title: A discussion regarding the contribution of intrapulmonary gas mixing to O2 isotope fractionation by respiration using experimental data for 36Ar and 40Ar.
abstract: We determined the argon (Ar) isotope ratio in samples of expired alveolar gas gathered during Ar washout from residual gas relative to this ratio in samples of expired alveolar gas gathered just before the beginning of this washout in 13 young, healthy human subjects at rest. These data were determined for a limited number of breaths in early washout and were used to calculate the relative difference between the alveolar ventilations of (36)Ar and (40)Ar (Delta(rel)V (A)((36)Ar,(40)Ar)). Mean Delta(rel)V (A)((36)Ar,(40)Ar) amounted to 1.6 per thousand (S.D.=1.3 per thousand). This result was then used to discuss the contribution of intrapulmonary gas mixing by diffusion to oxygen isotope fractionation of alveolar gas by respiration. On the basis of our finding for Delta(rel)V (A)((36)Ar,(40)Ar) and further theoretical considerations we arrived at the conclusion that this contribution for subjects at rest is small (about 1 per thousand) and that this contribution is negative irrespective of the level of exercise.
authors.affiliation: Department of Respiratory Medicine, University Hospital Maastricht, P.O. Box 5800, 6202 AZ Maastricht, The Netherlands.
authors.forename: S C M
authors.initials: SC
authors.lastname: Luijendijk
authors.forename: I H A
authors.initials: IH
authors.lastname: Zegers
authors.forename: C P M
authors.initials: CP
authors.lastname: van der Grinten
mesh_terms: D000328:Adult; D001128:Argon / Q000032:analysis*; D006801:Humans; D010100:Oxygen / Q000378:metabolism*; D010103:Oxygen Isotopes / Q000032:analysis; D011650:Pulmonary Alveoli / Q000502:physiology; D011653:Pulmonary Diffusing Capacity / Q000502:physiology*; D011868:Radioisotopes / Q000032:analysis*
chemical_list: D010103:Oxygen Isotopes; D011868:Radioisotopes; D001128:Argon; D010100:Oxygen