Changes in diffusing capacity of isolated cat lungs with blood pressure and flow

Abstract

Nine isolated cat lungs were perfused with the animals' own blood at 37°C and ventilated by negative pressure. The diffusing capacity for CO, Dl, was measured at constant lung volume and various blood pressures and flows by a modified 10-second, breath-holding technique. In each of seven preparations in which mean intravascular pressure was raised, either by raising left atrial pressure while keeping blood flow constant, or by increasing blood flow while keeping left atrial outflow level Dl increased about 33%/10 mm Hg increase in mean intravascular pressure. In one lung, in which left atrial pressure was increased by 10 mm Hg while pulmonary artery pressure was kept constant by lowering the blood flow, Dl increased by 50%. In four preparations, in which left atrial pressure was lowered while blood flow was increased so that mean intravascular pressure remained approximately constant, there was no demonstrable increase in Dl. We conclude that the pressure across the walls of the pulmonary blood vessels is a primary factor in controlling the size of the pulmonary capillary bed as measured by Dl. No independent effect of flow was observed. Submitted on September 9, 1959