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.

High frequency oscillatory ventilation versus conventional ventilation in a newborn piglet model with acute lung injury.

BACKGROUND: High frequency oscillatory ventilation (HFOV) is considered a protective strategy for human lungs. This study was designed to define microscopic structural features of lung injury following HFOV with a high lung volume strategy in newborn piglets with acute lung injury. METHODS: After acute lung injury with saline lavage, newborn piglets were randomly assigned to 5 study groups (6 in each group): control (no mechanical ventilation), conventional mechanical ventilation for 24 hours, conventional ventilation for 48 hours, HFOV for 24 hours, and HFOV for 48 hours. The right upper lung tissue was divided into the gravitation-dependent and gravitation-nondependent regions after the completion of mechanical ventilation. Under light microscopy, the numbers of polymorphonuclear leukocytes (PMNLs), alveolar macrophages, red blood cells, and hyaline membrane/alveolar edema were assessed in all lung tissues. Oxygenation index was continuously monitored. RESULTS: Our results showed that the degree of histopathologic lung damage in the gravitation-dependent region was greater than that in the gravitation-nondependent region. Compared with the control group, PMNLs, red blood cells and hyaline membrane/alveolar edemas were significantly increased and alveolar macrophages were significantly decreased in lung tissues of conventional ventilation and HFOV piglets. In HFOV with high lung volume strategy piglets, lung tissues had significantly fewer PMNLs, red blood cells, and hyaline membrane/alveolar edemas, and oxygenation was improved significantly, compared to those of the conventional ventilation piglets. CONCLUSIONS: Histopathologic lung damage in newborn piglets with lung injury was more severe in the gravitation-dependent region than in the gravitation-nondependent region. HFOV with high lung volume strategy reduced pulmonary PMNL infiltration, hemorrhage, alveolar edema, and hyaline membrane formation with improved oxygenation.