GB2360663A

GB2360663A - Implantable hearing aid

Info

Publication number: GB2360663A
Application number: GB9929631A
Authority: GB
Inventors: John Nicholas Marshall
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-12-16
Filing date: 1999-12-16
Publication date: 2001-09-26
Also published as: GB9929631D0; EP1240806A2; AU2191501A; WO2001045457A2; WO2001045457A3

Abstract

A hearing aid, which incorporates a modified electro-dynamic exciter, implanted into the bone of the skull to cause vibration of the bone of the inner ear and the cochlear (inner ear) fluid. The exciter is surgically implanted into the temporal bone. The exciter is modified by encasement in a shell made of titanium or other biocompatible material and is secured in place by drilling a hole in the surface of the mastoid bone, which fits the exciter tightly. Bone cement or osseointegration is used to fix the baseplate of the exciter securely. A microphone, battery, amplifier, volume control, on/off switch and output limiter are also required. Three versions of this design are described. In Type 1 the microphone, battery, amplifier, volume control, on/off switch and output limiter and are externally located and directly connected. In Type 2 these components are external and not directly connected, and a radiofrequency transmitter and receiver are employed, and in Type 3 all components are implanted.

Description

DescriDtion 2360663 This implantable hearing aid uses a modified

electro-dynarnic exciter 1 as the implanted transduzer to cause complex vibration of the temporal bone and subsequent vibration of the endolymph and perilymph within the cochlea. This in turn causes vibration of the basilar membrane which is necessary for the generation of the nerve impulses which result in hearing.

The exciter is surgically implanted into the temporal bone (the part of the skull in which the inner ear is located) under local or general anaesthetic.

An electro-dynamic exciter is modified by encasement in a casing made of titanium or other biocompatible material and is secured in place by drilling a hole in the surface of the mastoid bone which would fit the exciter securely. Bone cement or osseointegration 2 (a. process whereby titanium is anchored securely to bone as new bone develops on the surface of the titanium) is used to fix the baseplate of the exciter firmly. Three different versions of this are described, which will be suitable for different patient requirements and also form a stepwise development program.

T"e 1 (Drawing 2) A microphone, battery, amplifier, output limiter volume control and on/off switch are externally located (these could be incorporated into either a ear-wom device looking similar to a conventional hearing aid, or a body worn device allowing greater component weight). There is a direct connection to the transducer via an external coupling located in the skin behind the ear. This would be suitable for patients with severe/profound hearing loss, as higher power would be achieved from an externally worn battery. This would also be the first development sta as the external components would be easily adjusted or altered.

1 Q Type 2 (Drawing 3) The transducer, battery and a radiofrequency receiver are implanted. A microphone, amplifier,. battery, output limiter, volume control, on/off switch and radiofrequency transmitter are located externally. This suitable for both moderate and severe hearing loss.

LTe 3 (Drawing 4) All components (microphone, battery, amplifier, transducer, output limiter) are implanted. This would be suitable for patients with a moderate hearing loss, especially those for whom the benefits of having no externally visible components are important.

3 Backeround A The problems that this design addresses:

Patients with hearing loss may not benefit from or wish to use a conventional external hearing aid for a number of reasons:

1 Dislike of the appearance of externally worn hearing aids or the stigma associated with wearing an external aid.

2 Chronic ear infection with discharge may be made worse by the earpiece of an external aid, and this discharge may interfere with the functioning of the aid.

3 Physical abnormalities may preclude the use of an external hearing aid.

4 The hearing loss may be too severe to gain benefit from a conventional aid.

B Types of hearinz loss There are two main types of hearing loss, conductive and sensorineural, although some patients may have an element of both. Sensorineural hearing loss is more common. A conductive loss is when there is a problem with the passage of sound through the ear canal and/or middle ear, and the cochlea (organ of hearing) works normally. This type of hearing loss is normally suitable for amplification with a conventional hearing aid, although the problem with the appearance of the hearing aid and associated stigma may apply. Sensodneural hearing loss is more common. In sensorineural loss the middle ear is normal but the problem lies in the cochlea, auditory nerve or the brain itself. In most cases the cochlea itself is the site of the problem. In these cases the hearing loss may be more severe and the quality of sound perceived after amplification is often poorer. It is mainly (but not exclusively) for cases of sensorineural loss that implantable hearing aids are targeted.

C Current progress with implantable hearing aids No fully implantable hearing aids are commercially available at present, although research into implantable hearing aids is ongoing, and some related devices are available (see below). Researchers have to address several problems:

1 Inadequate gain (i.e. inadequate amplification of the sound) so that the benefit is limited.

2 Excessive power requirements making an implantable battery unfeasible unless a rechargeable battery is used. If a rechargeable battery is required, the longer the time between charging the better.

3 Most recent research in developing an implantable hearing aid involve implants that attach to the ossicles (the chain of three bones within the middle ear). These have the disadvantage that the patient's hearing may be made worse by scarring after surgery, damage to the ossicles themselves, or displacement of the implant. This is a particular risk because the ossicles are extremely small and delicate. Removal of the implant may therefore leave the patient with poorer hearing than before implantation, affecting later use of a conventional hearing aid.

This design has the potential to address all of the above problems. The gain is high, power consumption low and the middle ear is not affected by the implantation. Removal of the implant should leave the patient with hearing unaffected by the implantation.

D Other related devices There are two related devices of note that are currently in use.

1 Bone anchored hearing aid. This is similar to a conventional hearing aid but sound is transmitted via an implanted screw, which is inserted into the temporal bone and fixed by osseointegration.

The screw is connected to an external mounting, to which the other components are attached. Thi,, causes bone vibration and is currently used in cases of conductive hearing loss where middle ear abnormalities or infection preclude the use of a conventional hearing aid. Sound is transmitted to the cochlea by passive vibration of the implanted screw rather than by the use of an implanted transducer.

2 Cochlear Implants. These are only used in cases of profound hearing loss where the patient has no useful hearing even with the most powerful hearing aids. An array of electrodes is inserted into the cochlea itself, allowing direct electrical stimulation of the 'hair cells' in the inner ear. Cochlear implants are very successful in cases of profound hearing loss, although extensive rehabilitation is necessary. Cochlear implants are only suitable in a very small number of cases and are very expensive, as well as causing permanent damage to the inner ear.

E The electro-d ynamic exciter In 1991, Ken Herron, working for the DERA (part of the Ministry of Defence) found that composite panels could act as efficient sound radiators. Subsequently, this technology was developed by the UK company NXT (New Transducers Ltd, formerly Verity) who have used the concept to create flat panel loudspeakers. By using one or more exciters (typically 15-25min in size), panels only a few millimetres thick can be made to behave as loudspeakers, with a completely different mode of action to conventional loudspeakers. This technology also works with curved panels. Different materials have been used to make the panel, and recently the company has announced that totally transparent speakers can be manufactured. 1 am unaware of any research into the vibration of bone using this technology, or of any design in which the exciter is used other than in the production of different types of loudspeakers. The exciter in this design is not being used in a loudspeaker, but is being implanted to cause direct vibration of the bone of the skull, and hence vibration of the inner ear fluids.

1 1 c References 1 NXT exciter. Patent number W09834320 Publication date: 1998-08-06 Inventor(s): AZIMA HENRY (GB); JARVIS EDWARD (GB); ROBERTS TIN (GB) Applicant(s):: NEW TRANSDUCERS LTD (GB); AZIMA HENRY (GB); JARVIS EDWARD (GB); ROBERTS MARTIN (GB) Requested Patent: W09834320 Application Number: W01998GB00307 19980130 Priority Nurnber(s): GB1900001983 19970131 1PC Classification: H02K EC Classification: H04R1 1102 Equivalents: AU5874098, EP0956736, N0993719, ZA9800782 2 Osseointegration Patent Number: US4330891 Publication date: 1982-05-25 Inventor(s): BRANEMikRK PER I; THURESSON AF EKENSTAM BO Applicant(s):: BRANEMARK PER INGVAR; THURESSON AF EKENSTAM BO Requested Patent: CAl 157694 Application Number: US 19800125654 19800228 Priority Number(s): SE19790002035 19790307 1PC Classification: A61F1/00; A61F1/24 EC Classification: A61F2/30L; A61L27/00H2 Equivalents: AT127680, AT399096B, BE881953, CH653245, DE3007446, DK96880, ES489204, F1800706, FR2450599, GB2045083, IE49186, ITI 130275, JP1033180B, JPI 838708C, JP5345014, JP55120864, LU82222, N1,185390B, NLI85390C, NL8001241, N0149373B, N0149373C, N0800651, SE416175, SE7902035

Claims

Claims

The inventive steps in this design are:

1 the modification of the electro-dynamic exciter by encasing it in titanium to allow biocompatibility without impeding the internal movement of the exciter.

2 the use of this modified, exciter as an implanted hearing aid transducer.

3 the use of an exciter as a tranducer to cause bone vibration but not sound radiation.

4 the use of a modified exciter in conjunction with other components to create a fully or partially implantable hearing aid.