Use of Krypton 85 for the Measurement of Cardiac Output by the Single-Injection Indicator-Dilution Technique

When krypton85 in saline solution is injected into the left side of the heart and sampled from a systemic artery, or is injected into a peripheral vein and sampled from the pulmonary artery, only the primary time-concentration curve is obtained. Recirculation is eliminated by the diffusion of this indicator into the extravascular space and its loss from the pulmonary capillary bed. Determination of the radioactivity in a single blood sample, withdrawn at a constant rate throughout the period during which the Kr85 passes across. the sampling site, permits calculation of the average concentration of Kr85 during the inscription of the primary curve. The validity of this technique was tested in a circulatory model against actual flow determined by timed collection. One standard deviation of the differences in 27 trials equaled 5.1 per cent. In 26 comparisons of cardiac output determined simultaneously in dogs by a rotameter and the Kr85 technique, one standard deviation of the differences equaled 8.4 per cent. In 19 comparisons of cardiac output in patients, determined by dye-dilution and Kr85 techniques, one standard deviation of the differences equaled 11 per cent. The Kr85 technique is simpler technically and requires less blood, instrumentation, and calculation than the standard dye techniques.