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HANDBOOK OF PHYSIOLOGY 



CIRCULATION I 



TABLE 9. Average and Range of Hemodynamic Data 

 in j6 Patients With Tetralogy of Fallot 



* Average of 17 patients. 



flow (29), indicating that when the pulmonary 

 stenosis is very severe the major pathway for blood 

 flow to the lungs may be via collateral vascular chan- 

 nels (bronchial arteries). This was found to be par- 

 ticularly true in the older age groups studied. 



The systolic gradient between the right ventricle 

 and the pulmonary artery in Brotmacher & Camp- 

 bell's series (44) was between 35 and 52 mm of mer- 

 cury in five and between 60 and 99 mm in the re- 

 mainder of the patients. The systolic right ventricular 

 pressure was elevated in all cases, and in all but five 

 instances it was within 20 mm of the peripheral 

 systemic arterial systolic pressure. 



Pulmonary and systemic blood flow. In patients with 

 more severe degrees of pulmonary stenosis a right-to- 

 left shunt is present and frequently exceeds i liter 

 per min per m^. A left-to-right shunt may also exist 

 but is usually of a lesser order. The determining factor 

 in the direction and magnitude of the shunt is the 

 relative resistances to blood flow through the stenotic 

 pulmonary valve or outflow tract and flow through 

 the systemic vascular bed via the unobstructed aorta. 

 Hemodynamically these patients are similar to pa- 

 tients with a large ventricular septal defect without 

 pulmonary stenosis but with severely elevated pul- 

 monary vascular resistance. In one instance the resist- 

 ance to pulmonary blood flow is due to the stenosis, 

 and in the other to the decreased caliber of the resist- 

 ance vessels in the pulmonary vascular bed. 



In tetralogy of Fallot, in addition to pulmonary 

 stenosis and ventricular septal defect, there is over- 

 riding of the aorta which in tlie past has been con- 

 sidered an important causative factor in the cyanosis 

 characteristic of this condition. Brotmacher & Camp- 

 bell (44) have pointed out that varying degrees of 

 overriding occur and that the degree of overriding may 

 be secondary to the right-to-left shunt rather than pri- 

 mary. That overriding of the aorta may be present 

 without cyanosis is demonstrated by many patients 

 with tetralogy of Fallot who ha\c had a successful 

 valvotom\' or infunclilnilar resection and exhibit no or 



only minimal cyanosis following the operation. Camp- 

 bell and co-workers (51) discussed some of those pa- 

 tients who had been recatheterized after operation 

 and were acyanotic with an arterial oxygen saturation 

 between 92 and 98 per cent, although it had averaged 

 as low as 81 per cent prior to operation. Wood (276) 

 also has described several cases of this type. On the 

 basis of these findings, Brotmacher & Campbell (43) 

 concluded that the presence or absence of a right-to- 

 Icft sliunt depends primarily on the relative resistances 

 to blood flow in the pulmonary and systemic circuits 

 and not on the degree of overriding of the aorta. 

 Present-day investigators are in general agreement 

 that the relationship of the aortic root to the ven- 

 tricular septal defect plays no significant role in the 

 altered hemodynamics (47). 



Collateral pulmonary blood flow. Pulmonary arterial 

 blood flow is greatly reduced in many patients with 

 .severe pulmonarv stenosis, and in these instances, 

 owing to the small amount of blood that is oxygenated 

 and to the right-to-left shunt that is present, systemic 

 arterial blood may be severely desaturated. This pul- 

 monary blood flow may be augmented by collateral 

 flow to the lungs \'ia large bronchial and other 

 accessory arteries, which are usually noted during 

 operation in these cases. Bing et al. (29) calculated the 

 pulmonary capillary blood flow, utilizing the Fick 

 principle, by determining the output of carbon dioxide 

 and indirectly determining the concentrations of car- 

 bon dioxide entering and leaving the pulmonary 

 capillary bed. Although these results can be accepted 

 as only approximations, he found that in most of the 

 younger individuals the values for pulmonary capil- 

 lary flow agreed closely with those determined for 

 pulmonary-artery flow. In older individuals, however, 

 pulmonary capillary flow was found to exceed pul- 

 monary-artery flow In those patients in whom calcu- 

 lations indicated the presence of extensive collateral 

 circulation to the lungs, large bronchial arteries were 

 found. Bing and co-workers found that this collateral 

 blood flow frequently exceeded i liter per min per m'-. 

 They pointed out that the collateral circulation to the 

 lungs represents an important factor in the phy.siologic 

 adjustments of these individuals to their abnormally 

 low pulmonary -artery flow. By increasing the pul- 

 monary blood flow the per cent of fully oxygenated 

 blood entering the .systemic circulation is increased, 

 thus increasing the systemic arterial oxygen saturation. 

 Ventricular septal defect with tricuspid stenosis. Stenosis 

 of the tricuspid valve would have no direct hemody- 

 namic effect on the hemodynamic alterations due to 

 a coexisting ventricular septal defect. If the tricuspid 



