Identification of neonatal hearing impairment: Ear-canal measurements of acoustic admittance and reflectance in neonates

Objectives: 1) To describe broad bandwidth measurements of acoustic admitta nce (Y) and energy reflectance (R) in the ear canals of neonates. 2) To des cribe a means for evaluating when a YR response is valid. 3) To describe th e relations between these YR measurements and age, gender, left/right ear, and selected risk factors. Design: YR responses were obtained at four test sites in well babies withou t risk indicators, well babies with at least one risk indicator, and gradua tes of neonatal intensive care units. YR responses were measured using a ch irp stimulus at moderate levels over a frequency range from 250 to 8000 Hz. The system was calibrated based on measurements in a set of cylindrical tu bes. The probe assembly was inserted in the ear canal of the neonate, and c ustomized software was used for data acquisition. Results: YR responses were measured in over 4000 ears, and half of the resp onses were used in exploratory data analyses. The particular YR variables c hosen for analysis were energy reflectance, equivalent volume and acoustic conductance. Based on the view that unduly large negative equivalent volume s at low frequencies were physically impossible, it was concluded that appr oximately 13% of the YR responses showed evidence of improper probe seal in the ear canal. To test how these outliers influenced the overall pattern o f YR responses, analyses were conducted both on the full data set (N = 2081 ) and the data set excluding outliers (N = 1825). The YR responses averaged over frequency varied with conceptional age (conception to date of test), gender, left/right ear, and selected risk factors; in all cases, significan t effects were observed more frequently in the data set excluding outliers. After excluding outliers and controlling for conceptional age effects, the dichotomous risk factors accounting for the greatest variance in the YR re sponses were, in rank, order, cleft lip and palate, aminoglycoside therapy, low birth weight, history of ventilation, and low APGAR scores. In separat e analyses, YR responses varied in the first few days after birth. An analy sis showed that the use of a YR test criterion to assess the quality of pro be seal may help control the false-positive rate in evoked otoacoustic emis sion testing. Conclusions: This is the first report of wideband YR responses in neonates. Data were acquired in; a few seconds, but the responses are highly sensiti ve to whether the probe is fully sealed in the ear canal. A real-time acous tic test of probe fit is proposed to better address the probe seal problem. The YR responses provide information on middle-ear status that varies over the neonatal age range and that is sensitive to the presence or absence of risk factors, ear, and gender differences. Thus, a YR test may have potent ial for use in neonatal screening tests for hearing loss.