BIOELECTRICAL-IMPEDANCE TECHNIQUES IN MEDICINE .1. BIOIMPEDANCE MEASUREMENT - FIRST SECTION - GENERAL CONCEPTS

After a brief historical overview, the concept of electrical impedance is introduced as a principle of transduction calling attention to the possible mechanisms by which a physiological event may change impedan ce, i.e., by geometric, resistivity, and/or permittivity changes. Ther eafter, since impedance measurements usually require the injection of current, its biological effects are discussed in order to establish th e safety criteria. Finally, the elements found in an impedancimetric c ircuit and their respective nature are presented and described. The pa rticular behavior of the biological impedance and the electrode/electr olyte interface appear immediately as strikingly important. The sectio n ends with a bird's-eye view of the basic circuitry to measure impeda nce. Each subsection is closed by partial conclusions to underline the relevant concepts.