Effect of Hypervolemia on Ratio of Pulmonary to Systemic Vascular Volume ∗ †

Abstract

Conclusion

Since the L.L.H.V. remained a relatively constant percentage of total blood volume even when the latter was increased by an average of 46%, there was no selective storage of blood in the lungs. Thus the reservoir function of the lungs is equivalent to that of the systemic vascular bed as a whole. The lungs and the vascular system accommodated this large increase in volume without any evidence of inconvenience to the animal, and the right atrial pressure increased by only 5 mm of mercury (average value) 15 minutes after the last transfusion. This tolerance to hypervolemia was shown especially by the conscious dogs, who performed severe exercise as easily under these conditions as in the control state. Although the dextran infusions increased the L.L.H.V. and the filling pressure of the ventricles as much as blood, cardiac output increased in proportion with the decrease in hematocrit when dextran was used and was little changed when blood was used. Thus increases in L.L.H.V. are not necessarily associated with increases in cardiac output. Also, as the cardiac output increased during exercise (up to 3 times the control value), there was little change in the L.L.H.V. from the initial value when the animal was at rest, regardless of the amount of initial volume.

The volume of blood in the lungs and the left side of the heart (L.L.H.V.) and total blood volume were determined in 15 anesthetized dogs. L.L.H.V. averaged 12 ml per kilo of body weight or 12.5% of total blood volume. Infusion of fresh blood or of dextran, 6%, produced hypervolemia sufficient to increase the total blood volume by an average of 46%. During the hypervolemia, the proportion of L.L.H.V. to total volume was essentially unchanged. This was also true in 3 conscious dogs.