Definition and Overview
Transcutaneous vagus nerve stimulation (tVNS) is a neuromodulation treatment that non-invasively stimulates the vagus nerve (10th cranial nerve) by attaching a skin electrode to the auricle or neck without surgery.
The vagus nerve originates from the brainstem and is widely distributed in the neck, chest, and abdomen, and plays a key role in regulating the autonomic nervous system of the cardiovascular, respiratory, and digestive systems and in regulating immune and inflammatory responses. tVNS is attracting attention as an alternative to existing implantable vagus nerve stimulation (implantable VNS) in that it can activate this nerve without invasive procedures.
Stimulation methods are broadly divided into two types. Auricular tVNS (atVNS) stimulates Arnold's nerve, a peripheral branch of the vagus nerve that innervates the ear canal or tragus. The cervical type (cervical tVNS, ctVNS) stimulates the vagus nerve trunk that runs through the skin on the front of the neck to the neck.
Mechanism of Action
The main mechanisms of action of tVNS are as follows.
The afferent fibers of the vagus nerve reach the nucleus tractus solitarius (NTS) in the brainstem and transmit signals throughout the central nervous system. Projections are made from the NTS to the locus coeruleus, hypothalamus, and limbic system, and various physiological effects are induced through this.
The cholinergic anti-inflammatory pathway is one of the important mechanisms of tVNS. Vagus nerve activation induces the secretion of acetylcholine through T cells in the spleen and suppresses the production of pro-inflammatory cytokines such as TNF-α in macrophages.
Stabilizing blood pressure and heart rate through baroreflex control, increasing parasympathetic tone, and changing synaptic plasticity are also being studied as major effects of tVNS.
Indications
The main clinical applications of tVNS are as follows:
In migraine prevention, a significant reduction in monthly headache days was reported in a study of patients with episodic migraine.
For cluster headaches, cervical devices (gammaCore, electroCore) were approved by the US FDA in 2019 for the prevention and acute treatment of cluster headaches.
In depression and anxiety disorders, aural tVNS has shown significant mood improvement effects compared to placebo (sham) in some studies, but large-scale RCT results are not yet sufficient.
Applications to epilepsy and autonomic dysfunction are also in the research phase.
Treatment method
Auricular tVNS places a small electrode clip or attachable electrode around the tragus or external auditory canal and then periodically delivers low-current (1 to 2 mA) electrical stimulation. The treatment time is usually 20 to 30 minutes per time, applied 1 to 2 times a day, and can be used by yourself depending on the device.
Cervical tVNS is a method of delivering stimulation by attaching an electrode handpiece coated with gel to the cervical skin, and devices that can be used in medical institutions or at home have been developed.
Stimulation intensity, frequency, and waveform vary from device to device, and protocols vary depending on clinical indications.
Effectiveness and Evidence
For migraine prevention, a study by Silberstein et al. (2016) reported that cervical tVNS significantly reduced the number of monthly headache days. Barbanti et al. (2015) confirmed significant effects even in patients with high frequency migraine.
In terms of effects on autonomic function, studies have reported that auricular tVNS tends to increase heart rate variability (HRV) and decrease resting heart rate.
With regard to central nervous system action, Frangos et al. (2015) confirmed with fMRI that auricular tVNS changes the activity of brain NTS and related structures.
Basic and clinical research on anti-inflammatory effects is also accumulating, but optimal protocols and long-term effects for each indication are still in the establishing stage.
Precautions and contraindications
Caution is necessary or contraindicated in the use of tVNS in the following cases:
People with pacemakers, implantable cardioverter-defibrillators (ICDs), and other active implantable medical devices are restricted from using the product due to concerns about electromagnetic interference. Patients with a history of carotid artery stenosis or neck surgery, as well as skin infections or wounds at the electrode attachment site, also require a specialist evaluation before the procedure.
There are not yet sufficient data on the safety of tVNS during pregnancy, and specialist consultation is recommended when using it.
Common side effects include redness of the skin at the electrode site, itchiness, and mild discomfort, and in the case of the cervical type, voice changes, coughing, and nausea are rarely reported.
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This information is provided for medical educational purposes and is not a substitute for individual medical care or treatment. If you have any symptoms, be sure to seek professional advice. Inquiries: Osang Neurosurgery 1599-5453 | osns.co.kr