Passive Expiratory Flow-Volume Recordings in Immature Newborn Rabbits

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Abstract
Immature newborn rabbits with a gestational age of 27 days were paralyzed and kept in body plethysmographs. They were ventilated for 10 min with a tidal volume of approximately 10 ml/kg, with or without previous surfactant treatment via the airways. Tidal volumes and flow were recorded with a pneumotachograph connected to the body plethysmograph, and the expiratory time constant of the respiratory system (trs) was determined from flow-volume diagrams. The values of trs after 10 min were significantly higher in surfactant-treated animals than in controls (50 ± 7 vs. 23 ± 4 ms; p < 0.002), indicating stabilization of the alveoli. There was also a close correlation between trs and the compliance values calculated from tidal volumes and ventilator pressure (r = 0.80; p < 0.001), as well as between trs and the alveolar volume density in histological lung sections, determined by automated image analysis (r = 0.71; p < 0.001)