What Is the Diaphragm and What is its Function?

The diaphragm is a muscle that separates the chest from the abdomen and plays a very important role in breathing. When the diaphragm contacts (either automatically or through voluntary effort), air is drawn into the lungs, and when it relaxes, air is expelled. In addition to its role in respiration, it is involved in coughing, vomiting, and even in defecation and childbirth. Medical conditions involving the diaphragm can range from minor concerns, such as hiccups, to Hiatal hernias, to paralysis (partial or total) caused by a number of underlying problems. Let's look at the structure and function of the diaphragm in greater detail, followed by the most important conditions affecting this structure.

The diaphragm is a parachute-shaped muscle that separates the chest from the abdomen. It represents the floor of the thoracic cavity and the ceiling of the abdominal cavity.

There are 3 openings (holes) through the diaphragm:

• The esophageal opening: Through which the esophagus passes
• The aortic opening: Through which the aorta, thoracic duct, and azygous vein pass
• The caval opening: Through which the inferior vena cava (the large blood vessel returning blood from the legs and lower body to the heart) travels

The esophageal opening, when too wide, can lead to the symptoms of a Hiatal hernia discussed below.

The diaphragm can be seen as being divided into two halves, or “Hemi-diaphragms.” (Hemi is a word that means half.) Each side of the diaphragm is supplied by a nerve (the left phrenic nerve and the right phrenic nerve) which control the muscle. The phrenic nerves begin in the cervical plexus (nerves exiting the spinal cord in the neck) which carries nerves that begin in the C3 to C5 nerve roots (nerves arising near the neck by the 3^rd through 5^th cervical vertebrae). Conditions that affect these nerves anywhere along their course, from the vertebrae in the neck to where they insert in the diaphragm, can result in paralysis of the muscle.

The diaphragm plays an integral role in breathing (respiration). When the diaphragm contracts and flattens, it decreases pressure in the thoracic cavity, creating a vacuum which air then enters. When the diaphragm relaxes, air is released. 

Most of the time the diaphragm contracts in an involuntary manner (which is the reason we continue to breathe when we sleep), but it can be contracted voluntarily as well. The muscle is used not only in inhalation and forced exhalation, but in coughing, sneezing, vomiting, urinating, defecating (passing a bowel movement), and childbirth.

Diaphragmatic breathing is a technique that is used to strengthen the diaphragm, allowing more air to enter and exit the lungs without tiring the chest muscles. This is also referred to as "belly breathing" and is used by singers as well.

There are several medical conditions which may be related to the diaphragm or abnormalities of the diaphragm. Some of these include:

When the diaphragm is irritated, such as when drinking carbonated soda, it can contract involuntarily resulting in what we know as hiccups. The sound of hiccups is caused when air is exhaled at the same time that the diaphragm contracts.

When the diaphragm is weakened in the region through which the esophagus passes through the diaphragm, this is called a hiatal hernia. A hiatal hernia allows the lower esophagus and sometimes the stomach to pass from the abdominal cavity into the chest cavity. This, in turn, can result in gastroesophageal reflux disease (GERD) leading to heartburn and indigestion. There are a number of conditions that can result in weakness of the diaphragm and cause a hiatal hernia, including increased pressure in the abdomen (from obesity or pregnancy), or straining (such as with heavy lifting, coughing, or having a bowel movement). Smoking increases the risk, as do some genetic conditions such as Ehlers-Danlos syndrome.

Diaphragmatic Hernias may be present from birth, or, less commonly occur in adults with trauma.

Congenital Diaphragmatic Hernia

In roughly 1 in 2000 births, either one side or the whole diaphragm fails to develop. When this happens, the contents of the abdominal cavity enter the chest cavity, often resulting in the incomplete development of the lungs (pulmonary hypoplasia). In recent years major strides have been made in supporting babies with a diaphragmatic hernia, including surgeries in which an artificial diaphragm which can expand with growth may be constructed.

Acquired Diaphragmatic Hernias

Diaphragmatic hernias may also occur in adults due to trauma, such as blunt trauma (often in motor vehicle accidents), gunshots, or stab wounds.

The diaphragm may be paralyzed either partially or completely due to damage to the nerves supplying the diaphragm. These nerves can be damaged in several ways:

• From compression due to a tumor pressing on the phrenic nerve in the chest (such as with lung cancer) or near the cervical spine or brainstem.
• From damage to the phrenic nerve during surgery, such as during coronary artery bypass surgery, esophageal surgery, and others.
• From trauma to the chest cavity or anywhere along the distribution of the nerve. 
• From neurological conditions such as diabetic neuropathy, Guillain-Barre syndrome, and muscular dystrophy. 
• Infections: Viral infections such as HIV, West Nile, and much more commonly in the past, polio, as well as bacterial infections such as Lyme disease

When only one side of the diaphragm is paralyzed, it moved in the opposite way of what would be expected, moving up during inspiration and down during exhalation. This can result in shortness of breath, especially when lying down, among other symptoms.

Surgery on the diaphragm is sometimes needed for severe Hiatal hernias or cancer.

Most of the time, treatment for Hiatal hernias can be accomplished with lifestyle measures and medications alone. With paraesophageal Hiatal hernias, however, surgery is often recommended to reduce the risk of complications (such as volvulus (twisting) and strangulation (cutting off the blood supply) of tissues). With paraesophageal hernias, the stomach slides up through the hernia and lies alongside the esophagus. Surgery may be performed either through an open incision, or through laparoscopic techniques in which several small incisions are made in the abdomen, and the repair is done through special instruments.

Sometimes part of the diaphragm is removed surgically. This procedure may be done for people having surgery for mesothelioma—a cancer of the lung linings (the pleura)—which can spread to and involve the diaphragm.

The diaphragm plays a vital role in breathing, that's often taken for granted unless problems occur. Fortunately, advances in medicine are helping people to cope with conditions involving the diaphragm ranging from Hiatal hernias to the absence of a diaphragm in newborns.