Development of thoracic injury risk functions for the THOR ATD.

The Test Device for Human Occupant Restraint (THOR) 50th percentile male anthropomorphic test device (ATD) aims to improve the ability to predict the risk of chest injury to restrained automobile occupants by measuring dynamic chest deflection at multiple locations. This research aimed to describe the methods for developing a thoracic injury risk function (IRF) using the multi-point chest deflection metrics from the 50th percentile male THOR Metric ATD with the SD-3 shoulder and associating to post-mortem human subjects (PMHS) outcomes that were matched on identical frontal and frontal-oblique impact sled testing conditions. Several deflection metrics were assessed as potential predictor variables for AIS 3+ injury risk, including a combined metric, called PC Score, which was generated from a principal component analysis. A parametric survival analysis (specifically, accelerated failure time (AFT) with Weibull distribution) was assessed in the development of the IRF. Model fit was assessed using various modeling diagnostics, including the area under the receiver operating characteristic curve (AUC). Models based on resultant deflection consistently exhibited improved fit compared to models based on x-axis deflection or chord deflection. Risk functions for the THOR PC Score and Cmax (maximum resultant deflection) were qualitatively equivalent, producing AUCs of 0.857 and 0.861, respectively. Adjusting for the potential confounding effects of age, AFT survival models with Cmax or PC Score as the primary deflection metric resulted in the THOR injury risk models with the best combination of biomechanical appropriateness, potential utility and model fit, and may be recommended as injury predictors.

Incorporation of CPR Data into ATD Chest Impact Response Requirements.

Pediatric and adult ATD's are key tools for the development of motor vehicle crash safety systems. Previous researchers developed size-based scaling methods to adapt blunt chest impact data from adult post-mortem human subjects (PMHS) for pediatric ATD chests design requirements, using skull or femur elastic modulus ratios to estimate the change in whole chest stiffness during maturation. Recently, the mechanics of chest compression during cardiopulmonary resuscitation (CPR) of patients spanning the pediatric and elderly ages have been reported. Our objective was to integrate these pediatric and adult chest stiffness data from CPR into the established scaling methods to 1) compare new CPR-based and existing pediatric ATD chest biofidelity response requirements and 2) develop new CPR-based corridors for ages 12 and 20 years, which do not currently exist. Compared to the current 6-year-old ATD corridor, the maximum force of the CPR-based 6-year-old corridor was 7% less and the maximum displacement was 8% greater, indicating a softer chest. Compared to the current 10-year-old corridor, the new 10-year-old corridor peak force was 12% higher and the peak displacement was 11% smaller, suggesting a stiffer chest. The 12-year-old corridor developed in this paper was 10% higher in maximum force and 4% lower in maximum displacement compared with the adult 5(th) percentile female (AF05). Finally, the 20-year-old 50(th) percentile male (AM50(20)) corridor was 24% higher in maximum force and 19% lower in maximum displacement than 63-year old 50(th) percentile adult male (AM50(63)) corridor, suggesting a stiffer chest. We consider all the new corridors preliminary, as data collection is ongoing for CPR subjects under age 8 years and in the young and middle adult age ranges.