Abstract
Functional anatomy of 0.87 gestation (immature) rabbit fetal lungs was studied by direct stereomicroscopic observation as the first air volume-pressure (VP) diagrams were recorded. Lungs were airless, but contained normal volume of fetal pulmonary fluid (FPF) prior to air-inflation. Volume was recorded 0, 15 and 120 sec after stepwise changes of 5 cm H2O pressure. Inflation pressures up to 25 cm H2O (P25) produced large, time-dependent, volume changes in which the conducting airways were distended and FPF moved to the periphery of the parent airway before lateral branches were inflated. Characteristically, there was no saccular aeration below P25. At pressures greater than P25, but below Pmax, subpleural saccules were the first to aerate; repeated inflation-deflation cycles in this pressure range produced preferential aeration of the same saccules, which thereby became vulnerable to rupture. As pressure was raised from ∼P25to Pmax(i.e., P35-P40), saccules were recruited by both time- and pressure-dependent processes and recruitment continued, but at a slower rate, during early deflation. Time-dependent changes predominated at high pressures and were related to FPF flow through terminal ducts, formation of transient labile bubbles, and progressive enlargement of saccules. During deflation from P25, derecruitment of saccules was largely time-dependent and air-trapping by FPF locks in the airways accounted for most of the residual air at PO. We conclude that time can be as significant a factor as pressure in the initial inflations of immature lungs.
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Kumar, A., Clutario, B., Doyle, C. et al. 1678 PRESSURE PLUS TIME: REQUISITES FOR INFLATION OF IMMATURE LUNGS. Pediatr Res 15 (Suppl 4), 723 (1981). https://doi.org/10.1203/00006450-198104001-01697
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DOI: https://doi.org/10.1203/00006450-198104001-01697