Cardiovascular adaptation of newborn lambs to hypervolemia with polycythemia

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Abstract
Hemodynamic studies were carried out in five newborn lambs before, during, and for a period of 3 h after an increase of approximately 50% in blood volume. Four other animals served as a control group. The animals were delivered by cesarean less than 1 week before the anticipated date of birth. Pressures were continuously recorded in aorta, pulmonary artery, and right and left atrium. Pulmonary and systemic flows as well as the possible shunts through the ductus arteriosus and the foramen ovale were calculated according to the Fick principle. The results showed a marked increase in systemic flows, followed by a progressive reduction but no return to the base-line level, closure of the ductus arteriosus during or shortly after the infusion, and a transient systemic and pulmonary hypertension associated with a marked elevation in left and right atrial pressures. No change was observed in the cardiac rhythm or the O2 consumption. These data suggest that the venous vascular bed of newborn lambs is less able than that of adult animals to cope with an acute increase in blood volume.

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