PULMONARY VASCULAR ADJUSTMENTS IN THE NEONATAL PERIOD

Abstract

Pulmonary arterial or right ventricular pressures were measured repeatedly in 18 puppies and 2 goats, from 1 to 36 days of age; these pressures were measured with the use of indwelling catheters in unanesthetized animals. In puppies the systolic pressure in the pulmonary circulation decreased rapidly to near adult levels in 5 to 10 days after birth, and then more slowly to adult levels by 5 to 6 weeks of age. In goats the pressures decreased more slowly, reaching near adult levels in about 12 to 14 days. Acetylcholine produced a decrease in pulmonary arterial pressure in the puppy in the first 5 days of life, but an increase in pulmonary pressure after that time in the resting animal. In the hypoxic puppy, a reduction in pulmonary arterial pressure was induced by acetylcholine. These findings suggest that the pulmonary vessels in the young puppy are actively constricted but that relaxation occurs after the first few days of life.