Comportamento da impedância elétrica dos tecidos biológicos durante estimulação elétrica transcutânea

OBJECTIVE: To analyze the electrical impedance of biological tissues during electrical stimulation in relation to different segments, surfaces and current frequencies, with increasing distance between electrodes. METHOD: 20 female volunteers of mean age 23 ± 2.25 years and mean body mass index 20.65 ± 1.44 kg/m2 were positioned in decubitus with one electrode placed proximally to the wrist and ankle joint lines, anteriorly and posteriorly, or on the posterosuperior iliac spine, and the other electrode was placed at distance of 10, 20, 30 and 40 cm, sequentially. Two currents (100 us and 10 mA) were applied: one at 100 Hz (LF) and the other at 2000 Hz modulated at 100% of the amplitude for 100 Hz (MF), with a minimum interval of seven days. The impedance was calculated indirectly using Ohm's Law, from the applied intensity and the electrical voltage picked up by a system consisting of a digital oscilloscope (TDS 210, Tektronix®) and a direct current generator (Dualpex 961, Quark®). For statistical analysis, Anova-F and Kruskal-Wallis were applied, with post hoc (SNK), Friedman test and Spearman correlation coefficient, taking p< 0.05. RESULTS: Despite similar electrical impedance behavior with increasing distance between electrodes for the two currents, there was a reduction in impedance under MF stimulation. In the limbs, approximately 50% of the impedance variance was explained by the increase in electrode separation, although this relationship was not observed on the posterior surface of the trunk. Independent of the current type, the trunk presented the lowest electrical impedance, followed by the lower limbs. CONCLUSION: The electrical impedance of the tissues was influenced by current frequency and the positioning and distance between electrodes, thus presenting a non-uniform pattern in the different segments.