Perilymphatic pressure in the cat. Description of a new method for study of inner ear hydrodynamics

Continuous recordings of the perilymphatic (Pp), cerebrospinal fluid (PCSF), central venous (PCV) and arterial (PA) pressures have been performed on anesthetized cats. The perilymphatic space was reached by an extraural 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 PP and PCSF were found to be equal, whereas the maximum pressure during expiration was significantly higher in the CSF. not affected by the given anesthetics. Ligation of the external jugular veins had a minor and temporary effect on the PP and PCSF. 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.