A rapid analytical technique for the determination of energy expenditure by the doubly labelled water method

✍ Scribed by A. Barrie; W. A. Coward

• Publisher: John Wiley and Sons
• Year: 1985
• Tongue: English
• Weight: 699 KB
• Volume: 12
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/bms.1200120916

✦ Synopsis

The doubly labelled water method involves the administration of water enriched in 'H and "0 followed by determination of the turnover rates of these isotopes. Since I8O is eliminated from the body as both CO, and water, while 'H leaves only as water, the difference between the two turnover rates provides a measure of CO, 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 (H2 and C02) 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 'H and "0. The single bench system comprises two mass spectrometer analysers, one for measuring 'H from H, gas, the other for measuring "0 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 l80 measurement and into a uranium reduction furnace for conversion to H , prior to *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.