Hydrostatic shock

The term hydrostatic shock describes the theory that a penetrating projectile produces remote wounding and incapacitating effects in living targets, in addition to local effects in tissue caused by direct impact, through a hydraulic effect in liquid filled tissues. There is scientific evidence that “hydrostatic shock" can produce remote neural damage and produce incapacitation more quickly than blood loss effects. The debate between proponents of bullets that are "light and fast" versus bullets that are "slow and heavy" often refers to this phenomenon.

Theory's introduction

It is unclear when the term "hydrostatic shock" first came into use to describe remote effects of penetrating projectiles, but Frank Chamberlin, a World War II trauma surgeon and ballistics researcher, noted remote pressure wave effects. Col. Chamberlin described what he called “explosive effects” and “hydraulic reaction” of bullets in tissue.

"...liquids are put in motion by ‘shock waves’ or hydraulic effects... with liquid filled tissues, the effects and destruction of tissues extend in all directions far beyond the wound axis". Chamberlin FT, Gun Shot Wounds, in Handbook for Shooters and Reloaders, Vol. II, Ackley PO, ed., Plaza Publishing, Salt Lake City, Utah, 1966. ]

He avoided the ambiguous use of the term “shock” because it can refer to either a specific kind of pressure wave associated with explosions and supersonic projectiles or to a medical condition in the body.

Col. Chamberlin recognized that many theories have been advanced in wound ballistics. During World War II, he commanded an 8,500 bed hospital center that treated over 67,000 patients during the fourteen months that he operated it. P.O. Ackley estimates that 85% of the patients were suffering from gun shot wounds. Ackley PO, Col. Frank T. Chamberlin, in Handbook for Shooters and Reloaders, Vol. II, Ackley PO, ed., Plaza Publishing, Salt Lake City, Utah, 1966.] Col. Chamberlin spent many hours interviewing patients as to their reactions to bullet wounds. He also conducted many live animal experiments after his tour of duty. On the subject of wound ballistics theories, he wrote:"If I had to pick one of these theories as gospel, I’d still go along with the Hydraulic Reaction of the Body Fluids plus the reactions on the Central Nervous System." Chamberlin FT, Gun Shot Wounds, in Handbook for Shooters and Reloaders, Vol. II, Ackley PO, ed., Plaza Publishing, Salt Lake City, Utah, 1966. ]

Other World War II era scientists noted remote pressure wave effects in the peripheral nerves. Livingstone WK, Davis EW, Livingstone KE: Delayed recovery in peripheral nerve lesions caused by high velocity wounding. J. Neurosurg., 2: 170, 1945. ] Puckett WO, Grundfest H, McElroy WD, McMillen JH, Damage to peripheral nerves by high velocity missiles without a direct hit. J. Neurosurg., 3: 294, 1946. ] There was support for the idea of remote neural effects of ballistic pressure waves in the medical and scientific communities, but the phrase "’hydrostatic shock’" and similar phrases including “shock” were used mainly by gunwriters (such as Jack O'ConnerO’Conner J, The Hunting Rifle, McMillian, 1970. ] ) and the small arms industry (such as Roy Weatherby Gresham T, Gresham G, Weatherby: The Man, The Gun, The Legend, Cane River Publishing, 1992.] , and Federal “Hydrashock.”)

Dr. Fackler's contra-claim

Dr. Martin Fackler, a Vietnam-era trauma surgeon and wound ballistics researcher, claimed that hydrostatic shock had been disproved and that the assertion that a pressure wave plays a role in injury or incapacitation is a myth. cite web | title=The Shockwave Myth | work= Fackler ML: Literature Review and Comment. Wound Ballistics Review Winter 1991: pp38-40.| url=http://www.btammolabs.com/fackler/shock_wave_myth.pdf | accessmonthday=April 11 | accessyear=2007] Others expressed similar views.Patrick UW: Handgun Wounding Factors and Effectiveness. FBI Firearms training Unit, Quantico, VA. 1989. ] MacPherson D: Bullet Penetration—Modeling the Dynamics and the Incapacitation Resulting From Wound Trauma. Ballistics Publications, El Segundo, CA, 1994.]

Dr. Fackler based his argument on the lithotriptor, a tool commonly used to break up kidney stones. The lithotriptor uses sonic pressure waves which are stronger than those caused by most handgun bullets, yet it produces no damage to soft tissues whatsoever. Hence, Fackler argued, ballistic pressure waves cannot damage tissue either.Fackler ML, Gunshot Wound Review, Annals of Emergency Medicine 28:2; 1996.]

However, tissue damage due to lithotriptors has been documented.Evan AP, Willis LR Lingeman JE, McAteer JA, Renal Trauma and the Risk of Long-Term Complications in Shock Wave Lithotripsy, Nephron 78(1):1-8, 1998.] Lingeman JE, Kim SC, Keo RL, McAteer JA, Evan
] Lokhandwalla M, Sturtevant B: Mechanical Haemolysis in Shock Wave Lithotripsy (SWL): I. Analysis of Cell Deformation due to SWL Flow-Fields.” Physics in Medicine & Biology 46(2):413-437; 2001.]

Dr. Fackler also claimed that a study of rifle bullet wounds in Vietnam (Wound Data and Munitions Effectiveness Team) found “no cases of bones being broken, or major vessels torn, that were not hit by the penetrating bullet. In only two cases, an organ that was not hit (but was within a few cm of the projectile path), suffered some disruption.” Dr. Fackler cited a personal communication with R. F. Bellamy.cite web | title=The Shockwave Myth | work= Fackler ML: Literature Review and Comment. Wound Ballistics Review Winter 1991: pp38-40.| url=http://www.btammolabs.com/fackler/shock_wave_myth.pdf | accessmonthday=April 11 | accessyear=2007] However, Bellamy’s published findings the following yearBellamy 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. available for download: http://www.bordeninstitute.army.mil/published_volumes/conventional_warfare/conventional_warfare.html] estimated that 10% of fractures in the data set might be due to indirect injuries, and one specific case is described in detail (pp. 153-154). In addition, the published analysis documents five instances of abdominal wounding in cases where the bullet did not penetrate the abdominal cavity (pp. 149-152), a case of lung contusion resulting from a hit to the shoulder (pp. 146-149), and a case of indirect effects on the central nervous system (p. 155). Rather than contradict distant injuries, as Fackler claimed, the WDMET data from Vietnam actually provides supporting evidence.

Inferences from Blast Pressure Wave Observations

A shock wave can be created when fluid is rapidly displaced by an explosive or projectile. Tissue behaves similarly enough to water that a sonic pressure wave can be created by a bullet impact, generating pressures in excess of 100 atmospheres (1500 PSI). Harvey EN, Korr IM, Oster G, et al.:Secondary Damage in wounding due to pressure changes accompanying the passage of high velocity missiles. Surgery 21:218-239; 1947.]

Duncan McPherson, a former member of the International Wound Ballistics Association and author of the book, Bullet Penetration, claimed that shock waves cannot result from bullet impacts with tissue. MacPherson D: Bullet Penetration—Modeling the Dynamics and the Incapacitation Resulting From Wound Trauma. Ballistics Publications, El Segundo, CA, 1994.] In contrast, Brad Sturtevant, a leading researcher in shock wave physics at Caltech for many decades, found that shock waves can result from handgun bullet impacts in tissue.Sturtevant B, Shock Wave Effects in Biomechanics, Sadhana, 23: 579-596, 1998.] Other sources also indicate that ballistic impacts can create shock waves in tissue.Roberts JC, Ward EE, Merkle AC, O’Conner JV, Assessing Behind Armor Blunt Trauma, The Journal of Trauma, 62, 1127-1133, 2007. ] Roberts JC, O’Conner JV, Ward EE, Modeling the Effect of Nonpenetrating Ballistic Impact, The Journal of Trauma, 58: 1241-1251, 2005. ] Suneson A, Hansson HA, Seeman T: Pressure Wave Injuries to the Nervous System Caused by High Energy Missile Extremity Impact: Part I. Local and Distant Effects on the Peripheral Nervous System. A Light and Electron Microscopic Study on Pigs. The Journal of Trauma. 30(3):281-294; 1990.]

Blast and ballistic pressure waves have physical similarities. Prior to wave reflection, they both are characterized by a steep wave front followed by a nearly exponential decay at close distances. They also have similarities in how they cause neural effects in the brain. In tissue, both types of pressure waves have similar magnitudes, duration, and frequency characteristics. Both have been shown to cause damage in the hippocampus.Wang Q, Wang Z, Zhu P, Jiang J: Alterations of the Myelin Basic Protein and Ultrastructure in the Limbic System and the Early Stage of Trauma-Related Stress Disorder in Dogs. The Journal of Trauma. 56(3):604-610; 2004.] Cernak I, Wang, Z, Jiang J, Bian, X, Savic J, Ultrastructural and Functional Characteristics of Blast Injury-Induced Neurotrauma, The Journal of Trauma, 50:695-706, 2001.] Cernak I, Wang, Z, Jiang J, Bian, X, Savic J, Cognitive deficits following blast injury induced neurotrauma, Brain Injury, 15(7):593-612, 2001.] It has been hypothesized that both reach the brain from the thoracic cavity via major blood vessels.

For example, Ibolja Cernak, a leading researcher in blast wave injury at the Applied Physics Laboratory at Johns Hopkins University, hypothesized, "alterations in brain function following blast exposure are induced by kinetic energy transfer of blast overpressure via great blood vessels in abdomen and thorax to the central nervous system." Cernak I, Blast (Explosion)-Induced Neurotrauma: A Myth Becomes Reality, Restorative Neurology and Neuroscience, 23:139-140, 2005.] This hypothesis is supported by observations of neural effects in the brain from localized blast exposure focused on the lungs in experiments in animals. Cernak I, Wang, Z, Jiang J, Bian, X, Savic J, Ultrastructural and Functional Characteristics of Blast Injury-Induced Neurotrauma, The Journal of Trauma, 50:695-706, 2001.]

“Hydrostatic shock” expresses the idea that organs can be damaged by the pressure wave in addition to damage from direct contact with the penetrating projectile. If one interprets the "shock" in the term "hydrostatic shock" to refer to the physiological effects rather than the physical wave characteristics, the question of whether the pressure waves satisfy the definition of “shock wave” is unimportant, and one can consider the weight of scientific evidence and various claims regarding the possibility of a ballistic pressure wave to create tissue damage and incapacitation in living targets.

Physics of Ballistic Pressure Waves

A number of papers describe the physics of ballistic pressure waves created when a high-speed projectile enters a viscous medium.Lee M, Longoria RG, Wilson DE, Ballistic Waves in High-Speed Water Entry, Journal of Fluids and Structures, 11, 819-844, 1997.] Hoover WR, Dawson VCD, Hydrodynamic pressure measurements of the vertical water entry of a sphere, U.S. Naval Ordnance Laboratory, White Oak, MD, U.S.A., Tech. Report 66-70, 1966.] Shi H, Kume M, An Experimental Research on the Flow Field of Water Entry by Pressure Measurements, Phys. Fluids 13(1), 347-349, 2001.] These results show that ballistic impacts produce pressure waves that propagate at close to the speed of sound.

Lee et al. present an analytical model showing that unreflected ballistic pressure waves are well approximated by an exponential decay, which is similar to blast pressure waves.Lee M, Longoria RG, Wilson DE, Ballistic Waves in High-Speed Water Entry, Journal of Fluids and Structures, 11, 819-844, 1997.] Lee et al. also note the importance of the energy transfer:

" As would be expected, an accurate estimation of the kinetic energy loss by a projectile is always important in determining the ballistic waves."

The rigorous calculations of Lee et al. require knowing the drag coefficient and frontal area of the penetrating projectile at every instant of the penetration. Since this is not generally possible with expanding handgun bullets, Courtney and Courtney developed a model for estimating the peak pressure waves of handgun bullets from the impact energy and penetration depth in ballistic gelatin.Courtney M, Courtney A: Ballistic pressure wave contributions to rapid incapacitation in the Strasbourg goat tests. http://arxiv.org/abs/physics/0701267 accessed 5/29/2007.] This model agrees with the more rigorous approach of Lee et al. for projectiles where they can both be applied. For expanding handgun bullets, the peak pressure wave magnitude is proportional to the bullet’s kinetic energy divided by the penetration depth.

Remote Cerebral Effects of Ballistic Pressure Waves

Goransson et al. were the first contemporary researchers to present compelling evidence for remote cerebral effects of extremity bullet impact.Göransson AM, Ingvar DH, Kutyna F: Remote Cerebral Effects on EEG in High-Energy Missile Trauma. The Journal of Trauma. 28(1 Supplement):S204-S205; January 1988. ] They observed changes in EEG readings from pigs shot in the thigh. A follow-up experiment by Suneson et al. implanted high-speed pressure transducers into the brain of pigs and demonstrated that a significant pressure wave reaches the brain of pigs shot in the thigh.Suneson A, Hansson HA, Seeman T: Pressure Wave Injuries to the Nervous System Caused by High Energy Missile Extremity Impact: Part I. Local and Distant Effects on the Peripheral Nervous System. A Light and Electron Microscopic Study on Pigs. The Journal of Trauma. 30(3):281-294; 1990.] Suneson A, Hansson HA, Seeman T: Pressure Wave Injuries to the Nervous System Caused by High Energy Missile extremity Impact: Part II. Distant Effects on the Central Nervous System. A Light and Electron Microscopic Study on Pigs. The Journal of Trauma. 30(3):295-306; 1990.] These scientists observed apnea, depressed EEG readings, and neural damage in the brain caused by the distant effects of the ballistic pressure wave originating in the thigh.

The results of Suneson et al. were confirmed and expanded upon by a later experiment in dogsWang Q, Wang Z, Zhu P, Jiang J: Alterations of the Myelin Basic Protein and Ultrastructure in the Limbic System and the Early Stage of Trauma-Related Stress Disorder in Dogs. The Journal of Trauma. 56(3):604-610; 2004.] which "confirmed that distant effect exists in the central nervous system after a high-energy missile impact to an extremity. A high-frequency oscillating pressure wave with large amplitude and short duration was found in the brain after the extremity impact of a high-energy missile . . ." Wang et al. observed significant damage in both the hypothalamus and hippocampus regions of the brain due to remote effects of the ballistic pressure wave.

Remote Pressure Wave Effects in the Spine and Internal Organs

In a study of a handgun injury, Sturtevant found that pressure waves from a bullet impact in the torso can reach the spine and that a focusing effect from concave surfaces can concentrate the pressure wave on the spinal cord producing significant injury.Sturtevant B, Shock Wave Effects in Biomechanics, Sadhana, 23: 579-596, 1998.] This is consistent with other work showing remote spinal cord injuries from ballistic impacts. Saxon M, Snyder HA, Washington HA, Atypical Brown-Sequard syndrome following gunshot wound to the face, Journal of Oral and Maxillofacial Surgery 40: 299-302, 1982.] Taylor RG, Gleave JRW, Incomplete Spinal Cord Injuries, Journal of Bone and Joint Surgery, B39:438-450, 1957. ]

Roberts et al. present both experimental work and finite element modeling showing that there can be considerable pressure wave magnitudes in the thoracic cavity for handgun projectiles stopped by a Kevlar vest.Roberts JC, Ward EE, Merkle AC, O’Conner JV, Assessing Behind Armor Blunt Trauma, The Journal of Trauma, 62, 1127-1133, 2007. ] Roberts JC, O’Conner JV, Ward EE, Modeling the Effect of Nonpenetrating Ballistic Impact, The Journal of Trauma, 58: 1241-1251, 2005. ] For example, an 8 gram projectile at 360 m/s impacting a NIJ level II vest over the sternum can produce an estimated pressure wave level of nearly 2.0 MPa (200 PSI) in the heart and a pressure wave level of nearly 1.5 MPa (150 PSI) in the lungs. Impacting over the liver can also produce an estimated pressure wave level of 2.0 MPa (200 PSI) in the liver.

Energy Transfer Required for Remote Neural Effects

The work of Courtney et al. also supports the role of a ballistic pressure wave in incapacitation and injury. Courtney A, Courtney M: Links between traumatic brain injury and ballistic pressure waves originating in the thoracic cavity and extremities. Brain Injury 21(7): 657-662, 2007. Pre-print: http://www.ballisticstestinggroup.org/tbipwave.pdf ] Courtney M, Courtney A: Review of criticisms of ballistic pressure wave experiments, the Strasbourg goat tests, and the Marshall and Sanow data.http://arxiv.org/abs/physics/0701268 accessed 5/29/2007.] Courtney M, Courtney A: Ballistic pressure wave contributions to rapid incapacitation in the Strasbourg goat tests. http://arxiv.org/abs/physics/0701267 accessed 5/29/2007.] Courtney M, Courtney A: Relative incapacitation contributions of pressure wave and wound channel in the Marshall and Sanow data set. http://arxiv.org/abs/physics/0701266 accessed 5/29/2007.] Courtney M, Courtney A: A method for testing handgun bullets in deer. http://arxiv.org/abs/physics/0702107 accessed 5/29/2007.] The work of Suneson et al. and Courtney et al. suggest that remote neural effects can occur with levels of energy transfer possible with handguns (roughly 500 ft·lbf/700 joules). Using sensitive biochemical techniques, the work of Wang et al. suggests even lower impact energy thresholds for remote neural injury to the brain. In analysis of experiments of dogs shot in the thigh they report highly significant (p < 0.01), easily detectable neural effects in the hypothalamus and hippocampus with energy transfer levels close to 550 ft·lbf (740 Joules). Wang et al. reports less significant (p < 0.05) remote effects in the hypothalamus with energy transfer just under 100 ft·lbf (130 Joules). Wang Q, Wang Z, Zhu P, Jiang J: Alterations of the Myelin Basic Protein and Ultrastructure in the Limbic System and the Early Stage of Trauma-Related Stress Disorder in Dogs. The Journal of Trauma. 56(3):604-610; 2004.]

Even though Wang et al. document remote neural damage for low levels of energy transfer (roughly 100 ft·lbf), these levels of neural damage are probably too small to contribute to rapid incapacitation. Courtney and Courtney believe that remote neural effects only begin to make significant contributions to rapid incapacitation for ballistic pressure wave levels above 500 PSI (corresponds to transferring roughly convert|300|ft.lbf|N.m|abbr=on in 12 inches of penetration) and become easily observable above 1000 PSI (corresponds to transferring roughly convert|600|ft.lbf|N.m|abbr=on in 1 foot of penetration).Courtney A, Courtney M: Links between traumatic brain injury and ballistic pressure waves originating in the thoracic cavity and extremities. Brain Injury 21(7): 657-662, 2007. Pre-print: http://www.ballisticstestinggroup.org/tbipwave.pdf ] Incapacitating effects in this range of energy transfer are consistent with observations of remote spinal injuries Sturtevant B, Shock Wave Effects in Biomechanics, Sadhana, 23: 579-596, 1998.] , observations of suppressed EEGs and apnea in pigs. Göransson AM, Ingvar DH, Kutyna F: Remote Cerebral Effects on EEG in High-Energy Missile Trauma. The Journal of Trauma. 28(1 Supplement):S204-S205; January 1988. ] Suneson A, Hansson HA, Seeman T: Peripheral High-Energy Missile Hits Cause Pressure Changes and Damage to the Nervous System: Experimental Studies on Pigs. The Journal of Trauma. 27(7):782-789; 1987. Suneson A, Hansson HA, Seeman T: Central and Peripheral Nervous Damage Following High-Energy Missile Wounds in the Thigh. The Journal of Trauma. 28(1 Supplement):S197-S203; January 1988. ] and with observations of incapacitating effects of ballistic pressure waves without a wound channel. Courtney M, Courtney A, Experimental Observations of Incapacitation via Ballistic Pressure Wave without a Wound Channel , 2007. Pre-print: http://www.ballisticstestinggroup.org/lotor.pdf ]

Other Scientific Findings

The scientific literature contains significant other findings regarding injury mechanisms of ballistic pressure waves. Ming et al. found that ballistic pressure waves can break bones. Ming L, Yu-Yuan M, Ring-Xiang F, Tian-Shun F: The characteristics of pressure waves generated in the soft target by impact and its contribution to indirect bone fractures. The Journal of Trauma 28(1) Supplement: S104-S109; 1988. ] Tikka et al. reports abdominal pressure changes produced in pigs hit in one thigh. Tikka S, Cederberg A, Rokkanen P: Remote effects of pressure waves in missile trauma: the intra-abdominal pressure changes in anaesthetized pigs wounded in one thigh. Acta Chir. Scand. Suppl. 508: 167-173, 1982. ] Akimov et al. report on injuries to the nerve trunk from gunshot wounds to the extremities. Akimov GA, Odinak MM, Zhivolupov SA, et al., The mechanisms of the injuries to the nerve trunk in gunshot wounds of the extremities: Experimental research. Voen Med Zh 80: 34, 1993.]

Recommendations

The FBI recommends that loads intended for self-defense and law enforcement applications meet a minimum penetration requirement of 12” in ballistic gelatin Patrick UW: Handgun Wounding Factors and Effectiveness. FBI Firearms Training Unit, Quantico, VA. 1989.] . Maximizing the ballistic pressure wave effects requires transferring maximum energy in a penetration distance that meets this requirement. In addition, bullets that fragment and meet minimum penetration requirements generate higher pressure waves than bullets which do not fragment.

ee also

*Stopping power

References