Impedance measurement as a noninvasive technique for the monitoring of intracranial pressure variations.

In previous reports it has been demonstrated that jugular compression causes a modification of middle ear acoustic impedance; this phenomenon has been named the jugulotympanic reflex (JTR). The aim of the present study was to contribute to the understanding of the origin of this reflex. We have analyzed the middle-ear impedance modifications induced by unilateral and bilateral jugular compression in 12 normal subjects, in 12 patients afflicted with otosclerosis, in 3 patients with Menière's disease and in 6 patients demonstrating intracranial hypertension. In the latter group, the cerebrospinal fluid (CSF) pressure was simultaneously recorded. The JTR was elicited in each normal subject and in each patient affected by Menière's disease and intracranial hypertension, while it was usually absent or modified in otosclerotic patients. The absence of the JTR in otosclerotic patients and, above all, the correspondence between CSF pressure and the middle-ear impedance modification induced by jugular compression suggest that it is due to the transmission of pressure changes from the CSF to the perilymph through the cochlear aqueduct.