How many people are injured and killed as a result of aging? Frailty, fragility, and the elderly risk-exposure tradeoff assessed via a risk saturation model

Center for Applied Biomechanics, University of Virginia, U.S.A.
Annals of advances in automotive medicine 01/2009; 53:41-50.
Source: PubMed

ABSTRACT Crash protection for an aging population is one of the primary drivers of contemporary passive safety research, yet estimates of the potential benefit of age-optimized systems have not been reported. This study estimates the number killed and injured in traffic crashes due to the age-related reduction in tolerance to loading. A risk-saturation model is developed and calibrated using 2000-2007 data for the age distribution of crash-involved adult occupants and drivers and the number of those injured and killed in 2006. Nonlinear functions describing the relationships between age and risk, adjusted for several confounders are developed using 10 years of NASS-CDS data and considered along with published risk functions for both mortality and injury. The numbers killed and injured as a result of age-related fragility and frailty are determined by setting the risk at all ages equal to the risk at age 20 (i.e., risk is assumed to "saturate" at age 20). The analysis shows that risk saturation at age 20 corresponds to 7,805-14,939 fewer driver deaths and 10,989-21,132 fewer deaths to all occupants. Furthermore, 1.13-1.32 million fewer occupants would be injured (0.80-0.93 million fewer drivers) per year. In other words, that number of deaths and injuries can be attributed to age-related reductions in loading tolerance. As the age of risk saturation increases, the benefit decreases, but remains substantial even in the age regime typically considered "elderly". For example, risk saturation at age 60 corresponds to 1,011-3,577 fewer deaths and 73,537-179,396 fewer injured occupants per year. The benefit of risk saturation is nearly log-linear up to approximately age 70, but drops off quickly thereafter due to the low exposures in the oldest age range. The key contribution of this study is the quantification of deaths and injuries that can be attributed to aging and the development of functions describing the relationship between age of risk saturation and the number of deaths and injuries averted.

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Available from: Francisco J Lopez-Valdes, Jan 07, 2014
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    • "Zhou et al. (1996) showed a reduction of injury tolerance in the elderly compared to the young of 20% in blunt impact and 70% in seatbelt frontal impacts. Using a risk saturation model, Kent et al. (2009) predicted that 1.32 million occupants each year were likely injured because they were older than the age of 20. Stitzel et al. (2010) reported an age threshold of 55 maximally discriminated the mortality rate from thoracic injuries. "
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    ABSTRACT: Pulmonary contusion (PC) is the most common injury following blunt thoracic trauma with an associated mortality of 10% to 20%. The purpose of this study is to determine how crash parameters correlate to the volume of pulmonary contusion. The Crash Injury Research Engineering and Network (CIREN) database was queried to extract data on all occupants sustaining PC in a near-side crash. The selected CIREN data included all completed cases from 2005 through 2010. Cases involving a roll-over or without a thorax CT uploaded to the database were excluded. After all cases had been examined the study had 64 occupants with varying volumes of PC. Specific crash characteristics compiled included change in velocity due to the impact, energy, occupant characteristics, side airbag deployment, and crush profile measurements. Crush metrics quantifying the area of the crush profile and the location of the crush relative to the occupant were calculated. The thoracic CT scans from these cases were downloaded and segmented to determine the percent volume of high attenuation lung and PC as compared to the total volume of the lung. The results of the general linear model analysis suggest that maximum crush was the best predictor of high attenuation lung and lung location best predicted PC. An analysis of NASS and CIREN demonstrated that crashes with PC tended to have crash parameters that indicated higher severity. These correlations can be used in the future to develop an injury criterion for PC using finite element metrics.
    Annals of advances in automotive medicine 01/2011; 55:217-30.
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    ABSTRACT: Pedestrian disability and fatality as a consequence of car crashes is a large global health problem. To introduce maximally effective car-based countermeasures it is important to understand which injuries are most common and from which car parts they originate. It is also important to focus on the most severe injuries resulting in disability or death. The aim of this thesis was therefore to determine priorities for and evaluate the potential of car-mounted safety systems designed to mitigate severe upper-body injuries (including disability and fatality) of pedestrians in car crashes. Accident data was collected from two areas; severe (AIS3+) accidents in Dresden/Hannover in Germany and fatal accidents in Sweden. For the surviving pedestrians an estimate of long-term injury was performed using accident dataderived risk matrices of permanent injury. Results showed that 31% would sustain a permanent impairment of some kind and 5% would sustain a more severe impairment, where the head was most susceptible to severe impairment. The car front frequently caused leg injuries, which is addressed in current regulations. However, current legal tests do not address the most common upper-body injury source, the windshield, which was found to be the dominating cause of head injuries. Chest injuries, frequently caused by both the hood and windshield areas in the severe and fatal crashes in this thesis, are also unaddressed in legal tests. Children are most commonly head-injured from the hood area, which is addressed in current regulations. Further, regulations do not fully consider brain injury with the current head test methods. Therefore, in this thesis focus was on upper-body injury/source combinations not addressed in the regulations, that is, the head-to-windshield area and chest-to-hood/windshield areas, and the evaluation of brain injury in hood and windshield impacts. Experimental head-to-hood component tests with succeeding brain simulations were performed to evaluate the influence of the under-hood distance and head impact speed. A hood designed to minimize linear head loading to acceptable injury levels was also found effective in reducing combined linear/rotational brain loading. Further, in full-scale car-to-pedestrian finite element simulations both a braking and deployable system alone proved efficient in reducing head and chest loading, and an integrated countermeasure of combining the two systems proved to increase the protection potential. While current pedestrian countermeasures focus on the head-to-hood impact, this thesis recommends extending countermeasures to the lower part of the windshield and the A-pillars, and adding brain and chest injury assessment for both hood and windshield areas to effectively minimize disabling and fatal injuries. Since head impact location and head impact speed is dependent on the car design, the introduction of full-scale simulations in the test methods to determine impact conditions for experimental component tests is recommended. If the deployable countermeasures are combined with autonomous braking in an integrated system the most effective system is achieved. Auto-brake systems should, in high speed impacts, aim to reduce speeds to where the secondary countermeasures can effectively mitigate injury. Future pedestrian test methods should therefore evaluate how primary and secondary countermeasures interact.
    04/2011, Degree: PhD, Supervisor: Anders Kullgren
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