Demonstration of the significance of pulmonary surfactants at birth

Abstract

A potent non-ionic surface active agent, Tween 20, that presumably would displace the normal pulmonary surfactants, was added to the fetal pulmonary fluid of goats to test its effects on the establishment of air-breathing in the early neonatal period. The newborns that were so-treated developed severe respiratory distress including tachypnea, retractions, flaring, hypoxemia, acidemia, and hypercapnia. They were unable to resorb pulmonary fluid after birth as large quantities of this fluid, which contained the normal phospholipid surfactants, flowed out of the airways during life. Morphological examinations demonstrated that (1) a normal alveolar lining layer was not formed, (2) Type I epithelial cells were detached from the basement membranes, and (3) there was significant collapse of the alveoli. The surface tension of the affected lungs was abnormal. These studies support the concept that the pulmonary phospholipid surfactants are essential for normal transition at birth. In their effective absence pulmonary fluid résorption is compromised, alveoli tend to collapse, and a picture analogous to respiratory distress syndrome ensues.