ABSTRACT
The endothelium is a complex, dynamic tissue that regulates multiple vascular wall processes, including smooth muscle tone, thrombogenesis, and angiogenesis, and provides a semiselective cellular barrier between the intravascular and extravascular fluid compartments. Given the vast surface area of the pulmonary microcirculation and the intimate association of the microvasculature with gas-exchanging alveolar elements, the integrity of the vascular barrier is a key consideration in lung homeostasis. Indeed, in pathological lung inflammatory states, the pulmonary endothelial barrier endures significant disruption leading to profound leakage of fluid and macromolecules into the lung interstitium, ultimately resulting in alveolar flooding when alveolar fluid clearance mechanisms are overwhelmed. The consequence of this imbalance in lung fluid homeostasis is clinically manifested as high-permeability, protein-rich pulmonary edema producing the characteristic physiological derangement of severe hypoxemia and reduced lung compliance observed in acute lung injury (ALI).
