As part of a health and safety assessment of ultrawideband sources, it was useful to determine stimulation thresholds for an electrically excitable tissue down into the low nanosecond range. Stimulation thresholds were measured using gastrocnemius muscles isolated from 16 frogs (Rana sp.). Single pulses were delivered with a pair of surface electrodes, and muscle twitch was measured with an isotonic transducer. Pulse durations of 100, 10, and 1 ms; 100, 10 and 1 s; and 100 and 1 ns were used. Tissue voltage and current strength-duration (S-D) curves on log-log plots had a classic appearance, with thresholds for ultrashort pulses being linear. For a pulse of 1 ns, the mean threshold voltage in the muscle was 4.5 kV and the mean threshold peak current was 35 A. When delivered by direct contact, a single ultrawideband pulse of 1 ns could reliably produce a biological effect, stimulation of an electrically excitable tissue. The observation that the S-D curves extended downward to 1 ns in a linear manner suggested that classical ion channel mechanisms regulated excitation and that other processes, such as electroporation, did not occur. Although a single nanosecond pulse delivered by direct contact can elicit a biological response, such a stimulus in air is unlikely to produce an effect.

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.

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Conducted energy weapons (CEWs) (including the Advanced TASER(®) X26 model produced by TASER International, Inc.) incapacitate individuals by causing muscle contractions. In this study using anesthetized swine, the potential incapacitating effect of primarily monophasic, 19-Hz voltage imposed by the commercial CEW was compared with the effect of voltages imposed by a laboratory device that created 40-Hz square waves. Forces of muscle contraction were measured with the use of strain gauges. Stimulation with 40-Hz square waves required less pulse energy than stimulation with the commercial CEW to produce similar muscle contraction. The square-pulse stimulation, at the higher repetition rate, caused a more complete tetanus at a lower energy. Use of such a simple shape of waveform may be used to make future nonlethal weapon devices more efficient.

Electronic control devices (including the Advanced TASER(®) X26 model produced by TASER International) incapacitate individuals by causing muscle contractions. To provide information relevant to development of future potential devices, effects of monophasic square waves with different parameters were compared with those of the X26 electronic control device, using two animal models (frogs and swine). Pulse power, electrical pulse charge, pulse duration, and pulse repetition frequency affected muscle contraction. There was no difference in the charge required, between the square waveform and the X26 waveform, to cause approximately the same muscle-contraction response (in terms of the strength-duration curve). Thus, on the basis of these initial studies, the detailed shape of a waveform may not be important in terms of generating electro-muscular incapacitation. More detailed studies, however, may be required to thoroughly test all potential waveforms to be considered for future use in ECDs.