A demonstration analogue for ventricular and intraspinal dynamics (DAVID)

Abstract

A fluid analogue model, attempting to reproduce the CSF pathways around the human brain and spinal cord is described, the emphasis in design being on visibility rather than upon accurate scaling of fluid behaviour. The following important features could be demonstrated: 1. (1) There were 3 mechanisms by which venous pulsation could impose energy on CSF pathways. 1.1. (a) Intermittent epidural vein distension and relaxation produced movement of CSF upwards more readily than downwards because of the anatomical configuration at the foramen magnum with a valve-like mechanism produced by the cerebellum and hindbrain. There was a resultant difference in baseline CSF pressures so that the intracranial pressure was higher than the spinal pressure. This has been called craniospinal pressure dissociation. 1.2. (b) Filling of a communicating syringomyelia has been demonstrated in response to intermittent epidural vein distension. This filling occurs during a period in which the intrasyrinx pressure is lower than the baseline pressure in the head, i.e. in response to cranio-spinal pressure dissociation and also proceeds further so that the baseline pressure within the syrinx exceeds that within the cranium or the spine and the syrinx is under tension. 1.3. (c) The imposition of energy upon a syringomyelic cavity could be shown when it was in either a full or a flaccid condition. This resulted from the transmission of CSF pressure waves across the subarachnoid space and the generation of waves within the syrinx which could be seen travelling up to the syringobulbic cavity. 2. (2) The capacitance effects were noted to be of importance in modifying behaviour. Of particular interest was the damping effect of a meningocele in lessening intraspinal pressure pulsations and thereby lessening the three mechanisms described above. 3. (3) A concept of “efficiency” for the transfer of energy to CSF pathways depending upon the state of filling of the blood system and CSF pathways has been evolved from a study of the model's behaviour. It is suggested that these mechanism may be of significance in human disease and the validity of the illustration provided by the model is discussed.