Non-invasive measurement of intracranial pressure changes by otoacoustic emissions (OAEs)--a report of preliminary data.

Up to now changes of intracranial pressure can only be objectively assessed by invasive measurement tools e.g. epidural transducers or intraventricular or intraparenchymatous catheters. Changes of intracranial pressure (ICP) are known to influence the inner ear since the subarachnoid space is linked to the perilymphatic space of the inner ear via the cochlear aquaeduct. A new method for assessing cochlear disorders is based on otoacoustic emissions (OAE) which are generated by the outer hair cells (OHCs) of the inner ear. The aim of the present study was to find out whether changes of intracranial pressure can be monitored by spontaneous otoacoustic emissions (SOAEs), transient evoked otoacoustic emissions (TEOAEs) and distortionproduct otoacoustic emissions (DPOAEs). SOAEs, TEOAEs and DPOAEs were measured in 12 young normally hearing subjects (volunteer group) in different body postures (horizontal, -30 degrees and +30 degrees supine position). In 5 patients undergoing continuous intraventricular pressure monitoring for the assessment of normal pressure hydrocephalus (NPH), DPOAEs were measured simultaneously in different body postures as well (patient group). At an increase of ICP the SOAE-level of the volunteer group decreased by -3.3 dB SPL (sound pressure level) and the TEOAE-level by -2.1 dB SPL. The DPOAEs showed a frequency dependent reduction of its level with maximal changes at the lowest frequency tested (f2 = 1 kHz; -7.9 dB SPL). In the patient group the ICP amounted to 19.2 cm H(2)0 and the DPOAE-level also decreased particularly at lower frequencies (-2.0 dB SPL). In conclusion otoacoustic emissions, particularly DPOAEs, may provide a new clinical tool for non-invasive monitoring of ICP.