Pulmonary hypoxia and venous admixture correlate linearly to the kinetic energy from porcine high velocity projectile behind armor blunt trauma.

Abstract

Purpose. Behind armor blunt trauma (BABT) is a non-penetrating injury caused by the rapid deformation of body armor, by a projectile, which may in extreme circumstances cause death. The understanding of the mechanisms is still low, in relation to what is needed for safety threshold levels. High velocity projectile BABT causes immediate and severe hypoxia by increased venous admixture (Q's/Q't), but it is not known whether the level of hypoxia correlates to the kinetic energy (E_k) of the projectile.Materials and Methods. We constructed a 65 mm BABT-simulator to measure the E_k absorbed by the thorax. The simulator was validated to 7.62 mm high velocity BABT (swine with removed organs) for 7.62 mm (n = 7) and 65 mm (n = 12). Physiological measurements during 60 minutes were performed in 40 anesthetized swine in groups control (n = 9), 7.62 mm (n = 7), 65 mm weight variation (n = 24), 65 mm speed variation (n = 12, included in the weight variation group). New calculations were done for a previously studied group of 7.62 mm with backing (n = 9).Results. 65 mm BABT simulation and 7.62 mm BABT had similar back-face signatures (24 mm), and maximum thoracic impression speed (24-34 m/s). Back-face signatures correlated linearly to E_k (R²=0.20). Rib fractures had a 50% likelihood at back-face signature 23.0 mm (95% CI 18.5 to 29.0 mm, area under ROC curve 0.93). E_k correlated linearly to pO₂ (R²=0.34, p = 0.0026) and venous admixture (R²=0.37, p = 0.0046). The extrapolated E_k at 5 minutes for pO₂=0 kPa was 587 J and for venous admixture = 100% 574 J.Conclusions. Hypoxia and venous admixture correlated linearly to E_k, allowing for a calculated predicted lethal E_k to ≥574 J, which should be verified in survival studies. Lethality predictions from lung physiology is an alternative to clay impressions and may facilitate the development of ballistic safety equipment and new BABT safety criteria.Supplemental data for this article is available online at https://doi.org/10.1080/01902148.2021.1950869 .