The effect of rise/fall time of 500 Hz short tone bursts on cervical vestibular evoked myogenic potential

Abstract

Background: Cervical vestibular evoked myogenic potential (cVEMP) is a biphasic potential recorded from the Sternocleidomastoid muscle in response to loud acoustic stimulation and assesses the intactness of the Sacculocolic pathway. The literature on clinical utility of cVEMP has been growing rapidly, though not without inconsistencies despite involving alike population. A close scrutiny of the methods across such studies revealed an inconsistent use of stimulus parameters; especially rise/fall times (RFTs). However the effect of RFTs on cVEMP has been largely unexplored. Objective: The study aimed at exploring the effect of varying RFTs on cVEMP and obtaining optimum RFT to enable reliable recording of cVEMPs. Methods: The cVEMPs were recorded from both ears of 30 healthy individuals with normal audio-vestibular system using 500 Hz short tone-bursts (STBs) at 95 dB nHL and varying the RFTs from 1 to 8 ms at all integer values. Results: There was significant prolongation of latencies with increasing RFTs (p< 0.05). The largest amplitudes were obtained for 2 to 3 ms RFTs, though significantly smaller amplitude was obtained only for 8 ms RFT (p< 0.05), thereby rendering 8 ms RFT unfit for cVEMP recording. The 1 ms RFT produced smallest variability across individuals and would also result in lesser duration of exposure to loud sound. Conclusions: The RFT of 1 ms of 500 Hz STBs are optimum for recording cVEMPs. This is owing to large amplitudes and least variability demonstrated for this RFT.