Comportamento da impedância elétrica dos tecidos biológicos durante estimulação elétrica transcutânea

Abstract

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/m 2 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.

Diferenças de gênero no limiar sensitivo para estimulação elétrica nervosa em adultos jovens

“…A convenience sample of 30 healthy youths of both genders (15 men and 15 women), undergraduate students of a certain institution 4 , was invited to take part in the study. The inclusion criteria were: young age, (between 19 and 25 years), normal body mass index (between 20 and 24.9 Kg.cm 2 ), sedentary (> 2 months), absence of neurological, cardiovascular, respiratory, metabolic, dermatological and musculoskeletal dysfunctions in the last two months.…”

“…Initially, the electrical current amplitude was gradually increased for determination of the perception threshold (ST) in each joint, then raised to the maximum limit tolerated (TT) by the individuals before pain. 1,2,4 The values of LS and TT for electrical current (mǖ)of each knee were acquired and recorded, and soon afterwards superficial thermotherapy was applied with rerecording of the sensitive thresholds.…”

“…[1][2][3][4][5] Particularly in rehabilitation medicine, as the main analgesic and non-pharmacological therapeutic methods, such as electrotherapy, thermotherapy (including cryotherapy) and phototherapy, depend directly on the sensorimotor pathways and on their adaptability. [1][2][3][4][5][6][7] To this effect, the evaluation of the sensory perception threshold (ST), that is, the lower quantity of energy capable of evoking a perception, and of the tolerance threshold (TT), the higher quantity of energy tolerated before pain, are essential measurements for studies of the superficial, thermal tactile and painful sensory pathways. 1,2 Recent investigations have evidenced that the NSS can undergo direct and indirect influences of various endogenous and exogenous physical and chemical factors for the regulation of sensory perception and of pain thresholds.…”

“…[1][2][3][4] The discovery that the circulating levels of sex hormones (SH), especially estrogen E2 and progesterone P2, besides the reproductive 8 and cardioprotective 9 roles, can exercise modulatory effects on the neuronal functions and alter the superficial cutaneous sensitivity 1,2 , gave rise to intriguing questions about the parameters of conformation/therapeutic modulation in analgesia in both genders, particularly in associations with thermal resources. [5][6][7][8][9][10][11] Considering that transcutaneous electrical nerve stimulation (TENS) appears as one of the most reliable and effective non-pharmacological resources for analgesia [3][4][5][6][7][10][11][12][13][14][15] , it became worth investigating the variations of the NSS between genders, and whether previous changes in skin temperature induced by heating/cooling would interfere in the adjustment/peripheral control of the NSS. Recently, experimental and clinical investigations showed that there are differences in the perception of the nociceptive stimulus, in the pain tolerance threshold and in cutaneous sensitivity to electrical stimuli between genders.…”

“…Although from the electrophysiological perspective this common practice does not seem adequate, due to factors such as: changes in skin impedance, variations of tissue water content, alterations of the enzymatic and energetic metabolism and actions in the impulse transmission speed in the nerve fibers, among others caused by thermotherapy. 4,5,[12][13][14] Nevertheless, there are few experimental and/or clinical studies demonstrating the differences of gender in the perception and tolerance of transcutaneous electrical stimuli, as well as the implications of SH in the regulation of final skin temperature after the use of thermotherapy. Therefore, the aim of this study was to investigate gender differences in the perception and tolerance thresholds (ST/TT) for TENS in healthy young adults, and whether previous thermotherapy (induced tissue heating or cooling) modifies cutaneous sensitivity thresholds.…”