Eleventh Edgar Mannheimer Lecture. Human fetal and neonatal circulation. Some structural and functional aspects

Normally the neonatal circulation adjusts itself gradually during the first days of extrauterine life. The different closure rates of the major fetal vascular channels (umbilical vessels, ductus venosus, ductus arteriosus, and foramen ovale) permits smooth alterations in direction and size of shunts, should the balance of vascular resistance and pressure become upset. The study of the influence of placental transfusion on the cardio-respiratory adaptation has again demonstrated the great capacity of the transitional circulation to cope with all the strains involved in the reorganization of the circulatory system at birth. Such a capacity proves the existence of an effective system of integrated baroreceptor--and chemoreceptor--reflexes (peripheral and central).