Differences in the suppression of distortion product otoacoustic emissions by contralateral white noise between patients with acute or chronic tinnitus

Magnitude of medial olivocochlear reflex assayed by tone-burst-evoked otoacoustic emissions: reliability and comparison with click-evoked emissions

OBJECTIVE

The purpose of this pilot study was to evaluate the magnitude of the medial olivocochlear reflex (MOCR) estimated by the reduction in tone-burst evoked otoacoustic emissions (TBOAEs) measured at three levels and at three frequencies in response to fixed contralateral white noise. Results were compared with commonly used click-evoked otoacoustic emissions (CEOAEs).

DESIGN

TBOAEs and CEOAEs, with and without contralateral 60 dB SPL white noise, were measured in response to stimulation at 55, 65, and 75 dB peSPL. In each subject, the set of measurements was performed twice. Of particular interest were the MOCR and its repeatability.

STUDY SAMPLE

15 normally hearing persons (13 women, average age 32.3 years, SD = 8.1).

RESULTS

For both CEOAE and TBOAEs, the reliability of the MOCR was much better for broadband measurements than for half-octave-band filtered estimates. At the same time, the reliability of MOCR in half-octave bands was higher for TBOAEs than for CEOAEs, especially at 2 and 4 kHz.

CONCLUSIONS

For general applications where broadband MOCR is of interest, the highest magnitude and reliability is provided by CEOAEs. However, TBOAEs may be better if a particular frequency band is of interest.

Evaluating the Function of the Medial Olivocochlear Bundle in Patients With Bilateral Tinnitus

Purpose No study has investigated the effects of contralateral noise (CN) on speech-in-noise perception (SINP) in listeners with tinnitus. The mechanisms underlying the involvement of medial olivocochlear (MOC) reflex with SINP remain to be elucidated. This study aimed to investigate the MOC function in patients with bilateral tinnitus by measuring distortion product otoacoustic emission and SINP. Method Eighteen patients with bilateral tinnitus (one male and 17 females; age: M ± SD = 45.61 ± 10.18 years) and 19 listeners without tinnitus (six males and 13 females; age: M ± SD = 34.11 ± 8.35 years) were recruited for the study. Each subject underwent distortion product otoacoustic emission measurement and the SINP test for both ears. The effects of CN on these two measurements were compared between tinnitus ears (TEs) and no-tinnitus ears (NTEs). Results The presence of CN significantly reduced distortion product (DP) amplitudes and improved SINP for TEs, and the amounts of DP suppression and SINP improvement were similar to those in NTEs. Improvement of SINP was positively correlated with DP suppression at 6185 Hz for NTEs and at 1640 Hz for TEs. Conclusions The results of this study suggest that the amounts of DP suppression and SINP improvement were similar between listeners with and without tinnitus. For both ear groups, the MOC reflex was involved with SINP at specific frequencies. Any clinical test outcomes with regard to the MOC bundle in patients with tinnitus should be interpreted with caution until further studies are conducted.

Untangling the genomics of noise-induced hearing loss and tinnitus: Contributions of Mus musculus and Homo sapiens

Acoustic trauma is a feature of the industrial age, in general, and mechanized warfare, in particular. Noise-induced hearing loss (NIHL) and tinnitus have been the number 1 and number 2 disabilities at U.S. Veterans hospitals since 2006. In a reversal of original protocols to identify candidate genes associated with monogenic deafness disorders, unbiased genome-wide association studies now direct animal experiments in order to explore genetic variants common in Homo sapiens. However, even these approaches must utilize animal studies for validation of function and understanding of mechanisms. Animal research currently focuses on genetic expression profiles since the majority of variants occur in non-coding regions, implying regulatory divergences. Moving forward, it will be important in both human and animal research to define the phenotypes of hearing loss and tinnitus, as well as exposure parameters, in order to extricate genes related to acoustic trauma versus those related to aging. It has become clear that common disorders like acoustic trauma are influenced by large numbers of genes, each with small effects, which cumulatively lead to susceptibility to a disorder. A polygenic risk score, which aggregates these small effect sizes of multiple genes, may offer a more accurate description of risk for NIHL and/or tinnitus.