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

Abstract

Introduction The inner ear is most susceptible to the ageing effects. The anatomical changes like loss of sensory hair cells, loss of spiral ganglion cells and atrophy of stria vascularis lead to changes in cochlear functions and cause age-related hearing loss. 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 audiometric testing. OAEs are proven more sensitive to cochlear insults than pure tone audiometry. The origin of both DPOAEs at EHF and conventional frequencies is via a similar biological mechanism in the inner ear. Aim of the study The present study aimed to see the effect of age on the DPOAEs at conventional extended high frequencies. Objectives This study assesses and compares the DPOAEs parameters at conventional frequencies to the DPOAEs parameters at extended high frequencies across different age groups and evaluates the association between the extended high-frequency thresholds and DPOAEs at conventional and extended high frequencies across different age groups. Materials and Methods Extended high-frequencies Audiometry (9000-16000 Hz) and DPOAEs from 500-16000 Hz were recorded on eighty adult (160 ears) participants with normal hearing sensitivity. The participants were 15-55 years old, with an equal number of males and females. The participants were further categorised into four groups to see the age-related changes: Group I (15 – <25 years), Group II (25-<35 years), Group III (35-<45 years) and Group IV (45-55 years). Results The results showed a significant difference between the four groups for extended high-frequency thresholds and DPOAEs parameters (amplitude and SNR) at conventional and EHF (p <0.05). A statistically significant reduction in EHF thresholds was observed in group II than I at 16000 Hz frequencies. The decline was observed from group III onwards and became poorer in group IV for EHF thresholds. However, the thresholds were comparatively better for group III at frequencies 9000,1000 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. Group IV (45-55 years) was significantly different from the other three groups for conventional frequencies. A weak negative correlation was observed between the DPOAE parameters and EHF thresholds. Conclusions This study suggests an effect of age on EHF DPOAEs before the EHF thresholds for frequencies 9000, 10000 and 11500 Hz. The EHF thresholds and DPOAEs start deteriorating from below 30 years onwards, with a rapid decline above 35 years. EHF DPOAEs can be used in clinics to identify early ageing signs and as a screening tool, as it is less time-consuming.