THE RELATION BETWEEN SYSTEMIC AND PULMONARY BLOOD PRESSURES IN THE FETUS

Abstract

Intraventricular pressures were taken from the right and left ventricles of immature and mature dog and rabbit fetuses immediately upon delivery, when the umbilical cord was clamped, when the fetus first breathed, and during the first 2 days of independent life. Right and left ventricular pressures were similar before breathing begins (20/0 mm Hg in rabbits, 45/0 mm Hg in dogs). They were less in the immature fetuses than in the mature. Clamping the cord produced little or no change in right or left ventricular pressure. Inspiration lowered right (8 mm Hg) ventricular pressure more than left (3 mm Hg). Pressure relationships were such that one must postulate an early functional closure of the foramen ovale and ductus arteriosus in these spp.