Severe, transient pulmonary ventilation-perfusion mismatch in the lung after porcine high velocity projectile behind armor blunt trauma.

Background: 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. Although there is not a high incidence of high energy BABT, the understanding of the mechanisms is still low, in relation to what is needed for safety threshold levels. BABT is also useful as a model for blunt thoracic trauma, with a compressive speed between traffic accidents and blast caused by explosives. High velocity projectile BABT causes severe hypoxia. The mechanisms are not fully known. We investigated the acute pulmonary consequences in the individual lungs, and the effects of alveolar recruitment.

Methods: 12 swine (mean weight 62.5 kg) were randomized to groups BABT by 7.62 × 51 mm NATO-type bullets (mean velocity 803 m/s) to a military grade ceramic plate armor (n = 7) or control (n = 5). Modified double lumen tracheal tubes provided respiratory dynamics in the lungs separately/intermittently for two hours, with alveolar recruitment after one hour.

Results: Venous admixture increased 5 min after BABT (p < .05) and correlated with increased cardiac output. Static compliance decreased 5 minutes after BABT (p < .05) and further by recruitment (p < .005). Physiological dead space decreased 5 minutes after BABT (p < .01) and further by recruitment (p < .01), while not in the contralateral lung. V'A/Q' decreased 5 minutes after BABT (p < .05), also shown in phase III volumetric capnography (p < .05). Most effects regressed after one hour.

Conclusions: High velocity projectile BABT caused hypoxia by a severe and transient decrease in V'A/Q' to <1 and increased venous admixture in the exposed lung. Alveolar recruitment was hemodynamically and respiratory tolerable and increased V'A/Q'. Body armor development should aim at ameliorating severe pulmonary consequences from high projectile velocities which also needs to include further understanding of how primary and secondary effects are distributed between the lungs.