THE VALIDITY OF THE ETHYL IODIDE METHOD FOR MEASURING THE CIRCULATION

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Abstract
The originators of the ethyl iodide method for measuring the circulation here discuss the papers of others on this subject and point out that on the whole they afford confirmation of the practicality and reliability of the method. The observation of Starr and Gamble (see B.A. 1 (6): Entry 8983) that blood is capable of taking up much larger amounts of ethyl iodide than Henderson and Haggard had originally found is confirmed; but it is pointed out that the coefficient needed for calculation of the circulation is not the amount of ethyl iodide held in the blood (presumably in close combination with hemoglobin), but the amount taken up by the blood during each passage through the lungs. This amount is correctly represented by the figure 2; that is, it is twice the amount in the alveolar air. Determinations of the circulation on dogs are reported in which the results by the usual calculations based on the ethyl iodide method are checked against analyses of the arterial and venous bloods, showing an average arterio-venous difference of 2, when the alveolar concentration is 1; and also against determinations by the Fick principle. The agreement is satisfactory. It is then shown that when a man inhales dilute ethyl iodide vapor for 40 min. the concentrations of ethyl iodide in the alveolar air and in the expired air are practically uniform throughout the whole time. The meaning and the advantage of this fact for measurement of the circulation are emphasized in contrast to the constantly changing conditions if other vapors are used.

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