The mysterious hiccup explained: reflex helps babies release swallowed air, drink more milk

News / General
By Matthew Manor

Ever wonder why we hiccup? A researcher from Kingston General Hospital and Queen's University has offered an explanation for the mysterious reflex, published today in the journal BioEssays.

Most common reflexes have been explained - sneezing clears irritants from our noses, coughing expels materials from our airways. The hiccup has long remained an enigma for clinicians and researchers, who have struggled to connect the actions of a hiccup to an explanation that offers a reasonable evolutionary advantage.

“Everyone has had the hiccups,” says Dr. Daniel Howes, a physician at Kingston General Hospital and an Associate Professor in Emergency Medicine & Critical Care at Queen's University, “but there hasn't really been a satisfying reason that explains why we have them.”

“The hiccupping reflex causes the muscles used for breathing to sharply contract. This is followed by a sudden closure of the vocal cords, making the classic ‘hic' sound.” Dr. Howes' hypothesis is that the vacuum created in the chest by the hiccup pulls air out of the stomach, effectively acting as a ‘burping' reflex.

“Having a natural reflex to remove air from the stomach represents an evolutionary advantage because it lets babies to drink more milk during feeding. This would also explain why hiccupping is so much more common in infants than adults.”

The detailed explanation can be found by accessing the complete article online at http://onlinelibrary.wiley.com/doi/10.1002/bies.201100194/full

Hiccup facts:

The word hiccup (sometimes spelt hiccough) is an onomatopoetic name that attempts to represent the sound made by someone while they hiccup. As a result, the word is very similar in its pronunciation in a range of languages: ‘Hoquet' in French, ‘hipo' in Spanish, ‘geehouk' in Hebrew, ‘hicka' in Swedish, ‘hikke in Norwegian and Danish.

The medical terms used for the hiccup are singultus or synchronous diaphragmatic flutter.

Hiccups have been observed in a wide range of mammals – cats, dogs, rabbits have all been observed hiccuping. In horses, hiccups are referred to as 'thumps'.

The hiccup is one of the earliest reflexes observed. It can be seen on ultrasound in the fetus.

Hiccups occur throughout life, but are much more common in newborns and infants.

Hiccups involve both diaphragms, or just the left.

During a bout, hiccups have a frequency between 4 and 60 per minute, and the frequency seems fairly constant in the same individual.

Although hiccups are ubiquitous and very normal, persistent hiccups can be a sign of serious disease. Causes include meningitis, stroke, liver disease, and diaphragmatic abscess.

A cure for the hiccups has been even more elusive than explaining the purpose, despite such great minds as Hippocrates, Celcus, Galen and Charles Mayo. Mayo is quoted as saying “The amount of knowledge on any subject such as this can be considered as being in inverse proportion to the number of different treatments suggested and tried for it. Perhaps one is justified in saying that there is no disease which has had more forms of treatments and fewer results from treatment than has persistent hiccup.”

Hippocrates wrote in the fourth century BC that “sneezing coming on remove the hiccough,” while Plato is credited with being the first to recommend ‘scaring away' hiccups with a sudden thump on the back. Eryximachus the physician is reported to have told Aristophanes to hold his breath, gargle with water, and tickle his nose to induce a sneeze – significantly raising the proposal up a notch and forming the foundation for many of today's proposed cures.