Numerical modeling of percutaneous auricular vagus nerve stimulation: a realistic 3D model to evaluate sensitivity of neural activation to electrode position

Abstract

Objective: Percutaneous stimulation of the auricular branch of the vagus nerve (pVNS) by miniaturized needle electrodes in the auricle gained importance as a treatment for acute and chronic pain. The objective is to establish a realistic numerical model of pVNS and investigate the effects of stimulation waveform, electrodes' depth, and electrodes' position on nerve excitation threshold and the percentage of stimulated nerves. Methods:Simulations were performed with Sim4Life. An electro-static solver and neural tissue models were combined for electromagnetic and neural simulation. The numerical model consisted of a realistic high resolution model of a human ear, blood vessels, nerves, and 3 needle electrodes. Results:A novel 3D ear model was established, including blood vessels and nerves. The electric field distribution was extracted and evaluated. Maximum sensitivity to needles' depth and displacement was evaluated to be 9.8% and 15.5% per 0.1mm, respectively. Stimulation was most effective using bi-phasic compared to mono-phasic pulses. Conclusion

High-Resolution Multi-Scale Computational Model for Non-Invasive Cervical Vagus Nerve Stimulation

“…We developed an approach whereby we modeled rheobase thresholds, namely the response to a long duration pulse. This allowed us, as a first approximation, to remove considerations of neuron dynamics and stimulation train parameters such a number, pulse shape, frequency, and duty‐cycle which while important would incur a large set of additional fiber specific parameterizations —whereas our focus was to address the role of tissue modeling. The assumption also supports future efforts to optimize stimulation approaches leveraging linearity (see “Discussion” section).…”

Sensitivity Analysis of a Numerical Model for Percutaneous Auricular Vagus Nerve Stimulation

“…The titration process provides a scaling factor of the actual modulated current needed to generate an action potential. Details of the simulation platform can be found in Reference [12]. The SENN model is based on the Frankenhaeuser and Huxley [19,20] equations to describe the time course of the membrane potential at all nodes of a myelinated fiber given by…”

“…Number of axons (1) 21-133 68 18 [24] Axon fiber diameter (µm) 7-12 8 0.5 [24] Model temperature ( • C) 35.6-37 36.3 0.2 [26] Ear conductivity (S/m) 0.1-0.7 0.4 0.1 [27] Electrode penetration depth (mm) 0.8-1.5 -* 0.1 [12] Electrode position (mm) (±0.1, ±0.1) 0 0.1 [12] * For sensitivity index simulations of other parameters the electrode penetration depth was fixed to 1.5 mm.…”

“…Omnipresent inter-patient variability is neglected, while safety margins when stimulating different fibers are missing. To elevate the understanding of stimulation mechanisms, a realistic numerical model for percutaneous auricular vagus nerve stimulation (pVNS) at the human auricle including nerves and vessels was recently developed by our group [12]. The study provides a better understanding of the electric potential and current distribution in tissues surrounding the stimulation electrodes.…”

“…By stimulation of different nerves, opposite physiological reactions and an even adverse therapeutic outcome may be elicited. Thus, a sensitivity analysis (SA) of the numerical model is an invaluable tool to better quantify the dependence of the numerical model developed in Reference [12] to different parameters. SA is used to link the uncertainty in the model output to different sources of uncertainty in the model parameters [13][14][15][16].…”