Evoked Acoustic Emissions from the Human Ear IV.Final Results in 100 Neonates

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Abstract
Evoked acoustic emissions were recorded from both ears in a series of 100 consecutive normal newborns. We used the same stimulus, a 2-kHz click, and recording technique as previously described. Analysis of the data showed that evoked emissions could be identified in all ears, except one at 70 dBaud (i.e. approximately 30 dB nHL). No significant differences could be demonstrated between males and females or between left and right ears with regard to the latency of the emissions, the peak-to-peak amplitude, the main frequency component, or the waveform correlation between the two 70 dBaud recordings in each ear. However, a significant correlation between left and right ears was found for the amplitude and frequency of the emissions. Practical and methodological problems related to the recording were elucidated. The tail of the stimulus artifact sometimes interfered with the first part of the emissions even though the recordings were made in a time window delayed 5 ms relative to the stimulus onset. We tried to solve this artifact problem by different off-line techniques, but found no useful solution. We therefore continued to use only a cosine tapering of the first 2 ms of the time window. Three different ways of determining latencies were evaluated and we found that the ‘envelope’ technique was the most simple and reliable. Recording of evoked acoustic emissions is a quick and non-invasive method and provided that the presence of the emissions is related to normal cochlear function, it can be used as a screening test in newborns. In the well-baby nursery, middle ear problems are uncommon, and otoscopy and tympanometry may therefore be superfluous as a check of middle ear normality before the emissions are recorded. However, in the neonatal intensive care unit, middle ear disorders have to be ruled out first.

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