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HANDBOOK OF PHYSIOLOGY 



CIRCULATION I 



monary artery. Shepherd et al. concluded that, in the 

 absence of any change in systemic blood pressure, 

 oxygen consumption or heart rate, acetylcholine had 

 dilated the pulmonary vessels with a consequent de- 

 crease in resistance to pulmonary flow and an in- 

 crease in the left-to-right shunt. 



Whatever the cause or causes, pulmonary vascular 

 disease, that is, obstruction to blood flow through the 

 lungs, is a major although relatively uncommon 

 complication of atrial septal defect. As a consequence 

 of this obstruction of flow, pulmonary and right ven- 

 tricular hypertension develop with a decrease in the 

 left-to-right shunt and eventual progression to a pre- 

 dominant right-to-left shunt and deterioration of the 

 cardiovascular status. 



Partial or Total Anomalous Pulmonary Venous Connection 



Partial anomalous pulmonary venous connection 

 with or without coexisting atrial septal defect is 

 usually hemodynamically similar to an uncomplicated 

 atrial septal defect. Right ventricular output is high 

 and little or no demonstrable venoarterial shunting 

 occurs unless pulmonary hypertension develops in 

 association with an atrial septal defect. The course of 

 flow of blood from an anomalously connected pul- 

 monary vein depends in part on its site of entrance to 

 the right side of the heart. If the connection is near or 

 into the superior vena cava, blood will flow preferen- 

 tially to the tricuspid valve. If the connection is into 

 the inferior vena cava and the atrial septal defect is 

 in the usual position, there is a greater tendency for 

 the anomalously drained blood to cross the defect into 

 the left atrium because of the anatomic relation of the 

 inferior vena cava to the foramen ovale. 



TOTAL ANOMALOUS PULMONARY VENOUS CONNECTION. 



When all of the pulmonary veins are transposed to 

 drain anomalously only into the right side of the 

 heart, it is evident that the left side of the heart is 

 bloodless unless there is a communication between 

 it and the right side. In its simplest form this com- 

 munication is a patent foramen ovale, although there 

 may be a true atrial septal defect. It is evident on re- 

 viewing the prenatal circulation that the anomalous 

 circulation associated with total pulmonary venous 

 drainage causes no disturbance in the fetus, but in 

 postnatal life a gross inefficiency in the mammalian- 

 type circulation exists owing to the mixture of pul- 

 monary and systemic venous blood that almost in- 

 variably occurs. 



The optimal condition of the circulation with this 



R.V. 



FIG. 37. Simplified diagram of circulation in total anomalous 

 pulmonary venous connection to right atrium with high pul- 

 monary blood flow. R.A.y L.A., R.V., and i.K. indicate right 

 and left atria and ventricles, respectively, and PA. and P.V. 

 the pulmonary artery and veins. Note that all blood entering 

 left side of heart must traverse atrial septal defect. 



defect is represented diagrammatically in figure 37 

 (46). The unobstructed pulmonary veins empty into 

 the right atrium instead of the left; the only way blood 

 can enter the left side of the heart is through a defect 

 in the atrial septum. From this diagram it can be seen 

 that there is a high-pressure, normal-volume left- 

 heart system, and a low-pressure, high-volume right- 

 heart system. As long as there is no vascular obstruc- 

 tion in the lungs, the cardiac work is not excessive 

 and, from the standpoint of cardiac -energy require- 

 ments, the situation is equivalent to that of an atrial 

 septal defect with a large left-to-right shunt without 

 significant pulmonary hypertension. 



It is apparent that if the communication between 

 the right and left atria were decreased below a critical 

 level, the flow and volume of blood in the left side of 

 the heart would be decreased. The major factor in de- 

 termining the flow of blood through the right side of 

 the heart would be the resistance offered to flow 

 through the lungs. 



Ranges oj hemodynamic values. Cyanosis is not uni- 

 formly present in this condition at birth, although all 

 infants are intermittently cyanotic. Later in life, 

 cyanosis becomes more evident, especially during exer- 

 cise. In a series of 10 cases reported by Swan and co- 

 workers (241) the systemic arterial oxygen saturation 



