Overview of Vagus Nerve Stimulator
The Vagus nerve is a very long nerve in the body that starts from a part of the brain called the medulla oblongata. This nerve is often referred to as the ‘wanderer’ because it connects various parts of the brain to the body. Of all the information that this nerve transmits, about 80% is moving from the body to the brain and about 20% is going from the brain to the body.
In the 1800s, a neurologist from New York named Dr. James Corning thought that seizures could be caused by too much blood in the veins. As a solution, he developed a technique to compress the carotid artery and stimulate the Vagus nerve at the same time to help control these seizures. However, his idea wasn’t fully explored until the late 20th century. In the 1980s, this technique was modernised through the use of a device known as a vagus nerve stimulator (VNS) to treat a type of epilepsy that doesn’t respond well to other treatments.
Today, the use of a VNS is approved by the Food and Drug Administration (FDA) for several conditions, including chronic epilepsy, refractory epilepsy (which is another term for epilepsy that is difficult to control with medication), and depression. Its use as a treatment for other conditions, such as autoimmune and chronic inflammatory disorders, is also being studied.
Anatomy and Physiology of Vagus Nerve Stimulator
The Vagus nerve is like a superhighway connecting many of our important internal organs with our brainstem and the outer parts of our brain. It is unique because its reach and distribution far surpass that of other cranial nerves in our autonomic nervous system, which is a complex network of nerves controlling bodily functions like heart rate and digestion. It starts from an area in the lower part of the brain called the medulla oblongata, growing into 8 to 10 strands from four main nodes.
Here’s a simple breakdown of these four nodes and their tasks:
1. Dorsal Motor Nucleus: This node is the source of the parasympathetic visceromotor fibers, which help control internal organ functions.
2. Nucleus Tractus Solitarius (NTS): This node receives sensory input from the digestive and respiratory system, as well as taste information. It forms over 80% of the vagus nerve. Messages from the NTS go to many different areas of the brain, brainstem, and the hypothalamus; a part of the brain which plays a crucial role in functions like sleep and appetite.
3. Nucleus Ambiguous: This node is involved with the output related to nerves 9, 10, and 11. It also helps control the neurons that regulate the heart’s functions.
4. Spinal Nucleus of Trigeminal Nerve: This node picks up sensory input from the back of the ear and the external part of the ear canal.
After starting its journey from the medulla oblongata, the vagus nerve leaves the skull through a hole called the jugular foramen. From there, it travels down the neck within a protective layer called the carotid sheath, alongside important blood vessels such as the common carotid artery and the internal jugular vein.
Why do People Need Vagus Nerve Stimulator
Vagus nerve stimulation (VNS) is a treatment method that aims to use the body’s chemicals to affect different areas of the brain. This method has been approved by the Food and Drug Administration (FDA) for two main uses; epilepsy and depression.
Epilepsy: The VNS device was first used to treat epilepsy in a patient in 1988 that didn’t respond to medication. In 1997, the FDA approved VNS to treat individuals over 12 years old suffering from partial-onset seizures who didn’t react well to drugs. By 2017, children over four years old were also included for this treatment. The device has been beneficial to treat additional conditions such as Lennox Gastaut syndrome, Rett syndrome, and epilepsy in pregnant women because it doesn’t have harmful side effects. Studies suggest that using VNS for a long time decreases the risk of unexpected death due to epilepsy.
How it works in epilepsy is not yet fully understood, but according to research, it disrupts an ongoing seizure and reduces the frequency of chronic seizures. It is said to interfere with synchronized brain networks, which contribute to complex partial seizures, thus reducing seizure activity.
Depression: The FDA approved the use of VNS for treating treatment-resistant depression in 2005. Several studies found that scores on depression scales improved after VNS treatment. When devices were removed or stopped working, patients who claimed improvement fell back into depression, suggesting the beneficial role of VNS.
The exact role of VNS in treating depression is still unclear, but some researchers suggest it may improve the transmission of certain brain chemicals, leading to an improvement in depressive symptoms.
Other Uses: VNS is being researched for various other uses due to its role in transmitting information about inflammation in the body. Our vagus nerve can sense the presence of substances that cause inflammation and send this information to various parts of the brain. By stimulating the vagus nerve, doctors hope to control conditions characterized by inflammation, such as inflammatory bowel disease, rheumatoid arthritis, diabetes, sepsis, heart diseases, Alzheimer’s disease, and chronic pain.
A non-invasive method of VNS, known as Transcutaneous Auricular Vagus Nerve Stimulation (taVNS), stimulates the vagus nerve branch near the ear. Two main methods are used: one that combines stimulation with inhalation (RAVANS) and may help with pain disorders and migraines, and another that combines stimulation with motor activity (MAAVNS), showing promise as a rehabilitation tool post-stroke and in infants’ motor learning.
When a Person Should Avoid Vagus Nerve Stimulator
Vagotomy is a type of surgery that involves cutting the vagus nerve, a crucial nerve in the body. Here’s something important: the right vagus nerve has the job of controlling the heart’s rhythm. So, to avoid messing up the heart’s rhythm, doctors put the VNS (vagus nerve stimulator) into the left vagus nerve. This means if you’ve had a surgery that has affected both or just the left vagus nerve (known as bilateral or left cervical vagotomy), you can’t receive a VNS.
We also need to talk about diathermy. This is a treatment method that uses different types of waves (like ultrasonic or microwaves) to generate heat. But if a person has a VNS implant, they cannot have diathermy treatment. This is because the heat from the treatment may cause the VNS system to become very hot, overheating the implant and damaging the nerves and blood vessels nearby. However, if you need to have an ultrasound for diagnostic purposes, meaning to help doctors figure out what’s wrong, that’s fine – there are no problems there.
Equipment used for Vagus Nerve Stimulator
Vagus nerve stimulator devices are generally made up of an implanted battery-powered generator and a special lead (a sort of medical wire). This battery cannot be recharged, so a new one is needed approximately every six years. An external system is also used to adjust the level of stimulation based on the patient’s needs.
The VNS lead is surgically placed around the left vagus nerve, which can be found in the carotid sheath (a protective layer in the neck) and is connected to a pacemaker-like device. This device, known as a pulse generator, is placed under the skin in the left side of the chest. There are two vagus nerves in the body, the left and the right, but the left one is generally chosen because it mainly connects to the AV node, a part of the heart’s electrical system, whereas the right one mainly connects to the SA node, which can cause a slower heart rate and other irregular heartbeats if disturbed. However, the belief that stimulating the right nerve can cause heart problems is being debated in current medical literature.
The pulse generator produces electric signals that are sent to the vagus nerve via the VNS lead. Patients have the ability to turn off the device or give an extra burst of stimulation by using a provided magnet on the pulse generator. Once the magnet is taken away, the device goes back to the previously set stimulation. The device can operate in three modes: manual, automatic, and chronic.
Who is needed to perform Vagus Nerve Stimulator?
The implantation of a device known as a vagus nerve stimulator is typically handled by a surgeon who specializes in neurology, general surgery, operating on blood vessels, or ear-nose-throat procedures. These surgeons have received special training for this particular procedure. But it’s not a one-person job. A team of healthcare professionals collaborate to decide if a patient is a good candidate for the procedure.
After the procedure, the same team continues to work closely with the patient. They monitor the patient’s progress and provide education to help manage their recovery. The vagus nerve stimulator device will sometimes need adjustments to make sure it’s working as effectively as possible for the patient. Therefore, regular follow-ups are necessary for the best result possible.
Preparing for Vagus Nerve Stimulator
The operation is carried out while the patient is completely asleep due to general anesthesia. During the procedure, the patient lies flat on their back with their neck slightly raised. This position is achieved by placing a pillow under their shoulders.
How is Vagus Nerve Stimulator performed
A Vagus Nerve Stimulation (VNS) device is similar to a pacemaker, and it’s placed under the skin during a surgical procedure. During this operation, two cuts are made – one slightly below the left collarbone and the other along a line in the neck where the skin folds naturally, at the same level as the thyroid cartilage, a type of tissue in your neck.
The battery, which powers the VNS, is placed deeply into the fat beneath the skin of the chest wall through the cut made below the collarbone.
Through the second incision on the neck, the surgeon creates a pathway under the skin and moves aside the sternomastoid muscle (a major muscle in the neck) to display the carotid sheath, a protective layer of tissue containing major blood vessels and nerves in the neck. The vagus nerve, a vital nerve that helps control the heart, lungs, and digestive tract, is typically deep inside this sheath. It’s usually found in a position deep to the internal jugular vein (a major vein in the neck) and to the side of the common carotid artery (a major artery in the neck). The vagus nerve is separated from surrounding tissues, and the leads (thin wires) of the stimulator are wrapped around the nerve.
The leads are then connected to the battery of the device. This is done through a protective silicone sleeve passed through a tunnel created under the skin linking the two incision sites. After this is done, the two incisions are closed carefully in stages, or “layers”.
To confirm that the VNS device is working as expected, the surgeon checks the heart rate from the signal sent by the vagus nerve and compares it to the heart rate shown on the anesthesiologist’s monitors. If they match, it shows that the device is correctly sensing the activity of the heart. This check ensures that the VNS device is able to work properly after the surgery is complete.
Possible Complications of Vagus Nerve Stimulator
In medical studies where people were closely observed (called randomized controlled trials), some people reported experiencing a few complications after undergoing surgery. These included a change in their voice, hoarseness, a persistent cough, a tingling sensation, and some difficulty breathing. However, most people found these symptoms became less bothersome over time.
Complications during the surgery itself were rare, but they did occasionally happen. These could include paralysis of the vocal cords, infection at the site where the device was implanted, paralysis on the left side of the face, and Horner syndrome (a condition affecting the nerves to the eyes and face).
Long-term use of vagus nerve stimulation – that’s the medical technique used during the surgery – does not appear to cause any notable or harmful changes to a person’s heart or lung function, according to the existing scientific evidence.
If someone with an implanted VNS device needs to have an MRI scan of their head, it’s really important that the guidelines from the maker of the VNS device are followed to the letter. This is for their safety.
The battery inside the VNS usually lasts for 3-5 years. After that period of time, it has to be replaced to keep everything working as it should.
What Else Should I Know About Vagus Nerve Stimulator?
Vagus nerve stimulation is a treatment that has been found to be helpful in managing various health conditions, as shown in medical literature. It’s a procedure that sends mild pulses of energy to the brain through the vagus nerve, which is one of the nerves in the body that connects the brain to other areas.
Here are some conditions that medical research shows may benefit from this treatment:
1. Hard to control epilepsy, a disorder causing unprovoked seizures.
2. Depression that doesn’t respond to usual treatments.
3. To encourage neuro-plasticity, which is the brain’s ability to change and adapt.
4. Cluster headaches and migraines, which cause intense, recurring head pain.
5. Adult stroke rehabilitation, to help adults recover from a stroke.
6. Tinnitus, a condition where you hear constant ringing or noise in your ears.
7. Alzheimer’s disease, a brain disorder that affects memory, thinking, and behavior.
8. Parkinson’s disease, a nervous system disorder impacting movement.
9. Autism Spectrum Disorders, a group of developmental disorders that affect communication and behavior.
10. Male infertility, which is when a man has a reduced ability to father a child.
Vagus nerve stimulation is also used as a preventative measure for the systemic inflammatory response syndrome, which is an excessive immune response in the body to an infection or injury, and for postoperative ileus, a condition where the intestines don’t move properly after surgery. Not only that, but it’s used for inflammatory bowel diseases, conditions that cause chronic inflammation in your digestive tract, and also for psoriatic arthritis and ankylosing spondylitis, both of which are types of arthritis.
