Videodensitometry in rats with pulmonary damage due to microembolism

Serial pulmonary angiography with videodensitometry was performed in 18 rats with pulmonary damage caused by administration of a fibrinolysis inhibitor, tranexamic acid (200 mg/kg body weight injected intraperitoneally) and bovine thrombin (500 NIH/kg body weight injected into the right femoral vein). The mean transit time (MTT) was calculated from videodensitometry, the observed area of interest consisting of approximately one-third of the right lung, including both central and peripheral parts. The impact of the pulmonary damage was analysed by morphologic methods and correlated to MTT. Although a pressure rise presumably occurred in the pulmonary circulation, no change in MTT was found after induction of pulmonary damage, indicating opening of actual and potential anastomoses between pulmonary arterioles and venules to serve as by-pass portions and as a safety-valve mechanism for the capillary bed and the right heart, respectively. Another explanation to unchanged MTT may be opening of resting capillary beds. Two rats with very severe pulmonary damage showed prolonged MTT. These rats may have suffered from cardiac failure.