Evaluation of two assays of functional surfactant in amniotic fluid: surface-tension lowering ability and the foam stability index test.
We characterize two assays of total amniotic fluid surfactant that are based on function: the surface-tension lowering ability of extracts of amniotic fluid lipid (I) and the foam stability index test (II). I is determined on chloroform extracts of amniotic fluid. II is defined as the highest ethanol volume fraction of an amniotic fluid-ethanol mixture that will permit a stable foam to form after 30 s of vigorous shaking. The relationship of I to disaturated phosphatidylcholine concentrations (after osmium tetroxide treatment of the amniotic fluid lipid extract) is in the expected theoretical form of a hyperbolic function. The relation between values for II and disaturated phosphatidylcholine concentrations showed a consistent bias, suggesting that components other than disaturated phosphatidylcholine contribute to stable foam formation. Phosphatidylclycerol concentrations did not appear to account for this bias. The relation between I to II values suggest that both assays measure total surfactant. I, II, and concentration of disaturated phosphatidyl choline are all excellent indicators of fetal pulmonary maturity. From a practical standpoint, the foam stability index test is the most efficient approach to routine assessment of fetal pulmonary status.
D000653:Amniotic Fluid / Q000032:analysis*; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D010743:Phospholipids / Q000032:analysis*; D011247:Pregnancy; D011296:Prenatal Diagnosis; D011663:Pulmonary Surfactants / Q000032:analysis*; D012127:Respiratory Distress Syndrome, Newborn / Q000175:diagnosis*; D013500:Surface Tension
D010743:Phospholipids; D011663:Pulmonary Surfactants