4 Effect of Alternations of Pulmonary Arterial and Alveolar Gas Tensions on the Pressure-volume Curve and Surface Tension of Dog Lungs

Abstract

The effect of acute alterations of pulmonary blood flow (Qp), pulmonary arterial blood gas tensions (Pvco2; Pvo2) and alveolar gas tensions on the mechanical properties of lungs has been studied in left lower lobes of open-chest dogs. Static deflation pressurevolume curves and the stability ratio (SR) of bubbles expressed from the lung were measured. In non-ventilated lobes, the absence of circulation for 4 hours did not produce a change in the percent of maximum air volume remaining at a transpulmonary pressure of 10 cm H2O (V %10). In non-ventilated lobes, perfusion with hypercapnic hypoxic blood (Ppvo2 > 60 mm; Pvo2 < 45 mm) caused a significant decrease in V %10. In lobes ventilated with 100 % nitrogen and perfused with hypercapnic hypoxic blood, V %10 decreased more than in the non-ventilated lobes. Change in V %10 could be reversed by perfusing with normal Pvco2 and Pvo2 for 3 hours. In contrast, V %10 was unaltered in lobes perfused with blood having normal Py gas tensions and ventilated with 100% nitrogen, even when QP was decreased to 15 to 20 % of control values. However, V %10 decreased in lobes perfused with blood having normal gas tensions but ventilated with 10% CO2 in nitrogen. A decrease in V %10 correlated with a decrease in SR. These studies suggest that the presence of normal surfactant depends upon the intimate gaseous environment of the alveolar cell. Both hypercapnia and hypox'a are required for the production of increased retractive forces on lung deflation. Reversal to normal deflation characteristics is possible by reverting to normal gas tensions. (Supported by the Medical Research Council of Canada) (SPR)