce vibrations by physical contact and before conduction. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a system which uses an electrically driven sound transducer, i.e., a speaker, implanted in the middle ear cavity. More particularly, in accordance with the invention, the speaker is implanted in the middle ear cavity inward of the tympanic membrane and oriented to direct sound energy toward the ossicles and thus, via the oval window, actuate the perilymph in the cochlea. In an alternative arrangement, the speaker functions to actuate the cochlea via sound injected into the round window. 
     Many prior art middle ear hearing aid devices rely on an actuator to physically vibrate one of the ear&#39;s components, typically one of the three ear bones (ossicles) or one of the cochlea membranes. Indeed, some devices require penetration of the cochlea. This level of invasiveness presents a risk of aggravating, rather than mitigating, hearing impairment. The present invention considerably reduces the risk by relying on sound energy, rather than physical contact. 
     In accordance with the invention, a microphone is supported and/or implanted adjacent to the ear canal sufficiently isolated from the implanted speaker. The microphone is configured to respond to sound energy to generate an electric signal which drives the implanted speaker which is preferably contained in a hermetically sealed housing fixed to bony material adjacent to the middle ear cavity. 
     In accordance with a preferred system embodiment, the microphone comprises a component of an integrated microphone module including an analog-to-digital converter, sound processing circuitry, and encoding/modulation transmitter circuitry, all contained in a hermetically sealed housing. The housing includes a battery, preferably a lithium ion battery, which can be charged from an external source, as by an alternating magnetic field source. 
     In accordance with a preferred embodiment, the speaker comprises a component of an integrated speaker module including demodulation/decoding receiver circuitry, processing circuitry, and a digital-to-analog converter, all contained in a hermetically sealed housing. The speaker module housing contains a battery similar to that contained in the microphone module. 
     In accordance with a preferred system embodiment, sound insulation is preferably provided to direct sound energy primarily to the ossicles and middle ear oval window and away from the microphone. In order to minimize signal cancellation which could occur by in-phase sound energy also entering the round window, it is preferable to seal the round window. This sealing can take the form of a passive sound insulator or an active device (e.g., a second speaker) which produces the same signal but out of phase. 
     In an alternative preferred embodiment, the speaker is mounted close to the round window and insulated to minimize sound transmission to the microphone and the oval window. 
     In accordance with a further aspect of a preferred embodiment, a speaker placed in one ear can be driven by a microphone placed in the other ear. This arrangement reduces feedback. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 schematically represents the internal structure of a typical ear showing an exemplary placement of a speaker and microphone in accordance with the present invention; 
     FIG. 2 is a schematic illustration similar to FIG. 1 but showing an alternative exemplary placement of a microphone and speaker in accordance with the invention; 
     FIG. 3 is a block diagram of a first embodiment for coupling a microphone and speaker in accordance with the present invention; 
     FIG. 4 is a block diagram of a preferred microphone module in accordance with the present invention; 
     FIG. 5 is a block diagram of a preferred speaker module in accordance with the present invention; and 
     FIG. 6 is a block diagram of an alternative speaker module for generating out-of-phase sound energy to reduce in-phase signal cancellation. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Attention is initially directed to FIG. 1 which schematically represents the internal structure of a typical ear. The internal ear structure is generally considered to be comprised of three portions, namely, the outer ear, the middle ear, and the inner ear. The outer ear is in part defined by the cochlea and the ear canal leading to the tympanic membrane. Across the tympanic membrane is the middle ear cavity defined essentially by the tympanic membrane and peripheral bony structure. The cavity contains three primary ear bones, i.e., the ossicles. The inner ear is comprised in large part by the cochlea and related structure. 
     In the operation of the healthy ear, sound enters the ear canal. At the tympanic membrane, sound energy (air pressure changes) is transformed into mechanical energy acting to vibrate the ossicles. The middle ear serves essentially as an impedance matching transformer, matching the impedance of air in the ear canal to the impedance of the perilymph of the inner ear. The ossicles couple mechanical energy to the perilymph in the cochlea primarily by way of the oval window. 
     In accordance with the present invention, an electrically driven speaker  10  is implanted adjacent to the middle ear cavity  12 . FIG. 1 shows the speaker  10  in a superior placement fixed to bony structure defining the upper periphery of the cavity  12 . The speaker  10  in a first arrangement is preferably oriented to direct sound energy to vibrate the ossicles  14 . In an alternative arrangement, the speaker can be placed proximate to the round window (not shown) and oriented to direct its sound energy into the round window. 
     The speaker  10  is driven by a microphone  20  which is mounted adjacent to the ear canal  22 . The microphone  20  is preferably subcutaneously implanted but may alternatively be placed above the skin within the ear canal. Two small isolated wires (not shown) can be provided to couple the microphone  20  to the speaker  10 . However, as will be discussed hereinafter, it is far preferable for the microphone  20  to be physically associated with sound processing and RF transmitting circuitry in order to transmit radio signals to the speaker  10 . 
     Whereas FIG. 1 shows an exemplary superior placement of both the microphone  20  and speaker  10 , FIG. 2 shows an alternative inferior placement of the microphone  20  and speaker  10 . Although not shown, it is pointed out that the microphone and speaker need not be placed in the same relative position. That is, where appropriate, the speaker  10  can be placed in a superior position and coupled to a microphone  20  in an inferior position or vice versa. 
     Regardless of the precise placement of the speaker  10 , the speaker is to be implanted adjacent to the middle ear cavity  12  to direct sound energy either to the ossicles  14  or to the round window (not shown). In either case, the sound energy is air conducted and neither the ossicles nor the round window are physically contacted by any actuator member. In both cases, it is preferable to use insulating material to restrict the sound energy to the intended target, e.g., the ossicles or round window. 
     Attention is now directed to FIG. 3 which depicts a first embodiment for connecting the microphone  20  to the speaker  10 . The circuitry includes an amplifier  21 , a filter  22 , e.g., antialiasing, an analog-to-digital converter  23 , a digital sound processor  24 , a digital-to-analog converter  25 , and an amplifier  26 . All the blocks are preferably powered by a battery  27 , e.g., a rechargeable lithium ion battery. All of the blocks depicted in FIG. 3, except for the speaker  10  are preferably contained in a hermetically sealed housing  28  and connected to speaker  10  by surgically placed wires  29 . 
     Attention is now directed to FIG. 4 which illustrates a preferred microphone module  30  intended to be implanted as depicted in FIGS. 1 and 2. The module  30  is comprised of a microphone  32 , an amplifier  34 , a filter  36 , e.g. antialiasing, an analog-to-digital converter  38 , a digital sound processing circuit  40 , a parallel to serial converter  42 , and an encoding/modulating transmitter circuit  44 . The output of the transmitter circuit  44  is coupled through amplifier  46  to an antenna  48 . The blocks of the microphone module  30  depicted in FIG. 4 are all powered by a battery  50 . The battery is preferably of the rechargeable type, e.g., a lithium ion battery, which can be charged by charging circuit  52  from, for example, energy extracted from an alternating magnetic field provided by an external source (not shown). All of the elements of FIG. 4 are preferably contained in a hermetically sealed housing  54  to be implanted adjacent the middle ear cavity, e.g., at the microphone sites depicted in FIGS. 1 and 2. 
     In use, sound energy detected by microphone  32  is, after filtering, converted to digital form and appropriately processed by a programmable sound processing circuit  40  to best mitigate the particular hearing impairment of the patient. The resulting digital signal produced by sound processing circuit  40  is then used to modulate RF carrier signal in circuit  44  which is then applied to antenna  48 . 
     FIG. 5 depicts a preferred embodiment of speaker  10  comprising a speaker module  60  containing output speaker  62 . Module  60  functions to receive the signal transmitted by antenna  48  to drive output speaker  62 . 
     Speaker module  60  is comprised of an antenna  64  coupled via an amplifier  66  to a demodulation/decoding circuit  68 . The output of circuit  68  is converted from serial to parallel form in block  70  and then processed in block  72  prior to being applied via converter  73  and amplifier  74  to drive speaker  62 . All of the blocks in FIG. 5 are intended to be powered by a battery  75  and charging circuit  76 , similar to aforementioned battery  50  and charging circuit  52 . All of the elements of module  60  are contained in a hermetically sealed housing  77 . 
     As previously mentioned, it is intended that the speaker  62  of FIG. 5 be mounted adjacent the middle ear cavity  12  directed toward the ossicles  14  as shown in FIGS. 1 and 2 or round window (not shown). If directed toward the ossicles. The speakers will vibrate the ossicles which will transfer mechanical energy via the oval window to the cochlea. In order to minimize noise and signal cancellation which could occur attributable to signal energy transfer via the round window, it is preferable to seal the round window. Sealing can be provided by a passive insulating material properly mounted adjacent the round window. Alternatively, a second speaker can be provided directed at the round window to emit the same signal as the primary speaker but of opposite phase. FIG. 6 illustrates an alternative speaker module  80  which is similar to the module  60  of FIG. 5 except that it requires the processing circuit  82  to generate identical out-of-phase signals S 1  and S 2 . Signals S 1  and S 2 , via D/A converters  83 , respectively drive speakers  84  and  85 . Speaker  84  can be the primary speaker as aforediscussed for driving the ossicles  14  to transfer energy through the oval window. Speaker  85  can be directed toward the round window to produce an out-of-phase sound signal which adds to, rather than cancels out the primary energy coupled to the cochlea. 
     In the discussion thus far, and as depicted in FIGS. 1 and 2, it has been assumed that the primary speaker in the middle cavity is driven by a microphone associated with the same ear. Although this arrangement can be satisfactorily implemented, it is subject to typical feedback limitations. That is, the microphone, as depicted in FIG. 1, could pick up sound energy from the speaker  10  depicted in FIG.  1 . Although in many situations this feedback may not present a major problem, it does limit the level of amplification which can be used. This feedback limitation can be significantly minimized when using RF communication as represented by the modules of FIGS. 4-6. Utilizing RF communication, it is now quite feasible to drive a speaker  10  in one ear from a microphone  20  placed in the opposite ear. That is, a left ear speaker can be driven by a right ear microphone via a first RF channel and a right ear speaker can be driven by a left ear microphone via a second RF channel. 
     From the foregoing, it should now be apparent that applicants have disclosed a system for improving the hearing of impaired persons by implanting an electrically driven speaker so as to generate sound energy in the middle ear cavity to vibrate the ossicles or round window by air conduction without physical contact.