Aspects of spontaneous otoacoustic emissions in healthy newborns

Abstract

Spontaneous otoacoustic emissions (SOAEs) are pure-tone like signals, spontaneously present in the ear canal. In normal adult ears the prevalence of SOAEs is reported to be 30–70%, probably depending on the noise floor of the recordings. In infant studies, results on the SOAE prevalence are rare. SOAEs as well as evoked otoacoustic emissions (EOAEs) were recorded in healthy newborns. Their ages varied between 1 and 10 days. The recordings were done with commercially available equipment in a separate not sound treated room of the obstetric department. The prevalence of SOAEs was 78%, which is higher than previously reported for adults as well as healthy newborns. The prevalence was not significantly different between left and right ears, or genders. The number of emissions per emitting ear amounted on average 5.5. The median number of SOAEs in boys (3.3) is significantly lower than in girls (4.6). The SOAE levels were between — 2 and 42 dB SPL. The mean level per emitting ear was 8.0 dB SPL and not significantly different between right and left ears or genders. However, the level of the strongest emission per emitting ear was significantly higher for right than for left ears. In contrast with adults most of the emissions (70%) are at frequencies above 2 kHz. Comparing the levels of the EOAEs between ears with and without SOAEs we found a statistically significant higher EOAE level in ears with SOAEs. This supports our previous hypothesis that the higher EOAE level found in healthy newborns is partly due to the more frequent presence of stronger SOAEs in healthy newborns. Given these results in newborns and in view of the literature, we hypothesize that major developmental changes in the OAE phenomenon occur between 0 and 6 years of age.