Dosimetry considerations for electrical stun devices.

Electrical dosimetry issues are discussed in relation to electrical stun devices (ESDs). A measure of effectiveness is based on a 'threshold factor,' F(T), calculated with a myelinated nerve model that simulates stimulation of a reference-case neuron (20 microm diameter, 1 cm distant). Several ESDs were measured in the laboratory using resistive loads of 100-1000 Omega; some included air gaps bridged via an electric arc. Conducted current waveform parameters and the associated threshold factors depend on the resistance of the load. Thresholds were also determined for ideal monophasic and biphasic square-wave stimuli, and compared with measured ESD waveforms. Although F(T) is proposed as a metric of strength, an approximate surrogate is the charge within the largest phase of the current versus time waveform. The approximation is reasonably accurate for monophasic waveforms with phase durations below about 100 micros, and for charge-balanced biphasic square-wave stimuli with phase durations between about 40 and 100 micros.