Short trains of transcutaneous auricular vagus nerve stimulation (taVNS) have parameter-specific effects on heart rate

Background: Optimal parameters of transcutaneous auricular vagus nerve stimulation (taVNS) are still undetermined. Given the vagus nerve's role in regulating heart rate (HR), it is important to determine safety and HR effects of various taVNS parameters. Objective: We conducted two sequential trials to systematically test the effects of various taVNS parameters on HR. Methods: 15 healthy individuals participated in the initial two-visit, crossover exploratory trial, receiving either tragus (active) or earlobe (control) stimulation each visit. Nine stimulation blocks of varying parameters (pulse width: 100 mu s, 200 mu s, 500 mu s; frequency: 1 Hz, 10 Hz, 25 Hz) were administered each visit. HR was recorded and analyzed for stimulation-induced changes. Using similar methods and the two best parameters from trial 1 (500 mu s 10 Hz and 500 mu s 25 Hz), 20 healthy individuals then participated in a follow-up confirmatory study. Results: Trial 1- There was no overall effect of the nine conditions on HR during stimulation. However multivariate analysis revealed two parameters that significantly decreased HR during active stimulation compared to control (500 mu s 10 Hz and 500 mu s 25 Hz; p < 0.01). Additionally, active taVNS significantly attenuated overall sympathetic HR rebound (post-stimulation) compared to control (p < 0.001). Trial 2-For these two conditions, active taVNS significantly decreased HR compared to control (p = 0.02), with the strongest effects at 500 mu s 10 Hz (p = 0.032). Conclusion: These studies suggest that 60s blocks of tragus stimulation are safe, and some specific parameters modulate HR. Of the nine parameters studied, 500 mu s 10 Hz induced the greatest HR effects. (C) 2018 Elsevier Inc. All rights reserved.