A soft-surgery approach to minimize hearing damage caused by the insertion of a cochlear implant electrode: a guinea pig animal model.

OBJECTIVE: A "soft surgery" technique was applied, using various types of specifically designed dummy electrodes, to mimic cochlear implantation in a guinea pig model, and the degree of hearing-preservation/cochlear damage was assessed. METHODS: Tricolor guinea pigs were divided into 3 groups: group A were implanted with electrodes without any contacts or wires (soft electrode), group B were implanted with electrodes having a metallic wire inside (stiff electrode), and group C underwent a cochleostomy procedure without implantation. Compound action potentials, in the range of 4 to 32 kHz, were used to assess electrophysiologic changes in the hearing function presurgery and postsurgery. Data were collected before surgery, at times t = 0 (immediately after surgery) and at 3, 7, 14, and 30 days. RESULTS: At low frequencies (4-8 kHz), an immediate elevation of hearing threshold was observed in all 3 groups. Higher threshold shifts were more consistent for group B implanted with a stiff electrode, in comparison to the other 2 groups. Animals from group C presented a recovery from hearing loss, starting 3 days after surgery. At high frequencies (16-32 kHz), the elevation of hearing threshold was higher, as compared with the data from the low frequencies. Group C animals presented oscillatory threshold shifts twice, and the recovery to normal threshold values occurred approximately at t = 14 days. CONCLUSION: The data suggest that cochleostomy is minimally harmful to the inner ear and that a soft electrode might better preserve the inner ear integrity than a rigid electrode.

A new oral otoprotective agent. Part 1: Electrophysiology data from protection against noise-induced hearing loss.

BACKGROUND: Data from animal studies show that antioxidants can compensate against noise-induced stress and sensory hair cell death. The aim of this study was to evaluate the otoprotection efficacy of various versions of orally administered Acuval 400 against noise damage in a rat animal model. MATERIAL/METHODS: Fifty-five Sprague Dawley rats were divided into 4 groups: A) noise-exposed animals; B) animals exposed to noise and treated with the Acuval; C) animals exposed to noise and treated with a combination of Coenzyme Q10 and Acuval; D) animals treated only with Acuval and Coenzyme Q10 and with no exposure to noise. All solutions were administered orally 5 times: 24 and 2 hrs prior to noise exposure, and then daily for 3 days. The auditory function was assessed by measuring auditory brainstem responses (ABR) in the range from 2 to 32 kHz at times =1, 7, 14 and 21 days after noise exposure. RESULTS: At low frequencies (click and 4 kHz) animals from both A and B groups showed significant threshold shifts in the majority of the tested frequencies and tested times. For the same frequencies, animals from group C presented threshold levels similar to those from group D. At frequencies ≥ 8 kHz the protective performance of the 2 Acuval groups is more clearly distinguished from the noise group A. At 32 kHz the 2 Acuval groups perform equally well in terms of otoprotection. Animals in Group D did not show any significant differences in the hearing threshold during the experiment. CONCLUSIONS: The data of this study suggest that a solution containing Coenzyme Q10 and Acuval 400, administered orally, protects from noise-induced hearing loss.

Speech recognition with BAHA simulator in subjects with acquired unilateral sensorineural hearing loss.

CONCLUSION: We question the justification for the cost of a surgically implanted device for the restoration of limited circumstances of audible communication, although we understand that the decision is taken depending on the social relevance of communication or personal criteria. OBJECTIVES: The purpose of this study was to evaluate the effect of the BAHA simulator (BAHAS) system in subjects with acquired unilateral sensorineural hearing loss. In particular we tested the changes of speech reception threshold (SRT) in relation to different speech source positions, with a background of diffuse noise. METHODS: The primary message consisting of lists of Italian sentences was delivered from a loudspeaker placed at horizontal azimuths of 0°, 90°, 180° and 270°; the interference consisted of uncorrelated speech-shaped noise simultaneously delivered by four loudspeakers at a fixed intensity. The speech recognition tests were administered to 11 patients with BAHAS either on or off; hence each patient underwent 8 acoustic conditions (4 primary message directions × 2 BAHAS conditions). The SRT (50% correct responses) was measured by a simple 2 dB step adaptive procedure. Ten normal-hearing subjects served as the control group. RESULTS: Our data demonstrated that even for the acoustic condition where BAHAS should be more useful (i.e. lateral speech toward the impaired side), it was definitely ineffective in the study conditions.

Threshold estimation in adult normal- and impaired-hearing subjects using auditory steady-state responses.

BACKGROUND: The aim of the study was to compare the estimation of hearing threshold values by behavioral and electrophysiological (ASSR) methods in subjects with normal hearing and those with sensorineural hearing impairment. MATERIAL/METHODS: Thirty-two subjects (17 male and 15 female) were tested, with a total of 61 ears. Of these, 11 (22 ears) presented normal hearing threshold values (0-19 dBHL) and 21 (39 ears) sensorineural deficits. RESULTS: The data showed that for the normal-hearing subjects the mean +/-SD ASSR threshold was approximately 20+/-11 dB for frequencies of 0.25-1.0 kHz. For higher frequencies the ASSR threshold increased to 40+/-12.5 dB at 8.0 kHz. Regression analysis confirmed that the difference between the ASSR-estimated and behavioral threshold values decreased significantly with the amount of hearing loss. The data showed that for a 10-dB increment of the behavioral threshold, the ASSR threshold increased by 7 dB. The difference of about 27 dB between the two methods observed in normal subjects tends to cancel in hearing loss greater than 95-100 dBHL. CONCLUSIONS: The results of these analyses indicate that the threshold estimates are rather discordant with the behavioral thresholds. in particular it seems that the correction factor applied here does not rely on factors adequately modeled (in terms of instrumentation) to compensate for the effects of hearing loss on ASSR thresholds. The threshold estimation is adequately modeled for high levels of hearing loss, particularly for patients requiring a cochlear implant.

Coupling the Vibrant Soundbridge to cochlea round window: auditory results in patients with mixed hearing loss.

OBJECTIVE: To assess the functional results of the Vibrant Soundbridge (VBS) placed on the round window (RW) in patients with mixed hearing loss. STUDY DESIGN: Retrospective evaluation of functional hearing, with measurements performed 7 to 9 months postoperatively. SETTINGS: Two tertiary referral hospital centers. SUBJECTS: Twelve individuals with mixed severe hearing loss associated with chronic suppurative otitis media and otosclerosis. INTERVENTION: Surgical placement of the VBS mechanical effector in close contact with the RW membrane to directly drive the inner ear fluids. MAIN OUTCOME MEASUREMENT: Functional hearing gain as analyzed via pure-tone audiometry and speech audiometry with VBS off and on in quiet and in noise. RESULTS: We observed a mean gain of 37.5 dB (0.5-4 kHz) with wide individual differences. The overall gain is mainly due to the air-bone gap recovery, whereas a further 12-dB mean improvement of air-conducted threshold is evident at 2 kHz. The speech reception threshold in quiet shows a mean gain of 24 dB, whereas in noise, it requires a signal-to-noise ratio 7 to 13 dB greater than normal-hearing controls. All patients are daily users of their VBS device. CONCLUSION: A middle ear implant capable of directly driving the cochlear fluids seems to be a promising alternative for individuals with a severe to profound mixed hearing loss. However, variability in hearing recovery is great, likely reflecting variability in responsiveness of the cochlea associated with chronic pathologic findings and, possibly, variability in how the VBS effector interfaces with the RW. Modifying the shape of the VBS effector can improve the mechanical coupling to the RW to better exploit the device's amplification power.