What happens during a stroke? - Vaibhav Goswami

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Every two seconds, someone in the world has a stroke. One out of every six people will have a stroke 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. But what causes strokes in the first place? And what can doctors do to treat them? Vaibhav Goswami takes us into the body to find out.

Lesson by Vaibhav Goswami, animation by Artrake Studio.

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 past 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.