Lung inflation: can you get too much of a good thing?

Ventilator-induced lung injury is characterized by edema with and without increases in alveolar epithelial permeability. Thus, we hypothesized that Na/sup +/-K/sup +/-ATPase (Na-pump) activity and epithelial barrier properties are both affected by increasing stretch magnitude. Measurements of Na-pump activity and tight junction permeability demonstrate that Na transport increases with cyclic stretch amplitude, but permeability is compromised only at high levels of cyclic stretch. These results support in vivo data that demonstrate impairment of alveolar fluid clearance and barrier function with large tidal volumes.