Hydrostatic shock, also known as hydro-shock, is the controversial concept that a penetrating projectile (such as a bullet) can produce a pressure wave that causes "remote neural damage", "subtle damage in neural tissues" and "rapid effects" in living targets.Deadly fighting skills of the world, Steve Crawford (1999) pp. 68–69AK-47: the weapon that changed the face of the war, Larry Kahaner, John Wiley and Sons (2007) p. 32 It has also been suggested that pressure wave effects can cause indirect bone fractures at a distance from the projectile path, although it was later demonstrated that indirect bone fractures are caused by temporary cavity effects (strain placed on the bone by the radial tissue displacement produced by the temporary cavity formation).
Proponents of the concept argue that hydrostatic shock can produce remote neural damage and produce incapacitation more quickly than blood loss effects. In arguments about the differences in stopping power between calibers and between cartridge models, proponents of cartridges that are "light and fast" (such as the 9×19mm Parabellum) versus cartridges that are "slow and heavy" (such as the .45 ACP) often refer to this phenomenon.
Martin Fackler has argued that sonic pressure waves do not cause tissue disruption and that temporary cavity formation is the actual cause of tissue disruption mistakenly ascribed to sonic pressure waves. One review noted that strong opinion divided papers on whether the pressure wave contributes to wound injury. It ultimately concluded that no "conclusive evidence could be found for permanent pathological effects produced by the pressure wave".
Origin of the hypothesis An early mention of "hydrostatic shock" appeared in Popular Mechanics in April 1942. In the scientific literature, the first discussion of pressure waves created when a bullet hits a living target is presented by E. Harvey Newton and his research group at Princeton University in 1947:
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 gunshot wounds. Col. Chamberlin spent many hours interviewing patients as to their reactions to bullet wounds. He conducted many live animal experiments after his tour of duty. On the subject of wound ballistics theories, he wrote:
Other World War II era scientists noted remote pressure wave effects in the peripheral nerves. 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 "Hydra-Shok.")
Arguments against Martin Fackler, a Vietnam-era trauma surgeon, wound ballistics researcher, a colonel in the U.S. Army and the head of the Wound Ballistics Laboratory for the U.S. Army's Medical Training Center, Letterman Institute, 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. 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.
Fackler based his argument on the lithotriptor, a tool commonly used to break up kidney stones. A 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.
Fackler 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." Fackler cited a personal communication with R. F. Bellamy. 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). Fackler's critics argue that his evidence does not contradict distant injuries, as Fackler claimed, but the WDMET data from Vietnam actually provides supporting evidence for it.
A summary of the debate was published in 2009 as part of a Historical Overview of Wound Ballistics Research.
Distant injuries in the WDMET data
The Wound Data and Munitions Effectiveness Team (WDMET) gathered data on wounds sustained during the Vietnam War. In their analysis of this data published in the Textbook of Military Medicine, Ronald Bellamy and Russ Zajtchuck point out a number of cases which seem to be examples of distant injuries. Bellamy and Zajtchuck describe three mechanisms of distant wounding due to pressure transients: 1) stress waves 2) shear waves and 3) a vascular pressure impulse.
After citing Harvey's conclusion that "stress waves probably do not cause any tissue damage" (p. 136), Bellamy and Zajtchuck express their view that Harvey's interpretation might not be definitive because they write "the possibility that stress waves from a penetrating projectile might also cause tissue damage cannot be ruled out." (p. 136) The WDMET data includes a case of a lung contusion resulting from a hit to the shoulder. The caption to Figure 4-40 (p. 149) says, "The pulmonary injury may be the result of a stress wave." They describe the possibility that a hit to a soldier's trapezius muscle caused temporary paralysis due to "the stress wave passing through the soldier's neck indirectly [causing] cervical cord dysfunction." (p. 155)
In addition to stress waves, Bellamy and Zajtchuck describe shear waves as a possible mechanism of indirect injuries in the WDMET data. They estimate that 10% of bone fractures in the data may be the result of indirect injuries, that is, bones fractured by the bullet passing close to the bone without a direct impact. A Chinese experiment is cited which provides a formula estimating how pressure magnitude decreases with distance. Together with the difference between strength of human bones and strength of the animal bones in the Chinese experiment, Bellamy and Zajtchuck use this formula to estimate that assault rifle rounds "passing within a centimeter of a long bone might very well be capable of causing an indirect fracture." (p. 153) Bellamy and Zajtchuck suggest the fracture in Figures 4-46 and 4-47 is likely an indirect fracture of this type. Damage due to shear waves extends to even greater distances in abdominal injuries in the WDMET data. Bellamy and Zajtchuck write, "The abdomen is one body region in which damage from indirect effects may be common." (p. 150) Injuries to the liver and bowel shown in Figures 4-42 and 4-43 are described, "The damage shown in these examples extends far beyond the tissue that is likely to direct contact with the projectile." (p. 150)
In addition to providing examples from the WDMET data for indirect injury due to propagating shear and stress waves, Bellamy and Zajtchuck expresses an openness to the idea of pressure transients propagating via blood vessels can cause indirect injuries. "For example, pressure transients arising from an abdominal gunshot wound might propagate through the vena cavae and jugular venous system into the cranial cavity and cause a precipitous rise in intracranial pressure there, with attendant transient neurological dysfunction." (p. 154) However, no examples of this injury mechanism are presented from the WDMET data. However, the authors suggest the need for additional studies writing, "Clinical and experimental data need to be gathered before such indirect injuries can be confirmed." Distant injuries of this nature were later confirmed in the experimental data of Swedish and Chinese researchers, in the clinical findings of Krajsa and in autopsy findings from Iraq.YS Selman et al., Medico-legal Study of Shockwave Damage by High Velocity Missiles in Firearm Injuries, Fac Med Baghdad 2011; Vol. 53, No. 4 https://www.academia.edu/2087375/Medico-legal_Study_of_Shockwave_Damage_by_High_Velocity_Missiles_in_Firearm_Injuries
Autopsy findings Proponents of the concept point to human autopsy results demonstrating brain hemorrhaging from fatal hits to the chest, including cases with handgun bullets.Krajsa, J. Příčiny vzniku perikapilárních hemoragií v mozku při střelných poraněních (Causes of pericapillar brain haemorrhages accompanying gunshot wounds), Institute of Forensic Medicine, Faculty of Medicine, Masaryk University, Brno, Czech Republic, 2009. Thirty-three cases of fatal penetrating chest wounds by a single bullet were selected from a much larger set by excluding all other traumatic factors, including past history.
An 8-month study in Iraq performed in 2010 and published in 2011 reports on autopsies of 30 gunshot victims struck with high-velocity (greater than 2500 fps) rifle bullets. The authors determined that the lungs and chest are the most susceptible to distant wounding, followed by the abdomen. The study noted that the "sample size was so small [too small] to reach the level of statistical significance". Nevertheless, the authors conclude:
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 .