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What is a stroke:

A stroke is the sudden death of brain cells due to a problem with the blood supply. When blood
flow to the brain is blocked, oxygen enriched blood cannot be delivered. The result is abnormal
brain function. Blood flow to the brain can be disrupted by either a blockage or rupture of an
artery to the brain. There are many causes for a stroke, as shown below in the tables. A stroke
is also referred to as a CVA.

Blockage of artery

  •   Clogging of arteries within the brain(e.g. lacunar stroke)
  •   Hardening of the arteries leading to the brain (e.g. carotid artery occlusion)
  •   Embolism to the brain from the heart or an artery.


Rupture of an artery (i.e. hemorrhage)

  •   Cerebral hemorrhage (bleeding within the brain substance)
  •   Subarachnoid hemorrhage (bleeding between the brain and the inside of the skull)

What causes a stroke

The blockage of an artery in the brain by a clot (thrombosis) is the most common cause of a
stroke. The part of the brain that is supplied by the clotted blood vessel is then deprived of
blood and oxygen. The cells of that part of the brain die as a result. Typically, a clot forms in a
small blood vessel within the brain that has been previously narrowed due to the long-term,
damaging effects of high blood pressure (hypertension) or diabetes. The resulting strokes are
called lacunar strokes because they look like little lakes. In other situations, usually because of
hardening of the arteries (atherosclerosis), a blood clot can obstruct a larger vessel going to
the brain, such as the carotid artery in the neck.

Another type of stroke occurs when a blood clot or a piece of atherosclerotic plaque
(cholesterol and calcium deposits on the wall of the inside of the heart or artery) breaks loose,
travels through open arteries, and lodges in an artery of the brain. When this happens, the flow
of oxygen-rich blood to the brain is blocked and a stroke occurs. This type of stroke is referred
to as an embolic stroke. For example, a blood clot might originally form in the heart chamber as
a result of an irregular heart rhythm, such as occurs in atrial fibrillation. Usually, these clots
remain attached to the inner lining of the heart, but occasionally they can break off, travel
through the blood stream, form a plug (embolism) in a brain artery, and cause a stroke. An
embolism can also originate in a large artery (for example, the carotid artery, a major artery in
the neck that supplies blood to the brain) and then travel downstream to clog a small artery
within the brain.

A cerebral hemorrhage occurs when a blood vessel in the brain bursts and bleeds into the
surrounding brain tissue. A cerebral hemorrhage (bleeding in the brain) can cause a stroke by
depriving blood and oxygen to parts of the brain. The accumulation of blood from a cerebral
hemorrhage can also press on parts of the brain and cause damage. A subarachnoid
hemorrhage is caused by the rupture of a blood vessel that is usually located between the
outside of the brain and the inside of the skull. The blood vessel at the point of rupture is often
previously abnormal, such as from an aneurysm (an abnormal ballooning out of the wall of the
vessel). Subarachnoid hemorrhages usually cause a sudden, severe headache and are often
complicated by further neurological problems, such as paralysis, coma, and even death.

Overall, the most common risk factors for stroke are high blood pressure and increasing age.
Diabetes and certain heart conditions, such as atrial fibrillation, are other common risk factors.
When strokes occur in younger individuals (less than 50 years old), less common risk factors
are often involved. These risk factors include drugs, such as cocaine or amphetamines,
ruptured aneurysms, and inherited (genetic) predispositions to blood clotting. Another example
of a genetic predisposition to stroke occurs in a rare condition called homocystinuria, in which
there are excessive levels of the chemical homocystine in the body. Furthermore, scientists are
trying to determine whether the non-hereditary occurrence of high levels of homocystine at any
age can predispose to stroke. Another rare cause of stroke is vasculitis, a condition in which the
blood vessels become inflamed. Finally, there appears to be a very slight increased occurrence
of stroke in people with migraine headache.

What is a TIA?

A transient ischemic attack (TIA) is a short-lived episode (less than 24 hours) of temporary
impairment to the brain that is caused by a loss of blood supply. A TIA causes a loss of function
in the area of the body that is controlled by the portion of the brain affected. The loss of blood
supply to the brain is most often caused by a clot that spontaneously forms in a blood vessel
within the brain (thrombosis). However, it can also result from a clot that forms elsewhere in the
body, dislodges from that location, and travels to lodge in an artery of the brain (emboli). A
spasm and, rarely, a bleed are other causes of a TIA. Many people refer to a TIA as a "mini-
stroke."

Some TIAs develop slowly while others develop rapidly. By definition, all TIAs resolve within 24
hours. Strokes take longer to resolve than TIAs and reflect a more permanent and serious
problem. Although TIAs often last only a few minutes and then end, most experts believe TIAs
should be evaluated with the same urgency as a stroke in an effort to prevent recurrences
and/or strokes. TIAs can occur once, multiple times, or precede a permanent stroke.

A TIA from a clot to the eye can cause temporary visual loss, which is often described as a
curtain coming down. A TIA that involves the carotid artery (the largest blood vessel supplying
the brain) can produce problems with movement or sensation on one side of the body, which is
the side opposite to the actual blockage. An affected patient may experience paralysis of the
arm, leg, and face, all on one side. Double vision, dizziness (vertigo) and loss of speech,
understanding, and balance can also be symptoms depending on what part of the brain is
lacking blood supply.

TIAs are often warnings of an impending, more severe or permanent stroke and must be
immediately evaluated by a physician. TIAs can reflect a local problem in the brain, a plugging
of the arteries to the brain such as the carotid arteries, or they can reflect a heart problem in
which clots dislodge and flow into the brain. Examples of these heart conditions include atrial
fibrillation, valve problems, and poorly beating or weak heart walls.

TIAs and hardening of the heart arteries can occur together and can reflect an underlying
disease such as diabetes mellitus, high cholesterol, or high blood pressure (hypertension).
What is the impact of strokes?

What is the impact of strokes?

In the United States, about 400,000 people a year suffer from a stroke, and up to 40% of these
strokes may be fatal. The cost of strokes is not just measured in the billions of dollars lost in
work, hospitalization, and the care of survivors in nursing homes. The major cost or impact of a
stroke is the loss of independence that occurs in 30% of the survivors. What was a self-
sustaining and enjoyable lifestyle may lose most of its quality after a stroke and other family
members can find themselves in a new role as caregivers.

How is a stroke recognized?

When brain cells are deprived of oxygen, they cease to perform their usual tasks. The
symptoms that follow a stroke depend on the area of the brain that has been affected and the
amount of brain tissue damage.

Small strokes may not cause any symptoms, but still damage brain tissue. These strokes that
do not cause symptoms are referred to as silent strokes. The most common symptom of a
stroke is weakness or paralysis on one side of the body or the other. There may be a partial or
complete loss of voluntary movement and/or sensation in a leg and/or arm. A stroke can cause
speech problems and weak muscles of the face, which can cause drooling. Numbness or
tingling in the leg, arm, or face is very common. A stroke involving the base of the brain can
affect balance, vision, and swallowing functions. A stroke can cause difficulty breathing and
even unconsciousness.

What should be done if you suspect you or someone else is having a stroke?

If any of the symptoms mentioned above suddenly appear, emergency medical attention should
be sought. The sooner treatment is started, the better the eventual outcome will be. Therefore,
the first action should be to call 911 (or whatever number activates the emergency medical
response in your area). The family doctor and/or neurologist should also be contacted.
However, the first priority is ensuring that the ambulance arrives as soon as possible. The
affected person should lie flat to promote an optimal blood flow to the brain. If drowsiness,
unresponsiveness, or nausea are present, the person should lie on one side to prevent choking
on his/her vomit. Although aspirin plays a major role in stroke prevention (see below), once the
symptoms of a stroke begin, it is generally recommended that additional aspirin not be taken
until the patient receives medical attention. If stroke is of the bleeding type, aspirin could
theoretically make matters worse.

http://www.medicinenet.com/stroke/article.htm
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