Perilymphatic and endolymphatic pressures during endolymphatic hydrops.

We analysed the fluid pressure in the perilymphatic and endolymphatic spaces of the cochlea in eight guinea pigs after endolymphatic hydrops (EH) was surgically created. The control experiments were done in the opposite ears. EH was histologically confirmed after the conclusion of the pressure measurements. No statistically significant pressure difference between the scala media and the scala tympani was found, either in ears with EH or the control ears. However, the endocochlear potential, which we evaluated for position verification of the measurement pipette in the cochlea, was statistically significantly decreased in ears with EH.

Perilymphatic and endolymphatic pressure in the guinea pig after distal dissection of the endolymphatic sac.

HYPOTHESIS: The study was designed to investigate whether endolymphatic pressure exceeds perilymphatic pressure in an endolymphatic hydrops model with a partially functioning endolymphatic sac. BACKGROUND: Previous investigations of perilymphatic and endolymphatic pressure measurements during endolymphatic hydrops were done in a classic endolymphatic hydrops model, with a surgically blocked endolymphatic duct and sac. This model, in contrast to the clinical situation of Meniere's patients, totally lacks the functional contribution of the endolymphatic sac. METHODS: In the guinea pig, a partially functioning endolymphatic sac was created via dissection of the distal portion of the sac from the sigmoid sinus. Three (n = 5) and 6 months (n = 3) later, perilymphatic and endolymphatic pressures were measured consecutively using a WPI 900A micropressure system. RESULTS: It was observed that damage to the distal part of the endolymphatic sac caused endolymphatic hydrops in 58% of the cases. The hydrostatic pressure in hydropic ears did not differ from that of control ears. There was no pressure difference between the perilymphatic and endolymphatic compartments in ears with endolymphatic hydrops. The endocochlear potential in ears with hydrops was statistically significantly decreased (p < 0.002). CONCLUSION: In a hydrops model developed to be more comparable to the histopathologic appearance of Meniere's disease in the inner ear, no hydrostatic pressure difference was measured between the perilymphatic and endolymphatic spaces. The only functional difference from control ears we found was a decreased endocochlear potential.

Measurement of the mechanical compliance of the endolymphatic compartments in the guinea pig.

During injection of artificial endolymph into scala media of the guinea pig, fluid pressure was simultaneously measured in endolymph and perilymph with micropipettes. Pressure differences in the order of 10 Pa could reproducibly be measured upon injection of 2-4 microl of artificial endolymph with a rate of 50 nl/s. Injection of larger volumes damaged the endolymphatic system. From the results, values were derived for the compliances of the membranes surrounding scala media and the vestibular part of the endolymphatic system. The shape of the pressure-time curve during and between repetitive injections of fluid could well be described with a two-component model for the endolymphatic system, consisting of two compartments with compliant walls, connected through a flow resistance. With this model, a larger compliance was found for the second compartment (vestibular part of endolymphatic system) than for the first compartment, into which fluid was injected (scala media).

Perilymphatic and endolymphatic pressure in the normal guinea pig.

Perilymphatic and endolymphatic pressures were measured consecutively in the normal guinea pig using a WPI 900A micropressure system. The mean (n = 10) perilymphatic and endolymphatic pressures were 2.26 and 2.31 cm H2O, respectively. There was no statistically significant difference between the pressures of the endolymphatic and perilymphatic compartments. The measured values were within the range of pressures found in the literature.