- Kenneth J. Dormer and Rong Z. Gan (College of Medicine, University of Oklahoma Health Sciences Center, Oklahoma City (KJD); the Oklahoma University Bioengineering Center, Norman (RZG); and the Hough Ear Institute, Oklahoma City (KJD, RZG), Oklahoma
Biomaterials for Implantable Middle Ear Hearing Devices
Ortolarygn. Cl. of N. A. April 2001 Vol. 34(2) P. 289-297
Four general categories of Biomaterials:
(1) Metals and their alloys.
(2) Polymers and composites.
(3) Ceramics and carbons.
(4) Biologic materials such as cells, tissues, and organs.
Three basic requirements of these materials are:
(1) Correct the anatomic, physiologic or mechanical defect.
(2) Be biologically acceptable to the host tissue.
(3) Remain stable and functional over a lifetime.
Such are the considerations incumbent on Implantable Hearing Devices (I.H.D.) for middle ear amplification.
Biomaterials used in Otology
Number of biomaterials in the form alloplastic materials are used in tympanoplasty and stapedectomy by otolaryngologist.
Metals, ceramics, polymers are used, including biomaterials like autograft materials in the form of residual ossicles, temoralis, faseia, homograft ossicles are used in tympanoplasty.
Biomaterials in implantable hearing devices
Presently different companies in different countries are developing these devices in the list given in Table I.
- Wen H. Ko, W. L. Zhu, M. Kane and Anthony J. Maniglia (Electronics Design Center (WHK), and the Otolaryngology Dept, School of Medicine (AJM), Case Western Reserve Univ., Cleveland, Ohio; Lucent Technologies, Holmdel, New Jersey (ZHZ); Guidant Corporation, Minneapolis, Minnesota (MK); and the Department of Otolaryngology, University of Miami School of Medicine, Miami, Florida (AJM)
Engineering Principles Applied to Implantable Otologic Devices
Ortolarygn. Cl. of N. America. April 2001 Vol. 34(2) P. 299-314
Engineering Principles of Mechanical Vibration Transducers
The major components in an implantable hearing device, as shown in the block diagram (Fig. 1) are
1. A microphone or input sensor that senses the acoustic sound wave or vibration and converts it into electrical signal.
2. An electronic amplifier and signal processor, which amplify the signal strength and process the electrical signal representing
the sound to match individual output requirements.
3. A transmission link that transmits the processed electrical sound signal to the next compartment.
4. An output transducer or actuator that converts the electrical signal to mechanical vibration coupled to the middle ear structure
or converts the signal into current pulses in many narrow frequency bands fed to the cochlear implant electrodes to stimulate
the nerves in the cochlea.
The external acoustic microphone, the electronic signal processors, and the transmission link for hearing aids have been studied extensively. The implant transducers – the input sensor and the output actuator – and the technique for coupling the actuator and sensor to the middle ear structure are critical components to be developed. This section discusses the engineering principles involved, the possible selections, and the relative merit of each option. In the following discussions, the implantable middle ear hearing aid output transducer and the implant microphone or input sensor coupled to the middle ear structure are used as examples.
Anders Tjellstrom, Bo Hakansson and Gosta Granstrom (Department of Otolaryngology, Sahlgrens University Hospital (AT, GG); and the Department of Signals and Systems, Chalmers University of Technology (BH), Goteborg, Sweden).
Bone-Anchored Hearing Aids
Current Status in Adults and Children
Ortolanryn. Cl. of N. A. April 2001 Vol. 34(2) P. 337-364
With experience dating from 1977, the use of direct bone conduction hearing aids is today a well-established treatment in selected cases. The BAHA is approved by FDA in the United States for adults and children. The cochlear reserve should be better than 45dB for the ear-level device, and not worse than 65 dB for the body-worn aid. The better the cochlear function is, the better satisfaction can be expected. The ideal candidate is a person with bilateral external ear canal atresia in whom the cochlear function is normal. In such a patient, the functional gain will be maximal. The size of the air-bone gap is of no significance. If, after trying the BAHA for sometime, the patient is dissatisfied with the arrangement, the surgeon can easily remove the device. The patient thus does not make any life-long commitment when choosing a BAHA.
All middle ear surgery involves a risk of cochlear damage. This risk does not occur with the BAHA, and in patients who need amplification in the only hearing ear this technique could be used. Many patients emphasize that one big advantage is the absence of occlusion effect because the external ear canal is left open. Some patients even claim that the wearing comfort is as great an advantage as the improved hearing with the BAHA. Binaural fitting is becoming increasingly common. The use of a BAHA in a dead ear in a person with a normal hearing in the other ear is also an interesting development being tested currently.
Ad F. M. Snik, Emmanuel A. M. Mylanus and Cor W. R. J. Cremers (Department of Otolaryngology, University Hospital Nijmegen, St. Radboud, Nijmegen, The Netherlands)
The Bone-Anchored Hearing Aid
A Solution for Previously Unresolved Otologic Problems
Ortolanryn. Cl. of N. A. April 2001 Vol. 34(2) P. 365-372
Most patients who had previously used a bone conduction hearing aid preferred the BAHA. On average, the reported audiologic results with the BAHA were superior. This advantage was found consistently in a significant number of studies and indicates that for these patients the value of the BAHA is no longer in debate. It has even been argued that because of the superior results and the relatively minor surgery required to place the implant for the BAHA, the BAHA should be offered to all patients who need a bone conduction device, whether or not they experience problems with a conventional bone conduction device.
For patients who had previously used air conduction hearing aids, the results are somewhat ambiguous and seem to be influenced by the width of the air-bone gap. If the air-bone gap exceeds about 30 dB, better results can be expected with the BAHA. The authors believe that an air conduction hearing aid should no longer be considered as the first choice for patients with severe chronically draining ears.
The BAHA is an alternative treatment with proven positive effects on ear discharge. Whether air conduction hearing aids should be omitted completely for patients with chronically draining ears has been questioned, because the effect on hearing and other complications has never been studied in detail. Cochlear damage in patients with severe chronic middle ear inflammation is not uncommon, however.
Before these patients are selected for a BAHA, they should be informed that speech recognition may be poorer than with the air conduction hearing aid. The authors believe it is helpful to introduce the patient to a conventional bone conduction hearing aid for a trial period before the application of a BAHA, to help shape the patient’s expectations.
The BAHA Cordelle can be used by patients with profound mixed hearing loss with a sensorineural component up to 60 dB. For such patients, there is hardly any alternative.
Thus the BAHA has established its place in hearing rehabilitation and in the management of draining ears for patients who need amplification. It should be offered more frequently to the patients with chronically draining ears
Ad F. M. Snik, Emmanuel A. M. Mylanus, Cor W. R. J. Cremers, et al (University Hospital Nijmegen, The Netherlands, (AFMS, EAMM, CWRJC); the Ospedale Civile di Venezia, Italy, St. Thomas’ Hospital, London, England, the Universitat Wurzburg, Germany (WESD)
Multicenter Audiometric Results with the Vibrant Soundbridge (Symphonix Devices, San Jose, CA)
A Semi-implantable Hearing Device for Sensorineural Hearing Impairment
Ortolanryn. Cl. of N. A. April 2001 Vol. 34(2) P. 373-388
The overall conclusion is that most patients clearly benefited from the Vibrant Soundbridge. There was, however, a subgroup of patients with low gain. The main reason for the low gain seemed to be limited bandwidth of the amplified sound signals. The positioning and fixation of the transducer might also have been involved. It can also be concluded that when speech was audible, it was also recognizable, suggesting that the quality of amplified speech is adequate.
The present study focused on sound-field measurements to evaluate the effectiveness of the Vibrant Soundbridge. As indicated earlier, because of the set-up of the study, no conclusion can be drawn about the possible surplus value of the Vibrant Soundbridge over today’s advanced conventional devices. Crossover studies are needed to the study this topic. A further important research question concerns the patients’ opinions about aspects such as sound quality, comfort, ease of listening, and so forth, and how such aspects of the Vibrant Soundbridge compare with those of conventional hearing aids. Early results from a large series of subjects at the Hannover clinic, comparing the Vibrant Soundbridge with the patient’s previous conventional hearing aid, are encouraging.
Naoaki Yanagihara, Hidemitu Sato, Yasuyuki Hinohira, Kiyohumi Gyo and Kiyoharu Hori (Department of Otolaryngology, Ehime University Medical School, Ehime (NY, HS, YH, KG); Takanoko Hospital, Matsuyama (NY); and the Department of Hearing Aid Technology, Rion Company, Kokubunji City, Tokyo (KH), Japan)
Long-term Results Using A Piezoelectric Semi-implantable Middle Ear Hearing Device
The Rion Device E-type
Ortolarygn. Cl. of N. A. April 2001 Vol. 34(2) P. 389-400
From the long-term follow-up studies, the authors derived the following conclusions:
1. The device can function safely in the ear for more than 10 years.
2. The device provides a natural sound quality without feedback and wearing discomfort. The quality of hearing afforded by the device is very close to that perceived by physiologic hearing.
3. Sensorineural hearing loss attributable to long-term use of the device was not recognized in any of the patients.
4. The implant operation could be repeated safely and provided the patient with high levels of satisfaction.
The studies indicate that Rion Device E-type can be used to rehabilitate mixed deafness that cannot be satisfactorily rehabilitated by either surgical means or a conventional hearing aid.
J. V. D. Hough, R. Kent Dyer, Pamela Matthews and Mark W. Wood (The Hough Ear Institute (JVDH, MWW, RKD); Department of Otorhinolaryngology-Head and Neck Surgery, University of Oklahoma Health Sciences Center (JVDH, RKD); Otologic Medical Clinic, Inc. (JVDH); and SOUNDTEC Inc. (PM), Oklahoma City, Oklahoma)
Semi-implantable Electromagnetic Middle Ear Hearing Device For Moderate to Severe Sensorineural Hearing Loss
Ortolanryn. Cl. of N. A. April 2001 Vol. 34(2) P. 401-416
Recent technologic advances in biomedical engineering have made possible the development of several implantable hearing devices which promise to bring greatly improved hearing to individuals suffering from sensorineural hearing loss. The feasibility study demonstrated that the SOUNDTEC DDHS offers many significant advantages to individuals with mild, moderate, and moderately severe sensorineural hearing loss who are dissatisfied with conventional hearing aids. The improvements noted in functional gain, speech discrimination, the functional absence of acoustic feedback, and subjective measures of patient satisfaction with the SOUNDTEC DDHS make it an attractive alternative to conventional hearing aids in individuals with mild to moderately severe sensorineural hearing impairment. For this large population, the SOUNDTEC DDHS seems to provide these benefits while embodying the characteristics of simplicity, safety, and efficiency.
Hans Peter Zenner and Hans Leysieffer (Department of Otolaryngology, The University of Tubingen, Tubingen (HPZ); and Implex AG Hearing Technology, Munich (HL), Germany)
Total Implantation of the Implex TICA Hearing Amplifier Implant for High-frequency Sensorineural Hearing Loss
The Tubingen University Experience
Ortolanryn. Cl. of N. A. April 2001 Vol. 34(2) P. 417-446
A TICA implantation may be indicated when a patient fulfills three selection criteria: lack of benefit from conventional hearing aids, moderate to severe high-frequency SNHL, and adequate space in the mastoid for implantation.
Lack of Benefit from Conventional Hearing Aids
Medical and psychosocial problems include
· Intolerance of the occlusion of the auditory canal by the ear-fitting device
· Ear-mold-induced repeated inflammation and pressure-induced skin lesions of the external auditory canal
· Manual motor impairment (e.g., from tremor or paralysis) making the daily use of tiny hearing aids or the use of tiny elements impossible
· Discrimination resulting from use of a visible hearing aid
Auditory problems include
· Intolerable feedback
· Distortion, low speech comprehension, strong amplification of background noise
· Reduced ability to communicate in the presence of background noise (party effect)
· Steep slope of hearing loss
Professional problems can be experienced by
· Professional athletes, sports instructors
· Language professionals (translators, language teachers)
· Persons whose work requires the use of earphones or stethoscopes
· Persons whose professional activities require telephone use and who cannot conduct telephone conversations using a conventional hearing aid
· Persons whose activities are associated with heat, sweat production, fat production, steam production, or dust production that can result in loss or damage to conventional hearing aids.
Moderate to Severe High-frequency Sensorinueral Hearing Loss
Maximum high frequency hearing loss (³ 3 kHz) may be 90 dB. Maximum low-frequency hearing loss should be no more than 30 dB at 0.5 kHz. In addition, the slope of hearing loss between 0.5 and 2 kHz should be 30 dB or more. The addition between the two ears should be no more than 20 dB (Zenner et al, unpublished data)
The Schuller’s radiograph should display normal mastoid pneumatization.
David W. Proops (Department of Otolaryngology, University Hospital Birmingham; and Diana Princess of Wales Children’s Hospital, Birmingham, United Kingdom)
Adult Cochlear Implantation
The Birmingham and United Kingdom Experiences
Ortolanryn. Cl. of N. A. April 2001 Vol. 34(2) P. 417-446
Cochlear implantation has been called a modern miracle and has probably exceeded the expectations of even its most ardent early pioneers. The capabilities of the preprogrammed brain permits patients, within minutes of activation, to appreciate common sounds not heard for many years and within days and weeks to comprehend open-set language without lip reading and even to use the telephone. In the last 2 decades cochlear implantation has been widely accepted by the medical community, and rapid developments have been made in the technology and reliability of the devices by the manufacturers.
Despite objections by the deaf community, there are active adult cochlear implant programs in all the countries of the developed world and many developing nations. There have been frequent conferences and many good-quality peer review papers concerning the scientific basis, the technical aspects of sound processing, the developments in electrode design, and surgical aspects of cochlear implantation. There is now a major corpus of published information about the measurable benefits of cochlear implantation to the patients.
Now that the technology has matured and more than 30,000 cochlear implantations have been performed worldwide.
Thomas J. Balkany, Annelle Hodges, Richard T. Miyamoto, Kevin Gibbin and Onur Odabasi (Divisions of Audiology (AH), Department of Otolaryngology (OO, TJB), University of Miami School of Medicine, Miami, Florida; the Department of Otolaryngology, Indiana University School of Medicine, Indianapolis, Indiana (RTM); and Nottingham, England (KG)
Cochlear Implants in Children
Ortolarygn. Cl. of N. A. April 2001 Vol. 34(2) P. 455-467
Although deafness was recognized in ancient civilizations, only in the past 2 decades has effective treatment with cochlear implants become available. Electrical stimulation of the auditory system is effective, because almost all sensorineural deafness is caused by receptor cell dysfunction (hair cells of the organ of Corti), whereas the auditory nerve itself remains responsive to stimulation (presumably through spiral ganglion cells) and can conduct impulses carrying auditory information to the brain (through cochlear nerve axons). Cochlear implants are electronic prostheses that replace the function of the damaged hair cells by transducing sound energy into coded electrical signals that can be received and transmitted by the cochlear nerve.
On the basis of a number of studies demonstrating safety and efficacy, multichannel cochlear implants first received approval by the Food and Drug Administration (FDA) for use in adults in 1984 and in children in 1990. Although different in many ways from those early devices, current-generation cochlear implants still consist of both external and surgically implanted internal components. The external portion of the device includes a microphone, a microprocessor-based speech processor, and a radiofrequency transmitting coil. The implanted portion houses a radiofrequency receiver coil, a microprocessor-based stimulator, and a mutichannel electrode array.
The cost of the device alone ranges from $20,000 to $25,000 with additional costs in the range of $15,000 to $20,000 associated with implantation and rehabilitation. Devices currently being used in children in the United States and United Kingdom include those manufactured by Advanced Bionics Corporation (Sylmar, California), Cochlear Corporation (Sydney, Australia), and MedEl Corporation (Innsbruck, Austria).
At the time of writing, approximately 20,000 children have received cochlear implants throughout the world. Although almost all pediatric cochlear implant recipients are successful users, results vary. Both congenitally deaf and postlingually deafened children have demonstrated development of hearing and oral language abilities using implants.
Cochlear implant surgery and technology continue to evolve, resulting in enhanced hearing, language, speech, and cost-effectiveness outcomes. Indications for implantation in children have expanded, including consideration of candidates as young as 12 months of physiologic age and those with residual amplified open-set speech recognition abilities. Certain basic tenets of implanting children remain paramount: careful evaluation over time including hearing aid trial, appropriate expectations and involvement of parents, auditory-based therapy, and life-long commitment of the team to the child.
Steven R. Otto, Derald E. Brackmann, William E. Hitselberger and Robert V. Shannon (House Ear Institute (SRO, RVS); the House Ear Clinic (DEB); and Private Practice (WEH), Los Angeles, California).
Brainstem Electronic Implants for Bilateral Anacusis Following Surgical Removal of Cerebello Pontine Angle Lesions
Ortolanrygn. Cl. of N. A. April 2001 Vol. 34(2) P. 485-499
Unfortunately, cochlear implantation will not benefit a relatively small but significant group of deafened individuals-those with neurofibromatosis type 2 (NF-2). Designed to stimulate auditory neurons in the cochlear nucleus complex, the auditory brainstem implant (ABI) has proven helpful for these patients. Trials with the device have successfully concluded, and worldwide approximately 150 recipients have received implants. The device has been shown to provide information about the sound environment and has demonstrated improvement in communication ability over lip reading alone in most recipients. In a few users, some open-set speech recognition has been observed.
Bilateral tumors of the eighth cranial nerve are generally considered pathognomonic of NF-2 and historically have caused bilateral deafness in most of these individuals.
In 1979 William House and William Hitselberger implanted the first brainstem electrode to treat deafness from NF-2. When the original electrode proved unstable, a second design was implanted in 1981 which is still in daily use by the original recipient. Her performance with a single-channel speech processor is comparable to that observed in many patients with more technologically sophisticated multichannel ABI. In general, however, performance with the multichannel ABI is better than that seen in the original 25 patients with the single-channel device.
Implantation of the ABI has been primarily undertaken as part of surgery to remove eighth nerve tumors in patients with NF-2; however, implantation may now occur in individuals who have already had both vestibular schwannomas removed. In summary, a translabyrinthine approach is used which provides an optimal exposure for tumor removal as well as access to the foramen of Luschka, the opening into the lateral recess of the fourth ventricle. The ABI electrode array is placed within this opening. Monitoring of intraoperatively evoked electrical potentials assists in identifying the optimal target for placement of the array. The array is positioned to span the surface of the ventral and dorsal cochlear nuclei.
Approximately 4 to 8 weeks after implantation, the device is activated for the first time. Subsequent follow-up includes regular assessment of responses to stimulation and appropriate reprogramming of the sound processor. Learning to use and benefit from the ABI is a gradual process that requires some measure of determination and motivation. Initial responses to sound vary, but most patients have reported extensive use and benefit from their implants on a daily basis, with improvements in performance occurring over many years.
The ABI has been used to treat deafness from NF-2 since 1979. Clinical trials with an eight-electrode multichannel version have recently successfully concluded. An upgraded 21-electrode version is presently in use. The device has provided useful information about the sound environment and improves communication ability for most recipients. The case studies presented here illustrate that
1. Initially some recipients may be disappointed with the sound quality of the ABI, but this initial response does not mean that long-term performance or benefit necessarily will be minimal.
2. Motivation to use the ABI regularly is very important.
3. Mild nonauditory sensations, although common, are usually manageable; in occasional cases of only nonauditory responses, implantation of the second side has been beneficial.
4. Electrode-specific pitch percepts, although helpful, are not essential for good performance with the ABI.
5. Improvements in sound perception can continue over many years, including a degree of open-set sentence recognition in some patients.
James F. Kasic and John M. Fredrickson (Otologics, LLC., Boulder, Colorado (JFK); and the Department of Otolaryngology, Washington University, St. Louis, Missouri (JMF).
The Otologics Met Ossicular Stimulator
Ortolanryn. Cl. of N. A. April 2001 Vol. 34(2) P. 501-513
Early preclinical research demonstrated that the MET Ossicular Stimulator can effectively benefit patients with moderately severe to severe sensorineural hearing loss. The MET Ossicular Stimulator is now in an FDA-approved clinical study. To demonstrate benefit over conventional hearing aids, the MET Ossicular Stimulator is compared with state-of-the-art digital conventional hearing aids using the same signal processing programs. The device program and performance are then verified in the clinic using referenced and calibrated measurement tools.