Vagal nerve stimulation

Electrical stimulation of vagus nerve.

A medical treatment that involves delivering electrical impulses to the vagus nerve.

It is used as a treatment for certain types of intractable epilepsy and treatment-resistant depression.

About half of epileptic patients have a 50% reduction on seizures.

It uses a small device that is surgically implanted into a patient’s chest in order to emit electrical pulses into the vagus nerve for 30 seconds every five minutes.

The efficacy or treating major depression is unclear.

In the treatment of epilepsy, randomized control trials conducted in the United States indicated many patients have some type of an increase in seizures.

Other adverse effects include voice alteration and hoarseness, cough, stomach upset, pain, tingling sensations, nausea, and headache.

The vagus is the tenth cranial nerve and arises from the medulla; it carries both afferent and efferent fibers.

The afferent vagal fibers connect to the nucleus of the solitary tract which in turn projects connections to other locations in the central nervous system.

The stimulator device is implanted under the skin below the patient’s clavicle.

Lead wires from the generator are wrapped around the left vagus nerve at the carotid sheath, where it delivers electrical impulses to the nerve.

The generator sends electric impulses to the vagus nerve at regular intervals.

The left vagus nerve is stimulated rather than the right because the right plays a role in cardiac function such that stimulating it could have negative cardiac effects.

The device is set, adjusted include current, frequency, pulse width, and duty cycle.

VNS pilot study showed that 40 percent of the treated patients displayed at least a 50 percent or greater improvement in treat ent resistant depression.

In the only randomized controlled trial VNS failed to perform any better when turned on than in otherwise similar implanted patients whose device was not turned on.

Around 80% of these nerve fibers are directed outwards from the brain, while the remaining 20% or so work in reverse to send commands back to the brain from the various corners of the body.

Vagus nerve involved in regulation of breathing, control of digestion and satiety, taste response, hearing, vocalization. relaxation response, blood circulation, and parasympathetic nervous system.

With eating the volume of food in the stomach stimulates the vagus nerve to message the brain, indicating fullness.

Suboptimal function of the vagus nerve is associated with overeating or getting insatiable cravings for the wrong kinds of foods.

Vagus dysfunction can prevent glucose receptors from signaling to the brain that sufficient sugars and carbs have been consumed, leading to a glucose overdose and impaired insulin secretion and obesity.

The vagus nerve is a key component of the parasympathetic nervous system, and is associated with pro or anti-inflammatory response in the brain by producing or inhibiting production of cytokines.

Depressed patients have a reduction in appetite while undergoing the VNS treatment.

Healthy vagal tone is indicated by a slight increase of heart rate when inhaling, and a decrease of heart rate when exhaling.

The technique of deep diaphragmatic breathing can stimulate the vagus nerve and slow heart rate and blood pressure.

A high vagal tone is linked to physical and psychological well-being, while a low vagal tone is linked to inflammation, negative moods, loneliness, and cardiovascular disease.

Physical activity, including cardiovascular training, strength training and yoga can all stimulate vagal tone.

Vagal activation decreases cAMP. 

Gi-protein activation also leads to the activation of KACh channels that increase potassium efflux and hyperpolarizes the cells.

Increases in vagal activities to the SA node decreases the firing rate of the pacemaker cells, decreasing  heart rate.

Vagal activity changes  the phase 4 slope from alterations in potassium and calcium currents, as well as the slow-inward sodium current that is thought to be responsible for the pacemaker current.

 Vagal activation, hyperpolarizing the cells, and increases the cell’s threshold for firing, reducing the firing rate. 

Similar changes occur at the AV node, with a reduction in impulse conduction velocity through the AV node.

During rest vagal activity is large  on the heart, and responsible for low resting heart rates.

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