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

Fluid filtration rate (FFR) was measured under predominantly zone-three conditions in isolated rabbit lung perfused at constant flow. During forward and reverse perfusion, alveolar hypercapnia significantly increased mean pulmonary artery pressure but did not change FFR. We conclude that the pulmonary vasoconstriction induced by alveolar hypercapnia occurs on both arterial and venular sides of the pulmonary circulation.