Lung solute permeability and lung liquid absorption in premature ventilated fetal goats

Abstract

In 21 premature fetal goats ventilated at low tidal volumes, measurements were made of alveolar surfactant activity by bubble stability tests on alveolar liquid, lung epithelium solute permeability using radiolabeled tracer molecules, lung liquid absorption from wet and dry lung weights, effectiveness of lung gas exchange, and lung mechanics. Arterial pO2 and residual gas volume were higher and arterial pCO2 and specific compliance were lower in animals whose bubble stability test was >1:5 on alveolar liquid aspirated following one hr of ventilation. Animals without detectable surfactant in fetal lung liquid before ventilation had transfer of all size tracer solutes between alveolar liquid and blood, whereas those with detectable surfactant did not allow tracers 14 Å or larger in radius to cross the lung epithelium. Lung liquid absorption rate in animals without lung liquid surfactant in fetal lung liquid before ventilation averaged 25%/hr, whereas those with surfactant absorbed liquid at only 2%/hr in this protocol. All differences in solute permeability and lung liquid absorption were related to preventilation surfactant levels in fetal lung liquid, and not to postventilation surfactant levels or to lung function. Speculation: These studies demonstrate that initiation of aeration of surfactant deficient fetal lungs at low tidal volumes causes abnormalities in the lung epithelium’s normal barrier to large solutes. This may be the mechanism that allows plasma proteins to enter air spaces in human respiratory distress. Monotonous low tidal volume ventilation in animals with surfactant in fetal lung liquid resulted in retention of large volumes of alveolar liquid and suggested that occasional breaths of high tidal volumes are essential for normal lung liquid absorption. © 1980 International Pediatric Research Foundation, Inc.