Strength-Duration Curve for an Electrically Excitable Tissue Extended Down to Near 1 Nanosecond

Abstract

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.

Advances in Therapeutic Electroporation to Mitigate Muscle Contractions

“…For unipolar pulses of this nature, cell death can be induced with a significant drop in muscle contractions as compared to unipolar microsecond-long pulses [23]. Experimentally derived strength-duration curves indicate that a 100 ns pulse requires a voltage two orders of magnitude greater than a 10 µs pulse to excite muscle [37].…”

Frequency-dependent interaction of ultrashort E-fields with nociceptor membranes and proteins

“…Accordingly, nociceptor activation would play a critical role in immobilization. Other evidence suggests that TASER waveforms are capable of directly activating muscle in areflexive conditions [Rogers et al, 2004;Jauchem et al, 2006Jauchem et al, , 2008. Whether or not nociceptor activation has direct links to TASER immobilization, it is clearly an important component of TASER deterrence.…”

“…Ultrashort pulses have been shown to exhibit exceptional safety factors, by some measures, and have the capacity to activate nociceptors and cause muscle twitching [Rogers et al, 2004;Nene et al, 2006]. It is likely that there are durations at which E-fields will no longer effectively couple to excitable tissue.…”

Services to Operate and Maintain a Microwave Research Laboratory

“…Until the availability of pulses with UWB characteristics, die shortest durations of applied pulses were typically 10 jxs-l ms, e.g., [9], [36]. Recent research shows that voltage pulses of ~1 ns duration, or at least 10 000 times shorter than those previously studied, can stimulate excitable tissue when applied with sufficient amplitude directiy to the tissue preparation [37]. However, the lack of change in ECG intervals here indicated that energy coupled to tissue from the propagating UWB pulses was not capable of stimulating nerve cells or heart cells in a way that would cause a change in measured endpoints.…”

“…(Abstracts 8,37,38,46;Publication 17) o Motor functions, locomotor activity, rearing activity, movement initiation and step test, tyrosine hydroxylase immunoreactivity in the striatum, microglial activation in the striatum, and lethality were used as endpoints. o Intravenous and subcutaneous dose response characteristics (0.0, 2.0, 2.5, 3.5 mg/kg/day) were assessed, o Lethality was dose and route dependent.…”