Organ-specific characteristics of blood supply in acute hemorrhage in rats with different resistance to circulatory hypoxia.

The present study is aimed toward a comparative real-time analysis of organ-specific characteristics of the liver, kidney and brain blood supply in the dynamics of acute massive hemorrhage in rats with different resistance to circulatory hypoxia. The survival time of experimental animals after the arrest of bleeding was used as a criterion of their resistance to acute blood loss. The rats with high resistance (HR) to hypoxia had the survival time not less than 3 h, while the rats with low resistance (LR) to hypoxia lived not more than 1.5 h. A marked decrease in arterial organ blood flow velocity and tissue perfusion of the liver, kidney and brain in LR and HR rats was observed at the end of acute massive hemorrhage in ultrasonic and Doppler flowmetry. In the post-hemorrhagic period the organ hemodynamics and microcirculation showed a tendency to a further decrease in LR rats. In HR animals the blood flow velocities in hepatic, renal and common carotid arteries were temporarily restored to 115-120, 85-90 and 60-65%, respectively, following the bleeding arrest. In the compensated phase of the post-hemorrhagic period the brain blood flow was maintained at this new post-hemorrhagic level due to autoregulatory changes in the carotid resistance. Such a response of brain blood vessels of HR rats is considered to be an adaptive response which protects the brain from autoreperfusion- and reoxygenation-induced injuries under conditions of posthemorrhagic autorestoration of tissue circulation.