Alveolar liquid pressure measured using micropipets in isolated rabbit lungs

Abstract

The relationships among alveolar liquid pressure (Pliq), transpulmonary pressure (Ptp), and alveolar edema were studied in isolated rabbit lungs. Different amounts of edema were induced by instilling measured amounts of normal saline via the trachea. Micropipets wre used in conjunction with a servonulling pressure measuring system to measure Pliq. Pliq was −1 cm H 2O relative to alveolar air pressure (Plav) at Ptp of 3 cm H 2O and decreased to −16 cm H 2O at Ptp of 25 cm H 2O. Pliq increased slightly as wet-to-dry weight ratio (W/D) of the lungs increased from 5.8 to 16. Alveolar surface tension estimated from these values of Pliq - Plav using an alveolar radius of curvature of 40 μm at Ptp of 25 cm H 2O was consistent with the direct measurements of Schürch. In lungs made edmatous by treating with oleic acid, values of Pliq were not different from those measured in lungs made edmatous by normal saline instillation (control). Pressure-volume behaviour of the oleic acid treated lungs showed a marked reduction in lung volume at each Ptp value compared to the behavior in the control lungs. Most of this reduction in lung volume was removed by washing the airways with the bronchodilator, isoprotenol. We conclude the alveolar surface tension was not increased in the oleic acid treated lungs. The apparent increase in lung static recoil was not most likely caused by the constriction of small airways.