Christoph Fusch
Measurement of Water Turnover Using Deuterium Dilution: Impact of Periodically Varying Turnover Rates on Precision and Accuracy
Water metabolism may be non-invasively investigated
using deuterium elimination from the body. Evaluation
of elimination constants (kD) and pool sizes (N) becomes
complicated when turnover rates vary periodically - a realistic scenario in free-living subjects.
Unfortunately, phase and frequency of periodic variations
are not a priori known and can therefore not be
used for a sampling protocol. This study investigates
the impact of periodical flux variations on the measurement
of water turnover. For two models of periodic
variation with identical apparent kD, data sets of
tracer concentrations in body water were generated
for two-hour intervals using a monoexponential decay
equation. Data were analyzed using the two- and the
multi-point method increasing observation periods
stepwise. Apparent values for kD, N and water turnover
(RH?O) were compared with values originally used
in the model. Periodically varying turnover rates introduce
considerable errors for kD and RH?O when the two-point
method is used. The multi-point method gives a
more robust estimate of RH?O already after short observation
periods, however, due to slope-intercept
correlations, still tends to overestimate RH?O. Errors
are more pronounced the more uneven flux rates are
distributed. Stepwise analysis of tracer enrichments
using the multi-point approach identifies periodical
variation of flux rates.
Clinical Chemical Laboratory Medicine, Walter de Gruyter
Print ISSN: 1434-6621
Volume: 38, 10/2000
Pages: 961 - 964
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