Neuromodulation: Use of Transcutaneous Vagal Nerve Stimulation
The vagal nerve can be stimulated from the surface of the skin using an electrical device similar to a TENS unit often used to treat muscle of soft tissue injuries. While a TENS unit uses a pulsed amplitude of 5–80mA, transcutaneous vagal nerve stimulation opperates at a constant 1–2mA.
How does this electrotherapeutic modality (HVG= high voltage Galvanic) differ from others? HVG utilizes high voltage and direct current (DC), thus differentiating this device from transcutatneous electrical nerve stimulation (TENS) and neuromuscular (NMES), which uses a low voltage and alternating current (AC). This allows HVG to penetrate tissue in a more effective manner due to the reduction in pulse duration that reduces the skin’s impedance.
There is a polarity specific effect of DC current. The positive pad (anode +) emits an ice-like, cooling sensation which tends to reduce circulation and decrease swelling in the region beneath the pad. In contrast, the negative pad (cathode -) has heat-like properties, emitting warmth, promoting increased circulation and improving the overall rate of healing.
Alternating current (TENS) switches between positive and negative, so there is no polarity specific effect.
So, let’s compare DC and HVG?
- Low voltage DC and HVG both have Anode (+) and Cathode (-)
- Properties of HVG cause deeper penetration with less risk of tissue injury.
- Applied average current for HVG is 1–2mA or virtually the same as Low Voltage DC used in tDC with less risk.
For these reasons, HVG is the stimulation method of choice for Vagal nerve stimulation.
Vagus nerve stimulation in the neck has shown great promise in suppression of epilepsy. Because some patients who received vagus stimulation for their seizures also reported relief of pain, the technique has been studied in animal pain models and in experimentally induced pain in humans. These initial reports of pain suppression by use of vagal nerve stimulation have led to it’s application in chronic pain syndromes, like migraines and cluster headaches. Like vestibular and direct current brain stimulation, it appears that vagal nerve stimulation can be done non-invasively through stimulation of the vagus nerve transcutaneously at the auricular branch of the ear.
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