Circulatory Changes Following Birth of the Calf and the Effect of Hypoxia

Abstract

Circulatory and ventilatory measurements were made during the course of 66 cardiac catheterizations in 20 unanesthetized Jersey calves, age two hours to eight weeks. The salient findings were:1. The pulmonary arterial pressure was high during the first two to three hours of extra-uterine life (up to 80 mm Hg) and it decreased rapidly (30 to 40 mm Hg) during the next nine to ten hours.2. The pulmonary ventilation appeared good, judging by the active appearance of the calves, the volumes of respired air, the arterial blood gases, and the ventilatory response to hypoxia.3. The pulmonary blood flows in these calves were not higher in the first hours of life than on subsequent days, and there was little contribution to the pulmonary blood flow by a left to right shunt through the ductus arteriosus.4. Hypoxia, if severe, could increase the pulmonary arterial pressure to systemic levels on the day of birth, but not in older calves.5. Pulmonary vasoconstriction sometimes followed puncture of the aorta or other procedures in calves less than twelve hours old. The lability of the pulmonary blood vessels during the first hours of extra-uterine life suggested that large changes in pulmonary vascular tone also occur in utero.