The pathophysiology of neonatal
meconium aspiration syndrome (MAS) is related to mechanical obstruction of the airways and to chemical
pneumonitis. It has also been suggested that meconium causes inhibition of
surfactant function. To assess its in vitro effect on
surfactant function and morphology, we used a pulsating bubble surfactometer to measure the dynamic surface tension of meconium-
surfactant mixtures and observed their electron microscopic structures. The mixtures were prepared by adding serial dilutions of human meconium to various concentrations of
Surfactant-TA (Surfacten) that had been used for the prevention and treatment of
neonatal respiratory distress syndrome. Inhibition of the surface tension-lowering properties of
Surfactant-TA was caused by the addition of meconium and depended on the concentration of the
surfactant; the inhibition could be overcome by increasing the
surfactant concentration. When meconium was added to
Surfactant-TA, the characteristic ultrastructural features of the latter, the loosely stacked layers, changed to a spherical lamellar structure and folded linear structures. These results suggest that meconium inhibits
surfactant function by altering
surfactant morphology. Our morphologic and functional findings support the new concept that
surfactant inhibition may play a role in the pathophysiology of MAS.