(PP702) Otoacoustic Emission and Inhibitory Effect of efferent System: Indicators of Hidden Hearing Loss?

Our purpose was to compare transient otoacoustic emissions (TEOAE) and the inhibitory effect of the efferent auditory pathway in normal hearing individuals exposed and not exposed to occupational noise, seeking to identify parameters that may suggest the presence of hidden hearing loss. Current results showed lower TEOAE amplitudes in normal hearing individuals exposed to noise, as well as lower occurrence of efferent inhibitory effect, when compared to individuals without noise exposure, suggesting that these procedures can be risk indicators for the presence of hidden hearing loss. 

Summary: 

Background: Exposure to intense noise can cause changes in the peripheral and central auditory system, even in the presence of normal hearing thresholds in pure-tone audiometry. Among the methods to assess hidden hearing loss, otoacoustic emissions (OAE) and the inhibitory effect of the efferent auditory system have been used. Researchers have found higher rate of absence results for OAE in individuals exposed to noise, when compared to individuals without exposure, even in the presence of normal hearing. Other studies have proposed that the efferent system has a protective role in the auditory system against cochlear synaptopathy. Thus, the assessment of transient OAEs (TEOAE) and the inhibitory effect of the efferent auditory pathway can help identify the first signs of damage to the auditory system, serving as risk markers for hearing alterations, even before the audiometry shows hearing loss.

Purpose: To compare TEOAE and the inhibitory effect of the efferent auditory pathway in normal hearing individuals exposed and not exposed to occupational noise.

Methods: Sixty male adults, normal hearing (< 25 dBHL at all frequencies), without tinnitus or dizziness, were divided into: study group (SG) with 34 workers exposed to occupational noise (mean age: 37.5 years) and control group (CG) with 26 workers without exposure to occupational noise (mean age: 35.2 years). The following procedures were carried out: TEOAE with non-linear stimulus at 80 dBSPL (presence of TEOAE: Signal/Noise ratios ≥3 dBSPL in three consecutive frequencies); and evaluation of the inhibitory effect of the efferent auditory pathway, in participants who had present TOAE. For this, linear click stimuli at 60 dBSPL were used, in the presence and absence of White Noise at 60 dBSPL in the contralateral ear. To analyze the amplitude of the TEOAE response and the inhibitory effect of the efferent pathway, the results were transformed into microPascal (µPa). For statistical analysis, Anova and Chi-square tests were used.

Results: In the qualitative analysis, the CG showed presence of TEOAE response in 96% of the evaluations, against 72% of the SG. Regarding the TEOAE amplitudes, the CG presented higher values for all frequencies evaluated, in both ears, with significant differences in the right ear (RE) for 1.4kHz (p-value=0.04), 2kHz (p-value=0.03), 4kHz (p-value=0.002) and in the left ear (LE) for 4kHz (p-value=0.02). In the evaluation of the inhibitory effect of the efferent auditory pathway, only the results of the RE were considered, due to the advantage of the RE over the LE. In the qualitative analysis, the CG showed a higher occurrence of inhibition of the efferent pathway (92% against 63% for the SG) (p-value=0.021). There was no difference between groups for the amplitude of the inhibitory effect (p-value=0.913).

Conclusion: We verified lower TEOAE amplitudes in normal hearing individuals exposed to noise, as well as lower occurrence of efferent inhibitory effect, when compared to individuals without noise exposure, suggesting that these procedures can be risk indicators for the presence of hidden hearing loss.