A hiccup or hiccough (normally pronounced "HICK-up"; ), also known as a condition of singulitis, is the spasmodic contraction of the diaphragm that repeats several times per minute. In humans, the abrupt rush of air into the lungs causes the epiglottis to close, creating the "hic" noise. In medicine, it is known as synchronous diaphragmatic flutter (SDF), or singultus.
The term "hiccup" is also used to describe a small and unrepeated aberration in an otherwise consistent pattern.
A bout of hiccups generally resolves itself without intervention, although many home remedies claim to shorten the duration, and medical treatment is occasionally necessary.
Christian Straus and co-workers at the Respiratory Research Group, University of Calgary, Canada, propose that the hiccup is an evolutionary remnant of earlier amphibian respiration; amphibians such as frogs gulp air and water via a rather simple motor reflex akin to mammalian hiccuping. In support of this idea, they observe that the motor pathways that enable hiccuping form early during fetal development, before the motor pathways that enable normal lung ventilation form; thus according to recapitulation theory the hiccup is evolutionarily antecedent to modern lung respiration. Additionally, they point out that hiccups and amphibian gulping are inhibited by elevated CO2 and can be completely stopped by the drug Baclofen (a GABAB receptor agonist), illustrating a shared physiology and evolutionary heritage. These proposals would explain why premature infants spend 2.5% of their time hiccuping, indeed they are gulping just like amphibians, as their lungs are not yet fully formed.
Babies in-utero experience hiccups. The amniotic/atmospheric hypothesis suggests that hiccups are a muscle exercise for the respiratory system prior to birth, or that they prevent amniotic fluid from entering the lungs. The amniotic/atmospheric hypothesis holds that there are two distinct systems in the brain for controlling respiration: one that is used when the fetus is respiring amniotic fluid during its time in the womb, and another that only comes into use following birth, used for breathing air. Since amniotic fluid is much more viscous than air, a much greater effort is required from the diaphragm to inhale it. If this amniotic breathing system becomes dominant for any reason during life outside the womb, the result will be a momentary, very forceful effort at inhalation. The body senses that things are not correct, and since so much force is actually dangerous to the lungs and other organs, the system is immediately preempted and switched back to the atmospheric system. However, this preemptive control gradually relaxes, making the phenomenon cyclic as long as there is underlying activation of the amniotic respiration system: as the preemptive control falls below the threshold, the amniotic routine resumes control, only to be preempted again, and this cycle continues until the underlying conditions leading to the amniotic breathing activation revert to their normal state – at which point the hiccups stop. This theory is supported by the finding that hiccups are more common in premature newborns, as in these cases the atmospheric respiration system is less prepared to take precedence over the amniotic respiration system.
Ordinary hiccups are cured easily without medical intervention; in most cases they can be stopped simply by forgetting about them. However, there are a number of anecdotally prescribed treatments for casual cases of hiccups. Some of the more common home remedies include: scaring the afflicted, drinking water (sometimes in an unorthodox manner), and altering one's breathing.
Hiccups are treated medically only in severe and persistent (termed "intractable") cases, such as in the case of a 15 year old girl who in 2007 hiccuped continuously for five weeks. Haloperidol (Haldol, an anti-psychotic and sedative), metoclopramide (Reglan, a gastrointestinal stimulant), and chlorpromazine (Thorazine, an anti-psychotic with strong sedative effects) are used in cases of intractable hiccups. In severe or resistant cases, baclofen, an anti-spasmodic, is sometimes required to suppress hiccups. Effective treatment with sedatives often requires a dose that renders the person either unconscious or highly lethargic. Hence, medicating singultus is done short-term, as the affected individual cannot continue with normal life activities while taking the medication.
Persistent and intractable hiccups due to electrolyte imbalance (hypokalemia, hyponatremia) may benefit from drinking a carbonated beverage containing salt to normalize the potassium-sodium balance in the nervous system. The carbonation promotes quicker absorption.
The administration of intranasal vinegar is thought to be safe and handy method to stimulate dorsal wall of nasopharynx, where the pharyngeal branch of the glossopharyngeal nerve (afferent of the hiccup reflex arc) is distributed. Digital rectal massage has also been reported to be effective in a single case report.
Dr. Bryan R. Payne, a neurosurgeon at the Louisiana State University Health Sciences Center in New Orleans, has had some success with an experimental new procedure in which a vagus nerve stimulator is implanted in the upper chest of patients 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 2005, the agency endorsed the use of the stimulator as a treatment of last resort for people with severe depression.
While numerous home remedies are offered, they mostly fall into three broad categories. These categories include purely psychosomatic cures centered around relaxation and distraction, cures involving swallowing and eating (with the rationale generally that this would remove irritants or reset mechanisms in the affected region), and cures involving controlled/altered breathing.
In January 2007, teenager Jennifer Mee from Florida in the United States hiccuped for five weeks, from January 23, 2007 until February 28, 2007. After her hiccups returned, her neurologist suggested that she may actually have Tourette syndrome.