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Bulk flow of brain interstitial fluid under normal and hyperosmolar conditions
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1980
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White MatterBrain CirculationBrain LesionCerebral Vascular RegulationBulk FlowBlood FlowBrain Interstitial FluidCerebrospinal FluidDiffusion CoefficientIntracranial PressureTransport PhenomenaEdemaNeurologyHyperosmolar ConditionsNeuropathologyHealth SciencesNeuroimagingCerebral Blood FlowNeurophysiologyNeuroanatomyPhysiologyNeuroscienceCentral Nervous SystemMedicine
Bulk flow of brain interstitial fluid occurs with hydrostatic and osmotic pressure changes, but under normal conditions only diffusion has been reported. The authors measured extracellular molecule penetration in gray and white matter during 1–4‑hour ventriculocisternal perfusions and, in additional animals, administered 20 % mannitol intravenously before a 1‑hour perfusion to assess its effect on ISF flow. The study found that while gray‑matter diffusion remained constant, white‑matter diffusion coefficients declined over time, indicating bulk ISF flow toward the ventricle at ~10.5 µm/min; mannitol induced bulk flow away from the ventricle in gray matter, and the authors estimate that 30 % of extrachoroidal CSF production derives from ISF flow in white matter.
Although bulk flow of brain interstitial fluid (ISF) occurs with changes in hydrostatic and osmotic pressures, under normal conditions only diffusion of molecules in the ISF has been reported. Extrachoroidal cerebrospinal fluid (CSF) production and intracerebral injection studies, however, provide indirect evidence for the bulk flow of ISF under normal conditions. We studied tissue penetration profiles of an extracellular molecule in gray and white matter after 1-, 2-, 3-, and 4-h ventriculocisternal perfusions. Gray matter apparent diffusion coefficients were similar at different times as expected with diffusion; however, white matter coefficients decreased significantly with time, suggesting bulk flow of ISF. White matter data was reanalyzed for both bulk flow and diffusion; we calculated a diffusion coefficient of 3.00 x 10(-6) cm2/s and a velocity for ISF of 10.5 micrometers/min toward the ventricle. Additional animals were given 20% mannitol (1.5--3 g/kg) intravenously prior to a /-h ventriculocisternal perfusion. Mannitol produced a significant bulk flow of ISF away from the ventricle in gray matter. We estimate that 30% of extrachoroidal CSF production is from flow of ISF in white matter.