Phrenic Nerve: What to Know

Medically Reviewed by Mahammad Juber, MD on September 29, 2022
4 min read

The phrenic nerve controls the diaphragm, the dome-shaped muscle that is primarily responsible for breathing. Contraction of the diaphragm expands the lungs and draws air into them. The phrenic nerve performs this function multiple times per minute throughout your lifetime.

Minor irritation of this nerve can cause hiccups. More serious phrenic nerve damage can paralyze the diaphragm and cause difficulty breathing.

You actually have two of these nerves — the right and left phrenic nerves. They both stem from spinal nerves in the neck. They provide both muscle movement and sensation to the diaphragm, the chief muscle in breathing. The left phrenic nerve controls the left side of the diaphragm, and the right phrenic nerve controls the right side of the diaphragm.

Breathing is an involuntary act. You don't have to think about or control it in normal situations.

The diaphragm is a dome-shaped muscle. The phrenic nerve regularly stimulates it to contract. This contraction makes it flatter, creating negative pressure in the chest. This causes the lungs to expand, drawing air into them.

The phrenic nerves also carry sensations from the diaphragm and pleura (the covering of the lungs). They similarly connect to the pericardium, the covering of the heart. Sensations from these structures are carried to the brain but perceived as coming from the area supplied by the third, fourth, and fifth cervical nerves, so disorders of the pericardium and pleura actually cause pain in the shoulder and side of the neck.

Nerve fibers from the third, fourth, and fifth spinal nerves emerge from the spinal cord in the neck. They come together to form the phrenic nerve in the neck, with the fourth cervical nerve primarily contributing.

The newly formed nerve travels a long distance through the chest to reach the diaphragm. In the chest, it passes through the mediastinum, a space between the lungs that also contains the heart, blood vessels, esophagus (food pipe), and other nerves.

The phrenic nerves pass through the diaphragm upon reaching it. They enter the muscle and innervate it from the lower surface.

Fortunately, injuries affecting the spinal cord in the lower neck or chest area do not affect breathing. This is because the phrenic nerve leaves the spinal cord high in the neck.

The chief function of the phrenic nerve is to stimulate breathing, so its disorders may cause symptoms related to breathing. If only one phrenic nerve is injured or diseased, you may not immediately notice anything wrong because enough air is being drawn in and out by one side of the diaphragm. You may notice breathlessness during physical activity, though, or when you are lying down (orthopnea). A phrenic nerve disorder on one side can especially cause breathing difficulty in people with obesity, heart disease, or lung disorders. 

Other possible effects include tiredness, sleepiness during the day, and snoring.

If both the phrenic nerves are damaged, breathing immediately becomes difficult. The lungs can still partially function due to rib movements, but this type of breathing is not adequate. You will feel short of breath, especially when lying down. You may experience pneumonia frequently, have difficulty sleeping, and feel tired during the day.

This diaphragmatic paralysis is a serious disorder and can lead to respiratory infections and neurological problems. If you notice such symptoms, you should meet your doctor.

The phrenic nerve lies deep in the chest and is rarely injured. Even in the case of spinal injuries, the phrenic nerve often maintains its function because its source is high in the neck. Even people paralyzed because of a spinal injury can often breathe by themselves because the phrenic nerves remain functional.

The phrenic nerves may be damaged during chest surgery, though. The internal mammary artery in the chest is sometimes removed for use in coronary bypass surgery, and this procedure sometimes injures the phrenic nerve, which is close by. Some children undergoing surgery to treat heart defects also suffer damage to the phrenic nerve.

Additionally, phrenic nerves can be damaged by:

  • Compression by the other structures in the chest
  • Viruses
  • Diabetes
  • Tumors
  • Radiation therapy

You should consult your doctor if you have trouble breathing at any time. Your doctor may order an x-ray of the chest, which might show the paralyzed side of the diaphragm is stuck in a higher position. A fluoroscopy or ultrasound will confirm that one side of the diaphragm is not moving.

Fortunately, you can usually live a normal life even with one-sided diaphragmatic paralysis. If both phrenic nerves are damaged, though, breathing is dramatically impaired. Procedures like intercostal nerve transfer or phrenic nerve stimulation may then be required to restore diaphragmatic movement. If these aren't successful, you may need mechanical ventilation for the rest of your life.

Diaphragmatic pacing. This is a method of restoring phrenic nerve function. If the phrenic nerve is intact but not working, an electronic pacer can be implanted in the body and attached to it. This stimulates the phrenic nerve periodically, causing diaphragmatic activity and breathing.

This surgery can be done by laparoscopy now. It grants freedom from the mechanical ventilator, enables speech, and improves quality of life.

Microsurgery. If the phrenic nerve has been damaged, microsurgery is an option. An expert surgeon will join the two ends of the phrenic nerve. A nerve graft may be needed to avoid stretching.

No techniques specifically improve the health of your phrenic nerves, but certain measures improve the overall health of your nervous system. You should:

  • Eat a balanced, nutritious diet.
  • Maintain a healthy weight.
  • Be physically active.
  • Get adequate, restful sleep.
  • Avoid smoking.
  • If you have diabetes or high blood pressure, engage in prescribed treatments diligently.