Michael A. Brave

Cardiac fibrillation risks with TASER conducted electrical weapons.

The TASER® conducted electrical weapon (CEW) delivers electrical pulses that can temporarily incapacitate subjects. We analyzed the cardiac fibrillation risk with TASER CEWs. Our risk model accounted for realistic body mass index distributions, used a new model of effects of partial or oblique dart penetration and used recent epidemiological CEW statics.

Validity of the small swine model for human electrical safety risks

Small swine are the most common model now used for electrical safety studies. Because of the significant anatomical and electrophysiological differences and the effect of animal size on the ventricular fibrillation (VF) threshold, there are concerns that these differences may exaggerate the risks of electrical devices to humans. We chose, as an illustrative and relevant example, swine studies of the TASER® conducted electrical weapon (CEW) as it has numerous published VF studies. We reviewed the published electrical swine safety studies for CEWs and compared them to finite element modeling studies, electrical safety standards, and epidemiological experience from field usage. We also compared the body weights of the swine to those of law enforcement arrest-related deaths. Studies of small swine exaggerate the risks of CEWs to humans. This conclusion may be extrapolated to suggest that the use of small swine for electrical safety studies should be questioned in general.

Transthoracic cardiac stimulation thresholds for short pulses.

The most common cause of death due to electric shock is ventricular fibrillation (VF). This work reviews applicable results from the literature and provides an estimation model for the risk of VF with short-duration pulses. Methods and Results - For 1 ms pulses, the predicted current and charge thresholds required for successful transthoracic cardiac stimulation were 1.12 A and 1.12 mC, respectively. For pulses of 0.1 ms durations, the transthoracic current and charge thresholds predicted by the model are 10.9 A and 1.09 mC, respectively. Conclusion - In humans, the charge required for single-response cardiac capture using transthoracic electrodes and 0.1 ms pulses is at least 0.5 mC. The transthoracic charge required to trigger repetitive ventricular responses in humans is at least several times higher than that for single responses. Hence, in adult humans, the transthoracic charge threshold required to induce repetitive ventricular responses, tachycardia, or fibrillation, with 0.1 ms pulses is expected to be significantly greater than 1 mC.

Limitations of animal electrical cardiac safety models.

Introduction - Human electrical safety standards are based almost exclusively on animal studies and there is an unjustified assumption that ventricular fibrillation (VF) thresholds in animals are the same as those in humans. Methods and Results - We analyzed differences between animals and humans in cardiac stimulation. A broad literature survey revealed that swine are a fragile electrophysiologic research species and have a dense intramural Purkinje fiber network, which is not found in some other species, including humans. Anesthesia agents have to be chosen carefully as swine are prone to malignant hyperthermia. Cardiac stimulation thresholds depend on weight and capture rates. Thus, the animal weight has to be representative of the weight of human subjects. Studies have shown significant ECG differences between humans and other species, including swine and canine. At least one study suggested that rabbit hearts tend to develop VF in a manner more similar to that seen in humans. Conclusion - Animal studies can play a role in conservatively evaluating cardiac safety. However, while still abiding by the precautionary principle, animal study design has to take into account the significant anatomical and electrophysiological differences between humans and other mammals. Data from multiple animal models may offer broader perspectives. If attempts are made to extrapolate animal results to humans then appropriate numerical correction factors should be applied, such as some of those discussed in this article.

Eye injuries from electrical weapon probes: Incidents, prevalence, and legal implications

PURPOSE While generally reducing morbidity and mortality, electrical weapons have risks associated with their usage, including burn injuries and trauma associated with uncontrolled fall impacts. However, the prevalence of significant eye injury has not been investigated. METHODS We searched for incidents of penetrating eye injury from TASER® conducted electrical weapon (CEW) probes via open source media, litigation filings, and a survey of CEW law-enforcement master instructors. RESULTS We report 20 previously-unpublished cases of penetrating eye injury from electrical weapon probes in law-enforcement field uses. Together with the 8 previously published cases, there are a total of 28 cases out of 3.44 million field uses, giving a demonstrated CEW field-use risk of penetrating eye injury of approximately 1:123 000. Confidence limits [85 000, 178 000] by Wilson score interval. There have been 18 cases of total unilateral blindness or enucleation. We also present legal decisions on this topic. CONCLUSIONS The use of electrical weapons presents a rare but real risk of total or partial unilateral blindness from electrical weapon probes. Catastrophic eye injuries appear to be the dominant non-fatal complication of electronic control.

On positional asphyxia and death in custody.

Custody-related deaths are problematic. There clearly is a link between stress, exertion, restraint and SCD, but no consensus about causation, other than general agreement that most such deaths are multifactorial. The article by Krexi et al. in the January 26 issue of Medicine, Science and the Law goes a long way towards untangling the possible factors and confounders to be considered by investigators. They are to be congratulated. We were, however, disappointed to see the authors inappropriately elevate a case series to a causal relationship by accepting a now thoroughly defunct theory, one that was even retracted by its author while testifying at trial. Specifically, Krexi states, ‘Restraint, especially in the face down position, leads to significant reduction in lung function’. In support of this position, she cites a 15-year-old case series by O’Halloran. The results lead many to believe that position-induced reductions in lung function are accepted fact. They are not. O’Halloran’s case series was not a research study but rather a collection of partly complete case reports, useful for hypothesis generating but probative of nothing. Fifteen years have passed since publication of the O’Halloran unblinded case series, and during that time a substantial number of blinded, peer-reviewed studies have shown that the prone position has relatively little impact on oxygenation. In 2007, Michaelwitz investigated the ventilatory and metabolic demands in healthy adults who had been placed in the prone maximal restraint position (PMRP). Maximal voluntary ventilation (MVV) was measured in seated subjects (n1⁄4 30), in the PMRP (hogtied), and when prone with up to 90.1 or 102.3 kg of weight on their backs. MVV with >100 kg on their backs was 70% of the seated MVV (122 28 and 156 38L/min, respectively; p< .001). However measurable decreases were observed in a second phase of the study when subjects were made to struggle vigorously before being studied; a decline in maximal minute ventilation (MMV) of 44% was observed. The researchers concluded the decrease in MVV was of no clinical importance in these subjects, and that even in PMRP ventilatory exchanges was still adequate to supply the ventilatory needs, a judgement that would be shared by any pulmonologist. In 2012, Hall published her epidemiological study ‘Incidence and outcome of prone positioning following police use of force’. In her study, data from a single police force serving >1.1 million people were collected for three consecutive years. Officers prospectively documented the final position of the subject, among other data points, via electronic study forms embedded in standard force reporting forms. Final resting position was available for 1255/ 1269 subjects. Force was required in 1269 cases. The majority (52%) were not even left in a prone position. There was one death, and that occurred in a prisoner not in the prone position. The authors concluded ‘prone positioning was common and was not associated with death in our cohort of consecutive subjects following police use of force’. In 2014, Hall published her further study reporting 4828 consecutive force events in seven police agencies in four cities, concluding that their data support the human laboratory data that the prone position has no clinically significant effects on subject physiology. In 2013, Savaser’s group evaluated the effect of maximal prone restraint (PMPR) on a group aged 22–42 years old. Each volunteer was hogtied and tested in five different positions: supine, prone, prone maximal restraint with no weight force, prone maximal restraint with 50 lbs added to the subject’s back, and prone maximal restraint with 100 lbs added to the subject’s back for three minutes. Heart rate (HR), blood pressure (BP) and oxygenation saturation (O2 sat) were monitored for each volunteer in each position. In addition, echocardiography was performed to measure left ventricular outflow tract diameter. HR, MAP or O2 sat were statically no different in any of the positions. In 2014, Sloane extended the work even further measuring the ventilatory and cardiovascular parameters in 10 intensely exercising volunteers (85% of their measured VO2 max) who were placed in PMPR after exercising and then studied while in three different positions for 15minutes: (1) seated with hands behind the back, (2) prone with arms to the sides, and (3) PMPR position. Cardiovascular parameters (oxygenation, stroke volume, inferior vena cava diameter, cardiac output, cardiac index, oxygenation, stroke volume, IVC diameter, cardiac Medicine, Science and the Law 0(0) 1–2 ! The Author(s) 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0025802415598807 msl.sagepub.com Med Sci Law OnlineFirst, published on August 5, 2015 as doi:10.1177/0025802415598807

Eye injury from electrical weapon probes: Mechanisms and treatment

Purpose While generally reducing morbidity and mortality, TASER® electrical weapons have risks associated with their usage, including burn injuries and head and cervical trauma associated with uncontrolled falls. The primary non‐fatal complications appear to be significant eye injury but no analysis of the mechanisms or suggested treatments has been published. Methods We used a biomechanical model to predict the risk of eye injury as a function of distance from the weapon muzzle to the eye. We compared our model results to recently published epidemiological findings. We also describe the typical presentation and suggest treatment options. Results The globe rupture model predicted that a globe rupture can be expected (50% risk) when the eye is within 6 m of the muzzle and decreases rapidly beyond that. This critical distance is 9 m for lens and retinal damage which is approximately the range of the most common probe cartridges. Beyond 9 m, hyphema is expected along with a perforation by the dart portion of the probe. Our prediction of globe rupture out to 6 m (out of a typical range of 9 m) is consistent with the published risk of enucleation or unilateral blindness being 69 ± 18%, with an eye penetration. Conclusions Significant eye injury is expected from a penetration by an electrical weapon probe at close range. The risk decreases rapidly at extended distances from the muzzle. Not all penetrating globe injuries from electrical weapon probes will result in blindness.

Current distribution in tissues with conducted electrical weapons operated in drive-stun mode

Introduction: The TASER® conducted electrical weapon (CEW) is best known for delivering electrical pulses that can temporarily incapacitate subjects by overriding normal motor control. The alternative drive-stun mode is less understood and the goal of this paper is to analyze the distribution of currents in tissues when the CEW is operated in this mode. Methods and Results: Finite element modeling (FEM) was used to approximate current density in tissues with boundary electrical sources placed 40 mm apart. This separation was equivalent to the distance between drive-stun mode TASER X26™, X26P, X2 CEW electrodes located on the device itself and between those located on the expended CEW cartridge. The FEMs estimated the amount of current flowing through various body tissues located underneath the electrodes. The FEM simulated the attenuating effects of both a thin and of a normal layer of fat. The resulting current density distributions were used to compute the residual amount of current flowing through deeper layers of tissue. Numerical modeling estimated that the skin, fat and skeletal muscle layers passed at least 86% or 91% of total CEW current, assuming a thin or normal fat layer thickness, respectively. The current density and electric field strength only exceeded thresholds which have increased probability for ventricular fibrillation (VFTJ), or for cardiac capture (CCTE), in the skin and the subdermal fat layers. Conclusion: The fat layer provided significant attenuation of drive-stun CEW currents. Beyond the skeletal muscle layer, only fractional amounts of the total CEW current were estimated to flow. The regions presenting risk for VF induction or for cardiac capture were well away from the typical heart depth.