11/26/2012 01:32 EST | Updated 01/26/2013 05:12 EST

Why Do We Hiccup? Common Fetus Behaviour Leads To Many Questions


TORONTO - You drink too much, you eat the wrong thing — and suddenly you're battling a bout of the hiccups.

What's up with that?

Why do seemingly insignificant triggers sometimes prompt your body to produce weird and irritating noises in sequences? Why in some rare and unfortunate cases do those spells of involuntary hiccups last for a really long time — even sometimes years?

The short and truthful answer: Science doesn't know.

Though they are a fairly common occurrence, especially in childhood, science doesn't really know what if any purpose is served by fits of funny sounding intakes of breath that the medical world calls singultus and we call hiccups.

"Hiccupping has no obvious function. That doesn't mean it doesn't have one. But it hasn't been discovered," says Robert Provine, a neuroscientist and professor of psychology at the University of Maryland, Baltimore County.

Provine studies the origins and social functions of some seemingly odd things humans do, like hiccupping. Earlier this year, he published a book on the topic called "Curious Behaviour: Yawning, Laughing, Hiccupping and Beyond."

While there isn't a firm answer to why we do it, there are lots of interesting facts about hiccupping. Let's start with what makes the unusual noise.

Hiccups occur when two things happen in rapid succession. There's a sharp and involuntary inhalation of breath, followed by the abrupt closure of the glottis, the opening between the vocal cords at the top of the larynx.

"What gives the hiccup the 'hic' sound is the glottis slamming shut," Provine says.

Hiccupping could be vestigial, something evolution inadvertently left in the mix as humans developed past the point where its purpose — whatever it was — was needed. Or it could be something we need in our early development, but grow out of as we age.

Fetuses hiccup in the womb, from about the eighth week after conception. "It not only is present, it's one of the most common of all prenatal behaviours. It's more common than breathing movements," Provine says.

Premature babies hiccup a lot. In fact, a commentary on hiccupping that ran a number of years ago in the journal Gut said preemies spend on average about 2.5 per cent of their time hiccupping.

The commentary, by Peter Kahrilas and Guoxiang Shi of Northwestern University Medical School, says both fetuses and premature babies have hiccupping spells that don't seem to be triggered by an identifiable stimulus.

"This suggests that during the perinatal period, when the respiratory tract needs to mature rapidly, hiccupping does have a survival value," they say.

"Perhaps hiccupping is essentially a programmed isometric exercise of the inspiratory muscles which are superfluous in utero but afforded no time for maturation after birth."

Kahrilas and Shi suggest that after birth, hiccupping may be a vestigial reflex.

In fact, it's known that the tendency to develop hiccups declines with age. Children hiccup more than adults and the frequency of hiccupping continues to drop as people move into old age, Provine says.

The one exception: older men who have chest surgery sometimes develop intractable — prolonged — bouts of hiccups, he says. While hiccups are generally just an embarrassing inconvenience, after surgery they can actually get in the way of healing.

Provine offers another gender-based hiccup oddity: After puberty, females hiccup more frequently than males, most commonly in the days before ovulation and rarely, apparently, during pregnancy.

Hiccups generally come in series, either of relatively short duration — a few minutes — or quite a bit longer.

How long? The record for the longest continuous spell of hiccupping is held by the late Charles Osborne, of Anthon, Iowa. Osborne hiccupped for 68 years, stopping two years before his death in 1991 at the age of 98.

According to the Guiness Book of Records, Osborne hiccupped about 40 times a minute. That slowed to about half that in the later years of his spell.

While hiccups are normally just an annoyance, persistent hiccups can be a sign of disease. The medical literature on hiccups suggests they can be brought on by a long list of ailments, including brain trauma and lesions, infections, peptic ulcers, central nervous system conditions, metabolic disorders and even anesthesia.

Possible cures may be more numerous than the causes, the experts suggest. And what works for one person may not work for another.

The letters to the editor section of the journal BMJ hosted a discussion of a "miracle cure" for hiccups in 2006. It involves plugging both ears by pressing on the tragus — the nub of cartilage that protrudes at the front of the ear canal — and then drinking an entire glass of water through a straw without pausing.

Other proposed cures include drinking water from the opposite side of a glass, swallowing a teaspoon of sugar, or sipping lemon juice.

Provine thinks merely having someone watch the afflicted person may inhibit the hiccups. He tried recording children hiccupping for his research and the mere act of being observed seems to have shut down the behaviour.

"In fact, my first nine attempts to do this in every case the hiccupping stopped as soon as I turned the tape recorder on," he says. "That's my tape recorder cure."

Other cures he lumps into a category he calls neurological rebooting. So the water tricks, the swallowing of sugar, it's all about having one primal motor pattern competing with, and over-riding, the hiccupping, he says.

"In all of these cases, you're having a strong sensory experience. And it's unclear to me whether it's the sensory component or whether it's causing a swallowing or other response, where you're triggering one response that's blocking another."

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