赤外線眼球運動記録装置による電気性眼振の解析

抄録

The Galvanic test has been studied as a test of equilibrium. However, it has been less applied clinically than other tests, partly because analysis of the ENG records is difficult due to contamination by electric stimulation. In this study, to overcome this problem, we recorded and analyzed galvanic nystagmus using infrared video-oculography.
The subjects were 14 healthy volunteers (8 males and 6 females; mean age 32.6 years).
Electrodes were taped to the mastoid processes in both ears. The right electrode was the cathode, and the left electrode was the reference electrode. Direct current stimulations at 1, 2, 3, and 4 mA each with a 30 second duration were applied using a direct current stimulator.
Nystagmus was provoked toward the cathodes in all subjects. The threshold of provocation was 1 mA in 10 and 2 mA in 4 of 14 subjects. The average frequency of nystagmus was 0.645 Hz at 1 mA, 1.088 Hz at 2 mA, 1.348 Hz at 3 mA, and 1.592 Hz at 4 mA. The average slow phase velocity was 2.121, 5.053, 7.564, and 9.130 deg/sec, respectively. Both the frequency of nystagmus and average slow phase velocity tended to increase linearly with the intensity of the electric current.
Since nystagmus was provoked toward the cathode, the cathodic current is considered to have increased the firing of the vestibular afferent pathway. Zinc et al., who performed experiments using an infrared video-oculography and a similar stimulation pattern, reported that there was a difference in the threshold of provocation by galvanic vestibular stimulation between the otolith and semicircular canal. According to our results, nystagmus was provoked at 1-2 mA, and the threshold of provocation by galvanic stimulation is not considered to differ between the otolith and semicircular canal.