UMBILICAL 

 VEIN 



THE FETAL AND NEONATAL CIRCULATION 1 625 



s.v.c. 



fig. 5. Fetal circulation and probable course of the blood 

 through the fetal heart. [After G. S. Dawes (Bell el al. Textbook 

 of Physiology and Biochemistry, 5th ed., 1961).] 



upper part of the body, carried by the superior vena 

 cava, and passes into the right ventricle; most of this 

 blood short-circuits the lungs, through the ductus 

 arteriosus, and passes to the descending aorta to sup- 

 ply the lower extremities or become oxygenated in the 

 placenta. 



The presence of the ductus arteriosus and the 

 foramen ovale and their functional significance, 

 allowing the two ventricles to work in parallel, did 

 not escape William Harvey: "Thus, in the embryo, 

 while the lungs are idle and devoid of activity or 

 movement, as though they did not exist, Nature uses 

 the two ventricles of the heart as one for the trans- 

 mission of the blood." Harvey used the fetal circula- 

 tion to support his general thesis of the circulation of 

 the blood. Barclay et al. (27) review the history of the 

 anatomical evidence for the present concept of the 

 fetal circulation : Sabatier, nearly two hundred years 

 ago, observed that the foramen ovale did not lie be- 

 tween the two atria, but at the junction of the two 

 venae cavae with the left auricle, and directed the 

 inferior caval blood into the left auricle; it was he who 



CRISTA 

 OIVIOENS 



PULMONARY 

 VEINS 



I.V.C. 



VALVE OF 



FORAMEN 



OVALE 



fig. 6. Diagram of the great veins to show that in the fetus 

 the inferior vena caval blood divides into two streams, one of 

 which enters the right atrium while the other passes through 

 the foramen ovale into the left atrium. [From Dawes (66).] 



first suggested the figure-of-eight-like course for the 

 circulation shown in figure 5. Shortly afterwards, 

 Wolf also found that the two atria were not in com- 

 munication with each other, that the inferior vena 

 cava lay between them with openings in each, and 

 that the relationship of these communications was 

 such that the major portion of the inferior caval 

 stream would pass into the left auricle. It was not 

 until 1939 that the pathways of the inferior and su- 

 perior caval streams, in the chest and heart, were 

 actually observed in the sheep by Barclay et al., using 

 rapid serial radiography following the injection of 

 radiopaque substances (26). Similar observations have 

 been made, most elegantly, in the full-time human 

 infant by Lind and Wegelius who were able to make 

 the injections and perform the angiocardiography be- 

 fore the first breath (129). The latter have also con- 

 firmed the functional relationship between the venae 

 cavae and the atria in early nonviable infants at thera- 

 peutic abortion. 



Regional Blood Flow 



Was Sabatier correct in suggesting that the brain is 

 supplied by the most arterial blood? How much mix- 

 ing is there of the superior and inferior caval blood 

 in the right auricle? How much pulmonary venous 

 blood is added to the inferior caval blood in the left 

 atrium? Huggett, who was the first to carry out ex- 

 periments on the living fetus with an intact placental 

 circulation, found that the oxygen content of the 

 carotid artery exceeded that of the umbilical artery 

 in goats (112); Barcroft observed a 10 to 20 per cent 



