NASS and Miami Trauma Center data were analyzed to determine the crash environments that produce aortic injuries in lower severity side impacts. Crash tests were analyzed to determine the injury producing acceleration and intrusion environments. Cadaver tests were conducted using high speed X-ray to examine aortic displacements in response to impacts. Biaxial tensile tests of aortic tissue were conducted to determine their dynamic response to loading. FEM and MADYMO models were run to determine the response of the vehicle structure, the human and the aorta when exposed to injury producing environments.

For the seriously or fatally injured population in the William Lehman Injury Research Center (WLIRC) database who were exposed to side impacts, 24% had aortic injuries. By contrast, the injury rate in NASS was about 5%. In WLIRC data, 60% of the aortic injuries occurred at crash severities below 30 mph delta-V. In NASS, 28% occurred at the lower crash severity.

Crash factors in lower severity near-side crashes that influence aortic injury risk include the extent of intrusion, the occupant age, and a D or Y vehicle damage pattern. The best predictor of aortic injury risk, based on currently available cadaver tests utilizes a combination of spinal z acceleration and chest viscous criterion. Based on this metric, the IIHS test condition produced a higher risk of aortic injury than the side NCAP or the side Y-NCAP tests.

Testing of aortic tissue found a general weakness in tension. The inner layer of aortic tissue was found weaker during tension tests of the tissue and initialized tearing under yield tensile loading to the tissue. Rupture of the inner layer may not produce physiological changes immediately but sudden death can result should all three layers rupture. Death caused by delayed rupture of all layers occurred for 60% of the WLIRC patients with side impact induced aortic injuries who survived more than one hour. This result suggests that a large fraction of those with aortic injury produced in low severity side impacts could be treated successfully if diagnosed in time.