Impactor Displacement as a Predictor of Thoraco-Abdominal Organ Injury: Comparison of Isolated Organ to Whole Body Tests.

Purpose: Body armor is used to protect the wearer from penetrating injuries. However, when the armor defeats the projectile, it deforms at high rates into the wearer, referred to as back face deformation (BFD). This deformation can cause a variety of superficial and internal injuries and consequently should be considered when designing body armor. However, current design standards do not adequately consider the effects of BFD, and new data are necessary to inform future design thresholds for BFD. The objective of this study was to develop blunt impact injury risk curves for in vitro thoraco-abdominal organs and determine their applicability in predicting in situ BABT injuries.

Methods: In vitro tests Healthy isolated liver and heart specimens were perfused and placed on a bed of gelatin underneath a drop tower and impacted with a 3-cm hemisphere impactor. Each organ was exposed to an incremental loading protocol, wherein initial displacement of penetration was 2 mm, and increased by 2 mm for each subsequent impact on the organ. Injury was defined as the presence of laceration. Injury probability curves were developed using a generalized mixed linear model (proc GENMOD). Univariate models were analyzed for predictive variables, including peak displacement, percent compression, and peak force. In situ tests An intact postmortem human subject (PMHS) was instrumented and subsequently impacted with an impactor that had a profile representative of BFD and a velocity of 65 m/s. One impact was aimed at the heart and one impact was aimed at the liver.

Results: The final predictive models for isolated organ injuries demonstrated 50% probability of injury for impact displacement of 12.4 mm (95% CI [10.1 mm, 17.6 mm]) and 13.8 mm (95% CI [11.5 mm, 16.8 mm]) for the liver and heart, respectively. During the PMHS tests, total impactor displacement into the PMHS was 45.8 mm and 59.2 mm for the impacts aimed at the liver and heat, respectively. Post-rib fracture impactor displacement did correlate to the isolated organ risk curves, equating to an 88% and 86% of liver and heart injury risk, respectively. Despite high risk of injury for both organs, only the liver was lacerated, suggesting that isolated organ risk curves do not fully translate to in situ testing.

Conclusion: These experimental tests and developed risk curves can be used as validation and injury risk estimates for future isolated organ and whole body computational models. Simulated BFD impacts with PMHS tests highlight the complexity of BABT injury mechanisms and shows the significant anisotropy of the thoraco-abdominal region that should be considered when developing future protective equipment.