Download Comparative Analysis of Three Projectile Stun Guns

Comparative Analysis of Three Projectile Stun Guns
By:
Wayne McDaniel, Ph.D.
Purpose:
To compare the output of three commercial projectile stun guns, the Taser M26, Taser
X26, and Stinger S200. These devices were compared by applying the stun guns to a resistive
load, and also by applying the stun guns to a live, human-sized animal.
Background:
Electronic stun guns were originally developed as hand-held weapons with two
electrodes on the end, which would be held against the subject to directly apply the electric
shock. Projectile stun guns (PSGs) have extended the range of application of these stun guns, by
shooting two barbed electrodes to the subject, which trail wires back to the device to conduct the
electricity from the device to the subject. The maximum range of PSGs is now about 20 to 22
feet. Presently available PSGs include the Taser M26 and the Taser X26 (Taser International,
Scottsdale, AZ), and the Stinger S200 (Stinger Systems, Tampa, FL).
Field use of PSGs typically involves shooting the barbed electrodes towards the torso of
the subject to be subdued. These barbed electrodes either stick into the skin of the subject, or
more likely stick into the clothing of the subject and the electricity arcs through the clothing to
the skin. Frequently one or both of the electrodes strike the thorax of the subject. Any
application of electricity to the thorax raises the concern that the electrical stimulation will
induce ventricular fibrillation (VF) in the subject, which is a potentially lethal cardiac
arrhythmia. These devices have been shown to be capable of incapacitating humans, but they do
so with very different electrical waveforms and shock amplitude (See figs 1-3). The goal of this
study was to characterize the output of these three PSGs in both a resistive model and an animal
model.
Figs. 1, 2, 3. Output waveforms of the Taser M26, Taser X26, and Stinger S200. In each
projectile stun gun, the waveform shown is repeated 15-19 times per second. [Note different
time and amplitude scales in these figures]
Literature Review:
The first modern PSG was the Taser M26, and this device was therefore the first to be
studied in an animal model. This device was tested in a canine model and was found to not
induce VF in 192 applications, when the darts were applied to various locations on the chest and
abdomen [McDaniel et al, 2000]. The Taser X26 was tested in a porcine model with animals
having a range of body weights. In this study, the electrical output could be increased up to 50
times the output charge of the normal X26, and the electrical output was increased in each
animal until VF was observed. A safety factor was then estimated for each animal, which was
found to be weight dependent, ranging from 15X to 42X the normal X26 output, as the animal
weight ranged from 30 to 117 kg. [McDaniel et al, 2004]. Our conclusion from these two studies
was that the initiation of VF by the commercial devices would be a rare event.
The Taser devices have now been applied to humans over 600,000 times, without an
observed episode of inducing VF [Upson, 2007]. However, there have also now been more than
250 deaths of subjects, after having received one or more shocks from either the Taser M26 or
the Taser X26 [Walter et al, 2008]. The number of these deaths has caused some to question the
safety of these devices, and has motivated many investigators to study these devices more
thoroughly.
There have been several published studies of the application of Taser devices in healthy,
human volunteers. These studies have looked at various cardiovascular and physiologic
parameters [Ho et al, 2006] and have not documented any changes that would provide a causal
link between exposure to the Taser device and death [Ho et al, 2007].
However, there have been other studies that have found that the Taser devices
consistently pace the heart of experimental animals, and that they can induce VF in experimental
animals under certain conditions. One study in pigs found that when the Taser X26 was applied
to the chest for either 5 or 15 seconds, it capture paced the heart in 98% of the shocks. When the
Taser M26 was applied to the chest, it captured the heart in 54% of the shocks. The mean heart
rate during stimulation and capture was 324 beats/min [Nanthakumar, 2006].
Another study of the Taser X26 in pigs gave two 40 second exposures. Two deaths were
observed in this group of animals from acute onset VF. No cardiac capture data was available,
as they were not able to observe the cardiac rhythm during the X26 applications, due to device
limitations [Dennis, 2007]. Another study of the Taser X26 also gave a protocol of two 40
second exposures, and followed the animals for 48 hours after the exposure. They found cardiac
capture pacing in all experimental animals, with a rate of 301 beats/min. The cardiac rhythm of
one of these experimental animals degenerated into VF [Walter et al, 2008].
Another study of the Taser X26 looked at the dart to heart distance that could induce VF.
They found an average distance of 17 mm for the first induction of VF, and an average distance
of 13.7 mm for successive VF events. They observed a higher frequency of VF when the dart to
heart distance was smaller. The authors interpreted their data as indicating that the current
density at the heart needed to be a certain level to induce VF. By increasing the dart to heart
distance, the current density at the heart decreased, and VF was less likely. They further report
skin to heart distances in humans of 10 to 57 mm, as measured by echocardiography [Wu et al,
2006].
These studies just described, which demonstrated cardiac pacing and the induction of VF
with thoracic application of Tasers, were performed in animal models. Recently, a case study
detailed a human subject with a pacemaker who was subjected to a Taser discharge. The internal
memory of the pacemaker recorded two high ventricular rate episodes, which corresponded to
the Taser application. The authors interpreted this as demonstrating myocardial capture pacing
in humans [Cao et al, 2007]. Finally, there has been one published case report of VF being
documented shortly after Taser application in a human subject. The authors interpreted the VF
as having been induced by the Taser [Kim et al, 2005].
Another consideration of the use of these devices relates to physiological changes
brought about by extended duration near-maximal muscle contractions. One study applied the
Taser X26 repeatedly for 5 seconds on and 5 seconds off, which was repeated for 3 minutes.
They found the blood pH was significantly decreased for 1 hour following exposure, and that the
lactate level was highly elevated [Jauchem, 2007]. This study demonstrated another
consideration to repeated use of the Taser devices. It is possible that the cause of the deaths after
Taser application will be multi-factorial, and could include a combination of drug use,
compromised physiological status, and cardiac stimulation.
The Stinger S200 is the latest PSG to enter the market, and it generates the radically
different waveform shown in Fig. 3. A safety study has now been completed of the S200, and
this study has been accepted for presentation and publication [McDaniel, 2008]. This study
confirmed the experience in human subjects, wherein the S200 has been applied to several
thousand subjects with no observation of ventricular fibrillation or ventricular tachycardia.
This literature review found studies that indicate cardiac stimulation and capture pacing is
possible with the application of the Taser devices in both experimental animals and humans.
These studies further indicate that the shock intensity, in particular the current density at the
heart, and the manner in which the current varies with time, are important determinants of the
ability to stimulate and pace the heart. Finally, they indicate that physiological changes may also
accompany prolonged exposure to these Taser devices.
Further research will be required to fully understand the mechanism of death after the
application of a projectile stun gun. However, it appears that achieving neuromuscular
incapacitation with the smallest electrical shock is very desirable. Here we performed two
studies to characterize the output of these projectile stun guns, one with a resistive load, and one
with a human-sized pig.
Study 1
The objective of this study was to evaluate the output of the 3 projectile stun guns with a
resistive load.
METHODS
In this study, the three PSGs were applied to a 430 ohm non-inductive resistor. The
voltage across the resistor and the current through the resistor were captured on a digital
oscilloscope with the use of high voltage probes and an inductive current probe (Model 2877,
Pearson Electronics, Palo Alto, CA). From these tracings, the other electrical parameters were
measured and/or calculated.
RESULTS
The electrical parameters observed when the PSGs were applied to the resistive load are
shown in the following table. We used published values for the pulse repetition frequency in our
calculations, due to possible variation with battery status.
Energy per pulse (J)
Power (W)
Current – pk (A)
Current – rms (mA)
Voltage – pk (V)
Votage – rms (V)
Taser M26
0.565
10
15.6
153
6,320
63
Taser X26
0.084
1.59
4.0
61
1,520
26.2
Stinger S200
0.053
0.92
2.14
47
864
19.7
DISCUSSION
Our study found that the Stinger S200 delivered substantially less of each of the relevant
electrical parameters than either the Taser X26 or the Taser M26. For example, the S200
delivered 63% of the energy/pulse of the X26, and less than 10% of the energy/pulse of the M26.
The X26 delivered a peak current almost twice that of the S200, and the M26 delivered a peak
current more than 7 times that of the S200. Perhaps the best descriptor of current delivered by
PSGs is rms current, and the X26 delivered an rms current 30% higher than the S200, while the
M26 delivered an rms current more than 3 times that of the S200.
CONCLUSIONS
The Stinger S200 was found to deliver less energy, power, current, and voltage than both
the Taser M26 and X26 when applied to a resistive load. The Taser X26 was also found to
deliver less energy, power, current, and voltage than the Taser M26 when applied to the same
resistive load. By delivering less of each of the relevant electrical parameters, the S200 could
have a larger safety margin for the induction of VF than the Taser devices. This will need to be
tested in future studies.
Study #2
This study was performed to characterize the electrical current that flows when three
commercial projectile stun guns were applied to the thorax and abdomen of a pig, in three
different orientations of the darts.
METHODS
A 72 kg pig was anesthetized and placed in dorsal recumbency on an insulated table. The
darts from the stun gun being studied were applied in each of the following orientations: Side to
Side across the heart (S-S), Sternal Notch to Xiphoid (SN-X), and Sternal Notch to Umbilicus
(SN-Umb). One of the probes from the stun gun was fed through an inductive current probe
(Model 2877, Pearson Electronics, Palo Alto, CA), which was then connected to a digital
oscilloscope (Model 3014B, Tektronix, Beaverton, OR). Each stun gun was applied to the pig in
each of the three orientations, while recording the current waveform that actually flowed into the
pig. The peak current and rms current were then measured and/or calculated.
RESULTS - Measured and calculated current values are shown in the table below.
Device
Stinger S-200
Stinger S-200
Stinger S-200
Taser X-26
Taser X-26
Taser X-26
Taser M-26
Taser M-26
Taser M-26
Orientation
S-S
SN-X
SN-Umb
S-S
SN-X
SN-Umb
S-S
SN-X
SN-Umb
Peak Current (A)
1.96
1.88
2.12
3.48
3.40
3.64
14.6
15.3
15.3
RMS Current (mA)
43.1
40.1
40.5
51.2
56.7
53.3
147
137
145
Probe orientation abbreviations:
S-S
Side to side across heart
SN-X
Sternal notch to Xiphoid
SN-Umb
Sternal notch to Umbilicus
We used the following published values for the repetition frequency of each stun gun in our
calculations, due to possible variation with battery status:
S-200
17.5 pulse groups per second
X-26
19 pulses per second
M-26
17 pulses per second
The peak current of the X-26 was approximately 75% higher than the peak current of the
S-200. The peak current of the M-26 was approximately 7 times the peak current of the S-200,
and 5 times the peak current of the X26.
The rms current delivered by the X-26 was approximately 28% higher than the rms
current delivered by the S-200. The rms current delivered by the M-26 was more than 3 times
the rms current delivered by the S-200 and about 2.5 times the rms current delivered by the X26.
DISCUSSION
Projectile stun guns apply high voltage, pulsatile shocks to the thorax of subjects, which
raises concerns about the induction of ventricular fibrillation. The critical electrical parameter
that could actually induce ventricular fibrillation is the electrical current that flows from the stun
gun into the subject. The present study characterized the current that flows into the subject
during actual application of the projectile stun guns to a human-sized pig.
Here we characterized this current in two different ways. We found that the Stinger S200 delivers appreciably less peak current and rms current than both the Taser X-26 and the
Taser M-26, and the X-26 delivers appreciably less peak current and rms current than the M-26.
CONCLUSIONS
The current delivered by three commercial projectile stun guns into a pig model was
characterized. We found that the Stinger S-200 delivered less peak and rms current than the
Taser X-26 and the Taser M-26. We further found that the Taser X-26 delivers less peak and
rms current than the Taser M-26. Further studies will be necessary to test whether delivering
lower peak and rms current translates into a reduced ability to pace the heart and whether the
device that generates the lowest peak and rms current proves to be the safest device.
ANALYSIS
The Taser M26 and Taser X26 have now been applied to over 600,000 human subjects
without an observed episode of initiating ventricular fibrillation. However, there have now been
over 250 deaths associated with the application of one of these Taser devices. There have been
several studies of Taser device application in human volunteers that have failed to demonstrate a
causal link between the Taser application and death. However, there have been several studies
of the Taser M26 and the Taser X26 in experimental animals, which have demonstrated the
ability of these devices to capture pace the heart and to induce ventricular fibrillation. There has
also now been one published case report of a Taser capture pacing in a human, and another case
report documenting VF shortly after a Taser application.
There is a general consensus among those that work in this area, that the electrical current
density at the heart is the most important electrical parameter to quantify the ability to pace the
heart and to induce VF. Measuring the current density at the heart represents a very difficult
technical challenge, but we were able to measure the current that was delivered to the chest.
The present report has characterized the output of the 3 commercial projectile stun guns
in two different studies. The first study demonstrated that the Stinger S200 delivers less energy,
power, current, and voltage than both of the Taser devices. The second study found that the
S200 delivers less peak and rms current than either of the Taser devices, when the devices were
applied to the torso of a human-sized pig. This data suggests that the S200 will be less likely to
pace capture the heart and less likely to induce VF. Further studies will be necessary to test
whether it is in fact a safer stun gun than the Taser devices.
References:
1.
McDaniel WC, Stratbucker RA, Smith RW: Surface application of Taser stun guns does
not cause ventricular fibrillation in canines. Proceedings: Annual International Conference of
the IEEE Engineering in Medicine and Biology Society, 2000.
2.
McDaniel WC, Stratbucker RA, Nerheim M, et al: Cardiac safety of neuromuscular
incapacitating defensive devices. PACE 2005; 28:S284-287.
3.
Upson S: How a Taser works. IEEE Spectrum, December, 2007, p.23-27.
4.
Walter RJ, Dennis AJ, Valentino DJ, et al: Taser X26 discharges in swine produce
potentially fatal ventricular arrhythmias. Acad Emerg Med 2008; 15:66-73.
5.
Ho JD, Miner JR, Lakireddy DR, et al: Cardiovascular and physiologic effects of
conducted electrical weapon discharge in resting adults. Acad Emerg Med 2006; 13:589-95.
6.
Ho JD, Dawes DM, Bultman LL, et al: Respiratory effect of prolonged electrical weapon
application on human volunteers. Acad Emerg Med 2007; 14:197-201.
7.
Nanthakumar K, Billingsley IM, Masse S, et al: Cardiac electrophysiological
consequences of neuromuscular incapacitating device discharges. J Am Coll Cardiol 2006;
48:798-804.
8.
Dennis AJ, Valentino DJ, Walter RJ, et al: Acute effects of Taser X26 discharges in a
swine model. J Trauma 2007; 63:581-590.
9.
Wu J-Y, Sun H, O’Rourke AP, et al: Dart-to-heart distance when Taser causes ventricular
fibrillation in pigs. IFMBE Proc., 2006; 15: 578-583.
10.
Cao M, Shinbane JS, Gillberg JM, et al: Taser-induced rapid ventricular myocardial
capture demonstrated by pacemaker instracardiac electrograms. J Cardiovasc. Eectrophysiol.
2007; 18:876-9.
11.
Kim PJ, Franklin WH: Ventricular fibrillation after stun-gun discharge. N Engl J Med.
2005; 353:958-9.
12.
Jauchem JR, Sherry CJ, Fines DA, et al: Acidosis, lactate, electrolytes, muscle enzymes,
and other factors in the blood of Sus scrofa following repeated TASER exposures. Forensic Sci
International 2006; 161:20-30.
13.
McDaniel WC: Cardiac Safety of the Surface Application of the Stinger S-200, (accepted
for presentation and publication), 2008.
Wayne McDaniel, Ph.D.
Ph.D. – Electrical Engineering (Bioengineering emphasis)
Presently – Adjunct Associate Professor of Electrical & Computer Engineering at the University
of Missouri - Columbia
Over 20 years experience performing research related to electricity and the heart, primarily
related to electrical defibrillation of the heart.
Performed the first animal study of the Taser M26 in 1999
PI of the animal portion of the testing of the Taser X26 in 2003
Frequent presenter on the subject of the cardiac safety of stun guns
Author and co-author of multiple articles related to the cardiac safety of stun guns
Representative Publications:
1.
McDaniel WC, Stratbucker RA, Smith RW: Surface application of Taser stun guns does
not cause ventricular fibrillation in canines. Proceedings: Annual International Conference of
the IEEE Engineering in Medicine and Biology Society, 2000.
2.
McDaniel WC, Nerheim M, Stratbucker R: Assessing the Cardiac Rhythm Safety of
Thoracic Application of Tasers. Europace, 6(Suppl. 1):96, 2004.
3.
McDaniel WC, Stratbucker R, Nerheim M, Brewer J: Cardiac Safety of Neuromuscular
Incapacitating Defensive Devices. PACE 28:S284-S287, 2005.
4.
Stratbucker RA, Kroll MW, McDaniel WC, Panescu D, Cardiac Current Density
Distribution by Electrical Pulses from TASER devices, Proc. 28th IEEE EMBS Intl. Conf., New
York, August-September 2006.
5.
McDaniel WC, Stratbucker RA: Testing the Cardiac Rhythm Safety of the Thoracic
Application of TASER Devices. Europace, 8(Suppl 1):58P/23, 2006.
6.
Panescu D, Kroll MW, McDaniel W, Stratbucker RA: Cardiac Current Density
Distribution by Electrical Pulses from TASER Devices, Conf Proc IEEE Eng Med Biol Soc.
1(1):6305-6307, 2006.