Cardiac output measurement by the injection method without arterial sampling

Cardiac output was measured by the injection method, using I131-labeled human serum albumin as indicator, and measuring concentration-time curves through the intact skin with a collimated scintillation counter. Although, in principle, any number of blood vessels could be used as the measuring site, it was found that because of recirculation, suitable curves were obtained only if the counter was directed toward the head or the heart. Cardiac output values calculated from these curves were compared with values found with the classical sampling method. Head, heart, and arterial sampling curves were measured simultaneously with one injection of radioactive indicator. The measurements show that a head curve could be used in measuring cardiac output by the injection method, but it is not very successful because of the rather high standard deviation of the result (25 per cent). A heart curve, however, can successfully replace an arterial sampling curve. The accuracy of heart and arterial values is about the same (standard deviation 10 per cent). The systematic error of +12 per cent found for our heart values might be reduced by using a collimator that gives the counter a half-value angle of not more than 25°