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Objective. Evoked tympanic membrane displacement (TMD) measurements show a correlation with intracranial pressure (ICP). Attempts to use these measurements for non-invasive monitoring of ICP in patients have been limited by high measurement variability. Pulsing of the tympanic membrane at the cardiac frequency has been shown to be a significant source of the variability. In this study we describe a post processing method to remove the cardiac pulse waveform and assess the impact of this on the measurement and its repeatability. Approach. Three-hundred and sixteen healthy volunteers were recruited for evoked TMD measurements. The measurements were quantified by V m, defined as the mean displacement between the point of maximum inward displacement and the end of the stimulus. A sample of spontaneously pulsing TMDs was measured immediately before the evoked measurements. Simultaneous recording of the ECG allowed a heartbeat template to be extracted from the spontaneous data and subtracted from the evoked data. Intra-subject repeatability of V m was assessed from 20 repeats of the evoked measurement. Results with and without subtraction of the heartbeat template were compared. The difference was tested for significance using the Wilcoxon sign rank test. Main results. In left and right ears, both sitting and supine, application of the pulse correction significantly reduced the intra-subject variability of V m (p value range 4.0 × 10−27 to 2.0 × 10−31). The average improvement was from 98 ± 6 nl to 56 ± 4 nl. Significance. The pulse subtraction technique substantially improves the repeatability of evoked TMD measurements. This justifies further investigations to assess the use of TMD measurements in clinical applications where non-invasive tracking of changes in ICP would be useful.

Evoked tympanic membrane displacement (TMD) measurements, quantified by VSpontaneous and evoked TMD data from each ear in the sitting and supine position were recorded from 100 healthy volunteers using the MMS-14 CCFP analyser. ECG was also recorded to identify each heartbeat. Using bespoke software written in Matlab, spontaneous data were analysed to produce average pulse amplitude (PA) waveforms and evoked data were analysed to calculate average VThere was a strong positive correlation between PA and VThis study shows that large V

Objectives: Evoked tympanic membrane displacement (TMD) measurements, quantified by Vm, record small volume changes in the ear canal following stimulation of the acoustic reflex. Vm shows a correlation with intracranial pressure (ICP) and has been proposed as an option to non-invasively measure ICP. The spontaneous pulsing of the tympanic membrane, driven by the cardiovascular pulse, may contaminate the recordings and contribute to high measurement variability in some subjects. This study hypothesised that the larger the spontaneous vascular pulse, the larger the variability in Vm.

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.