Direct measurement flow resistance of cochlear aqueduct in guinea pigs

Objective - The cochlear aqueduct connects the scala tympani to the subarachnoid space and is the main pressure equalization canal for the inner ear. Increases in inner ear volume and pressure are thought to cause clinical symptoms such as vertigo, tinnitus and fluctuating hearing loss. In this study the flow resistance of the cochlear aqueduct was determined and its relation with inner ear pressure was studied. Material and Methods - Inner ear pressure was measured in the scala tympani through the round window using a micropipette. Through a second micropipette, artificial perilymph was infused into, or withdrawn from, the scala tympani at various constant rates. From the infusion rate and the change in perilymphatic pressure during infusion the flow resistance of the cochlear aqueduct was calculated. Results - The flow resistance was found not to be constant but to depend on the position of the round window membrane and possibly on the magnitude and direction of fluid flow through the aqueduct. Measured flow resistance values were in the range 11 - 45 Pa s/nl. For very small flow values the flow resistance averaged over 6 animals was 21 Pa s/nl. Conclusions - The flow resistance of the cochlear aqueduct is not a constant value. The cochlear aqueduct is a canal with dynamic properties and may play a role in the complicated process of inner ear pressure regulation