The simple act of drinking can sometimes result in an involuntary spasm known as a hiccup. This reflex is triggered by changes in the upper digestive tract and the chest cavity, often linked to the speed or type of liquid consumed. This article explores the specific scientific mechanisms connecting drinking activities to the activation of the body’s hiccup reflex.
The Physiological Mechanism of a Hiccup
A hiccup, medically termed singultus, is an abrupt, involuntary movement of the diaphragm, the large, dome-shaped muscle beneath the lungs that controls breathing. This spasm causes a sudden, rapid intake of breath. Immediately following this muscular contraction, the glottis—the opening between the vocal cords—snaps shut.
The sudden closure of the glottis traps the incoming air, producing the characteristic “hic” sound. This sequence is mediated by a reflex arc involving specific nerves that transmit signals between the digestive system, the central nervous system, and the diaphragm. The primary nerves in this arc include the phrenic nerve, which controls the diaphragm, and the vagus nerve, which runs through the chest and abdomen.
How Rapid Drinking and Distension Trigger the Reflex
The most common trigger for hiccups while drinking is mechanical irritation caused by rapid gastric distension, or the quick stretching of the stomach. When a person drinks quickly, a large volume of liquid fills the stomach rapidly, causing it to expand suddenly. This sudden expansion irritates the nerve endings of the vagus nerve located along the esophagus and the stomach lining.
The vagus nerve senses this rapid stretch and sends a signal to the brainstem, the control center for the hiccup reflex. This signal is interpreted as a mechanical disruption and triggers the efferent response: the involuntary spasm of the diaphragm. Drinking quickly also often involves swallowing excess air, known as aerophagia, which contributes to the stomach’s rapid distension.
Specific Roles of Carbonation and Alcohol
Certain properties of beverages can significantly intensify the gastric distension and irritation that trigger the hiccup reflex.
Carbonation
Carbonated drinks, such as sodas, beer, and sparkling water, contain dissolved carbon dioxide gas. When these liquids enter the warm environment of the stomach, the dissolved gas is released and rapidly expands, drastically increasing the internal pressure. This sudden increase in pressure from the expanding gas bubbles exaggerates the stretching of the stomach wall, further irritating the vagus nerve and making a hiccup more likely.
Alcohol
Alcohol acts as a direct chemical irritant to the mucous lining of the esophagus and stomach. This irritation stimulates the vagus and phrenic nerves, lowering the threshold needed to activate the reflex arc. Alcohol can also cause the lower esophageal sphincter, the muscle separating the esophagus and stomach, to relax. This relaxation can lead to acid reflux, where stomach contents back up into the esophagus. Acid reflux is a known irritant that stimulates the nerves and triggers hiccups.
Simple Techniques to Stop Hiccups
Interrupting the hiccup reflex often involves methods that either manipulate the diaphragm or overload the nerves involved in the reflex arc.
Methods to manipulate the diaphragm include holding one’s breath for a short period to increase the carbon dioxide level in the lungs, which helps reset the diaphragm’s rhythm. Performing the Valsalva maneuver, which involves exhaling forcefully against closed airways, also works by applying pressure that disrupts the nerve signals.
Other methods focus on stimulating the vagus nerve to override the involuntary spasm. These include:
- Gargling with ice water or slowly sipping very cold water.
- Swallowing a teaspoon of dry sugar.
- Gently pulling on the tongue.
These strategies create a strong sensory input in the mouth and throat to distract the vagus nerve. If hiccups persist for longer than 48 hours, they are considered protracted and warrant medical attention.