Otoacoustic Emissions III. Contralateral Acoustic Suppression of Otoacoustic Emissions
J. Valvoda; T. Haas *; J. Popelář **
Klinika ORL a chirurgie hlavy a krku FN Motol a 1. LF UK, Praha, katedra otorinolaryngologie IVPZ, Praha, vedoucí prof. MUDr. J. Betka, DrSc. III. interní klinika VFN, Praha, vedoucí prof. MUDr. J. Marek, DrSc. *Ústav experimentální medicíny AV ČR, Praha,
Otorinolaryng. a Foniat. /Prague/, , 1998, No. 4, pp. 185-192.
The phenomenon of the contra lateral acoustic suppression of otoacoustic emissions is at presently accepted generally as an objective phenomenon and is ascribed in particular to the activation of the efferent part of the acoustic pathway. Its clinical application is intensely investi- gated. It involves in particular diagnosis of disorders of the efferent olivocochlear system in retrocochlear lesions. The authors decided to conduct tests of contralateral suppression of EOAE a group of otologically normal subjects. The aim was to assess reference values of the test before its application in clinical audiometry. For contralateral stimulation wide-band noise of intensity of 76.5 dB SPL for TEOAE were recorded and 76.5 and 66.5 resp. dB SPL for DPOAE. TEOAE were recorded in a non-linear stimulation mode. Normal values of DPOAE suppression were assessed only for the stimulation mode L1 = 65, L2 = 55 dB SPL. Reduction of the amplitude of TEOAE occurred in all 26 examined probands in both ears. The mean value of suppression of the TEOAE amplitude (response dB) was 1.5 ± 1.1 (0.2 - 4.1) dB on the right and 1.6 ± 1.0 (0.3 - 3.9) dB on the left. No statistically significant differences were revealed between suppression values on the left and right ear, in men and women nor a relationship with the suppression (dB reduction of amplitudes) with the amplitude (dB response) of TEOAE. Reduction of the DPOAE amplitude occurs mainly at low frequencies, at levels above 4 kHz the suppression values are close to zero. The variability of changes in the amplitude of DPOAE is fairly high. In 10 ears of six subjects at least in two neighbouring frequencies during contralateral stimulation an increase of the DP amplitude occurred. When using the above method it is possible to consider as the lower borderline of normal values suppression of 0.5 dB and an interaural difference of a maximum of 1.0 dB for TEOAE; in DPOAE it must be striking if a change does not occur (reduction of DP amplitude) at lower frequencies. Changes of DPOAE at frequencies above 3.5 - 4.0 kHz should not be evaluated in the stimulation mode of 65/55.
otoacoustic emissions, contralateral suppression, normal findings.
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