Abstract
The application of the foreign-gas principle for the determination of the arteriovenous oxygen difference and cardiac output in man is beset by two difficulties; first, the attainment of a homogeneous mixture in the gaseous system with which the arterial blood is assumed to be in equilibrium; second, the termination of the procedure before recirculation of blood takes place. The demonstration that the latter occurs within 10 seconds 1 renders unavailable the mixing technique of Marshall and Grollman 2 which requires 15 seconds, and a fortiori their rebreathing procedure which lasts for 23 seconds.
To restrict the procedure to the time available, the writer has introduced a method for attaining homogeneity of composition that can be finished in 3 1/2 to 4 seconds, and is accomplished by dividing the inhaled foreign-gas mixture into 2 portions, such that the gas filling the dead space approximates in composition the alveolar contents, and further by washing out and discarding the contents of the dead space before the first alveolar sample is drawn.
The apparatus consists of 2 three-way aluminum valves (bore 2 cm.), 2 rubber breathing bags (capacity 4 liters) connected as shown in diagram. Lead tubes 15 cm. in length and of capillary (0.5 mm.) bore permit the drawing of samples from the mouth side of the valve into evacuated sampling tubes. Bag contents are
After the nose clip is applied, the subject expires to residual air, and then inspires the contents of the side bag followed by the contents of the front bag. The experimenter turns valve I so that approximately the first liter of the ensuing expiration is discarded into the side bag, the rest of the expiration being directed into the empty front bag and at the end of this deep expiration the first sample is drawn.
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