Electrical Brainstem Response Research Articles

Clinical characteristics, recurrent etiological analysis of recurrent purulent meningitis in children and its treatment strategy

Objective To investigate the clinical characteristics and causes of recurrent purulent meningitis and its treatment. Methods The clinical data of 36 children with recurrent purulent meningitis were analyzed retrospectively at Tianjin Children′s Hospital from 1995 to 2014.Based on the underlying illness, the following examinations were done respectively: brainstem electric response audi-ometry(BERA), temporal bone computed tomography, head magnetic resonance imaging(MRI), spinal core MRI, and blood immunoglobulin, etc. Results There were 24 boys and 12 girls involved in this study.The age of the initial onset in these patients ranged from 20 months old to 15 years old, with the average age of 5 year and 9 months old.There were 2 to 7 episodes in these cases.The etiology was identified: 19 cases (52.78%) with congenital anatomical abnormalities, 12 cases of congenital inner ear malformation with cerebrospinal fluid(CSF) leakage, 1 case of ear-nose CSF leakage, 6 cases of pilonidal sinus.Fifteen cases (41.67%) had anatomical abnormalities, 12 cases had head and facial trauma, 1 case had nasal polyps surgery, 1 case (2.77%) had a history of chronic mastoiditis, and 1 case had a history of cochlear implant surgery; 1 case of congenital humoral immunodeficiency disease X-linked agammaglobulinemia-free; 1 case (2.77%) had humoral immunodeficiency disease.The anti-infection treatment was adopted in the acute-phase and then CSF rhinorrhea repair, CSF otorrhea, cerebrospinal fluid leakage, repair of the inner ear, pilonidal sinus resection, supplementary intravenous immunoglobulin around once every 3 months was given respectively in the restoration-phase.Thirty-three cases revealed no recurrence up to 8 months till 10 years follow-up, 3 cases lost-to-follow-up. Conclusions The recurrent purulent meningitis is a serious infectious disease of the central nervous system, which may result in disabled condition even life-threatening.In order to avoid purulent meningitis recurrence, the corresponding treatment should be chosen according to different causes. Key words: Purulent meningitis; Recurrent; Etiology; Remedies; Child

Use of auditory evoked potentials in screening children for integrity of auditory pathways

Background: Auditory evoked potentials (AEP) can be used to assess the integrity of auditory pathway for early hearing loss and planning rehabilitative procedures. It is noninvasive and can be performed in uncooperative and difficult-to-test children under mild sedation. Aims and Objective: To determine the hearing threshold to assess the integrity of auditory pathway in children of suspected hearing loss and to find out the importance of AEP where other screening tests cannot be performed. Materials and Methods: This retrospective study was conducted in Acharya Vinoba Bhave Rural Hospital and Department of Physiology, Jawaharlal Nehru Medical College, Sawangi (Meghe), Wardha, Maharashtra, India. It included 80 children of suspected hearing loss in the age group of 1–12 years, referred under Sarva Shiksha Abhiyan program. Brainstem auditory responses were recorded in these children using multichannel polyrite system. Silver chloride disk electrodes were used on standard scalp locations. Results: Our results showed that 40 of 80 children were having definite mild-to-severe hearing loss. In nearly 50% children hearing loss was confirmed by AEP. In remaining 40 children, brainstem electric response audiometry showed normal responses indicating normal hearing. Of 80 suspected children, 20 were either uncooperative or not fit for any other screening tests for hearing. AEP showed that of these 20 children, 12 (15% of total), were having sensorineural loss that helped them in seeking treatment. Conclusion: Our results concluded that AEP at present is one of the most useful tools for assessment of integrity of auditory pathway and detection of early hearing loss, and it can greatly contribute in its management. It can definitely be used in screening for deafness and assessing the nature of hearing loss, particularly in patients who cannot perform in the usual audiometric procedures. It can also be used to assess the maturity of central nervous system in newborn and young children.

Improved outcomes in auditory brainstem implantation with the use of near-field electrical compound action potentials.

To compare the outcomes (auditory threshold and open-set speech perception at 48-month follow-up) of a new near-field monitoring procedure, electrical compound action potential, on positioning the auditory brainstem implant electrode array on the surface of the cochlear nuclei versus the traditional far-field electrical auditory brainstem response. Retrospective study. Tertiary referral center. Among the 202 patients with auditory brainstem implants fitted and monitored with electrical auditory brainstem response during implant fitting, 9 also underwent electrical compound action potential recording. These subjects were matched retrospectively with a control group of 9 patients in whom only the electrical auditory brainstem response was recorded. Electrical compound action potentials were obtained using a cotton-wick recording electrode located near the surface of the cochlear nuclei and on several cranial nerves. Significantly lower potential thresholds were observed with the recording electrode located on the cochlear nuclei surface compared with the electrical auditory brainstem response (104.4 ± 32.5 vs 158.9 ± 24.2, P = .0030). Electrical brainstem response and compound action potentials identified effects on the neighboring cranial nerves on 3.2 ± 2.4 and 7.8 ± 3.2 electrodes, respectively (P = .0034). Open-set speech perception outcomes at 48-month follow-up had improved significantly in the near- versus far-field recording groups (78.9% versus 56.7%; P = .0051). Electrical compound action potentials during auditory brainstem implantation significantly improved the definition of the potential threshold and the number of auditory and extra-auditory waves generated. It led to the best coupling between the electrode array and cochlear nuclei, significantly improving the overall open-set speech perception.

Zur Verlässlichkeit hirnstammaudiometrischer Hörschwellenbestimmungen

Brainstem electric response audiometries (BERA) are in clinical use for a number of years. The aim of our study was to evaluate data regarding the long-term reliability of BERA-determined frequency specific thresholds in hearing disabled children. In a group of 97 hearing disabled children we sought to compare Notched-Noise- (NN) BERA threshold as well as Click-BERA thresholds taken shortly after birth with behavioral audiometry thresholds determined after 3.2 years (mean). We found a significant correlation between both BERA methods and the behavioral tests. However, the correlation coefficients for NN-BERA were higher than for Click-BERA thresholds. Our results provide evidence for a high reliability of the NN-BERA for characterization of early onset hearing disabilities in children. Our data suggest that pathologic findings in the Click-BERA should always be followed by a frequency specific analysis with NN-BERA.

Hearing loss after noise exposure

The higher field strength magnetic resonance imaging (MRI) such as 3 Tesla (T) and above generates noise that has potential detrimental effects on the hearing. Temporary threshold shifts following MRI examination have been reported for MRI with lower field strength. Such effect, however, have not been reported so far for a 3T MRI. We report a case that exemplifies the possible detrimental effects of a 3 T MRI generated noise on the auditory system. Our patient underwent investigation of his chronic backache in a 3 T MRI unit and developed hearing loss and tinnitus post-MRI examination. Hearing assessment was done using pure tone audiogram, distortion product otoacoustic emission (DPOAE) and brainstem electrical response audiometry (BERA) which revealed a unilateral sensorineural hearing loss which recovered within 3 days. However the tinnitus persisted. This is possibly a case of temporary threshold shift following noise exposure. However a sudden sensorineural hearing loss remains the other possibility.

Auditory double click evoked potentials in multiple sclerosis

Brain stem electric responses (BSER), evoked by acoustic stimuli, were investigated in 29 patients with multiple sclerosis and compared with the responses in a control group of 26 young adults without neurological disease or hearing defect. The procedure included monaural and binaural stimulus presentation of single clicks and pairs of clicks. In the evaluations the vertex-positive Jewett I, III and V response components, and the vertex-negative "FFP7" peak were considered. In the assessment of the BSER components, the FFP7 (the vertex-negative 7 ms far field potential following the JewettV wave) proved to be the best single component with respect to reproducibility in normal subjects. In addition the FFP7 was the single most consistently abnormal component in the patient group. Determination of the latency of the Jewett components and the interpeak conduction times, however, contributed further to the disclosure of the abnormal cases. Five of the patients whose hearing was impaired were considered separately. Of the remaining 24 patients, 20 (83%) had BSER abnormalities. Further analysis did not reveal a clear correlation between BSER abnormalities and clinical signs of brain stem dysfunction.

High Incidence of GJB2 Mutations During Screening of Newborns for Hearing Loss in Austria

The aim of the present study was to evaluate gap junction protein beta2 (GJB2) genetic testing within a national neonate screening program for hearing loss (HL) in a European population. Neonatal cases of nonsyndromic HL (N = 21) were identified by postpartal otoacoustic emissions (OAE) and brain stem electric response audiometry (BERA) analysis. GJB2 testing was performed by direct sequencing. Mutations in GJB2 were found in 15 of 21 children (71.4%) identified by neonatal audiological screening. The 35delG mutation in GJB2 was found homozygous in 10 cases (47.6%) and also as a clear cause of HL as the heterozygous alterations 35delG/del311-324 and 35delG/L90P. In a single case, L90P/R143Q was also identified as a cause of HL. In 3 HL cases that were not identifiable during initial OAE testing, homozygous 35delG and 35delG/R184P defined the genetic basis for HL in 2 cases, whereas one case had wild-type GJB2. Our findings of the high mutation rate in the Austrian population, especially in neonates identified during the newborn screening program, confirm the importance of screening for mutations in GJB2.

Wirkung elektromagnetischer Felder des GSM-Mobilfunksystems auf auditives und vestibuläres Labyrinth und Hirnstamm

It is the subject of this study to investigate the biological effect of the HF radiation produced by the Global System for Mobile Communications-( GSM)-mobile phone on the inner ear with its sensors of the vestibular and auditive systems. Thermographic investigations made on various model materials and on the human temporal bone should show whether mobile phone does induce any increases of temperature which would lead to a relevant stimulus for the auditive and vestibular system or not. We carried out video-nystagmographic recordings of 13 subjects, brainstem electric response audiometry of 24 ears, and recordings of distorsion products of otoacoustic emissions of 20 ears. All tests were made with and without a mobile phone in use. The data was then analyzed for variation patterns in the functional parameters of the hearing and balance system that are subject to the (non)existence of electromagnetic radiation from the mobile phone. The thermographic investigations suggest that the mobile phone does not induce any increases of temperature which would lead to a relevant stimulus for the auditive and vestibular system. Video-nystagmographic recordings under field effect do not furnish any indication of vestibular reactions generated by field effects. Compared with the recording without field, the brainstem electric response audiometry under field effect did not reveal any changes of the parameters investigated, i. e. absolute latency of the peaks I, III, V and the interpeak latency between the peaks I and V. The distorsion products of otoacoustic emissions do not indicate, comparing the three measuring situations, i. e. before field effect, pulsed field and continuous field, any possible impacts of the HF field on the spectrum or levels of emissions for none of the probands. The investigations made show that the electromagnetic fields generated in using the mobile phone do not have an effect on the inner ear and auditive system to the colliculus inferior in the brainstem and on the vestibular receptors in the inner ear and the vestibular system.

Chromosom-1q-Syndrom und Innenohrschwerhörigkeit: ein ungewöhnlicher Fall

The interstitial deletion of chromosome 1q is a disease of rare incidence, which might be hereditary or caused by spontaneous changes within the chromosome respectively. The phenotype in most cases is based on the loss of macrochromosomal material within the long arm of chromosome 1. The characteristics of this syndrome include pre- and postnatal growth retardation, severe psychomotor retardation, microbrachycephaly, sparse fine scalp hair and eyebrows, deformity of skull with cleft of lips and palate, scoliosis, small hands and feet hernias, genital defects, clinodactyly of the fifth fingers and campylodactyly. Other morphological characteristics that have been reported are mainly kidney and cardiac abnormalities. The number of symptoms are related to the loss of genetic material. To our knowledge this is the first description of a patient with interstitial deletion of chromosome 1 (q23-q31). We report an eleven year old boy with interstitial deletion of chromosome 1(q23-q31). In addition to the known skeletal, orofacial disorders, hypothrophia and retardation we discovered a unilateral high-graded and contralateral middle-graded hearing loss. In infants with chromosome 1q syndrome adequate diagnostic procedures have to be employed to unveil sensineural hearing losses that might be overseen because of mental retardation. In particular a brainstem electric response audiometry should be considered for early diagnosis and treatment of a possible hearing-loss.

A pilot case control follow-up study on hearing in children treated with tobramycin in the newborn period

Objective: To assess the occurrence of hearing loss in children due to neonatal exposure to long courses of tobramycin and/or high tobramycin serum concentrations. Methods: This was a pilot case–control study in 3–4-year old children. Data on tobramycin administration were abstracted from the patient files of an earlier study. Patients exposed in the neonatal period to either long courses (>7 days) or high serum concentrations of tobramycin constituted the study group. The control group consisted of patients without tobramycin exposure. Patients were matched for other risk factor according to criteria of the joint committee on infant hearing. All patients underwent the following investigations: otoscopy and pneumatic otoscopy, followed by impedance audiometry, to exclude middle ear effusion. Click-evoked oto-acoustic emissions (ce-OAE) as well as distortion product oto-acoustic emissions (dp-OAE), tested at f2 frequencies ranging from 1 to 10 kHz, were measured to assess hearing. All patients with abnormal ce-OAE results underwent brainstem electric response audiometry (BERA) as well. Since aminoglycoside ototoxicity is usually bilateral, results were compared per patient and not per ear. Results: A total of 29 patients were tested. Eleven patients were excluded due to middle ear effusion. Data for 18 patients were analyzed. In the tobramycin treated group ( n=9) both ce-OAE and dp-OAE (at all tested frequencies) were not detectable in six ears of three patients. All other patients had normal ce-OAE's as well as normal dp-OAE's in this frequency range. Difference between the tobramycin treated and control group for OAE as well as dp-OAE showed a trend ( P=0.08). In all three patients with undetectable emissions BERA confirmed a cochlear loss of 60–70 dB at 3 kHz in both ears. These three patients had the longest total exposure to tobramycin: 20–24 days and 84–92 mg/kg, respectively. No relation to either peak or trough serum concentrations could be detected. Conclusion: There was no statistical relation between hearing loss and tobramycin exposure, probably due to sample size. Our results do indicate a need for a case–control follow-up study of hearing in neonates exposed to long courses of aminoglycosides.

Electrically Evoked Potentials Recorded in Adult and Pediatric Clarion® Implant Users

The purpose of this study was to record electrical auditory brain stem responses (EABRs) and electrical middle latency responses (EMLRs) in the clinic from 3 adult CLARION Multi-Strategy Cochlear Implant subjects and to record EABRs in the operating room from 3 pediatric subjects. For 2 of the 3 adult subjects, EABR thresholds were within the subject's behavioral dynamic range, whereas 1 adult subject's EABR thresholds were either absent or, when present, exceeded the upper limit of the dynamic range. For this subject, EMLRs were absent or of poor morphology for the channels tested. Moreover, this subject was not able to understand speech in an open-set, auditory-only format. The EABR thresholds obtained with children were within the behavioral dynamic range for 2 of the 3 subjects, but exceeded comfortable loudness levels for 1 subject. Although the EABR thresholds were measured at stimulus levels that were audible for all subjects, the relationship of the EABR threshold levels to behavioral measures of loudness varied. Evoked potentials that originate more centrally, such as the EMLR, should be investigated further to determine the possible relationship to postimplant performance.

Radiosurgery or microsurgery of vestibular schwannomas?

Microsurgical excision is the reference treatment of vestibular schwannomas. Yet, morbidity and functional risk of this surgery is significant, as Pellet et al have demonstrated in their study. In order to define the role of gamma knife surgery we have designed a prospective study concerning effectiveness and tolerance of this treatment. Between July 14, 1992 and August, 1997, 400 patients were included. All the treatments were carried out according to a homogeneous methodology, with multiisocentric planning. We use low marginal doses dependent mainly on the treatment volume: 14 Gy for small stade II tumors, 12 Gy or less for larger tumors and 16 Gy for intracanalicular tumors. The evaluation protocol included preoperative examination with clinical examination, House grading, Shirmer's test, tonal and vocal audiometry, brain stem electrical response audiometry (BERA), vestibular caloric and pendular tests, magnetic resonance imaging (MRI) or computerized tomography (CT) scan; control at 6 months, 1 year and 2 years with clinical examination, tonal audiometry and MRI and/or CT scan; at 3 years the preoperative examination was repeated and a questionnaire based on Pellet's concerning functional results was completed. Among the 400 treatments, 80% were first intended treatment of unilateral vestibular schwannoma. At the time of the analysis, 100 consecutive patients with unilateral schwannoma (treated in first intention) had a 3 year follow-up (results concerned these 100 patients). Average age was 61 years (17-82 years). According to Portmann's classification, five patients presented a stade 1 tumor, 60 a stade 2 tumor, 33 a stade 3, and two a stade 4 tumor. According to House's grading at preoperative examination, there was 86 (86%) grade 1 tumors, 12 grade 2, two grade 3, and at 3 year follow-up: 77 (94%) grade 1 and five grade 2 (17 patients had no House grading). At preoperative examination, three patients presented an hemispasm; at 3 years this had disappeared for all patients. Two others patients presented a transient hemispasm at 8 and 11 months, respectively. At preoperative examination, four patients presented with facial numbness and 14 with hypoesthesia. At 3 year follow-up, trigeminal function was normal for all patients but one, for whom this had only improved. Seven others patients presented a transient numbness or hypoesthesia. At preoperative examination, five patients presented hydrocephalus without cerebro spinal fluid (CSF) shunting. At 3 year follow-up, seven patients presented CSF shunting: three presented a preoperative hydrocephalus, three a hydrocephalus after treatment and one a hydrocephalus secondary to tumor growth. Average age for these six patients was 71 years. Audiological classification was based on Gardner-Robertson's. Seventy percent of patients with normal hearing maintained useful hearing, and 50% of patients with useful hearing maintained serviceable hearing. Three (3%) patients (two with stade 2 tumors and one with a stade 3) had microsurgical excision at 16, 35 and 36 months, respectively. During microsurgical excision no unusual difficulty was encountered. Seventeen questionnaires investigating functional outcome and quality of life were completed: 100% (63% in Pellet's study) of the patients answered they had no facial motion disturbance, 49% (17% in Pellet's study) had no ocular problems, 20% (in Pellet's study 55%) had subjective trigeminal problems, 8% (in Pellet's study 13%) had deglutition problems, none (16% in Pellet's study) had other eating problems, 91% (61% in Pellet's study) had no change in their life. Mean hospitalization stay was 3 days (for 23 days in Pellet's study). All the patients who worked, except one, had the same professional activity (66% in Pellet's study). Mean work cessation was 7 days (130 days in Pellet's study). (ABSTRACT TRUNCATED)

Differential effects of glucocorticoids on human auditory perception

It is assumed that glucocorticoids and mineralocorticoids, the hormones produced by the adrenal cortex, act as modulators of central nervous functions in addition to their well known role in endocrine stress responses. More specifically, it has been suggested that adrenal corticoids cause changes in sensory thresholds. In two double-blind crossover studies we evaluated auditory perception in healthy volunteers after treatment with hydrocortisone, dexamethasone, and the respective placebos. Stapedial reflexes, pure tone and speech audiograms, and brainstem electric response audiometry served as the dependent variables. As circadian changes in the density and occupancy of the brain corticosteroid receptors have been postulated, we performed Study I in the morning and Study II in the evening. Treatment effects clearly varied with time of day. A differential effect of the two corticoids occurred on contralateral stapedial reflexes. These results parallel results obtained with gustatory stimuli, and suggest that glucocorticoids modulate sensory perception across modalities.

Brain stem electric response audiometry in neonates with hyperbilirubinemia.

Auditory evoked responses using BERA were studied in 30 newborn babies with plasma bilirubin > or = 15 mgm/dl and repeated after treatment of neonatal jaundice with bilirubin levels of < or = 10 mgm/dl. A few jaundiced babies (16.5%) showed absent BERA response at the initial/subsequent examination. After treatment, 3/30 babies showed absent wave form responses and 2 of these were clinically kernicteric. Jaundiced babies had prolonged wave peak latencies and inter peak latencies. Treated babies showed a tendency towards recovery in their BERA responses which were however not complete. Total plasma bilirubin value at the time of BERA examination and mean maximal bilirubin values had no correlation with the incidence and degree of BERA abnormalities.

The masked threshold to noise ratio in brainstem electric response audiometry: assessment of the conductive loss component by bone-conducted masking.

The aim of this study was to assess the conductive loss component (CLC) by brainstem electric response audiometry. A bone-conducted noise was used to mask out the response to a conventional air-conducted click stimulus. The difference between the levels of the click and the noise is defined as the masked threshold to noise ratio (MTNR). This MTNR was determined for 21 normal ears (MTNR = -13 +/- 5 dB). The increase in MTNR compared to this normative value is a measure of the CLC. For 10 ears with an artificially induced purely conductive loss, the increase in MTNR is in good agreement with the results of conventional pure-tone and brainstem electric response audiometry.

Intraoperative monitoring by transtympanic electrocochleography and brainstem electrical response audiometry in acoustic neuroma surgery

The preservation of hearing is a major aim of contemporary temporal bone surgery. Our present findings demonstrate that intraoperative monitoring is a key method for attaining serviceable postoperative hearing after the removal of an acoustic neuroma. Both electrocochleography (ECoG) and brainstem electrical response audiometry were performed in 96 patients operated on for acoustic neuromas. The specificity of the different monitoring methods was affected by surgical manipulations in addition to such non-specific influences as CSF drainage, core body temperature and anesthesia. In the present study ECoG was found to be more reliable in assessing the intra- and postoperative course with respect to the preservation of cochlear function.

Prognostic Validity of Brainstem Electric Response Audiometry in Infants of a Neonatal Intensive Care Unit

This study compared the results of brainstem electric response audiometry (BERA) in infants of a neonatal intensive care unit to those obtained on the same children with pure-tone audiometry at 3 years of age. Six hundred children were initially tested in infancy, and complete follow-up information was obtained on 333. In 297 (89%) the BERA results accurately predicted the hearing status at the age of 3 years. Twenty-nine (9%) of the discrepancies were related to conductive hearing losses: 17 patients with a conductive hearing loss in the first few months of life had normal hearing at 3 years, and 12 patients normal in infancy had a conductive loss at 3 years. Two patients evaluated as a sensorineural hearing loss by BERA had normal hearing. These may have been due to a conductive loss. Six patients assessed as normal by BERA had significant hearing losses at the age of 3 years. Five of these had normal hearing at one frequency between 1,000 and 4,000 Hz. The sixth may have developed a sensorineural hearing loss after birth.

Evaluation of Electrocochleographic Audiogram Determination in Infants

An evaluation was made of results of electrocochleography (ECoG) in a group of 75 children, tested during the last four years in the ENT department of the Leiden University Hospital. Eleven years was taken as the upper age limit; 79% of our group were younger than three and a half years. In only 60% of the children the cause of the hearing loss was clarified. In this group maternal rubella followed by meningitis and retardation were the most frequent cases of deafness. Cochlear microphonics (CM) could be measured in all the children. Examples are given of cochlear responses of children belonging to 6 different threshold categories. The responses of the largest category (56 children) with the highest loss (larger than 80 dB) were very abnormal. For the categories with less hearing loss the ECoG was not restricted to threshold determination and the origin of the hearing loss could be demonstrated, while a contribution of conduction loss could be derived from a horizontal shift of the latency-intensity function to higher intensity levels. The potentialities and limitations of ECoG and brainstem electric response audiometry (BERA) for threshold determination are discussed, particularly against the background of the time consumption of both procedures and the invasive character of ECoG.

Acoustic Value of Brain-stem Audiometry in Infancy

At the 1989 meeting of the Triological Society in San Francisco, Calif, Drs Peter W. Alberti, Martyn L. Hyde, and Krista Riko, Toronto, Canada, presented a study regarding the validity of brain-stem audiometry in high-risk infants. The study group consisted of 731 high-risk infants comparing early brain-stem audiometry with results of later behavioral testing done at ages 3 to 5 years. Children were initially selected for evaluation from a high-risk registry and underwent brain-stem electric response audiometry at 3 to 4 months of age. Approximately 5% had moderate-to-severe hearing losses. The infants who had conductive losses due to middle ear effusion were excluded from the study. When a threshold for sensorineural loss of 40 dB or worse was utilized, brain-stem electric response audiometry was 94% sensitive, with a 96% specificity. For lesser degrees of hearing loss, the testing was considerably less sensitive, and the authors recommend that the 40-dB criterion

A prospective study of the application of click evoked oto-acoustic emissions and brainstem electric response audiometry to detect hearing impairment at birth : J.C. Stevens, H. Webb, J. Hutchinson a, J. Connell a, M.F. Smith b and J.T. Buffin a Department of Medical Physics and Clinical Engineering Royal Hallamshire Hospital, Sheffield, S10 2JF, aDeparment of Audiology, Sheffield Childrens Hospital and

A prospective study of the application of click evoked oto-acoustic emissions and brainstem electric response audiometry to detect hearing impairment at birth : J.C. Stevens, H. Webb, J. Hutchinson a, J. Connell a, M.F. Smith b and J.T. Buffin a Department of Medical Physics and Clinical Engineering Royal Hallamshire Hospital, Sheffield, S10 2JF, aDeparment of Audiology, Sheffield Childrens Hospital and