Enhanced transcutaneous electrical nerve stimulation achieved by a localized virtual bipole: a computational study of human tibial nerve stimulation

• Published in: Journal of neural engineering 2020-05, Vol.17 (2), p.026041-026041
• Main Authors: Roointan, Sohrab, Tovbis, Daniel, Elder, Chris, Yoo, Paul B
• Format: Article
• Language: English
• Subjects: activating function; cuff electrodes; finite element model; mrg model; neural interface; tibial nerve stimulation; transcutaneous electrical nerve stimulation
• ISSN: 1741-2560; 1741-2552; 1741-2552
• DOI: 10.1088/1741-2552/ab85d3

Objective. Electrical neuromodulation is a clinically effective therapeutic instrument, currently expanding into newer indications and larger patient populations. Neuromodulation technologies are also moving towards less invasive approaches to nerve stimulation. In this study, we investigated an enhanced transcutaneous electrical nerve stimulation (eTENS) system that electrically couples a conductive nerve cuff with a conventional TENS electrode. The objectives were to better understand how eTENS achieves lower nerve activation thresholds, and to test the feasibility of applying eTENS in a human model of peripheral nerve stimulation. Approach. A finite element model (FEM) of the human lower leg was constructed to simulate electrical stimulation of the tibial nerve, comparing TENS and eTENS. Key variables included surface electrode diameter, nerve cuff properties (conductivity, length, thickness), and cuff location. Enhanced neural excitability was predicted by relative excitability (RE > 1), derived using either the activating function (AF) or the nerve activation threshold (MRG model). Main results. Simulations revealed that a localized 'virtual bipole' was created on the target nerve, where the isopotential surface of the cuff resulted in large potential differences with the surrounding tissue. The cathodic part (nerve depolarization) of the bipole enhanced neural excitability, predicted by RE values of up to 2.2 (MRG) and 5.5 (AF) when compared to TENS. The MRG model confirmed that action potentials were initiated at the cathodic edge of the nerve cuff. Factors contributing to eTENS were larger surface electrodes, longer cuffs, cuff conductivity (>1×103 S m−1), and cuff position relative to the cathodic surface electrode. Significance. This study provides a theoretical basis for designing and testing eTENS applied to various neural targets and data suggesting function of eTENS in large models of nerve stimulation. Although eTENS carries key advantages over existing technologies, further work is needed to translate this approach into effective clinical applications.