[A study of the Galvanic Body Sway Test--reproducibility of test results]

Although the Galvanic Body Sway Test (GBST) has been considered useful for differential diagnosis between labyrinthine and retrolabyrinthine lesions, it does not always yield clear wave forms, since the test results are inevitably contaminated by basic body sway in the standing position. In our previous study, in which the effects of duration of stimulation, current intensity and frequency were examined in 13 normal subjects, we found that the clearest GBST wave forms were obtainable when 20 responses to successive monopolar 0.5mA galvanic stimuli for 5 sec at 4 sec intervals were averaged. In the present study, GBSTs were conducted repeatedly in 10 normal subjects using the stimulation conditions mentioned above in order to assess the reproducibility of the test responses. In all of the subjects, monoaural galvanic stimuli were delivered separately to each ear twice on the same day at a fixed intervals and the averaged wave forms were obtained. The same tests were repeated twice more in the following 3 weeks after an interval of at least 7 days. As a result, it was found that very similar responses were obtained from both ears, and there was remarkable reproducibility of both the latency and the amplitude of the GBST response in a given subject. It was also found that while inter-individual differences in latency were minimal, differences in amplitude were fairly large. The results suggest that comparison of response amplitude on both sides in the same subject is significant in evaluating the results of GBST.