Venous Return at Various Right Atrial Pressures and the Normal Venous Return Curve

The normal venous return curve has been determined in 12 open-chest dogs with intact circulatory reflexes and in 14 open-chest areflex dogs. These curves show that venous return reaches a maximum value when the right atrial pressure falls to –2 to –4 mm Hg and remains at this maximum value down to infinitely low negative pressures. As the right atrial pressure rises to positive values venous return falls and reaches zero when the right atrial pressure has risen to equal the mean circulatory pressure. A venous return curve for the normal, intact dog has been tentatively formulated on the basis of these studies and previous studies in which individual points on the venous return curves of intact dogs have been measured.