468 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION I 



FIG. 39. Calculated relationship between pulmonary blood 

 flow and arterial oxygen saturation in total anomalous pulmon- 

 ary venous connection to right atrium at assumed values of 

 200, 350, and 500 ml/nnin for oxygen uptake, .\ssumptions 

 made are discussed in text. Oxygen capacity of blood = 200 

 ml/liter. 



tion of the blood in the hings and complete mixing of 

 blood in the right atrium. As has been shown, the 

 latter assumption is not strictly correct; however, in 

 general it is accurate enough to allow one a general 

 understanding. If this assumption is overlooked, one 

 may calculate the arterial oxygen saturation for any 

 hemoglobin content of the blood, metabolic rate and 

 pulmonary flow (fig. 39). When high pulmonary flows 

 are present, the arterial saturations will be high, ap- 

 proaching normal. The upper curve shows calcula- 

 tions based on an arbitrary resting oxygen uptake of 

 200 ml per min. The lower curve shows the predicted 

 arterial oxygen saturation when the oxygen uptake is 

 500 ml per min, such as might occur with mild exer- 

 cise. 



The relation between pulmonary blood flow and 

 systemic arterial oxygen saturation in eight patients 

 with total anomalous pulmonary venous connection is 

 shown in figure 40. It is apparent that these data fit 

 well with the theoretic curves. In this series of cases a 

 reduced pulmonary flow was always associated with 

 increased pressure in the pulmonary artery, and from 

 this it may be deduced that a reduction in systemic 

 arterial oxygen saturation is associated with an in- 

 crease in pulmonary vascular resistance. 



When any condition, such as exercise, increases the 

 metabolic rate the arterial oxygen saturation would be 

 expected to decrease also, and this has been found to 

 be so. Burchell (46) reported that in four patients with 

 high pulmonary flows the systemic arterial oxygen 

 saturation decreased from rest to exercise from go to 

 86, gi to 86, g2 to gi, and 92 to 84 per cent, respec- 



FIG. 40. Relation of systemic and pulmonary-artery blood 

 oxygen satuiations to the ratio of pulmonary flow (Qp) to 

 systemic flow (Qs) in eight patients with total anomalous 

 pulmonary venous connection. Two values are given for each 

 patient (open and solid circles, respectively). When values coincide, 

 case is represented by a circle with one segment closed. Note 

 positive correlation between magnitude of pulmonary blood 

 flow and level of blood oxygen saturation. 



tively. In one patient with low pulmonary flow and a 

 saturation of 76 per cent at rest, the saturation dropped 

 to 40 per cent with exercise. 



Persistent Common Atrioventricular Canal 



There is a wide possibility for hemodynamic altera- 

 tions in patients with persistent common atrioven- 

 tricular canal, depending on the degree of the ana- 

 tomic malformation that is present in an individual 

 case. Many patients with this defect die in early in- 

 fancy and in this respect are similar clinically and 

 probably hemodynamically to patients with large 

 ventricular septal defects. On the other hand, patients 

 may live to adult life and be relatively asymptomatic. 

 This situation would be more like that seen in patients 

 with atrial septal defect. 



When the communication is mainly between the 

 atria one would expect to find relatively normal pres- 

 sures in the right side of the heart and a high pul- 

 monary blood flow. If the communication is prin- 

 cipall\' between the two \entricles, pressures in the 

 right ventricle and pulmonary artery would be ele- 

 vated, and if the pulmonary vascular resistance were 

 not severely increased, the pulmonary blood flow 

 would be increased. 



HEMODYNAMIC FINDINGS. Seventeen cases of proved 

 persistent common atrioventricular canal were studied 

 1)\- Wakai et al. (254). In this series were 7 adults 

 ranging in age from 21 to 28 years and 10 children 

 whose ages ranged from 4 months to 13 years. The 

 .svstemic blood flow was normal in all cases when ex- 



