Current concepts on respiratory and circulatory adaptation of the fetus and newborn

Abstract

Abstract A brief review on some of the recent works in cardiovascular and respiratory physiology of the fetus and newborn were made. The recording of fetal breathing in normal and high risk pregnancies promises to be useful tool for assessing condition of the fetus in utero. Simultaneous measurements of pulmonary gas exchange and blood gases from birth through the first minutes and hours of life in the human infant showed that an oxygen uptake of more than 7 ml/kg/min is required to raise the Pa O 2 after birth. The pulmonary vagal and the thoracic cage mechanoreceptors interact in the regulation of breathing in both preterm and term infants. Preterm infants manifest low threshold response of the pulmonary vagal inspiration terminating reflex. The inspiratory inhibitory reflex becomes less active with maturation of the infant and its thoracic cage. Peripheral chemoreceptors are active early in gestation. Responses to hypoxia or high CO 2 appeared to relate to age. The fetus adapts to hypoxemia in a number of ways. Placental transfusion influenced early extrauterine adaption and in excess may cause disease. Term newborn shows evidence of an actively functioning peripheral circulatory regulating system. The autonomic nervous regulation of circulation required more studies. Mechanisms of closure of the umbilical artieres and ductus arteriosus and their clinical significance are reviewed.