S. K. Lo

1815 PULMONARY VASCULAR PERMEABILITY TO PROTEINS INCREASES AFTER THROMBIN-INDUCED INTRAVASCULAR COAGULATION

Since intravascular coagulation is a proposed etiologic factor in acute lung injury, we examined whether thrombininduced intravascular coagulation results in increased lung vascular permeability to proteins. Sheep (n=5) were prepared with lung lymph fistulas and balloon-tipped left atrial catheters. The sheep were studied in the unanesthetized state. The left atrial balloon was inflated to produce step increases in left atrial pressure (Pla) to a maximum of 25 Torr. Pulmonary lymph flow (Qlym) and lymph-to-plasma protein concentration ratio (L/P) were measured. The protein reflection coefficient (σd), a measure of pulmonary vascular permeability, was determined by increasing Pla until Qlym approached the filtration-independent state; i.e. further increases in Qlym did not further decrease L/P and σd approached (1–L/P). α −thrombin (80 U/kg) was then infused and a new steady-state Qlym was reached to allow σd to be determined after thrombin. (σd=1 indicates complete impermeability to proteins and d=0 indicates complete permeability). In the present study, σdd before thrombin was 0.70±0.03 (mean±SE) and decreased to 0.59±0.01 after thrombin (p<0.05). We conclude that pulmonary intravascular coagulation increases pulmonary vascular permeability to proteins and that this may be a factor in mediating acute lung injury. (Supported by HL17355, HL26551 and GM07033).