Otoacoustic emissions in newborns evoked by 0.5kHz tone bursts.

BACKGROUND: Otoacoustic emissions (OAEs) are currently widely used in newborn hearing screening programs. OAEs evoked by transients (TEOAEs) in newborns are usually characterized by large response levels at higher frequencies but lower frequencies are affected by physiological noise. The purpose of the present study was to acquire responses at lower frequencies by measuring OAEs evoked by 0.5kHz tone bursts (TBOAEs).

METHODS: Otoacoustic emissions (OAEs) were recorded from 49 newborns. Measurements were made using the ILO 292 equipment from Otodynamics. In each ear, three measurements were made: first with a standard click stimulus at 80dB pSPL (CEOAEs), a second using a 0.5kHz tone burst at 80dB pSPL (TBOAEs), and a third recording of spontaneous OAEs (SOAEs). Global and half-octave-band values of OAE signal-to-noise ratio (SNR) and response level were used to assess statistical differences between CEOAEs and 0.5kHz TBOAEs. Additionally, time-frequency (TF) analysis of signals was performed using the matching pursuit method.

RESULTS: Global levels were highest for CEOAEs. However, at low frequencies (0.7-1kHz), 0.5kHz TBOAEs had significantly higher levels and SNRs than CEOAEs. At these frequencies, SNRs of CEOAEs were usually below 0dB. At 0.5kHz there were no statistically significant differences between CEOAEs and TBOAEs. In ears with recordable SOAEs, CEOAEs and TBOAEs had higher levels and SNRs than in ears without SOAEs.

CONCLUSIONS: Use of 0.5kHz TBOAEs may be a useful addition to standard CEOAE tests in newborns. They provide information about lower frequencies, a region where CEOAEs are usually prone to noise. The presence of SOAEs affects the magnitudes of both CEOAEs and TBOAEs.