Reference intervals for the evoked tympanic membrane displacement measurement: a non-invasive measure of intracranial pressure.

OBJECTIVE: Evoked tympanic membrane displacement (TMD) is a non-invasive technique for assessing intracranial pressure (ICP). The aim of this study was to define reference intervals (RIs) in the healthy population.

APPROACH: Measurements were made in 154 healthy adults. Results were quantified by V m , which is the most frequently described TMD measurement. Distributions were determined for sitting and supine posture. Differences between right and left ears were explored using a Wilcoxon signed-rank test. Postural changes were used to assess pressure transfer between the cerebral spinal fluid (CSF) and the perilymph.

MAIN RESULTS: The range in which 95% of scores fall is  -283 to 722 nl (M  =  132 nl) left sitting, -232 to 623 nl (M  =  97 nl) right sitting, -543 to 717 nl (M  =  37 nl) left supine and  -584 to 504 nl (M  =  -15 nl) right supine. No significant difference was seen between the left and right ears in the sitting position; a significant difference was seen in the supine position. A significant effect of posture was seen for both the left and right ears. Postural changes indicated pressure transfer between the CSF and perilymph more often in the right ear (75.3%) than the left (61.9%). Pressure transfer could not be assumed in either ear for 13.4% of participants.

SIGNIFICANCE: We present the largest dataset of evoked TMD in healthy individuals and the first set of RIs for V m . A patient cohort with both invasive ICP and evoked TMD measurements is needed to validate the technique for clinical use.