A new lumped-parameter model of cerebrospinal hydrodynamics during the cardiac cycle in healthy volunteers

Our knowledge of cerebrospinal fluid (CSF) hydrodynamics has been considerably improved with the recent introduction of phase-contrast magnetic resonance imaging (phase-contrast MRI), which can provide CSF and blood flow measurements throughout the cardiac cycle. Key temporal and amplitude parameters can be calculated at different sites to elucidate the role played by the various CSF compartments during vascular brain expansion. Most of the models reported in the literature do not take into account CSF oscillation during the cardiac cycle and its kinetic energy impact on the brain. We propose a new lumped-parameter compartmental model of CSF and blood flows in healthy subjects during the cardiac cycle. The system was divided into five submodels representing arterial blood, venous blood, ventricular CSF, cranial subarachnoid space, and spinal subarachnoid space. These submodels are connected by resistances and compliances. The model developed was used to reproduce certain functional characteristics observed in seven healthy volunteers, such as the distribution (amplitude and phase shift) of arterial, venous, and CSF flows. The results show a good agreement between measured and simulated intracranial CSF and blood flows.

Brain hydrodynamics study by phase-contrast magnetic resonance imaging and transcranial color doppler

PURPOSE

To evaluate the contributions of phase-contrast magnetic resonance (PCMR) and transcranial color Doppler (TCCD) imaging in the investigation of cerebral hydrodynamics.

MATERIALS AND METHODS

A total of 13 healthy subjects were studied. Blood velocity measurements were performed with TCCD and gated PCMR imaging in major intracranial and extracranial arteries stages. Peak systolic velocity and end-diastolic velocity were extracted to establish correlations between TCCD and PCMR imaging. Cerebral blood flow (CBF) and intracranial volume change (IVC) during the cardiac cycle were calculated, taking into account cerebrospinal fluid (CSF) oscillations.

RESULTS

Despite an underestimation of velocities with PCMR imaging, significant correlations were observed for velocity measurements between the two modalities in extracranial vessels, but were poorly correlated in intracranial vessels. PCMR data processing gave a mean CBF of 690+/-90 mL/minute.

CONCLUSION

PCMR imaging provides complementary information to TCCD to assess various intracranial parameters such as instantaneous velocities, blood and CSF flow distributions, volume variation, or pressure regulation mechanisms during cardiac cycles.

Ventricular dilation as an instability of intracranial dynamics

We address the question of the ventricles' dilation as a possible instability of the intracranial dynamics. The ventricular system is shown to be governed by a dynamical equation derived from first principles. This general nonlinear scheme is linearized around a well-defined steady state which is mapped onto a pressure-volume model with an algebraic effective compliance depending on the ventricles' geometry, the ependyma's elasticity, and the cerebrospinal fluid (CSF) surface tension. Instabilities of different natures are then evidenced. A first type of structural instability results from the compelling effects of the CSF surface tension and the elastic properties of the ependyma. A second type of dynamical instability occurs for low enough values of the aqueduct's conductance. This last case is then shown to be accompanied by a spontaneous ventricle's dilation. A strong correlation with some active hydrocephalus is evidenced and discussed. The transfer function of the ventricles, compared to a low-pass filter, are calculated in both the stable and unstable regimes and appear to be very different.