title: The ¹³C bicarbonate method: an inverse end product method for measuring CO₂ production and energy expenditure.
abstract: We reconsider the principle of the (13)C bicarbonate (NaH(13)CO3) method ((13)C-BM) for the determination of the CO2 production to obtain an estimate of energy expenditure (EE). Its mathematical concept based on a three-compartmental model is related to the [(15)N]glycine end product method. The CO2 production calculated by the (13)C-BM, RaCO2((13)C) is compared to the result from the indirect calorimetry, RCO2(IC). In an interspecies comparison (dog, goat, horse, cattle, children, adult human; body mass ranging from 15 to 350 kg, resting and fasting conditions) we found an excellent correlation between the results of (13)C-BM and IC with RCO2(IC) = 0.703 × RaCO2((13)C), (R(2) = 0.99). The slope of this correlation corresponds to the fractional (13)C recovery (RF((13)C)) of (13)C in breath CO2 after administration of NaH(13)CO3. Significant increase in RF((13)C) was found in physically active dogs (0.95 ± 0.14; n = 5) vs. resting dogs (0.71 ± 0.10, n = 17; p = .015). The (13)C recovery in young bulls was greater in blood CO2 (0.81 ± 0.05) vs. breath CO2 (0.73 ± 0.05, n = 12, p < .001) and in ponies with oral (0.76 ± 0.03, n = 8) vs. intravenous administration of NaH(13)CO3 (0.69 ± 0.07; n = 8; p = .026). We suggest considering the (13)C-BM as a 'stand-alone' method to provide information on the total CO2 production as an index of EE.
authors.affiliation: a Leibniz Institute for Farm Animal Biology, Institute of Nutritional Physiology 'Oskar Kellner' , Dummerstorf , Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Junghans
authors.affiliation: b Department of Veterinary Clinical and Animal Sciences, Faculty of Health and Medical Sciences , University of Copenhagen , Frederiksberg C , Denmark.
authors.forename: Caroline
authors.initials: C
authors.lastname: Larsson
authors.affiliation: b Department of Veterinary Clinical and Animal Sciences, Faculty of Health and Medical Sciences , University of Copenhagen , Frederiksberg C , Denmark.
authors.forename: Rasmus Bovbjerg
authors.initials: RB
authors.lastname: Jensen
authors.affiliation: b Department of Veterinary Clinical and Animal Sciences, Faculty of Health and Medical Sciences , University of Copenhagen , Frederiksberg C , Denmark.
authors.forename: Anne-Helene
authors.initials: AH
authors.lastname: Tauson
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000818:Animals; D001639:Bicarbonates / Q000032:analysis*; D019296:Capnography / Q000379:methods* / Q000662:veterinary*; D002245:Carbon Dioxide / Q000378:metabolism*; D002247:Carbon Isotopes / Q000032:analysis*; D002648:Child; D002675:Child, Preschool; D004285:Dogs / Q000502:physiology; D004734:Energy Metabolism; D005260:Female; D006801:Humans; D058751:Livestock / Q000502:physiology; D008297:Male; D008875:Middle Aged; D008956:Models, Chemical; D010827:Physiology / Q000379:methods*; D055815:Young Adult
chemical_list: D001639:Bicarbonates; D002247:Carbon Isotopes; D002245:Carbon Dioxide
keywords: CO2 production; carbon dioxides; carbon-13 bicarbonate; compartmental model; end product method; energy expenditure; indirect calorimetry; nitrogen-15 glycine; stable isotope tracer technique