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A rapid analytical technique for the determination of energy expenditure by the doubly labelled water method
Author(s) -
Barrie A.,
Coward W. A.
Publication year - 1985
Publication title -
biomedical mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 0306-042X
DOI - 10.1002/bms.1200120916
Subject(s) - analyser , doubly labeled water , chemistry , isotope , water vapor , isotope ratio mass spectrometry , mass spectrometry , δ18o , stable isotope ratio , heavy water , body water , process engineering , analytical chemistry (journal) , environmental science , chromatography , body weight , deuterium , nuclear physics , physics , medicine , biochemistry , organic chemistry , basal metabolic rate , engineering
The doubly labelled water method involves the administration of water enriched in 2 H and 18 O followed by determination of the turnover rates of these isotopes. Since 18 O is eliminated from the body as both CO 2 and water, while 2 H leaves only as water, the difference between the two turnover rates provides a measure of CO 2 production and hence energy expenditure. Isotopic analysis by conventional stable isotope ratio analysis (SIRA) is labour intensive and time consuming, as it requires off‐line conversion of water samples to gases (H 2 and CO 2 ) followed by sequential analysis for each of the two isotopes using the mass spectrometer. Lack of suitable automated instrumentation with the ability to process large numbers of samples has prevented routine application of the method. We describe here an automated technique in which body water samples (urine, saliva, breath water or milk) are analysed simultaneously for 2 H and 18 O. The single bench system comprises two mass spectrometer analysers, one for measuring 2 H from H 2 gas, the other for measuring 18 O from the water vapour (masses 18, 20). Both analysers share a common heated inlet system into which microlitre quantities of the body fluids are injected from an autosampler (102 samples). The water vapour flows both directly to one analyser for 18 O measurement and into a uranium reduction furnace for conversion to H 2 , prior to 2 H measurement by the second analyser. Both analysers also share vacuum and electronic components, enabling savings in both space and cost. In this paper we present results illustrating performance characteristics and procedures for routine application to human subjects. Energy expenditure determinations can be made using less than three hours of instrument time per subject.