Inasmuch as current represents the rate of change of charge over time, a quasistatic model of volume conduction through a conductive medium may be proposed, with properties that precisely parallel those of a point charge in free space (Freeman and Nicholson, 1975). The voltage potential O produced by a point current source I thereby takes the form of: Eq. 1Φ(d)=I/(4πσd) where the potential at a radial distance (d) from the generator is directly proportional to the injected current (I), and inversely related to a resistive impedance term related to the conductivity of the medium (σ; analogous to permittivity in free space; cf. Nicholson and Freeman, 1975, Eq. 1).
