Electrochemical skin conductance

Electrochemical skin conductance (ESC) is an objective, non-invasive and quantitative electrophysiological measure. It is based on reverse iontophoresis and (multiple) steady chronoamperometry (more specifically chronovoltametry). ESC is intended to provide insight into and assess sudomotor (or sweat gland) function and small fiber peripheral neuropathy. Currently, ESC measurement can be obtained with the use of a medical device, called Sudoscan. No specific patient preparation or medical personnel training is required. The measure lasts less than 3 minutes, and is innocuous and non-invasive. The apparatus consists of stainless-steel electrodes for the hands and the feet which are connected to a computer for recording and data management purposes. To conduct an ESC test, the patients place their hands and feet on the electrodes. Sweat glands are most numerous on the palms of the hands and soles of the feet, and thus well suited for sudomotor function evaluation. The electrodes are used alternatively as anode or cathode. A direct current (DC) incremental voltage under 4 volts is applied on the anode. This DC, through reverse iontophoresis, induces a voltage on the cathode and generates a current (of an intensity less than 0.3 mA) between the anode and the cathode, related to electro-active ions from sweat reacting with the electrodes. The electrochemical phenomena are measured by the two active electrodes (the anode and the cathode) successively in the two active limbs (either hands or feet), whilst the two passive electrodes allow retrieval of the body potential. During the test, 4 combinations of 15 different low DC voltages are applied. The resulting Electrochemical Skin Conductances (ESC) for each hand and foot are expressed in μS (micro-Siemens). The test also evaluates the percentage of asymmetry between the left and right side, for both hands and feet ESC, providing an assessment of whether one side is more affected than the other.