578 HANDBOOK OF PHYSIOLOGY -^ CIRCULATION I 



RIGHT SELECTIVE RCC 



■Alveoli 





CPM 



Time 



LEFT SELECTIVE RCG 



CPM 



WASHOUT LIV 



Time 



FIG. 19. Selective radiocardiography. Rate of radiation 

 from the right \entricle is measured after injecting radioactive 

 krypton solution into the right atrium and evaluating its 

 passage by means of a coUimated rate counter over the pre- 

 cordium. Since it is dissipated in the lungs no measurable 

 amount appears in left ventricular blood. Radioactivity from 

 the left ventricle only is evaluated by injecting a nonvolatile 

 indicator into the pulmonary artery. [From Cournand et al. 



in)-] 



the left ventricular curve and the last of the right 

 heart curve in the radiocardiogram are superim- 

 posed and hidden. Extrapolating the right heart 

 downslope exponentially and subtracting this from 

 the left heart curve gives two discrete curves which 

 were used (86) in the central blood volume calcula- 

 tion. This is a rather precarious procedure and it is 

 not always po.ssible to find a downslope of the right 

 heart curve which can be extrapolated. This is par- 

 ticularly true in a patient with enlarged heart or 

 pulmonary congestion. 



Workers in Cournand's laboratory have sur- 

 mounted these difficulties (17) by tracing the left 

 heart curve from an injection into the pulmonary 

 artery and thus eliminating the display of radioac- 

 tivity from the right heart. Also a tracing from the 

 right heart alone was made by injecting into a vein 

 a solution of a radioactive substance which is highly 

 volatile and is hence eliminated by the lungs before 

 arriving at the left heart (see fig. 19). The substance 

 of choice has been radioactive krypton (Kr*^). 



The most widely used property of blood to make 

 continuous tracings of indicator dilution cvirves is its 



optical density as modified by admixture of various 

 injected substances. By means of photoelectric cells 

 these changes are transduced into electric signals 

 which, with or without amplification, actuate re- 

 cording galvatiometers. 



On a priori grounds it would seem that the simplest 

 method of influencing the optical density of a flowing 

 stream would be to inject a transparent substance to 

 reduce the optical density of hemoglobin by simple 

 dilution. Experience and calculation, however, show 

 that very large quantities of such fluid (saline, plasma 

 dextran) would have to be injected in order to bring 

 about the change in optical density produced by a 

 few milligrams per liter of T- 1824 at the proper wave- 

 length. We have not found that this inethod has had 

 any practical employment for measuring the cardiac 

 output quantitatively. 



The use of a dye as an indicator, the dilution of 

 which is continuously recorded, has gi\en rise to a 

 great deal of fruitful work. One line of attack stems 

 from the development of the oximeter. This instru- 

 ment was based on the early researches of Matthes 

 (95) and Kramer & Winton (85). It was further de- 

 veloped by Millikan (99) and Wood & Geraci (148). 

 The oximeter is used by Wood (147) not only to 

 measure oxygen saturation but also to inscribe dye 

 dilution curves for measuring the cardiac output and 

 for the diagnosis of cardiac abnormalities (see Chapter 

 14). The oximeter was designed to measure the blue- 

 ness and hence the unsaturation of blood. It can also 

 measure the blueness of blood to which blue dye has 

 been added and thus quantitate the dye. 



It has two photoelectric cells which are filtered so 

 that one is sensitive to red light (about 625 m^) and 

 the other sensitive to infrared light (about Boo mix). 

 The apparatus measures the difference between the 

 transmissions of red and infrared light by the blood 

 sample (37, 149). This dual circuit reduces the effect 

 of fluctuations of light transmission due to changes in 

 the amount of hemoglobin in the light path. Since the 

 blue dye T-1824 absorbs light at wavelength 625 m^u 

 quite strongly, as does reduced hemoglobin, the oxi- 

 metric deflection is proportional to the amount of the 

 dye just as it is to the amount of reduced hemoglobin. 

 Therefore, it will produce a deflection that is propor- 

 tional to the amount of blue dye in the light path, pro- 

 vided the hemoglobin is itself completely o.xygenated. 



Dye dilution curves obtained in this way have been 

 widely used in measuring the output of the heart 

 under varying conditions, and their accuracy seems to 

 be accepted. 



A blue dye "Coomassie blue"' has been suggested as 



