EFFECT OF TRANSPULMONARY PRESSURE ON AIRWAY-CLOSURE IN IMMATURE AND MATURE RABBITS

The transpulmonary pressures (Ptp values) at which airway closure occu rred during maximal stimulation with methacholine were compared in 10 mature and 9 immature rabbit lungs by using an alveolar capsule techni que to assess airway closure. After maximal constriction, airway openi ng and alveolar capsule pressures were recorded during small volume os cillations as Ptp was lowered from 12 to 4 cmH(2)O. At each Ptp, the p roportion of alveolar capsules indicating airway closure was greater f or the immature than for the mature lungs (P < 0.025). At Ptp of 4 cmH (2)O, only 20% of alveolar capsules indicated airway closure in the ma ture lungs in contrast to 85% indicating closure in the immature lungs (P < 0.001). The in vitro sensitivity of tracheal smooth muscle to ac etylcholine and histamine was greater in tissues from immature than fr om mature rabbits. We conclude that the more frequent airway closure o bserved in immature rabbits could reflect maturational differences in the structure of the bronchi or lung parenchyma or differences in the coupling between the parenchyma and the airways.