Measurement of soft tissue temperature and impedance following the application of transdermal direct current

ObjectiveTo measure temperature and impedance changes at various depths in human tissue in vivo, after the application of transdermal direct current (TDC).DesignProspective experimental single cohort study.SettingGenesis Surgery Center.ParticipantsEight patients who underwent a lumbar rhizotomy for chronic low back pain consented to an additional procedure involving TDC with saline solution. Two TDC electrodes (active, 55 mm; dispersive, 62 mm) were placed 51–56 cm apart, and a current amplitude of 4.0 mA was delivered for an average of 18.4 minutes.Main outcome measuresTemperature and impedance readings recorded by the RFG-3CF Lesion Generator probe, from depths of 5 cm to the skin surface were obtained before TDC, and just before TDC was terminated. Data were analyzed using non-parametric statistics.ResultsA statistically significant decrease in impedance (mean 48 Ω, 95% confidence interval: 26–70) was detected, but there was no interaction of impedance change with tissue depth. Overall, tissue temperature decreased by 2 °C (95% confidence interval: 1.9–2.8) from baseline to the second measurement and the change was greatest within 1 cm of the surface.ConclusionThe data suggest that transdermal delivery of medications to deep tissues of the lumbar region may not be enhanced by use of direct current as applied clinically.