The Effect of Moderate Changes in Blood Volume on Left and Right Atrial Pressures

The blood volume of 15 dogs was progressively increased an estimated 30 per cent by repeated blood infusions and decreased 30 per cent by stepwise hemorrhage. The pressures in the venous system, both atria and the pulmonary artery, rose and fell in unison with these moderate changes in blood volume and the new levels remained stable for at least 10 to 20 minutes. Although the right ventricle anatomically separates the systemic venous bed from the pulmonary circulation, small hemorrhages and transfusions have so little effect on its activity that, from the point of view of pressure volume relationships, the systemic veins and the left atrium are parts of the same functional unit.