[Method of automatic modal analysis of variations in intracranial pressure in man]

When ICP measurement is used for a neuro-surgical patient we wonder about two questions: --which are the highest and the mean ICP value? --is there some spontaneous pathological variations like plateau wave or b wave? To answer these questions it is necessary to record ICP for extended periods of time. Numerical values are difficult and tedious to set up from ICP standard recordings. To resolve this practical problem, JANNY and KULLBERG had proposed a statistical automatic analysis of the different ICP values using a computer. The modal curve of the different classes of ICP amplitudes is then recorded. For 62 patients with various pathological situations (head injury subarachnoid hemorrhage, posterior fossa tumor, normal pressure hydrocephalus and dementia with symetric ventricular enlargement...) ICP has been recorded during 12 hours at the same time on the standard ink-writer recorder, and on a standard multichannels automatical analysis giving the modal curve of ICP amplitudes. On the round-headed modal curve obtained, ICP modal value i.e. the most frequent pressure value, can be read directly. ICP variations beyond this modal value like plateau wave or vasomotor variations modify the general aspect of this modal curve and sometimes in a specifical manner as regarded to the pathological situation. In our findings posterior fossa tumor without high modal ICP level are frequent but in these cases vasomotor response are nevertheless always present. In cases of normal pressure hydrocephalus as defined by clinical aspect, ventriculography and cisternography, the ICP modal value is higher than 12 mm Hg and vasomotor variations like B wave occurs frequently. The most typical monophasic aspect has been noticed in cases of metastatic meningitis. This technical approach of ICP measurement is very useful and gives immediately to the clinician the exact mean or modal ICP value as measured on the modal curve of the different ICP amplitudes with more accuracy and attainability than on the usual long term recordings.