Electrical resistance of gels and liquids used in electrotherapy for electrode-skin coupling

Abstract

Objective: To evaluate the initial and ongoing electrical resistance of different coupling agents used in the skin-electrode interface. The agents were submitted to electrical stimulation with biphasic and direct currents. Methods: The electrical resistance was calculated indirectly by Ohm's Law. The tension was generated by a constant current generator (10 mA, 100 Hz, 100 μs and symmetrical biphasic square pulse) and captured by a digital oscilloscope. Ten coupling agents (gels, n=5; liquids, n=5) were submitted to electrolysis with symmetrical biphasic square current (BC), 0.0134 mA/mm2, 100 Hz, 100 μs or with direct current (DC) at 0.0017 mA/mm2 for 30 minutes, being reassessed every 5 minutes. For data analysis the Friedman and Kruskal-Wallis tests were applied, followed by the rank test and the Dunn test respectively. Also, Spearman's coefficient test was used for correlation analysis (α=0.05). Results: The initial resistance values of the gels varied between 116.00 and 146.00 Ω and of the liquid coupling agents, between 106.00 and 4726.67 Ω, with mostly positive correlation with the time of electrolysis. Conclusions: We concluded that gels, drinking water and saline solution are recommended for the practice of therapeutic electrical stimulation because they maintain low resistance during stimulation. In contrast, the use of distilled or deionized water is not recommended due to the high resistance to the passage of electrical current. © Revista Brasileira de Fisioterapia.