[Clinical application of distortion products of otoacoustic emissions in presbycusis].

BACKGROUND

DPOAE are still undergoing evaluation for clinical use. The aim of the present study is to assess DPOAE in a clinical setting in order to examine the response of 15 normally hearing adults and to compare the results with those of 15 people with presbycusic ears of known sensorineural high-frequency hearing loss.

METHODS

For realizing DPOAE input-output (I/O) functions, the two primary stimuli were presented at intensities of the same level ranging from 20 to 71 dB SPL. The geometric mean of primaries represented auditory frequencies varying between 1.0 and 8.0 kHz.

RESULTS

We found two clearly separated portions in I/O functions of normally hearing ears. The first portion, in response to primary intensities of 60 dB SPL and below, showed saturation behavior. If primary intensities exceeded 60 dB SPL, I/O functions became more linear. In presbycusic ears, the loss of a saturation portion in response to stimulus levels below 60 dB SPL shows two particularities: Firstly, the linearity in I/O functions, as a response to geometric mean value of primaries with elevated audiometric threshold (above 1.5 kHz), could be explained by lesions in the active properties of the outer hair cells, revealing the cochlear nature of presbycusis. Secondly, the additional loss of a saturation portion in frequencies with normally pure-tone audiometric threshold (up to and including 1.5 kHz) could be interpreted as a result of onset of injury in the active micromechanics of the cochlea--just before its clinical manifestation.

CONCLUSIONS

DPOAE growth functions may reveal discrete pathological alterations both in the active cochlear signal processing and in the passive mechanisms of the presbycusic cochlea prior to their detection by clinical audiometric tests.