Effect of varying indicator injection sites on values for cardiac output

¹ Duke University Medical Center, Durham, North Carolina

Simultaneous injections of Evans blue dye (T-1824) and iodinated (I¹³¹) human serum albumin (IHSA) into the antecubital or femoral veins of four normal subjects gave the same values for cardiac output when arterial samples were analyzed. Two indicator dilution curves were constructed from arterial samples collected after the simultaneous injection of dye into the superior vena cava and IHSA into the antecubital or femoral vein. A third dilution curve was recorded by a crystal placed against the chest in a position where it was activated by IHSA in both right and left chambers of the heart. Observations were made in the resting state and after the circulation was increased by atropine or isoproterenol. In the analysis of arterial samples, injection of an indicator into the superior vena cava gave lower values for cardiac output than injection into the antecubital or femoral veins. When the isotope was injected (in a volume of 1.5–2 ml) into an antecubital vein, the values for cardiac output calculated by external counting were similar to values obtained by arterial sampling of dye injected into the superior vena cava. The values for cardiac output by external counting after femoral injection of the indicator were consistently higher than the values obtained with the centrally injected dye.