Proceedings of The Physiological Society

Kings College London (2005) J Physiol 565P, C19

Communications

Non-invasive assessment of intracranial arterial and respiratory pressure waves via the trans aural route in man.

Lin, Jean-Pierre ; Rosenthal, Eric ; Marchbanks, Robert ;

1. Paediatric Neurology, Guy's & St Thomas' Foundation NHS Trust, London, United Kingdom. 2. Paediatric Cardiology, Guy's & St Thomas' Foundation NHS Trust, London, United Kingdom. 3. Department of Physics and Bioengineering, SouthamptonGeneral Hospital, Southampton, United Kingdom.


The clinical measurement of intracranial pressure usually requires invasive access to the cerebrospinal fluid compartment which is painful, hazardous in the unconscious patient and impractical for long-term follow-up studies. The trans-aural route of intracranial pressure monitoring has been previously described (Marchbanks 1987, Samuel et al 1998). Ethical permission was obtained for systematic study of trans-aural intracranial pressure measurements in children. A 16 year old girl with longstanding headache, papilloedema and congenital heart disease underwent general anaesthesia and mechanical ventilation for replacement of her cardiac pacemaker and an opportunistic lumbar puncture was performed. The continuous cerebrospinal fluid (CSF) pressure is shown (fig. 1)with the arterial and mechanical ventilation waveforms indicated by thin & thick arrows respectively (top trace: pressure in cmH2O). The trans-aural (TMD) air volume changes (bottom trace: volumes of air displaced in nanolitres) clearly match the CSF arterial and ventilation pulse wave changes. The arterial interpulse intervals range from 900-1000ms. Ventilated CSF respiratory pressure waves of 3.6cmH20 produced TMD volume displacements of 1684nl (peak-peak). This gives a CSF/TMD calibration factor of 0.021 mm saline / nl and the TMD will resolve displacements to less than 5nl or 0.10 mm saline. The CSF & TMD arterial pulse & mechanical ventilation amplitudes diminished with removal of CSF to reduce intranial pressure. This represents the first description of accurate intracranial respiratory and cardiovascular pulse waves via the trans-aural route in humans & may contribute to the management of acute & chronic ehcephalopathy in children and adults. Figure 1. Simulatneous intra-cranial CSF pressures (cmH20) & intra-aural air volume displacements (nl).

Where applicable, experiments conform with Society ethical requirements