Assessing the effect of chest orientation on pulmonary pressure under free field shock waves: a numerical analysis

Purpose: This study explores how thoracic orientation affects lung pressure and injury outcomes from shock waves, building on earlier research that suggested human posture impacts injury severity. Methods: A layered finite element model of the chest was constructed based on the Chinese Visual Human Dataset (CVH), including the rib and intercostal muscle layers. The dynamic response of the chest under 12 different angle-oriented shock waves under incident pressures of 200 kPa and 500 kPa was calculated. The correspondence between lung pressure at various angles, chest wall motion velocity and lung stress, and differences in pressure/stress of lung tissue behind ribs and intercostal muscle were analyzed. Results: The dynamic response of the chest can be roughly divided into four processes. High local intrapulmonary pressure areas were primarily in the anterior lobe margin and the lung's central region. A 500 kPa incident wave at 0° could cause slight lung injury, whereas at 240°, the pressure was non-harmful. Lung tissue pressure and stress induced by chest wall movement were significantly higher behind the intercostal muscles than behind the ribs, with a difference of about 2-3 times. Conclusions: This layered model provides a cost-effective tool for large-scale shock wave impact simulations on the chest. Chest wall movement velocity strongly correlates with lung stress distribution. The significant density and sound velocity differences among ribs, intercostal muscles and lungs cause an acoustic impedance mismatch, leading to "striped bleeding" marks in post-impact lungs. This research enhances understanding of chest and lung injury mechanisms and informs the development of protective measures.