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

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

Strokes deprive brain cells of oxygen

and are one of the most 
common causes of death,

and a leading cause 
of preventable disability.

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

and can often help avoid 
permanent brain damage.

But what causes strokes 
in the first place?

And what can doctors do to treat them?

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

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

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

Carotid arteries supply 
the front of the brain,

and vertebral arteries supply the back.

These are connected to each other,

and divide into smaller 
and smaller vessels

that get billions of neurons 
the oxygen they need.

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

There are two ways this can happen.

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

But the more common type 
is the ischemic stroke,

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

Where do these clots come from?

On rare occasions,
a sudden change in heart rhythm

prevents the upper chambers of the heart
from contracting normally.

This slows down blood flow,

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

The clot can be carried up

towards the arteries
and blood vessels supplying the brain

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

This is called an embolism,

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

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

But oxygen deprivation 
slows brain function

and can have sudden, noticeable effects.

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

an individual’s words may be slurred.

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

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

When this happens, the body 
will immediately try to compensate

by diverting blood flow 
to the affected area,

but this isn’t a perfect solution.

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

leading to brain damage 
that may be severe or permanent.

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

The first line of treatment
is an intravenous medication

called Tissue Plasminogen Activator,

which can break up the blood clot

and allow blood to flow again
in the compromised artery.

If it’s delivered within a few hours,

this medication greatly increases
the chance of surviving the stroke

and avoiding permanent consequences.

If Tissue Plasminogen Activator
cannot be given

because the patient 
is on certain medications,

has history of major bleeding,

or the clot is particularly large,

doctors can perform a procedure
called an endovascular thrombectomy.

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

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

into an artery in the leg,

and maneuvers
it all the way to the blockage.

A retriever is passed
through this catheter.

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

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

These treatments need to be delivered
as soon as possible

to preserve brain function,

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

So how can you tell?

Here are three quick things to try.

1: Ask the person to smile;

A crooked mouth or facial drooping 
can indicate muscle weakness.

2: Ask them to raise their arms;

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

3: Ask them to repeat 
a simple word or phrase;

if their speech sounds
slurred or strange,

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

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

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

Lives may depend on it.