Practica oto-rhino-laryngologica. Suppl.

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Ambient pressure changes have been shown to induce vertigo and bodily disequilibrium, but their direct effect upon the vestibular apparatus remains obscure. In order to clarify the mechanism of this phenomenon, we investigated the effect of middle ear pressure changes upon the primary semicircular canal neurons and perilymphatic pressure in guinea pigs. The roles of the pressure conducting system (the round and oval windows)and the pressure regulating system (the vestibular and cochlear aqueducts) were also investigated.
1) The vestibular nerve response was found to be related to middle ear pressure levels with the response rate for positive pressure changes being significantly larger than that for negative pressure changes.
2) The pattern o f perilymphatic pressure change was correlated with the response pattern of the vestibular nerve, indicating that the vestibular response is elicited by middle ear pressure change acting via inner ear pressure change.
3) Guinea pigs with obstructed round wind ows (the closed RW group) showed neural response rate significantly lower than that of the control group, while that of guinea pigs with obstructed oval windows (the closed OW group) was significantly higher than that of the control group.
4) The pe rilymphatic pressure changes in the closed RW group were significantly smaller than, while those in the closed OW group were similar to, those in the control group.
5) Guinea pigs with obstructed vestibular aqueducts (the closed VA group ) showed neural response rate similar to that in the controls, while that in those with obstructed cochlear aqueduct (the closed CA group) was significantly higher than that in the control group.
6) Perilymphatic pressure changes in the closed VA group were similar to, while those in the closed CA group were significantly larger than, those in the control group.

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