Does Baseline Autonomic Nervous System Activity Affect the Outcomes of Transcutaneous Auricular Vagus Nerve Stimulation?

Abstract

Aim: Transcutaneous auricular vagus nerve stimulation (taVNS) has recently emerged as an effective neuromodulation method. A preliminary evaluation based on heart rate variability (HRV) could predict those who would benefit most from taVNS. This study investigated the efficacy of taVNS in healthy subjects according to the baseline activity range of the parasympathetic (PNS) and sympathetic nervous system (SNS) indexes.

Methods: 76 healthy participants were enrolled in the study. HRV, pulse rate, and systolic and diastolic blood pressure (SBP and DBP) were measured at baseline and after taVNS. The procedure was repeated after 48-72 h.

Results: In the first intervention, the PNS index increased in group 1 (p <0.001), and the SNS index decreased in groups 1 and 3 (p <0.001). In the second intervention, the PNS index increased in groups 1, 2, and 4 (p = 0.001, p = 0.018, and p = 0.003, respectively), while the SNS index decreased in groups 1 and 3 (both p = 0.001). SBP and DBP decreased in all groups after both interventions. After the first intervention, the PNS index was higher in group 1 than in groups 3 and 4 (p = 0.001 and p <0.001, respectively), and the SNS index and SBP were lower in group 1 than in group 3 (both p <0.05). After the second intervention, the PNS index was higher and the SNS index was lower in group 1 than in group 3 (p <0.05).

Conclusions: Subjects with low parasympathetic or high sympathetic activity may be more responsive to taVNS.

Keywords: Autonomic nervous systems; Heart rate monitoring; Parasympathetic nervous systems; Sympathetic nervous systems; Vagus nerve stimulations.