Introduction

The unique characteristics of electrical burn injury can make initial assessment of trauma very difficult. Techniques that are more deterministic could greatly enhance treatment and reduce morbidity. One technique that is potentially valuable is to measure the complex electrical impedance of the tissue. To understand fully the evaluation of electrical injury by measuring tissue impedance one must be familiar with the concepts of electrical impedance. To this end, this chapter will present first the general theory of complex electrical impedance, then the fundamental properties of tissue impedance and its relationship to electrical injury. The final segment of this chapter will describe the impedance technique and the results of experimental work using this technique.

Theory

The basis for the electrical impedance technique relies on the application of Ohm's law to the passage of current through tissue. This law is expressed as the electromotive force (voltage, V) needed to push electrons (current, I) through a media is directly proportional to the quantity of electrons being pushed and the resistance (R) of the media to the movement of electrons; more simply expressed as V = I × R. The term resistance here is used in a broad sense, however, it will be defined more strictly in the following paragraph.

To correctly define the term ‘impedance’ one expresses the resistance of the media to the flow of current in terms of the utilization of energy. Electrical energy is either dissipated (converted to heat) or stored (in an electrostatic field or a magnetic field).