Changes in 2f₁-f₂ distortion product otoacoustic emission detection thresholds in human neonates

Abstract

Evoked otoacoustic emissions (EOAEs) are widely used as a neonatal hearing-screening tool. During the first postnatal days, marked changes in the characteristics of EOAEs have been reported in human neonates. These changes have been mainly attributed to changes in middle-ear pressure and external ear-canal obstruction. The aim of the study was to examine changes in 2f [Formula: See Text]-f [Formula: See Text] distortion product otoacoustic emission (DPOAE) detection thresholds in healthy term newborns over the first three postnatal days and to determine the contributing factors. One hundred and forty newborns without any known risk indicator for permanent childhood hearing impairment were tested daily over the first three postnatal days. 2f [Formula: See Text]-f [Formula: See Text] DPOAE input-output (I-O) functions were registered at f [Formula: See Text] = 2.0 kHz and f [Formula: See Text] = 4.0 kHz with a fixed f [Formula: See Text]/f [Formula: See Text] ratio of 1.2. L[Formula: See Text] was descended by 5 dB steps from 70 to 35 dB SPL and L[Formula: See Text]-L[Formula: See Text] was 10 dB. In total, 264 ears tested 226-Hz probe tone tympanometry was performed and the degree of external ear canal obstruction was obtained. Ipsilateral stapedial reflexes were registered in 147 ears; 678-Hz probe tone tympanometry was carried out in 107 ears and 1000-Hz probe tone tympanometry in 40 ears. The results showed that the degree of external ear canal obstruction decreased each day. The degree of external ear canal obstruction proved a statistically significant factor which determined whether or not an ear showed DPOAEs on day 1, but not on subsequent days. All middle ear values showed a trend to improve over the first three days of life. Regardless of the frequency of the probe tone, the presence of a normal tympanogram correlated significantly with the presence of DPOAEs on day 1. On day 1 the presence of a stapedial reflex was significantly associated with the presence of DPOAEs. Depending on the method of middle-ear assessment, 45-57% of the ears that did not demonstrate DPOAEs on day 1 had normal middle ear values and clear external ear canals on day 1. These ears developed DPOAEs by day 3 without any statistically significant changes either in the external or middle ear system. It was concluded that there is a significant improvement in the DPOAE detection thresholds over the first three days of life. Changes in the outer- and middle-ear status contribute to the improvement of DPOAE detection thresholds during the first postnatal days. However, the results from the present study support the hypothesis that there may be other mechanisms independent of the external and middle ear that play an equally important role.

• distortion product otoacoustic emissions
• external ear canal
• middle ear
• neonates