Optimal stimulation mode for galvanic-evoked myogenic potentials

The vestibular-evoked myogenic potential elicited from galvanic stimulation (g-VEMP) has several promising uses in the clinical setting. However, optimal stimulus parameters have yet to be established. This study was conducted to quantify the effects of galvanic stimulus intensity and duration on VEMP responses.

Fourteen male volunteers underwent VEMP tests using clicks stimulation and galvanic stimulation with various intensities (1, 2, 3, 5, and 6 mA under 1.0 ms duration) and durations (0.1, 0.2, 0.5, and 1.0 ms under 5 mA intensity). The response rate, latencies of peak p13 and n23, p13-n23 interval and amplitude of each stimulation mode were compared.

Because less than 50% of subjects could tolerate the 6 mA stimuli, they were dropped from further study. Galvanic stimulation at 3 mA/1.0 ms, 5 mA/0.5 ms, or 5 mA/1.0 ms had the highest g-VEMP response rates (89-100%). The latencies and p13-n23 interval did not differ significantly among them, but the p13-n23 amplitude in group of 5 mA/1.0 ms were significantly larger than those in groups of 3 mA/1.0 ms and 5 mA/0.5 ms. In addition, g-VEMPs evoked by 5 mA/1.0 ms had significantly shorter latencies but similar p13-n23 interval and amplitude, when compared with those triggered by clicks stimulation.

Galvanic stimulation using the intensity of 5 mA with a duration of 1 ms can elicit higher response rates and larger g-VEMP amplitudes relative to less intense stimuli, without exceeding subject pain tolerances. Amplitude and p13-n23 interval were not significantly different from those elicited by click stimuli. Hence, galvanic stimulation at 5 mA/1 ms may be a preferable stimulation mode for evoking g-VEMPs.