Effects of Continuous Negative Pressure on Lung Mechanics in Idiopathic Respiratory Distress Syndrome

Changes in lung mechanics produced by continuous thoracic negative pressure, (CNP) were determined in twelve newborn infants with idiopathic respiratory distress syndrome (IRDS). CNP produced a significant increase in arterial oxygen tension, with no change in pH, and HCO-3. Minute ventilation decreased with CNP but Paco2 did not change significantly, suggesting a reduction in physiologic dead space while CNP was applied. Functional residual capacity increased to 127% of its initial value, after the institution of CNP. Dynamic lung compliance decreased to approximately 56% of its previous value with CNP. This change in compliance may be explained if the increase in FRC was not only due to expansion of collapsed alveoli, but also to overdistention of the functioning units.