Lung Injury Risk Curves From Behind Armor Blunt Trauma Using a Live Swine Model

From structural, anatomical, and functional perspectives, components of the thoracoabdominal region are heterogeneous and physiologically and functionally different. Although their tolerances to injury are expected to be different, the current Roma Plastilina No. 1 clay penetration criterion for behind armor blunt trauma (BABT) is not specific to the body region. It is important to develop regional injury criteria to ensure its specificity. The objective of the study is to conduct impact tests on the lung region using a live animal model and develop injury risk curves using velocity and deflection metrics via parametric survival analysis.

Live swine tests were conducted after obtaining animal use approvals from the local institution and the U.S. Department of Defense. An indenter simulating backface deformation profiles from a live fire round to human surrogates covered with body armor was used to deliver impact loading to the lung region. The animals were monitored for 6 hours following the initial impact, necropsies were performed, and injuries were categorized as no injury, mild injury (termed as Group A), or severe injury (termed as Group B). Injury risk curves were developed for both groups using parametric survival analysis, and 95% confidence interval (CI) bounds were used to assign the adjectival ratings of good, fair and marginal to determine the quality of injury risk curves.

At the mean risk level, the mean viscous criterion was 3.65 m/s (CI range: 2.85-4.45 m/s) for Group A and 5.72 m/s (CI range: 5.00-6.43 m/s) for Group B injuries. Quality indexes ranged from good to marginal for both groups. The developed mean injury risk curves, along with 95% CI bounds and quality indices, are presented in the body of the manuscript.

This is the first study to develop BABT lung injury criteria from live animal tests by applying impact loading with an indenter that simulated backface deformation profiles from a hard body armor to human surrogates. The developed injury risk curves can be used as preliminary lung tolerance criteria for BABT applications. They may also be used to improve the assessment of current and future body armor and improve Warfighter safety and medical readiness for injuries to the lung region.