The correlation of tympanic membrane displacement measurements to direct intracranial pressure recordings in cat [poster]

Abstract

In the present experiments, direct, invasive assessment of intracranial (ICP) pressure was correlated to the non-invasive tympanic membrane displacement (TMD) technique registering intracranial and intracochlear pressure changes, respectively. As shown in children with hydrocephalus, direct recordings of the ICP can be correlated to TMD recordings. However, in these clinical studies the TMD recordings have a large inter-individual variation and do not monitor absolute pressure changes. In cats (n = 6), the ICP was therefore continuously changed from 15 - 35 mm Hg and recorded in the cisterna magna. The TMD recordings (mean volume displacement, Vm in nl) performed at the same time could be statistically significantly correlated to the observed ICP changes. Moreover, the clinically important shift from linear into the exponential fit of the volume-pressure curve of ICP ( at 15 mm Hg) is accompanied by a clear change from (Vm) +34 (± 8) to - 74 (±12) which was reversible and repeatable. This indicates that the ICP and the intracochlear pressure are closely correlated when the cochlear aqueduct is patent. ICP pressure fluctuations could contribute to the low-frequency tinnitus and sensorineural hearing loss as observed in patients with an elevated ICP. The TMD technique seems to be well suited to contribute to the diagnosis of such changes.