What exactly is the vagus nerve?
The Vagus nerve is the 10th and longest cranial nerve that constitutes the main component of the parasympathetic nervous system. This nerve is responsible for a wide range of important bodily functions, including heart rate, control of mood, digestion, immune response, and heart rate variability. Through the afferent fibers, it sends information about the internal organs to the brain. The vagus nerve also establishes connections between the brain and the GI (gastrointestinal) tract. (1)

The vagus nerve is in control of the regulation of internal organ functions, such as certain reflex actions like vomiting, sneezing, coughing, swallowing, and vasomotor activity. Its activation leads to the release of acetylcholine (ACh) at the synaptic junction with intrinsic nervous fibers, secreting cells, and smooth muscles. ACh binds to nicotinic and muscarinic receptors and stimulates muscle contractions in the parasympathetic nervous system.

What Are The Functions of the Vagus Nerve In The Autonomic Nervous System

The parasympathetic nervous system represents one of the three branches of the autonomic nervous system (ANS) alongside the enteric nervous system (ENS) and sympathetic nervous system (SNS). The vagus nerve is the major benefactor of the parasympathetic nervous system. It’s principal function is to pass information from the inner organs, such as the heart, liver gut, and lungs to the brain and Vice versa. This indicates that the inner organs are major sources of sensory information to the brain. Researchers have identified a positive feedback loop between positive emotions, good physical health, and high vagal tone. This means the higher your vagal tone, the higher your mental and good physical health will improve. Before we discuss the treatment of anxiety using vagus nerve stimulation, we need to understand what Anxiety is and how to identify the disorder.

In recent years, the number of psychological distress disorders like depression and anxiety has increased enormously. They are one of the most common mental disorders diagnosed among the ages of 18 to 64 years old. General anxiety disorder (GAD) is characterized by both physical and psychological symptoms such as poor concentration, excessive anxiety, irritability, impaired social or occupational functioning, poor sleep, and muscle tension. Anxiety is your body’s natural reaction to stress. It’s a feeling of apprehension or fear of what’s to come. For example, giving a speech on the first day of work or going for a job interview may cause you to feel nervous and fearful. This anxiety becomes a disorder when it lasts for at least 6 months, and interferes with your life. This disorder alters how you behave and process emotions, also causing physical symptoms. Having mild anxiety might be unsettling and vague, while having severe anxiety may seriously impact one’s day-to-day living.

Factors That Causes Anxiety Disorder

Environmental stress. This refers to stressful happenings you have lived through or seen. Life events often linked to anxiety disorders could be seeing violence, childhood abuse, and neglect, being attacked, or the death of a loved one.
Genetics. Anxiety disorders can run in families.
Drug misuse or withdrawal- Certain drugs may cause withdrawal symptoms after being used for a long time (Use of an illicit drug like cocaine). Overuse of drugs can also cause certain anxiety symptoms.
Brain chemistry. Some research indicates that anxiety disorders are linked to faulty circuits in the brain which controls emotions and fear
Medical conditions. Some lung, heart, and thyroid conditions can cause symptoms synonymous with anxiety disorders or make anxiety symptoms worse. In this case, you must get a full physical exam to rule out other medical conditions.

Types of Anxiety Disorders

There are several types of anxiety disorders you might be experiencing. They include (6)

Panic disorder: This is when you feel unexpected intense fear that causes you a panic attack. You might experience palpitations, chest pain, or break out in a sweat during a panic attack. Sometimes you may also feel like you’re having a heart attack or choking.
Specific phobias: this occurs when You feel an extreme fear of a specific situation or an object, such as a knife, flying, or swimming. The fear may cause you to avoid ordinary situations.
Medication-induced anxiety disorder. Use of certain medications or illegal drugs, or withdrawal from certain drugs, can trigger some symptoms of anxiety disorder.
Agoraphobia: This is known as a severe fear of being in a place that seems hard to get help or escape in case of emergency. For instance, feeling anxious when standing in line with a crowd or being on an airplane, or taking public transport.
Social Anxiety Attack: this occurs when you experience overwhelming worry about everyday social events. You compulsively worry about others judging you or being ridiculed.
Generalized Anxiety Disorder: You feel unrealistic worry and excessive tension with little or no cause

What Are The Symptoms of Anxiety?

The feeling of anxiety varies and depends on the person experiencing it.
You may have a general feeling of fear and worry, or you may fear a specific event or place. Other symptoms of anxiety include

Restlessness
Anxious thoughts or beliefs that are difficult to control
Having headaches, muscle aches, stomachaches, or unexplained pains
Difficulty falling asleep
Trouble concentrating
Being irritable
Fatigue
Unexplained aches and pains

What Is Vagus Nerve Stimulation

Vagus nerve stimulation (VNS) involves the use of a device that sends electrical charges to stimulate the vagus nerve. This treatment is used to alter the activity of the vagus nerves. VNS requires using a device that sends mild impulses of electrical charges through the vagus nerve in your neck to your brainstem. The electrical impulse is distributed to different parts of the brain when it reaches the brainstem, it alters how the brain cells work. Vagus nerve stimulation has exhibited the ability to treat anxiety, epilepsy, depression, cluster headache, and migraine(2)

The anatomy of the nervous system in the study of anxiety control indicates that manipulation of the vagus nerve affects anxiety. The sensory afferent nerve ﬁbers that vagus nerve stimulation excites, travels to the brain, and ends in the nucleus solitary tract (NTS). The afferent ﬁbers are the primary source by which the brain gets information from the organs within the gut. From there, information travels to the main site of all norepinephrine ﬁbers in the brain called the locus coureulus. Norepinephrine (NE) is an important neurotransmitter involved in the regulation and pathogenesis of anxiety. Reasonably, a device that directly stimulates this neurotransmitter control site might have important effects on anxiety.

Vagus nerve stimulation has been known to increase activity in the amygdala, thalamus, brainstem, and insula, which are the regions involved in anxiety perception and modulation. (4)

According to research, It has been estimated that between 25%- 45% of patients either failed to respond to conventional antidepressant/ anxiety treatment or withdrew from treatment due to intolerable side effects. Because of the wide influence of the Vagus nerve on multiple systems and its primary role in maintaining homeostasis, energizing the VN to modulate the function of related organs drew the attention of researchers.
In 2005, cervical vagus nerve stimulation as a slow-acting therapy was endorsed by the US FDA for the treatment of refractory epilepsy and treatment of chronic resistant depression. (5)
Vagus nerve stimulation (VNS), is known to cause changes in the neurotransmitters involved in the pathophysiology of anxiety and depression, which includes serotonin, norepinephrine, glutamate, and GABA.

Types Of Vagus Nerve Stimulation

Invasive Vagus Nerve Stimulation

This conventional vagus nerve stimulation involves surgical implants done by a neurosurgeon. This implanted device sends mild, regular pulses of electrical energy to your brainstem via your vagus nerve in the neck. After reaching the brainstem, an electrical impulse is released to different areas of the brain to change the way brain cells work. It is commonly done on an outpatient basis. As with all surgeries, there is a risk of infection. Other possible risks of an invasive VNS surgery include pain at the incision site, inflammation, nerve constriction, and damage to nearby nerves.

Non-Invasive Vagus Stimulation

Transcutaneous vagus nerve stimulation (tVNS) was developed to reduce the risks of invasive vagus nerve stimulation (iVNS).
Through the skin, transcutaneous VNS stimulates afferent fibers of the vagus nerve using small electrical currents. This is primarily done at the outer ear, stimulating the ABVN (auricular branch of the vagus nerve). cervical stimulation of the vagus nerve is also used as a non-invasive VNS. The ABNV innervates the antitragus, cymba concha, and antihelix of the ear. There is notable variance with the right branch of the vagus nerve innervating the SA (sinoatrial) node of the heart than the left branch of the vagus nerve which preferentially innervates the AV (atrioventricular) node. Research has shown that tVNS can drastically reduce multiple symptoms of depression, including anxiety, psycho-motor deceleration, sleep disturbance, and hopelessness. Presently, there are two principal ways to use transcutaneous vagus nerve stimulators.

Trans-cutaneous cervical vagus nerve stimulation (tcVNS)

This stimulation is done by using two skin electrodes (by a hand-held device to the cervical portion of the vagus nerve).

Trans-cutaneous auricular vagus nerve stimulation (taVNS).

This stimulation is mainly done at the auricular branch of the vagus nerve by using two surface electrodes to the ear.

The main rationale for ear stimulation (tVNS) is based on the anatomical studies that indicate afferent vagus nerve distribution in some parts of the ear (lower half of the back ear close to the mastoid process and concha). Research has shown that stimulation of the vagus nerve's auricular branch stimulates the inferior ganglion which projects to the nucleus tractus solitarii and thus produces the same therapeutic effects as invasive VNS.
Using VNS to decrease fear responses in recent technological developments, allows transcutaneous stimulation of the vagus nerve (tVNS) through a vagally innervated part of the outer ear. tVNS is a safe technique used to stimulate this auricular branch of the vagus nerve. Small impulses from the tVNS immediately reduce the activation of brain areas related to extinction learning eg, the amygdala, prefrontal cortex, and hippocampus. This increases performance in cognitive tasks that are dependent on norepinephrine activity.

Common Side Effects of Transcutaneous VNS

The tVNS as a whole is a well-tolerated treatment option, but as with any medical treatment, has a few mild side effects.
Common side effects may include

Tingling or pain around the site of stimulation
Voice hoarseness
Soreness at the site of contact
Pharyngitis
Redness or itching

Uncommon side effects you may experience include heart palpitations, gastrointestinal issues like nausea or vomiting, facial dropping, etc.

When Is The Use of tVNS Contraindicated?

It is contraindicated in Pediatric patients as studies have not been concluded.
Patients diagnosed with carotid atherosclerosis
Patients who already have a functioning implantable medical device, such as a hearing aid, cardiac pacemaker, or any implanted electronic or metallic device.
It is contraindicated in patients diagnosed with irregular heart rhythm.
It is contraindicated in patients who have had surgery done to cut the vagus nerve in the neck
Patients who have had a history of congestive heart failure, myocardial infarction, or any atherosclerotic cardiovascular disease

Precautions To Adhere To When Using a tVNS

Do not apply stimulation over open wounds, rashes, swollen, red, and inflamed areas.
Do not apply stimulation in the shower.
Do not place electrodes near the thorax because introducing electrical current may elevate the risk of cardiac fibrillation.
Do not use tVNS while driving and operating machinery.
Do not get the tVNS device wet.
Do not use tVNS across the chest area as this may cause disturbances to the normal rhythm of the heart.
Do not apply stimulation over the mouth or neck because it could lead to severe
muscle spasms resulting in the closure of the airway.

Does VNS help with anxiety?

Yes, vagus nerve stimulation has been approved by the FDA for the treatment of anxiety. This because the vagus nerve sends information to the brain area that is important in anxiety regulations.

What condition is a VNS used to treat?

Vagus nerve stimulation causes a significant decrease in frequency, duration, and severity of headaches in patients with cluster headaches who did not respond not previously respond to treatments.
tVNS has also been endorsed for the treatment of drug-resistant epilepsy, a brain disorder characterized by abnormal discharge of neurons in the brain. It works by Increasing blood flow in key brain areas, Increasing the levels of neurotransmitters responsible for controlling seizures, and monitoring any sharp increase in the heart rate
Researchers have found that tVNS can lessen multiple symptoms of depression including hopelessness, sleep disturbance, psychomotor deceleration, and anxiety.
tVNS has shown increased improvement in cognitive function, behavior, and seizure frequency.
Tvns decreased the frequency of ringing in the ear

What are the types of tVNS?

⦁ Transcutaneous auricular vagus nerve stimulation (taVNS)
This stimulation is mainly performed at the auricular branch of the vagus nerve in the ear by using two surface electrodes.
⦁ Transcutaneous cervical vagus nerve stimulation (tcVNS) This stimulation is done by using two skin electrodes (by a hand-held device to the cervical portion of the vagus nerve)

When is a Tvns contraindicated?

⦁ In Pediatric patients
⦁ Patients diagnosed with carotid atherosclerosis
⦁ Patients who already have a functioning implanted electronic or metallic device.
⦁ It is contraindicated in patients who have had surgery done to cut the vagus nerve in the neck
⦁ It is contra-indicated in patients diagnosed with irregular heart rhythms.