step stimulusによる温度眼振反応のon, off特性の解析

抄録

The effect on the vestibulo-ocular reflex (VOR) is evaluated by using a caloric stimulation in which the ears of subjects in the supine position are irrigated with water or air. Studies on the clinical application of caloric stimulation have shown that the stimulation results in a gentle rise of VOR response, which does not precisely reveal the time course of VOR onset. In our study, 14 healthy subjects were evaluated with a step stimulus technique, which showed the onset and offset of caloric stimulation with a rapid change of the position of the subject's head during continuous irrigation of his or her ear. The technique showed a rapid rise (indicating an activation) and consequent gentle attenuation (indicating a compensation) of VOR response. On-step (from sitting to supine position) and off-step (the opposing maneuver) stimulation delivered the same characteristics of this rise and attenuation with opposing direction, through the ampulo-petal and ampulo-fugal convection along their lateral semi-circular canals respectively. Repeated ipsi-lateral stimulation with an interval of 4 minutes caused an increased adaptation of VOR during the on-step response. Some possible reasons for these results might be the occurrence of a central adaptation of VOR or a mechanism involving the peripheral vestibular apparatus such as depletion of the synaptic transmitting substance. Step stimulus of one side did not demonstrate any contribution to subsequent contra-lateral stimulation with the same 4-minute interval. This finding supports the idea that the peripheral vestibular system contributes to the adaptation of VOR. Introducing this step stimulus technique into the clinical examination setting would facilitate the elucidation of the pathophysiological basis of vestibular deficits.