Effects of changes in topographical distribution of lung blood flow on gas exchange

The left lung of a dog was suspended in a Lucite box, ventilated with negative pressure, and perfused with venous blood from another dog at 37 C. By varying the pulmonary artery pressure, it was possible to perfuse all the lung or leave increasing proportions of the upper and middle lobes unperfused. The mean Pco2 difference between end-tidal gas and pulmonary venous blood was 1.7 mm Hg (se mean 0.6) when all the lung was perfused, but steadily …