Pulmonary metabolic function can serve as a monitor for lung preservation

A minimally invasive method for detecting early signs of pulmonary injury through the examination of peripheral blood samples was investigated as a potential method for assaying the effectiveness of lung preservation techniques. A mild, ischemic injury was imposed on lungs in situ by diverting total pulmonary artery blood flow to a pump oxygenator for 1 to 4 hours (average 2 hours) in 16 dogs. Before bypass and at 1/2, 1, and 2 hours following bypass, pulmonary metabolic function was determined by injecting known amounts of the metabolizable vasoactive hormones 14C-5-hydroxytryptamine and 3H-norepinephrine into venous blood and then measuring their single pass concentration-time curves in arterial blood in relation to the concentration of the nonmetabolizable intravascular reference marker indocyanine green (Cardio-Green). The results showed that the ischemic injury produced a significant and reproducible reduction of amine metabolism by the lung. In addition, metabolites of 14C-5-hydroxytryptamine showed a 50% decrease in left atrial blood at the 40% decay point of the intravascular marker, thereby further reflecting the inability of the lung to metabolize 14C-5-hydroxytryptamine in the presence of endothelial injury. The method is a sensitive assay for lung injury that can be performed in serial fashion in the closed-chest experimental animal or patient. The procedure may have potential evaluating techniques of lung preservation or for detecting early signs of rejection in the transplanted lung before histologic or radiographic changes become apparent.