Hydrostatic Shock - Distant Injuries in The WDMET Data

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 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.