The dye dilution method for describing the central circulation. An analysis of factors shaping the time-concentration curves.

T HE method for measuring cardiac output based on the "dye dilution" principle of Stewart and Hamilton" 2 involves the injection of a known amount of colored substance into a vein and collection of serial samples of blood from an artery for determination of the concentration of dye. Other substances have been used for injection, such as salt solution and radioactive cells.3' 4 The validity of this method of measurement of flow depends on the assumption that the dye is distributed throughout a "central" pool of blood as it passes from the vein into the right heart chambers, the lungs, the left heart and out into the arterial system of vessels. The validity and accuracy of the method for determining rates of flow in mechanical systems and the cardiac output in animals and human subjects have been determined by other workers.5 6 Our interest in the dye dilution curves has