Interrelationship of Velocity and Chest Compression in Blunt Thoracic Impact to Swine 811016

As part of a continuing study of thoracic injury resulting from blunt frontal loading, the interrelationship of velocity and chest compression was investigated in a series of animal experiments. Anesthetized male swine were suspended in their natural posture and subjected to midsternal, ventrodorsad impact. Twelve animals were struck at a velocity of 14.5 ± 0.9 m/s and experienced a controlled thoracic compression of either 15, 19, or 24%. Six others were impacted at 9.7 ± 1.3 m/s with a greater mean compression of 27%.

For the 14.5 m/s exposures the severity of trauma increased with increasing compression, ranging from minor to fatal. Injuries included skeletal fractures, pulmonary contusions, and cardiovascular ruptures leading to tamponade and hemothorax. Serious cardiac arrhythmias also occurred, including one case of lethal ventricular fibrillation. The 9.7 m/s exposures produced mainly pulmonary contusion, ranging in severity from moderate to critical. Cardiac arrhythmias occurred but were typically minor. In contrast to the lower compression impacts at 14.5 m/s, there were no rib fractures or cardiovascular ruptures. In general, peak sternal acceleration and applied force correlated with impact velocity but not with normalized compression; and spinal acceleration did not correlate with any parameter.

Overall, the high velocity exposures, produced higher mechanical responses, more severe gross trauma and more serious cardiac arrhythmias despite lower compression levels. The results of this study while reconfirming normalized compression as one correlate of injury, emphasize the importance of loading velocity in determining the overall severity of blunt thoracic impact.