arXiv subjects

Amy Courtney

Publications and source records attributed to Amy Courtney.

At least 37 records · Page 2Linked to original sources

arXiv2011

Cerebrovascular injury caused by a high strain rate insult in the thorax

Primary blast-induced traumatic brain injury (TBI) has increased in documented incidence and public prominence in recent conflicts. Evidence for a thoracic mechanism of blast-induced TBI was recently reviewed and, while the totality is compelling, data from experiments isolating this mechanism is sparse. Notably, one recent study showed pericapillar haemorrhage in brain tissue from victims of single, fatal gunshot wounds to the chest. Here, qualitative results are reported for a small field study that isolated a thoracic mechanism for TBI caused by a high strain rate insult in white-tailed deer (Odocoileus virginianus, mass 49-80 kg) in a natural environment. In each of three cases, petechiae were present on the surface of the frontal, occipital and/or left parietal lobes, along with capillary damage in the choroid plexus. The location of the projectile impact to the thorax seemed to affect the degree of damage. This may be due to the proximity to the great vessels. The data reported here provides direct evidence of a thoracic mechanism resulting in gross injury to the cerebral vasculature.

physics.med-ph↗

arXiv2011

High-speed measurement of rifle primer blast waves

This article describes a method and results for direct high-speed measurements of rifle primer blast waves employing a high-speed pressure transducer located at the muzzle to record the blast pressure wave produced by primer ignition. Our key findings are: 1) Most of the primer models tested show 5-12% standard deviation in the magnitudes of their peak pressure. 2) For most primer types tested, peak pressure magnitudes are well correlated with measured primer masses so that significant reductions in standard deviation are expected to result from sorting primers by mass. 3) A range of peak pressures from below 200 psi to above 500 psi is available in different primer types.

physics.pop-ph↗

arXiv2011

Working toward exposure thresholds for blast-induced traumatic brain injury: thoracic and acceleration mechanisms

Research in blast-induced lung injury resulted in exposure thresholds that are useful in understanding and protecting humans from such injury. Because traumatic brain injury (TBI) due to blast exposure has become a prominent medical and military problem, similar thresholds should be identified that can put available research results in context and guide future research toward protecting warfighters as well as diagnosis and treatment. At least three mechanical mechanisms by which the blast wave may result in brain injury have been proposed - a thoracic mechanism, head acceleration and direct cranial transmission. These mechanisms need not be mutually exclusive. In this study, likely regions of interest for the first two mechanisms based on blast characteristics (positive pulse duration and peak effective overpressure) are developed using available data from blast experiments and related studies, including behind-armor blunt trauma and ballistic pressure wave studies. These related studies are appropriate to include because blast-like pressure waves are produced that result in neurological effects like those caused by blast. Results suggest that injury thresholds for each mechanism are dependent on blast conditions, and that under some conditions, more than one mechanism may contribute. There is a subset of blast conditions likely to result in TBI due to head acceleration and/or a thoracic mechanism without concomitant lung injury. These results can be used to guide experimental designs and compare additional data as they become available. Additional data are needed before actual probabilities or severity of TBI for a given exposure can be described.

physics.med-ph↗

arXiv2011

A Table-top Blast Driven Shock Tube

The prevalence of blast-induced traumatic brain injury in conflicts in Iraq and Afghanistan has motivated laboratory scale experiments on biomedical effects of blast waves and studies of blast wave transmission properties of various materials in hopes of improving armor design to mitigate these injuries. This paper describes the design and performance of a table-top shock tube that is more convenient and widely accessible than traditional compression driven and blast driven shock tubes. The design is simple: it is an explosive driven shock tube employing a rifle primer which explodes when impacted by the firing pin. The firearm barrel acts as the shock tube, and the shock wave emerges from the muzzle. The small size of this shock tube can facilitate localized application of a blast wave to a subject, tissue, or material under test.

physics.med-ph↗

arXiv2011

History and evidence regarding hydrostatic shock

This paper reviews the history and evidence related to remote wounding effects of ballistic pressure waves imparted to tissue by the impact of a bullet. Such remote effects are often referred to as hydraulic or hydrostatic shock. In spite of considerable published evidence and a long history, some medical professionals continue to regard the ability of a bullet to injure tissue that is not directly crushed or stretched as mythical (Jandial R, Reichwage B, Levy M, Duenas V, Sturdivan L. Ballistics for the neurosurgeon. Neurosurgery. 2008:62:472-480.) Early references to these effects date to the 19th century; however, compelling experimental support and medical findings in human case studies did not become available until the late 20th and early 21st century.

physics.med-ph↗

arXiv2009

Measuring thrust and predicting trajectory in model rocketry

Methods are presented for measuring thrust using common force sensors and data acquisition to construct a dynamic force plate. A spreadsheet can be used to compute trajectory by integrating the equations of motion numerically. These techniques can be used in college physics courses, and have also been used with high school students concurrently enrolled in algebra 2.

physics.pop-ph↗

arXiv2008

Misleading reference to unpublished wound ballistics data regarding distant injuries

An article (J Trauma 29:10-18, 1989) cites unpublished wound ballistics data to support the authors' view that distant injuries are a myth in wound ballistics. The actual data, published in 1990, actually contains a number of detailed examples of distant injuries. (Bellamy RF, Zajtchuk R. The physics and biophysics of wound ballistics. In: Zajtchuk R, ed. Textbook of Military Medicine, Part I: Warfare, Weaponry, and the Casualty, Vol. 5, Conventional Warfare: Ballistic, Blast, and Burn Injuries. Washington, DC: Office of the Surgeon General, Department of the Army, United States of America; 1990: 107-162.)

physics.med-ph↗

arXiv2008

Comments on "Ballistics: a primer for the surgeon"

In response to a published assertion to the contrary, this paper briefly reviews many studies that document remote wounding effects of ballistic pressure waves including experiments in pigs and dogs that find brain injury resulting from animal models shot in the thigh and case studies in humans that document both remote brain and spinal cord injuries ascribed to ballistic pressure waves.

physics.med-ph↗

arXiv2008

Comments Regarding "On the Nature of Science"

An attempt to redefine science in the 21st century (BK Jennings, On the Nature of Science, Physics in Canada, 63(7) 2007) has abandoned traditional notions of natural law and objective reality, blurred the distinctions between natural science and natural history, elevated Occam's razor from an epistemological preference to a scientific principle, and elevated peer-review and experimental care as equals with repeatable experiment as arbiters of scientific validity. Our comments review the long-established axioms of the scientific method, remind readers of the distinctions between science and history, disprove the generality of Occam's razor by counter example, and highlight the risks of accepting additional scientific arbiters as equal to repeatable experiment.

physics.hist-ph↗

arXiv2008

A method for testing bullets at reduced velocity

Reconstruction of shooting events occasionally requires testing of bullets at velocities significantly below the typical muzzle velocity of cartridge arms. Trajectory, drag, and terminal performance depend strongly on velocity, and realistic results require accurately reconstructing the velocity. A method is presented for testing bullets at reduced velocities by loading the bullet into a sabot and firing from a muzzle loading rifle with a suitably reduced powder charge. Powder charges can be safely reduced to any desirable level when shooting saboted bullets from a muzzleloader; in contrast, cartridge arms can only be safely operated within a narrow window of powder charges/muzzle velocities. This technique is applicable to a wide range of both pistol and rifle bullets at velocities from 700 ft/s to 2000 ft/s.

physics.med-ph↗

arXiv2008

Apparent measurement errors in "Development of biomechanical response corridors of the thorax to blunt ballistic impacts"

"Development of biomechanical response corridors of the thorax to blunt ballistic impacts" (Bir, C., Viano, D., King, A., 2004, Journal of Biomechanics 37, 73-79.) contains apparent measurement errors. Areas under several force vs. time (Fig. 2) and force vs. deflection curves (Fig.4) differ significantly from the momentum and kinetic energy changes, respectively. These differences violate Newton's second law and the work-energy theorem.

physics.med-ph↗

arXiv2008

A Thoracic Mechanism of Mild Traumatic Brain Injury Due to Blast Pressure Waves

The mechanisms by which blast pressure waves cause mild to moderate traumatic brain injury (mTBI) are an open question. Possibilities include acceleration of the head, direct passage of the blast wave via the cranium, and propagation of the blast wave to the brain via a thoracic mechanism. The hypothesis that the blast pressure wave reaches the brain via a thoracic mechanism is considered in light of ballistic and blast pressure wave research. Ballistic pressure waves, caused by penetrating ballistic projectiles or ballistic impacts to body armor, can only reach the brain via an internal mechanism and have been shown to cause cerebral effects. Similar effects have been documented when a blast pressure wave has been applied to the whole body or focused on the thorax in animal models. While vagotomy reduces apnea and bradycardia due to ballistic or blast pressure waves, it does not eliminate neural damage in the brain, suggesting that the pressure wave directly affects the brain cells via a thoracic mechanism. An experiment is proposed which isolates the thoracic mechanism from cranial mechanisms of mTBI due to blast wave exposure. Results have implications for evaluating risk of mTBI due to blast exposure and for developing effective protection.

physics.med-ph↗

arXiv2008

Links between traumatic brain injury and ballistic pressure waves originating in the thoracic cavity and extremities

Identifying patients at risk of traumatic brain injury (TBI) is important because research suggests prophylactic treatments to reduce risk of long-term sequelae. Blast pressure waves can cause TBI without penetrating wounds or blunt force trauma. Similarly, bullet impacts distant from the brain can produce pressure waves sufficient to cause mild to moderate TBI. The fluid percussion model of TBI shows that pressure impulses of 15-30 psi cause mild to moderate TBI in laboratory animals. In pigs and dogs, bullet impacts to the thigh produce pressure waves in the brain of 18-45 psi and measurable injury to neurons and neuroglia. Analyses of research in goats and epidemiological data from shooting events involving humans show high correlations (r > 0.9) between rapid incapacitation and pressure wave magnitude in the thoracic cavity. A case study has documented epilepsy resulting from a pressure wave without the bullet directly hitting the brain. Taken together, these results support the hypothesis that bullet impacts distant from the brain produce pressure waves that travel to the brain and can retain sufficient magnitude to induce brain injury. The link to long-term sequelae could be investigated via epidemiological studies of patients who were gunshot in the chest to determine whether they experience elevated rates of epilepsy and other neurological sequelae.

physics.med-ph↗

arXiv2008

Epistemological Distinctions Between Science and History

This article describes epistemological distinctions between science and history. Science investigates models of natural law using repeatable experiments as the ultimate arbiter. In contrast, history investigates past events by considering physical evidence, documentary evidence, and eyewitness testimony. Because questions of natural law are repeatably testable by any audience that exercises due experimental care, models of natural law are inherently more objective and testable with greater certainty than theories of past events.

physics.gen-ph↗

arXiv2008

Scientific Evidence for Hydrostatic Shock

This paper reviews the scientific support for a ballistic pressure wave radiating outward from a penetrating projectile and causing injury and incapacitation. This phenomenon is known colloquially as "hydrostatic shock." The idea apparently originates with Col. Frank Chamberlin, a World War II trauma surgeon and wound ballistics researcher. The paper reviews claims that hydrostatic shock is a myth and considers supporting evidence through parallels with blast, describing the physics of the pressure wave, evidence for remote cerebral effects, and remote effects in the spine and other internal organs. Finally, the review considers the levels of energy transfer required for the phenomenon to be readily observed.

physics.med-ph↗

arXiv2008

The Ballistic Pressure Wave Theory of Handgun Bullet Incapacitation

This paper presents a summary of seven distinct chains of evidence, which, taken together, provide compelling support for the theory that a ballistic pressure wave radiating outward from the penetrating projectile can contribute to wounding and incapacitating effects of handgun bullets. These chains of evidence include the fluid percussion model of traumatic brain injury, observations of remote ballistic pressure wave injury in animal models, observations of rapid incapacitation highly correlated with pressure magnitude in animal models, epidemiological data from human shootings showing that the probability of incapacitation increases with peak pressure magnitude, case studies in humans showing remote pressure wave damage in the brain and spinal cord, and observations of blast waves causing remote brain injury.

physics.med-ph↗

arXiv2007

Sheep Collisions: the Good, the Bad, and the TBI

The title page of Chapter 9 in Fundamentals of Physics (Halliday, Resnick, and Walker, 8th Edition, p. 201) shows a dramatic photograph of two Big Horn sheep butting heads and promises to explain how sheep survive such violent clashes without serious injury. However, the answer presented in sample problem 9-4 (p. 213) errs in presuming an interaction time of 0.27 s which results in an unrealistically long stopping distance of 0.62 m. Furthermore, the assertion that the horns provide necessary cushioning of the blow is inconsistent with the absence of concussions in domestic breeds of hornless sheep. Results from traumatic brain injury (TBI) research allow acceleration tolerance of sheep to be estimated as 450 g facilitating an analysis of sheep collisions that is more consistent with available observations (stopping distance less than 1 cm, impact time of roughly 2 ms).

physics.ed-ph↗

arXiv2007

Relative incapacitation contributions of pressure wave and wound channel in the Marshall and Sanow data set

The Marshall and Sanow data set is the largest and most comprehensive data set available quantifying handgun bullet effectiveness in humans. This article presents an empirical model for relative incapacitation probability in humans hit in the thoracic cavity by handgun bullets. The model is constructed by employing the hypothesis that the wound channel and ballistic pressure wave effects each have an associated independent probability of incapacitation. Combining models for these two independent probabilities using the elementary rules of probability and performing a least-squares fit to the Marshall and Sanow data provides an empirical model with only two adjustable parameters for modeling bullet effectiveness with a standard error of 5.6% and a correlation coefficient R = 0.939. This supports the hypothesis that wound channel and pressure wave effects are independent (within the experimental error), and it also allows assignment of the relative contribution of each effect for a given handgun load. This model also gives the expected limiting behavior in the cases of very small and very large variables (wound channel and pressure wave), as well as for incapacitation by rifle and shotgun projectiles.

physics.med-ph↗