Influence of impact velocity on the severity of nonpenetrating hepatic injury.

The effect on nonpenetrating hepatic injury of varying impact velocity was investigated in a series of abdominal impact experiments with rabbits. In these tests, a constant level of 16% anterposterior compression was produced by a flat aluminum disc driven by a pneumatic impactor at velocities of 5 to 20 m/s to investigate an impulsive as opposed to a crushing mechanism of injury. Laceration of the liver regularly occurred for impact velocity and available energy greater than 12 m/s and 9.1 joules, respectively (p less than 0.01). In addition, a gradation of hepatic injury, probably caused by local strain energy density in the soft tissue, was observed through the range of impact velocity, i.e., minor subcapsular contusion at low velocity to extensive deep laceration and hemoperitoneum at high velocity. With impact applied only to the abdomen, there were associated thoracic and renal injuries at impact velocities greater than 14 m/s. The Abbreviated Injury Scale (1) was extended for classification and quantification of injury. The peak reactive force, peak esophageal pressure, and impulse transfer increased with impact velocity. It appears that there may be two regions of biomechanical response, one at 12 m/s or below, and one at greater than 12 m/s.