430 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION I 



cycles/minute: 



APPARENT 



DYE CONTENT 



OF BLOOD 



IN CUVETTE 



1-1624 



mq./L. 



Or 



\0 

 20 



40 



RESPONSE AS % OF 

 STATIC sensitivity: 



POSITION OF VALVE 

 (Dye Content Of Bloodf 



LIGHT TRANSMISSION 

 OF BLOOD 



B&SE UNE- 



Undjed B/ )od 



1.0 



99 % 



(30 



Dy(d Blool 



mg./L.) 



10 sec. 



5 cm, 



4.1 



83 % 



9.9 



67% 



20.2 



'VJV\ 



43% 



: s 



31 



15 



FIG. I . Response of cuvette oximeter to variations in dye content of v/hole blood of equal am- 

 plitude and variable frequency. Square-wave variations in dye content of whole blocd were pro- 

 duced by drawing blood at constant rate through mechanically operated two-position valve system. 

 In one position of valve, blood containing 30 mg of Evans blue per liter was drawn into cuvette 

 system; in the other position undyed blood entered system. Apparent dye content of blood, de- 

 termined by cuvette oximeter, is shown above actual dye content as fixed by position of valve. 

 Note / ) delay and distortion in response of cuvette-oximeter system to change in dye content, and 

 2) decrease in amplitude of response of system to same change in dye content of blood as frequency 

 of variations in dye concentration increased. Blood flow through cuvette, which was attached to a 

 20-gauge needle (5 cm long, 0.6 mm in internal diameter), a system identical to that used for re- 

 cording arterial dilution curves, was 26.5 ml/min. [From Fox el al. (109).] 



(appearance time) equal to the shortest traversal 

 time of the indicator particles to the sampling site, 

 dye is detected at the sampling site. Successively 

 greater numbers of particles then rapidly arrive at 

 the sampling site until a maximum (peak concen- 

 tration) is reached, whereupon their number de- 

 creases, the rate of decline being slower than that of 

 the increase. Before the number of particles declines 

 to zero, it increases again because of arrival of the 

 more slowly moving particles on their first circulation, 

 coinciding with arrival of the faster particles that 

 have already made one complete circulation and are 

 appearing at the arterial sampling site a second time. 

 A second peak (recirculation peak) occurs when the 

 maximal amount of recirculating indicator arrives at 

 the sampling site. 



It has been stated that a recording of the dilution 

 of an indicator during its initial traversal of a circula- 

 tion provides more information concerning the status 

 of this circulation than does observation of any other 

 single physiologic variable (273). From such a 

 dilution curve one can determine such factors as a) 

 volume rate of flow through this circulation, b) 

 volume of the system between injection and sampling 



sites, c) fastest and mean circulation times through 

 the system, and d) presence or absence of abnormal 

 circulatory pathways, as well as magnitude of the 

 flow through such pathways when present. 



A number of excellent recent reviews of indicator- 

 dilution curves have been published that discuss the 

 theoretic implications in determining blood flow and 

 N'olume (82, 1 12). 



Records of rapidh' changing concentrations of 

 indicator in the blood are affected by the dynamic- 

 response characteristics of the particular detecting 

 instrument and recording assembly used. The 

 dynamic-response characteristics of various cuvette- 

 oximeter assemblies have been studied by Fox and 

 co-workers (log) (fig. i). At a frequency of 10 cycles 

 per min these recording assemblies show a definite 

 decrease in response. Ultimately the relatively poor 

 dynamic response of instruments, such as the cuvette 

 oximeter or densitometer, is determined chiefly by the 

 hydraulic components of the system, namely, the 

 volume of the detecting chamber and the length and 

 internal diameter of the connecting tubes and the 

 linear velocity of blood flow through them, rather 

 than by the dynamic-response characteristics of the 



