PHYSIOLOGIC CONSEQUENCES OF CONGENITAL HEART DISEASE 



467 



TABLE 7. Average and Range of Hemodynamic Variables 

 in 10 Cases of Total Anomalous Pulmonary Venous 

 Connection Studied by Cardiac Catheterization 



averae;ed 85 per cent, with a range from 70 to 94 per 

 cent (table 7). However, 6 of these 10 patients studied 

 were aduhs. In the patients with the more nearly 

 normal systemic arterial oxygen saturation the pres- 

 sures in the pulmonary artery were normal and these 

 patients had the highest values for pulmonary flow. 



The saturation of blood in the common venous pool 

 (right atrium) might be expected to be the same as 

 that in the pulmonary artery and the aorta, as pointed 

 out in the precatheterization era by Taussig (247). 

 Actually in this series of cases the o.xygen saturations 

 of pulmonary and systemic -artery blood were equal in 

 four cases, whereas in the remaining cases the satura- 

 tion of pulmonary-artery blood exceeded that of 

 systemic blood by i to 7 per cent (fig. 38). 



This difference indicates that complete mixing of 

 blood has not occurred in the atrium and that a greater 

 proportion of desaturated systemic venous blood passes 

 to the systemic than to the pulmonary circulation. This 

 situation is the result of a combination of circum- 

 stances. It has been well documented that inferior 

 venacaval blood shunts preferentially across the inter- 

 atrial communications located at the site of the 

 foramen ovale; consequently superior vena caval 

 blood under such circumstances passes preferentially 

 into the tricuspid valve. If the pulmonary veins con- 

 nect directly to, in juxtaposition to, or to a tributary 

 of, the superior vena cava and if the atrial septal defect 

 is in the usual location, then, owing to these flow pat- 

 terns in the right atrium, a greater proportion of pul- 

 monary-vein blood flows into the right ventricle than 

 into the left ventricle via the interatrial communica- 

 tion. In the case of total anomalous connection to the 

 inferior vena cava or its tributaries it would be ex- 

 pected that the oxygen saturation of systemic arterial 

 blood would exceed that in the pulmonary artery. In 

 general, however, there is a close similarity in systemic 

 and pulmonary-artery blood oxygen saturation, the 

 greatest difference in the oxygen saturation in this 

 series being 7 per cent. 



Factors that determine the arterial oxygen saturation. In all 



BREATHING;-^ 



FIG. 38. Comparison of oxygen saturation of pulmonary 

 and systemic -artery blood in lo patients with total anomalous 

 pulmonary venous connection. Patients i through g were 

 studied while breathing air. Patient 10, 5 months old, was 

 studied while breathing 100 per cent oxygen. In patients i, 2, 

 3, and 10, saturation of systemic-artery blood equaled that of 

 pulmonary-artery blood, but in the other patients oxygen 

 saturation of pulmonary-artery blood exceeded systemic-artery 

 value by 1 to 7% (see text for discussion). Patients i through 

 4 were not cyanotic while at rest. 



types of this anomaly, all blood from both the pul- 

 monary and the systemic circulation returns to the 

 right atrium (fig. 37). If the pulmonary resistance is 

 low there will be a very inuch greater flow of blood 

 through the lung than through the systemic circuit. As 

 a consequence, a great quantity of highly saturated 

 blood from the lung returns to mi.x with a lesser quan- 

 tity of desaturated systemic venous blood. Thus the 

 oxygen saturation of systemic arterial blood remains 

 high as long as the high pulmonary blood flow is 

 maintained. As Burchell (46) has pointed out, the 

 level of arterial blood saturation will be dependent, at 

 any specific blood hemoglobin content and in the 

 presence of healthy lungs, on only two factors: /) 

 the amount of oxygen extracted by the tissues, and 2) 

 the pulmonary blood flow. This may be expressed as 

 follows : 



Ca = 



Qp Cpv - Vo, 



Qp 



= Cpv 



Vo, 



Qp 



where Ca and Cpv equal the oxygen content of sys- 

 temic arterial and pulmonary venous blood (ml/liter), 

 respectively, Qp equals pulmonary blood flow (liters/ 

 min) and Voj equals the oxygen consumption 

 (ml/min). 



The assumptions are that there are normal oxygena- 



