PHYSIOLOGIC CONSEQUENCES OF CONGENITAL HEART DISEASE 



429 



sampling blood from the right side of the heart 

 through the expedient of analyzing for the gas in the 

 air equilibrated with this blood in the lungs and then 

 expired, and b) "injecting" the foreign-gas indicator 

 into the left atrium by the expedient of introducing 

 the gas into the inspired air, where it is equilibrated 

 in the lungs with the blood which flows to the left 

 side of the heart. 



The development of miniature detectors suitable 

 for introduction into the vascular system for recording 

 of the indicator concentration in blood at desired 

 sites in the circulatory system has also expedited the 

 application of these techniques (26, 60, 100). 



Although the advent of these new types of detectors 

 and new indicators, particularly of the gaseous types, 

 has in many instances greatly facilitated various 

 applications of these techniques, these applications 

 are basically closely similar to those previously 

 described, irrespective of the type of indicator and 

 detector used. An important exception to this general 

 statement is the application of gaseous indicators to 

 the detection of blood traversing the pulmonary 

 circulation ijut bypassing aerated alveoli (56, 113). 

 This type of arteriovenous shunt can be detected by 

 dyes or other nongaseous indicators only when the 

 transit time of the shunted blood is significantly 

 shorter than that of blood traversing normally aerated 

 alveoli. Since under this circumstance the transit 

 times of the shunted and the nonshunted blood from 

 the right to the left side of the circulation may be 

 closely similar, this type of shunt would escape 

 detection by the usual nongaseous indicator-dilution 

 methods. Since with this exception the methods are 

 basically closely similar, this discussion of the applica- 

 tion of indicator-dilution techniques to the study of 

 congenital heart disease will be carried out from the 

 viewpoint of the use of an indicator dye injected at 

 any desired site or sites in the circulation, with its 

 concentration being recorded continuously and 

 simultaneously in the blood stream at any other 

 desired site or sites in the circulation. As implied 

 above, the use of conventional dye techniques in 

 these applications has the disadvantage that the 

 required direct access to the injection and sampling 

 sites in the circulation by suitable catheters or needles 

 may, in some applications, pose considerable technical 

 difficulties. The techniques do, however, have the 

 advantage that methods for obtaining quantitative 

 information as to the relative and particularly the 

 absolute magnitudes of systemic, pulmonary, and 

 shunt flows have been developed and are for the most 



part more readily applicable than are the gaseous- 

 indicator and intravascular-detector techniques. 



A number of indicators, such as saline solution, 

 various "blue" dyes and other dyes, and radioactive 

 substances, with the corresponding detecting and 

 recording systems, have been employed (82). Besides 

 causing no cardiovascular disturbance and being 

 readily measurable with precision, an indicator 

 suitable for most quantitative purposes should not be 

 lost from the blood stream during its passage through 

 the segment of the circulation under study. 



Application of oximetric methods to continuous 

 recording of changes in the concentration of indicator 

 in the blood stream was first demonstrated by Matthes 

 (174) in Germany in 1936. Intensive use of earpiece 

 and cuvette oximeters for continuous recording of 

 dye-dilution curves in investigations of cardiovascular 

 physiology in health and disease has been under way 

 since 1950 (273). Other photometric methods for 

 continuous recording of dilution curves have also 

 been introduced. This discussion will deal with the 

 continuous recording of indicator-dilution curves in 

 the blood stream by means of an oximeter or a 

 densitometer, although the same principles will apply 

 to other types of dilution curves or methods of record- 

 ing. In this regard the o.ximeter is used as a dichro- 

 matic densitometer (112), whereas the term 

 "densitometer" connotes a monochromatic device 

 which utilizes, that is, measures, the light transmitted 

 through blood at only one rather than two spectral 

 regions as does the oximeter. The importance of the 

 use of a dichromatic instrument to avoid large 

 possible errors due to nonspecific variations in the 

 optical density of blood that occur with changes in 

 rate of blood flow, carbon dioxide tension, and other 

 factors has recently been emphasized (224, 234). 



For the purposes of this presentation, dilution 

 curves are separated into arterial dilution curves and 

 venous dilution curves (268). An arterial dilution 

 curve is defined as a recording of the concentration 

 of an indicator from any site in the arterial circulation 

 or from the left side of the heart (244). A venous 

 dilution curve is defined as a recording of the con- 

 centration of an indicator at any site in the right side 

 of the heart or the venous circulation (245). 



NORMAL ARTERIAL INDICATOR-DILUTION CURVE. In 



dilution curves recorded by o.ximetry an increasing 

 concentration of indicator usually is recorded as a 

 downward deflection, corresponding to the decreasing 

 light transmission of the blood. Thus after an interval 



