Since the actual site of thoracic load is not a fully controlled factor in an automobile crash, the significance of variations in the location of a thoracic impact seems to warrant clarification as a potential factor influencing biomechanical responses and resultant trauma. In particular, closed-chest trauma to intrathoracic organs and vessels frequently results in a "life-threatening" experience. Various clinical investigation teams associate ruptures or tears of major thoracic vessels as a primary cause of death in 20 to 40% of automobile accident fatalities. The thoracic aorta is the most significant anatomical region of serious vascular injury. Certainly an understanding of the mechanisms of aortic trauma initiation is fundamental to improving occupant protection. Arteriosclerosis is an additional confounding factor, which is frequently observed at autopsy, and has been suspected of predisposing the aorta to injury.

Pertinent literature and accident statistics are reviewed to establish a field-relevant framework for an experimental traumatology study. Fiftyeight anesthetized rabbits, eight with hyperlipemia induced atherosclerosis, were exposed to blunt loadings of the thorax at various locations. The site of sternal impact was found to be a significant factor influencing the occurrence of serious intrathoracic injuries, such as aortic trauma. Midsagittal impacts centered above the midsternum produced frequent aortic, major vascular, and pulmonary injuries with minimal concomitant rib fractures, while impacts below midsternum resulted in diffuse liver lacerations and more extensive skeletal damage. Interestingly, intra-aortic overpressures were highest for impacts below midsternum, thus reducing the significance of this parameter as a dominant mechanism of aortic trauma. In a pilot study, match-tested atherosclerotic animals developed higher aortic overpressures and were more vulnerable to vascular and liver injuries.