Latencies of the 2f1-f2 distortion product otoacoustic emissions measured using a phase-gradient method in young people, in the elderly and in people exposed to noise.

Distortion product otoacoustic emissions (DPOAE) are generally accepted as a good tool for investigating the micromechanics of the cochlea. The 2f1-f2 DPOAE latencies provide significant data regarding travelling waves. In this study the 2f1-f2 DPOAE latencies were measured using a phase-gradient method, with a swept-f2 procedure, for three groups: Group I comprised 60 healthy young people, aged 17-32 years; Group II comprised elderly patients, aged 56-72 years, with presbyacusis; and Group III consisted of 74 miners, aged 19-35 years, who had been exposed to noise for 2-15 years. Measurements were performed for frequencies between 1.0 and 6.0 kHz. In all groups the latencies were fitted using a non-linear regression model. The aim of the study was to compare the latency and amplitude of 2f1-f2 DPOAE in different inner ear pathologies. The highest DPOAE amplitudes were recorded in Group I and in miners with 2-4 years noise exposure (Group IIIa), and the latencies showed a similar pattern. The lowest DPOAE amplitudes were recorded in the elderly and in miners with 8-15 years noise exposure (Group IIIc), but in contrast the longest latencies were measured in miners and the shortest in the elderly. The latency analysis significantly reinforces opinions on the micromechanics of the cochlea, mostly in terms of the cochlear functioning as a filter and amplifier and with regard to the elasticity of the basilar membrane.