Hiccups, medically termed singultus, are sudden, repetitive spasms of the diaphragm. Burps, or belching (eructation), are the expulsion of air from the upper digestive tract. The overlap in sound is not a coincidence, as the two processes share adjacent anatomy and can influence one another.
The Mechanism of a Hiccup
The process of a hiccup begins with an involuntary contraction of the diaphragm, the large, dome-shaped muscle beneath the lungs. This sudden spasm pulls air into the lungs quickly. The impulse for this action travels along a neurological pathway known as the reflex arc, involving the phrenic and vagus nerves.
Immediately following this rapid intake of air, the glottis—the opening between the vocal cords in the larynx—slams shut. This abrupt closure stops the airflow, creating the characteristic “hic” sound. The entire sequence is a reflex action, meaning it is not under conscious control and is often triggered by irritation of the nerves that supply the diaphragm.
Irritation can result from causes like stomach distention from eating or drinking too quickly. The hiccup reflex is a rhythmic, repetitive cycle. The defining audible feature is the sound produced by the sudden closure of the vocal cords against the rush of air.
The Mechanism of a Burp
Belching is the body’s method for venting excess gas from the stomach or esophagus. The most common form, gastric belching, occurs when swallowed air, or aerophagia, accumulates in the stomach. When the stomach stretches due to this gas buildup, a reflex is triggered that causes the lower esophageal sphincter to relax briefly.
This transient relaxation allows the gas to move upward from the stomach into the esophagus. The air then passes through the upper esophageal sphincter and is expelled through the mouth. The sound of a burp is produced by the vibration of this escaping gas against the structures of the upper airway.
A different mechanism, known as supragastric belching, does not involve gas from the stomach at all. Instead, air is rapidly sucked into the esophagus from the mouth and immediately pushed back out. This type of belching is often a learned behavior, frequently associated with anxiety or a response to an uncomfortable sensation in the throat.
Why Hiccups Can Sound Like Belching
The reason a hiccup can sound like a burp lies in the close anatomical relationship and shared nerve pathways of the respiratory and digestive systems. The phrenic nerve (hiccup reflex) and the vagus nerve (belching) are both irritated by similar triggers. The diaphragm’s sudden, downward spasm is central to both the hiccup and a type of belch.
A particularly powerful hiccup spasm may momentarily exert pressure on the abdominal cavity and the stomach. This forceful contraction can trigger a transient relaxation of the lower esophageal sphincter, causing residual gas to rush up the esophagus at the same time the glottis snaps shut. The resulting sound is a combination of the percussive “hic” from the vocal cords and the rumbling expulsion of gas, leading to the burp-like noise.
A true hiccup may also occur almost simultaneously with a supragastric belch. The diaphragm’s sharp contraction creates negative pressure in the chest, drawing air into the esophagus, which is then immediately expelled. The confusing sound is often the result of two separate, yet closely timed, events: the glottis-closing reflex of the hiccup and the gas expulsion of a belch.
Immediate Relief Techniques
Since the burp-like hiccup often involves both the diaphragm spasm and excess air, relief techniques should aim to interrupt the hiccup reflex and address gas buildup. One common method is to hold the breath, which increases the carbon dioxide level in the lungs. This buildup helps to relax the diaphragm and disrupt the involuntary reflex arc.
Stimulating the vagus nerve can also be effective, as this nerve is part of the hiccup pathway. Simple actions like slowly sipping a glass of ice water, gargling with cold water, or swallowing a teaspoon of granulated sugar can provide this stimulation. These sensory inputs can override the signals that are causing the diaphragm to spasm.
To address the gas component, try positional changes that compress the chest and abdomen. Leaning forward or bringing the knees to the chest can apply gentle pressure, which may help expel trapped gas. Slowing the rate of eating and drinking, and avoiding carbonated beverages, can also reduce the amount of air swallowed, lowering the likelihood of triggering both the hiccup and the burp.