Robert A. Stratbucker

Cardiac Safety of Neuromuscular Incapacitating Defensive Devices

Neuromuscular incapacitation (NMI) devices discharge a pulsed dose of electrical energy to cause muscle contraction and pain. Field data suggest electrical NMI devices present an extremely low risk of injury. One risk of delivering electricity to a human is the induction of ventricular fibrillation (VF). We hypothesized that inducing VF would require a significantly greater NMI discharge than a discharge output by fielded devices. The cardiac safety of NMI discharges was studied in nine pigs weighing 60 ± 28 kg. The minimum fibrillating level was defined as the lowest discharge that induced VF at least once, the maximum safe level was defined as the highest discharge which could be applied five times without VF induction, and the VF threshold was defined as their average. A safety index was defined as the ratio of the VF threshold to the standard discharge level output by fielded NMI devices. A VF induction protocol was applied to each pig to estimate the VF threshold and safety index. The safety index for stored charge ranged from 15X to 42X as weight increased from 30 to 117 kg (P < 0.001). Discharge levels above standard discharge and weight were independently significant for predicting VF inducibility. The safety index for an NMI discharge was significantly and positively associated with weight. Discharge levels for standard electrical NMI devices have an extremely low probability of inducing VF.

Optimization of cardiac defibrillation by three-dimensional finite element modeling of the human thorax

The goal of this study was to determine the optimal electrode placement and size to minimize myocardial damage during defibrillation while rendering refractory a critical mass of cardiac tissue of 100%. For this purpose, the authors developed a 3D finite element model with 55,388 nodes, 50,913 hexahedral elements, and simulated 16 different organs and tissues, as well as the properties of the electrolyte. The model used a nonuniform mesh with an average spatial resolution of 0.8 cm in all three dimensions, To validate this model, the authors measured the voltage across 3-cm/sup 2/ Ag-AgCl electrodes when currents of 5 mA at 50 kHz were injected into a human subjects thorax through the same electrodes. For the same electrode placements and sizes and the same injected current, the finite element analysis produced results in good agreement with the experimental data. For the optimization of defibrillation, the authors tested 12 different electrode placements and seven different electrode sizes. The finite element analyses showed that the anterior-posterior electrode placement and an electrode size of about 90 cm/sup 2/ offered the least chance of potential myocardial damage and required a shock energy of less than 350 J for 5-ms defibrillation pulses to achieve 100% critical mass. For comparison. The average cross-sectional area of the heart is /spl ap/48 cm/sup 2/, about half of the optimal area. A second best electrode placement was with the defibrillation electrodes on the midaxillary lines under the armpits. Although this placement had higher chances of producing cardiac damage, it required less shock energy to achieve 100% critical mass.<<ETX>>

A nonlinear electrical-thermal model of the skin

Presents a model for the skin which accounts for both the nonlinearities and the asymmetries in its voltage-current characteristic. This model consists of an electrical submodel and a heat transfer submodel. The electrical submodel uses nonlinear devices in which some parameters depend on skin temperature. The heat transfer submodel models the heat exchange between the skin, the surrounding tissues, and the ambient medium and calculates the temperature of the skin to update the necessary parameters of the electrical submodel. The model is based on experiments designed to determine: (1) the dry skin voltage-current characteristic; (2) the changes in the skin breakdown voltage with location; (3) the moist skin voltage-current characteristic; (4) the changes in the voltage-current characteristic of the skin with duration after the onset of stimulation; and (5) the effect of skin temperature on its voltage-current characteristic. During these experiments the authors used 84-mm/sup 2/ square Ag-AgCl electrodes to apply sinusoidal voltage of 0.2 and 20 Hz. The simulations were performed using the Advanced Continuous Simulation Language (ACSL), capable of solving differential and integral equations with variable coefficients. The model predicted the skin behavior satisfactorily for a large range of amplitudes and frequencies. The authors found that the breakdown occurred when the energy delivered to the skin exceeded a threshold. Above this threshold the voltage-current characteristic of the skin became nonlinear and asymmetric and, in a real situation, the subject would experience an uncomfortable sensation which could rapidly develop into pain.<<ETX>>

Modeling current density distributions during transcutaneous cardiac pacing

The authors developed a two-dimensional finite element model of a cross-section of the human thorax to study the current density distribution during transcutaneous cardiac pacing. The model comprises 964 nodes and 1,842 elements and accounted for the electrical properties of eight different tissues or organs and also simulated the anisotropies of the intercostal muscles. The finite element software employed was a version for electrokinetics problems of Finite Element for Heat Transfer (FEHT) and the authors assessed the effects upon the efficacy of transcutaneous cardiac pacing of several electrode placements and sizes. To minimize pain in the chest wall and still be able to capture the heart, the authors minimized the ratio, R, between the current density in the thoracic wall (which causes pain) and the current density in the heart wall (which captures the heart). The best placement of the negative electrode was over the cardiac apex. The best placement of the positive electrode was under the right scapula, although other placements mere nearly as good. The efficiency of pacing increased as electrode size increased up to 70 cm and showed little improvement for larger areas. Between different configurations of the precordial electrodes V1, V2, /spl middot//spl middot//spl middot/, V6 the most efficient configuration to pace with was V1 and V2 positive and V5 and V6 negative. A more efficient configuration uses an auxiliary electrode located at the right subscapular region.<<ETX>>

Theoretical possibility of ventricular fibrillation during use of TASER neuromuscular incapacitation devices

Introduction: TASER devices deliver electrical pulses that temporarily incapacitate suspects. This study analyzes the theoretical possibility of ventricular fibrillation (VF) induction by TASER currents.

Medical safety of TASER conducted energy weapon in a hybrid 3-point deployment mode

Introduction: TASER conducted energy weapons (CEW) deliver electrical pulses that can temporarily incapacitate subjects. The goal of this paper is to analyze the distribution of TASER CEW currents in the heart and surrounding organs and to understand theoretical chances of triggering cardiac arrhythmias, of capturing the vagus and phrenic nerves and producing electroporation of skeletal muscle structures. The CEW operates in either probe mode or drive-stun (direct contact) mode. There is also a hybrid mode in which current is passed from a single probe to either or both of 2 drive-stun electrodes on the weapon, presumed to be in direct contact with the skin. Methods and Results: The models analyzed herein describe strength-duration thresholds for myocyte excitation and ventricular fibrillation (VF) induction. Finite element modeling (FEM) was used to approximate current density in the heart for worst-case TASER electrode placement. The FEMs theoretically estimated that maximum TASER CEW current densities in the heart and in neighboring organs are at safe levels. A 3-point deployment mode was compared to probe-mode deployment. The margins of safety for the 3-point deployment were estimated to be as high as or higher than for the probe-mode deployment. Conclusion: Numerical modeling estimated that TASER CEWs were expected to be safe when deployed in 3-point mode. In drive-stun, probe-mode or 3-point deployments, the CEWs had high theoretically approximated safety margins for cardiac capture, VF, phrenic or vagus nerve capture and skeletal muscle damage by electroporation.

A Multipurpose, Self-Adhesive Patch Electrode Capable of External Pacing, Cardioversion Defibrillation, and 12-Lead Electrocardiogram

Since the inception of Advanced CardiaG Life Support in Lincoln, Nebraska, over 2 decades ago.^ great strides have been made in the successful diagnosis and treatment of life-threatening cardiac conditions outside the hospital environment. Several recent technical advances have made it possible to identify, monitor, and treat patients with potential cardiac catastrophes. One of these technical advances, the cellular telephone, permits transmission of ECG rhythm strips and diagnostic quality 12-lead ECGs to hospital-based monitoring physicians from the scene of the emergency. This communication breakthrough has led several authors to advocate not only the diagnosis of acute myocardial infarctions in the field but also the initiation of thrombolytic therapy for these patients,^-^