The Variability of the Galvanic Body-Sway Test

Abstract

The variability of galvanic unilateral weakness (UW) and directional preponderance (DP) was studied in 31 normal subjects. Variability of absolute UW and DP increased linearly with increasing response amplitude. Variability of percent UW and DP was very high at low response amplitudes. However, it declined rapidly as response amplitude increased and reached a relatively constant level at a total response amplitude of about 25 mm (though continuing to decline slightly). The percent measurements thus appear best for clinical use, provided the total response amplitude is greater than 25 mm. Increasing stimulus current caused a marked decrease in percent UW and DP variability. Therefore, for clinical testing we use the highest stimulus that does not produce discomfort (1.0 mA). Varying stimulus rise-fall time did not affect test variability. Subjects with greater spontaneous sway tended to have less variable percent UW and DP, thus suggesting that reducing subject stability might improve the galvanic test. Test-retest variability differed significantly from subject to subject. Standard deviations from subjects with the most variable responses did not differ significantly from standard deviations across all subjects. This result suggested that the primary determinant of limit of normal is the inherent variability of the test rather than differences among subjects.