Effect of lung surface tension on pulmonary vascular mechanics in excised dog lungs

We measured pulmonary vascular pressure (Pvas)-volume (Vvas) relationships in excised air and oil-filled dog lungs. First, pulmonary vessels were perfused with dextran and Pvas-Vvas curves of the total pulmonary circulation were measured. Second, air was perfused into the artery or vein, and the arterial or venous extra-alveolar Pvas-Vvas curves were measured. Alveolar vessel Pvas-Vvas curve was obtained by the substraction of both the arterial and venous extra-alveolar Pvas-Vvas curves from the total vascular Pvas-Vvas curves. When lung recoil pressure (PL) was reduced by filling the lung with oil at a given lung volume (VL), the determinants of pulmonary vascular dimensions and compliances were compared in terms of PL and VL. The arterial vascular area (Avas) was correlated with PL, while venous Avas was correlated with both PL and VL. Alveolar vessel Vvas at high Pvas reached its peak at PL 5 cm H2O. Compliance of arteries, veins, and alveolar vessels were correlated with PL. We concluded that lung surface tension contributes to the lung parenchyma's radial traction to the extra-alveolar vessels and that it also contributes to the stabilization of the alveolar vessels.