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Every two seconds, someone somewhere 
in the world experiences a stroke.

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And one out of every six people will have 
one at some point in their lives.

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Strokes deprive brain cells of oxygen

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and are one of the most 
common causes of death

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and a leading cause 
of preventable disability.

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When someone experiences a stroke,
quick medical care is critical,

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and can often help avoid 
permanent brain damage.

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But what causes strokes 
in the first place?

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And what can doctors do to treat them?

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The brain makes up just 2% 
of your body’s mass

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but consumes more than 20%
of the oxygen in your blood.

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That oxygen is carried to the brain
through a system of arteries.

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Carotid arteries supply 
the front of the brain,

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and vertebral arteries supply the back.

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These are connected to each other,

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and divide into smaller 
and smaller vessels

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that get billions of neurons 
the oxygen they need.

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If the blood flow is interrupted, 
oxygen delivery stops and brain cells die.

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There are two ways this can happen.

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Hemorrhagic strokes are when a perforated
vessel allows blood to leak out.

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But the more common type 
is the ischemic stroke,

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when a clot blocks a vessel 
and brings blood flow to a halt.

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Where do these clots come from?

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On rare occasions,
a sudden change in heart rhythm

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prevents the upper chambers of the heart
from contracting normally.

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This slows down blood flow,

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allowing platelets, clotting factors, 
and fibrin to stick together.

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The clot can be carried up

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towards the arteries
and blood vessels supplying the brain

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until it gets to one 
it can’t squeeze through.

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This is called an embolism

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and it cuts off the oxygen supply 
to all the cells downstream.

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The brain doesn't have pain receptors,
so you can't feel the blockage itself.

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But oxygen deprivation 
slows brain function

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and can have sudden, noticeable effects.

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For example, if the affected area 
is responsible for speech,

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an individual’s words may be slurred.

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If the stroke affects a part of the brain 
that controls muscle movement,

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it can cause weakness, 
often just on one side of the body.

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When this happens, the body 
will immediately try to compensate

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by diverting blood flow 
to the affected area,

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but this isn’t a perfect solution.

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Eventually, the oxygen-deprived cells 
will start to die,

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leading to brain damage 
that may be severe or permanent.

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That’s why it’s important to get
medical care as fast as possible.

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The first line of treatment
is an intravenous medication

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called Tissue Plasminogen Activator,

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which can break up the blood clot

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and allow blood to flow again
in the compromised artery.

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If it’s delivered within a few hours,

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this medication greatly increases
the chance of surviving the stroke

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and avoiding permanent consequences.

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If Tissue Plasminogen Activator
cannot be given

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because the patient 
is on certain medications,

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has history of major bleeding,

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or the clot is particularly large,

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doctors can perform a procedure
called an endovascular thrombectomy.

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Using a fluorescent dye that illuminates 
the blood vessels under a strong x-ray,

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the physician inserts a long, 
thin, flexible tube called a catheter

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into an artery in the leg

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and maneuvers
it all the way to the blockage.

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A retriever is passed
through this catheter.

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It expands and anchors into the clot 
when it’s just past it.

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The catheter then pulls the clot out 
when it’s removed.

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These treatments need to be delivered
as soon as possible

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to preserve brain function,

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which means figuring out fast 
if someone is having a stroke.

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So how can you tell?

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Here are three quick things to try:

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1. Ask the person to smile.

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A crooked mouth or facial drooping 
can indicate muscle weakness.

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2. Ask them to raise their arms.

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If one drifts downward, that arm weakness
is also a sign of a stroke.

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3. Ask them to repeat a
simple word or phrase.

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If their speech sounds
slurred or strange,

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it could mean that the language area 
of their brain is oxygen-deprived.

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This is sometimes called the FAST test,
and the T stands for time.

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If you see any of those signs, 
call emergency services right away.

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Lives may depend on it.