Carbon isotope fractionation between blood and expired CO2 at rest and exercise.
Carbon isotope fractionation occurs between bicarbonates and gaseous CO2. Accordingly, expired CO2 could be impoverished in 13C vs. blood CO2 (approximately 90% bicarbonates). The ratio 13C/12C in expired and blood CO2 was measured in six healthy subjects at rest and at the end of exercise (90 min; 65+/-5% VO2max), with ingestion of water (300 ml) without or with glucose (30 g) naturally or artificially enriched in 13C, in order to study a range of 13C/12C in blood (-17.5+/-0.3 to 3.4+/-0.6% delta 13C PDB-1). At rest, 13C/12C in expired CO2 was 4.7+/-0.2% delta 13C PDB-1 lower than in blood CO2. This difference was not modified in response to exercise with ingestion of water or 13C-glucose (average difference 4.6+/-0.4 % delta 13C PDB-1). Carbon isotope fractionation across the lung was approximately 30% lower than predicted from the fractionation factor between bicarbonates and gaseous CO2 (1.00674 at 37 degrees C, or a approximately 6.6% delta 13C PDB-1 difference). This is consistent with the fact that approximately 40% of expired CO2 is released from carbamates and dissolved CO2. From a methodological point of view, these results indicate that 13C/12C in expired CO2 adequately tracks 13C/12C in blood CO2 with a constant approximately 4.6 % delta 13C PDB-1 difference.
Département de Kinésiologie, Université de Montréal, Québec, Canada.
N
N
Panteleev
F
F
Péronnet
C
C
Hillaire-Marcel
C
C
Lavoie
D
D
Massicotte
D000328:Adult; D001944:Breath Tests; D002245:Carbon Dioxide / Q000032:analysis / Q000097:blood*; D002247:Carbon Isotopes; D015444:Exercise; D005947:Glucose / Q000378:metabolism; D006801:Humans; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology; D012044:Regression Analysis; D012146:Rest
D002247:Carbon Isotopes; D002245:Carbon Dioxide; D005947:Glucose