ABR recordings in newborns using an ear canal electrode

The objective of this study was to improve the sensitivity of ABR recordings in newborns via a procedure that utilizes the ear canal as a recording site. Conventional recordings were compared to ear canal recordings of the ABR in 45 normally-hearing newborns who passed their newborn hearing screening. Responses were obtained at stimulus levels of 80, 60, 40, and 20 dBnHL using forehead (+) to ear canal (-), versus forehead (+) to mastoid (-) electrode configurations. ABR parameters evaluated included measurement of component amplitudes of wave I and V, absolute latencies of I and V, the I-V interwave interval, and amplitude ratio. At stimulus levels of 80, 60, and 40 dBnHL, wave I amplitude was significantly larger using the ear canal configuration. This investigation shows that the amplitude of wave I is significantly larger and easier to identify when the ear canal is used as one of the recording sites in comparison to more conventional scalp (mastoid) recordings.     

ABR recordings in newborns using an ear canal electrode

The objective of this study was to improve the sensitivity of ABR recordings in newborns via a procedure that utilizes the ear canal as a recording site. Conventional recordings were compared to ear canal recordings of the ABR in 45 normally-hearing newborns who passed their newborn hearing screening. Responses were obtained at stimulus levels of 80, 60, 40, and 20 dBnHL using forehead (+) to ear canal (?), versus forehead (+) to mastoid (?) electrode configurations. ABR parameters evaluated included measurement of component amplitudes of wave I and V, absolute latencies of I and V, the I-V interwave interval, and amplitude ratio. At stimulus levels of 80, 60, and 40 dBnHL, wave I amplitude was significantly larger using the ear canal configuration. This investigation shows that the amplitude of wave I is significantly larger and easier to identify when the ear canal is used as one of the recording sites in comparison to more conventional scalp (mastoid) recordings.     

Vestibular and cochlear ototoxicity of topical antiseptics assessed by evoked potentials

OBJECTIVES/HYPOTHESIS: To evaluate and compare the effect of chlorhexidine gluconate, povidoneiodine, and alcohol-three antiseptics used before ear surgery-on the function of the vestibular and cochlear parts of the sand rat's inner ear. The assessment of damage is based on the recording of vestibular evoked potentials (VsEPs) and auditory brainstem response (ABR). STUDY DESIGN: Prospective controlled animal study. METHODS: Fat sand rats were randomly assigned to five different groups, each receiving topical application of a different agent: saline (control), gentamicin (ototoxic control), chlorhexidine, povidone-iodine, and alcohol. Right-side total labyrinthectomy was performed, and a polyethylene tube was inserted into the left (contralateral) middle ear. After baseline recordings were taken of VsEPs and ABR, each animal received five consecutive daily applications of the specific agent into the left middle ear. Three days after the fifth application, evoked potential recordings (VsEPs and ABRs) were repeated and compared with baseline measurements. RESULTS: Administration of saline affected neither VsEPs nor ABR. In contrast, as expected, neither of these responses could be recorded after gentamicin application. After application of chlorhexidine all waves disappeared in all sand rats. Alcohol caused the waves to disappear in some of the animals only. Povidone-iodine did not affect VsEP recordings and had only a small effect on ABR. CONCLUSIONS: Chlorhexidine and alcohol had a clear toxic effect on the vestibular and cochlear function of the inner ear of the sand rat, whereas povidone-iodine did not. Thus, taking into consideration that this is an animal study, it appears that povidone-iodine might be preferable to the other agents tested in disinfecting ears with a perforated tympanic membrane.     

Inner ear effects of exogenous hyaluronan in the middle ear of the rat

1.9% hyaluronan (HA) (mol. wt. 3 x 10(6] was applied repeatedly into the middle ear of rats through a myringotomy. The function and structure of the cochlea was analysed by auditory brainstem recordings (ABR) at 2-31.5 kHz and by light microscopy. The myringotomy significantly impaired the ABR thresholds at frequencies below 8 kHz. Five days after the last application of HA, the ABR thresholds showed minor improvements at 6-8 kHz but were impaired at 12 and 20 kHz, as compared with control levels. One month after the last administration of HA, ABR thresholds were significantly improved as compared with the initial level at 2-6 kHz but normal at all other frequencies. After 3 months, all ABR thresholds had returned to the pre-treatment (normal) level. Five days after the last application of HA, the latencies for almost all frequencies were significantly prolonged for waves II and IV at the ABR threshold. After 3 months all latencies had returned to their pre-treatment (normal) values. Highly concentrated hyaluronan (1.9%) is free from ototoxicity but does have transient functional effects on the inner ear.     

Early changes of auditory brain stem evoked response after radiotherapy for nasopharyngeal carcinoma--a prospective study.

A prospective study of the effect of radiotherapy for nasopharyngeal carcinoma on hearing was carried out on 49 patients who had pure tone, impedance audiometry and auditory brain stem evoked response (ABR) recordings before, immediately, three, six and 12 months after radiotherapy. Fourteen patients complained of intermittent tinnitus after radiotherapy. We found that 11 initially normal ears of nine patients developed a middle ear effusion, three to six months after radiotherapy. There was mixed sensorineural and conductive hearing impairment after radiotherapy. Persistent impairment of ABR was detected immediately after completion of radiotherapy. The waves I-III and I-V interpeak latency intervals were significantly prolonged one year after radiotherapy. The study shows that radiotherapy for nasopharyngeal carcinoma impairs hearing by acting on the middle ear, the cochlea and the brain stem auditory pathway.     

Auditory brainstem response in neonates during the first 48 hours after birth

Auditory brainstem response (ABR) has been recorded in 20 neonates at three different time intervals during the first 48 hours after birth. The first recording was performed about 15 min after delivery, when the babies were in their first period of postnatal reactivity. During this period, we were unable to obtain reliable ABR data. During the second and third ABR test performed 2 and 48 hours after birth the babies revealed gradually better responses. Data from these recordings suggest no significant change in middle ear function during the time interval between 2 and 48 hours after birth. Observations of amplitude ratio wave V/wave I are presented. Finally, reservations regarding the interpretation of the results are discussed.     

ABR in multiple sclerosis. Ipsi- versus contralateral derivation

Brainstem auditory evoked potentials (ABR) were recorded simultaneously between vertex and ear lobe, ipsi- and contralateral to the stimulated ear in 53 subjects with confirmed (19) or undefined (34) multiple sclerosis. Results were compared with those obtained in a control group of 20 normal-hearing adults. The control group showed that significant latency differences exist between ipsilateral and contralateral recordings. Definition of abnormality was based on absence and separation of waves. The results showed that the use of contralateral derivation in ABR recordings increased detectability from 74% to 89% in patients with confirmed MS and from 9% to 21% in cases of undefined MS. It is proposed that parameters of contralateral ABRs be included among the criteria used for the otoneurological diagnosis of patients with CNS lesions.     

Comparison of ABR amplitudes with TIPtrode and mastoid electrodes

ABR evaluations were completed for 36 adults (18 males, 18 females) having normal hearing sensitivity and for 91 adult patients having various degrees of sensorineural hearing loss. Amplitudes of waves I and V were compared for ear canal (TIPtrode) electrode and mastoid electrode recordings. Interpeak intervals (I-III, III-V, and I-V) were determined and upper 95% confidence limits defined for normative data. In general, amplitude of wave I was larger when TIPtrodes were used. Wave V amplitude was nearly identical for the two electrodes. Wave I was identified more frequently for TIPtrode than for mastoid recordings of ABR waveforms for the sensorineural hearing loss subjects.     

Neuro-otologic applications of simultaneous multi-channel auditory evoked response recordings

Multichannel auditory brain stem response (ABR) recordings were obtained in 75 acute, severely brain injured patients. The purpose of the study was to assess, in patients with varied neuro-otologic pathology, the clinical feasibility and value of measuring the ABR simultaneously with more than one electrode array. The use of alternative electrode arrays, in addition to the conventional (vertex to stimulus ipsilateral ear) array, augmented confident identification of wave components I through VI, and was particularly useful in patients with marked middle ear pathology which confounded ABR interpretation. The ABR recorded with an indifferent (noncephalic) reference electrode, e.g., was characterized by increased Wave V amplitude, and improved definition of Wave IV vs. V. Case studies are presented to illustrate neuro-otologic applications of the multichannel recording technique.     

Auditory brain stem response in newborn infants--masking effect on ipsi- and contralateral recording

Ipsilateral and contralateral auditory brain stem responses (ABR) were recorded in 10 full-term neonates. We investigated the effect of the masking level on the peak latency and amplitude on ipsi- and contralateral recordings. Clicks were presented at 85 dB HL to the ipsilateral ear and the masking white noise was presented at 75, 65, 55, 45 and 0 dB HL on the contralateral one, respectively. Masking had no significant effect on the ipsi- and contralateral recording in regard to latency and amplitude except for wave CVI (contralateral wave VI). In addition, ABR was recorded in an infant with total unilateral hearing loss. Crossover responses on both sides were observed with-out contralateral masking, but these responses were completely eliminated when 45 dB HL contralateral masking masked the 85 dB HL clicks to the dead ear. Therefore, it is suggested that such crossover responses will contribute to the ipsi- and contralaterally recorded ABR waveform when an ABR recording is carried out without contralateral masking. Our results indicate that contralateral masking is necessary and should be used in cases of unilateral hearing loss.     

The central auditory conduction at term date and three months after birth. II. Auditory brainstem response

This communication describes the results of auditory brainstem responses (ABRs) obtained in 25 healthy mature newborns with a follow-up at 3 months of age. The combination of ipsi- and contralateral recordings, the intensity series and the comparison with the composite group averages are useful for the identification of the separate ABR components. Differences between the records after right or left ear stimulation were not observed. Comparing our data with those obtained by others, we conclude that the interpeak latency differences (IPLDs) offer a more consistent measure of ABR latency values than the peak latencies measured from stimulus onset. The simultaneously recorded ABRs ipsi- and contralateral to stimulation show both at term, and at 3 months, an equal central conduction time. The ABR II-V complex shows contralaterally a significant shift compared with the ipsilateral II-V complex. The significant latency changes observed between term and at 3 months are due mainly to the latency decrease in the II-III IPLD.     

Objective assessment of frequency-specific hearing thresholds in babies

OBJECTIVE: To report on clinical experience using dichotic multiple-stimulus auditory steady-state responses (ASSRs) as an objective technique to estimate frequency-specific hearing thresholds in hearing-impaired infants. METHODS: A comparison was made between the click-evoked auditory brainstem response (ABR), auditory steady-state responses and behavioral hearing thresholds (BHTs). Both ears of 10 infants between 3 and 14 months of age were tested. ABR and ASSRs were recorded during the same test session. ABR was evoked by 100 micros clicks. ASSRs were evoked by amplitude- and frequency-modulated tones with carrier frequencies of 0.5, 1, 2 and 4 kHz and modulation frequencies ranging from 82 to 110 Hz. Eight signals (four to each ear) were presented simultaneously. ASSR thresholds were derived after separate recordings of approximately 5, 7.5 and 10 min to compare the influence of test duration. BHTs were defined in later test sessions as soon as possible after the ASSR test, dependent on medical and developmental factors. RESULTS: For the subjects tested in this study 60% of ABR thresholds and 95% of ASSR thresholds for 1, 2 and 4 kHz were found at an average age of 7 months. Only 51% of frequency-specific BHTs could be obtained but on average 5 months later. The correlation of ABR thresholds and ASSR thresholds at 2 kHz was 0.77. The correlation of ASSRs and BHTs was 0.92. The mean differences and associated standard deviations were 4 +/- 14, 4 +/- 11, -2 +/- 14 and -1 +/- 13 dB for 0.5, 1, 2 and 4 kHz, respectively. The average test duration was 45 min for ABR (one threshold in both ears) and 58 min for ASSR (four thresholds in both ears). By reducing the duration of the separate recordings of ASSR, the precision of the hearing threshold estimate decreased and the number of outlying and missing values increased. Correlation coefficients were 0.92, 0.89 and 0.83 for recordings of maximum 10, 7.5 and 5 min, respectively. A compromise between test duration and precision has to be sought. CONCLUSIONS: Multiple-frequency ASSRs offer the possibility to estimate frequency-specific hearing thresholds in babies in a time-efficient way.     

Auditory brainstem response changes during exposure to GSM-900 radiation: an experimental study

The objective of the present study was to investigate the possible electrophysiological time-related changes in auditory pathway during mobile phone electromagnetic field exposure. Thirty healthy rabbits were enrolled in an experimental study of exposure to GSM-900 radiation for 60 min and auditory brainstem responses (ABRs) were recorded at regular time-intervals during exposure. The study subjects were radiated via an adjustable power and frequency radio transmitter for GSM-900 mobile phone emission simulation, designed and manufactured according to the needs of the experiment. The mean absolute latency of waves III-V showed a statistically significant delay (p < 0.05) after 60, 45 and 15 min of exposure to electromagnetic radiation of 900 MHz, respectively. Interwave latency I-III was found to be prolonged after 60 min of radiation exposure in correspondence to wave III absolute latency delay. Interwave latencies I-V and III-V were found with a statistically significant delay (p < 0.05) after 30 min of radiation. No statistically significant delay was found for the same ABR parameters in recordings from the ear contralateral to the radiation source at 60 min radiation exposure compared with baseline ABR. The ABR measurements returned to baseline recordings 24 h after the exposure to electromagnetic radiation of 900 MHz. The prolongation of interval latencies I-V and III-V indicates that exposure to electromagnetic fields emitted by mobile phone can affect the normal electrophysiological activity of the auditory system, and these findings fit the pattern of general responses to a stressor.     

Electrophysiological effects of the clinically used local anesthetics lidocaine,lidocaine-prilocaine and phenol on the rat's inner ear

Summary Local anesthetics, even if applied to the outer ear canal, may still enter the middle ear, running the risk of penetrating the round window. To elucidate the effect of certain topical anesthetics on the inner ear, the round window niche in the laboratory rat's middle ear was exposed separately to lidocaine, lidocaine-prilocaine and phenol. Auditory brain-stem responses (ABR) were recorded at 2, 4, 6, 8, 12, 16, 20, and 31.5 kHz before the application, and 24 h, 3 weeks, 2 months and 6 months after exposure. After terminating the 6-month ABR measurements, the animals were sacrificed and the temporal bones fixed and decalcified for light microscopic analysis. All three drugs affected the ABR thresholds and the cochlear morphology with a pattern characteristic for each drug. At 24 h, all three substances caused severe impairment of ABR thresholds, followed by a period of restitution lasting up to 2 months. Even 6 months after exposure, the ABR thresholds at and above 12 kHz were impaired, as compared with the pre-treatment level, for all substances tested. In the lower frequencies the original ABR threshold was reached in the order: (1) lidocaine, (2) lidocaine-prilocaine, (3) phenol. The cochlear structures were unaffected by lidocaine, whereas lidocaine-prilocaine and phenol caused morphological damage which was most pronounced after exposure to phenol. The heterogeneity of the changes in the ABR thresholds suggests differences in the mechanism of action of each type of local anesthetic investigated. The effects following lidocaine were transient. However, clinicians must be aware of the ototoxic potential of both lidocaine and phenol.     

Ipsilateral and contralateral vestibular schwannomas in unilateral long-term deaf ears

In the past decade, we have encountered two patients with unilateral long-term deaf ear having vestibular schwannoma. One was on the deaf ear in a 53 years’ woman and the other was on the contralateral hearing ear in a 62 years’ woman. These two patients had total deafness on the right ear since childhood, associated with absent auditory brainstem response (ABR) and caloric responses, whereas normal ABR and caloric responses were shown on the left ear. Although similar physiological findings were disclosed on the deaf ears, MRI scan demonstrated vestibular schwannoma on the different side, that is, one in deaf ear and the other in hearing ear. For the former, absent ABR and caloric results indicate that the tumor originates from the superior vestibular nerve. In contrast with the latter, normal ABR and caloric responses, but absent vestibular-evoked myogenic potentials on the hearing ear imply that the tumor originates from the inferior vestibular nerve. The ipsilateral tumor on the deaf ear underwent intracranial surgical excision, followed by radiosurgery due to tumor recurrence 10 years later, while the contralateral one on the only hearing ear received radiosurgery only. Both patients were rather well, 3 years after last treatment.     

Outer- and middle-ear contributions to presbycusis in the Brown Norway rat

This paper examines the contribution of the outer and middle ears to the hearing loss associated with presbycusis in Brown Norway rats. Animals were formed into two groups; young adults (2-3 months old) and aged animals (approximately 34 months old). Auditory brainstem response (ABR) thresholds were obtained with the outer ear intact or surgically removed. Tympanic membrane (TM) velocity transfer functions were measured from the umbo with the outer ear removed. The length of the auditory meatus, TM surface area, and TM thickness were quantified. The ABR thresholds were 17-26 dB less sensitive in the aged animals between 8.0 and 40.0 kHz when the outer ear was intact. A significant and reliable reduction in the aged rat velocity transfer function of 5-8 dB occurred between 10.0 and 32.0 kHz, while the low frequency velocity response was only a few decibels greater in the younger animals. The ABR threshold differences between young adult and aged ears were compensated by removing the outer/middle ear effects of aging to reveal a purely sensorineural component of presbycusis. The outer and middle ear effects were calculated directly when the ABR and TM velocity data were obtained with the outer ear removed. The outer ear intact condition was modeled in order to compare the ABR data obtained with the outer ear intact with the TM velocity data obtained with the outer removed. With either procedure, removal of the age-related contributions of the outer and middle ear to the ABR threshold resulted in similar age-related ABR threshold shifts between the two age groups. The pure sensorineural threshold shift component of the ABR response was restricted to frequencies between 5.0 and 20.0 kHz and reached a maximum of approximately 15 dB. These results support the conclusion that there is an outer- and middle-ear contribution to the threshold loss defining presbycusis.     

Effect of middle ear fluid on sound transmission and auditory brainstem response in guinea pigs

Combined measurements of middle ear transfer function and auditory brainstem response (ABR) in live guinea pigs with middle ear effusion (MEE) are reported in this paper. The MEE model was created by injecting saline into the middle ear cavity. Vibrations of the tympanic membrane (TM), the tip of the incus, and the round window membrane (RWM) were measured with a laser vibrometer at frequencies of 0.2-40?kHz when the middle ear fluid increased from 0 to 0.2?ml (i.e., full fill of the cavity). The click and pure tone ABRs were recorded as the middle ear fluid increased. Fluid introduction reduced mobility of the TM, incus and RWM mainly at high frequencies (f?>?1?kHz). The magnitude of this reduction was related to the volume of fluid. The displacement transmission ratio of the TM to incus varied with frequency and fluid level. The volume displacement ratio of the oval window to round window was approximately 1.0 over most frequencies. Elevation of ABR thresholds and prolongation of ABR latencies were observed as fluid level increased. Reduction of TM displacement correlated well with elevation of ABR threshold at 0.5-8?kHz. Alterations in the ratio of ossicular displacements before and after fluid induction are consistent with fluid-induced changes in complex ossicular motions.     

Effect of round window membrane application of nitric oxide on hearing and nitric oxide concentration in perilymph

Nitric oxide (NO), a free radical, has been found to be important in the development of middle ear effusions. However, the effect of NO in the middle ear effusion on cochlear function and on perilymph concentrations of NO has not been reported. We placed S-nitroso-N-acetylpenicillamine (SNAP), a NO donor compound, on the round window membrane (RWM) of adult chinchillas. Auditory brainstem response (ABR) thresholds were measured before and after the placement of SNAP on the RWM and hourly for 8 h after SNAP placement. Samples of perilymph were collected 2 h after application of SNAP and were assayed for total nitrate and nitrite, the end products of NO. Experimental ears demonstrated significant ABR threshold elevations after 5 h and elevated nitrate/nitrite in the perilymph. These findings suggest that NO present in the middle ear passes through the RWM into the inner ear and can cause significant hearing loss.     

Math1基因内耳导入后噪声性聋豚鼠听功能改变观察

目的观察Math1基因内耳导入对噪声性聋豚鼠听功能的影响,探讨Math1基因过表达对噪声损伤耳蜗的生物学效应,为内耳基因治疗提供实验基础和理论依据。方法经脉冲噪声致聋的豚鼠45只（各频率ABR阈值均≥95dB SPL）,雌雄不限,实验开始时体草250～300g。随机分为3组：Ad—Math1-EGFP组（30只）;Ad—EGFP组（5只）;空白组（10只）。各组豚鼠在基因转导后4周、8周分别测试双耳ABR。测试完毕后处死动物,观察听泡及耳蜗尤炎性病变者记录听阈结果。结果Math1导入后4周,导入耳各频率ABR阈值低于对照耳（右耳）,也低于Ad—EGFP组及空内组,平均达到85dBSPL。Math1导入后8周,导入耳各频率ABR阂值低于对照耳（右耳）,也低于Ad—EGFP组及空白组,与4周时比较,进一步好转,平均达到75dB SPL。结论Math1基因内耳导入可使噪声导致全聋的豚鼠听功能部分恢复,为噪声性聋的治疗打开了新的思路和手段。     

Transient infantile auditory neuropathy and its clinical implications

OBJECTIVE: Auditory neuropathy (AN) has been a well-accepted clinical entity during the last years. Though we are able to diagnose AN reliably, little is known concerning its epidemiology, etiology and prognosis. This study is aimed at presenting a particular characteristic of the disease, namely its potential transient behaviour, observed in a group of high risk neonates suffering from AN. The ensuing clinical implications are underlined. METHOD: From 1995 to 2004, 1150 high risk (HR) neonates were subjected consecutively to audiological evaluation by auditory brain stem responses (ABR), participating in a targeted hearing screening program for HR neonates. All neonates with ABR threshold >40 dBnHL and middle ear free from disease underwent otoacoustic emissions (OAEs) testing as well. Children with elevated ABR thresholds were scheduled for re-examination after 4-6 months. Only infants demonstrating considerably elevated thresholds (>70 dBnHL), absent or atypical ABR in combination with normal OAEs were considered as suffering from AN. RESULTS: One hundred and seventy-seven neonates showed elevated ABR thresholds (15.4%). Seventy-nine of them demonstrated ABR thresholds >or=75 dBnHL, absent or strongly atypical waveforms at maximum test intensity and among them 25 displayed findings consistent with AN. Follow-up examination revealed a resolution of AN in 13 out of 20 infants retested, that is a restoration of ABR to normal and typical OAEs recordings. Using multiple logistic regression, we found that low birth weight may represent a reliable predictor for clinical recovery of AN infants. CONCLUSION: This article bring to light the temporary character that AN could show in HR neonates and especially in those with low birth weight. Based on the results of our study, the higher the birth weight, the less likely it is for neonates to recover from AN. From a practical point of view, these findings suggest that hearing screening protocols for HR neonates should be revised in both their methodology and time of application. Finally, the decision for amplification or cochlear implantation in HR infants with AN should be made very carefully and well after the 6th month of age, since the maturation process may still be in progress.