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).