Effect of hypoxia on fluid filtration rate during forward and reverse perfusion of isolated rabbit lungs

Fluid filtration rate (FFR) was measured under predominantly zone 3 conditions in isolated rabbit lungs perfused at constant flow. During forward perfusion, alveolar hypoxia produced a significant increase in mean pulmonary artery pressure and a significant decrease in FFR. During reverse perfusion, alveolar hypoxia produced a similar increase in the pressure gradient across the lung, but a significant increase in FFR. It is concluded that the pulmonary vasoconstriction induced by alveolar hypoxia occurs predominantly on the arterial side of the pulmonary circulation.