hiccup or hiccough, involuntary spasmodic contraction of the diaphragm followed by a sharp intake of air, which is abruptly stopped by a sudden, involuntary closing of the glottis (opening between the vocal cords); the consequent blocking of air produces a repeated characteristic sharp sound, or hic. It is believed that hiccup is caused by stimulation of the nerve pathways or centers that control the muscles of respiration, particularly the diaphragm. In most instances hiccups are transient, although their course may sometimes be shortened by such measures as holding the breath, deep regular breathing, or rebreathing into a paper bag to increase the carbon dioxide content of the body. However, persistent hiccups may last for weeks, months, or even years. When hiccups are prolonged, therapy may include the administering of certain drugs, inhalation of carbon dioxide, and even interruption of the phrenic nerve either by injection of an anesthetic or by surgery.

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