PP504 - Tuning Characteristics of Bone-Conduction Ocular Vestibular-Evoked Myogenic Potentials: A Large Sample Study

Ocular vestibular evoked myogenic potentials (oVEMPs) assess the function of the utricle and its associated afferent pathways of the superior vestibular nerve. These are contralateral responses indicated by a negative excitatory peak (N1) at approximately 10ms and a positive peak (P1) at approximately 15ms. The clinical utility of oVEMPs includes assessing the utricle and superior portion of the vestibular nerve in addition to testing for third window conditions (TWCs). Rosengren et al., (2019) reported that bone conduction (BC) oVEMPs might be a better screener for detecting TWC with high sensitivity and specificity than air conduction (AC) oVEMPs. Fröhlich et al., (2021) indicated that BC elicits higher amplitudes and lower thresholds of oVEMP than AC stimulation. BC is also the preferred mode of stimulation for patients with conductive pathologies. The newer B-81 bone oscillator creates less harmonic distortion and higher dynamic range at lower frequencies over the B-71 (Jansson et al., 2015). Frequency tuning is essential for differentiating normal and pathological conditions. This large sample study aims to characterize the frequency tuning of BC oVEMP responses in healthy participants using a B-81 bone oscillator.

BC oVEMPs were collected from 60 ears from participants with no history of neurologic disease, chronic noise exposure, vestibular disorders, and conductive hearing loss. For oVEMP recording, the positive electrode was placed on the right inner canalith, the negative electrode on the contralaterally inferior oblique, and the ground electrode on the sternum. oVEMP recording was performed while participants fixated on a point in the wall, approximately 60 cm from the participant at a 30-degree angle from an optimal gazing position. Tone burst stimuli were randomly presented at 500 Hz, 750 Hz, 1,000 Hz, 2,000 Hz, and 4,000 Hz. The initial intensity presentation was 75 dBnHL for 500 Hz, 750 Hz, 1,000 Hz, and 2,000 Hz, and 70 dBnHL for 4,000 Hz. The modified Hughson-Westlake method was utilized at each frequency to measure oVEMP thresholds. The oVEMP response metrics, such as N1, P1, P2, N2 latency, and N1-P1, P1-N2, N2-P2 peak-to-peak amplitude, are considered for analysis.

The preliminary findings from 60 ears indicated that oVEMPs were present in all participants between 250-1000 Hz at maximum intensity levels. < 25% of participants had present oVEMPs between 2,000-4,000Hz. The responses had maximum amplitude and lowest thresholds at 500 Hz than other frequencies evaluated. The average threshold at 500 Hz, 750 Hz, 1,000 Hz were 65 dBnHL, 71 dBnHL, and 73 dBnHL respectively. Despite a large decrement in peak-to-peak amplitude, there was only a minor shift in peak latencies with decreasing intensity across frequencies.

Similar to previous studies using AC stimulation and BC stimulation with B-71, oVEMPs are 500 Hz tuned responses with a very low incidence of responses between 2,000-4000Hz. The study's findings can be considered when diagnosing pathological conditions such as TWC.