Skin microcirculation during tapwater iontophoresis in humans: cathode stimulates more than anode

The aim of this controlled study was to evaluate the influence of anode and cathode on skin blood flow by using direct current. Skin microcirculation and skin temperature of 26 healthy subjects (17 men and 9 women, 20-64 years of age) without any vascular diseases were registered when a tapwater iontophoresis was applied. Thermoindifferent water temperature was used to prevent thermic effects on microcirculation. The blood flow measurement was conducted by laser-Doppler flowmetry on the proximal forearm and on the back of the wrist. The skin temperature was measured before and after treatment by an infrared thermometer. In 19 persons there was an intense erythema on the side of the cathode and an only modest one on the side of the anode, while 7 persons showed meager reactions on both sides. The erythema rose strongly from the distal (back of the hand) to the proximal forearm. The comparison of the microcirculation of the arms showed an increase of 120% at the anode and of 700% at the cathode. The differences between the two sides were significant (P < 0.001). After the end of tapwater iontophoresis the skin temperature increased more on the side of the cathode than on the anode side (P < 0.001). The frequency of vasomotion did not change. The vasomotion amplitude increased 67% at the anode (P < 0.05) and 175% at the cathode (P < 0.001). The increased blood flow effect was not age or sex dependent. Although the increased blood flow effect was six times larger on the cathode side, the subjects did not perceive any subjective difference.