Introduction

As shown in Chapter 14, along the track of current flow, there are measurable changes in temperature due to the effect of joule heating. That is, the tissue in the current path presents a finite resistance to the flow of current which, in turn, leads to a local dissipation of electrical energy given by I2R where I is the local current and R is the electrical resistance measured at the same point. According to the first law of thermodynamics, this energy appears as an increase in the internal energy of the tissue and manifests itself as a rise in the local temperature. Tropea and Lee (Chapter 14) show that these temperature increases can be substantial depending upon proximity to the point of entry and the type of tissue. Because of these elevated temperatures, it is highly likely that the injury experienced by tissue, and hence, the cells that make up the tissue, has two components, one electrical and the other thermal. It is also just as likely that these two modes of cellular injury can be uncoupled and addressed independently of one another. The only coupling that exists is a consequence of the fact that all the thermodynamic and electrical tissue properties depend upon the local temperature.

In order to develop therapeutic protocols for the treatment of tissue damaged by either of these modes of injury, it is essential to understand both the fundamental mechanisms and the time progression of the injury, i.e. the kinetics of the damage processes.