This image shows the two fluid spaces of the cochlea, the perilymph shown orange and the endolymph shown blue. For years it was believed that endolymph and perilymph flowed along the fluid spaces. We developed a method to measure the flow rate in the living ear. The method used an ionic marker which was iontophoresed into the fluids at low concentration. The concentration of the marker was measured simultaneously by two ion-selective microelectrodes at locations "upstream" and "downstream" of the injection site. Analysis involved simulations of the combined effects of flow and diffusion along the spaces.Ê We were able to show that the rate of flow of these fluids is extremely slow, with endolymph flow shown to be less than 1 nanoliter per minute. The method is extremely sensitive and detects very slow flow rates in small compartments.

For further details see Prof. Alec N. Salt's home page.