CSF Physiology and Cerebral Blood Flow

Posted by e-Medical PPT Thursday, September 13, 2012
CSF Functions
provide mechanical protection
maintain a stable extracellular environment for the brain
Remove some waste products
Convey messages? (hormones/releasing factors/neurotransmitters)

CSF Production
70 % CSF produced in choroid plexuses of lateral, third and fourth ventricles
produced at rate of 500 cc/day or approximately 20cc/hour (0.3-0.5 cc/kg/hr)
eliminated by being absorbed into the arachnoid villi --> dural sinus --> jugular system
The secretion of fluid by the choroid plexus depends on the active Na+-transport across the cells into the CSF. The electrical gradient pulls along Cl-, and both ions drag water by osmosis. The CSF has lower [K+], [glucose], and much lower [protein] than blood plasma, and higher concentrations of Na+ and Cl-. The production of CSF in the choroid plexuses is an active secretory process, and not directly dependent on the arterial blood pressure.
Other sources of CSF production from capillary ultrafiltrate (Virchow-Robin spaces)
Additionally some produced from metabolic H2O production

CSF is produced by choroid plexus and secreted at ciliated cuboidal epithelial cell surfaces of the  microvilli into the ventricles

CSF Circulation
lateral ventricles--> foramen of Monro third ventricle --> aqueduct of Sylvius --> fourth ventricle --> foramina of Magendie and Luschka --> subarachnoid space over brain and spinal cord --> reabsorption into venous sinus blood via arachnoid granulations

Lundberg Waves
Lundberg has described 3 wave patterns ICP waves (A, B, and C waves). A waves are pathological. There is a rapid rise in ICP up to 50-100 mm Hg followed by a variable period during which the ICP remains elevated followed by a rapid fall to the baseline and when they persist for longer periods, they are called 'plateau' waves which are pathological. 'Truncated' or atypical ones, that do not exceed an elevation of 50 mm Hg, are early indicators of neurological deterioration. B & C waves are related to respiration and 'Traube-Hering-Mayer' waves (rhythmical variations in blood pressure) respectively and are part of normal physiology with little clinical significance.

A- waves/Plateau Waves
Steep rises and abrupt falls in ICP, peaking at 50-100 mm Hg, that last 5- 20 minutes (also known as plateau waves).
May signify intracranial vasomotor decompensation. May or may not be associated with clinical deterioration.
Pathogenesis related to dilation of resistance vessels, increased intracranial blood volume, decreased flow, and increased pressure.
“Loss of Autoregulation”

Route and Absorption of CSF
Arachnoid villi are microscopic one-way valves (modified pia and arachnoid) that penetrate the meningeal dural layer that line the sinuses; hence, arachnoid villi reside within the sinuses (especially the superior sagittal sinus).
Clumps of arachnoid villi = arachnoid granulations = macroscopic.
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