Establishing the test retest reliability of contralateral auditory suppression of Transient Evoked Otoacoustic Emissions in a cohort of healthy individuals

In clinical practice, Transient Evoked Otoacoustic Emissions (TEOAE) are used to assess hearing impairments in several cohorts. The TEOAE can be evoked in healthy cochlea by presenting a brief auditory stimulus in the form of a series of clicks. Similarly, TEOAE signals can be suppressed in the ipsilateral ear by presenting an alternative sound to the contralateral ear through stimulation of either the medial olivo-cochlear (MOC) reflex or acoustic reflex (AR). The suppression effect results from either due to attenuation of the otoacoustic emissions generation through the activation of MOC reflex or due to the obliteration of their transmission by the activation of middle ear muscle reflex (acoustic reflex). In individuals that suffer from brain injury, such as a concussion, the neuronal pathways that enable CASTEOAE may be disturbed which in turn will restrict the ability to generate TEOAEs and to invoke the contralateral suppression effect. Moreover, since a person performing the test cannot manipulate TEOAE signals, the technique could provide an objective measure of concussion status and severity. The following study was designed to measure the test-retest reliability of the CASTEOAE as a first step in establishing the CASTEOAE phenomenon as an evaluation tool for concussion assessment. A convenience sample of 30 healthy individuals, 16-50 years of age completed the CASTEOAE test on two separate occasions, using a 14-day between test interval. The MOC reflex was activated using broadband noise of 60 dB SPL while the Acoustic Reflex was elicited by presenting a broadband noise of 80 dB SPL to the contralateral ear. The OAE amplitudes were recorded across 5 half octave bands in each ear. The test-retest reliability was estimated with the intraclass correlation coefficient procedure using a one-way random effects model for n=30, k (trials)=2. Confidence intervals for the Intraclass Correlation Coefficients (ICCs) and measures of homogeneity of variance were also calculated for each condition. The reliability estimates for CASTEOAE test scores were calculated for TEOAE scores with and without contralateral suppression (Primary measures) of the MOC reflex and separately for the acoustic reflex. The ICCs of the total OAE responses for both MOC reflex and acoustic reflex demonstrated as high as 0.9 in both ears and the ICCs of the fractional octave band for the MOC reflex ranged from 0.6 (left ear @1000 Hz) to 0.95 (right ear @ 4000 Hz), and 0.75 (left ear @1000 Hz) to 0.97 (right ear @ 4000 Hz) for the AR. This data suggests that the MOC and AR reflexes were each significantly repeatable upon test and retest in the sample. In addition, CASTEOAE suppression of the acoustic reflex was greater than MOC reflex suppression; and each participant showed unique TEOAE distribution pattern across the 5 half octave frequency bands, which were consistent over time. The results support the use of the CASTEOAE test as a reliable non-invasive approach to evaluate the functional status of the auditory efferent system and its neural connections with the rest of the brain and the use of this stable and objective measure as a clinical tool to assess a concussion injury.