[Dynamic surface tension measurements and L/S-ratio in amniotic fluid before birth in comparison with the respiratory compliance of the newborns immediately after parturition (author's transl)].

In 65 pregnant women between 27th and 42nd gestational week amniotic fluid was collected on average of 4,2 hours before birth and its amount of surfactant determined by means of the dynamic surface tension measurement in the Wilhelmy-balance and the L/S-ratio. These values were compared to the respiratory compliance of the newborns after birth. The respiratory compliance was measured by means of the airway occlusion technique. So far the measurement of dynamic surface tension has made it possible to predict the lungmaturity and the incidence of RDS. Our study for the first time describes a quantitative relationship between the surface tension of the amniotic fluid and the surface tension of the lungs in form of the respiratory compliance. The surface tension, measured by the Wilhelmy-balance, was better correlated (r = -0.85) than the L/S-ration (r = 0,58) with the respiratory compliance of the newborns. The surface tension measurement allows therefore a better prediction of the severity of the RDS than the determination of the L/S-ratio. This can be explained by the fact that the surface tension measurement in the amniotic fluid represents the total effect of SAM (Surface active material) while the L/S-ratio represents only about 60% of SAM. On the other hand the L/S-ratio gave a better correlation to the general maturity of the fetus than the surface tension; therefore we consider that the L/S-ratio is partially influenced by the lungmaturity and partially by gestational age of the fetus.