Contralateral suppression of transient evoked otoacoustic emissions in adults: A normative study.

Background:  Whilst otoacoustic emission (OAE) testing has proved to be valuable in revealing information about cochlear outer hair cell integrity, it does not provide insight into the afferent and efferent pathways once the stimulus has reached neural receptors. This information can be obtained objectively through contralateral acoustic stimulation (CAS) suppression. However, obtaining normative data is essential in the implementation of such tests.

Objectives:  The primary aim was to undertake a small pilot study to collect the CAS suppression across a predefined frequency range in order to provide a preliminary normative data set to be used with the newly developed transient evoked otoacoustic emission (TEOAE)-CAS module (PATH MEDICAL, Germering, Germany). Secondary aims included the analysis of the relationships between left and right CAS suppression, between male and female CAS suppression and between TEOAE signal-to-noise ratio (SNR) and CAS suppression.

Methods:  The purpose of this study was to determine preliminary normative data for contralateral TEOAE suppression from 40 normal ears of 20 healthy young adults (10 males and 10 females). Subjects were recruited using purposive sampling. The CAS suppression responses were obtained automatically by means of the data-collection protocol on the device used. From the data obtained, correlations between TEOAE SNR and CAS suppression were made using Pearson's correlation coefficient.

Results:  The data were statistically processed to form a normative database which possesses the potential of serving as a basis for further research aimed at determining the utility of CAS suppression testing when evaluating ear pathology. A mean CAS suppression of 0.8 decibels (dB) (0.61 SD) was obtained. There was no statistically significant relationship between TEOAE SNR and CAS suppression. There was no significant suppression difference in terms of laterality of ears or gender.

Conclusion:  Normative values for CAS suppression of TEOAEs in a group of normal-hearing individuals were obtained using the newly developed TEOAE-CAS module (PATH MEDICAL, Germering, Germany). The availability of normative data for contralateral TEOAE suppression using the studied module allows for it to become commercially available, which will enable researchers and audiologists to perform this measurement in different populations in the evaluation of ear pathology.