Vestibular evoked myogenic potential (VEMP) test
Patients underwent cVEMP and oVEMP tests 1 week prior to CI and then again 1–3 months after. The electromyography signal from the stimulated side was amplified using the Neuro-audio Auditory evoked potentiometer system (version 2010, Neurosoft Ltd., Ivanov, Russia) in a soundproof examination room. The cVEMP test was performed with the electromyogram auto-correction mode. The children were tested in a natural awake state. Older children with the ability to cooperate were asked to obtain a sitting position, and younger children were placed in a 30° forward head tilt position with their parents holding them. The sound was emitted through a calibrated earphone, with an air-conducted 500 Hz short pure tone (tone burst) and a stimulation intensity of 105 dB nHL. The active electrode was placed in the middle of the sternocleidomastoid muscle (SCM), the reference electrode was placed above the sternoclavicular joint, and a ground electrode was placed on the midline of the forehead. The inter-electrode resistance should be <5 kΩ. The head of the children was turned to the opposite side during the cVEMP test. The SCM force in the test ear was maintained between 30 and 70 μV. The signal was recorded ipsilaterally by monitoring electromyography.
oVEMP testing was performed in the sitting position. An active electrode was placed 0.5 cm below the lower lid of each eye in line with the pupil, a reference electrode was placed below the active electrode, and a ground electrode was placed on the midline of the forehead. The inter-electrode resistance was also <5 kΩ. Each child was instructed to gaze upward, focus on one specific place, and avoid blinking. The stimulation sound was similar to that of the cVEMP and administered bilaterally. The signal was recorded on the opposite side. If the test ear had CI, the test was performed with the CI device turned off.