Cerebrospinal Fluid Flow Dynamics in the Central Nervous System

Abstract

Cine-phase-contrast-MRI was used to measure the three-dimensional cerebrospinal fluid (CSF) flow field inside the central nervous system (CNS) of a healthy subject. Image reconstruction and grid generation tools were then used to develop a three-dimensional fluid-structure interaction model of the CSF flow inside the CNS. The CSF spaces were discretized using the finite-element method and the constitutive equations for fluid and solid motion solved in ADINA-FSI 8.6. Model predictions of CSF velocity magnitude and stroke volume were found to be in excellent agreement with the experimental data. CSF pressure gradients and amplitudes were computed in all regions of the CNS. The computed pressure gradients and amplitudes closely match values obtained clinically. The highest pressure amplitude of 77 Pa was predicted to occur in the lateral ventricles. The pressure gradient between the lateral ventricles and the lumbar region of the spinal canal did not exceed 132 Pa (~1 mmHg) at any time during the cardiac cycle. The pressure wave speed in the spinal canal was predicted and found to agree closely with values previously reported in the literature. Finally, the forward and backward motion of the CSF in the ventricles was visualized, revealing the complex mixing patterns in the CSF spaces. The mathematical model presented in this article is a prerequisite for developing a mechanistic understanding of the relationships among vasculature pulsations, CSF flow, and CSF pressure waves in the CNS.

The role of brain barriers in fluid movement in the CNS: is there a ‘glymphatic’ system?

“…Because peak CSF pulse velocity corresponds with the elevated systolic blood pressure during each heart beat, the increased volume and pressure of blood entering the brain tissue and plexuses is thought to cause transient tissue swelling, squeezing the ventricles and subarachnoid space (SAS), mixing and moving the bulk CSF toward drainage sites. Mathematical models developed by Linninger and colleagues to inform a mechanistic understanding of the relationship between vascular pulsation and CSF flow correlate well with in vivo data from healthy humans and help explain in more detail the clinical observation that CSF flow reversal is seen first in the cisterns, then in the lateral ventricles during the cardiac cycle [170]. Their models predict that vascular expansion following cardiac systole occurs first at the base of the brain, so reversing the flow of cisternal CSF, followed by dilation of arterioles in brain parenchyma, compressing both subarachnoid space and lateral ventricles and displacing fluid toward the spinal canal.…”

The pulsatility volume index: an indicator of cerebrovascular compliance based on fast magnetic resonance imaging of cardiac and respiratory pulsatility

“…This will not be the case for capillaries (spin velocity approx. 0.5-2 mm s −1 ), nor the ventricular, sulcal and brain parenchymal interstitial CSF (CSF bulk flow velocity is in the range 1-4 mm s −1 , with the maximum bulk flow velocity of 2 cm s −1 in the cerebral aqueduct [10]), whose spins will belong to regime 2.…”

“…Previous work with Doppler ultrasound methods [25] and gated CINE MRI methods [10] mainly focuses on measuring blood/CSF velocity during the cardiac cycle only; further, to probe brain tissue elasticity, other techniques (MR elastography) employ external mechanical vibrations at high frequency (range 25-100 Hz [26,27]). The possibility, demonstrated by our results, to map the effects of two different endogenous (cardiac and respiratory) pressure waves enables one to probe brain tissue compliance at two physiological modes of vibration, hence possibly providing complementary information on cerebrovascular and brain parenchymal compliance (for instance because of different compliance mechanisms at different frequencies, namely approx.…”

“…Magnetic resonance angiography [3] can be employed to investigate structural abnormalities of extracranial and intracranial arteries in a non-invasive manner. Gated CINE-MRI [9] is a functional technique that has been mainly used to measure intracranial compliance to cardiac pulsatility in the ventricles and CSF spaces by measuring CSF velocity across the cardiac cycle [10,11]. Gated CINE-MRI has also been employed for imaging of the cardiac function [12], but is not currently employed to measure cerebrovascular compliance, most probably because of limited speed and spatial coverage (few minutes per slice to quantify bulk flow velocity in three directions).…”

Assessment of intracranial dynamics in hydrocephalus: effects of viscoelasticity on the outcome of infusion tests

“…Over the last decade, basic research in this area has seen a veritable renaissance, drawing in researchers from diverse fields such as biology 14,16,27 and engineering. 15,19,31 Therefore, it is only a matter of time until interdisciplinary teams of neurosurgeons and basic researchers will uncover the workings of intracranial dy namics and hydrocephalus.…”