Effect of Age on Distortion Product Otoacoustic Emissions at Extended High Frequencies

The inner ear is most susceptible to the aging effects. Distortion product otoacoustic emissions (DPOAEs) are a good indicator for interpreting the age effects but are usually recorded at up to 8000 Hz frequencies in routine audiologic testing. The present study was designed to assess and compare the DPOAEs at conventional frequencies and at extended high frequencies (EHFs) across different age groups. Extended high-frequency audiometry (9000-16000 Hz) and DPOAEs from 500-16000 Hz were recorded on 80 adult (160 ears) participants (15-55 years) with normal hearing sensitivity. The participants were categorized into 4 groups: group I (15-<25 years), group II (25-<35 years), group III (35-<45 years), and group IV (45-55 years). A statistically significant reduction in EHF thresholds was observed from group III onward. However, the thresholds were comparatively better for group III at frequencies 9000, 10000, and 11500Hz than group IV. No significant difference was observed for EHF DPOAEs in groups I and II (except at 16000 Hz) and III and IV. Distortion product otoacoustic emissions at conventional frequencies in group IV were significantly poorer than the other 3 groups. A weak negative correlation was observed between the DPOAE parameters and EHF thresholds. The effect of age was more pronounced on EHF DPOAEs than EHF thresholds for frequencies 9000, 10000, and 11500 Hz. Distortion product otoacoustic emissions at EHF started deteriorating below the age of 30 years and showed a rapid decline above 35 years. Extended high-frequency DPOAEs can be used as screening tools to assess the function of the basal part of the cochlea.