Output of Electronic Muscle Stimulators: Physical Therapy and Police Models Compared.

INTRODUCTION: Both physical therapists and police officers use electrical muscle stimulation. The typical physical therapist unit is attached with adhesive patches while the police models use needle-based electrodes to penetrate clothing. There have been very few papers describing the outputs of these physical therapy EMS (electrical muscle stimulator) units. METHODS: We purchased 6 TENS/EMS units at retail and tested them with loads of 500 Ω, 2 kΩ, and 10 kΩ. RESULTS: For the typical impedance of 500 Ω, the EMS units delivered the most current followed by the electrical weapons; TENS units delivered the least current. At higher im-pedances (> 2 kΩ) the electrical weapons delivered more current than the EMS units, which is explained by the higher voltage-compliance of their circuits. Some multi channel EMS units deliver more calculated muscle stimula tion than the multi-channel weapons. CONCLUSION: Present therapeutic electrical muscle stimula-tors can deliver more current than present law-enforcement muscle stimulators.

Safety of a High-Efficiency Electrical Fence Energizer.

INTRODUCTION: Our primary goal was to evaluate the performance of a new high-efficiency electric fence energizer unit using resistive load changes. Our secondary goal was to test for compliance with the classical energy limits and the newer charge-based limits for output. METHODS: We tested 4 units of the Nemtek Druid energizer with 2 channels each. We used a wide load-resistance range to cover the worst-case scenario of a barefoot child making a chest contact (400 Ω) up to an adult merely touching the fence (2 kΩ). RESULTS: The energy output was quite consistent between the 8 sources. Even at the lowest resistance, 400 Ω, the outputs were well below the IEC 60335-2-76 limit of 5 J/pulse. The charge delivered was also quite consistent. Even at the lowest resistance, 400 Ω, the outputs (679 ± 23 µC) were well below the proposed limits of 4 mC for short pulses. CONCLUSIONS: The high-efficiency electric fence energizers satisfied all relevant safety limits. Charge, energy, voltage, and current outputs were consistent between channels and units.

Cardiac safety profile for Random Complex Waveforms.

INTRODUCTION: A rigorous method for assessing the Ventricular Fibrillation (VF) risk of a Random Complex Waveform (RCW) has not been previously available. Real-life hazardous events motivated us to develop such method. An RCW is observable and recordable. It consists of multiple different components randomly added one to the other. Assessment for VF risk exists for non-random waveforms, particularly VF thresholds for 50/60 Hz alternating currents, but not for RCWs. METHODS: We developed a method which considers exposure to a segment of an RCW. It transforms complex segment exposure to values which can be compared with AC root-mean-square (rms) magnitude/duration curves, for determination of VF risk. Human contact could occur for any given time duration within the segment. The current of most risk is the greatest found for all possible instances of that duration. This is termed the "Probable Current" (PC) for that duration. All possible exposure durations in the waveform segment are considered, giving a set of PCs, thus allowing the plotting of a PC curve. The PC set is compared with a criterion for VF risk, termed the Justified Current (JC) curve. RESULTS: The theory is presented. Demonstrations and examples are given. Code is shown for generating the PC curve. CONCLUSION: VF risk can be found for an RCW using the rigorous algorithm presented. SIGNIFICANCE: The VF for RCWs has not been considered previously. A rigorous statement of a method for VF risk assessment allows extension from regular waveforms to RCWs.

Transthoracic ventricular fibrillation charge thresholds.

UNLABELLED: Standards, including IEC 60479-1 and -2, provide current-based ventricular fibrillation thresholds (VFT) for stimuli durations between 0.1 ms and 10 s. It has been established that the amount of electrical charge, not the current calculated by root-mean-square, is most representative of the effects of cardiac stimulation. There are no unified models that present transthoracic charge VFTs for a wide range of stimuli durations. This work proposes a new unified charge model applicable to transthoracic stimuli durations ranging over 1 µs - 300 s. VFTs were compiled from our previous animal work and from other published reports, including from the studies that provided the raw data for IEC 60479-1 and -2. Our study goal was to cover a wide range of stimuli durations, for which reliable data exists. Consistent data were found for stimuli durations covering the range of 1 µs - 300 s where VFTs were expressed as charge. The model predicted a transthoracic charge VFT of 1 mC at 1 µs duration. The charge VFT increased with stimulus duration and reached 10 C at 300 s. Presenting the first charge-based transthoracic VFT model covering stimuli durations over 1 µs - 300 s, we found 3 behavioral regions of charge VFT vs. DURATION: For short stimuli durations, 1 µs - 10 ms, VFTs followed a classic Weiss charge strength-duration curve. For long stimuli, longer than 5 s, charge VFTs can be approximated using a 38 mArms constant current model. From 10 ms to 5 s, charge VFTs tracked through a transition zone that could be approximated as a constant charge model Q≈100 mC.