Vestibular responses of normal and hydropic ears of the guinea pig to middle ear pressure application.

The pressure in the middle ears of normal and hydropic guinea pig ears was increased, and nystagmographic recordings were compared. Two-month unilateral hydropic guinea pigs and normal control guinea pigs underwent pressure treatments in which pressure was introduced into the middle ear. Significantly lower pressure was needed to elicit nystagmus in hydropic ears (mean 1.00 psi or 70.3 cm H2O) compared with normal control ears (mean 1.27 psi or 89.3 cm H2O). All of the normal control guinea pigs showed fast phase nystagmus toward the pressure-applied side, while hydropic guinea pigs showed nystagmus toward the normal ear. The duration of nystagmus was slightly longer in hydropic animals than in normal control animals. The slow phase velocity was slightly higher in the hydropic guinea pigs. Histologic examination revealed that the vestibular sensory cells remained normal and that changes in the organ of Corti were similar between the hydropic ears with and without pressure treatment at equal survival times.