The Galvanic whole-body sway response in health and disease

Objective: To explore the galvanic-evoked vestibulospinal reflex in health and disease. Methods: Vestibular-evoked whole-body movement was measured in 60 controls and eight patients with bilateral vestibular impairment, using 1 mA X2 s Galvanic Vestibular Stimulation (GVS). The displacement (s) and velocity (v) of 7 markers placed on the head, neck, shoulders, mid-thorax and hips and ground reaction forces (F) were recorded. Results: Monaural GVS evoked anterolateral whole-body movement away from the cathode. For controls, peak response magnitudes were 22.3 +/- 12.4 mm, 25.9 +/- 14.3 mm s(-1) and 3.2 +/- 1.3 N for s, v and F. Left right asymmetry measured using the Jongkee's formula was 12.59 +/- 8.64%, 11.94 +/- 11.09% and 11.68 +/- 8.99% for s, v and F. All three measures were symmetrical for left and right mastoid stimulation and showed good to excellent test retest reliability. Patients with bilateral vestibular failure had absent or attenuated responses. For this patient group, the ("R/B'') ratios between the "response period'' and baseline body-sway for s, v and F were 2.1 +/- 0.8, 1.7 +/- 1.1 and 1.3 +/- 0.6, which were significantly lower than 5.4 +/- 4.2, 4.1 +/- 2.5 and 2.3 +/- 0.8 for controls, with s and v providing better separation between controls and patients. There were no significant correlations between the amplitudes of galvanic body sway responses and vestibular-evoked myogenic potentials (VEMPs). Conclusion: GVS enables non-invasive assessment of the vestibulospinal reflex. Significance: This method offers a clinically applicable, test of vestibular contributions to standing balance. (C) 2013 Published by Elsevier Ireland Ltd. on behalf of International Federation of Clinical Neurophysiology