The Determination of the Cardiac Output of Man by the Use of Acetylene

The various methods described in recent years for determining the cardiac output of man consist essentially either 1, in an application of the Fick principle, or 2, in measuring the rate with which either a normally present gas (nitrogen) or a foreign gas (nitrous oxide, ethyl iodide or ethylene) is exchanged during the passage of the blood through the lungs. Results obtained by the carbon dioxide methods, which are based on the Fick principle, have been criticized in previous publications (Marshall and Grollman, 1928; Grollman, 1928b), and the difficulty of measuring the rate of elimination of nitrogen has also been demonstrated (Marshall, Harrop, and Grollman, 1928). The idea entertained by Henderson and Haggard (1925) that in ethyl iodide they had found a gas which was completely destroyed in the organism before the completion of a circuit by the blood, has been shown to be erroneous. It is only by abandoning this idea and actually determining the amount of this gas in the venous blood, as has been done recently by Starr and Gamble (1928), that any values worthy of consideration have been obtained. In the case of the other foreign gases-nitrous oxide and ethylene-as used in the procedures of the hope of any destruction of these gases was never entertained, and the methods were elaborated so as to complete the determination in the time of a single circuit of the blood. In the present communication the use of another gas, acetylene, is advocated for the determination of the cardiac output of man. This gas will be shown to have many advantages over the gases heretofore used both as regards ease of manipulation and degree of accuracy obtainable. Comparative value of di$erent gases. In the comparative evaluation of any gas for the determination of the cardiac output, aside from the considerations regarding the method itself, the following are the chief factors which must be considered: 1, the solubility of the gas in blood; 2, the variation of this solubility in the blood of different individuals; 3, the ease of manipulation of the gas, and 4 the analytical determination of the gas. Solubility of gases in blood. The absolute value of the solubility of the