Perilymphatic Pressure in the Cat: Description of a New Method for Study of Inner Ear Hydrodynamics

Abstract

Continuous recordings of the perilympahtic (P_P), cerebrospinal fluid (P_CSF), central venous (P_cv) and arterial (P_A) pressures have been performed on anesthetized cats. The perilymphatic space was reached by an extra-aural approach that leaves the ear canal and middle ear intact. A conical canal was drilled into the temporal bone down to the vestibule. The position of the canal was later confirmed histologically. A small, threaded, metallic cannula was screwed into the bone. For pressure measurements Millar microtip transducers were used, thus giving minimum measurement volume displacement. The mean P_p and P_CSF were found to be equal, whereas the maximum pressure during expiration was significantly higher in the CSF. The mean P and P_Csf were not affected by the given anesthetics. Ligation of the external jugular veins had a minor and temporary effect on the P_P and P_CSF. The method is considered to be suitable for studies on the inner ear hydrodynamics as well as for audiophysiological measurements with an intact middle ear transmission system.