Postural-induced changes in intracranial pressure evaluated non-invasively using the MMS-10 tympanic displacement analyser in healthy volunteers.

Inner ear pressure reflects intracranial pressure (ICP) primarily because of the direct communication of perilymph and cerebrospinal fluid (CSF) through the cochlear aqueduct (CA). The MMS-10 tympanic displacement analyser (TDA) is a relatively new device for measuring perilymphatic pressure non-invasively, and thereby also indirectly measuring intracranial pressure. The aim of the present study was to evaluate the use of the TDA in a daily clinical setting. Other aims were to investigate changes in perilymphatic pressure from sitting to lying position in healthy volunteers in two age groups (mean age: 33 years and 50 years) and to compare the patency of the CA in these groups using the MMS-10 TDA. Tympanic membrane displacement (TMD) analyses were performed in the test subjects initially twice in sitting position (test-retest) and then in sitting and supine positions. We found that the MMS-10 TDA is easy to use, and that it gives reproducible values in repeated tests, but with large inter-subject differences. The TMD test showed curves, which, in the whole test group, were more negative in supine position, in accordance with an increasing intracranial and inner ear pressure when lying down. The change from sitting to lying position was larger in the younger group than in the older group. In 11% of the younger group (males) and in 30% of the older group (females), the CA was considered to be non-patent, although the difference was not statistically significant. However, the finding is in keeping with the hypothesis of a greater proportion of patent CA in younger than in older individuals.