Page 6, O2 Uptake, Exercise & Cor. Circ., Dr. D. Penney
Cardiac Output Determination (continued..)
A dye-dilution curve from a normal conscious dog is shown in Figure 3.03. The dye (2.5 mg cardiogreen) was injected rapidly into the jugular vein at 0 time and blood samples were obtained from the thoracic aorta through a cuvette densitometer by means of a motorized syringe that withdrew 28 ml of arterial blood per minute. The dye first appeared in the densitometer 6 seconds after the injection (6 sec. = appearance time). Recirculation of the dye began 9 seconds later and the peak of the recirculation curve was noted at 20.4 sec. The time from the peak of the first curve to the peak of the second curve is called the mean recirculation time (11.2 sec.).
To calculate cardiac output from the dye curve, we need the average dye concentration under the curve (determined to be 0.0037 mg/ml) and the duration of the dye curve (actual + extrapolated; 15.6 sec.). The calculation is done as below:
C.O. = 2.5 mg. x 60 sec./min. / (0.0037 mg/ml.) x (15.6 sec.) = 2,600 ml./min.
Note: cold saline is used clinically as the "dye"
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