Electrical Characteristics of an Electronic Control Device Under a Physiologic Load: A Brief Report DONALD M. DAWES, M.D.,* JEFFREY D. HO, M.D.,† MARK W. KROLL, PH.D.,‡ and JAMES R. MINER, M.D.§ From the *Lompoc Valley Medical Center, Lompoc, California; †Hennepin County Medical Center, Minneapolis, Minnesota; ‡University of Minnesota, Minneapolis, Minnesota; and §Hennepin County Medical Center, Minneapolis, Minnesota
Background: Law enforcement officers use electronic control devices (ECDs), such as the TASER X26 (TASER International, Inc., Scottsdale, AZ, USA), to control resisting subjects. Some of the debate on the safety of the devices has centered on the electrical characteristics of the devices. The electrical characteristics published by TASER International have historically based on discharges into a 400 resistor. There are no studies that the authors are aware of that report the electrical characteristics under a physiologic load. In this study, we make an initial attempt to determine the electrical characteristics of the TASER X26 during a 5-second exposure in human volunteers. Methods: Subjects received an exposure to the dry, bare chest (top probe), and abdomen (bottom probe) with a standard TASER X26 in the probe deployment mode for 5 seconds. There were 10–11 pulse captures during the 5 seconds. Resistance was calculated using the sum of the absolute values of the instantaneous voltage measurements divided by the sum of the absolute values of the instantaneous current measurements (Ohm’s Law). Results: For the eight subjects, the mean spread between top and bottom probes was 12.1 inches (30.7 cm). The mean resistance was 602.3 , with a range of 470.5–691.4 . The resistance decreased slightly over the 5-second discharge with a mean decrease of 8.0%. The mean rectified charge per pulse was 123.0 μC. The mean main phase charge per pulse was 110.5 μC. The mean pulse width was 126.9 μs. The mean voltage per pulse was 580.1 V. The mean current per pulse was 0.97 A. The average peak main phase voltage was 1899.2 V and the average peak main phase current was 3.10 A. Conclusions: The mean tissue resistance was 602.3 in this study. There was a decrease in resistance of 8% over the 5-second exposure. This physiologic load is different than the 400 laboratory load used historically by the manufacturer. We recommend future characterization of these devices use a physiologic load for reporting electrical characteristics. We also recommend that all the electrical characteristics be reported. (PACE 2009; 1–7) resistance, charge, TASER X26 , electronic control device Introduction Law enforcement officers are increasingly using electronic control devices (ECDs), such as the TASER X26 (TASER International Inc., Scottsdale, AZ, USA), to control resisting and combative subjects. The devices discharge electrical current into
TASER International provided funding and equipment support for this study. Author Disclosure: Drs. Ho and Dawes are independent consultants to TASER International and own shares of stock. Dr. Kroll is a consultant, a member of the Board of Directors of TASER International, and the chairman of the Scientific and Medical Advisory Board. Address for reprints: Jeffrey Ho, M.D., Department of Emergency Medicine, Hennepin County Medical Center, 701 Park Avenue South, Minneapolis, MN 55415. Fax: 612-904-4241; e-mail:
[email protected] Received December 19, 2008; revised April 2, 2009; accepted September 7, 2009. doi: 10.1111/j.1540-8159.2009.02612.x
the subject leading to depolarization of afferent sensory neurons, causing pain, and efferent motor neurons, causing regional, involuntary, subtetanic muscle contraction and therefore incapacitation. There is a small component of direct muscle capture in the immediate vicinity where the current is applied. There is also likely some activation of reflex arcs that cause involuntary contraction more distant from the applied current.1 There has been controversy in the lay press and medical literature about the use of these devices and temporally associated arrest-related deaths. Amnesty International claims that these devices have been associated with more than 300 deaths.2 Critics have cited animal studies as evidence that these devices can electrically capture the myocardium and induce ventricular arrhythmias.3,4 Prospective human studies to date, however, have not demonstrated evidence of myocardial capture, and there are no reported cases of ventricular fibrillation occurring after an exposure in a prospective human study.5,6
C 2009 Wiley Periodicals, Inc. C 2009, The Authors. Journal compilation
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The discrepancy between the animal findings and human findings may be weight-related, speciesrelated (differences in susceptibility, chest shape, and charge distribution; cardiac anatomy), related to experimental conditions (anesthesia and ventilation vs awake humans), or be related to specific positioning of the probes or the use of taped wires in some human studies. This discrepancy certainly merits additional investigation. Some of the debate on the safety of ECDs has centered on the electrical characteristics of the devices.7,8 The electrical characteristics published by TASER International are based on discharges into a 400 resistor. There are no studies that the authors are aware of which report the electrical characteristics under a physiologic load. Furthermore, decreasing resistance, and therefore increased current, has been described with repeated shocks from an external defibrillator.9 It is not known if the same could occur with an electronic control device which applies multiple, sequential pulses over a short period of time. In this study, we make an initial attempt to determine the electrical characteristics of the TASER X26 during a 5-second exposure in human volunteers.
to the training exposure itself. Their exposure was no different from the other class participants except that the device was initially fired without delivering the charge (as described below) to allow the experimental set-up. The subjects provided informed consent and completed a medical screening questionnaire that was reviewed by a study physician. The questionnaire was used to obtain demographic data such as height, weight, past medical history, and current medication use. There were no specific exclusion criteria, but all study subjects had to be on unrestricted duty status with their employers. A commercial skin resistance analyzer (Omron Fat Loss Monitor HBF-306, Omron Healthcare, Inc., Bannockburn, IL, USA) was used to determine body fat percentage. Body mass index (BMI) was calculated based on stated heights and weights. Subjects received a TASER X26, donated by TASER International, as compensation for study participation. Subjects were provided face, neck, and groin protection. A training instructor from TASER International discharged a modified TASER X26 into the dry, bare chest (top probe) and abdomen (bottom probe) of the subjects at a distance of about 7 feet (2 m) in the probe deployment mode. The spread between the probes was measured after the initial discharge. The device was modified to only deliver a single pulse that discharged the primer in the cartridge but did not deliver a shock to the subject. The subject was then laid supine on a training mat. The cartridge was disconnected from the original device and connected to a factory standard (unmodified) TASER X26. The current and voltage probes were then connected. The device was discharged for 5 seconds (one trigger pull). After the 5-second discharge, the probes were removed and the wounds were dressed with a topical antibiotic ointment and an adhesive bandage. Subjects
Methods This was a prospective, observational study of human subjects. The Human Subjects Research Committee at Hennepin County Medical Center (Minneapolis, MN) approved the study. The subjects were a convenience sample of law enforcement officers already receiving a training exposure to a TASER X26 as part of a class held at TASER International in Scottsdale, AZ. Subjects were recruited after they had agreed to receive the exposure as part of the class, but prior
Table I. Demographics
2 3 4 5 6 7 8 10
Age
Sex
25 29 47 23 32 41 48 31
M M F M M M M M
Past Medical History Neg Neg Asthma Neg Neck/back injuries Neg Neg Seasonal allergies
Meds
BMI
Body Fat (%)
Spread (inches)
Neg Neg Combivent Neg Neg Neg Neg Flonase
29.9 25.9 24.2 29.0 29.0 35.2 27.5 26.6
21.8 11.9 29.5 ND 20.9 32.5 28 23.2
16 10 10 10.5 12.5 10.5 13.5 14
ND = not determined.
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Pulse width (μsec) Net charge (μC) Rectified charge (μC) Pulse average voltage (V) Pulse average current (A) Resistance () Resistance change (%) Peak main phase voltage (V) Peak main phase current (A) Main phase charge (μC) Peak arc phase voltage (V) Peak arc phase current (A)
Pulse width (μs) Net charge (μC) Rectified charge (μC) Pulse average voltage (V) Pulse average current (A) Resistance () Resistance change (%) Peak main phase voltage (V) Peak main phase current (A) Main phase charge (μC) Peak arc phase voltage (V) Peak arc phase current (A)
2060.00 3.13 109.42 −2120.00 −3.35
Last
−7.5 1960.00 3.14 117.26 −2020.00 −3.38
133.60 108.50 130.19 572.96 0.972 589.7
Last
−2.7 1460.00 3.28 121.51 −1540.00 −3.24
128.40 113.73 133.32 485.09 1.035 468.6
Subject 6
121.20 100.94 121.70 638.36 1.001 637.8
First
1500.00 3.33 120.53 −1560.00 −3.23
128.80 112.66 131.20 489.10 1.016 481.6
First
Subject 2
−0.7 1820.00 2.71 99.46 −1900.00 −2.93
132.40 91.71 112.94 555.90 0.850 653.7
Last
2160.00 3.12 102.28 −2220.00 −3.28
116.80 94.04 113.93 660.00 0.972 678.9
First
Last
−2.4 2260.00 3.25 109.06 −2280.00 −3.47
120.80 100.28 121.47 664.36 1.002 662.9
Subject 7
Individual Results
1740.00 2.67 95.43 −1780.00 −2.53
130.40 88.75 106.98 538.29 0.818 658.2
First
Subject 3
Individual Resistance Results
Table II.
1820.00 3.17 111.99 −1860.00 −3.27
Last
−9.3 1680.00 3.20 111.14 −1720.00 −3.32
123.20 102.90 122.96 524.47 0.995 527.2
Last
−21.4 2060.00 3.09 107.35 −2120.00 −3.35
124.00 98.31 120.05 609.10 0.962 633.2
Subject 8
127.60 103.42 123.98 562.81 0.969 581.1
First
2540.00 3.09 94.31 −2560.00 −3.19
110.00 85.98 105.97 775.85 0.963 805.4
First
Subject 4
1879.91 2.67 92.86 −1960.09 −3.17
116.80 85.05 105.72 609.14 0.902 675.3
First
2179.92 3.28 113.43 −2260.08 −3.52
−2.1
130.80 104.63 125.98 634.92 0.960 661.2
Last
1640.00 3.34 122.00 −1820.00 −3.50
−17.6
Last 128.00 113.19 134.47 545.09 1.044 522.1
Subject 10
1900.00 3.08 102.50 −1940.00 −3.24
117.60 94.19 113.92 612.00 0.965 633.9
First
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131.88 114.66 135.00 673.85 1.04386 691.4 −21.4 2250.00 3.33 123.11 −1564.00 −2.87 125.24 126.88 119.76 98.23 101.97 89.57 120.43 123.03 110.18 632.91 580.05 491.08 0.95843 0.96734 0.83322 660.5 602.3 470.5 −2.1 −8.0 −0.7 2111.92 1899.24 1498.00 3.09 3.10 2.64 107.24 110.51 97.22 −2168.08 −1964.81 −2298.00 −3.58 −3.35 −3.58 Pulse width (μs) 128.92 131.85 119.76 126.72 131.88 120.16 130.48 Net charge (μC) 114.66 89.57 96.43 104.75 105.57 98.90 107.64 Rectified charge (μC) 135.00 110.18 117.19 125.69 127.14 119.99 128.61 Pulse average voltage (V) 491.08 550.46 673.85 536.31 578.84 645.91 531.05 Pulse average current (A) 1.04386 0.83322 0.97521 0.98809 0.96178 0.99544 0.98267 Resistance () 470.5 660.9 691.4 543.1 601.7 649.5 540.6 Resistance change (%) −2.7 −0.7 −21.4 −17.6 −7.5 −2.4 −9.3 Peak main phase voltage (V) 1498.00 1800.00 2250.00 1652.00 1974.00 2182.00 1726.00 Peak main phase current (A) 3.33 2.64 3.13 3.17 3.08 3.20 3.18 Main phase charge (μC) 123.11 97.22 105.01 113.36 114.25 107.64 116.24 Peak arc phase voltage (V) −1564.00 −1856.36 −2298.00 −1784.00 −2024.00 −2242.00 −1782.00 Peak arc phase current (A) −3.35 −2.87 −3.33 −3.36 −3.41 −3.57 −3.36
Subject 2 Subject 3 Subject 4 Subject 5 Subject 6 Subject 7 Subject 8 Subject 10 Average Average Average Average Average Average Average Average Average
Results Ten subjects were enrolled. No subjects were excluded based on their medical screening questionnaire. However, one subject was excluded from the analysis because the TASER device malfunctioned and delivered only a 1-second discharge. A second subject was excluded because the recording device malfunctioned and did not collect data appropriately. Eight subjects completed the testing. Their demographic data are presented in Table I. There were seven males and one female. The median age was 31.5, with a range of 23–47. The median BMI was 28.3 kg/m2 , with a range of 24.2–35.2. The median body fat was
Averages
Table III.
All Subjects
were reevaluated by a study physician after the discharge. The load current was measured using a Tektronix TCP 202 (Tektronix, Beaverton, OR, USA) current probe clamped around the wire extending from the cartridge to the top dart. The load voltage was measured using a Tektronix P5100 100X voltage probe that was connected to the top dart and grounded to the bottom dart. The current and voltage waveforms were captured using a Tektronix TDS-3034B oscilloscope. All data captured by the oscilloscope were exported to ASCII files on the computer using LabVIEW (National Instruments, Austin, TX, USA) Signal Express. The LabVIEW program brought in 10–11 evenly spaced pulse captures of 500 samples per pulse capture during the 5-second exposure. These files were then imported into Microsoft Excel (Microsoft Corp., Redmond, WA, USA). Pulse width was measured from the initiation of the pulse until it reached less than 50 V on the decay. Rectified charge was determined by the integration of the absolute value of the current, whereas net charge was determined by the integration of the signed value of the current. Resistance was calculated using the sum of the absolute values of the instantaneous voltage measurements divided by the sum of the absolute values of the instantaneous current measurements (Ohm’s Law). This gave the resistance for the entire pulse and is referred to throughout the paper as “resistance.” The instantaneous resistance was also calculated using instantaneous values of voltage and current, but the results using this method were not significantly different and are not reported here. As seen in Figure 2, the waveform of the TASER X26 is a biphasic, noncharge balanced waveform. The initial (very short duration) negative lobe of the pulse is referred to as the arcing phase, and the subsequent (much longer duration) positive lobe is referred to as the stimulation or main phase. Main phase charge is as above using just the data during the main phase.
Minimum Maximum
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Figure 1. Individual Values for resistance.
25.1%, with a range of 11.9–32.5. The probes pierced the bare skin in all the subjects. There was no syncope during the exposures. There were no significant adverse outcomes observed or re-
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erage peak arcing phase voltage was −1964.8 V and the average peak arcing phase current was −3.35 A. Discussion The TASER X26 is the most widely used ECD by law enforcement in the United States. A single trigger pull initiates a 5-second discharge of discrete electrical pulses at a rate of 19 pulses per second leading to depolarization of skeletal muscles at a subtetanic rate causing the loss of voluntary muscle control in the stimulated muscles and therefore incapacitation. The device can be deployed in two modes: the drive stun mode and the probe mode. In the drive stun mode, two metal contact plates at the end of the device, separated by 40 mm, deliver the current to the skin. In this mode, because the distance between the entrance and exit current is so small, there are a small number of motor neurons to capture and there is less incapacitation. In addition, because the current is applied at the skin, the electric fields may not penetrate deeply enough to capture deeper neurons. The effect of the device in this mode is generally pain compliance (using the pain of the shock to induce voluntary compliance). In the probe deployment mode, two metal probes with an unbent #8 fishhook on each are fired from the device with an 8◦ separation. The farther the probes travel in the air, the wider the spread. In this mode, because the distance between the entrance and exit current is much greater, there are more captured motor neurons and, therefore, incapacitation. Additionally, in this mode, depending on the length of the probe (9–13 mm in the commonly used cartridges), the current is delivered deeper into the tissues.1 In our study, we chose to study the electrical characteristics in the probe deployment mode both because this is the mode more likely to deliver current to deeper structures, and because it is the most commonly used mode in field use.10 In our study, the mean resistance was 602.3 . In the Deakin et al. study of defibrillation, there
Figure 2. Current for the last sampled pulse in subject 4.
each subject in Table II. The averages for each subject are presented in Table III. The individual values for resistance are presented graphically in Figure 1. Figure 2 shows the last sampled pulse current waveform for one of the subjects. Figure 3 shows a typical skin wound from the TASER X26 exposure. The mean spread between the top and bottom probes was 12.1 inches (30.7 cm). The mean resistance was 602.3 , with a range of 470.5– 691.4 . The resistance decreased slightly over the 5-second discharge with a mean decrease of 8.0% (P = 0.05 by paired t-test). There was no correlation of resistance and spread by linear regression (P = 0.08). The mean rectified charge per pulse was 123.0 μC (range 110.2–135.0). Both mean net charge (average 102.0 μC) and main phase charge (average 110.5 μC) are included in the results. The mean pulse width was 126.9 μs (range 119.8– 131.9). The mean voltage per pulse was 580.1 V (range 491.1–673.9). The mean current per pulse was 0.97 A (range 0.83–1.04). The average peak main phase voltage was 1899.2 V and the average peak main phase current was 3.10 A. The arcing phase was negative as shown in Figure 2. The av-
Figure 3. Wound from a 5-second probe discharge.
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was a 2.7% decrease in resistance with each successive shock. In our study, the mean decrease in resistance over the 5-second discharge was 8%, but this represents 95 pulses or shocks. The decrease in resistance following electrical shock has been attributed to increased tissue blood flow and edema from electrical injury and possibly a contribution from tissue ionization (the latter factor at higher energy levels). Shocks delivered in quick succession have been found to decrease the resistance less than shocks delivered over a longer time interval.9 Our smaller decrease per shock was likely related to the quick succession of the shocks, decreased injury due to decreased energy of the TASER X26 compared with defibrillator energies, and a decreased contribution from ionization due to the lower energy (0.1 J vs 360 J) used in defibrillation. Bozeman et al. found that 54.9% of uses were for 5 seconds or less (and 81.5% were for 10 seconds or less).10 So, these electrical characteristics are probably valid for the majority of field uses. While it has been proposed that the critical parameter for the stimulation of excitable tissues with short duration pulses is charge, given the novelty of this type of stimulation, we elected to report all the electrical characteristics.1,11–13 A possible limitation of the study includes the ability to only capture 10–11 pulses in the 5-second discharge, which was a data processing limitation. This limitation is unlikely to affect the
results significantly. In addition, the number of subjects in this study was small. With more subjects, differences related to subject characteristics could have become more apparent. We found no correlation of body fat or BMI with resistance values in our small number of subjects. The mean BMI of our subjects was reasonably close to that of subjects with arrest-related deaths. In a study by Stratton et al., the mean BMI was 30 kg/m2 and14 in a study by Strote and Hutson, the mean BMI was 30.8.15 Lastly, the shocks were delivered for only 5 seconds. It is not clear how the resistance would change if the shocks were delivered over a longer time period. Conclusions The mean tissue resistance was 602.3 in this study. There was a decrease in resistance of 8% over the 5-second exposure. This physiologic load is different than the 400 laboratory load used historically by the manufacturer. We recommend future characterization of these devices use a physiologic load for reporting electrical characteristics. We also recommend that all the electrical characteristics be reported. Acknowledgments: The authors would like to acknowledge Andrew Hinz, Matt Carver, Erik Lundin, and Bryan Chiles for their technical and logistic contributions on this project.
References 1. Reilly JP, Diamant AM, Comeaux J. Dosimetry considerations for electrical stun devices. Phys Med Biol 2009; 54:1319–1335. 2. Amnesty International Canada. Canada: Inappropriate and excessive use of TASERS. AMR 2007; 20:002. 3. Nanthakumar K, Billingsley IM, Masse S, Dorian P, Cameron D, Chauhan VS, Downar E, et al. Cardiac electrophysiological consequences of neuromuscular incapacitating device discharges. J Am Coll Cardiol 2006; 48:798–804. 4. Walter RJ, Dennis AJ, Valentino DJ, Margeta B, Nagy KK, Bokhari F, Wiley DE, et al. TASER X26 discharges in swine produce potentially fatal ventricular arrhythmias. Acad Emerg Med 2008; 15:66–73. 5. Ho JD, Dawes DM, Reardon RF, Lapine AL, Dolan BJ, Lundin EJ, Miner JR. Echocardiographic evaluation of a TASER X26 application in the ideal human cardiac axis. Acad Emerg Med 2008; 15:838–844. 6. H Ho JD, Reardon RF, Dawes DM, Johnson MA, Miner JR. Ultrasound measurement of cardiac activity during conducted electrical weapon application in exercising adults. Ann Emerg Med 2007; 50:S108. 7. Valentino DJ, Walter RJ, Dennis AJ, Margeta B, Starr F, Nagy K, Bokhari F, et al. Taser X26 discharges in swine: Ventricular rhythm capture is dependent on discharge vector. J Trauma 2008; 65:1478– 1487.
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8. The Canadian Press. RCMP to test TASERs after study raises questions. The Spec.com; Dec 4, 2008. Downloaded from http://www. thespec.com/News/article/477121 on 2/22/09. 9. Deakin CD, Ambler JJ, Shaw S. Changes in transthoracic impedance during sequential biphasic defibrillation. Resuscitation 2008; 78:141–145. 10. Bozeman W, Hauda W, Heck J, Graham D, Martin B, Winslow J. Safety and injury profile of conducted electrical weapons used by law enforcement officers against criminal suspects. Ann Emerg Med 2009; in press., DOI: 10.1016/j.annemergmed.2008.11.021 11. Weiss G. Sur la possibilite’ de rendre comparable entre eux les appareils survant a l’excitation electrique. Arch Ital de Biol 1901; 35:413–446. 12. Roy OZ, Mortimer AJ, Trollope BJ, Villeneuve EJ. Effects of shortduration transients on cardiac rhythm. Med Biol Eng Comput 1984; 22:225–228. 13. Georges IW. Weiss’ fundamental law of electrostimulation is 100 years old. Pacing Clin Electrophysiol 2002; 25:245–248. 14. Stratton SJ, Rogers C, Brickett K, Gruzinski G. Factors associated with sudden death of individuals requiring restraint for excited delirium. Am J Emerg Med 2001; 19:187–191. 15. Strote J, Hutson HR. Taser use in restraint-related deaths. Prehosp Emerg Care 2006; 10:447–450.
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