Low-Intensity Distortion Product Otoacoustic Emission Protocols in Infants and Young Children: Contributions of Age-Specific Ear Characteristics.

Abstract

Purpose: Despite almost complete cochlear maturity at birth, distortion product otoacoustic emission (DPOAE) levels in neonates and infants are typically higher than those measured in older children and adults, depending on the type and frequency stimulus, which suggests functional immaturity of the cochlea as well as the role of the outer and/or middle ear. This study aimed to investigate the relationship between outer and middle ear characteristics, using wideband tympanometry (WBT), and DPOAEs and to evaluate the applicability of normative criteria at reduced stimulus intensities in children aged between 6 days and 5 years.

Method: A total of 109 ears from 60 participants were examined and categorized into three age groups: newborns, infants (6-8 months), and children (3-5 years). The following measurements were analyzed: ear canal volume, compensated acoustic admittance (with 1-kHz probe tone and 226-Hz probe tone), acoustic absorbance, and DPOAEs with two stimulus intensity protocols (L₁-L₂ = 65-55 and 55-45 dB SPL). Statistical analyses included nonparametric tests and correlation models.

Results: WBT measures reflect the age-related maturation of the conductive pathway. Absorbance, DPOAE response levels, and signal-to-noise ratios (SNRs) were higher in neonates and 6- to 8-month-olds than in the 3- to 5-year group, especially at high frequencies. Lower stimulus levels (L₁-L₂ = 55-45 dB SPL) led to reduced DPOAE amplitudes and increased rates of absent responses across all groups, although the SNR remained above 6 dB in most ears.

Conclusions: The findings suggest that the structural characteristics of the outer and middle ears alter both the forward and reverse sound transmission properties, impacting DPOAE detectability. Reducing stimulus intensities affected DPOAE measures differently across age groups; however, the use of age-specific normative data may improve the accuracy of result interpretation.