[Clinical use of transitory otoacoustic evoked emissions in therapeutic follow-up].
The suitability of transiently evoked otoacoustic emissions (TEOAE) for the observation of changes in inner ear function was examined in 28 normal hearing subjects and 25 patients with sudden deafness. The measurements were performed with the ILO88 system using a nonlinear sequence of click stimuli. The TEOAEs of both ears of each control subject were measured in 7 sessions at 4 different stimulus levels. The evaluation involved visual inspection of the time-dependent records and an analysis of response amplitudes and cross correlational coefficients. Minor changes in curve appearance and variations of the response level in the order of +/- 4 dB could be detected which were attributed to the noise floor and variations in probe application. Within the patient group, at least three TEOAE measurements were performed during the course of rheologic therapy. Pure-tone audiograms were recorded prior to each TEOAE session for comparison. The most significant result from the data analysis is that response amplitudes increase significantly in almost all cases in which pure-tone audiometry reveals normalization of hearing threshold. This indicates a recovery of outer hair cells. Furthermore, comparison of TEOAE records obtained in different sessions shows an initial growth of correlation coefficients followed by a final saturation. These findings indicate that the combination of amplitude evaluation and correlation analysis is suitable for observing changes in intensity and waveform of cochlear emissions.