Assessment of cerebrospinal fluid outflow resistance

Abstract

The brain and the spinal cord are contained in a cavity and are surrounded by cerebrospinal fluid (CSF), which provides physical support for the brain and a cushion against external pressure. Hydrocephalus is a disease, associated with disturbances in the CSF dynamics, which can be surgically treated by inserting a shunt or third ventriculostomy. This review describes the physiological background, modeling and mathematics, and the investigational methods for determining the CSF dynamic properties, with specific focus on the CSF outflow resistance, R out. A model of the cerebrospinal fluid dynamic system, with a pressure-independent R out, a pressure-dependent compliance and a constant formation rate of CSF is widely accepted. Using mathematical expressions calculated from the model, along with active infusion of artificial CSF and observation of corresponding change in ICP allows measurements of CSF dynamics. Distinction between normal pressure hydrocephalus and differential diagnoses, prediction of clinical response to shunting and the possibility of assessment of shunt function in vivo are the three most important applications of infusion studies in clinical practice.

CSF dynamic analysis of a predictive pulsatility-based infusion test for normal pressure hydrocephalus

“…The derivative of ICP with respect to volume is the elastance of the system, the inverse of which is compliance (C) [18]. According to an established mathematical model of the CSF dynamics [25] the relationship between ICP and volume is exponential, and compliance can be described as:…”

“…As formation is generally considered pressure independent [4,18] this means that equation (3) can be rewritten (see Appendix) as:…”

“…[11,18,25]. It is a lumped model, and thus the sites of secretion and absorption are not specifically modelled.…”

Effect of infusion tests on the dynamical properties of intracranial pressure in hydrocephalus

“…Participants presented different combinations of Hakim's triad: gait disturbances, cognitive deterioration and urinary incontinence [9]. Lumbar ITs were performed as a supplementary hydrodynamic study to help in the decision on the surgical management of patients [8].…”

“…Then, pressure is recorded and the resistance to CSF outflow is calculated [8]. Additionally, the applications of ITs include the assessment of shunt function [9], the analysis of metabolic changes in periventricular white matter [10] and the study of the haemodynamic response associated with ICP [11].…”