tVNS acutely improves cBRS and autonomic modulation in healthy young men.

BackgroundDespite positive outcomes across a variety of disease states, invasive vagus nerve stimulation (VNS) has been associated with adverse side‐effects. Given this, non‐invasive VNS (tVNS) via the auricular branch of the vagus nerve (ABVN) has been proposed as an alternative approach. However, the mechanisms underlying these positive outcomes remain unclear. Therefore, we controlled the sensory effects (placebo) to investigate if tVNS acutely improves blood pressure (BP) control.MethodsThirteen healthy men (23±1yrs) were randomized across three experimental visits in a random order. In active tVNS, electrodes were placed on the tragus of the ear and electrical current was applied by using a Transcutaneous Electrical Nerve Stimulation device. A time‐ control visit was performed with the electrodes placed on tragus, but no current was applied (sham‐T). Additionally, to avoid a confounding sensory effect, another sham protocol was performed with same electrical current of the active visit, but the electrodes were placed on the ear lobe (an area without cutaneous nerve endings from the vagus – sham‐L). Before interventions were applied, we inform to subjects that both active tVNS and sham‐L would not cause any harm. Beat‐to‐beat heart rate (HR) and BP were monitored at rest, during tVNS (active, sham‐T and sham‐L) and recovery. Spontaneous cardiac baroreflex sensitivity (cBRS) was measured via sequence technique. Both HR (LF/HF) and BP variability (BPV) were also measured.ResultsArterial BP and BPV were not affected by any active or sham protocols (P>0.05). HR and LF/HF ratio decreased (Δ–3.4±1% and Δ–17±10%, P<0.05, respectively) and cBRS increased (Δ20±7%, P<0.05) only during active tVNS, but were unchanged during both sham protocols (P>0.05).ConclusionThe results of the present study provide evidence that tVNS acutely improves neural control of BP in healthy young men. These findings allow us to suggest that spontaneous cBRS and cardiac sympathovagal balance could play a role in the mechanisms involved in previously reported beneficial outcomes caused by tVNS. Future studies are needed to confirm these findings in older and diseased populations.Support or Funding InformationJ.L.S., A.L.T., P.M.M. have been supported by scholarships from Coordination for the Improvement of Higher Education Personnel (CAPES).