We measured the impedance of skin coated with gel, but otherwise unprepared from 1 Hz to 1 MHz at ten sites on the thorax, leg, and forehead of ten subjects. For a 1 cm2 area, the 1 Hz impedance varied from 10 kΩ to 1 MΩ, which suggests that biopotential amplifier input impedance should be very high to avoid common mode to differential mode voltage conversion. 1 MHz impedance was tightly clustered about 120 Ω. 100 kHz impedance was about 220 Ω,which suggests that the variation in skin impedance may cause errors in two electrode electrical impedance tomographs.

Peer Reviewed