Experimental and clinical aspects of carbon as a middle ear prosthesis

The biocompatibility of vitreous carbon and carbon fibre reinforced carbon (CFRC) as middle ear implants was investigated. In separate animal model systems, vitreous carbon was implanted in the middle ear of 20 DA rats for up to 6 months, whilst 3 varieties of CFRC (basic or crude, ultrasonically cleaned, glazed) were implanted in 98 guinea-pig middle ears for up to 4 months. Tissue reactions to implantation were assessed by means of stereoscopic and standard light microscopy, and scanning electron microscopy with chemical analysis facilities (EDAX, WDAX). Vitreous carbon and glazed CFRC were considered suitable for human implantation and a trial of the latter was started in 23 patients (14 partial, 9 total ossicular implants). At 9 months, only 52% of the implants were still in situ; 40% had been extruded and 8% had elicited inflammatory responses which would undoubtedly result in extrusion. Carbon particle dissemination with carbon fibre destruction and exposure as a result of peroperative prosthesis drilling were considered the likely causes for the failure of this implant.     

Central auditory development in children with bilateral cochlear implants

OBJECTIVE: To examine the time course of maturation of P1 latencies in infant sequential and simultaneous bilateral cochlear implant recipients. DESIGN: Retrospective case series. SETTING: Pediatric collaborative cochlear implant program. PATIENTS: Four children who received bilateral cochlear implants prior to age 2 years. INTERVENTION: Cortical auditory evoked potential was completed to determine the latency of the P1 response in 4 children with bilateral cochlear implants. MAIN OUTCOME MEASURES: Longitudinal development of the latency of the P1 cortical auditory evoked potential in children who received bilateral cochlear implants prior to age 2 years. RESULTS: In 2 patients who received sequential bilateral implants, P1 latencies recorded from the first implanted ear were within normal limits after 3 to 6 months of implant use. By comparison, P1 latencies from the second implanted ear reached normal limits as early as 1 month after implant use. In 2 patients who received simultaneous bilateral implants, P1 latencies from both ears were also within normal limits in a very short time frame (ie, by 1 month poststimulation). CONCLUSIONS: Our data suggest a high degree of plasticity of the central auditory pathways after early bilateral implantation. We find that P1 latencies provide a clinically useful biomarker of central auditory system development in children after cochlear implantation.     

Abnormal timing delays in auditory brainstem responses evoked by bilateral cochlear implant use in children.

HYPOTHESIS: A period of unilateral implant use before bilateral implantation affects timing of brainstem processes measured by the electrically evoked auditory brainstem response (EABR). BACKGROUND: EABR latencies decrease with unilateral implant use potentially disrupting binaural timing cues important in auditory brainstem processing of bilateral input. METHODS: EABRs were evoked by electrical pulses from the left, right, and both implants simultaneously in 3 groups of children. All were initially implanted at ages younger than 3 years and had the following: 1) a long delay (>2 yr [n = 16]), 2) a short delay (<1 yr [n = 15]), or 3) no delay (n = 15) between left and right ear implantation. Responses were recorded on the first day of bilateral implant use and 3 and 9 months thereafter. RESULTS: Relative to responses evoked in the experienced ear, the naive ear showed prolonged latency in both the EABR peaks and the binaural difference response. After 3 and 9 months of bilateral implant use, the relative prolongation decreased in the long and short delay groups, but significant differences persisted in the former. No clear differences in latencies evoked by the left versus right implant were found at any time point in children receiving bilateral implants simultaneously. CONCLUSION: Results suggest potential disruptions to binaural brainstem processing based on timing cues in children receiving a second cochlear implant after more than 2 years of unilateral implant use that persist through at least the first 9 months of bilateral implant use.     

Cortical auditory evoked responses from an implanted ear after 50 years of profound unilateral deafness

A male with unilateral deafness in the right ear since 8 years of age developed a sudden hearing loss in the left ear at age 63. A hearing aid was fitted in the left ear with limited benefit. The right ear received a cochlear implant (CI) 20 months later. Cortical auditory evoked potentials (CAEPs) and speech recognition scores (SRS) were measured in free-field three, six and nine months after implantation with the hearing aid alone, CI alone and bimodal condition (hearing aid and CI together). Three months after implantation the cortical responses for the two ears were similar, despite more than 50 years of unilateral auditory deprivation. CAEPs measured over time show evidence of binaural interaction and improvements in SRS.     

Cortical activity evoked by a multichannel cochlear prosthesis

We have recorded electric potentials and neuromagnetic fields evoked by electric stimulation of the auditory nerve in a totally deaf patient with an implanted multichannel prosthesis. The evoked electric responses were a vertex-negative deflection at about 70 ms after stimulus onset and a vertex-positive deflection at about 180 ms. Evoked magnetic responses coinciding with the vertex potential were found in the right hemisphere, ipsilateral to the stimulated ear. The equivalent source of these responses corresponds to activation of the right auditory cortex. In the left hemisphere, the magnetic responses were considerably smaller and less reliable. These results suggest an abnormality of the central auditory pathways in this patient. In the future, neuromagnetic recordings might be used preoperatively to forecast the effectiveness of the possible implantation.     

Cortical auditory evoked responses from an implanted ear after 50 years of profound unilateral deafness

Abstract

A male with unilateral deafness in the right ear since 8 years of age developed a sudden hearing loss in the left ear at age 63. A hearing aid was fitted in the left ear with limited benefit. The right ear received a cochlear implant (CI) 20 months later. Cortical auditory evoked potentials (CAEPs) and speech recognition scores (SRS) were measured in free-field three, six and nine months after implantation with the hearing aid alone, CI alone and bimodal condition (hearing aid and CI together). Three months after implantation the cortical responses for the two ears were similar, despite more than 50 years of unilateral auditory deprivation. CAEPs measured over time show evidence of binaural interaction and improvements in SRS. Copyright © 2007 John Wiley & Sons, Ltd.     

Effect of human fibrin adhesive on the ear. An electrophysiological study of auditory function in the guinea pig correlated to light and electron microscopy of middle ear mucosa and inner ear structures

The effect of human fibrin adhesive applied to the middle ear has been studied in guinea pig. Auditory function was measured using acoustically evoked brainstem responses. Middle and inner ear structures were studied with light, transmission and scanning electron microscopy. A transitory conductive hearing loss was observed, but after 8 weeks the auditory function appeared normal. Microscopy of the middle and inner ear failed to show any tissue damage.     

Changes in auditory function associated with 2-cyano-butyl-acrylate adhesive implanted in the middle ear of experimental animals

The effects on auditory function caused by the implantation of 2-cyano-butyl-acrylate adhesive in the middle ear was investigated in experimental animals. Auditory brain-stem responses to click stimuli were used to measure hearing thresholds prior to and following implantation of 2-cyano-butyl-acrylate adhesive in the middle ear of guinea pigs. A permanent and deep threshold shift observed at 2 months in 62% of the examined animals, suggested that this tissue adhesive is an ototoxic middle ear implant material and should not be considered in reconstructive middle ear surgery. The functional data correlate well with some of the previous morphological observations.     

Artificial activation and degeneration of the cochlear nerve in guinea pigs

Degeneration of the cochlear nerve was produced in guinea pigs after treatment with high doses of ototoxic antibiotics completely destroying the cochlear receptor. An effective electric stimulation of the inner ear inducing evoked potentials at the auditory cortex was applied over a period of 3.5 months in half of the animals, while the other half was kept for control. The artificial stimulation had no effect on the sensitivity of the inner ear to electric stimulation and did not modify the extent of degeneration of the cochlear nerve.     

Bilateral electrical stimulation of a congenitally-deaf ear and of an acquired-deaf ear

Two identical multichannel intracochlear prostheses were implanted in the same patient. The first prosthesis, implanted in the congenitally-deaf right ear, elicited clear sound perception but no speech recognition. After 2 years, a second prosthesis, implanted in the acquired-deaf left ear, enabled the patient to understand speech without lip-reading. Brainstem and middle-latency evoked potentials were similar with electrical stimulation of both ears and resembled those evoked by acoustic stimuli in subjects with normal hearing. Cortical electric and magnetic responses differed for right- and left-sided electrical stimulation suggesting that stimulation of the congenitally-deaf ear elicited an abnormal activation of the auditory cortex. These results suggest that only cortical responses were affected by the different histories of deafness of the ears.     

Auditory brainstem activity in children with 9-30 months of bilateral cochlear implant use

Bilateral cochlear implants aim to restore binaural processing along the auditory pathways in children with bilateral deafness. We assessed auditory brainstem activity evoked by single biphasic pulses delivered by an apical or basal electrode from the left, right and both cochlear implants in 13 children. Repeated measures were made over the first 9-30 months of bilateral implant use. In children with short or long periods of unilateral implant use prior to the second implantation, Wave eV of the auditory brainstem response was initially prolonged when evoked by the na?ve versus experienced side. These differences tended to resolve in children first implanted <3 years of age but not in children implanted at older ages with long delays between implants. Latency differences were projected to persist for longer periods in children with long delays between implants compared with children with short delays. No differences in right versus left evoked eV latency were found in 2 children receiving bilateral implants simultaneously and their response latencies decreased over time. Binaural interaction responses showed effects of stimulating electrode position (responses were more detectable when evoked by an apical than basal pair of implant electrodes), and duration of delay between implants (measured by latency delays). The trends shown here suggest a negative impact of unilateral implant use on bilateral auditory brainstem plasticity.     

Histopathology of biocompatible hydroxylapatite-polyethylene composite in ossiculoplasty

The biocompatibility of hydroxylapatite-polyethylene composite implants (HAPEX, Smith and Nephew) was investigated in this study. Eleven middle ear prostheses, removed during revision surgery, have been examined by light microscopy, transmission electron microscopy and scanning electron microscopy. The results show that the middle ear prostheses become overgrown by fibrous tissue inside a thin epithelial layer. In some cases the prosthesis is covered by fibrous tissue without an outer layer of epithelial cells. No arguments have been found for the accumulation of macrophages and foreign body giant cells associated with a foreign body reaction to the material. Therefore, hydroxylapatite-polyethylene composite implants (HAPEX, Smith and Nephew) would seem to be very suitable for reconstructive middle ear surgery.     

Using Evoked Potentials to Match Interaural Electrode Pairs with Bilateral Cochlear Implants

Bilateral cochlear implantation seeks to restore the advantages of binaural hearing to the profoundly deaf by providing binaural cues normally important for accurate sound localization and speech reception in noise. Psychophysical observations suggest that a key issue for the implementation of a successful binaural prosthesis is the ability to match the cochlear positions of stimulation channels in each ear. We used a cat model of bilateral cochlear implants with eight-electrode arrays implanted in each cochlea to develop and test a noninvasive method based on evoked potentials for matching interaural electrodes. The arrays allowed the cochlear location of stimulation to be independently varied in each ear. The binaural interaction component (BIC) of the electrically evoked auditory brainstem response (EABR) was used as an assay of binaural processing. BIC amplitude peaked for interaural electrode pairs at the same relative cochlear position and dropped with increasing cochlear separation in either direction. To test the hypothesis that BIC amplitude peaks when electrodes from the two sides activate maximally overlapping neural populations, we measured multiunit neural activity along the tonotopic gradient of the inferior colliculus (IC) with 16-channel recording probes and determined the spatial pattern of IC activation for each stimulating electrode. We found that the interaural electrode pairings that produced the best aligned IC activation patterns were also those that yielded maximum BIC amplitude. These results suggest that EABR measurements may provide a method for assigning frequency–channel mappings in bilateral implant recipients, such as pediatric patients, for which psychophysical measures of pitch ranking or binaural fusion are unavailable.     

术中经蜗窗龛电刺激记录听性脑干反应方法的建立及初步应用

目的 建立人工耳蜗手术中经蜗窗龛电刺激记录听性脑干反应的方法.方法 应用自制铂铱合金球形电极作为刺激电极,改装的人工耳蜗植入体连接体外言语处理器作为电刺激仪及Bio-logic Navigator Pro诱发电位仪,对17例不同病因(包括听神经病2例、耳蜗骨化1例、内耳畸形5例、脑白质异常1例,原因不明8例),不同年龄的人工耳蜗植入患者在手术中进行测试.植入人工耳蜗装置前,将刺激电极放置在蜗窗龛内,用电荷平衡双相脉冲电流经蜗窗龛进行电刺激,记录电诱发听性脑干反应.结果 17例患者均记录到明确的电诱发听性脑干反应波形,Ⅲ波和Ⅴ波的潜伏期分别为(2.12±0.18)ms 和(4.18±0.19)ms,阈值为(220.00±16.04)CL.其中2例听神经病、5例内耳畸形、1例耳蜗骨化、1例脑白质异常患者均记录到分化良好的波形.结论 电诱发听性脑干反应是一项能够较准确地反映听觉传导通路功能完整性的客观神经电生理测试方法,对于判断人工耳蜗植入后患者能否获得听性反应,具有重要的应用价值.本研究方法的安全性符合要求,听性反应的引出率高,值得推广应用.     

The effect of hydrogen peroxide applied to the middle ear on inner ear function

OBJECTIVES/HYPOTHESIS: The objective was to assess the effect of hydrogen peroxide applied to the middle ear on cochlear and vestibular function. STUDY DESIGN: Prospective animal study. METHODS: Sand rats underwent a right-side total labyrinthectomy, and a polyethylene tube was inserted into the left-side middle ear. Following baseline recordings of vestibular evoked potentials in response to linear acceleration stimuli and auditory brainstem response, each experimental animal received five daily applications of hydrogen peroxide into the left-side middle ear. Two control groups received saline and gentamicin, respectively. Subsequently, recordings were repeated and compared with baseline measurements. RESULTS: Saline administration affected neither vestibular evoked potentials nor auditory brainstem response. In contrast, both responses could not be recorded following gentamicin application. After hydrogen peroxide administration, auditory brainstem response could not be recorded in 25% (3 of 12) of the animals, whereas in the remaining nine animals the average auditory brainstem response threshold was significantly elevated by 55 dB (P =.000002). Linear vestibular evoked potentials could not be recorded in 42% (5 of 12) of the animals. CONCLUSION: It appears that topical hydrogen peroxide adversely affects both cochlear and vestibular function of the sand rat. The study demonstrated the effect of a reactive oxygen species on inner ear function and may be useful in the study of mechanisms responsible for this damage and its protection. Clinically, although an animal model was used in the present study, caution should be exercised when large amounts of hydrogen peroxide are applied to a dry, perforated ear.     

Auditory evoked potentials as measures of plasticity in humans.

There is increasing evidence from animal studies for plasticity of auditory function. This has prompted research to determine whether such plastic changes occur in adults and children with hearing disorders. Behavioural measures such as speech perception scores do show improvements after hearing aid fitting and cochlear implantation. Several studies have also shown changes in cortical auditory evoked potentials after cochlear implantation and after auditory training. These studies indicate that improvements in speech perception ability are associated with changes in the central auditory system, particularly at the cortical level.     

交叉听力对豚鼠听性脑干反应测试的影响

报告对８只听觉正常的及鼠，观察交叉听力对其耳蜗动作电位和听怀脑干反应测试结果的影响。先手术造成其左耳全聋，然后用四种方法分别记录ＡＢＲ反应阈和Ⅰ波潜伏期。结果发现，术耳虽已全聋，但该侧给声强度达１０ｄＢＨＬ以上时仍可记录到ＡＢＲ，而ＡＰ未能引出，代之出现的却是清晰的ＡＢＲ波形。     

Characteristics of electrically evoked potentials in patients with auditory neuropathy/auditory dys-synchrony

The primary goal of this study was to compare the characteristics of the post-implant evoked potentials with preimplant evoked potentials in patients with auditory neuropathy (AN) or dys-synchrony. AN is typically characterized by sensorineural hearing loss, reduced speech perception, abnormal temporal processing, and unusual patterns of results with various objective audiological tests. In some cases, these patients may be appropriate candidates for a cochlear implant. In this article, we highlight evoked potential findings in two children diagnosed with AN who were provided with multichannel cochlear implants. Preoperative, interoperative and postoperative evoked potential measures show that the restoration of neural synchrony may occur at multiple levels of the auditory pathways in patients with AN when appropriate diagnostic tests, cochlear implantation and rehabilitation are provided.