What is a Hiccup?
Hiccups are the repeated involuntary spasm of the diaphragm which causes a sudden intake of air. This is followed by the abrupt closure of the glottis (the vocal cords and space between it) which then restricts the air rushing in. These two actions, diaphragmatic spasm resulting in rapid air intake and closure of the glottis resulting in obstruction of the air flowing in, results in the characteristic sound that we know as a hiccup.
A hiccup is also known as a hiccough or is referred to by the medical term, singultus.
Hiccups usually occur in episodes lasting a few minutes to a few hours. These episodes come and go, often without warning or any clear cause and do not pose any risk to your health. These odd incidents of hiccups are known as transient hiccups.
However, there are cases of persistent hiccups which lasts for more than 2 days or intractable hiccups which can last for more than a month. Persistent or intractable hiccups can be embarrassing, affect daily functioning and even cause pain and distress to the sufferer.
The exact causes of hiccups are not known but transient hiccups are known to occur in certain conditions and situations. While hiccups are not a harmful phenomenon, it can sometimes be a symptom of an underlying cause which may be serious or life threatening.
Why Do We Hiccup?
The diaphragm is a dome shaped muscle sheet that makes up the base of the thorax (chest) cavity. When this muscle contracts, its causes a negative pressure (vacuum) causing the lungs to expand and draw in air from the environment (inhalation or inspiration). When the diaphragm muscle relaxes, the elastic lungs return to their normal size and pushes out the air within it (exhalation or expiration). The diaphragm is not the only muscle of respiration and the intercostal muscles (between the ribs), neck and abdominal muscles also play a part in breathing. Irritation of the diaphragm, like with any muscle, can cause spasmodic attacks which may lead to hiccups.
The main nerve innervating the diaphragm is the phrenic nerve. This nerve arises from the cervical part of the spinal cord, specifically at the level of C3, C4 and C5. There is a right and left phrenic nerve which runs down to the diaphragm. Irritation of the phrenic nerve(s) can stimulate sudden and repeat contractions of the diaphragm muscle resulting in hiccups and cause referred pain to the tip of the shoulder blade (Kehr’s sign) or to the clavicle (collarbone). It is important to note that the phrenic nerve does not exist in isolation within the thoracic cavity. It lies near many structures and to some extent interacts with other nerves in the vicinity.
The respiratory centers in the medulla and pons (brainstem) coordinates respiration by monitoring pH changes and oxygen levels in the blood stream. This will alter the breathing rate by regulating the movement and rhythm of the respiratory muscles. Other nerves, like the glossopharyngeal nerve (cranial nerve IX) and particularly the vagus nerve (cranial nerve X) also play crucial roles in regulating breathing. Irritation or damage of the vagus nerve or of the respiratory centers as well as brain injuries can therefore also trigger hiccups.
Causes of Hiccups
While the physiology of a hiccup is understood, the exact cause is still unknown although certain conditions and situations seem more likely to trigger hiccups.
The causes of transient or short episodes of hiccups include :
- Alcohol consumption.
- Eating or drinking quickly. This is a common cause of hiccups in babies.
- Acid reflux.
- Intestinal gas causing bloating.
- Constant vomiting.
- Gastric distention.
- Excessive belching.
- Consuming very hot and very cold foods and drinks.
- Spicy foods.
- Emotional stress.
- Sudden bouts of laughing, sneezing and coughing.
- Irritation of the ear drum (tympanic membrane)
- Sore throat.
- Side effects of certain drugs, especially anesthetics, barbituates, tranquilizers and hypertensive drugs.
- Stimulants like nicotine (nicotine replacement products side effects) and narcotic drugs.
Persistent hiccups lasting for more than 2 days and intractable hiccups lasting for more than one month may be considered as chronic hiccups. The causes of chronic hiccups include persisting factors mentioned in acute causes as well as the following :
- Injury to the brain and/or brainstem.
- Brain tumors.
- Stroke (cerebrovascular accident).
- Multiple sclerosis.
- Gastroesophageal reflux disease (GERD).
- Chronic bronchitis.
- Smoke inhalation.
- Chest trauma.
- Bowel disorders.
- Gallbladder disease.
- Abdominal or thoracic surgery.
- Kidney failure.
Hiccups are not considered to be a medical emergency. However, if they are accompanied by any neurological signs and symptoms of sudden onset, immediate medical attention is required.