Transmission of cerebrospinal fluid pressure changes to the inner ear and its effect on cochlear microphonics.

Alterations in inner ear fluid pressure and cochlear microphonics (CM) associated with increased cerebrospinal fluid (CSF) pressure were studied in the guinea pig. Hydrostatic pressure in the endolymph and perilymph of the cochlea were measured by use of a servo-controlled micropipet system. Endolymphatic and perilymphatic pressure increased in a linear manner with little or no time lag following pressure increases of 0-50 mm Hg. There was no pressure gradient between the endolymph and perilymph. CM in response to 500 Hz and 4000 Hz tone bursts was recorded before, during and after CSF pressurization. The input-output function of CM showed suppression of 2-8 dB in both maximum output and sensitivity unless the increase in CSF pressure exceeded a level which reduced the cochlear blood flow.