Auditory Brainstem Response Assessment Research Articles

The British Columbia's Children's Hospital Tone-Evoked Auditory Brainstem Response Protocol: How Long Do Infants Sleep and How Much Information Can Be Obtained in One Appointment?

There are few published reports providing quantitative information of clinical feasibility for tone-evoked auditory brainstem response (ABR) protocols. In this study, the authors reviewed charts of 188 ABR assessments during a 20-mo period: 116 sedated (median age, 23 mos) and 72 nonsedated (median age, 4 mos). Fifty-one percent of infants had normal thresholds. The average amount of sleep time was 58 mins for sedated assessments, during which an average of 7.6 measures were obtained; nonsedated assessments averaged 49 mins with 6.2 measures obtained. Thus, a substantial amount of both test time and information about hearing can be obtained within one ABR appointment.

Temporary reduction of distortion product otoacoustic emissions (DPOAEs) immediately following auditory brainstem response (ABR)

The hearing status of an experimental animal is typically assessed in the laboratory setting by the combined use of auditory brainstem response (ABR) and distortion product otoacoustic emissions (DPOAEs), carried out in succession, with the former assay preceding the latter. This study reports a cautionary finding that the use of this accepted regimen yields a reduced DPOAE response. When the DPOAEs were performed after ABR testing, transient reduction of the DPOAE amplitudes was observed at all frequencies in both the inbred, C57/B6 and FVB/N, and the outbred, SW mouse strains. DPOAEs were reduced post-ABR in multiple mouse strains which suggests that this finding is not strain-specific but a general consequence of the preceding ABR analysis. The reduction in DPOAE was temporary: when re-tested at one hour, DPOAE amplitudes recovered to pre-ABR levels. In contrast to the ABR’s impact on DPOAE response, ABR thresholds were not altered or reduced when preceded immediately by DPOAE measurements. The molecular alterations underlying the ABR-induced transient reduction of DPOAE remain to be determined. To investigate the potential role of reactive oxygen species in post-ABR DPOAE reduction, transgenic mice over-expressing SOD1, the cytoplasmic enzyme critical for removal of superoxide radicals were subjected to the same auditory testing regimen. Similar to their wild type littermates, the SOD1 transgenic mice also demonstrated post-ABR DPOAE reduction, and thus do not support a role for superoxide radicals in transient reduction of DPOAE. While toxic noise exposure is known to negatively impact OAE, transient decrease in DPOAE levels following standard ABR assay has not been previously described. A practical outcome from this study is a recommendation for reversal of the traditional order for carrying out auditory tests, with the OAE measurements preceding ABR assessment, thus ensuring that the DPOAE response is unaffected.

Gene transfer using bovine adeno-associated virus in the guinea pig cochlea

Gene transfer into cells of the cochlea is useful for both research and therapy. Bovine adeno-associated virus (BAAV) is a novel viral vector with potential for long term gene expression with little or no side effects. In this study we assessed transgene expression using BAAV with ß-actin-GFP as a reporter gene, in cochleae of normal and deafened guinea pigs. We used two different routes to inoculate the cochlea: scala media (SM) or scala tympani (ST). Auditory brainstem response assessments were done prior to inoculation, 7 days after inoculation and immediately prior to sacrifice, to assess the functional consequences of the treatment. We observed threshold shifts due to the surgical invasion, but no apparent pathology associated with the virus. Fourteen days after the injection, animals were sacrificed and cochleae assessed histologically. Epi-fluorescence showed that BAAV transduced the supporting cells of both normal and deafened animals through SM and ST inoculations. Transgene expression in cells of the membranous labyrinth following ST inoculation is an important outcome because of the greater feasibility of this route for future clinical application. BAAV facilitates efficient transduction of the membranous labyrinth epithelium with minimum pathogenicity and may become clinically applicable for inner ear gene therapy.

Infant hearing screening: effects of timeline

Universal infant hearing screening using otoacoustic emission and auditory brain-stem response audiometry is widely administered to attain the goals of early identification of, and intervention for hearing impairment. Concerns regarding screening specificity have, however, been raised. False positives may result from vernix occlusion in the ear canal or transient middle ear effusion, and can result in substantial costs to health care systems. The current study investigates the effects of age and time interval between tests on hearing assessment results. Three hundred and seventeen positive screens from a 2-stage distortion product otoacoustic emission (DPOAE) screening programme in Hong Kong, who subsequently received diagnostic auditory brainstem response (ABR) assessment and monitoring, were investigated. Differences in diagnostic ABR results were compared among infants of different ages at tests, and with different time lapses after DPOAE screening. The proportion of those having persistent hearing impairment, conductive loss and impairment of moderate degree or above, were also compared. A significantly higher rate of normal ABR thresholds (60%versus 24%) was noted in infants assessed after age 50 days, and in infants diagnostically assessed with a time lapse of over 20 days post-DPOAE screening (65%versus 42%). Delaying diagnostic ABR assessment may reveal a higher percentage of normal thresholds, and hence probably higher specificity. Time delay may allow for spontaneous resolution of transient outer and middle ear conditions. However, the goals of early identification and intervention, as well as possible parental anxiety with delayed assessment, should also be considered when reviewing infant hearing screening schedules.

Risk Factors for Auditory Neuropathy/Auditory Synaptopathy

Aims: It was the aim of this study to describe risk factors in auditory neuropathy/auditory synaptopathy (AN/AS). Methods: Between 1997 and 2005, we diagnosed 37 children with AN/AS. They underwent a critical chart review for risk factors and etiological coincidences in this idiosyncratic disorder. Results: Eighteen neonates had a history of prematurity and low birth weight. Hyperbilirubinaemia was present in 13 children. Three patients had evidence of infection during pregnancy, and AN/AS was associated with complex syndromal diseases in 2 cases. A congenital, familial pattern was seen in 2 siblings. Seven patients had idiopathic AN/AS. Conclusion: Rather than being a single etiological entity, AN/AS comprises a spectrum of risk factors and associated problems affecting the cochlea and the auditory pathway. This study shows that the majority of AN/AS in children is the result of perinatal problems and is not genetic in origin. Hyperbilirubinaemia is a common and etiologically significant finding in infants suffering from AN/AS. Thus, early hearing screening for AN/AS including transient evoked otoacoustic emissions and auditory brainstem response assessment among neonates with risk factors for AN/AS is crucial in order to better manage patients suffering from this disorder.

Investigation of ototoxic effects of Taxol on a mice model

To investigate the effects of taxol on the inner ear in a mice model. This study was performed on 112 ears of 56 albino Swiss mice. All animals underwent baseline auditory brainstem response (ABR) testing bilaterally and baseline Peak Equivalent Sound Pressure Levels (PESPLs) were obtained. The mice were randomly assigned to seven groups consisting of one control and six study groups. The control group received no medications while the mice in groups 1-6 received 1 x 60, 1 x 20, 2 x 20, 3 x 20, 4 x 20 and 5 x 20 mg/kg taxol intraperitoneally. Control ABR assessments were performed 3 weeks after the last dose. The animals were then sacrificed while still anaesthetised and the bullae (cochleae included) were dissected from their temporal bones. Haematoxylin-eosin and Masson's trichrome stains were used to demonstrate connective tissue, and periodic acid Schiff (PAS) stain was used to highlight epithelial elements. Significant decreases in the hearing levels were observed in all the groups which received taxol. No correlation was observed between the dose given and the degree of hearing loss. The sections from the control group showed no histopathologic abnormalities while the sections from the study groups demonstrated vacuolisation in the epithelial cells of the spiral limbus, and the stria vascularis, vacuolisation of the fibroblasts and decreasing the number of the fibroblasts in the spiral limbus. Taxol causes mild to moderate sensorineural hearing loss in mice. Histopathologically, there were degenerative changes in the cochlea resembling the ones that take place in salisylate and interferon alpha 2a ototoxicity which are thought to be reversible. There was no sensory cell loss. The hearing loss begins with doses less than or equal to 20mg/kg and is not dose dependent after this dose. Hearing monitorisation with audiologic evaluation is strongly recommended before and during the use of the drug in human subjects.

Differential auditory signal processing in an animal model

Auditory evoked responses were collected in male zebra finches (Poephila guttata) to objectively determine differential frequency selectivity. First, the mating call of the animal was recorded and analyzed for its frequency components through the customized program. Then, auditory brainstem responses and cortical responses of each anesthetized animal were routinely recorded in response to tone bursts of 1–8 kHz derived from the corresponding mating call spectrum. From the results, most mating calls showed relatively consistent spectral structures. The upper limit of the spectrum was well under 10 kHz. The peak energy bands were concentrated in the region less than 5 kHz. The assessment of auditory brainstem responses and cortical evoked potentials showed differential selectivity with a series of characteristic scales. This system appears to be an excellent model to investigate complex sound processing and related language behaviors. These data could also be used in designing effective signal processing strategies in auditory rehabilitation devices such as hearing aids and cochlear implants. [Work supported by Brain Science & Engineering Program from Korean Ministry of Science and Technology.]

A universal newborn hearing screening program in Taiwan

Objective: Mackay Memorial Hospital and the Children's Hearing Foundation established a pilot universal newborn hearing screening program in November 1998. Our objective was to assess the feasibility, accuracy and cost effectiveness of implementing universal newborn hearing screening in Taiwan. Method: Between November 1998 and October 2000 a total of 6765 newborns were screened for hearing loss prior to discharge from the wellborn nursery at Mackay Memorial Hospital. The average age of the subjects at the initial screening test was 52 h. The program employed a three stage hearing screening protocol using transient evoked otoacoustic emmisions (TEOAE) screening with referral for diagnostic auditory brainstem response assessment. Results: The mean TEOAE screening time per ear was 41.43 s. The overall pass rate at the time of hospital discharge was 93.6%. Thus achieving an acceptable referral rate of 6.4% for diagnostic audiological assessments. Nine newborns were identified with permanent bilateral hearing impairment. 26 newborns were identified with permanent unilateral hearing impairment. Infants identified with bilateral hearing loss were immediately referred to the Children's Hearing Foundation for hearing aid assessment and fitting. Infants as young as 5 weeks of age were successfully fitted with hearing instruments and enrolled in the family centered early intervention program at the Children's Hearing Foundation. Conclusion: The frequency of bilateral congenital hearing loss requiring amplification in this population is shown to be approximately 1 in 752 newborns. This finding is consistent with previous research, which has indicated hearing loss to be the most frequently occurring birth defect. Universal newborn hearing screening using TEOAEs proved to be a cost effective and feasible method of identifying congenital hearing loss in Taiwan. The existence of many successful screening programs worldwide and the availability of fast, objective, reliable and inexpensive hearing screening procedures means that universal newborn hearing screening is becoming the standard of care.

Pediatric Auditory Brainstem Response Assessment: The Cross-Check Principle Twenty Years Later

Pediatric Auditory Brainstem Response Assessment: The Cross-Check Principle Twenty Years Later

Evaluation of a computer-automated program for clinical assessment of the auditory brain stem response.

An evaluation of an automatic auditory brain stem evaluation (AABE) for waves I, III, and V, of the auditory brain stem response (ABR) is presented. The on-line procedure performs a mathematical analysis of ABR waveforms using principles similar to those used by experienced clinicians to make threshold and latency decisions. It has been tested and applied to normal and pathologic traces at stimulus levels from 20 to 100 dB HL. Subject ages ranged from 6 months through adulthood. Latencies and thresholds determined by the analytic technique were examined and found to be indistinguishable from decisions of two "expert" observers and four practicing clinical audiologists experienced in ABR. Speed, practicality, and limitations of the software for routine ABR assessments are discussed.

Auditory brainstem response in auditory assessment of acute severely burned children.

The burn population often requires ototoxic drugs in the treatment of infection. Previous investigations indicate that cochlear damage and auditory impairment may result from this medical therapy. In recent years, the auditory brainstem response (ABR) has assumed an important role in pediatric auditory assessment. We describe a test protocol for ABR assessment in the severely burned child. In a series of 69 acute severely burned children, 13% showed evidence of auditory deficit by the ABR. Based on our experiences, we recommend the inclusion of routine auditory evaluations, including ABR, in the diagnosis and rehabilitation of these children.

Strategies for infant auditory brain stem response assessment.

The use of auditory brain stem response (ABR) represents a new dimension in auditory and neurological pediatric assessment. Because the ABR may be altered by stimulus and procedural variables, the lack of an established standard has reduced its clinical efficiency. This paper describes a suggested ABR protocol for infants. Included are stimulus and electrode considerations, measurement criteria, and procedures. In addition, ABR results are presented from 125 newborns ranging between 40 and 49 weeks gestational age. The effects of age and intensity on latency and amplitude are discussed.