CHAPTER 46 



The fetal and neonatal circulation 



MAUREEN YOUNG Department of Medicine, St. Thomas's Hospital, London, England 



CHAPTER CONTENTS 



The Fetal Placenta 



Implantation 



Placentation and Placental Function 

 Early Development of the Cardiovascular System 



Peripheral Circulation 



The Heart 



Congenital Malformation 

 Course of the Circulation of the Fetus 



Regional Blood Flow 



Hepatic Blood Supply and the Ductus Venosus 

 Fetal Heart 



Heart Rate. Regulating Mechanisms 



Cardiac Output 

 Arterial Blood Pressure 



Systemic Pressure 



Pulmonary Artery Pressure 



Development of the Cardiovascular Reflexes and the 

 Responses to Asphyxia and Hormones 

 Fetal Placental Blood Flow 



Effective Perfusion Pressure. Resistance of the Placental 

 Circulation 



Umbilical Blood Flow 



Oxygen Environment and Requirements of the Fetus 

 Influence of Hypoxia and Asphyxia on the Fetus 



Hemoglobin 



Blood Flow- 

 Oxygen Consumption 



Heart Rate During Reduction in Maternal Placental Blood 

 Flow 

 Changes in Fetal Circulation at Birth and in the Neonatal 

 Period 



Umbilical Cord; Ductus Venosus 



Fetal Channels in the Thorax 



Pulmonary Vascular Resistance, Arterial Pressure, and 

 Blood Flow 



The Heart 



Systemic Pressure; Cardiovascular Reflexes, and Peripheral 

 Resistance 



Viability 



Congenital Heart Disease 



thirty years have passed since the inspiration and 

 eloquence of Sir Joseph Barcroft gave the functional 

 development of the cardiovascular system its place 

 in circulatory physiology. In the intervening vears 

 histochemical techniques and the electron microscope 

 have shown how complex is the placental structure 

 between the maternal and fetal circulations: advances 

 in knowledge of transport mechanisms and the use of 

 isotopically labeled compounds begin to clarify the 

 active processes occurring within this structure: the 

 pathways of the circulation "in utero,"' in both the 

 placenta and the fetus, and the changes of the latter 

 at birth, have been confirmed : studies of the develop- 

 ment of the regulatory mechanisms of the fetal circula- 

 tion have been extended into the neonatal period 

 (70, 83); finally, obstetricians and pediatricians have 

 accumulated circulatory information on the human 

 infant which demonstrates the value and limitations 

 of applying observations from one species to another. 

 Detailed reviews have been written on each of these 

 subjects both from the historical viewpoint and that of 

 comparative physiology: it falls to this chapter to do 

 justice to the main facts with particular reference to 

 the higher mammals and to the human infant. 



In acute experiments on the fetus with an intact 

 placental circulation, the possibilities of departure 

 from the physiological state are even more numerous 

 than in the grown animal. Understanding of the precise 

 influence of the disturbances due both to the anesthetic 

 and to removal from the uterine environment awaits 

 the development of intrauterine techniques such as the 

 chronic implantation of electrodes and catheters. 

 Many workers have tried to minimize these disturb- 

 ances by working on the fetus delivered into a saline 

 bath at 37 C; however, particular attention must be 

 paid to the position of the fetus in relation to the 

 placenta; further, interference with the maternal 



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