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Title: Doubly labeled water method: in vivo oxygen and hydrogen isotope fractionation

The accuracy and precision of the doubly labeled water method for measuring energy expenditure are influenced by isotope fractionation during evaporative water loss and CO/sub 2/ excretion. To characterize in vivo isotope fractionation, we collected and isotopically analyzed physiological fluids and gases. Breath and transcutaneous water vapor were isotopically fractionated. The degree of fractionation indicated that the former was fractionated under equilibrium control at 37/sup 0/C, and the latter was kinetically fractionated. Sweat and urine were unfractionated. By use of isotopic balance models, the fraction of water lost via fractionating routes was estimated from the isotopic abundances of body water, local drinking water, and dietary solids. Fractionated water loss averaged 23% (SD = 10%) of water turnover, which agreed with our previous estimates based on metabolic rate, but there was a systematic difference between the results based on O/sub 2/ and hydrogen. Corrections for isotopic fractionation of water lost in breath and (nonsweat) transcutaneous loss should be made when using labeled water to measure water turnover or CO/sub 2/ production.
Authors:
; ;
Publication Date:
OSTI Identifier:
6928931
Resource Type:
Journal Article
Resource Relation:
Journal Name: Am. J. Physiol.; (United States)
Research Org:
Univ. of Chicago, IL
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; DOUBLE LABELLING; ACCURACY; WATER; CARBON DIOXIDE; EXCRETION; HEAVY WATER; IN VIVO; METABOLISM; OXYGEN ISOTOPES; CARBON COMPOUNDS; CARBON OXIDES; CHALCOGENIDES; CLEARANCE; HYDROGEN COMPOUNDS; ISOTOPES; LABELLING; OXIDES; OXYGEN COMPOUNDS 551001* -- Physiological Systems-- Tracer Techniques