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Previous studies have shown that supplemental magnesium administered prior to exposure to noise has an alleviating effect on temporary threshold shift (TTS). These studies have only used audiometric thresholds to demonstrate changes in the auditory system. However, to help determine the effects on outer hair cells (OHCs), a more sensitive measure should be used. The purpose of this study was to determine if supplemental magnesium administration prior to noise exposure has a beneficial effect on acoustic overexposure using a double-blind research design. This was determined by measuring distortion product otoacoustic emissions (DPOAEs) to determine any changes in cochlear OHC function. DPOAE amplitude and signal-to-noise ratio (SNR) measurements were analyzed for two groups of twenty participants (an experimental group and a control group). The experimental group received 150 mg of magnesium gluconate one hour prior to noise exposure. The control group received a placebo pill that was identical in appearance to the magnesium pill. Following noise exposure, the greatest changes in DPOAE amplitude and SNR occurred for the frequencies that were one-half to one octave above the frequency of the stimuli used. The greatest changes in DPOAE measurements were present immediately post TTS-inducing stimulus, with only slight changes present after 30 minutes and no difference between 30 minutes and 60 minutes post-exposure. These results were the same for both groups. It was concluded that this dosage of supplemental magnesium had no apparent protective effect on DPOAEs following intense noise exposure.

This study aimed to investigate the effectiveness of the Quiet earplug noise protectors worn by a group of South African industrial workers exposed to excessive noise in the workplace. This was achieved by investigating the prevalence and amplitudes of distortion product otoacoustic emissions (DPOAEs), as they have been found to be sensitive to the effects of noise on the cochlea (Vinck, Van Cauwenberge, Leroy,&Corthals, 1999, p. 52). DPOAEs were recorded before and after noise exposure and were compared in order to determine whether the earplugs are providing sufficient protection against cochlear damage. DPOAEs were recorded using a test protocol where the primaries are fixed at L1 = 60dB SPL and L2 = 35dB SPL (L1 - L2 = 25dB) with an f2/f1 ratio of 1.18. The f2 frequencies were selected to correspond closely to the audiometric test frequencies of 2000Hz, 3000Hz, 4000Hz, 6000Hz and 8000Hz. The study found the prevalence of DPOAEs to be statistically stable and repeatable. This was true for DPOAEs measured successively during the same test sitting, as well as comparing prevalence determined before and after exposure to eight hours of noise. DPOAE prevalence alone was therefore not found to be a good indication of the temporary threshold shift (TTS) associated with the effects of noise on the cochlea. However, a significant finding of the study was that normal DPOAEs were recorded in only six right ears (24%) and seven left ears (28%) before noise exposure, even though all the subjects presented with hearing thresholds better than 25dB SPL. This may mean that cochlear pathology is already evident in some of the subjects tested. Further results of the study showed DPOAE amplitudes to be sensitive to the negative effects of excessive noise, as there was a significant difference between DPOAE amplitudes measured before and after the noise exposure. DPOAE amplitudes, specifically in the frequencies that are known to be affected by noise such as 4000Hz and 6000Hz, measured after the work-shift were significantly smaller than those measured before exposure to noise. Although correct usage of the earplugs could not be controlled for the duration of the noise exposure, each subject was instructed on the correct usage of the hearing protection before entering the noise zone. Bearing this limitation of the study in mind, because DPOAE amplitudes were reduced the implication is that the Quiet earplugs are not providing sufficient protection against the harmful effects of noise. / Dissertation (M (Communication Pathology))--University of Pretoria, 2005. / Speech-Language Pathology and Audiology / Unrestricted

In the evaluation of special populations, such as neonates, infants and malingerers, audiologist often have to rely heavily on objective measurements to assess hearing ability. Current objective audiological procedures such as tympanometry, the acoustic reflex, auditory brainstem response and transient evoked otoacoustic emissions, however, have certain limitations, contributing to the need of an objective, non¬invasive, rapid, economic test of hearing that evaluate hearing ability in a wide range of frequencies. The purpose of this study was to investigate distortion product otoacoustic emissions (DPOAEs) as an objective test of hearing. The main aim was to attempt to predict hearing ability at 500 Hz, 1000 Hz, 2000 Hz and 4000 Hz with DPOAEs and artificial neural networks (ANNs) in normal and hearing-impaired ears. Other studies that attempted to predict hearing ability with DPOAEs and conventional statistical methods were only able to distinguish between normal and impaired hearing. Back propagation neural networks were trained with the pattern of all present and absent DPOAE responses of 11 DPOAE frequencies of eight DP Grams and pure tone thresholds at 500 Hz, 1000 Hz, 2000 Hz and 4000 Hz. The neural network used the learned correlation between these two data sets to predict hearing ability at 500 Hz, 1000 Hz, 2000 Hz and 4000 Hz. Hearing ability was not predicted as a decibel value, but into one of several categories spanning 10-15dB. Results indicated that prediction accuracy of normal hearing was 92% at 500 Hz, 87% at 1000 Hz, 84% at 2000 Hz and 91% at 4000 Hz. The prediction of hearing-impaired categories was less satisfactory, due to insufficient data for the ANNs to train on. The variables age and gender were included in some of the neural network runs to determine their effect on the distortion product. Gender had only a minor positive effect on prediction accuracy, but age affected prediction accuracy considerably in a positive way. The effect of the amount of data that the neural network had to train on was also investigated. A prediction versus ear count correlation strongly suggested that the inaccurate predictions of hearing-impaired categories is not a result of an inability of DPOAEs to predict pure tone thresholds in hearing impaired ears, but a result of insufficient data for the neural network to train on. This research concluded that DPOAEs and ANNs can be used to accurately predict hearing ability within 10dB in normal and hearing-impaired ears from 500 Hz to 4000 Hz for hearing losses of up to 65dB HL. / Dissertation (MCommunication Pathology)--University of Pretoria, 2009. / Speech-Language Pathology and Audiology / unrestricted

Made available in DSpace on 2016-04-27T18:11:46Z (GMT). No. of bitstreams: 1 VanessaSinelliPinto.pdf: 2216187 bytes, checksum: a967a05c6a769a97c9e8960060d16e6c (MD5) Previous issue date: 2005-08-23 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Introduction The distortion product otoacoustic emission has been used because its specific features evaluate high frequencies and can identify hearing losses in initials stages. It is an important tool to neonatal hearing screening and test battery that includes audiologic assessment in infants. Therefore, there is a necessity to set up parameters to analyse DPOAE records in infants in order to be used as clinic criterion in audiologic assessment. Objective To describe the findings of DPOAE records in infants from birth to two months old, through analysis of response level, the noise level and the signal to noise ratio in all frequencies; the analysis of response level according to variables: age in days, gender, timpanometry pression peak, infant state during test and distribution of percentile from the response level. Methodology 138 infants were evaluated, being all full term, without risk indicators to hearing loss and who passed in hearing screening. The parameters used in this record were: L1= 65 dBSPL and L2= 50 dBSPL in equipment ILO292 Otodynamic. Results 70 male infants and 68 female infants were evaluated, with ages between 6 to 65 days. The medians from DPOAE level were: 6,7 dBSPL to f2 1001 Hz; 11,5 dBSPL to f2 1257 Hz; 14,2 dBSPL to f2 1587 Hz; 14,2 dBSPL to f2 2002 Hz; 13,7 dBSPL to f2 2515 Hz; 13,7 dBSPL to f2 3174 Hz; 15,5 dBSPL to f2 4004 Hz; 16,3 dBSPL to f2 5042 Hz e 6,0 dBSPL to f2 6348 Hz. The medians from the noise level were: 4,9 dBSPL to f2 1001 Hz; 5,9 dBSPL to f2 1257 Hz; 6,0 dBSPL to f2 1587 Hz; -2,1 dBSPL to f2 2002 Hz; -12,5 dBSPL to f2 2515 Hz; -5,6 dBSPL to f2 3174 Hz; -8,9 dBSPL to f2 4004 Hz; -9,5 dBSPL to f2 5042 Hz e -4,4 dBSPL to f2 6348 Hz. The medians from the signal to noise ratio were: 1,5 dBSPL to f2 1001 Hz; 5,4 dBSPL to f2 1257 Hz; 7,7 dBSPL to f2 1587 Hz; 16,4 dBSPL to f2 2002 Hz; 18,9 dBSPL to f2 2515 Hz; 19,3 dBSPL to para f2 3174 Hz; 24,2 dBSPL to f2 4004 Hz; 25,5 dBSPL to f2 5042 Hz e 10,5 dBSPL to f2 6348 Hz. Conclusions There was a tendency to decrease from the response level around 30 days of life, being more evident in 2002 Hz frequency (f2). The timpanometry pression peak defined by three groups (among -50 and +50 daPa; <-50 daPa and >+50 daPa) showed no influence on records from the response level. There was no statistically significant difference between genders and between ears to the response level. The baby state (light sleep, deep sleep and alert) had influence on signal to noise ratio in deep sleep state. The findings of percentile were similar to the ones found in the literature, therefore for clinical interpretation, the percentile 5 can suggest hearing loss and the percentile 95 can suggest a normal hearing, so the results of the two percentiles, a place uncertainty refering to hearing losses / Introdução A emissão otoacústica-produto de distorção tem sido utilizada devido às suas características específicas de avaliar bandas de freqüências altas e de detectar perdas auditivas em estágios iniciais, sendo essencial na triagem auditiva neonatal e na bateria de testes que envolvem a avaliação audiológica infantil. Portanto, há uma necessidade de se estabelecer parâmetros para análise do registro das EOAPD em lactentes, com a finalidade de utilizá-los como critério clínico na avaliação audiológica. Objetivo Descrever os achados do registro das emissões otoacústicas-produto de distorção em lactentes de até dois meses de idade por meio da análise do nível de resposta, do nível de ruído e da relação sinal/ruído em todas as bandas de freqüências; da análise do nível de resposta em relação às variáveis: dias de vida, gênero, pico de pressão na timpanometria e estado do lactente durante o exame e da distribuição do percentil do nível de resposta. Metodologia Foram avaliados 138 lactentes, todos nascidos a termo, sem indicadores de risco para perda auditiva e que passaram na triagem auditiva. Os parâmetros utilizados para este registro foram: L1= 65 dBNPS e L2= 50 dBNPS no equipamento ILO292 Otodynamic. Resultados Foram avaliados 70 lactentes do gênero masculino e 68 do feminino, com idade variando de 6 a 65 dias de vida. As medianas do nível de resposta das EOAPD para cada freqüência (f2) foram de: 6,7 dBNPS para 1001 Hz; 11,5 dBNPS para 1257 Hz; 14,2 dBNPS para 1587 Hz; 14,2 dBNPS para 2002 Hz; 13,7 dBNPS para 2515 Hz; 13,7 dBNPS para 3174 Hz; 15,5 dBNPS para 4004 Hz; 16,3 dBNPS para 5042 Hz e 6,0 dBNPS para 6348 Hz. As medianas do nível de ruído para cada freqüência (f2) foram de: 4,9 dBNPS para 1001 Hz; 5,9 dBNPS para 1257 Hz; 6,0 dBNPS para 1587 Hz; -2,1 dBNPS para 2002 Hz; -12,5 dBNPS para 2515 Hz; -5,6 dBNPS para 3174 Hz; -8,9 dBNPS para 4004 Hz; -9,5 dBNPS para 5042 Hz e -4,4 dBNPS para 6348 Hz. As medianas da relação sinal/ruído para cada freqüência (f2) foram de: 1,5 dBNPS para 1001 Hz; 5,4 dBNPS para 1257 Hz; 7,7 dBNPS para 1587 Hz; 16,4 dBNPS para 2002 Hz; 18,9 dBNPS para 2515 Hz; 19,3 dBNPS para 3174 Hz; 24,2 dBNPS para 4004 Hz; 25,5 dBNPS para 5042 Hz e 10,5 dBNPS para 6348 Hz. Conclusões Houve uma tendência de diminuição do nível de resposta a partir dos 30 dias de vida. O pico de pressão na timpanometria definido por três grupos (entre -50 e +50 daPa; <-50 daPa e >+50 daPa) não influenciou no registro do nível de resposta. Não houve diferença estatisticamente significante entre gêneros e entre orelhas para o nível de resposta. O estado do lactente influenciou na relação sinal/ruído, sendo a melhor relação sinal/ruído no estado sono profundo. Os achados do percentil foram semelhantes aos encontrados na literatura. Portanto, para uma interpretação clínica, o percentil 5 pode sugerir perda auditiva e o percentil 95 pode sugerir audição dentro da normalidade, sendo os resultados entre esses dois percentis uma região de incerteza quanto às perdas auditivas

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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.

Intratympanic injection of various otoprotectants through the round window membrane (RWM) might become available in the near future as an alternative to the currently available medical and surgical methods used to treat several inner ear diseases. The most common outcome of such diseases is sensorineural hearing loss (SNHL). Two examples of  these otoprotectants are Edaravone and Brain-Derived Neurotrophic Factor (BDNF), both of which have already proved effective against  noise-induced hair cell loss, barotrauma  and ototoxicity caused by cisplatin. In four different studies we used two electrophysiological methods, auditory brainstem response (ABR) and distortion product otoacoustic emission (DPOAE), to study the effects of tobramycin and Pseudomonas aeruginosa exotoxin A (PaExoA) on the inner ears of 129 male Sprague-Dawley rats. In two investigations, not only the otoprotective effects of Edaravone on tobramycin-induced ABR threshold shifts and PaExoA-induced DPOAE  threshold changes, were studied but even different application times, in order to establish in which interval it was still possible to achieve effective otoprotection.We found that Edaravone gave otoprotection from tobramycin when injected simultaneously or within 7 days, but it had only a limited effect on the changes in DPOAE thresholds caused by PaExoA when injected 1, 2, or 4 hours after the exotoxin. The effect of BDNF on PaExoA-induced ABR threshold shifts was investigated in two studies, where different doses of intratympanically injected PaExoA were used and where BDNF was applied simultaneously, 12 or 72 hours efter exotoxin instillation. We found that BDNF had an otoprotective effect on SNHL induced by different doses PaExoA when injected simultaneously or with no more than 12 hours delay.

The study investigated the feasibility of including DPOAEs in the annual medical surveillance test battery for the identification of NIHL in a group of employees in a manufacturing industry in KwaZulu-Natal. Feasibility was investigated by exploring the sensitivity, specificity and predictive efficiency of DPOAEs, the ability of DPOAEs to detect subtle noise-induced cochlea changes, the test-retest reliability of DPOAEs and lastly, the duration of time taken to conduct the DPOAE test bilaterally. A cross-sectional and repeated measures within-in participant design was utilized in the study. A purposive convenience sampling technique was used, as well as a stratified sampling approach in order to realize objective two of the study. The study consisted of 60 participants, which were further stratified into four test groups, i.e. Group A: 0-3 years, Group B: 3.1-6 years and Group C: 6.1-9 years and Group D: 9.1-13 years of working within the beverage manufacturing industry. A high sensitivity and negative predictive value was reported in the current study, suggesting that DPOAEs may be able to identify those who present with subtle cochlea changes as a result of exposure to occupational noise. The sensitivity of DPOAEs was 100% at 1, 2, 4, 6 and 8kHz in the right ear and at 4 and 6kHz in the left ear. The specificity of DPOAEs in the current study ranged between 55%-97% across the frequency range in the right ear and 49%-88% in the left ear. A negative predictive value of 100% was obtained bilaterally across the frequency range, except at 8kHz in the left ear. Visual inspection of the DPgram in the current study revealed a bilateral reduction in DPOAE amplitudes for all test groups in the high frequency region of the DP-Gram, namely, 5477Hz and 7303Hz, in the absence of a statistically significant difference (p>0.05). A greater frequency range appears to be affected in this group of workers, indicating that the type of noise, namely, impulse noise, may result in cochlea changes. Corresponding changes on the pure tone audiogram were not observed, however, noise notch configurations were observed for the groups with a longer history of noise exposure. This was not seen bilaterally as is typically expected with NIHL. Good test-retest reliability across the frequency range obtained in the current study further indicates the feasibility of including DPOAEs in the annual medical surveillance test battery. Additionally, the current study calculated an average of 86 seconds (1 minute 26 seconds) to conduct the DPOAE test bilaterally, confirming that DPOAEs are a quick test to administer. The findings of this study suggest that DPOAEs may be used to monitor early subtle noise-induced cochlea changes for workers exposed to noise in the beverage manufacturing industry as part of the annual medical surveillance test battery. / Thesis (M.Comm.Path.)-University of KwaZulu-Natal, Westville, 2013.

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