PHYSIOLOGIC CONSEqUENCES OF CONGENITAL HEART DISEASE 



443 



in the blood could give rise to contraction of the 

 vessels in the upper half of the body vvas likewise 

 untenable. He suggested that some abnormality of the 

 peripheral arterioles might explain an increase in 

 resistance in the upper extremities. 



The observations by Goldbiatt and co-workers 

 (ii6) in 1939 that constriction of the aorta in dogs 

 above the origin of the renal arteries would lead to 

 the development of hypertension, whereas con- 

 struction below these vessels resulted in no change in 

 pressure proximal to the constriction, led many 

 observers to postulate the release of a renal pressor 

 substance (humoral theory) to explain the hyper- 

 tension in coarctation. Steele (229) observed that the 

 femoral diastolic pressure was elevated in some cases 

 of coarctation of the aorta and interpreted this as 

 evidence of a general increase in arteriolar tone 

 throughout the body. Stewart & Bailey (231) and 

 Page (183) arrived at similar conclusions. Sealy and 

 colleagues (213), Scott & Bahnson (211) and Scott 

 and co-workers (212) have also studied the effect of 

 constricting the aorta in dogs and have confirmed 

 the observations of Goldbiatt and co-workers. In 

 addition, Scott and colleagues found that trans- 

 plantation of one kidney of a dog to a site above the 

 constriction of the aorta and removal of the second 

 kidney below the coarctation led to a return of the 

 blood pressure to normal levels. 



Genest and co-workers (114) and Tonelli et al. 

 (249) observed an improvement in renal function and 

 renal blood flow following surgical relief of coarctation 

 of the aorta which they felt was evidence for the 

 humoral theory in producing the hypertension. 



VVerko and collaborators (259), however, pointed 

 out that the slight decrease of renal iilood flow in 

 patients with coarctation prior to surgical correction 

 was of the same magnitude as in patients with atrial 

 septal defect or patent ductus arteriosus. They con- 

 cluded that the decreased renal blood flow showed no 

 relation to the origin of increased blood pressure in 

 coarctation of the aorta. 



Gupta cS: VViggers (126) analyzed the changes in 

 left ventricular, aortic, and femoral pressure pulses in 

 dogs before and after graded constriction of the 

 aorta. They concluded that hypertension in the aorta 

 above a coarctation is not due solely to an increase in 

 resistance. Equally important, they thought, were the 

 reduced capacity and the reduced distensibility of the 

 aortic compression chamber into which the left 

 ventricle empties its ijlood during each systole. They 

 also found some evidence that the systolic discharge 

 from the left ventricle was increased. Gupta & 



Wiggers (126) also pointed out that the maintenance 

 of femoral diastolic pressure at or above normal levels 

 as the systolic pressure falls may be an indirect effect 

 of damping, since damping tends to reduce pressure 

 variations toward a mean level. 



If purely mechanical factors were sufficient to 

 account for the hypertension and if the resistance to 

 flow through the upper limbs were normal, then the 

 flow through these limbs would be greater than 

 normal because of the increased perfusion pressure. 

 On the other hand, neurogenic or humoral factors 

 would be expected to increase the vascular resistance 

 both above and below the coarctation. 



Bing et al. (28) reported an increase in flow through 

 the upper and a decrease through the lower extremity. 

 Lewis (162), Pickering (190), and Wakim and 

 colleagues (255) found normal values for these flows, 

 whereas Prinzmetal & Wilson (194) found a de- 

 creased flow through the upper extremities. Although 

 these results appear to conflict, they can probably be 

 explained by the wide range of flow through both the 

 upper and the lower limbs of normal people, and it 

 seems clear that at least in the majority of patients 

 with coarctation of the aorta the blood flow is within 

 normal limits. 



The wide range of blood flow in the forearm and 

 calf means that no accurate prediction of the vascular 

 resistance can be made unless both flow and pressure 

 are measured above and below the site of the coarcta- 

 tion. This study was made by Patterson and co- 

 workers (188), who found increased resistance in the 

 forearm and normal resistance in the calf. 



Bayliss (22) and Folkow (105) have demonstrated 

 that blood vessels respond to a rise in blood pressure 

 by increasing their tone. This occurs even when the 

 limb is denervated and is probably a direct response 

 of the smooth muscles of the arterioles. This finding 

 has been confirmed in man by Patterson & Shepherd 

 (187) and by Coles & Greenfield (63). Although this 

 phenomenon may play a part in the increase in 

 resistance to flow in the upper limb seen in coarcta- 

 tion, it would follow an increase in transmural 

 pressure and not in itself initiate the hypertension. 

 Such a mechanism could operate to augment the 

 pressure, however, if mechanical factors initiated the 

 hypertension. 



Surgical removal of the coarcted segment of the 

 aorta has generally resulted in improvement of the 

 circulatory dynamics of these patients. Wright and 

 collaborators (283) reported on the immediate as 

 well as the long-term results of surgical correction 

 of coarctation. They found, in addition to a dramatic 



