"Linear" and "derived" otoacoustic emissions in newborns: a comparative study.

OBJECTIVE: To investigate the effects of a specific aspect of the acquisition procedure, the averaging technique, on the evaluation of click-evoked otoacoustic emissions (CEOAEs) in newborns. DESIGN: CEOAEs were recorded by an Otodynamic ILO88 system from 89 full-term newborns at the third day after delivery. For each ear and in the same test session, CEOAEs were evoked by 75 to 85 dB pSPL acoustic clicks and averaged according to two different modes: the "linear" (classic average) and the "derived" mode, which allows the cancellation of linear behaving components (such as acoustic artifacts). All examined ears had a normal auditory function as assessed by conventional ABR between the ages of 2 and 4 mo. CEOAEs obtained by both averaging techniques were compared on the basis of several quantitative parameters: the waveform similarity; the levels of signal and noise and the inter-test reproducibility of the broadband response and of four different frequency bands centered at 1.6, 2.4, 3.2, and 4 kHz; the amplitude as a function of time; the test time. To eliminate the contribution of the stimulus artifact, linear CEOAEs were windowed 6 to 20 msec, whereas derived emissions were windowed using the default ILO88 window (2.5 to 20 msec). Additionally, CEOAEs were classified as "pass" or "fail" accordingly to screening criteria used in the daily clinical practice. RESULTS: Linear and derived emissions had very similar wave shapes and no time shifts during the first 12.5 msec. On the contrary, clear differences in the waveforms and time shifts were observed at longer latencies. The use of both averaging techniques resulted in identical CEOAE levels for both the broadband response and for the first two tested frequencies. For the last two frequencies, emission levels were lower when averaged with the linear technique owing to the use of the time window 6 to 20 msec, which reduces the amplitudes of high-frequency components. The residual noise in derived traces is 6 dB higher than that from linear traces. Also, derived CEOAEs had a lower inter-test reproducibility in both the broadband compound emission and in the four frequency bands examined here. The greatest difference in reproducibility was observed at the lowest band (1.2 to 2 kHz). Scoring of emissions was influenced by the averaging technique: 14% CEOAEs obtained with linear averaging and scored as passes were classified as fails when averaged with the derived mode. Moreover, if a CEOAE was scored as pass when using the derived technique, it also was scored as pass when using linear averaging. The increased number of false positives most likely was due to the higher noise floor/lower signal to noise ratio (SNR) of CEOAEs obtained with the derived technique. CONCLUSIONS: In the tested newborns and at the levels of stimulation used in this study, the emissions obtained with the derived technique were noisier than those obtained with the linear technique, this being intrinsically due to the type of averaging. Therefore, screening criteria based on the evaluation of the SNR (or similar parameters) could be influenced by the type of averaging used during the acquisition.

[Evaluation of hearing by studying acoustic distortion products in noise-induced hearing loss]. / Prévision de l'audition par les produits de distorsions chez les sourds par le bruit.

In this work, the Authors want to verify the possibility of an objective method of cochlear function evaluation in subjects affected by chronic acoustic trauma, through the study of the acoustic distortion products. Undertaking 46 subjects, the researchers have demonstrated a direct correlation between the tonal acoustic threshold and that of the distortion products. This method was able to show the useful indications of an objective evaluation of acoustic capacity in non collaborating subject. Because of the large variability of intensity of the distortion products and their absence when the acoustic threshold is more than 50-60 dB HL, they by themselves, don't permit exact evaluation of the tonal threshold for a given frequency.

[Otoacoustic distortion products in infants and adults: a comparative study]. / I prodotti di distorsione otoacustici nel neonato e nell'adulto: analisi comparativa.

Distortion Products (DP) are otoacoustic emissions evoked by emitting two pure tones. The principle advantage of this method vs. transient evoked otoacoustic emissions is the specificness of frequency. The purpose of the present work was to determine whether this technique could be applied in objective study of cochlear function in infants. This was done by setting standard data for infants and comparing them with the data obtained in a control population of adults. The input/output functions of the DP and the DP audiograms for 8 f2 frequencies ranging from 696 to 6006 Hz were studied in a group of 15 healthy, full-term infants. The data obtained were statistically compared to the data taken from a control group of 8 normal hearing adults. The infants showed significantly more intense DPs in the intermediate frequencies, with a greater detection threshold and dynamic range. On the other hand, at the high frequencies the amplitude of infant DPs was the same or lower than (f2 = 5005) those found in the adults. These differences can partially be attributed to the fact that the outer auditory channel is smaller in infants thus the probe and the middle ear are better matched. There is significantly greater background noise in infant DPs, particularly at low frequencies. This may be due to the fact that the skin of the outer auditory duct--which acts as a low-pass filter allowing suction and movement of the cervical muscles to contaminate the tracing--is thinner in infants. In conclusion, the study of DPs has shown its potential in the study of cochlear function in infants because it is non invasive and objective, it can be performed quickly and shows frequency specificness. Unfortunately, it cannot be considered a valid method for determining cochlear function at the low frequencies.

[Results and considerations regarding auditory neonatal screening based on the use of transient evoked otoacoustic emission]. / Risultati e considerazioni a proposito di uno screening audiologico neonatale basato sull'impiego delle otoemissioni acustiche evocate transienti.

The authors present a 5-year clinical experience in audiological screening performed at the neonatal center of the Policlinico of Perugia, Italy. The study was performed using an IL088 Otodynamics unit produced by Bray & Kemp. A total of 1328 newborns (2656 ears) were tested on the 4th day of life and during spontaneous sleep. None of the children had any audiological risk factors. The test was repeated one month later for all subjects who lacked Transient Evoked Otoacoustic Emissions and in many cases ABR testing was performed by 3 months of age. The authors present the undoubted advantages of the present method which include the fact that it is a) easy to perform, b) non invasive, c) sensitive and d) effective. They then discuss the main problems which arose during the course of the screening and advance some solutions. For the most part these problems involved the high number of false positives (13.1%) and the high percentage of subjects who were lost to subsequent controls (approximately 6% of the total population). The number of false positives could be reduced by using a linear acoustic stimulation (rather than the non-linear stimulation which is the default parameter for the machine). Such a linear stimulation can improve the signal-to-noise ratio, thus making it possible to adopt a reproducibility index lower than the 70% presently used (however, this brings with it the risk of including a certain number of false negatives). Finally, they discuss the possibility of only retesting those subjects with bilateral lack of TEOAEs, thus reducing the number of check-ups to be performed a month later.

[Evoked otoacoustic emissions using clicks in detection of deafness in young children]. / Les oto-émissions acoustiques provoquées (OEAP) par des transitoires dans le dépistage de la surdité du jeune enfant.

Click-evoked otoacoustic emissions (EOAEs) are sounds emitted by the cochlea due to active outer hair cell contraction following stimulation of the stereocilia. The purpose of this study was to evaluate the use of testing for EOAEs as a valid auditory screening method in newborns, and 1074 healthy fullterm babies (2148 ears) with an Apgar score higher than 8 at birth were examined. EOAEs were elicited 4 days after birth and a correlation index higher than 70% represented normal response criteria. If there was no response, EOAEs and brainstem response potentials were tested at the age of one month. On the fourth day after birth. EOAEs specificity and efficiency were found to be 92.3% and 92.4% respectively, while sensitivity was 100%. Specificity and efficiency at one month were rated at 100%. The use of EOAEs offers numerous advantages over traditional auditory screening methods, thus suggesting that this technique is suitable for the mass-screening of infants.

[Products of acoustic distortion in the examination of deafness in an infant]. / Les produits de distorsion acoustique dans le dépistage de la surdité du jeune enfant.

Distortion-product otoacoustic emissions (DPOAEs) are otoacoustic emissions evoked by two pure tones. The greatest advantage of DPOAEs is their frequency specificity with respect to the eliciting bitonal stimuli. The purpose of this study was to compare DPOAEs in two populations. This paper reports input/output DPOAEs functions and DPOAE-audiograms for audiometric frequencies of f2 between 696 and 6006 Hz in a normal neonate population and in an adult control group. Fifteen healthy fullterm newborns (29 ears) and 8 normal-hearing adults (16 ears) participated as subjects. Results at medium frequencies indicate that the maximum amplitudes of the DPOAEs were generated by neonates, the detection threshold was better and the dynamic range was greater than in adults, making them potentially valid for studying cochlear functioning in infants.

[Otoacoustic distortion products in adults with normal hearing]. / I prodotti di distorsione otoacustici nei soggetti adulti normoacusici.

Distortion Product Otoacoustic Emissions (DPOEs) are otoacoustic emissions evoked by two pure equilevel tones (f1, f2) called primaries and are believed to provide frequency-specific information regarding cochlear function. We recorded DPOEs at 2f1-f2 frequency with a constant frequency ration (f2/f1 = 1.22) in 8 normal hearing subjects (16 ears, mean age 28 +/- 1.5) to establish the characteristics of these emissions in the adult population. DPOEs were measured at the following F2 frequencies and respective fp geometric mean frequencies: 696/632, 1001/904, 1501/1360, 2002/1809, 3003/2714, 4004/3626, 5005/4531 e 6006/5435 Hz. Detailed testing included the recording of DPOE "audiograms" and input-output functions depicting the relationship of the amplitudes of DPOE to primary-tone levels ranging from 25 to 70 dB SPL in 5 dB steps. The present findings are in good agreement with investigations based on evoked otoacoustic emissions published by other researchers. The average DPOE "audiograms" demonstrated a low-frequency maximum at 1501 Hz (f2)/1360 (fp) and a high-frequency peak at 5005 Hz (f2)/4531 (fp). The two maximum regions were separated by a minimum around 3003 Hz (f2)/2714 (fp). This study confirms the feasibility of DPOE measurements among adults and provide a normal baseline for this age group. DPOEs could be useful, in association with evoked otoacoustic emissions and with auditory brainstem responses, in obtaining a precise evaluation of the peripheral auditory system.

[Short-term reproducibility of acoustic oto-emissions induced by clicks in adults]. / Reproductibilité à court terme des oto-émissions acoustiques provoquées par des clics chez des sujets adultes.

Otoacoustic emissions (OAE) are sounds emitted by the cochlea and recordable in the external ear canal by a miniature microphone. The OAE reflect the existence of an active mechanism within the cochlea. Development of the OAE has spurred much interest because they may used as a valid test for screening and monitoring cochlear changes. The OAE were recorded in 8 normal hearing subjects (15 ears) during nine test sessions under similar conditions. The aim of this work was to study the short-term variability in the amplitude of the emissions. Results of the study indicate that response levels are stable over time in the same ear therefore changes in the response level can be associated with changes in the cochlea.

[Evoked oto-acoustic potentials in the first 60 hours of life]. / Les otoémissions acoustiques évoquées pendant les 60 premières heures de vie.

In order to verify how age influences in the first days of life the presence of Evoked Otoacoustic Emissions (EOAE), the authors tested 52 newborns. They conclude that EOAE is a reliable technique as an early detection test of hearing loss in children. However, a high percentage of false positive cases during the very first days of life advises against its too early utilization.

[Evoked oto-acoustic emissions (EOE) as screening method in infants]. / Die evozierten otoakustischen Emissionen (EOE) als pädaudiologische Screeningmethode.

The authors consider the problems of the early diagnosis of paediatric hypoacusis, presenting a study done on twenty audiological high risk children that were subjected to audiometric screening by delayed cochlear otoacoustic emissions (EOE) and brainstem auditory evoked potentials (BEAPs). Eighteen of twenty children that were examined were normal, while two had bilateral sensorineural hearing loss. EOE were evoked in all patients that presented normal BAEP thresholds, while they were absent in deaf subjects. Evoked otoacoustic emissions research allows us to identify two groups of subjects: those with normal EOE who can be considered normal hearing subjects, and those without EOE who may present a disturbed auditory system. Nevertheless, EOE testing does not allow us to judge the type of hearing loss. The time for EOE testing is approximately five minutes for each subject. On the grounds of their experience, the authors conclude that EOE testing represents a useful and reliable test which differentiates normal auditory function subjects from hypoacoustic ones. Compared to other techniques used in audiological paediatric diagnosis, such as reactometry, BOEL test and Crib. O. Gram, which present the possibility of false positive and false negative results, and BSERA, which even if reliable, must be limited to few selected audiological high-risk subjects, EOE is easy to implement and readily available. Major limitations of this technique seem to be the possibility of false positives, and the impossibility to specify localisation and type of the hearing loss by EOE only.