Abstract Otology 2000 B11-1

Euan Murugasu MD

California Ear Institute atStanford Dr. Joseph Roberson USA-Palo Alto, CA

The cochlea is the most sophisticated mechano-sensory transducer in our body, regulated by the voltage-dependent motility of its outer hair cells (OHCs). Anatomically, impressive boutons of the olivo-cochlear bundle (OCB) terminate on the OHCs. It is believed that, by modifying OHC electro-mechanical properties, the OCB may regulate feedback gain and control the sensitivity and frequency selectivity of the cochlea. Tone-evoked basilar membrane (BM) displacements were measured in-vivo with a laser diode interferometer in the basal turn of the guinea pig cochlea. The OCB was electrically stimulated via electrodes placed along the floor of the fourth ventricle. For tones close to the characteristic frequency (CF), OCB stimulation linearized the highly compressive displacement-level functions and displaced the steep, low-level region toward higher intensities along the intensity axis by < 27 dB SPL. This shift resulted in a desensitization of the tip of the BM displacement tuning curve, but there was no associated broadening of the tuning curve, changes in the phase response or BM motion at frequencies in the low-frequency tail. These effects were abolished by perfusing the scala tympani with 1mM strychnine. For the first time, we show that the OCB can directly influence cochlear mechanics and postulate that the OCB-OHC complex provides a template for higher auditory centres to orchestrate frequency focusing within the cochlea, by way of a highly accurate yet mobile "acoustic fovea" adjusting instantaneously through OCB-OHC interaction. If so, it would be prudent for surgeons to try and preserve the OCB efferents whenever possible.

Abstract Otology 2000 B11-2

Saumil N. Merchant MD, Michael E. Ravicz M.S., John J. Rosowski Ph.D.

Department of Otolaryngology and Eaton Peabody Lab. of Aud.Physiol. Mass. Eye and Ear Infirmary USA-Boston MA

We have utilized quantitative physics-based models and acoustic measurements in cadaveric temporal bone preparations to improve our understanding of structure-function relationships in the middle ear. This paper will discuss recent information about middle-ear mechanics and some acoustical principles that can be used by otosurgeons, along with illustrative clinical cases. Four major points will be discussed: (1) The air-bone gap after middle-ear surgery can be predicted by the interaction of ossicular coupling, acoustic coupling and stapes-cochlear input impedance. (2) In the normal ear, middle-ear sound pressure gain is frequency dependent and only 20-25 dB at its maximum (which is less than generally believed). Therefore, the air-bone gap can be closed to within 20 dB in certain circumstances even with less-than-optimal tympanic membrane/ossicle configurations (type II and type III) or in ears without ossicles (type IV). (3) In the normal ear and after most tympanoplasties, the difference in phase between the sound pressures at the oval and round windows is much less important than the difference in magnitude. Hearing can be improved in certain cases by simply increasing the acoustic shielding of the round window in order to decrease the magnitude of the round-window sound pressure without regard to phase (e.g., type IV, type Va, type Vb). (4) The mechanics of ossicular reconstruction depend on a number of factors including stiffness, mass, positioning, tension, coupling as well as middle-ear aeration. The effects of these will be discussed.

Abstract Otology 2000 B11-3

Alex M. Huber MD, Christoph Schwab MD, Mattia Ferrazzini Dipl.Ing.ETH, Thomas Linder MD, Ugo Fisch MD

ENT Department University Hospital CH-Zürich

The Laser Doppler Interferometer (LDI) is a device which allows contact-free analysis of vibration with a high degree of accuracy. Its potential for measuring the mobility of the tympanic membrane in response to defined acoustic signals has been documented. Although LDI has been used in the research of middle ear mechanics, it was not yet introduced in clinical practice as an adjunctive test for otological work-up. The aims of this study were to evaluate the LDI as a diagnostic tool in the clinical sphere and to investigate whether 1. the measurements are practical 2. sensitive parameters can be identified to distinguish different pathologies 3. additional information over the standard audiometric tests can be obtained. A measurement system was developed based on a scanning He-Ne laser Doppler Interferometer (Polytec GmbH). The study included more than 100 subjects that were divided into 3 groups: (a) normal subjects, (b) patients with sensorineural and (c) conductive hearing loss. All the patients suffering from conductive hearing loss underwent ossiculoplasty, which allowed confirmation of the final diagnosis, and patients were assigned accordingly to subgroups. The modified LDI system allowed complete bilateral tympanic membrane evaluation of a subject within 30 minutes. No significant difference between normal subjects and patients having sensorineural hearing loss were found. However, it was possible to distinguish between normal subjects and patients with conductive hearing loss. Furthermore, it had the ability to differentiate between various middle ear pathologies. These groups differed significantly in terms of manubrium vibration amplitude and resonance frequency as well as tympanic membrane amplitude and modes. Our modified LDI is applicable in clinical otological practice and serves as a valuable addition to the routine audiological investigations for preoperative evaluation of the mobility and integrity of the ossicular chain. The future goal of diagnostic LDI measurements is to identify partial ossicular fixation as a possible cause for poor results after ossiculoplasty and thereby assist in improving hearing results after otosurgery.

Abstract Otology 2000 B11-4

Sébastien Schmerber MD, J.P. Lavieille MD, PhD, M. Feige , Robert Charachon MD

Service ORL CHU de Grenoble F-Grenoble Cedex 09

The Vibrant Soundbridge is a partially implanted hearing device intended for patients with symetrical, bilateral moderate, to moderate-severe sensorineural hearing loss. The surgical implantation of the Vibrant Soundbridge is familiar to otologic surgeons performing cochlear implants. Each patient was evaluated against the selection criteria to determine suitability for implantation. 10 patients were implanted, 8 with Vibrant P Soundbridge and 2 with Vibrant Soundbridge HF. There was no acute per-operative or post-operative complication. In one patient, a delayed uncomplete Bell's palsy appeared 2 weeks after surgery, and recovered a normal facial function within 2 months.. The first fitting test session was conducted at 8 weeks post-surgery and the review fitting test session 4 weeks later. The audiologic tests were conducted by unaided air-conduction thresholds under headphones, in free field, and bone-conduction thresholds, and by Soundbridge aided air-conduction thresholds in free field. The patient's subjective comments were noted. The maximum and average functionnal gain at each frequency was calculated. Audiologic results and subjective impressions are discussed. In conclusion, The Vibrant Soundbridge seems to provide most patients with adequate functionnal gain in the speech frequencies.

Abstract Otology 2000 B11-5

Thomas Wilhelm MD (1), Rüdiger Junker MD (11), Dirk Hardick Dr.med. (1), Manfred Gross Prof.Dr. (2), Arne Ernst MD (1)

(1) Dept. Otolaryngology Unfallkrankenhaus Berlin D-Berlin
(11) Dept. Otolaryngology Unfallkrankenhaus Berlin D-Berlin

Since 1996, implantable hearing aids are commercially available. More than 200 patients were implanted world-wide with an electromagnetic device, attached directly to the ossicular chain (Symphonix Soundbridge). In October 1998 a newly developed high frequency-audioprocessor (Vibrant HF) permitted the rehabilitation of high and mid-frequency hearing losses. In a pilot study we have implanted five patients (3 male, 2 female) with an average age of 60 years and long-term SNHL. Conventional hearing aids did not more yield a sufficient gain. The surgical procedure was similar to a cochlear implant operation. Postoperative PTA showed stable inner ear function. After fitting of the audioprocessor, all patient reported improved benefit, especially for hearing-in-noise. Audiological and psychometric data (A-PHAB US) will be presented. We conclude that this audioprocessor might be advisable to patients with high-frequency SNHL.

Abstract Otology 2000 B11-6

Christophe Vincent MD, PhD (1), Henri Urgell MD (1), Christine Laroche MD (1), Jean-Noël Hanson MD (1), Armand Angot MD (1), François-Michel Vaneecloo MD (2)

(1) Service d'Otologie et d'Oto-Neurol. CHRU de Lille Hôpital Salengro F-Lille Cedex
(2) Service d'Oto-Rhino-Laryngologie Hôpital Claude Huriez F-Lille Cedex

By now, we have implanted 7 patients with the Vibrant Soundbridge Device. In order to compare between this new system and conventional hearing aid, post-op audiological tests have been done on the implanted ear. These tests, performed in silence and noise, comprise vowel and consonant recognition test as well as word and sentence recognition tests. The results of these tests were compared to the possibilities of audiological correction with the Vibrant Soundbridge device and the conventional hearing aid. Preliminary results indicate that most of our Vibrant Soundbridge implanted patients are able to perform better with the Symphonix device, especially in noise.

Abstract Otology 2000 B11-7

Bernard Fraysse MD (1), Olivier Sterkers MD (2), Thierry Houliat MD (1), Oliver Deguine MD (1), Corinne Berges MD (1)

(1) Service ORL CHU Purpan F-Toulouse Cedex
(2) Service d'ORL, Hôpital Beaujon Faculté Xavier Bichat Université Paris 7 F-Clichy

The authors report their experience in patients suffering from severe sensorineural hearing loss. - First, with a group of 20 patients having less than 30 % residual hearing at 70 dB with hearing aid. This group has cochlear implant. The results on open set word recognition and sentences will be presented. Secondly, with a group of 10 patients having discrimination between 50 % and 100 % at 65 dB with hearing aid. This group has received middle ear Symphonix® implant. The authors discuss the indications of both technique.