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36
PROGRESS IN ATOMIC MEDICINE
the determination of body water and electrolytes. The development of a
gas dilution device has made possible the convenient measurement of.
body volume. Analytical reviews of the concepts and principles of body
composition measurements‘"**"* have been published. This review will
be concerned with the measurement of body composition in mani by
isotopic means but must. of necessity, include at least reference to body
volume and body density. Two comprehensive reviews of body composition were published in 1963. The book by Moore et al.*° contains a
(letailed description of the methods developed by his group, their data
in normal subjects. together with a compilation of the data from the
literature and an extensive report of the application to a variety of
clinical problems. The New York Academy of Sciences, Volume 110,
ee
{September 26, 1963) contains an extensive review of many body com-
position studies.
.
Principles of Isotope Dilution: All measurements of body composition
by isotopic means depend upon the use of suitable tracer substances and
the measurement of their distribution in a specific biochemical or anatomical compartment. The principles of isotope dilution have been used
in a numberof studies and are widely known. The principle equation is
as follows:
C.iVi =C:V2
where C, = Cone.of isotope in Vol. Vi
C, = Conc. of isotope in Vol. V2,
or alternatively, where C represents the specific activity (in terms of
isotope/unit mass) and V represents mass. However, the requirements
for a satisfactory determination of quantity by the isotope dilution
method are muchless frequently discussed. These are as follows: (1) for
the measurement of any particular body component, there must be a
suitable isotopic tracer, either radioactive or an enriched stable atom,
as in the case of deuterated water; (2) it must be possible to place this
atom quantitatively in the compartment under study: (3) it must be
uniformly distributed within the compartment: (4) the rate of loss of
the label from the compartment under study should be measurable and
preferably slow when compared to the rate of mixing; and (5) facilities
for obtaining an adequate sample must be available. These requirements
are fully met for only a limited number of the body constituents.
Various methods of analysis of isotopic dilution data are possible.
*Reference to studies in experimental animals will be included where data for man
are not available or where implications for studies in man are apparent.
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