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Abstracts from the Association of British Neurologists Annual Meeting 2011
082 Non-invasive measurements of intracranial pressure: Can Coherent averaging show a tilt-dependent change in the measured Spontaneous Tympanic Membrane Displacement (STMD) signal in healthy volunteers?
  1. J D Davids,
  2. A A Birch,
  3. R J Marchbanks
  1. Southampton University Hospital NHS Trust


Introduction Spontaneous Tympanic Membrane Displacement can be measured quasi-continuously and shows a cardiovascular waveform (STMDVA). It is probable that this waveform is generated by intracranial pressure being transmitted to the ossicular chain. Its amplitude may relate to intracranial compliance.

Aims To test the hypothesis that there will be a significant change in the coherently averaged STMDVA with body-tilt from −15° head-down to +70° head-up.

Methods Continuous measurements of STMDVA and arterial pressure waveforms were recorded in healthy adults during body-tilts from −15° head-down to +70° head-up and returned to −15° head-down. Subjects were held at each position for 3 min and the final minute of heartbeats was coherently averaged to produce a single averaged STMDVA waveform for each body-angle. Repeated measures ANOVA was used to test the trend for significance considered at p<0.05.

Results 13 males and five females completed the protocol, age range 18–57 (mean 25). Within-subjects effects showed a significant change in STMDVA trend with body-tilt (p=0.005). There was a clear reduction in STMDVA with increasing body-tilt from −15° head-down to +30° head-up. A plateau was reached between +30° head-up and +70° head-up.

Conclusion A significant decrease (p<0.005) was found with increasing head-up body-tilt. The decrease was not seen at angles >30°. This may support 30° as optimal for cerebral perfusion pressure. STMDVA has potential to monitor changes in intracranial compliance.

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