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


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.

    • "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: This study developed a parametric methodology to robustly predict occupant injuries sustained in real-world crashes using a finite element (FE) human body model (HBM). One hundred and twenty near-side impact motor vehicle crashes were simulated over a range of parameters using a Toyota RAV4 (bullet vehicle), Ford Taurus (struck vehicle) FE models and a validated human body model (HBM) Total HUman Model for Safety (THUMS). Three bullet vehicle crash parameters (speed, location and angle) and two occupant parameters (seat position and age) were varied using a Latin hypercube design of Experiments. Four injury metrics (head injury criterion, half deflection, thoracic trauma index and pelvic force) were used to calculate injury risk. Rib fracture prediction and lung strain metrics were also analysed. As hypothesized, bullet speed had the greatest effect on each injury measure. Injury risk was reduced when bullet location was further from the B-pillar or when the bullet angle was more oblique. Age had strong correlation to rib fractures frequency and lung strain severity. The injuries from a real-world crash were predicted using two different methods by (1) subsampling the injury predictors from the 12 best crush profile matching simulations and (2) using regression models. Both injury prediction methods successfully predicted the case occupant's low risk for pelvic injury, high risk for thoracic injury, rib fractures and high lung strains with tight confidence intervals. This parametric methodology was successfully used to explore crash parameter interactions and to robustly predict real-world injuries.
    No preview · Article · Jul 2015 · Computer Methods in Biomechanics and Biomedical Engineering
    • "This shows that there is a huge difference in comparing fatalities and injuries leading to impairment. Previous studies have shown that older occupants differ in several aspects from younger and middle-aged occupants in terms of both crash exposure and outcomes (Kent et al. 2009;Li et al. 2003;Meuleners et al. 2006). Crash severity, together with occupant characteristics such as age, have been identified as important factors to predict injury outcome.Stigson et al. (2012)showed injury risk functions in frontal impacts using data from crash pulse recorders. "
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