Jacobo Antona-Makoshi

Age-Dependent Factors Affecting Thoracic Response: A Finite Element Study Focused on Japanese Elderly Occupants

Objectives: The ultimate goal of this research is to reduce thoracic injuries due to traffic crashes, especially in the elderly. The specific objective is to develop and validate a full-body finite element model under 2 distinct settings that account for factors relevant for thoracic fragility of elderly: one setting representative of an average size male and one representative of an average size Japanese elderly male. Methods: A new thorax finite element model was developed from medical images of a 71-year-old average Japanese male elderly size (161cm, 60 kg) postmortem human subject (PMHS). The model was validated at component and assembled levels against original series of published test data obtained from the same elderly specimen. The model was completed with extremities and head of a model previously developed. The rib cage and the thoracic flesh materials were assigned age-dependent properties and the model geometry was scaled up to simulate a 50th percentile male. Thereafter, the model was validated against existing biomechanical data for younger and elderly subjects, including hub-to-thorax impacts and frontal impact sled PMHS test data. Finally, a parametric study was conducted with the new models to understand the effect of size and aging factors on thoracic response and risk of rib fractures. Results: The model behaved in agreement with tabletop test experiments in intact, denuded, and eviscerated tissue conditions. In frontal impact sled conditions, the model showed good 3-dimensional head and spine kinematics, as well as rib cage multipoint deflections. When properties representative of an aging person were simulated, both the rib cage deformation and the predicted number of rib fractures increased. The effects of age factors such as rib cortical thickness, mechanical properties, and failure thresholds on the model responses were consistent with the literature. Aged and thereby softened flesh reduced load transfer between ribs; the coupling of the rib cage was reduced. Aged costal cartilage increased the severity of the diagonal belt loading sustained by the lower loaded rib cage. Conclusions: When age-specific parameters were implemented in a finite element (FE) model of the thorax, the rib cage kinematics and thorax injury risk increased. When the effect of size was isolated, 2 factors, in addition to rib material properties, were found to be important: flesh and costal cartilage properties. These 2 were identified to affect rib cage deformation mechanisms and may potentially increase the risk of rib fractures.

Effect of aging on brain injury prediction in rotational head trauma-a parameter study with a rat finite element model

Objective: The aim of this study was to investigate the possible effects of age-related intracranial changes on the potential outcome of diffuse axonal injuries and acute subdural hematoma under rotational head loading. Methods: A simulation-based parametric study was conducted using an updated and validated finite element model of a rat head. The validation included a comparison of predicted brain cortex sliding with respect to the skull. Further, model material properties were modified to account for aging; predicted tissue strains were compared with experimental data in which groups of rats in 2 different lifecycle stages, young adult and mature adult, were subjected to rotational trauma. For the parameter study, 2 age-dependent factors—brain volume and region-specific brain material properties—were implemented into the model. The models young adult and old age were subjected to several injurious and subinjurious sagittal plane rotational acceleration levels. Results: Sequential analysis of the simulated trauma progression indicates that an increase in acute subdural hematoma injury risk indicator occurs at an early stage of the trauma, whereas an increase in diffuse axonal injury risk indicators occurs at a later stage. Tissue stiffening from young adult to mature adult rats produced an increase in strain-based thresholds accompanied by a wider spread of strain distribution toward the rear part of the brain, consistent with rotational trauma experiments with young adult and mature adult rats. Young adult to old age brain tissue softening and brain atrophy resulted in an increase in diffuse axonal injuries and acute subdural hematoma injury risk indicators, respectively. Conclusions: The findings presented in this study suggest that age-specific injury thresholds should be developed to enable the development of superior restraint systems for the elderly. The findings also motivate other further studies on age-dependency of head trauma.

Accident analysis to support the development of strategies for the prevention of brain injuries in car crashes

This study estimated the frequency and risk of Moderate-to-Maximal traumatic brain injuries sustained by occupants in motor vehicle crashes in the US. National Automotive Sampling System - Crashworthiness Data System crashes that occurred in years 2001-2015 with light vehicles produced 2001 or later were incorporated in the study. Crash type, crash severity, car model year, belt usage and occupant age and sex were controlled for in the analysis. The results showed that Moderate concussions account for 79% of all MAISbrain2+ injuries. Belted occupants were at lower risks than unbelted occupants for most brain injury categories, including concussions. After controlling for the effects of age and crash severity, belted female occupants involved in frontal crashes were estimated to be 1.5 times more likely to sustain a concussion than male occupants in similar conditions. Belted elderly occupants were found to be at 10.5 and 8 times higher risks for sub-dural haemorrhages than non-elderly belted occupants in frontal and side crashes, respectively. Adopted occupant protection strategies appear to be insufficient to achieve significant decreases in risk of both life-threatening brain injuries and concussions for all car occupants. Further effort to develop occupant and injury specific strategies for the prevention of brain injuries are needed. This study suggests that these strategies may consider prioritization of life-threatening brain vasculature injuries, particularly in elderly occupants, and concussion injuries, particularly in female occupants.