Cerebrospinal Fluid Pulsatility: Design and Validation in Healthy Normals

Abstract

During the cardiac cycle a complex series of fluid shifts occur within the skull in order to protect the brain from the pressure variations which occur in the cerebral arteries. The extracerebral intracranial arteries dilate during systole generating a pressure wave within the cerebral spinal fluid (CSF). This pressure wave is dissipated by flow of CSF into the compliant spinal subarachnoid space and by direct transmission to the cerebral venous sinuses. This mechanism reduces the pulsatility of the pressure wave to which the brain is exposed during the cardiac cycle. Failure of this mechanism has been implicated in a number of cerebral diseases. The mechanism can be investigated using quantitative magnetic resonance phase imaging but results can be difficult to interpret due to the complexity of the interactions. We present a novel physiological model of this mechanism based on the concept of electrical equivalence. The model allows privation of seven parameters which are not directly measurable: 1) the arterial compliance, 2) brain compliance, 3) ventricular compliance, 4) venous compliance, 5) arterial impedance, 6) brain impedance and 7) impedance of the cerebral aqueduct. We tested the model in a group of 24 healthy normal volunteers. Analysis of individual subjects showed that the data contained in adequate information for reliable fitting. Groupwise analysis showed that the model described all of the statistically significant variation in the data. We conclude that this model forms a basis for the analysis of CSF flow studies although it will requir