Strain-induced pulmonary interstitial emphysema: Exploring trauma-associated injury mechanisms

The present study examines the effects of direct blunt impact trauma on deformation, strain, and subsequent mechanical tissue damage within fresh, inflated, ex vivo porcine lungs. As a result of the applied impact, adjacent segmental bronchi can either converge or diverge depending on their location relative to the impact site. This motion generates localized tensile and shear strains that exceed those measured at the impact site. Histological analysis of tissue excised from these regions found air-filled cystic lesions characteristic of pulmonary interstitial emphysema (PIE). These lesions were concentrated directly adjacent to perivascular, peribronchial, and interlobular boundaries. While perivascular injury aligns with the classical barotraumatic mechanism of PIE driven by pressure gradients across the perivascular sheath, mechanisms for PIE arising within peribronchial and interlobular connective tissues have not been considered. We propose two hypotheses for trauma-specific mechanisms of PIE initiation that relate the observed strain response to lesion formation within these structures. As adjacent segmental bronchi are driven apart, they may induce abnormal displacement of the sublobes that they supply, generating increased strain across the interlobular connective tissues that bind them together and resulting in emphysematous lesions. Alternatively, if the surrounding tissue is sufficiently stabilized, the bronchi themselves may become displaced within the lobar tissue, concentrating strains at the peribronchial interfaces. These regions appear to be most susceptible to tensile and shear strain damage since they represent junctions between tissues with dissimilar elastic properties.