The Effect of Auricular Vagus Nerve Stimulation on Heart Rate Variability

Autonomic nervous system (ANS) is a structure which operates involuntarily and controls vital functions. Vagus Nerve Stimulation (VNS) is a novel treatment method focused on addressing ANS dysfunctions in cases of imbalance between sympathetic and parasympathetic nervous system activation. With VNS, parasympathetic activity (PA) increases while sympathetic activity (SA) decreases, affecting cardiovascular parameters. Heart rate fluctuates with each beat, reflecting the influence of PA and SA signals on the sinoatrial node. Research indicates that as individuals age, PA in the heart diminishes, while SA tone increases. When heart rate variability (HRV) and respiratory sinus arrhythmia are used to assess vagal tone, reduced PA control over the heart is revealed. This shift in autonomic balance is linked to a higher risk of developing cardiovascular disease. Therefore, it is important to consider the restoration of this balance as a therapeutic goal. Heart rate variability is the most used method for evaluating ANS functions. In this review, studies investigating the effect of auricular VNS on HRV are evaluated. It has been observed that there is a need for research investigating the short- and long-term effects of stimulations performed with different parameters from different ears on cardiovascular parameters in healthy individuals and/or individuals with various clinical conditions. Thus, a more specific and effective use of auricular VNS for different clinical situations can be achieved.