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Carbon isotope fractionation between blood and expired CO2 at rest and exercise.

Authors
  • Panteleev, N
  • Péronnet, F
  • Hillaire-Marcel, C
  • Lavoie, C
  • Massicotte, D
Type
Published Article
Journal
Respiration physiology
Publication Date
Jun 01, 1999
Volume
116
Issue
1
Pages
77–83
Identifiers
PMID: 10421035
Source
Medline
License
Unknown

Abstract

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.

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