Whole-body impedance what does it measure ? ” 2

The electrical impedance of the body is measured by introducing a small alternating electrical current into the body and measuring the potential difference that results. The impedance magnitude Z is the ratio of the magnitude of the potential difference to the magnitude of the current. With suitable equipment one can also measure the phase difference 0 between the voltage and current. Alternating electrical current flows through the body by several different physical mechanisms. Current flows through physiologic fluids by the movement of ions. This movement is opposed by viscosity and other effects, which can be modeled electrically as a resistance. In addition, the applied current will charge cell membranes and other interfaces, which can be modeled electrically as capacitors. Thus, the impedance of the human body (and of material in general) can be modeled by a combination of capacitive and resistive elements. A capacitance and a resistance can be combined in two ways: in series or in parallel (Figure 1). In either case, the components can be chosen to produce the same impedance of the circuit; however, the component values will differ.