Ultrastructural study of alveolar epithelial type II cells by high-frequency oscillatory ventilation.

Alveolar epithelial type II cells (AECIIs) containing lamellar bodies (LBs) are alveolar epithelial stem cells that have important functions in the repair of lung structure and function after lung injury. The ultrastructural changes in AECIIs after high-frequency oscillatory ventilation (HFOV) with a high lung volume strategy or conventional ventilation were evaluated in a newborn piglet model with acute lung injury (ALI). After ALI with saline lavage, newborn piglets were randomly assigned into five study groups (three piglets in each group), namely, control (no mechanical ventilation), conventional ventilation for 24 h, conventional ventilation for 48 h, HFOV for 24 h, and HFOV for 48 h. The lower tissues of the right lung were obtained to observe the AECII ultrastructure. AECIIs with reduced numbers of microvilli, decreased LBs electron density, and vacuole-like LBs deformity were commonly observed in all five groups. Compared with conventional ventilation groups, the decrease in numbers of microvilli and LBs electron density, as well as LBs with vacuole-like appearance and polymorphic deformity, was less severe in HFOV with high lung volume strategy groups. AECIIs were injured during mechanical ventilation. HFOV with a high lung volume strategy resulted in less AECII damage than conventional ventilation.