Abstract
Distortion-product otoacoustic emissions (DPOAEs) elicited with high-frequency (HF; up to 16 kHz) stimuli are measurable and repeatable in normal-hearing adults and children, adult patients, and are sensitive to ototoxic insults in adults. However, objective tests for monitoring basal cochlear function in those too young to respond subjectively need to be developed. DPOAE levels recorded at frequencies <10 kHz are well characterized, but DPOAE levels measured up to 16 kHz do not exist for newborns. The goal of the current study is to determine if HF DPOAEs are measurable and repeatable in newborns. DPOAEs were measured from 2–16 kHz (f2/f1 of 1.22; L1/L2 = 65/55 dB SPL) using two different calibration methods (forward pressure level—FPL and in-the-ear—SPL) in 26 newborns. To assess repeatability, the probe was removed then re-inserted for a second round of testing. Results indicate that HF DPOAEs can be evoked and are repeatable in newborns and the use of FPL calibration shows promise for measuring HF responses and maximizing repeatability. To be implemented in monitoring programs where the highest frequencies with responses are continuously tested, stimulus parameters used to evoke newborn HF DPOAEs and calibration methods need further exploration.
Highlights
Otoacoustic emissions (OAEs) are low-level sounds generated by the active processes of the cochlea, namely outer hair cells (OHCs)
While Distortion-product otoacoustic emissions (DPOAEs) repeatability is similar between Forward pressure level (FPL) and sound pressure level (SPL) calibration methods, the results are promising for improved results with FPL
Deeper probe tip insertions resulted in a greater number of DPOAEs recorded in newborns, regardless of the calibration method used
Summary
Otoacoustic emissions (OAEs) are low-level sounds generated by the active processes of the cochlea, namely outer hair cells (OHCs). Distortion-product otoacoustic emissions (DPOAEs) are generated by presenting two closely spaced pure-tones simultaneously in the ear canal. The intermodulation distortion generated by the two pure tones at the level of the basilar membrane generates several new acoustic frequency components, the largest being 2f1 –f2 in humans [1,2]. To generate DPOAEs, the higher frequency evoking stimulus tone, f2 , and the lower frequency stimulus tone, f1 , must sufficiently overlap along the basilar membrane. This relationship of the evoking stimuli is dictated by the frequency ratio (f2 /f1 ).
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