Auditory Brainstem Response Audiometry Research Articles

Water‐Soluble Coenzyme Q10 in Chronic Hearing Loss

Objective: Q-TER is a multicomposite water-soluble formulation of CoQ10; in particular, Q-TER consists of a mixture of maltodextrin, acting as a carrier, of CoQ10 molecules of sucrester, which serves as bioactivator. The purpose of this study was to evaluate the efficiency of Q-TER in subjects with chronic sensorineural hearing loss. Method: A total of 80 patients affected by chronic sensorineural hearing loss were included. The patients were divided, at random, into 2 numerically equal groups (A and B). Group A underwent therapy with Q-TER, 160 mg, once a day for 30 days; group B received placebo, once a day for 30 days. Results: Before, at the end, and 6 months after the end of the treatment, all patients underwent: pure tone audiometry, transient evoked otoacoustic emissions (TEAOE) and otoacoustic products of distortion (DPOAE), auditory brainstem response and speech audiometry. Compared with group B, at the end of the treatment in group A the pure tone audiometry showed a significant ( P < .05) improvement of the audiometric thresholds at the 1.000, 2.000, 4.000, and 8.000 Hz. This improvement was confirmed by the data obtained with the speech audiometry and in the last check. We found no significant differences in the others parameters and in group B. Conclusion: It is quite early to be enthusiastic. There must be more studies with controlled results. However, this kind of therapy for chronic hearing loss seems to be interesting, especially to stop hearing decay. It is also remarkable that good results are found one month after the beginning of the treatment.

Auditory brainstem response audiometry in tinnitus patients

BackgroundTinnitus is hypothesized to be an auditory phantom phenomenon resulting from spontaneous neuronal activity somewhere along the auditory pathway. The neural abnormalities underlying tinnitus are largely unknown. ObjectivesThis study aims to study brainstem function in tinnitus patients using auditory brainstem response audiometry. MethodsThis study included 80 subjects classified into two main groups: Group I (GI): consists of 20 normal hearing subjects without tinnitus. Group II (GII): consisted of 60 normal hearing adults complaining of tinnitus. This group is further divided into three subgroups according to tinnitus laterality: GIIa (20 subjects with bilateral tinnitus), GIIb (20 subjects with right ear tinnitus and GIIc (20 subjects with left ear tinnitus). Both groups were submitted to full audiological history taking, otological examination, basic audiologic evaluation and Auditory brainstem response audiometry (ABR) which was recorded in both groups followed by calculation of the absolute latencies of wave I, III and V, interpeak latencies as well as the interaural latency difference of wave V. ResultsGenerally, there was no significant difference between both groups, however, some tinnitus patients showed abnormal prolonged absolute latencies, interpeak latencies and increased interaural latency difference of wave V. There was some asymmetry in results between different study subgroups. ConclusionsResults of ABR are variable in tinnitus patients. Some cases have normal results while others showed prolonged absolute or interpeak latencies or increased ILD-V difference.

Effect of Ganciclovir on Murine Cytomegalovirus-induced Hearing Loss in a Mouse Model

We evaluated the effect of Ganciclovir on murine cytomegalovirus (MCMV)-induced hearing impairment in a mouse model by studying modulations in auditory brainstem response (ABR) and pathological changes in the inner ear. MCMV infection was established via trans-brain. For this purpose, 24 BALB/c newborn mice were randomly and equally divided into control group (10 μl of sterile normal saline was injected); model group (10 μl of MCMV TCID50-10(4) IU/0.1 ml was injected); and interfered group (Trans-brain MCMV; Ganciclovir at the rate of 60 mg/kg was intraperitoneally injected). ABR audiometry was performed after 14 days. Acoustic vesicles were obtained for MCMV-PCR analysis and histopathological examination. Comparing ABR in model group against controls, incubation period of wave was lengthened (F = 9.151, P = 0.011-0.05) and wave amplitude was cut down (F = 5.095, P = 0.043-0.05). Comparing ABR in model group against interfered group, incubation period and amplitude of wave were F = 13.797 (P = 0.003-0.05) and F = 14.587 (P = 0.002-0.05), respectively. Cochlear histopathological changes in model group included thickening of vestibular membrane, lymphocytic infiltration, and fibrous degeneration of cochlear duct. In Ganciclovir interfered group, however, these pathologic changes were less significant as compared with those of model group. We, therefore, conclude that Ganciclovir treatment at the early stage of MCMV-induced hearing impairment inhibits the disease progression in infected mice.

Auditory function in patients with systemic lupus erythematosus

Objective Patients with systemic lupus erythematosus (SLE) may develop hearing and balance disorders as a result of the immune-mediated inner ear damage due to vasculitis or ototoxicity of drugs used in SLE treatment. The aim of the study was evaluation of the hearing organ disorders in patients with SLE with particular regard to their prevalence and relationship to duration and severity of disease. The severity was assessed from involvement of organs that resulted in poorer SLE outcome, i.e. kidneys and central nervous system (CNS), and from the presence of antibodies associated with unfavourable SLE prognosis. Methods Thirty-five unselected, consecutive patients (33 women, two men, mean age 47.8 years) with SLE diagnosed in compliance to the international diagnostic criteria of the American Rheumatism Association (1982) were enrolled into the study. The control group consisted of 30 otologically healthy persons matched to the SLE group for age and sex. Case history was recorded for all patients from questionnaire data and laryngological examinations were performed, followed by pure-tone, speech and impedance audiometry and auditory brainstem response audiometry (ABR). Results In the anamnesis 71.4% of patients reported vertigo, 62.9% headaches, 40% tinnitus, 25.7% hyperacusis, 17.1% hearing loss and 2.9% ear fullness. It was found that SLE patients had a significantly poorer mean hearing thresholds than the control group for all frequencies, except for 500; 2000 and 4000 Hz. Longer ABR latency averages were observed in the group of SLE patients compared to control. Ten patients (28.6%) developed high-frequency and symmetric sensorineural hearing loss (SNHL). Significant positive correlation between mean air-conduction hearing thresholds and SLE duration ( r = 0.46, p < 0.001) was found. After taking age into consideration, hearing acuity in SLE was related to duration of disease in younger patients. Furthermore, no relation was seen between hearing level and severity of disease. Conclusions Auditory system involvement ought to be considered as one of elements of the clinical picture of systemic lupus erythematosus while determination of its character, original or secondary, requires further research.

Audiological Deficits After Closed Head Injury

Damage to the peripheral auditory structures has long been recognized as a common component of head injury. It is estimated that a majority of patients with skull trauma have resultant hearing impairment. Damage to the peripheral and/or central auditory pathways can occur as a primary or secondary injury. Considering the high incidence of hearing loss, it was considered worthwhile to conduct an in-depth investigation by administering a comprehensive audiological test battery on head-injured patients. The sample population consisted of 290 subjects with closed head injury (study group) and 50 subjects with otologically normal subjects (control group). The subjects in the study group were further divided into mild (n = 150), moderate (n = 100), and severe (n = 40) category on the basis of Glasgow Coma Scale score. The audiological assessment consisted of pure tone audiometry, speech audiometry, tympanometry, acoustic reflex testing, auditory brain stem response audiometry, and middle latency response audiometry. It is concluded that there is higher prevalence of hearing impairment in the study group compared with control group. Majority of the patients who incur hearing loss after closed head injury have mild degree of hearing impairment. A significant difference between the study and control group observed on majority of the auditory brain stem response and middle latency response parameters studied.

Comparison of Porcine Acellular Dermis and Dura Mater as Natural Scaffolds for Bioengineering Tympanic Membranes

Tympanic membrane (TM) perforation is a frequent cause of conductive hearing loss. The most popular surgical repair is autografting with temporalis fascia, although some disadvantages have been found with this method. Whether xenogeneous grafts produced by a tissue engineering approach could be used is unclear. The purpose of this study was to evaluate the possibility of bioengineering TM using porcine acellular dermis and dura mater with TM fibroblasts and to compare the effects of these two natural scaffolds. Both of the materials were prepared by sequentially using Triton X-100, nuclease solution, and freeze-drying technique. Histologically, both had porous structures without any cellular components. After seeding with TM fibroblasts isolated from guinea pigs, it was found that both of the materials could be used as scaffolds for bioengineering TM in vitro. In the in vivo study, chronic TM perforation models were successfully established in guinea pigs. From gross and histological examinations, most of TM perforations were healed after grafting these two bioengineered TMs using an underlay technique. Furthermore, auditory brainstem response audiometry was applied to determine the auditory threshold in each group. Results showed that hearing in the dura mater group seemed to undergo faster recovery in the early stage but in the end, no differences were found between the two groups. Two kinds of materials without cell seeding were used as controls. Porcine acellular dermis and dura mater are suitable scaffolds for bioengineering TMs.

Is undernutrition a risk factor for sensorineural hearing loss in early infancy?

The present cross-sectional study set out to determine the nutritional status of infants aged 0-3 months with the WHO Multicentre Growth Reference (WHO-MGR) and examine the relationship between undernutrition and congenital or early-onset sensorineural hearing loss (CESHL) rarely reported for developing countries. The nutritional status of all infants attending community-based clinics for routine Bacille de Calmette-Guérin (BCG) immunisation from July 2005 to December 2006 was determined by weight-for-age, weight-for-length and BMI-for-age based on the WHO-MGR. Hearing loss status was determined by tympanometry, auditory brainstem response (ABR) and visual response audiometry after a two-stage screening with transient evoked otoacoustic emissions and automated ABR. The relationship between nutritional status and CESHL were explored after adjusting for potentially confounding maternal and infant characteristics using multivariable logistic regression analyses. Of the 3386 infants who completed the hearing evaluation protocol, seventy-one were confirmed with hearing loss (>30 dB hearing level). More than one-third (37.9 %) of all infants and over half (54.9 %) of those with CESHL were undernourished by at least one measure of growth. Stunting (35.3 %) was the most prevalent nutritional deficit in infants with CESHL. In the final logistic model, infants with any undernourished physical state were significantly likely to have CESHL (OR 1.67; 95 % CI 1.03, 2.77) and of a severe-to-profound degree (OR 3.92; 95 % CI 1.38, 11.17) compared with infants without any undernourishment. Prospective studies to establish the full spectrum of the relationship between undernutrition and CESHL, particularly in resource-poor countries, are therefore warranted.

Auditory development in progressive motor neuronopathy mouse mutants

The present study was performed to elucidate the hearing development in the progressive motor neuronopathy ( pmn) mouse mutant. This mouse has been used as a model for human motoneuron disease. A missense mutation in the tubulin-specific chaperon E (Tbce) gene on mouse chromosome 13 was localized as the underlying genetic defect. The protein encoded by the Tbce gene is essential for the formation of primary tubulin complexes. Studies on motoneurons show disorganization in microtubules and disturbed axonal transport, followed by retrograde degeneration of the motoneurons. A similar pathomechanism is also possible for hearing disorders where disrupted microtubules could cause functional deficits in spiral ganglion neurons or in cochlear hair cells. Click auditory brainstem response (ABR) audiometry in homozygous pmn mutants showed a normal onset of hearing, but an increasing hearing threshold from postnatal day 26 (P26) on to death, compared to heterozygous mutants and wild-type mice. Histological sections of the cochlea at different ages showed a regular morphology. Additionally, spiral ganglion explants from mutant and wild-type mice were cultured. The neurite length from pmn mutants was shorter than in wild-type mice, and the neurite number/explant was significantly decreased in pmn mutants. We show that the pmn mouse mutant is a model for a progressive rapid hearing loss from P26 on, after initially normal hearing development. Heterozygous mice are not affected by this defect. With the knowledge of the well-known pathomechanism of this defect in motoneurons, a dysfunction of cellular mechanisms regulating tubulin assembling suggests that tubulin assembling plays an essential role in hearing function and maintenance.

Place of birth and characteristics of infants with congenital and early-onset hearing loss in a developing country

Objective To determine the characteristics of infants with sensorineural hearing loss (SNHL) and the relationship with place of birth. Methods Subjects were drawn from hospital-based and community-based universal infant hearing screening programs concurrently conducted from May 2005 to April 2008 in Lagos, Nigeria. Maternal and infant characteristics of children born in hospitals and detected with SNHL were compared with those born outside hospitals. Each program consisted of a first-stage screening with transient-evoked otoacoustic emissions (TEOAE) followed by second-stage automated auditory brainstem response (AABR). Hearing status was confirmed by diagnostic auditory brainstem response, tympanometry and visual response audiometry. Results A total of 4718 infants were screened under the hospital-based program out of which 12 (0.3%) infants were confirmed with SNHL whereas 71 (1.0%) of the 7179 infants screened under the community-based program were confirmed with SNHL. Of all infants with SNHL 39 (47.0%) were born in hospitals suggesting that 27 (38.0%) of infants under the community-based program were born in hospitals. Prevalence of SNHL ranged from 4.0 per 1000 among infants born in government hospitals to 23 per 1000 among those born in family homes. Mothers of those born outside hospitals were significantly likely to belong to the Yoruba tribe ( p < 0.001), use herbal medications in pregnancy ( p < 0.001), deliver vaginally ( p = 0.004) but without skilled attendants at delivery ( p < 0.001). There were no significant differences among the infants themselves except that those born outside hospitals were significantly likely to be detected in the first 3 months of life compared to those born in hospitals ( p < 0.001). Conclusions A significant proportion of infants with SNHL in many developing countries are likely to be born outside hospitals thus underscoring the need for community-oriented UNHS to facilitate early detection and intervention. Conventional risk factors for SNHL are unlikely to discriminate across places of birth. Pediatricians and otolaryngologists should consider a more active role in fostering community-oriented delivery of primary ear care services in this and similar settings in the developing world.

Factors influencing the efficacy of round window dexamethasone protection of residual hearing post-cochlear implant surgery

Aim To protect hearing in an experimental model of cochlear implantation by the application of dexamethasone to the round window prior to surgery. The present study examined the dosage and timing relationships required to optimise the hearing protection. Methods Dexamethasone or saline (control) was absorbed into a pledget of the carboxymethylcellulose and hyaluronic acid and applied to the round window of the guinea pig prior to cochlear implantation. The treatment groups were 2% w/v dexamethasone for 30, 60 and 120 min; 20% dexamethasone applied for 30 min. Auditory sensitivity was determined pre-operatively, and at 1 week after surgery, with pure-tone auditory brainstem response audiometry (2–32 kHz). Cochlear implantation was performed via a cochleostomy drilled into the basal turn of the cochlea, into which a miniature cochlear implant dummy electrode was inserted using soft-surgery techniques. Results ABR thresholds were elevated after cochlear implantation, maximally at 32 kHz and to a lesser extent at lower frequencies. Thresholds were less elevated after dexamethasone treatment, and the hearing protection improved when 2% dexamethasone was applied to the round window for longer periods of time prior to implantation. The time that dexamethasone need be applied to achieve hearing protection could be reduced by increasing the concentration of steroid, with a 20% application for 30 min achieving similar levels of protection to a 60 min application of 2% dexamethasone. Conclusions Hearing protection is improved by increasing the time that dexamethasone is applied to the round window prior to cochlear implantation, and the waiting time can be reduced by increasing the steroid concentration. These results suggest that the diffusion dexamethasone through the cochlea is the prime determinant of the extent of hearing protection.

Inner ear pathology and loss of hearing in estrogen receptor-β deficient mice

There are well known differences between males and females in hearing. In the present study, the role of estrogen receptor-beta (ER-beta; listed as ESR2 in the MGI Database) in hearing was investigated by comparing hearing and morphology of the inner ear in ER-beta knock-out mice (ER-beta(-/-)) with that of wild-type (WT) littermates. Hearing was analyzed with auditory brainstem response audiometry at 3 and 12 months. The ER-beta(-/-) mice were deaf at 1 year of age, and the morphological analysis showed absence of hair cells and loss of the whole organ of Corti initiated in the basal turn of the cochlea. Furthermore, in ER-beta(-/-), but not in WT mice, the spiral ganglion was lacking many of its neurons. Immunostaining showed the presence of both ER-alpha (listed as ESR1 in the MGI Database) and ER-beta in the nuclei of some neurons in the inner ear in WT mice, but no ER-beta was found in the ER-beta(-/-) mice as expected. ER-alpha staining was predominant in the nuclei of large neurons and ER-beta in nuclei of small neurons and fibroblasts. These results reveal that both ERs are present in the inner ear at specific localizations suggesting subtype-specific functions. It is concluded that ER-beta is important for the prevention of age-related hearing loss. These findings strengthen the hypothesis that estrogen has a direct effect on hearing functions.

Association between surgical steps and intraoperative auditory brainstem response and electrocochleography waveforms during hearing preservation vestibular schwannoma surgery

Intraoperative monitoring of the auditory pathway by means of either electrocochleography or auditory brainstem response audiometry is valuable during hearing preservation vestibular schwannoma (VS) surgery. A more than 75% intraoperative reduction of the amplitude of these evoked auditory potentials was thought to be related with clear hearing compromise of hearing. We identified 22 patients who satisfied this intraoperative criterion in a cohort of 86 consecutive patients who had attempted hearing preservation VS surgery. The surgical step that temporally coincided with the above event was considered to be the most critical step for hearing monitoring during this kind of surgery. Most frequently, drilling of the internal auditory canal and direct tumor resection were associated with the aforementioned changes, but also drilling of the cortical temporal bone at the very beginning of surgery or the opening of the dura could be implicated. This profound intraoperative amplitude decrease was associated with a profound postoperative hearing impairment in 84% of the cases.

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.

Audiological Outcome of Infants with Congenital Cytomegalovirus Infection in a Prospective Study

The aim of this study was to evaluate the audiological outcome of long-term follow-up of infants with asymptomatic congenital cytomegalovirus (CMV) infection as defined by the presence of CMV DNA in neonatal urine. 12599 pregnant women underwent screening for CMV IgG and IgM antibodies between 1996 and 2003. Eighteen infants with congenital CMV infection were identified. These infants underwent the newborn hearing screening test or auditory brainstem response test. Follow-up hearing assessments were performed with the auditory brainstem response and behavioral audiometry. The seropositive rate of CMV IgG antibody among the pregnant women was 75.3%, and the yearly seropositive rate decreased over the study period. One hundred and forty-six pregnant women were positive for IgM antibody, and 18 neonates (12.3%) had congenital CMV infection. Sensorineural hearing loss (SNHL) was detected in 4 (25%) of the 16 infants with asymptomatic infection and 1 (50%) of the 2 infants with symptomatic infection during the first 6 months of life. Two infants who passed the newborn hearing screening had a delayed-onset SNHL in follow-up examinations up to 4 years of age. Two had progressive hearing loss and 2 had improvement of hearing loss. Screening of pregnant women for CMV infection and repeated audiological examinations of infants are necessary because there are infants with delayed-onset SNHL or improved SNHL caused by asymptomatic congenital CMV infection.

Evaluation of the mouse model for acute otitis media

Various animal models have been employed for otitis media research. The mouse has been studied less, in spite of its many advantages. To better understand the suitability of the mouse for studies of otitis media, an evaluation was made of its middle ear inflammatory processes following inoculation with heat-killed Streptococcus pneumoniae (strain 6A), one of the three most common bacteria to cause otitis media in the human. A total of 94 BALB/c mice were injected transtympanically with three concentrations of heat-killed bacteria (10 4, 10 6, and 10 9 organisms per ml) and inflammation evaluated with both histologic examination and auditory brainstem response audiometry. Dose-related measures of the time course of inflammation showed it was maximal at 3 days. PBS-injected control mice also demonstrated some degree of middle ear inflammation. Therefore, inflammation measures from PBS injected mice were used as the threshold above which histologic inflammatory changes would be considered a response to bacteria. These quantitative comparisons of bacterial and PBS inoculations revealed the most significant middle ear measures of inflammation were amount of fluid in the middle ear, tympanic membrane thickness, and number of inflammatory cells. The induction of middle ear inflammation in the mouse demonstrated the applicability of this model for investigations of otitis media.

Doxycycline Reduces Mortality and Injury to the Brain and Cochlea in Experimental Pneumococcal Meningitis

Bacterial meningitis is characterized by an inflammatory reaction to the invading pathogens that can ultimately lead to sensorineural hearing loss, permanent brain injury, or death. The matrix metalloproteinases (MMPs) and tumor necrosis factor alpha-converting enzyme (TACE) are key mediators that promote inflammation, blood-brain barrier disruption, and brain injury in bacterial meningitis. Doxycycline is a clinically used antibiotic with anti-inflammatory effects that lead to reduced cytokine release and the inhibition of MMPs. Here, doxycycline inhibited TACE with a 50% inhibitory dose of 74 microM in vitro and reduced the amount of tumor necrosis factor alpha released into the cerebrospinal fluid by 90% in vivo. In an infant rat model of pneumococcal meningitis, a single dose of doxycycline (30 mg/kg) given as adjuvant therapy in addition to ceftriaxone 18 h after infection significantly reduced the mortality, the blood-brain barrier disruption, and the extent of cortical brain injury. Adjuvant doxycycline (30 mg/kg given subcutaneously once daily for 4 days) also attenuated hearing loss, as assessed by auditory brainstem response audiometry, and neuronal death in the cochlear spiral ganglion at 3 weeks after infection. Thus, doxycycline, probably as a result of its anti-inflammatory properties, had broad beneficial effects in the brain and the cochlea and improved survival in this model of pneumococcal meningitis in infant rats.

Auditory Characteristics of Children with Autism

The objectives of this study were (1) to describe the auditory characteristics of children with autism relative to those of typically developing children and (2) to describe the test-retest reliability of behavioral auditory test measures with this population of children with autism. Audiometric data were obtained from 22 children diagnosed with autism and 22 of their typically developing peers. The audiologic test battery consisted of behavioral measures (i.e., visual reinforcement audiometry, tangible reinforcement operant conditioning audiometry, and conditioned play audiometry) and physiological measures (auditory brain stem response audiometry, distortion product otoacoustic emissions, and acoustic reflexes). Children with autism had physiologic test results equivalent to their typically developing counterparts. That is, no differences in auditory brain stem response audiometry, distortion product otoacoustic emissions, or acoustic reflex results were noted between the children with autism and typically developing children. However, behavioral measures revealed that about half of the children diagnosed with autism presented pure-tone averages outside of normal limits (i.e., >20 dB HL), although their response thresholds to speech were within normal limits. All behavioral test results were within normal limits (i.e., </=20 dB HL) for the typically developing children. In addition, test-retest variability was typically 15 dB or greater for children with autism as compared with variability of 10 dB or less for most of the typically developing children. Children with autism demonstrated essentially equivalent results on a battery of physiological auditory tests as those obtained from typically developing children. However, on average, behavioral responses of children with autism were elevated and less reliable relative to those of typically developing children. Furthermore, approximately half of the children with autism demonstrated behavioral pure-tone averages outside of the normal hearing range (i.e., >20 dB HL) despite having normal to near-normal hearing sensitivity as determined by other audiometric measures.

Meningitis‐associated hearing loss: Protection by adjunctive antioxidant therapy

Hearing loss is the most frequent long-term complication of pneumococcal meningitis, affecting up to 40% of survivors. Unfortunately, adjuvant therapy with dexamethasone has failed to satisfactorily reduce its incidence. Therefore, we evaluated the use of antioxidants for the adjunctive therapy of meningitis-associated deafness. Eighteen hours after intracisternal injection of 7.5 x 10(5) colony-forming units of Streptococcus pneumoniae, rats were treated systemically either with ceftriaxone and the antioxidants and peroxynitrite scavengers Mn(III)tetrakis(4-benzoic acid)-porphyrin (MnTBAP) or N-acetyl-L-cysteine (NAC) or placebo (1 ml phosphate-buffered saline) for 4 days. Hearing was assessed by auditory brainstem response audiometry. Adjunctive antioxidant therapy significantly reduced the long-term hearing loss (14 days after infection) for square wave impulses (mean hearing loss +/- SD: ceftriaxone and placebo, 45+/-26 dB; ceftriaxone and MnTBAP, 9+/-23 dB; ceftriaxone and NAC, 19+/-30 dB) as well as 1 kHz (ceftriaxone and placebo, 28+/-19 dB; ceftriaxone and MnTBAP, 10+/-16 dB; ceftriaxone and NAC, 10+/-17 dB), and 10 kHz tone bursts (ceftriaxone and placebo, 62+/-27 dB; ceftriaxone and MnTBAP, 16+/-13 dB; ceftriaxone and NAC, 25+/-26 dB). Furthermore, both antioxidants attenuated the morphological correlates of meningogenic hearing loss, namely, long-term blood-labyrinth barrier disruption, spiral ganglion neuronal loss, and fibrous obliteration of the perilymphatic spaces. Adjuvant antioxidant therapy is highly otoprotective in meningitis and therefore is a promising future treatment option.

Therapeutic Efficacy of Magnesium in Acoustic Trauma in the Guinea Pig

Comparative functional and morphological tests were performed in two groups of impulse noise-exposed guinea pigs treated either with magnesium (Mg) or isotonic saline as a placebo to extend the knowledge on the therapeutic efficacy of Mg in acoustic trauma demonstrated recently. The permanent threshold shifts were significantly lower in the Mg than in the placebo group as measured by auditory brainstem response audiometry, distortion product otoacoustic emissions and compound action potentials (CAPs) 1 week after exposure. This also applies to the damage to hair cell stereocilia tested with scanning electron microscopy. There were frequency-related differences in the individual functional responses. The CAP threshold shifts reflected the morphological damage most obviously.

Behavioural and Electroacoustic Calibration of Air-conducted Click and Toneburst Auditory Brainstem Response Stimuli

Although auditory brainstem response (ABR) audiometry is widely used to assess hearing sensitivity in infants and young children, normal calibration values vary across clinics. This study was undertaken to determine normal hearing thresholds for tonebursts and clicks with insert earphones. Techniques for performing electroacoustic and behavioural calibration of brief ABR stimuli are described. The average insert earphone thresholds for 25 young adults with normal hearing for 500, 1000, 2000, 4000 and 8000 Hz, 2-1-2 cycle tonebursts presented at 41 per second were: 24, 20, 23, 23 and 34 dB peak to peak equivalent (ppe) SPL (re 20 Pa), respectively. Average thresholds were about 30 dB ppeSPL for 100 s clicks. Results were generally consistent with normative values reported in the literature.