Phrenic Nerve: Structure, Function, Clinical Significance, Conditions, Causes, Symptoms and Treatment

It may not be something you have heard of before, but as you read this, it keeps it alive. This nerve controls the diaphragm muscle, which controls the breathing process.

When the diaphragm contracts, the chest cavity expands and creates space for inhaled air. Breathing is an involuntary action and something you do not have to think about. The primary function of the phrenic nerve is to carry out this process without you having to command your body to do it.

When the phrenic nerve is damaged, it can prevent normal respiratory processes and affect your health. Fortunately, there are treatments to remedy the disease.

The phrenic nerve is a bilateral mixed nerve that originates in the neck, runs down the thorax (C3-C5), and passes down between the lung and the heart to reach the diaphragm.

As the sole source of motor innervation to the diaphragm, this nerve plays a vital role in respiration. It passes information from the motor to the diaphragm and receives sensory information.

The phrenic nerve is a twin nerve, with one on the left and one on the right side of the diaphragm. Nerves serve to send signals between the brain and the diaphragm.

The phrenic nerve originates primarily from the fourth cervical nerve but also receives contributions from the fifth and third cervical nerves (C3-C5) in humans. Therefore, the phrenic nerve receives innervation from parts of the cervical plexus and the brachial plexus of nerves.


The phrenic nerves contain a motor, sensory, and sympathetic nerve fibers. These nerves provide the sole motor supply to the diaphragm and sensation to the central tendon. In the chest, each phrenic nerve supplies the mediastinal pleura and the pericardium.

Structure of the phrenic nerve

The phrenic nerve begins by descending obliquely with the internal jugular vein through the lateral border of the anterior scalene muscle. It then continues down the anterior surface of the anterior scalene, deep into the prevertebral layer of the deep cervical fascia and the transverse cervical and suprascapular arteries.

From here, the course of the phrenic nerve differs between the left and the right:

Right phrenic nerve: it is located in the anterior scalene muscle and passes through the anterior part of the second part of the subclavian artery and posteriorly through the anterior crossing to the second part of the subclavian artery. It enters the chest through the upper thoracic opening.

It descends anteriorly to the correct lung root, on the right side of the pericardium. It reaches the diaphragm and divides the muscle to supply the underlying surface.

Left phrenic nerve: the phrenic nerve crosses in front of the first part of the subclavian artery and posteriorly to the subclavian vein. It enters the chest through the upper thoracic opening.

It crosses the aortic arch and the vagus nerve and descends anteriorly to the left lung’s root, on the pericardium’s left side. It reaches the diaphragm and divides the muscle to supply the underlying surface.

On both sides, the phrenic nerve runs behind the subclavian vein as it enters the thorax, which runs anterior to the lung root and between the fibrous pericardium and the mediastinal aspect of the parietal pleura.

Found in the middle mediastinum, both phrenic nerves originate primarily from the C4 spinal root but also receive contributions from C3 and C5. It also receives communicating fibers from the cervical plexus and anterior scalene muscle to the carotid sheath.

The right phrenic nerve passes over the brachiocephalic artery, posterior to the subclavian vein, then crosses the root of the right lung anteriorly and exits the thorax by passing through the hiatus of the vena cava, which opens into the diaphragm at the level of T8. The right phrenic nerve passes over the right atrium.

The left phrenic nerve passes over the pericardium of the left ventricle and perforates the diaphragm separately. The pericardiacophrenic arteries and veins travel with their respective phrenic nerves.

The phrenic nerve can be marked with a line connecting these two points:

  1. The first point can be labeled 3.5 cm at the level of the thyroid cartilage from the midsagittal plane.
  2. The second point is at the medial end of the clavicle.


The contribution of the fifth cervical nerve may come from an accessory phrenic nerve. In its initial course near its origin, the phrenic nerve gave a communicating branch to the C5 root of the brachial plexus.

The phrenic nerve at the level of the root of the neck, just before entering the thorax, was placed in front of the subclavian vein. It is usually placed posteriorly between the subclavian vein and the artery.

It is often a branch of the subclavian nerve and may contain numerous phrenic nerve fibers. If the accessory phrenic nerve is present, it lies lateral to the central nerve, descends posteriorly, and is occasionally inferior to the subclavian vein. The accessory phrenic nerve connects to the phrenic nerve in the chest or at the root of the neck.

In canines, the phrenic nerve arises from C5-C7 with occasional small contributions from C4. In the cat, horse, ox, and small ruminant, the phrenic nerve variably originates from C4-C7.


Breathing is an enjoyable bodily process because, although you usually do not have to think about doing it, you can hold your breath or take a deep breath.

Motor functions

The phrenic nerve provides motor innervation to the diaphragm, the primary muscle of respiration. Since the phrenic nerve is a bilateral structure, each nerve supplies the ipsilateral side of the diaphragm (that is, the hemidiaphragm on the same side as itself).

The phrenic nerves possess both efferent and afferent fibers. Efferent fibers are the only nerve supply to the diaphragm muscle. The phrenic nerve supplies the ipsilateral diaphragm.

Sensory functions

The sensory fibers of the phrenic nerve supply the central part of the diaphragm, including the surrounding pleura and the diaphragmatic peritoneum. The nerve also provides sensation to the mediastinal pleura and fibrous pericardium.

Afferent fibers carry sensation to the central nervous system from the peritoneum covering the central region of the lower surface of the diaphragm, the pleura covering the central region of the upper surface of the diaphragm, and the pericardium and mediastinal parietal pleura.

The phrenic nerve provides motor innervation to the diaphragm. If the nerve is damaged, paralysis of the diaphragm will occur. The phrenic nerve is responsible for handling these decisions. When the nerve is damaged, this control is lost.

Some sources describe the right phrenic nerve as the innervation of the gallbladder; other sources do not mention it.

Clinical significance

The phrenic nerve begins in the brain and then continues to the first vertebrae of the spine, where it then divides.

The two nerves continue through each side of the body, with the right side coming into contact with the trachea and the heart as they pass through the lungs.

The left side also comes into direct contact with the heart, and both sides eventually end at the diaphragm.

Pain arising from structures supplied by the phrenic nerve often “shunts” to other somatic regions served by the C3-C5 spinal nerves. For example, a subphrenic abscess below the right diaphragm can cause the patient to feel pain in the right shoulder.

Irritation of the phrenic nerve (or the tissues it supplies) leads to the hiccup reflex. A hiccup is a spasmodic contraction of the diaphragm, pulling air against the closed folds of the larynx.

The phrenic nerve must be identified during thoracic surgery and preserved. To confirm the identity of the phrenic nerve, gently manipulate it to elicit a turtle response (diaphragmatic startle).

The vena cava clamp can crush the right phrenic nerve during liver transplantation. A rupture of the phrenic nerve, or a frenectomy, will paralyze that half of the diaphragm. Paralysis of the diaphragm is best demonstrated by ultrasound. Breathing will be more difficult but will continue as long as the other nerve is intact.

The phrenic nerve arises from the neck (C3-C5) and innervates the diaphragm much lower. Therefore, patients suffering from spinal cord injuries below the neck can still breathe effectively, despite paralysis of the lower extremities.

Brachial plexus injuries can cause paralysis in the various arm, forearm, and hand regions, depending on the severed nerves. The resulting paralysis has been clinically treated using the phrenic nerve as a donor for neurotization of the musculocutaneous and median nerves.

This treatment has a high success rate (84.6%) in partial to complete restoration of the innervation of the damaged nerve. Furthermore, this procedure has restored the nerves in the brachial plexus with minimal impact on the respiratory function of the phrenic nerve.

Cases in which vital pulmonary capacity is reduced have typically resulted from using the right phrenic as a donor for neurotization. In contrast, using the left phrenic nerve has not been significantly associated with reduced lung vital capacity.

Causes of phrenic nerve damage

If the phrenic nerve is damaged, it usually stops working. This can happen for several reasons, depending on the patient’s medical history.

Few diseases specifically damage the phrenic nerve, although a systemic problem with the nerves that also affects the phrenic nerve is more common than a specific disease that affects it.

If the nerve is damaged, shortness of breath is a common symptom, as well as shortness of breath when lying down. Phrenic nerve injury can occur by multiple mechanisms. Some of the common causes of phrenic nerve damage include:

Spinal cord injury: Nerve impulses can be altered depending on which vertebra is damaged. It is more likely if the injury occurs above the third vertebra. If the injury is lower in the spine, breathing is generally unaffected.

Physical trauma: neck injury related to the above.

Surgical complications or trauma: Surgery is a common etiology of phrenic nerve injury; up to 10% of cases of phrenic nerve damage are caused by operative trauma. Due to its location, the damage can occur mainly and unintentionally during thoracic and cardiac or abdominal surgery.

Phrenic nerve paresis is a widespread adverse effect of interscalene block, with rates up to 100%. The left phrenic nerve descends anteriorly between the pericardium and the mediastinal pleura.

The phrenic nerve can also be damaged by blunt or penetrating trauma, metabolic diseases such as diabetes, infectious causes such as Lyme disease and shingles, direct invasion by tumors, neurological diseases such as cervical spondylosis and multiple sclerosis, myopathy (e.g., dystrophy muscle) and immune disease (such as Guillain-Barre syndrome).

Phrenic nerve injury can present as diaphragmatic dysfunction, unilateral diaphragmatic paralysis, or bilateral diaphragmatic paralysis. One of the most common causes of unilateral diaphragmatic paralysis is iatrogenic.

In bilateral diaphragmatic paralysis, one of the most common causes is motor neuron disease, including amyotrophic lateral sclerosis and post-polio syndrome.

Therefore, it can be injured while dissecting near the area of ​​an internal thoracic artery. Canbaz et al. identified a vital factor causing injury during cardiac surgery: icy snow used for myocardial protection.

Phrenic nerve injury during catheter ablation

The right phrenic nerve runs anterior to the right superior pulmonary vein and posterior to the superior vena cava and descends adjacent to the free wall of the right atrium.

This puts you at risk of injury during radiofrequency ablation for atrial fibrillation (during isolation of the right superior pulmonary vein) and atrial tachycardias originating from the free wall of the right atrium.

The left phrenic nerve may also be involved in the ablation of Wolf-Parkinson-White syndrome in the left atrium. The potential damage to the nerve is believed to be due to direct thermal energy with secondary inflammation and edema.

The clinical manifestations can vary widely from asymptomatic to severe respiratory dysfunction requiring prolonged mechanical ventilation and mortality; however, most patients tend to be asymptomatic or have dyspnea.

Complete or partial recovery occurs in most patients. Phrenic nerve injury can be prevented with high-level stimulation to assess phrenic nerve capture in areas at risk for phrenic nerve damage prior to ablation.

Ablation should be avoided in areas where the phrenic nerve is captured. Another approach involves the placement of an epicardial balloon catheter to retract the phrenic nerve from the surface of the epicardium prior to ablation in an area where the potential for damage to the phrenic nerve is high.

Diaphragm paralysis

The phrenic nerve may be paralyzed due to pressure from malignant tumors in the mediastinum.

Surgical shredding or severing of the phrenic nerve in the neck, resulting in paralysis of the diaphragm on one side, was once used as part of the treatment of pulmonary tuberculosis, especially of the lower lobes. The immobile dome of the diaphragm rests on the lung.

What are the symptoms of phrenic nerve damage?

Symptoms are varied; irritation of the phrenic nerves can produce unusual symptoms, depending on whether the left or right nerve is damaged. If only one is damaged, the patient will continue to breathe, although it will be difficult.

If both nerves are damaged, it becomes medically urgent, as you can no longer breathe alone. Other symptoms include:

Problems with hiccupsThe hiccup reflex can be triggered by irritation of the phrenic nerve, causing the diaphragm to contract abnormally, resulting in a small air intake.

The most severe impact of phrenic nerve damage is paralysis of the diaphragm, which prevents the patient from regulating breathing independently.

A less common symptom is pain at the tip of the shoulder blade, a phenomenon known as Kehr’s sign. This type of pain can also have other more severe causes and should be evaluated by a health professional.

The tell-tale symptom of phrenic nerve damage is shortness of breath. Since there are two nerves, a person will still be able to breathe if one is damaged, but it will be difficult. Damage to both nerves is a medical emergency, as the diaphragm will become paralyzed, and a person will not be able to breathe.

Fortunately, there is a treatment for the damage, although treatments vary depending on the severity and presentation.


Respiratory distress caused by phrenic nerve damage can resolve on its own over time, as the nerves can regenerate and make new connections.

However, anyone with shortness of breath should be seen by a medical professional to rule out other causes.

As regulation of respiration is the main symptom of phrenic nerve damage, it is crucial that the solution restores a regular breathing pattern and enables the subconscious breathing process.

Patients get a pacemaker to normalize the rhythm when the heart beats irregularly. A similar concept is used for patients who have phrenic nerve damage.

Suppose a person continually has trouble breathing related to phrenic nerve damage. In that case, they can be given a breathing pacemaker, a battery-implanted surgical device that discharges regular electrical impulses that stimulate the diaphragm to contract.

Although each patient has an individual set of conditions and a treatment plan, eligible patients can use the Avery Diaphragm Stimulation System.

This is the only diaphragm stimulation system with full pre-market approval of marking privileges by the US government’s Food and Drug Administration agency and European Compliance under the European Active Implantable Medical Devices Directive.

Devices Directive for Adults and Pediatrics. It is available for patients with an intact phrenic nerve.

The pacemaker can be used for patients with phrenic nerve damage from the above causes and those suffering from congenital central hypoventilation syndrome (CCHS), amyotrophic lateral sclerosis (ALS), and paralysis of the lung. Diaphragm.

The pacemaker works by stimulating the phrenic nerve. The stimulator is surgically implanted with the surgeon placing an electrode next to the phrenic nerve.

Patients may receive one or two implants, depending on whether one or both nerves are damaged. The surgeon then implants a receptor just under the skin.

The receptors convert the radio waves into stimulating pulses sent by the electrodes to the phrenic nerves, causing the diaphragm to contract.

The surgery usually takes less than four hours, and the patient is discharged home after a day or two. Depending on the patient’s symptoms and medical history, it can sometimes be done in an outpatient setting.

Avery’s diaphragm stimulation system has been implanted in more than 2,000 patients worldwide.

It is an effective option for patients needing help with breathing, arguably one of the body’s most critical tasks.

Sometimes a procedure called a plication is also used. This involves surgically modifying the diaphragm to remain lower than usual, allowing the lungs more room to expand.