PRESSURE-GRADIENTS AFFECTING THE LABYRINTH DURING HYPOBARIC PRESSURE - EXPERIMENTAL-STUDY

Hypobaric effects on the perilymph pressure were investigated in 18 ca ts. The perilymph, tympanic cavity, cerebrospinal fluid, and systemic and ambient pressure changes were continuously recorded relative to th e atmospheric pressure. The pressure equilibration of the eustachian t ube and the cochlear aqueduct was studied, as well as the effects of b locking these channels opening of the eustachian tube reduced the pres sure gradients across the tympanic membrane. The patent cochlear aqued uct equilibrated perilymph pressure to cerebrospinal fluid compartment levels with a considerable pressure gradient across the oval and roun d windows. With the aqueduct blocked, the pressure decrease within the labyrinth and tympanic cavities was limited, resulting in large press ure gradients toward the chamber and the cerebrospinal fluid compartme nts, respectively. We conclude that closed cavities with limited press ure release capacities are the cause of the pressure gradients. The st rain exerted by these pressure gradients is potentially harmful to the ear.