SummaryWe studied transmission of a constant mean airway pressure through the lungs to the pleural space in nine mechanically-ventilated neonates with low-compliance lung disease. Infants were studied for 3.1 ± 1.6 hr during a period of clinical improvement, but at a time when lung compliance was still markedly reduced. Two of our infants were studied during recovery from fluid overload, while seven infants with hyaline membrane disease were studied at a stage of disease during which maximal diuresis has been found to occur. During the study period, mean esophageal pressuredecreasedin all infants from 5.6 ± 1.3 to 4.2 ± 1.8 cm H2O (P< 0.001) while total compliance increased slightly.SpeculationEdema of the pulmonary interstitium may contribute to airway-closure and gas-trapping. We propose that a loss of fluid from the interstitium during early recovery from low-compliance lung disease may lead to less gas-trapping and a fall in mean esophageal (pleural) pressure.