Effect of lung inflation on fluid flux in zone 1 lungs.

Because of conflicting data in the literature, we studied the effect of positive-pressure inflation on transvascular fluid filtration in zone 1 lungs. Lungs from New Zealand White rabbits (n = 10) were excised, perfused with saline and autologous whole blood (1:1), ventilated, and continuously weighed. Pulmonary arterial and venous pressures (Pvas) were referenced to the most dependent part of the lung. A change in vascular volume (delta Vvas) and a fluid filtration rate (FFR) were calculated from the change in lung weight that occurred from 0 to 30 s and from 3 to 5 and 5 to 10 min, respectively, after changing alveolar pressure (PA). FFR's and delta Vvas's were measured with Pvas equal to 2 or 10 cmH2O and PA changing from 15 to 30 cmH2O when the lungs were normal and after they were made edematous. When Pvas = 2 cmH2O, increasing PA increased the Vvas and the FFR in both normal and edematous lungs. However, when Pvas = 10 cmH2O, increasing PA only slightly changed the Vvas and reduced the FFR in the normal lungs, and decreased Vvas and markedly decreased the FFR in the presence of edema. Inflating zone 1 lungs by positive pressure has an effect on transvascular fluid flux that depends on the Pvas. The results suggest that the sites of leakage in zone 1 also vary depending on Pvas and PA.