Respiratory fluctuations of oxygen tension in central venous blood of anesthetized dogs

Abstract

Venous P Oin2 was continuously recorded in the superior and inferior caval veins and in the pulmonary artery by a catheter P O 2 electrode in the anesthetized dog breathing spontaneously or ventilated artificially. Venous P O 2 showed fluctuations with the same period as respiration at all places of measurement. The fluctuations were more pronounced in the inferior than in the superior caval vein, and largest just below the veno-atrial junction. The amplitude of P O 2 fluctuations in the pulmonary artery was smaller and did not show any correlation with breathing frequency, absolute value of Pv̄ O 2 , and level of oxygénation. Blocking of the renal veins by tourniquets reduced the amplitude of the fluctuations below the veno-atrial junction; blocking of the caval flow below the liver flattened them, whereas blocking below the renal veins did not elicit any clear-cut effect. These findings suggest a different effect of respiratory movement on the venous outflow from various organs (particularly the liver and the kidney), thus altering their relative contributions during the respiratory cycle.