A hiccup (scientific name singultus, from Latin for "sob, hiccup"; also spelled hiccough) is an involuntary contraction (myoclonic jerk) of the diaphragm that may repeat several times per minute. The hiccup is an involuntary action involving a reflex arc. Once triggered, the reflex causes a contraction of the diaphragm followed by the closure of the glottis, the space between the vocal cords, in about 35 milliseconds, which results in the "hic" sound. Hiccups may occur individually or in bouts. The rhythm of the hiccup, or the time between hiccups, tends to be relatively constant. A bout of hiccups generally resolves itself without intervention, although many home remedies are often used to attempt to shorten the duration. Medical treatment is occasionally necessary in cases of chronic hiccups.
Incidence Hiccups affect people of all ages, even being observed in utero. They become less frequent with advancing age. Intractable hiccups, lasting more than a month, are more common in adults. While males and females are affected equally often, men are more likely to develop protracted and intractable hiccups. Along with humans, hiccups have been studied and observed in cats, rats, rabbits, dogs, and horses.
Signs and symptoms
A hiccup consists of a single or a series of breathing diaphragm spasms, of variable spacing and duration, and a brief (less than one half second), unexpected, shoulder, abdomen, throat, or full body tremor.
Causes
Pathophysiological causes Food stuck in the esophagus Swallowing air excessively Gastroesophageal reflux Hiatal hernia Rapid eating Alcohol or carbonated beverages Spicy foods Opiate drug use Laughing vigorously or for a long time Several human conditions can trigger hiccups (such as diabetes mellitus or uraemia). In rare cases, they can be a sign of serious medical problems such as myocardial infarction.
Pre-phrenic nucleus irritation of medulla Kidney failure
CNS disorders Stroke Multiple sclerosis Meningitis
Nerve damage Damage to the vagus nerve after surgery
Other known associations Although no clear pathophysiological mechanism has been described, hiccups is known to have been the initial symptom of Plasmodium vivax malaria in at least one documented case. Consumption or injection of corticosteroids, most commonly dexamethasone.
Evolutionary theories
The burping reflex hypothesis A leading hypothesis is that hiccups evolved to facilitate greater milk consumption in young mammals. The coordination of breathing and swallowing during suckling is complicated. Some air inevitably enters the stomach, occupying space that could otherwise be optimally used for calorie-rich milk. The hypothesis suggests that the presence of an air bubble in the stomach stimulates the sensory (afferent) part of the reflex in the through receptors in the stomach, esophagus, and along the underside of the diaphragm. This triggers the active (efferent) part of the hiccup reflex process in the 'hiccup center' part of the brain, sharply contracting the muscles of breathing and relaxing the muscles of the esophagus, then closing the vocal cords to prevent air from entering the lungs. This creates suction in the chest, pulling air from the stomach up into the esophagus. As the respiratory muscles relax, the air is expelled through the mouth, effectively "burping" the animal. There are a number of characteristics of hiccups that support this theory. The burping of a suckling infant may increase its capacity for milk, bringing a significant survival advantage. There is a strong tendency for infants to get hiccups, and although the reflex persists throughout life, it decreases in frequency with age. The location of the sensory nerves that trigger the reflex suggests it is a response to a condition in the stomach. The component of the reflex that suppresses peristalsis in the esophagus while the airway is being actively blocked suggests the esophagus is involved. Additionally, hiccups are only described in mammals, the group of animals that share the trait of suckling their young.
Phylogenetic hypothesis It has been proposed that the hiccup is an evolutionary remnant of earlier amphibian respiration. Amphibians such as tadpoles gulp air and water across their gills via a rather simple motor reflex akin to mammalian hiccuping. The motor pathways that enable hiccuping form early during fetal development, before the motor pathways that enable normal lung ventilation form. Thus, the hiccup is evolutionarily antecedent to modern lung respiration. Additionally, hiccups and amphibian gulping are inhibited by elevated CO2 and may be stopped by GABAB receptor agonists, illustrating a possible shared physiology and evolutionary heritage. These proposals may explain why premature infants spend 2.5% of their time hiccuping, possibly gulping like amphibians, as their lungs are not yet fully formed.
Duration Episodes of hiccups usually last under 30 minutes. Prolonged attacks, while rare, can be serious. Root causes of prolonged hiccups episodes are difficult to diagnose. Such attacks can cause significant morbidity and even death. An episode lasting more than a few minutes is termed a bout; a bout of over 48 hours is termed persistent or protracted. Hiccups lasting longer than a month are termed intractable. In many cases, only a single hemidiaphragm, usually the left one, is affected, although both may be involved.
Treatment Hiccups are normally waited out, as fits will usually pass quickly. Folk cures for hiccups are common and varied. Hiccups are treated medically only in severe and persistent (termed "intractable") cases. Numerous medical remedies exist, but no particular treatment is known to be especially effective, generally because of a lack of high-quality evidence. A vagus nerve stimulator has been used with an intractable case of hiccups. "It sends rhythmic bursts of electricity to the brain by way of the vagus nerve, which passes through the neck. The Food and Drug Administration approved the vagus nerve stimulator in 1997 as a way to control seizures in some patients with epilepsy." In one person, persistent digital rectal massage coincided with terminating intractable hiccups.
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