Decrease of venous return caused by right atrial pulsation.

• For almost as long as the problem of venous return has been studied, two different factors have been claimed to be important in determining venous return to the heart." These are: (1) the force of the systemic arterial pressure pushing blood through the systemic circulation toward the heart, and (2) factors on the venous side of the heart that affect venous return, including rhythmic suction of blood from the veins. These two effects have also been called vis a tergo ("force from behind") and vis a f route ("force from the front"). The importance of the vis a tergo has never been doubted by any investigator; this has been reviewed in detail in a monograph by Franklin and in a review by Landis and Hortenstine. However, the importance of rhythmic suction of blood into the heart as the result of either cardiac or respiratory suction has been very controversial. Recently Brecher, in his monograph on venous return, has emphasized the importance of rhythmic suction, both cardiac and respiratory, as one of the important factors in promoting venous return to the heart. He has especially shown that suction resulting from respiratory movements enhances venous return and has also demonstrated that the heart can actually suck blood from the veins during certain phases of the cardiac cycle. Also, 0'Brian has confirmed the ability of the left ventricle to suck blood into its cavity."'