PHYSIOLOGIC CONSEQUENCES OF CONGENITAL HEART DISEASE 



431 



FISTULA OPEN 



orE CONC. 



T-1824 

 0.33 mg /kg 



FIG. 2. Dye-dilution curves recorded after injection of dye 

 into antecubital vein of i5-yeai--old youth having a femoral 

 arteriovenous fistula. Upper curve was recorded with fistula 

 open, and lower curve with flow to fistula abolished by manual 

 compression. To be noted are similar appearance times of the 

 two curves with markedly different peak concentrations and 

 systemic recirculation times (intervals between broken lines). 

 Upper curve reflects increased cardiac output and reduced 

 recirculation time owing to rapid flow of blood via shortened 

 vascular pathway through fistula. 



electric components of the transducer and recording 

 system. 



Proper design of these hydraulic components and 

 use of high rates of blood flow through the system 

 allows a more faithful recording of dilution curves. 



BASIC DILUTION-CURVE PATTERNS ASSOCIATED WITH 

 VARIOUS STATES OF THE CIRCULATORY SYSTEM IN MAN. 



The effect of a striking change in cardiac output can 

 be illustrated by comparing dilution curves recorded 

 immediately before and after manual occlusion of a 

 femoral arteriovenous fistula in an otherwise healthy 

 man (fig. 2). The bottom curve, witli the fistula 

 occluded, is normal. A downward deflection occurs 

 with increasing concentration of the dye. The second 

 concentration peak is caused by the dye's recirculating 

 after its first traversal of the systemic circulation. The 

 interval of 18 sec between the two concentration 

 peaks is related to the total circulation time, that is, 

 the time required for the blood to make a complete 

 traversal of the vascular system. 



The upper curve, recorded when the fistula was 

 open, shows the eflfect of a very high cardiac output. 

 The amplitude of the curve is reduced since the dye is 

 diluted in a greater volume of blood, and all the time 

 components are reduced since the velocity of blood 

 flow is increased by the high cardiac output, the 

 systemic recirculation time being decreased by almost 

 50 per cent. 



As would be expected, characteristic alterations in 

 the dilution curves are produced in patients with 

 congenital heart disease associated with left-to-right 



Normal 



L.-^R. 



FIG. 3. Diagram representing major differences from normal 

 of dilution curves characteristic of left-to-right and right-to- 

 left shunts. Distribution of paths of different traversal times has 

 been simplitied (upper panel) to a single circuit, representing 

 normal pathway from venous to arterial circulation. Normal 

 dilution curve obtained from such a circulation, when indicator 

 is injected rapidly into venous circulation (at arrow) and 

 resultant dye-blood mixture is sampled from a systemic artery, 

 is shown at right. Middle panel represents circulation char- 

 acterized by increased pulmonary blood flow due to large 

 left-to-right shunt. Indicator is not cleared rapidly but recircu- 

 lates via defect through central circulation. A constant fraction 

 (dependent on the magnitude of the left-to-right shunt and the 

 systemic flow) leaves this central pool on each circulation. 

 Dilution curve inscribed at right reflects this situation and 

 may be contrasted with normal (broken line). Maximal deflec- 

 tion is reduced, because indicator is dispersed and diluted in 

 the large volume of the central circulation and the high pulmon- 

 ary flow. Disappearance phase is prolonged owing to slow 

 clearance of dye from central pool. Circulation in cases of 

 right-to-left shunt, which is usually associated with reduced 

 pulmonary flow, is illustrated in bottom panel. .\ portion of 

 indicator passes directly to arterial circulation via defect with- 

 out tiaversing longer normal circulatory pathway through 

 lungs and arrives at arterial sampling site before portion that 

 traverses central circulation. Dilution curve inscribed to right 

 demonstrates this early arrival of the portion of indicator 

 shunted right to left by shortened appearance time and ab- 

 normal initial deflection superimposed on build-up portion of 

 curve. 



or right-to-left shunts or combinations of the two. 

 The characteristic curves and the basis for their 

 production are shown diagrammatically in figure 3. 

 The top panel represents the normal situation. The 

 dye is injected into the venous circulation, it traverses 

 a normal pulmonary circulation, and a normal 



