PP1506 - Comparing Bone-Conduction cVEMPs for Narrow-Band CE-Chirp LS and TB Stimuli

Abstract:
Vestibular-evoked myogenic potentials (VEMPs) are short-latency, otolith-dependent reflexes recorded from the neck (cervical) and eye (ocular) muscles measuring the functioning of each otolith organ and vestibular nerve branch. This study compared bone conduction (BC) cervical VEMP (cVEMP) response between narrow-band (NB) CE-chirp level-specific (LS) and Tone-burst (TB) stimuli in 15 healthy individuals and answered the following question: How do the amplitude, latency, and interaural asymmetry ratio (IAR) of NB CE-chirp LS compared to those of TB stimuli? Results indicated that the NB CE-chirp LS stimulus presented shorter N1 and P1 latencies; and larger P1-N1 amplitudes than the TB stimulus.

Summary:
Rationale/

Purpose:
VEMP has become an essential part of the comprehensive vestibular evaluation aiding in diagnosing various vestibular disorders. A BC transducer offers several clinical advantages over an AC transducer for measuring cVEMP. BC cVEMPs have been shown to produce larger N1-P1 peak-to-peak amplitudes and lower response thresholds compared to AC cVEMPs (McNerney & Burkard, 2011). BC is the preferred mode of stimulation for patients with conductive pathologies. For auditory brainstem response (ABR) and auditory steady-state auditory responses (ASSR), the Chirp family stimulus demonstrates larger amplitude responses and lower hearing thresholds (Elberling et al., 2007). Air conduction (AC) stimulation with 500 Hz TB is typically used in the clinic; an alternative stimulus that produces a robust and steady response can be considered. No published study investigates the difference in BC cVEMP in response to NB CE-chirp LS and tone-burst stimuli. The study aims to compare BC cVEMP responses between NB CE-chirp LS and TB stimulus.

Hypothesis:
We hypothesized that the NB CE-chirp LS stimulus would generate larger amplitudes and shorter latencies than TB stimulus. NB CE-chirp LS stimulus is designed by compensating for the traveling wave delay, increasing neural synchronization. This synchronized neural activity would result in a larger N1-P1 response amplitude for NB CE-chirp LS than TB stimuli. The shorter latencies in the NB CE-chirp LS are due to the differences in the temporal references used for the recording time window.

Methods:
The study recruited 15 adults with no history of neurologic disease, chronic noise exposure, vestibular disorders, and conductive hearing loss. The active electrode was placed on the upper third section of the ipsilateral SCM; the reference electrode was placed on the sternum's jugular notch of the manubrium, and the ground electrode was placed on the forehead. cVEMP was performed while the participants were lying in a 30-degree supine position. During recording, participants were instructed to turn their heads to the contralateral shoulder and received verbal feedback to maintain steady SCM contraction. Two tracings of BC cVEMP were measured for randomly presented TB and NB CE Chirp LS stimuli at 500Hz and 1000Hz presented at 65dBnHL and 75dBnHL, respectively. The response measurement was alternated between right and left SCM to prevent muscle tiring. Minimum 3 minutes break was provided between each stimulation. The cVEMP response metrics such as P1, N1 latency, P1-N1 peak-to-peak amplitude, and interaural asymmetry ratio (IAR) are considered for analysis.

Results:
NB CE-chirp LS stimulus presented shorter N1 and P1 latencies; and larger P1-N1 amplitudes at 500 (65 dBnHL) and 1000 Hz (75 dBnHL) than the TB stimulus. There was no statistical difference in the mean IAR for both frequencies.

Conclusions:
NB CE-chirp LS stimulus provides more robust waveforms than TB. Based on the study's results, NB CE-chirp LS stimulus could be used as a possible alternative to TB for BC clinical cVEMP evaluations. Further investigation is needed to evaluate the potential benefits of chirp family stimulus in older healthy individuals and patients with vestibular disorders comparing AC and BC stimulation.