Phrenic Nerve

Definition

The phrenic nerve can be defined as one of the nerves that stems from the cervical spinal roots and travels to the thorax, in order to innervate the diaphragm and guarantee the control of the breathing process. Each part of the body (left and right) has its own phrenic nerve. The phrenic nerve is also known in the medical field as the internal respiratory nerve of Bell.

Anatomy

The phrenic nerve has its origin in the cervical roots, mainly C3-C5. From there, it goes to the thorax, passing between the lungs and the heart and reaching the diaphragm. In the majority of the people, the phrenic nerve originates specifically from the C4 nerve root, but the contributions to the nerve also come from the C3 and C5 nerve roots. The phrenic nerve also receives a part of its fibers from both the cervical plexus and the brachial plexus. Just like the other nerves, the phrenic nerve has different types of fibers, such as: motor, sensory and sympathetic. While the phrenic nerve supplies the diaphragm with motor information, its fibers also reach a part of the pericardium and the mediastinal pleura.

The phrenic nerve travels at the same time with the internal jugular vein, crossing the anterior scalene muscle and going into the deeper levels of the cervical fascia, passing by two very important arteries: the cervical and the suprascapular arteries. On the two sides of the body, the phrenic nerve follows a different routes – on the left, it passes by the subclavian artery on the anterior part, while on the right, it crosses by the second part of the same artery. Then, it goes posterior to the subclavian vein and it enters the thorax. From there, it passes between the lungs and the heart, distributing some of its fibers to the pericardium.

At the level of the mediastinum, the phrenic nerve is found alongside the anterior scalene muscle, shielded in the fibrous connective tissue that surrounds the vascular structures of the neck (more commonly known as the carotid sheath). From there, the two phrenic nerves follow different directions one more. The right one will go over the brachiocephalic artery, then pass posteriorly to the subclavian vein and crossing the right lung root. It will leave the thorax passing through the hiatus of the vena cava and enter the diaphragm (T8 level). In leaving the thorax, the right phrenic nerve will pass the right atrium. The left phrenic nerve, on the other hand, will pass over the pericardium (left ventricle level) and enter the diaphragm after that (separate manner). The phrenic nerves are accompanied through their journey by the pericardiacophrenic arteries and veins.

Function

One of the most important functions of the phrenic nerve is related to the breathing. Innervating the diaphragm, the phrenic nerve controls and regulates the breathing process in healthy individuals. The phrenic nerve also provides the innervation of the pericardium, the mediastinal pleura and the diaphragmatic peritoneum.

Phrenic nerve palsy

Symptoms

These are the most common symptoms of the phrenic nerve palsy:

• Dyspnea (shortness of breath)
• Orthopnea (dyspnea that is relieved by assuming the orthostatic position)
• Hiccups (also caused by the irritation of the respective phrenic nerve)
• Diaphragm paralysis (the patient is no longer able to breathe on his/her own)
• Cyanosis can appear in newborns suffering from respiratory distress caused by the phrenic nerve palsy
• Chest wall pain
• Cough
• The symptoms can mimic the ones from cardiac dyspnea
• In case of bilateral phrenic nerve palsy, the patient can also present the following symptoms:
  • Anxiety
  • Insomnia
  • Headaches (predominantly in the morning)

Causes

These are the causes that lead to the appearance of the phrenic nerve palsy:

• Neoplasms (tumor compression of the phrenic nerve)
  • Bronchogenic carcinoma
  • Metastases at pulmonary level
  • Tumors of the mediastinum or at the level of the neck
• Blunt trauma and iatrogenic
  • Injuries with penetrating effect at the level of the chest
  • Inadequate chiropractic manipulation
• Surgical intervention
  • This is a problem that affects approximately 10% of the patients who have undergone surgical intervention for heart problems (cardiac surgery involving hypothermia)
• Central venous catheters
  • Direct trauma to the site of the catheter
  • Hematoma at the site, causing a compression
  • Infiltration of the local anesthetic substance
• Delivery of the newborns using the forceps and other invasive methods
• Neuromuscular medical conditions
  • CIDP (chronic inflammatory demyelinating polyradiculoneuropathy)
  • Parsonage-Turner syndrome
• Inflammatory conditions (pneumonia, emphysema, pleurisy, herpes zoster infection)
• Direct compression (occurs in patients who have been diagnosed with aortic aneurysm and cervical osteophytes)
• Cervical spondylosis
• Rare complication of radiofrequency catheter ablation (procedure recommended for those who are suffering from atrial fibrillation)
• Thoracic outlet syndrome

Treatment

These are the most common measures of treatment undertaken for the phrenic nerve palsy:

• In newborns
  • Continuous positive airway pressure (CPAP)
  • Mechanical ventilation
  • Surgical plication of diaphragm
  • Maintenance intravenous fluids
  • Oxygen support
  • Orogastric feeding tube
• Physiotherapy
  • Recommended in both children and adults
  • Can improve the respiratory capacity and the overall functioning of the diaphragm
• Avery Breathing Pacemaker System
  • Similar to the pacemaker used for those who suffer from cardiac dysfunction
  • Recommended for both adult and pediatric usage
  • Works by stimulating the phrenic nerve, being implanted in a surgical intervention
• The stimulation of the phrenic nerve can be made through two different methods:
  • Distal phrenic nerve stimulation
  • Direct muscular stimulation (implanted electrodes)

In conclusion, the phrenic nerve is a very important nerve of the body, as it provides the innervation of the diaphragm and contributes partially to the innervation of the pericardium, mediastinum and diaphragmatic peritoneum. It is important to acknowledge the symptoms of phrenic nerve palsy, especially in newborns. Otherwise, without the immediate support, serious neurological damage can occur, due to the lack of oxygen to the brain. Newborns are especially at risk for developing respiratory insufficiency and entering into vascular shock, which can threaten their existence. Immediate treatment is necessary to prevent such problems from occurring, with the neurological risk being reduced down to a minimum.