TISSUE STIMULATION - THEORETICAL CONSIDERATIONS AND PRACTICAL APPLICATIONS

The three electrical characteristics of a stimulus (current, charge and energy) are related and can be predicted from the nature of the tissue stimulated. The older empirically derived Weiss-Lapicque concepts of stimulation are compared with those predicted by membrane theory. It is shown that, from the strength/duration curve for charge, it is possible to determine the membrane time constant of the tissue being stimulated. Two practical cases of cardiac muscle stimulation (pacing and defibrillation) were chosen to illustrate that, although the goals are different in these two cases, the common denominator is excitation of cardiac muscle and that the membrane time constants so determined are similar to direct-heart and transchest electrode locations.