The Anatomy of the Diaphragm

The diaphragm, often called the thoracic diaphragm, is a large muscle that separates the chest from the abdomen. This muscle plays an important role in breathing as its alternating movement helps you inhale and exhale.

It isn't easy to recognize that you have a medical issue affecting your diaphragm. Symptoms, if present, can include issues like heartburn, nausea, and shortness of breath. Medical conditions involving the diaphragm can range from minor issues—such as hiccups—to more serious problems like hiatal hernias or paralysis. Typically, problems with the diaphragm can be managed medically or treated with surgical intervention.

The diaphragm is a parachute-shaped fibrous muscle that runs between the chest and abdomen, separating these two large cavities. It is asymmetric, as the right dome is larger than the left dome. The diaphragm has openings that allow certain structures to span the chest and abdominal cavities.

As it moves rhythmically, the diaphragm remains anchored to the ribs, sternum (breastbone), and the spine.

The diaphragm is primarily composed of muscle and fibrous tissue. The central tendon is a large part of the diaphragm that anchors the diaphragm to the ribs.

There are three large openings (holes) through the diaphragm:

• The esophageal opening (esophageal hiatus), through which the esophagus, right and left vagus nerves, and left gastric artery and vein pass
• The aortic opening (aortic hiatus), through which the aorta, thoracic duct, and azygous vein pass
• The caval opening (cavus hiatus), through which the inferior vena cava and parts of the phrenic nerve travel

In addition to these openings, several smaller openings also allow smaller nerves and blood vessels to run through.

The diaphragm spans across the body from the front to the back. It is the floor of the thoracic cavity and the ceiling of the abdominal cavity.

Your heart, lungs, and the upper part of your esophagus (food pipe) are in the thoracic cavity above the diaphragm. Your lower esophagus, stomach, intestines, liver, and kidneys are below the diaphragm, in your abdominal cavity.

The left and right phrenic nerves send signals to control the diaphragm, which receives its blood supply primarily from the inferior phrenic arteries.

A healthy person can have some minor variations in the diaphragm's anatomy. For example, the left or right side may be slightly higher or lower without affecting physical functions.

During pregnancy, a woman's enlarged uterus can shift the abdominal space a bit, raising the diaphragm and causing shortness of breath.

The diaphragm plays an integral role in respiration (breathing). Most of the time, the diaphragm moves involuntarily.

Your thoracic diaphragm also plays a role in helping the movement of muscles during childbirth, having a bowel movement, urinating, and lifting heavy objects. This muscle also helps maintain the flow of lymphatic fluid throughout the body.

When the diaphragm is activated by a nerve, it contracts and flattens. This action decreases pressure and increases the space in the thoracic cavity, allowing your lungs to expand as you inhale. When the diaphragm relaxes, your chest cavity becomes smaller and your lungs release air. 

Your diaphragm contracts rhythmically and involuntarily (such as during sleep) due to signals from your brain. You can also voluntarily contract your diaphragm to hold your breath, to breathe more deeply or faster, or to exert your muscles. 

There are several medical conditions that involve the thoracic diaphragm. Traumatic injuries or anatomical defects can interfere with the muscle's function, and the movement of the diaphragm can also be impaired by issues like nerve disease or cancer.

When the diaphragm is irritated, such as when eating or drinking quickly, it can repeatedly contract involuntarily, resulting in hiccups. The sound of hiccups is produced when air is exhaled at the same time that the diaphragm contracts.

Generally, hiccups tend to resolve on their own, but there are treatments for persistent cases.

A hiatal hernia is a protrusion of the lower esophagus (and sometimes the stomach, too) into the chest cavity. This defect can cause heartburn, indigestion, and nausea.

A number of conditions can 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.

Sometimes hiatal hernias can be treated with lifestyle measures and medications alone. In some cases, surgery is recommended to reduce the risk of complications, such as volvulus (twisting) and strangulation (cutting off the blood supply) of tissues.

Surgery may be performed either through an open procedure or laparoscopically. With the latter technique, several small incisions are made in the abdomen and the repair is done through special camera-equipped instruments.

Diaphragmatic hernias are structural defects that allow abdominal organs to enter the chest cavity. They may be present from birth, or, less commonly, can result from trauma.

• Congenital: The diaphragm doesn't develop as it should in roughly 1 in 2,000 births. As a result, some of the contents of the abdominal cavity can enter the chest cavity. This can result in incomplete development of the lungs (pulmonary hypoplasia). Major strides have been made in supporting babies with a congenital diaphragmatic hernia. For example, with surgery, an artificial diaphragm may be constructed.
• Acquired: Diaphragmatic hernias may also affect adults as a result of injuries, such as trauma due to motor vehicle accidents, gunshots, or stab wounds. These hernias can cause life-threatening issues, such as lung compression, and they generally need to be repaired surgically.

Conditions that affect the nerves that control the diaphragm can result in weakness or complete paralysis of the muscle.

These nerves can be damaged due to several mechanisms: 

• Tumor compression
• Damage during surgery
• Traumatic injury
• Neurological conditions, such as diabetic neuropathy, Guillain-Barré syndrome, and muscular dystrophy. 
• Viral infections, such as polio
• Bacterial infections, such as Lyme disease

Nerve injury-induced diaphragmatic weakness can result in shortness of breath, especially when lying down. Management may require medication, surgery, rehabilitation, or support with mechanically assisted breathing.

Lung disease, especially COPD, can cause weakness of the diaphragm. This happens through a progressive process that involves a number of contributing factors.

COPD results in hyperinflated lungs that physically push on the diaphragm. The whole muscle becomes flattened and its mobility declines. Over time, the cells of the diaphragm are altered due to excessive strain, causing them to lose the ability to function with maximal strength. Chronic oxygen deprivation due to COPD also damages these cells.

The result of COPD-induced diaphragmatic weakness is worsening shortness of breath.

Tumors can spread to the diaphragm or may take up space in the chest or abdominal cavity, placing physical pressure on the diaphragm and interfering with its ability to function. For example, mesothelioma—a cancer of the pleura (lining of the lungs)—can spread to the diaphragm. Lung cancer, lymphoma, and stomach cancer are other types of cancer that may affect the diaphragm.

The symptoms can be gradual or abrupt, and may include shortness of breath, pain with breathing, or loss of consciousness. Treatment generally involves surgical removal of the tumor, radiation treatment, and/or chemotherapy.

Evaluation of the diaphragm can include a variety of tests tailored to the suspected medical problem. Imaging tests such as chest or abdominal computerized tomography (CT), magnetic resonance imaging (MRI), or ultrasound may identify anatomical variations or tumors.

A hiatal hernia diagnosis may include tests like an upper endoscopy or a barium swallow, which evaluate the structure of the gastrointestinal system. And COPD-associated diaphragmatic problems may be assessed with breathing tests like spirometry or pulmonary function tests.