Deceleration energy and change in velocity on impact: key factors in fatal versus potentially survivable motor vehicle crash (mvc) aortic injuries (AI): the role of associated injuries as determinants of outcome.
OBJECTIVE
To examine the difference in force mechanisms between fatal and potentially survivable MVC aortic injuries (AI) compared to non-AI severe thoracic injuries (ST).


METHODS
Of 324 autopsied MVC driver or front seat passenger fatalities (1997-2000), there were 43 fatal AI (36 scene deaths, 7 hospital deaths) and 5 additional AI survivors.


RESULTS
Of the 48 AI, there was only a 42% survival for those reaching hospital alive. 80% of AI survivors had isthmus lesions and all had no or minimal brain injury (GCS >= 13), no cardiac injury and only 20% ribs 1-4 fx or shock; of AI non-survivors reaching hospital alive, 67% had GCS <= 12, 50% cardiac injury, 83% ribs 1-4 fx and 83% shock; AI scene deaths had 78% severe brain injury, 56% cardiac injury, 69% lung injury and 78% ribs 1-4 fx. Quantifying forces in AI scene mortality: the Instantaneous Velocity on Impact of the subject vehicle (delta V1) and the Impact Energy Dissipated (IE) on the subject vehicle (V1) in joules demonstrated a linear regression in fatal car MVC AIs: Energy dissipated (joules) = -56.65 x (delta V1)(2) + 15972 x delta V1 - 454661, r(2) = 0.83. However, for 27 patients with non-AI but severe thoracic (ST) injury (AIS>=3), the relationship of IE to delta V1 had a linear regression of Energy dissipated (joules) = -5.0787 x (delta V1)(2) + 4282.1 x delta V1 - 57182 1, r(2) = 0.84, with the slope difference between the regression for AI scene deaths and that of ST and AI survivors being significant (p<0.05). Based on these relationships, a Critical Zone limited by MVC Impact Energy level of 336000 joules and a delta V1 of 64 kph appears to be the limit of potential survivability in MVCs producing aortic injuries. All AI above these thresholds died. In contrast, ST had greater use of seatbelts (AI 10% vs all ST 60%) and airbags (AI 50% vs all ST 72%), and an 83% survival.


CONCLUSIONS
The data suggest different mechanisms of force delivery and injury patterns in fatal vs potentially survivable AI, and vs ST MVCs. They suggest that an approach to improving vehicle safety measures for AI may involve better safety devices and mechanisms for reducing that fraction of Impact Energy dissipated on V1 for a given delta V1 which is focused on the upper portion of the subject's thoracic cage between the levels of ribs1-8.
D000054:Acceleration; D000063:Accidents, Traffic; D001011:Aorta / Q000293:injuries*; D001696:Biomechanical Phenomena; D006801:Humans; D009104:Multiple Trauma / Q000401:mortality; D015996:Survival Rate; D013898:Thoracic Injuries / Q000401:mortality* / Q000503:physiopathology