DLO2 in excised lungs perfused with blood containing sodium dithionite (Na2S2O4)

If the excised lung is perfused with blood containing the chemical sodium dithionite (DDT), the PO2 of pulmonary capillary blood is everywhere zero and the membrane diffusing capacity for O2 (DmO2) can be measured by a standard rebreathing technique. The reaction rate of DDT with O2 is not rate limiting in the DmO2. In 15--25 kg dogs anesthetized with pentobarbital sodium (30 mg/kg, iv), left lower lobe was excised, suspended horizontally and perfused with autologous blood at 25--27 degrees C. DDT was added to the blood and the rebreathing alveolar disappearance curves for O2 were measured. The DmO2 ranged from 6 to 43 (ml/min.Torr, STPD) at lung volumes of 240--780 ml (FRC at 6 cmH2O end-expiratory pressure). Lung weight, pulmonary artery pressure, and the DmO2 were stable in the presence of DDT. Histopathology indicates that dithionite in the concentrations used does not harm the lung. Effects of inequalities in the distributions of ventilation, volume, and diffusing capacity were examined in a two-compartment model and compared with the experimental findings.