It is an involuntary contraction of the diaphragm – the muscle that separates the chest from the abdomen, located just below the lung. This muscle, responsible for controlling breathing, is triggered by the so-called phrenic nerve, also related to hiccups. The contraction usually occurs several times in a row, separated by a short time interval (sometimes less than a second) and can last for several days. They are followed by a sudden closure of the glottis (a kind of laryngeal lid) that suddenly cuts off the passage of air from the mouth to the lungs and causes the vocal cords to vibrate, causing the characteristic hiccup sound. Its main cause is irritation of the phrenic nerve – but most of the time it is not possible to identify what caused this irritation. “We know that abrupt changes in temperature trigger hiccups.
Another cause could be irritation of the esophagus (the entrance to the stomach)”, says general practitioner at Hospital das Clínicas de São Paulo, Arnaldo Lichtenstein. One of the main causes of this irritation is a reflux of stomach acid, which occurs, for example, in a hiatus hernia (passage hole, in the esophagus, between the thorax and the stomach). In this case, the closed angle that would serve as an impediment to reflux breaks down and the acid ends up attacking the esophagus. Irritation, in turn, causes the phrenic nerve to trigger the hiccup contraction. It’s not legend that a good scare can cure a hiccup attack, as it causes the body to release adrenaline, which activates the phrenic nerve, causing it to stop contractions. But a glass of ice water, which has the same effect, can also help.
uncontrollable reflex
1. Irritation of the esophagus (in the pit of the stomach) is one of the most common causes of hiccups
2. The reflex is triggered by the phrenic nerve, which triggers contraction of the diaphragm (solar plexus). The contraction is repeated over and over again – and can last for more than a day
3. As the diaphragm contracts, the larynx (in the throat) closes, trapping air. This second reflex makes the vocal cords vibrate, causing the typical hiccup noise.