Pulmonary Arterial Pressures of Newborn Infants Born with Early and Late Clamping of the Cord1

Abstract

Summary Hemodynamic studies were conducted on 32 normal, full‐term newborn infants, age 29 minutes to 11 hours, to determine the effect of placental transfusion upon the pulmonary circulatory adjustments after birth. In 10 infants, clamping of the cord was accomplished within 2 to 10 seconds after the delivery ( early clamping), and in the other 22 infants it was done after cessation of the umbilical arterial pulsations ( late clamping). For comparative purposes, the pulmonary arterial pressures were related to the corresponding aortic pressure in the form of a P/A mean pressure ratio, and these were correlated with age in the 2 groups of subjects. The observed pulmonary arterial pressures in the 2 groups differed significantly. During the first 9 hours, the pulmonary pressures of the late‐clamped infants were approximately 90 % that of the aortic. In contrast, those of the early‐clamped infants were as low as 70 % of the aortic pressures by the second hour, and nearly 50 % by the fourth hour. A hypothesis is presented that the higher pulmonary arterial pressures in the late‐clamped infants is due to greater pulmonary vasoconstriction resulting from greater pulmonary capillary…venous filling…a consequence of the large blood volume following maximal placental transfusion.