A METHOD FOR THE DETERMINATION OF THE CIRCULATORY MINUTE VOLUME IN MAN

Abstract

This method consists in rebreathing from a rubber bag a mixture of ethylene, O, and N or one of nitrous oxide, O and N. When complete mixture of these gases and the residual air of the lungs has been obtained (15 sec.) a sample of gas is taken and 10 or 12 sec. later a 2nd sample. These are analyzed for ethylene (or nitrous oxide), O, and CO2, and from the data obtained, together with the solubility of ethylene (or nitrous oxide) in blood, the amount of O taken up by 11. of blood in passing through the lungs is calculated. A determination of the O con-sumption completes the data necessary for calculating the minute volume of the circulation. Special experiments have proved that complete mixture of the gases in the lung-bag system takes place in 15 sec., and that equilibrium of the foreign gas with the blood is attained. No difference in the results is obtained if the whole experiment is prolonged for 10 sec., which indicates that no appreciable amount of the foreign gas is being returned by the mixed venous blood and that the 0 content of the mixed venous blood is unchanged from the normal. A series of determinations of the blood flow of various individuals using low concentrations of ethylene (1.5%), high concentration of ethylene (15%), and nitrous oxide (12%), respectively, gave identical results. The minute volume of the circulation determined in the basal condition varied from 3 to 5 1. in a series of 12 individuals.