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

It may not be something you’ve 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 don’t have to think about. The main 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 and 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 an important role in respiration, as it passes information from the motor to the diaphragm and receives sensory information from it.

The phrenic nerve is actually a twin nerve, with one on the left side 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 both the cervical plexus and the brachial plexus of nerves.

The phrenic nerves contain motor, sensory, and sympathetic nerve fibers. These nerves provide the sole motor supply to the diaphragm, as well as 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 right root of the lung, 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 root of the left lung, on the left side of the pericardium. 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 where it 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 some communicating fibers from the cervical plexus along the anterior scalene muscle to the carotid sheath.

The right phrenic nerve passes over the brachiocephalic artery, posterior to the subclavian vein, and then crosses the root of the right lung anteriorly and then 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.

Variation

The contribution of the fifth cervical nerve may come from an accessory phrenic nerve. The phrenic nerve in its initial course near its origin, was giving 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.

Most often it is 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 main nerve and 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.

Function

Breathing is an interesting bodily process because, although you usually don’t have to think about doing it, you have the ability to hold your breath or take a deep breath.

Motor functions

The phrenic nerve provides motor innervation to the diaphragm; the main muscle of respiration. Since the phrenic nerve is a bilateral structure, each nerve supplies the ipsilateral side of the diaphragm (that is, the hemi-diaphragm 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 right phrenic nerve can be crushed by the vena cava clamp 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, which is much lower. Therefore, patients suffering from spinal cord injuries below the neck are still able to breathe effectively, despite paralysis of the lower extremities.

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

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 resulted in restored function of the nerves in the brachial plexus with minimal impact on the respiratory function of the phrenic nerve.

Cases in which pulmonary vital capacity is reduced have typically been the result of use of the right phrenic as a donor for neurotization, whereas use of 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 stops working normally. This can happen for a number of reasons, depending on the patient’s medical history.

There are few diseases that 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 : Depending on which vertebra is damaged, nerve impulses can be altered. 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 : A common etiology of phrenic nerve injury is surgery, 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 an extremely common 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 (eg, 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 that an important factor causing injury during cardiac surgery is 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 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 some 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 on your own. Other symptoms include:

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

The most serious impact of phrenic nerve damage is paralysis of the diaphragm , which prevents the patient from regulating breathing on their own.

A less common symptom is a pain at the tip of the shoulder blade, a phenomenon known as Kehr’s sign. This type of pain can also have other more serious 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 of these 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 treatment for the damage, although treatments vary depending on the severity and presentation.

Treatment

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 normal breathing pattern and enables the subconscious process of breathing.

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

If a person continually has trouble breathing related to phrenic nerve damage, they can be given a breathing pacemaker, which is 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, those who are eligible 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, as well as for 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 of the nerves are damaged. The surgeon then implants a receptor just under the skin.

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

The surgery itself usually takes less than four hours, and the patient is usually 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.

The diaphragm stimulation system that Avery offers has been implanted in more than 2,000 patients in countries around the world.

It is an effective option for patients who need help with breathing, arguably one of the most important tasks the body performs.

Sometimes a procedure called a plication is also used. This involves surgically modifying the diaphragm so that it remains lower than normal, allowing the lungs more room to expand.