RESUMEN
OBJECTIVES: Can aortic isthmus disruption occurring in a lateral motor vehicle crash (LMVC) be explained by the Archimedes Lever Hypothesis, where the intrathoracic aorta, super-pressurized by the thoracic impact force, functions as a rigid lever system? The long arm of this lever system is the proximal aorta-aortic arch, the short arm is the aortic isthmus fixed distally at the descending aorta, and the fulcrum is at the great vessels, especially the left subclavian artery. METHODS: The theory was tested by a simulation technique using a computer-based finite element numerical model system. This simulation model included the dynamics of the crashed vehicles, the direction of force impact, and the structure of the thorax and intrathoracic viscera, including the entire intrathoracic aorta. The specific patient whose data were entered into the model was chosen from a study of 34 LMCV aortic injuries (AIs). The model was constrained by patient and vehicle data from this surviving case. RESULTS: Three sequential lateral thoracic levels impacted by the vehicle side structures were selected. At each level, the maximum mean intra-aortic pressure was 50 to 100 ms after impact, the structure dynamics of the actual crash and the resultant vehicle deformation were simulated; only when the lateral impact was induced in a transverse plane including the first 4 ribs at the level of the aortic arch/isthmus system, with intra-aortic pressures from 200 to 500 mm Hg, were AI-compatible stresses and deformations in the aortic wall achieved at the isthmus. CONCLUSIONS: In LMVC AI, the simulation suggests that the aorta functions as an Archimedes Lever System in which the magnified force mediated by the long lever arm produces sufficient strain on the short lever arm to rupture the aorta at the isthmus.
Asunto(s)
Accidentes de Tránsito , Aorta Torácica/lesiones , Rotura de la Aorta/fisiopatología , Biofisica , Simulación por Computador , Accidentes de Tránsito/mortalidad , Adulto , Airbags , Aorta Torácica/fisiopatología , Rotura de la Aorta/mortalidad , Automóviles , Fenómenos Biomecánicos , Ingeniería Biomédica , Fenómenos Biofísicos , Presión Sanguínea/fisiología , Causas de Muerte , Análisis de Elementos Finitos , Mortalidad Hospitalaria , Humanos , Masculino , Persona de Mediana Edad , Modelos Anatómicos , Músculo Liso Vascular/lesiones , Músculo Liso Vascular/fisiopatología , Investigación , Cinturones de SeguridadRESUMEN
OBJECTIVE: To examine the effect of change in velocity (DeltaV) and energy dissipation (IE) on impact, above and below the test levels for Federal MVC Safety Standards, on the incidence of spine fractures (SF), spinal cord injury (SCI)), SF mortality and the associated injury patterns in Frontal (F) and Lateral (L) MVCs. Comparison of 214 patients with SF or SCI with 938 patients who did not have SF or SCI. METHODS: 1152 MVC adult drivers or front-seat passengers (701 F & 451 L) evaluated at 10 Level I CIREN study Trauma Centers together with vehicle and crash scene engineering reconstruction. Patient seat belt (SB) and/or airbag (AB) use correlated with clinical, or autopsy findings. RESULTS: The relationship between DeltaV and IE rose exponentially as DeltaV increased. Of the 1152 patients, all with AIS> or =3 injuries, there were 214 patients with spine fractures of AIS > or =2. In FMVCs there were more SF patients with Cervical SF than in LMVCs (68F versus 64 L) and more Thoracic (35F versus 21L) and Lumbar (39F versus 16L) SF. However, the incidence of spinal cord injury was greatest in the Cervical SF (33%), compared with the Thoracic SF (18%), or Lumbar SF (2%). Most important, in FMVCs 49% of SF, 47% of SCI and 71% of the SF deaths (p < 0.05) occurred at > mean of 47.4 kph. In contrast, in LMVCs 51% of SF, 52% of SCI and 67% of the SF deaths occurred at DeltaV > mean of 35.3 kph. However, 80% of all deaths in SCI occurred in Cervical SF cases, in these 74% also had a brain injury. In contrast, the deaths in Thoracic SF were due to combinations of brain (45%), thorax (95%) or associated pelvic fracture injuries (50%). Airbag (AB), or Seat belt (SB) restraints appeared to protect FMVC SF patients from SCI at lower DeltaV, but 84% of Cervical SCI patients at DeltaV > 47 kph had AB protection and in a few cases the AB appeared responsible for the SCI. In contrast, 82% of Lumbar SF patients had SB, but in FMVCs where jackknifing due to backloading occurred, improper SB positioning may have contributed to the SF. CONCLUSIONS: The implication for SCI in both front seat drivers and passengers in either FMVC or LMVC crashes above their respective DeltaV means is that improved spine fracture protection is necessary at higher DeltaV levels. More effective safety systems to prevent Cervical SCIs should be developed using two-level frontal and side AB & SB+pretensioner devices, which protect against SF at DeltaV both at and 1SD above the FMVC (47 & 72 kph = 30 & 45 mph) and LMVC (35 & 54 kph =22 & 34 mph) means.
Asunto(s)
Aceleración , Accidentes de Tránsito/mortalidad , Traumatismos de la Médula Espinal/mortalidad , Fracturas de la Columna Vertebral/mortalidad , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Airbags/efectos adversos , Airbags/estadística & datos numéricos , Análisis de Varianza , Conducción de Automóvil , Automóviles , Fenómenos Biomecánicos , Femenino , Humanos , Puntaje de Gravedad del Traumatismo , Modelos Lineales , Masculino , Persona de Mediana Edad , New Jersey/epidemiología , Cinturones de Seguridad/efectos adversos , Cinturones de Seguridad/estadística & datos numéricos , Traumatismos de la Médula Espinal/etiología , Fracturas de la Columna Vertebral/etiologíaRESUMEN
OBJECTIVE: To examine the effect of change in velocity (MV) and energy dissipation (IE) on impact, above and below the test levels for federal motor vehicle crash (MVC) safety standards, on the incidence of aortic injury (AI) and its mortality and associated injury patterns in frontal (F) and lateral (L) MVCs. Comparison of 80 AI and 796 non-AI patients of AIS=3. METHODS: Eight hundred seventy-six MVC adult drivers or front-seat passengers (552 F and 324 L) evaluated by 10 Level I CIREN study Trauma Centers together with vehicle and crash scene engineering reconstruction. Patient seatbelt and/or airbag use correlated with clinical or autopsy findings. RESULTS: In AI, 63% of cases were dead at the scene and only 16% survived to leave hospital. The relation between IE dissipated in the MVC and the DeltaV on impact was exponential as DeltaV increased, but the rise in IE for a given DeltaV was greater in LMVC than in FMVC (p <0.05). A more rapid rise in IE/DeltaV occurred above the mean DeltaV of 48 +/- 19.7 kph (30 mph) in FMVC and above the mean DeltaV of 36 +/- 16.2 kph (23 mph) in LMVC. As DeltaV increased above these means, 65% of 46 FMVC aortic injuries (AIs) and 64% of 34 LMVC AIs occurred. In AI patients there was evidence of focusing of the point of IE impact on the upper chest with a higher incidence of rib1-4 fractures than in non-AI (p <0.01) and more brain, heart, lung and spleen injuries (p <0.01) consequent to lower seatbelt use (p <0.01), but LMVC also had more pelvic fx (p <0.05). Airbags + seatbelts in FMVC and seatbelts in LMVC reduced mortality (p <0.05) Comparison of AI incidence in three successive 4-year vehicle model year periods showed a progressive decrease as new safety devices were introduced (p < 0.05). CONCLUSIONS: The implications for AI of the focused IE at the upper chest suggest a probable mechanism for MVC AI with the pressurized aortic arch acting as the long arm of a lever system with the fulcrum at the subclavian artery, producing maximum torsional strain at the short arm of the isthmus where 75% of the AIs occurred. AI mortality is also influenced by the associated injuries. To develop more effective safety systems to prevent AI, MVC safety testing with airbags and seatbelts should be carried out at DeltaVs of 1 SD above means for FMVC and LMVC.
Asunto(s)
Aceleración , Prevención de Accidentes/métodos , Accidentes de Tránsito/mortalidad , Aorta Torácica/lesiones , Traumatismos Torácicos/etiología , Traumatismos Torácicos/mortalidad , Adolescente , Adulto , Distribución por Edad , Anciano , Anciano de 80 o más Años , Conducción de Automóvil , Fenómenos Biomecánicos , Estudios de Cohortes , Femenino , Humanos , Puntaje de Gravedad del Traumatismo , Masculino , Persona de Mediana Edad , Traumatismo Múltiple/mortalidad , Sistema de Registros , Seguridad , Distribución por Sexo , Estrés Mecánico , Análisis de Supervivencia , Traumatismos Torácicos/diagnóstico , Centros TraumatológicosRESUMEN
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. CONCLUSION: 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.