A Model of Intracranial Pulsations

Traditional models of intracranial dynamics describe the convective flow of blood and cerebrospinal fluid (CSF) in the cranium. Recent data from flow-sensitive MRI studies reveal that almost all motion of blood and CSF in the cranium is pulsatile. We have applied the mathematical description of a harmonic oscillator to the analysis of pulsatile motion within the cranium. Oscillations of blood and CSF can be represented mathematically by phasors on the complex plane, and their magnitude and phase relationships can be readily determined. The synchrony that characterizes normal vascular and CSF pulsations is characteristic of resonance, in which the heart rate is the same as the natural rate of oscillation of the cranial contents. Using this approach, pulsatile dynamics can be simulated on an analog electrical circuit, because the behavior of the circuit is governed by the same mathematics. Our simulations predict that diminished intracranial compliance will be associated with a phase lag of the intracranial pressure pulse with respect to the vascular pulse, which has been reported previously. Syrinxes and arachnoid cysts are modeled as capacitive diverticula 'in parallel' with the normal subarachnoid pathways. The pulsation model predicts CSF velocity waveforms that are in good agreement with MRI flow studies from other reports. The relationship between pulsatile cerebral blood flow and CSF pulsations suggests that the oscillating CSF functions as a pulsation absorber, which is the basis for the windkessel mechanism. The pulsation model provides a new tool for the study of intracranial dynamics. Copyright © 2001 S. Karger AG, Basel