Alveolar pressure measurement in open-chest rats.

In open-chest rats, alveolar pressure was measured with alveolar capsules connected via pliable tubing to inductive pressure transducers. By means of the interrupter technique during constant-flow inflation, it was possible to determine pulmonary static elastance (Est,L) and tissue and airway resistances (Rdiff,L and Rinit,L, respectively). In eight anesthetized paralyzed mechanically ventilated rats, 118 measurements of Rdiff,L and Est,L were performed over a wide range of flows and tidal volumes. There was excellent agreement between the data calculated using transpulmonary pressures and those computed using capsule pressures, the latter being measured at different points of the lung. In another group of rats studied under the same experimental conditions, two capsules were simultaneously placed on different pulmonary lobes. No regional differences in pulmonary mechanics could be detected in either experiment. In addition, alveolar pressure could also be measured accurately by a catheter inserted into lung parenchyma.