Tuesday, January 18, 2011

Memory Health Alert

How Does Hypertension Affect Memory?

No matter which way you look at it, hypertension
(high blood pressure) is bad for your brain. Hypertension
is an important risk factor for cognitive impairment and
Alzheimer's disease. And if you are diagnosed with
Alzheimer's, hypertension may hasten cognitive decline.
What's more, hypertension is the most significant risk
factor for strokes, which can lead to dementia by
destroying brain tissue. This form of dementia, called
vascular dementia, is the second most common type
after Alzheimer's. It is most frequently caused by chronic
hypertension, which can result in a series of small strokes.
It is the accumulation of damage caused by multiple
little strokes that commonly causes vascular dementia.
Of course, hypertension can also cause a significant
single stroke that can damage a large area of the brain
and also cause dementia.
How does high blood pressure impact memory?
The most obvious way is via stroke. High blood pressure
damages blood vessels that carry blood to the brain,
and this damage leads to the buildup of plaques,
accumulation of inflammatory cells, cholesterol, and other
tissue products within blood vessels. When one of these
plaques ruptures, it travels through an artery and eventually
gets lodged in a place where the diameter of the plaque is
larger that the diameter of the blood vessels. This causes
a blood clot to form at that spot. If the clot completely cuts
off blood supply to brain cells responsible for memory or
other cognitive functions, the cells die. The death of these
cells then leads to impairments in thinking. About one third
of people who suffer a stroke develop serious cognitive
problems that interfere with their ability to perform daily
activities.
Another way that blood pressure affects cognition is its
effect on the white matter, the portion of the brain that lies
below the surface. White matter is composed of nerve fibers
that conduct messages between brain cells and a surrounding
myelin sheath that acts as insulation and improves its function
as a conduit of electrical and chemical information. Scans
show that people with hypertension often have white matter
abnormalities, probably because the hypertension produces
impaired blood flow that starves nerve fibers of needed
oxygen and nutrients. This causes the myelin sheath to decay
and results in "demyelination," which shows up on magnetic
resonance imaging (MRI) scans as bright white spots known
as white matter hyperintensities (WMHs) or age-related white
matter changes (ARWMCs).
Research shows that the greater the amount of white matter
changes, the higher the risk of dementia. Reduced blood flow
from hypertension can also directly affect cells in such areas
of the brain as the hippocampus, which is involved in memory.
When these cells do not get enough nutrients and oxygen,
they cannot function properly. If this causes the death of cells,
those areas of  the brain may shrink. In addition, blood flow
reduction leads to less efficient removal of waste product
from brain tissue.
Last, hypertension may compromise the blood-brain barrier,
a relatively impenetrable shield that surrounds the brain.
This, in turn, allows toxic substances such as beta-amyloid
(a sticky protein associated with Alzheimer's)
to enter and accumulate in the brain.

No comments:

Post a Comment