Alveolar liquid pressure measured in the intact rabbit chest by micropuncture

Previous measurements in isolated lung showed that alveolar liquid pressure was near the pleural pressure at a lung volume near functional residual capacity (FRC). In this study we verified that alveolar liquid pressure in vivo was similar to that of the isolated lung. In anesthetized paralyzed rabbits (3-4 kg, n = 9) ventilated with 100% O2 in the left lateral position, we made a pleural window between the fifth and sixth ribs near midchest by removing tissue down to the parietal pleura. Window height was 6 cm above the base of the lung. During apnea, alveolar liquid and pleural pressures were measured by puncturing through the pleural window with micropipettes connected to a servo-nulling pressure-measuring system. Pressures were measured at airway pressures of 0 (FRC) and 10 cmH2O both in vivo and postmortem. In vivo, alveolar liquid and pleural pressures relative to ambient pressure averaged -2.3 +/- 1.4 (SD) and -1.8 +/- 0.9 cmH2O at FRC and increased to 3.3 +/- 1.8 and 1.8 +/- 1.6 cmH2O after inflation to an airway pressure of 10 cmH2O, respectively. Similar values were obtained postmortem. These results were similar to previous measurements in the isolated lung.