Feasibility in Recording Vestibular Evoked Myogenic Potentials from the Gastrocnemius Muscles Using Acoustic Stimulation.

Abstract

Background: Vestibulo-spinal reflexes (VSR) contribute to postural control from the neck to the lower extremities. The cervical vestibular evoked myogenic potential (cVEMP), recorded from neck muscles, assesses the upper VSR and is used in research and clinical settings. However, no clinical tools evaluate the full length of the VSR. Although lower-limb VEMP recordings show potential, previous studies have yielded inconsistent results.

Purpose: This study examines the feasibility of recording a VEMP from the gastrocnemius muscle using acoustic stimulation.

Research design: Feasibility study using single group cross-section research design.

Study sample: Thirteen healthy participants aged 20-26 years, all with present cVEMP responses.

Data collection and analysis: Participants underwent gastrocnemius VEMP recordings using stimuli, recording parameters, and electrode placements from previous studies. The stimuli included air-conduction clicks and 500-Hz tone bursts (132 dB peak SPL), as well as bone-conduction 500-Hz tone bursts (125 dB peak FL). Participants activated the gastrocnemius by leaning forward onto their toes, and recordings were obtained from both the ipsilateral and contralateral gastrocnemius muscles.

Results: Replicable gastrocnemius VEMPs were observed in only two participants, even though all exhibited robust cVEMPs. In these two participants, responses showed N1P1 and N2P2 peaks between 55 and 105 milliseconds. The amplitude decreased with lower electromyography contraction, but the wave morphology remained unaffected by head turn or eye closure. Some participants found the stimuli loud and uncomfortable and reported fatigue from prolonged toe-standing.

Conclusions: The response rates for gastrocnemius VEMPs are low. The findings suggest gastrocnemius VEMPs are observed in few individuals when using 132 dB peak SPL acoustic stimulation. The same stimulus and recording protocols are ineffective for most young, healthy individuals with present cVEMPs. A more intense stimulus may be needed to elicit gastrocnemius VEMPs; however, this approach is limited by potential hearing risks.

Clinical relevance statement: Recording vestibular spinal reflexes from lower limb muscles using acoustic stimulation appears clinically unfeasible. Alternative methods, such as galvanic stimulation, should be explored for assessing vestibulo-spinal function in the lower extremities.