MODE OF ACTION
The vagus nerve is a key component of the so-called parasympathetic nervous system1. In addition to the sympathetic nervous system as its opponent, it regulates vital mechanisms in the body, such as heart rate, blood pressure, respiration, etc. The parasympathetic nervous system takes on functions of regeneration, while the sympathetic nervous system is active during physical exertion and stress. In particular, many of the chronic diseases are caused by a dysregulation in these processes. This is often reflected in a reduced vagal activity, which in turn complicates a regeneration or recovery process, for example, chronic pain.
The vagus nerve innervates organs in the chest and abdominal region. In addition to its steering effect, the vagus nerve also transmits sensory information from the organs to the central nervous system and thus assumes a guardian function or a feedback function. Approximately 80% of all fibres of the vagus nerve are afferent (sensory) fibres, which underlines the relevance of this feedback. For example, this can be seen very impressively in the function of the vagus nerve in the immune regulation via the so-called cholinergic anti-inflammatory pathway2.
In addition to the innervation of chest and abdominal region, the vagus nerve also emits sensory fibres into the region of the auricle3 and the auditory canal. These nerve fibres can be found through the blood vessels aligned in parallel (vascular nerve bundles4,5). These afferent branches of the vagus nerve are stimulated in the auricle by means of AuriStim. An exclusively afferent stimulation prevents a direct impact on effector organs, such as the heart, and thus undesirable side effects. Instead, the electrical signals are transmitted to the brain stem via the vagus nerve in order to be processed any further. This provides extensive neuromodulatory possibilities.
With regard to the treatment of acute and chronic pain, the stimulation leads on the one hand to the blockage of pain impulses to the brain, and on the other hand, pain receptors are indirectly stimulated, inhibitory pain control systems are activated and endogenous neurotransmitters, such as endorphins and opioids are released6,7.
The therapeutic effects of the auricular vagus nerve stimulation have already been demonstrated in several clinical studies. Studies on the treatment of chronic cervical syndrome and chronic back pain show a persistent pain-reducing effect while the patient’s well-being, mobility and sleep quality improved at the same time and a reduced need for painkillers was also noticed6,7. Positive effects of electrical stimulation on the pain perception were also demonstrated postoperatively in tonsillectomy and laparoscopic nephrectomy9,10. A significant improvement in the painless walking distance in patients with Claudicatio Intermittens (intermittent claudication) as a result of peripheral arterial occlusive disease, was also shown11.
In contrast to other therapies of chronic pain, such as treatment with severe opioids or invasive spinal cord stimulation, the auricular vagus nerve stimulation offers a gentle, non-pharmacological therapy option with almost no side effects in case of acute and chronic pain.
1 E. Kandel, J. Schwartz, T. Jessel et al. McGraw-Hill, ISBN 978-0071390118, 2012.
2 H.R. Berthoud und W.L. Neuhuber. Auton Neurosc Basic 85: 1-17, 2000.
3 E.T. Peuker und T.J. Filler. Clin Anat 15: 35-37, 2002.
4 P. Carmeliet und M. Tessier-Lavigne. Nature 436(7048): 193-200, 2005.
5 E. Kaniusas, G. Varoneckas, B. Mahr und J.C. Széles. IEEE Trans on Instr and Meas 60(10): 3253-3258, 2011.
6 S.M. Sator-Katzenschlager, J.C. Széles, G. Scharbert et al. Anesth Analg 97: 1496-1473, 2003.
7 S.M. Sator-Katzenschlager, G. Scharbert, S.A. Kozek-Langenecker et.al. Anesth Analg 98: 1359-1364, 2004.
8 S. Kampusch, F. Thürk, E. Kaniusas und J.C. Széles. IEEE Sensors Applications Symposium: 79-84, 2015.
9 R. Likar, H. Jabarzadeh, I. Kager et al. Schmerz 21: 154-159, 2007.
10 H. Kager, R. Likar, H. Jabarzadeh et al. Acute Pain 11: 101-106, 2009.
11 T. Payrits, A. Ernst, E. Ladits et al. Zentralblatt Chirurgie 136: 431-435, 2011.