Although the suppressive effect of the medial olivocochlear system (MOCS) on peripheral auditory active mechanisms is well documented in humans, the effect of efferent inhibition over prolonged periods of acoustic stimulation is less well documented, especially as observed in suppression of transient evoked otoacoustic emissions (TEOAE’s). The present study therefore evaluated the relationship between the duration of contralateral acoustic stimulation and the suppression of TEOAE’s in ten adults with normal hearing. TEOAE recordings with linear clicks (60 dB sound pressure level) were measured at four intervals during 15 minutes of continuous contralateral white noise (45 dB sound pressure level), followed by two post-noise recordings. An identical within-subject control condition was recorded without contralateral noise. Experimental and control measurements were repeated three times, on separate days. Results revealed significant and sustained TEOAE amplitude reduction for the entire duration of contralateral stimulation. Suppression increased across the duration of contralateral noise, but not sufficiently to be statistically significant. After noise termination, TEOAE amplitudes increased to values significantly above control recordings. The sustained suppression of TEOAE’s indicates continuous efferent inhibition over time in normal adults, with a significant increase in TEOAE amplitude after noise cessation possibly indicating increased outer hair cell responsiveness after prolonged contralateral noise. / Dissertation (MCommunication Pathology)--University of Pretoria, 2009. / Speech-Language Pathology and Audiology / Unrestricted

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Made available in DSpace on 2016-04-27T18:12:05Z (GMT). No. of bitstreams: 1 Raquel Alves Nobre.pdf: 1069573 bytes, checksum: b8d1295a1b5de37c7e8a3aac4652d769 (MD5) Previous issue date: 2014-09-16 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The Universal Newborn Hearing Screening (UNSH) aims to provide early diagnosis in newborns. The procedure uses objective measures such as the Transient Evoked Otoacustic Emissions (TEOAEs) and the Auditory Brainstem Response (ABR). Different stages and protocols are broadly used in TANU, and that may change the values of passes and fails of each program. Purpose: To study the rate of passes and fails in the protocols and stages that are used at TANU, which were performed using electroacoustic (TEOAEs) and electrophysiological (ABR) procedures through an integrative review. Methods: Type of study: An integrative review. Search strategy: The following databases were examined: PubMed, SciELO and SCOPUS.Criteria for selecting the readings: Articles that have evaluated at least a minimum of 1,000 newborns; specifying the time (hours of life of the newborn) in which the test was accomplished; articles specifying how many days later the retest was performed after the hospital discharge, if the infant failed the test; in the article´s methodology the tests that were used and its stages must be included. The method of choice should be: TEOAEs test and retest in newborns with no risk; TEOAEs in conjunction with ABR and ABR in the retest in newborns with no risk and ABR on the test and retest in newborns with a risk factor; the results should present the pass and fail results of each step, such as the diagnosis result. Results: A total of 3950 references were found in English, Portuguese and Spanish. After removing duplicated studies (300), 3650 references were obtained, that were analyzed through titles and summaries. Of this total, 3500 were excluded for being researches with different topics. Hereby, 15 filled all the inclusion criteria. The final rates of pass and fail found in the studied protocols were the following: for the TEOAEs test/retest protocol the pass rate varied from 99,53% to 97,39% and the fail rate from 2,41% to 0,44%. In the TEOAEs and ABR test protocol and in the ABR retest the pass results ranged from 99,84% to 98% and fail from 0,35% to 0,16%. And in the ABR test/retest protocol in newborns with risk factors the pass rate was reached from 98,62% to 92,74% and the fail rate from 1,7% to 1,38%. All the pass and fail rates are within of what is recommended by literature. Conclusion: The protocol that presented the smaller number of false positives was the TEOAEs combined with the ABR in the test and ABR in retest. The findings indicate that the probability of fail for the TEOAEs in the test and retest is larger than the TEOAEs and ABR in the test and ABR in retest, both for the newborns screened until 24 hours of life and for the newborns screened between 25 and 72 hours of life / A Triagem Auditiva Neonatal Universal (TANU) tem como objetivo realizar o diagnóstico precoce em neonatos. A sua realização utiliza medidas, como as emissões otoacústicas evocadas por estímulo transiente (EOAET) e o potencial evocado auditivo de tronco encefálico (PEATE). Diferentes etapas e protocolos são utilizados na TANU, o que pode alterar os índices de passa e falha de cada programa. Objetivo: Estudar os resultados de índice de passa-falha dos protocolos e etapas utilizados na TANU, realizada com procedimentos eletroacústicos (EOAET) e eletrofisiolóficos (PEATE) por meio de uma revisão integrativa. Método: Tipo de estudo: Revisão integrativa Estratégia de busca: Foram pesquisadas as seguintes bases de dados: PUBMED, SCieLO e SCOPUS. Critério para a seleção dos estudos: artigos que avaliaram um número mínimo de 1000 neonatos; artigos que especificaram as horas de vida do neonato em que foi realizado o teste; artigos que especificaram quantos dias depois da alta hospitalar foi realizado o reteste, caso o neonato falhasse no teste; no método, deveriam constar quais os testes utilizados e suas etapas. Neste caso, os testes utilizados deveriam ser: EOAET no teste e no reteste em neonatos sem risco; EOAET combinado com PEATE no teste e PEATE no reteste em neonatos sem risco e PEATE no teste e no reteste em neonatos com risco; os estudos deveriam apresentar o resultado de passa e falha de cada etapa, assim como o resultado do diagnóstico. Resultados: Foi identificado um total de 3950 referências no idioma inglês, português e espanhol. Após a remoção dos estudos duplicados (300), foram obtidas 3650 referências, que foram analisadas por meio dos títulos e dos resumos. Deste total, 3500 foram excluídos por se tratarem de pesquisas com outro tema. Desta forma, 150 estudos foram selecionados, na íntegra. Deste total, 15 preencheram todos os critérios de inclusão. Os índices de passa e falha final encontrados nos protocolos estudados foi de: para o protocolo EOAET no teste e reteste, o índice de passa variou de 99,53 a 97,39% e falha de 2,41% a 0,44%. No protocolo de EOAET combinado com PEATE no teste, e PEATE no reteste foi de passa em 99,84% a 98%, e falha de 0,35% a 0,16%. No protocolo PEATE no teste e reteste em neonatos com risco o índice de passa foi de 98,62% e 92,74% e falha de 1,7% e 1,38%. Todos os índices de passa e falha estão dentro do que é recomendado pela literatura. Conclusão: O protocolo que apresentou menor número de falso-positivo foi o EOAET combinado com PEATE no teste, e PEATE no reteste. Os resultados mostram que a probabilidade de falha para protocolo- EOAET no teste e reteste é maior do que para o protocolo- EOAET combinado com PEATE no teste, e PEATE no reteste, tanto para o neonatos triados até 24 horas de vida, quanto para o grupo de neonatos triados entre 25 e 72 horas

Noise exposure is one of the most prevalent causes of irreversible occupational disease in Sweden and in many other countries. In hearing conservation programs, aimed at preventing noise-induced hearing loss, audiometry is an important instrument to highlight the risks and to assess the effectiveness of the program. A hazardous working environment and persons affected by it can be identified by monitoring the hearing thresholds of individual employees or groups of employees over time. However, in order to evaluate the prevalence of occupational noise-induced hearing loss, relevant reference data of unexposed subjects is needed. The first part of this dissertation concerns the changes in hearing thresholds over three decades in two occupational environments with high noise levels in the province of Östergötland, Sweden: the mechanical and the wood processing industries. The results show a positive trend, with improving median hearing thresholds from the 1970s into the 1990s. However, the hearing loss present also in the best period, during the 1990s, was probably greater than if the occupational noise exposure had not occurred. This study made clear the need for a valid reference data base, representing the statistical distribution of hearing threshold levels in a population not exposed to occupational noise but otherwise comparable to the group under study. In the second part of the dissertation, reference data for hearing threshold levels in women and men aged from 20 to 79 years are presented, based on measurements of 603 randomly selected individuals in Östergötland. A mathematical model is introduced, based on the hyperbolic tangent function, describing the hearing threshold levels as functions of age. The results show an age-related gender difference, with poorer hearing for men in age groups above 50 years. The prevalence of different degree of hearing loss and tinnitus is described for the same population in the third part of the dissertation. The overall prevalence of mild, moderate, severe or profound hearing loss was 20.9% collectively for women and 25.0% collectively for men. Tinnitus was reported by 8.9% of the women and 17.6% of the men. Approximately 2.4% of the subjects under study had been provided with hearing aids. However, about 7.7% were estimated to potentially benefit from hearing aids as estimated from their degree of hearing loss. Noise-induced hearing loss primarily causes damage to the outer hair cells of the inner ear. The fourth and last part of the dissertation evaluates the outer hair cell function, using otoacoustic emission measurements (OAE). Prevalence results from three different measuring techniques are presented: spontaneous otoacoustic emissions (SOAE), transient evoked otoacoustic emissions (TEOAE) and distortion product otoacoustic emissions (DPOAE). Gender and age effects on the recorded emission levels were also investigated. Women showed higher emission levels compared to men and for both women and men the emission levels decreased with increasing age. The results from the OAE recordings were shown to be somewhat affected by the state of the middle ear. The study included tympanometry, and the relation of the outcome ofthis test to the otoacoustic emissions is described, where high middle ear compliance resulted in low emission level. Reference data for the tympanometric measurements are also presented. The results of this project form an essential part of the important work against noiseinduced hearing loss, which needs continuous monitoring. The reference data presented here will provide a valid and reliable data base for the future assessment of hearing tests performed by occupational health centres in Sweden. This data base will in turn prove useful for comparison studies for Sweden as a responsible fellow EU member country setting high standards for work force safety. The statistical distribution of hearing threshold levels as a function of age for men and women in tabulated form is available on the Swedish Work Environment Authority (Arbetsmiljöverket) web site: http://www.av.se/publikationer/bocker/fysiskt/h293.shtm.

Le système auditif possède deux particularités. En périphérie, les mécanismes cochléaires actifs (MCA), sous-tendus par la motilité des cellules ciliées externes (CCE), interviennent dans la sensibilité auditive et la sélectivité fréquentielle. Sur le versant central, le système efférent olivocochléaire médian (SEOCM), qui se projette sur les CCE et module les MCA, améliore la perception auditive en milieu bruité. Sur le plan exploratoire, ces deux processus peuvent être évalués grâce aux otoémissions acoustiques provoquées (OEAP) et leur suppression controlatérale. Par ailleurs, des résultats expérimentaux chez l’animal ont montré l’existence d’un rétrocontrôle exercé par le système auditif corticofuge descendant (SACD) sur la cochlée, via le SEOCM.Le présent travail comporte trois études réalisées chez l’humain, visant à explorer les interactions entre SACD, SEOCM et MCA. Les études 1 et 2, utilisant une méthodologie innovante chez des patients épileptiques réalisant une stéréo-électroencéphalographie, ont révélé un effet atténuateur différentiel de la stimulation électrique intracérébrale sur l’amplitude des OEAP, en fonction des modalités de stimulation, ainsi qu’une variabilité de cet effet selon les caractéristiques de l’épilepsie. L’étude 3 a montré un renforcement bilatéral de l’activité du SEOCM chez des musiciens professionnels.Pris dans leur ensemble, ces résultats fournissent d’une part, des arguments directs et indirects en faveur de l’existence d’un SACD fonctionnel chez l’humain. D’autre part, des phénomènes de plasticité à long terme, pathologique ou supranormale, seraient susceptibles de modifier l’activité de cette voie cortico-olivocochléaire. / The auditory system has two special features. At peripheral level, active cochlear micromechanisms (ACM), underlain by motility of outer hair cells (OHC), are involved in auditory sensitivity and frequency selectivity. At central level, the medial olivocochlear efferent system (MOCES), which directly projects onto OHC to modulate ACM, improves auditory perception in noise. From an exploratory point of view, both processes can be assessed through transient evoked otoacoustic emissions (TEOAE) and the procedure of contralateral suppression. In addition, experimental data in animals have disclosed a top-down control exerted by corticofugal descending auditory system (CDAS) on cochlea, via MOCES.The present work comprises three studies carried out in human, aiming to investigate interactions between CDAS, MOCES and ACM. The first and second studies, based on an innovative experimental procedure in epileptic patients undergoing presurgical stereoelectroencephalography, have revealed a differential attenuation effect of intracerebral electrical stimulation on TEOAE amplitude depending on stimulation modalities, as well as a variability of this effect depending on the clinical history of epilepsy. The third study has shown a bilateral enhancement of MOCES activity in professional musicians.Taking together, these results provide direct and indirect evidence for the existence of a functional CDAS in humans. Moreover, possible long-term plasticity phenomenon, either pathological –as in epileptic patients– or supernormal –as in professional musicians– may change cortico-olivocochlear activity.