The effects of underwater pressure on the body - Neosha S Kashef

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Why would a fish throw up its stomach? What makes a scuba diver develop painful microbubbles in their joints? Neosha S Kashef details the basics of barotrauma, shedding light on how humans and fish alike are influenced by laws of physics under the sea.

Lesson by Neosha S Kashef, animation by The Moving Company Animation Studio.

Sometimes when a fish
is reeled up to the surface

it will appear inflated,

with its eyes bulging out of their sockets

and its stomach
projecting out of its mouth,

as if its been blown up like a balloon.

This type of bodily damage,
caused by rapid changes in pressure,

is called barotrauma.

Under the sea, pressure increases
by 14.7 pounds per square inch

for every 33 foot increase in depth.

So, take the yelloweye rockfish,

which can live as deep as 1800 feet,

where there's over 800 pounds of pressure
on every square inch.

That's equivalent to the weight of a
polar bear balancing on a quarter.

Now, Boyle's gas law states

that the volume of a gas
is inversely related to pressure.

So, any air-filled spaces,
like a rockfish's swim bladder,

or human lungs,

will compress as they descend deeper

and expand as they ascend.

After a fish bites a fisherman's hook
and is quickly reeled up to the surface,

the air in its swim bladder
begins to expand.

Its rapid expansion actually forces
the fish's stomach out of its mouth,

while the increased internal pressure
pushes its eyes out of their sockets,

a condition called exophthalmia.

Sometimes rockfish eyes will even have
a crystallized appearance

from corneal emphysemas,

little gas bubbles
that build up inside the cornea.

Thankfully, a scuba diver doesn't have
a closed swim bladder to worry about.

A diver can regulate pressure in her lungs
by breathing out as she ascends,

but must be wary of other laws of physics
that are at play under the sea.

Henry's law states that the amount
of a gas that dissolves in a liquid

is proportional to its partial pressure.

The air a diver breathes is 78% nitrogen.

At a higher pressure under the sea,

the nitrogen from the air in a scuba tank

diffuses into a diver's tissues in greater
concentrations than it would on land.

If the diver ascends too quickly,

this built up nitrogen
can come out of solution

and form microbubbles in her tissues,
blood and joints,

causing decompression sickness,
aka the bends.

This is similar to the fizz
of carbon dioxide coming out of your soda.

Gas comes out of solution
when the pressure's released.

But for a diver, the bubbles
cause severe pain

and sometimes even death.

Divers avoid falling victim to the bends
by rising slowly

and taking breaks along the way,
called decompression stops,

so the gas has time to diffuse
back out of their tissues

and to be released through their breath.

Just as a diver needs decompression,

for a fish to recover,
it needs recompression,

which can be accomplished
by putting it back in the sea.

But that doesn't mean that fish
should just be tossed overboard.

An inflated body will float

and get scooped up by a hungry sea lion
or pecked at by seagulls.

There's a common myth

that piercing its stomach
with a needle will let air escape,

allowing the fish to swim
back down on its own.

But that is one balloon
that shouldn't be popped.

To return a fish properly to its habitat,

fisherman can use
a descending device instead

to lower it on a fishing line
and release it at the right depth.

As it heads home and recompression
reduces gas volume,

its eyes can return
to their sockets and heal,

and its stomach can move back into place.

This fish will live to see another day,

once more free to swim, eat, reproduce
and replenish the population.