Determination of Total Body Water and Solids With Isotopes

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Abstract
D2O was found to be applicable for the measurement of total body water. After D2O was injected, samples of serum were analyzed, and the concn. of D2O in the serum was compared with the concn. injected. By use of the equation: V2 = C1V2/C2 where C1 and V1 represent, respectively, the concn. and vol. of the tracer before dilution in the subject, and C2 and V2, concn. and vol. after injn., the arat. of water in which the D2O had been mixed was computed. Densities were detd. in a gradient tube patterned after that of Lindstrom-Lang and Lowry. An accurate estimation of total body water was found by dividing the total amt. of D2O injected by the concn. in the serum in 1 hr. The simultaneous measurement of plasma vol. with dye, red cell vol. with radioactive red cells, extracellular vol. with radioactive Na and with thiocyanate, and total body water with D2O is technically feasible in the human subject. In addition, the total amt. of certain ions in the body can be detd. By allowing radioactive isotopes of these ions to reach equilibrium in body fluids and tissues and then by dividing the specific activity into the total activity, the total wt. of ion present in the body can be calculated. Such calculations were accomplished for K and Na.