This Is MS Multiple Sclerosis Community: Knowledge & Support

The brain's buffer

As well as delivering oxygen to the brain, cerebral blood flow has another vital role: the circulation and production of cerebrospinal fluid. This clear liquid surrounds the brain, carrying the nutrients that feed it and removing the waste it produces, including the tau and beta-amyloid proteins that have been implicated in the formation of plaques found in the brains of people with Alzheimer's (Cerebrospinal Fluid Research, vol 5, p 10).

How blood flow influences cerebrospinal fluid flow can be gauged from something called "cranial compliance", a measure of the elasticity of the brain's vascular system. "The cranium is a bony cavity of fixed volume, with the brain taking up most of the space," says Robin Kennett, a neurophysiologist from the Oxford Radcliffe Hospitals in the UK. "Every time the heart beats and sends blood into the cranium, something else has to come out to prevent the pressure rising to levels that would damage the brain." So, as fresh blood flows into the brain's blood vessels, cerebrospinal fluid flows out into the space around the spinal cord through a hole in the base of the skull called the foramen magnum.

As we age, the proteins in the brain harden, preventing this system from working as it should. As a result, the flow of both blood and cerebrospinal fluid is reduced, impairing the delivery of oxygen and nutrients as well as the removal of waste. Moskalenko's research suggests that this normally begins between the ages of 40 and 50. Moreover, in a study of 42 elderly people with dementia, he found that the severity of their cognitive disorder was strongly correlated with cranial compliance: those with the severest dementia had the lowest compliance (International Journal of Psychophysiology, vol 69, p 307). "Cranial compliance is a significant component of the origin of certain cases of brain pathology," he says.

Cerebrospinal fluid dynamics are dependent on venous drainage. It is a balance between CSF ultrafiltration from the veins of the lateral ventricles and the CSF reabsorption.

The velocity of the CSF- the average net CSF flow in MS patients was strongly associated with a retrograde flow- velocity is lower in both directions in MS

Data on CSF flow and the accumulation of lesions: Lower CSF pressure shows a correlation to lesion volume.