hiccough

hiccough or hiccup We are all familiar with the common occurrence of hiccup or hiccough. It consists of a series of forceful but abruptly blocked intakes of breath. Each abrupt blocking of inspiration gives rise to a characteristic sound. The condition is often triggered by gastric distension or alcohol intake, normally lasts for no longer than a few hours, and is either self-terminating or responds to simple folk remedies. However, on rare occasions hiccups can be present continuously for more than 24 hours or prolonged bouts may recur daily. Such cases of chronic hiccups may reflect a great variety of underlying disease processes. Chronic hiccups have been reported in association with disorders and lesions of systems as diverse as the gastrointestinal, hepatic, renal/urinary, and both the central and peripheral nervous systems. In addition, chronic hiccups can occur following the administration of certain drugs and as an accompaniment to psychiatric illness. The direct danger of severe hiccups, continuously present over a long period of time, is simply one of physical exhaustion, quite apart from any hazards relating to underlying disease or drugs.

A hiccup is produced by a sudden, forceful contraction of the diaphragm. This causes a rapid inspiration but the inflow of air through the larynx into the lungs is blocked by an almost immediate closure of the glottis, meaning that the vocal cords come together. This process has no known physiological function; in fact there is remarkably little information on the biology of hiccups. They can occur in a wide variety of circumstances, from those associated in the fetus with normal activity to those accompanying terminal disease. Some workers have suggested that there is a hiccup centre in the brain and experimental work in anaesthetized animals has located a region in the medulla which, when stimulated electrically, produces a powerful inspiration with sudden glottic closure. This can also be produced by mechanical stimulation of the back wall of the upper pharynx.

The general assumption is consequently that hiccups are due to activation of a reflex because of an adequate but abnormal or pathological sensory input, or because the threshold for the reflex is substantially lowered by excitation within the brain, or because an existing inhibition of the reflex is removed. It is difficult to envisage the circumstances in which such a reflex would have any utility. An alternative suggestion is that the condition is not a reflex but a myoclonus, which is defined in this context as a sudden, brief, involuntary movement, arising from abnormal spontaneous activity within the central nervous system, comparable to that occurring in epilepsy. Chronic hiccups have been associated with brain lesions in diverse areas including the temporal lobe, the thalamus, and understandably, the medulla.

Simple hiccups may respond to a variety of folk remedies, e.g. a sudden fright, breath-holding, or drinking a large glass of water without taking a breath. Most of such remedies have the common feature in that they interrupt breathing and so could increase the level of carbon dioxide circulating in the blood. An increased arterial carbon dioxide level in turn increases the drive to the respiratory system and the assumption is that this enables the medullary respiratory centre to suppress interruptions (hiccups) to its ongoing rhythmic activity. However, in the rare cases of chronic hiccups, attention has to be directed to diagnosis and treatment of the underlying disease state, to remove the triggering factors. If no underlying disease can be found, or if a drug is inducing the hiccups but that drug is essential to some other treatment, the condition may have to be treated symptomatically using an agent that will simply suppress it.

Despite many well-conducted investigations, the current state of knowledge of hiccups is still unsatisfactory.

Allan Thexton