Why do we hiccup? - John Cameron

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The longest recorded case of hiccups lasted for 68 years … and was caused by a falling hog. While that level of severity is extremely uncommon, most of us are no stranger to an occasional case of the hiccups. But what causes these ‘hics’ in the first place? John Cameron takes us into the diaphragm to find out.

Lesson by John Cameron, animation by Black Powder Design.

Charles Osborne began to hiccup
in 1922 after a hog fell on top of him.

He wasn't cured until 68 years later

and is now listed by Guinness as
the world record holder

for hiccup longevity.

Meanwhile, Florida teen Jennifer Mee

may hold the record
for the most frequent hiccups,

50 times per minute
for more than four weeks in 2007.

So what causes hiccups?

Doctors point out that a round
of hiccups often follows from stimuli

that stretch the stomach,

like swallowing air

or too rapid eating or drinking.

Others associate hiccups
with intense emotions

or a response to them:

laughing,

sobbing,

anxiety,

and excitement.

Let's look at what happens when we hiccup.

It begins with an involuntary spasm
or sudden contraction of the diaphragm,

the large dome-shaped muscle
below our lungs

that we use to inhale air.

This is followed almost immediately
by the sudden closure of the vocal chords

and the opening between them,

which is called the glottis.

The movement of the diaphragm
initiates a sudden intake of air,

but the closure of the vocal chords
stops it from entering the wind pipe

and reaching the lungs.

It also creates the characteristic sound:
"hic."

To date, there is no known function
for hiccups.

They don't seem to provide any medical
or physiological advantage.

Why begin to inhale air only to suddenly
stop it from actually entering the lungs?

Anatomical structures,

or physiological mechanisms,
with no apparent purpose

present challenges
to evolutionary biologists.

Do such structures serve some hidden
function that hasn't yet been discovered?

Or are they relics
of our evolutionary past,

having once served some important purpose

only to persist into the present
as vestigial remnants?

One idea is that hiccups began

many millions of years
before the appearance of humans.

The lung is thought to have evolved
as a structure to allow early fish,

many of which lived in warm, stagnant
water with little oxygen,

to take advantage of the abundant oxygen
in the air overhead.

When descendants of these animals
later moved onto land,

they moved from gill-based ventilation
to air-breathing with lungs.

That's similar to the much more rapid
changes faced by frogs today

as they transition
from tadpoles with gills

to adults with lungs.

This hypothesis suggests that the hiccup
is a relic of the ancient transition

from water to land.

An inhalation that could
move water over gills

followed by a rapid closure of the glottis
preventing water from entering the lungs.

That's supported by evidence

which suggests that the neural patterning
involved in generating a hiccup

is almost identical to that responsible
for respiration in amphibians.

Another group of scientists believe
that the reflex is retained in us today

because it actually provides
an important advantage.

They point out that true hiccups
are found only in mammals

and that they're not retained in birds,
lizards, turtles,

or any other exclusively
air-breathing animals.

Further, hiccups appear in human babies
long before birth

and are far more common in infants
that adults.

Their explanation for this

involves the uniquely mammalian
activity of nursing.

The ancient hiccup reflex may have been
adapted by mammals

to help remove air from the stomach
as a sort of glorified burp.

The sudden expansion of the diaphragm
would raise air from the stomach,

while a closure of the glottis would
prevent milk from entering the lungs.

Sometimes, a bout of hiccups will go
on and on,

and we try home remedies:

sipping continuously
from a glass of cold water,

holding one's breath,

a mouthful of honey or peanut butter,

breathing into a paper bag,

or being suddenly frightened.

Unfortunately, scientists have yet
to verify that any one cure

works better or more consistently
than others.

However, we do know one thing
that definitely doesn't work.