Transmission of Intracranial Pressure Signals to the Human Ear Robert J. Marchbanks1 Colin P. Please2 Tony Birch1 & David Schley1,2 1 Department of Medical Physics and Bioengineering, Southampton General Hospital. 2 School of Mathematics, University of Southampton. Accurate intracranial pressure (ICP) measurements are vital for treatment and monitoring of seriously ill patients. At present, however, the only precise measurement devices involve inserting a probe through the skull – a highly invasive and potentially risky procedure. The development of the ‘MMS-11 Cerebral and Cochlear Fluid Pressure (CCFP) Analyser’ by Marchbanks Measurement Systems has provided the opportunity for non-invasive measurements by studying the movement of the eardrum as induced by intracranial pressure waves and in response to various stimuli. 1, 2. The Signal Processing Challenge We know that these intracranial pressure waves contain significant information concerning the status of the brain, for example, in the brain-injured patient. The challenge is to find the best method of analysing the pressure signals so as to extract underlying baseline pressure shifts and interactions between different types of pressure waves, and to take account of distortions. The main interaction of interest is between cerebral cardiovascular and respiratory pressure waves and how this interaction changes with posture - finding a means of analysis and visualisation will provide major clinical benefits.3 Methods including spectrograms 4 and wavelet transforms 5 have been proposed but at present none of these have been applied to our non-invasive intracranial pressure recordings. Clinical data will be used to develop a model to explore these relationships and to ultimately help perfect CCFP measurements. There is a need for signal processing expertise to support this work. We are also directly involved in a joint US project commissioned by the NASA Johnson Space Centre. Project E148 is to use our technique aboard the Space Shuttles to investigate changes in crew-members’ intracranial pressure and any relationships with space-sickness as they adapt to zero gravity conditions. There is a need for suitable signal processing algorithms to analyse the intracranial pressure waves and to support the planned three Shuttle missions. Above: Spectrogram from McNames et al (2002) Left: Wavelet analysis from Addison (2004) From the NASA Photograph Archive The Applications As part of an EPSRC CASE funded Mathematics PhD, due to commence in October ’04, clinical data will be collected from patients who are fitted with a pressure probe. This, for the first time ever, will provide simultaneous CCFP and direct ICP wave data for comparison purposes. The proposed work includes the development of a mathematical model of the fluid dynamics and pressure transmission through the channels connecting the cerebral fluid to the inner ear. Appeal for Collaborators It is unclear to us what signal-processing approach is likely to work best, and we are keen to collaborate with experts to develop this exciting research that has major clinical benefits. Data should be collected during the year, and there is the potential for staff time to be made available at the hospital to carry out analysis under suitable guidance. It is believed that close collaboration between applied mathematicians, clinicians and signal processing experts will provide the opportunity for publications in principal medical journals and collaborative research on an international basis. In addition to providing an evidence base for current clinical practice at Southampton General Hospital, it is hoped that the work undertaken will provide an insight into the causes of certain hearing and balance disorders,6 If you are interested in collaborating with us, or discussing the potential application of signal processing techniques to this problem, please contact us via Robert.Marchbanks@suht.swest.nhs.uk, 1. Samuel, M., Marchbanks, R.J. and Burge, D.M. (1998) Tympanic membrane displacement test in regular assessment in eight children with shunted hydrocephalus. J Neurosurg 88:983-995. 2. Intracranial and Intralabyrinthine Fluids: Basic Aspect and Clinical Applications’. Editors A. Ernst, R Marchbanks, M.Samii. Springer Verlag, ISBN 3-540-60979-2, 1996. 3. Klose et al (2000) Detection of a Relation Between Respiration and CSF Pulsation With an Echoplanar Technique. J of Magnetic Resonance Imaging, 11:438-444. 4. McNames et al (2003) Significance of Intracranial Pressure Pulse Morphology in Pediatric Traumatic Brain Injury. IEEE, 2491-2494. 5. Addison, P. (2004) The Little wave with the big future. Physics World, March, 35-39. 6. Intracranial and Inner ear physiology and pathophysiology. Editors A. Reid, R Marchbanks, Whurr Publishers, ISBN 1 86156 066 4, 1998.