The function of hiccups

It is generally believed that these abrupt diaphragmatic contractions do not serve any useful purpose(1) or have only a nuisance value. After reviewing 192 references, Launois et al.(2) recently concluded "The purpose of hiccup is unknown."- an extraordinary deficiency when one considers that hiccups have engaged the attention of medical practitioners at least since the time of Hippocrates.

Most of our exact knowledge of hiccups comes from Davis(3) who studied the neurophysiology of hiccup in three patients in great detail, measuring the frequency and amplitude of hiccups in relation to phase of respiration, PCO2, integrated electromyogram, etc. He found that a hiccup is essentially an abrupt Mueller maneuver. The glottis closes to prevent inspiration 35 milliseconds after electrical activity rises above the baseline in the diaphragm and external intercostal muscles .

Because of the glottic closure, hiccups had little effect on respiratory exchange (although they did produce hyperventilation in a patient with a tracheostomy). Davis concluded they were not governed by the same centers that controlled inspiration and expiration. This and provocation by gastric distention caused him to conclude that hiccup was ". . . gastrointestinal rather than respiratory in nature." and ". . . more analogous to the vomiting reflex, for example, than to a respiratory reflex such as coughing." Davis also believed hiccups had no useful function in man and the literature echos this belief.

Yet it is hard to believe that a complex, exquisitely coordinated function of the diaphragm, intercostal muscles, glottis, brain stem and somatic and visceral nervous system does not in some way serve the organism. Overeating and ingestion of carbonated beverages are well known causes of hiccups. Parents of small babies are familiar with the hiccups that frequently follow a feeding (and are cured by feeding more!). An association of hiccup and GE reflux is well documented in the literature. One wonders, therefore, if hiccups are an attempt to open the sphincter.

In its effect on the PEL, and thus the sphincter, a sharp downward motion of the diaphragm is the precise mechanical equivalent of a sharp upward contraction of the esophagus. It will tension the PEL and so have the same sphincter-dilating effect. It may even activate an esophageal stretch reflex producing an amplified effect. Perfused catheter studies(4) have shown absence of a detectable LES during attacks. This would indicate reduced hiatal squeeze and as a consequence, hiatal widening.

Although hiccups are always spoken of in the pleural, I first conjectured they might open the sphincter when a solitary hiccup happened as a patient rolled from the supine to the prone position. It provoked gross GER. Attempts to produce reflux again with the usual maneuvers were unsuccessful. Subsequently I noted than many, perhaps most, belches are initiated by a single hiccup - not the repeated (up to 28,000 times a day(5)) rhythmic ones we usually think of in that regard - but by an isolated event preceding and inseparable from the belch it elicits. One alerted to this association will note a sudden tightness of the belt or out-thrust of the abdomen just before such a belch. A belch initiated by LMC would have a more subtle but reverse effect on the abdomen. A hiccup induced belch is often a cooperative effort with LMC: first the gas sensation of LMC, then the hiccup, then the eructation of gas. Or a LMC type belch may shortly be followed by one or more of the hiccup variety. Elaborate strain gages and strip chart recorders are not required to establish this hitherto unknown phenomenon. The reader will be able to observe it in him/her self. There is just one problem. Glancing downward to observe the abdomen will cause an automatic flexion of the neck. This may inhibit the LMC portion of the process and abort the eructation.

During a hiccup, the glottis either does not close completely or during its delayed closure emits an inspiratory croak as the abdomen expands with a downstroke of the diaphragm. Launois et al.(6) collected the words for hiccup in 23 languages. Many, but not all of them, are onomatopoetic. In English at least, the sound of a hiccup and the burp it produces are considered embarrassing but there is no help for it.(7)

A belch preceded by a premonitory "gas" sensation and gradual LMC can be suppressed.(8) It is due to LMC as described in the previous chapter. A burp initiated by a hiccup, however, may come without warning and be too abrupt and unexpected to be suppressed voluntarily. Recently I witnessed a dozen such affecting a noted economist being interviewed on C-Span. Given the capability, he could have been expected to suppress them on such a public occasion.



Such an isolated hiccups explain the episodes of "inappropriate"(9) transient complete loss of LES pressure(10) that result in reflux both in normal subjects and in esophagitis patients.(11) In another study by the Milwaukee group,(12) 27 % of transient increases in intraabdominal pressure (such as would be caused by a hiccup) were associated with reflux. The glottic closure in singultus is purposeful, therefore - it prevents aspiration on sudden sphincter release.

The concurrent onset and causal relationship of singultus and acid reflux in a patient with protracted and recurrent hiccups have been minutely documented symptomatically and by pH monitoring by Shay, Myers and Johnson.(13),(14) They reasoned that the downward excursion of the diaphragm in hiccup caused reflux by creating a negative intraesophageal pressure. It is not clear, however, how negative pressure per se could open the sphincter - it should merely collapse the lumen as is the case if one tries to suck water through a flaccid straw. It seems more probable that, just as LM tension causes reflux by upward traction on the PEL, a hiccup causes downward traction of the PEL with the same sphincter-opening effect.

Commenting on this case, Graham(15) alludes to his experience with manometry of hiccups.(16) He found hiccups caused ". . . . A great reduction (or absence) of the lower esophageal sphincter pressure. . . ." and also cessation of peristalsis. He believed these effects were as important as negative intraesophageal pressure in causing reflux.

There is an impression in the literature that complications associated with reflux stimulate vagal afferent nerves and cause singultus. Shay et al. make a good case that it is the other way around - singultus causes the complications. Their patient had no symptoms of reflux until after the onset of hiccups, symptoms were confined to the times the hiccups recurred, and pH monitoring documented that ". . . . acid reflux increased during hiccup episodes and returned to a normal level with their cessation." Gluck & Pope, nevertheless, could provoke hiccups at will in their patient with the Bernstein test. Both points of view may be correct, giving rise to a vicious circle and prolonged bouts of hiccup.

Ataractic drugs(17) such as haloperidol and chlorpromazine(18) as well as atropine(19) also have therapeutic value in otherwise intractable hiccups. Friedgood and Ripstein report an 82% permanent cure rate with 50 mg of chlorpromazine given IV. In one case the hiccups had been present 9 months. Launois, et. al.(20) name baclofen as the drug of choice for chronic hiccup.

We have seen that nausea and vomiting (as well as hyper salivation(21)) are caused by severe degrees of traction on the PEL by LMC. Ataractic drugs must ablate this traction to achieve their effect. Such LM relaxation, if it accounts for the therapeutic effect of these drugs on hiccups would suggest that there is feedback between the esophagus and diaphragmatic control centers or, more likely, that a LMC backs up the diaphragm to effect vector resolution on the sphincter. If the LM were flaccid when the diaphragm contracted, the PEL would be too slack to resolve the force generated.

This in turn suggests that clonic LMC may also be a feature of hiccups. Clonic LM contractions synchronized with hiccup would explain why the latter have persisted even after bilateral phrenic interruption.(22),(23) With the LM jerking on the PEL from above and the diaphragm from below, the sphincter-opening force would be augmented as the pull of one is opposed by that of the other. However, in a single case of hiccups in which I was able to obtain 10/sec 105 mm frames of the cardia, there was no evidence of such. Unfortunately, this patient had a ruptured PEL.

Stimulation of vagal afferents by a sudden influx of air has also been shown to cause a reflex loss of LES pressure, probably via the same mechanism.(24) This reflex is abolished by bilateral cervical vagotomy. The existence of such a reflex also suggests that LMC is an element of hiccup. Vagal cooling or vagotomy is said to abolish the belch reflex.

Although unstated, it seems implicit in Davis' results that there are not only somatic neuron discharges to the diaphragm and intercostals but visceral discharges to the glottis via the 10th cranial nerve and vagus that control it.(25) As the latter also supplies the esophagus, specifically the LM, it is tempting to postulate that this end organ too is neurologically activated in a hiccup.

A common denominator exists among the various maneuvers used to break up the hiccup cycle: most affect the esophagus. Many involve performing a Valsalva maneuver that, as we have seen, can cause a forceful, sustained LMC. The celebrated Hippocratic(26)

.Kellogg, Edward L. and Meyer, William, Hiccough. Medical Record 142:441-4, 1935.(27) maneuver is said to cause gagging (a single forceful LMC) as well as sneezing. The same may be said of depressing the tongue or pulling out the tongue or inducing vomiting.

Startling the hiccup sufferer, commonly with a loud and sudden sound, is a favorite and effective home remedy for hiccups. Such sounds, if in the 70-125 dBA sound level, uniformly produced tertiary contractions(28) in subjects exposed to 1000 Hz acoustic stimuli. TCs, as has been pointed out,(29) are markers for simultaneous CM and LM contraction. The production of LMC is the common thread. Perhaps inducing a different mode of LMC inhibits a mode of LMC associated with hiccup.

No one seems to have a good idea why hiccups are so often a cyclical phenomenon. Davis concludes, ". . . . there is some feature of the hiccup, itself which predisposes toward a further hiccup and thus perpetuates the bout." This could be the sudden impulse it transmits to the esophagus.




Although hiccups have engaged the attention of philosophers at least since the time of Plato, there was no reason to suspect their physiologic function until the function of the LM was known. The solution to one mystery was the key to another. The abrupt diaphragmatic downstroke of a hiccup generates the same sphincter-opening vector forces as does a contraction of the LM. A hiccup, therefore, rather than being a useless biological quirk at best and a nuisance at worst, is actually a useful physiologic mechanism. It performs the identical sphincter-opening function of LMC in eructation of gas. In addition, the associated glottic closure prevents aspiration should liquid as well as gas escape the stomach.

Hiccups are also useful in another sense - for the purposes of this monograph. Unless the reader has access to a fluoroscope and a ready supply of subjects, it is difficult for him/her to be totally convinced that it is vector resolution of the upward force of LMC that opens the sphincter. With hiccups, however, the reader can be self-convinced if a few days - a week at most - that a mechanically equivalent down stroke of the diaphragm will do the same thing.




Last Updated July 27, 2007 by David PJ Stiennon

1. .Golomb, B. -- Hiccup for hiccups. [Letter] Nature 345:774, 1990.

2. . Launois, J. L., Bizec, W.A., Whitelaw, J. C., et al. Hiccup in adults: an overview. Eur. Res. J. 6:563-75, 1993.

3. 3. Davis, John Newsom, An experimental study of hiccup. Brain 93:815-72, 1970.

4. 4. Mukhopadhya, A.K. and Graham, D.Y., Esophageal motor abnormality during hiccup. (Abstract) Gastroenterology 68:962, 1875.

5. 5.Gluck, Michael and Pope, Charles E. II, Hiccups and gastrointestinal reflux disease: the acid perfusion test as a provocative maneuver. Ann. Int. Med. 105:219-20, 1996.

6. 6.Launois, S., et al., op cit.

7. 1 The above research is best conducted when there are no ladies present.

8. 2 This involves a familiar maneuver in which the chin is depressed as far as possible giving the esophagus some slack and giving rise to a characteristic "pompous" expression.

9. 3 That is, unaccompanied by manometric signs of CM activity.

10. 7.Dent, John, Dodds, Wylie J., Friedman, Robert H., et al., Mechanism of gastroesophageal reflux in recumbent asymptomatic subjects. J. Clin. Invest. 65:256-67, 1980.

11. 8. Dodds, Wylie J., Dent, John, Hogan, Walter J., et al., Mechanisms of gastroesophageal reflux in patients with reflux esophagitis. NEJM 307:1547-52, 1983.

12. 9. Dodds, Wylie J., op cit..

13. 10. Shay, Steven D.S.., Myers, Robert L. and Johnson, Lawrence F., Hiccups Associated with reflux esophagitis. Gastroenterology 87:204-7, 1984.

14. 11.Kellog,Edward L.and Meyer, William, Hiccup, Medical Record 142:441-4, 1935.

15. 12. Graham, David Y., Letter to the Editor. Gastroenterology 90:2039, 1986.

16. 13. Mukhopadhyay, A.K. and Graham, David Y., Esophageal motor abnormality during hiccup. Gastroenterology 87:204-7, 1975.

17. 14. Korczyn, A.D., Hiccup, Brit. Med. J. 2:590-1, 1971.

18. 15. Friedgood, Charles E. and Ripstein, Charles B., Chlorpromazine (Thorazine) in the treatment of intractable hiccups. JAMA 157:309-10, 1955.

19. 16. Gigot, Alfred F. and Flynn, Paul D., Treatment of hiccups. JAMA 150:760-4, 1952.

20. 17.Lounois, L.J., et al., op. cit.

21. 18. Shay, et al., op cit..

22. 19. Campbell, M.F., Malignant hiccup with report of a case following transurethral prostatic resection and requiring bilateral phrenicectomy for cure. Am. J. Surg. 48:449-55, 1940.

23. 20. Kappis, M., Origin and Treatment of hiccup. Klinische Wochenschrift 3:1065, 1924.

24. 14. Boyle, J.T., Altschuler, S.M., Patterson, B.L., et al., Reflex inhibition of the lower esophageal sphincter following stimulation of pulmonary afferent receptors. Gastroenterology 90:1353, 1986.

25. 22.Licht, Stanley, Electrodiagnosis and Electromyography, Elizabeth Licht, New Haven, 1971.

26. 4 The scholarly will doubtless be interested in this bit of research and its quotation from Plato (a fifth century B.C. younger contemporary of Hippocrates) attributed to a Dr. Gibson by Kellogg and Meyer. "When Pausainis came to pause . . . Aristodemus said that the turn of Aristophanes was next, but either he had eaten too much or from some other cause he had the hiccough, and was obliged to change with Eryximachus, the physician, who was reclining on the couch below him. 'Eryximachus,' he said, 'you ought either to stop my hiccough or to speak in my turn until I am better.' 'I will do both,' said Eryximachus, 'I will speak in your place and do you speak in mine; and while I am speaking, let me recommend that you hold your breath, and if this fails, gargle with a little water; and if the hiccough still continues, tickle your nose with something and sneeze, and if you sneeze once or twice, even the most violent hiccough is sure to go. In the meantime, I will take your turn and you shall take mine.'"


28. 23. Stacher, Georg, Schmeierer, Giselheid and Landgraf, Monika, Tertiary esophageal contractions evoked by acoustical stimuli. Gastroenterology 77:49-54, 1979.

29. 24. Stiennon, O. Arthur, On the cause of tertiary contractions. AJR 104: 617-24, 1968.