Lung injury risk curves for behind armor blunt trauma using the abbreviated injury scoring system

Studies conducted more than 50 years ago have formed the basis for the current Behind Armor Blunt Trauma (BABT) 44 mm deflection criterion. The legacy criterion is independent of thoracoabdominal region. Thoracoabdominal components vary in anatomy, structure, function, material properties, and injury responses. A single deflection value metric cannot represent the same risk/tolerance to all organs. The objective of the present study was to develop lung injury risk curves using the viscous criterion. A custom indenter delivered impacts to anesthetized swine (velocities 13-64 m/s). After monitoring the animal for 6-h post impact, they were euthanized, and necropsies were done. Injuries were scored using the Abbreviated Injury Scale (AIS). Using parametric survival analysis and the Akaike Information Criterion, the optimal distribution function was identified, and risk curves were developed for AIS2+ and AIS3+ injuries. Nineteen animals sustained AIS 2+, 12 sustained AIS 3+, and five had no injuries. For AIS2+ injuries, the mean viscous criterion at 10, 25, and 50% risk levels were 1.6 m/s (confidence intervals: 1.1-2.6 m/s), 2.5 m/s (1.8-3.4 m/s), and 3.7 m/s (2.9-4.5 m/s). For AIS 3+ injuries, the viscous criterion at 10, 25, and 50% risk levels were 2.9 m/s (2.1-3.9 m/s), 3.8 m/s (3.0-4.7 m/s), and 4.7 m/s (4.0-5.5 m/s). The qualities of the risk curves were good to fair at these probability levels for both injury levels. The present injury risk curves and confidence intervals form a set of preliminary data for advancing safety in combat environments for BABT applications.