Alveolar air–fluid interface

The alveolar air–fluid interface is the physiological boundary in the lung where the air in the alveoli meets the thin layer of liquid lining the alveolar epithelium (StatPearls, 2023). This interface is the site of vital gas exchange, but it also generates significant surface tension that threatens to collapse the alveoli during expiration. To counteract this, the interface is naturally coated with pulmonary surfactant, a complex of lipids and proteins that reduces surface tension and maintains lung compliance (NIH, 2022). In clinical medicine, this interface is the primary target for exogenous surfactant replacement therapies used to treat Neonatal Respiratory Distress Syndrome (NRDS) and potentially Acute Respiratory Distress Syndrome (ARDS) (PubMed, 2019). These drugs work by spreading across the interface to restore mechanical stability and improve oxygenation. Beyond its mechanical role, the interface serves as a component of the innate immune system, utilizing surfactant proteins to neutralize pathogens (NCBI, 2021). Dysfunction at this interface, whether through surfactant deficiency or inactivation by inflammatory debris, leads to severe respiratory failure.

Other names

Alveolar air-liquid interfaceAlveolar surfacePulmonary air-liquid interfaceAlveolar lining layer

Reduction of surface tension at the air-liquid interface to prevent alveolar collapse and improve gas exchange.