Are brain displacements and pressures within the parenchyma induced by surface pressure differences? A computational...

Area of Science:

• Biophysics
• Neuroscience
• Fluid Dynamics

Background:

• Intracranial pressure (ICP) is vital for brain homeostasis and implicated in diseases like idiopathic normal pressure hydrocephalus (iNPH).
• A small, persistent pulsatile transmantle pressure gradient has been observed in hydrocephalus patients.
• The origin of pulsatile intracranial pressure and its role in fluid dynamics require further investigation.

Purpose of the Study:

• To investigate whether a small pressure gradient originating from the brain surface can induce pulsatile intracranial pressure and displacements.
• To model the brain parenchyma as an elastic or poroelastic medium to simulate pressure dynamics.
• To determine the primary drivers of interstitial fluid flow within the brain parenchyma.

Main Methods:

• Developed a high-resolution, physics-based computational model of the brain parenchyma.
• Modeled the parenchyma as linearly elastic or poroelastic materials.
• Applied in vivo pulsatile pressure gradients from iNPH subjects between ventricular and pial surfaces.

Main Results:

• Computed parenchyma displacement, volume change, fluid pressure, and fluid flux using the model.
• The resulting displacement fields were pulsatile and consistent with existing literature for both elastic and poroelastic models.
• Pulsatile forces applied at the brain surface boundaries were insufficient to propagate pressure pulses through the parenchyma.

Conclusions:

• Pressure differences at the brain surface are not sufficient on their own to drive interstitial fluid flow within the brain parenchyma.
• The study suggests that the brain's blood vessel network, including smaller vessels, is a more significant source of pressure gradients driving interstitial fluid flow.
• This finding has implications for understanding fluid dynamics in neurological conditions like hydrocephalus.