The mammalian lung is stabilized by a specialized material, the
pulmonary surfactant, which acts by reversibly reducing the surface tension at the air-liquid interface of the lung during breathing.
Pulmonary surfactant contains approximately 90%
lipid and 10%
proteins.
Dipalmitoyl phosphatidylcholine, the major
lipid component, appears to be primarily responsible for the ability to reduce surface tension to near 0 dyn/cm (1 dyn = 10 microN). The other components of
pulmonary surfactant promote the adsorption and spreading of this
disaturated lecithin at the air-liquid interface.
Surfactant activity can be accessed by physical and
biological assays. Apparent discrepancies between the results obtained with the Wilhelmy plate surface balance and the pulsating bubble surfactometer have led to the suggestion that separate "
protein-facilitated" (catalytic type) and "
protein-mediated" (chemical type) processes may be involved in adsorption and (or) spreading at the different
surfactant concentrations used with these two techniques. Artificial
surfactants, which mimic the essential properties of the
natural product with the pulsating bubble surfactometer, can be produced with synthetic
lipids. Treatment of prematurely delivered infants suffering from the
neonatal respiratory distress syndrome with
lipid extracts of
pulmonary surfactant leads to a marked improvement in gaseous exchange.