title: In vivo isotope-fractionation factors and the measurement of deuterium- and oxygen-18-dilution spaces from plasma, urine, saliva, respiratory water vapor, and carbon dioxide.
abstract: In vivo isotope-fractionation factors were determined for hydrogen and oxygen between plasma water samples and samples of urine, saliva, respiratory water vapor, and carbon dioxide in 20 normal adults. The isotope-fractionation factors ranged from 0.944 to 1.039 for 2H in breath water vapor and for 18O in breath CO2, respectively. When corrected for isotope fractionation, the 2H- and 18O-dilution spaces determined from urine, saliva, respiratory water, and CO2 were within -0.10 +/- 1.09 kg (mean +/- SD, n = 60) and 0.04 +/- 0.68 kg (n = 80), respectively, of the values determined from plasma. In the absence of these corrections, we observed a 6% overestimation of 2H-dilution space and a 1% overestimation of 18O-dilution space from the use of respiratory water values. A 4% underestimation of the 18O-dilution space was observed for breath CO2 without correction for isotope fractionation.
mesh_terms: D000328:Adult; D001825:Body Fluid Compartments; D001826:Body Fluids / Q000032:analysis*; D001944:Breath Tests / Q000379:methods; D002245:Carbon Dioxide / Q000032:analysis; D003903:Deuterium; D005260:Female; D006801:Humans; D007201:Indicator Dilution Techniques; D008297:Male; D010103:Oxygen Isotopes; D010949:Plasma / Q000032:analysis; D012016:Reference Values; D012463:Saliva / Q000032:analysis; D013997:Time Factors; D014556:Urine / Q000032:analysis
chemical_list: D010103:Oxygen Isotopes; D002245:Carbon Dioxide; D003903:Deuterium