The Overall Fractionation Effect of Isotopic Oxygen Molecules During Oxygen Transport and Utilization in Humans

Schuster, K.-D.; Pflug, K. P.

doi:10.1007/978-1-4684-5643-1_19

Cited by 11 publications

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“…There have been few studies of oxygen isotopic fractionation in human beings. Thus it is noteworthy that our Z resting values are similar in magnitude to the previous two studies reported in the literature (Epstein and Zeiri, 1988;Schuster and Pflug, 1988). We found a marked and reproducible reduction in oxygen isotopic fractionation associated with increased metabolic rate induced by exercise.…”

Section: Discussionsupporting

confidence: 90%

“…Secondly, transport processes involving gaseous diffusion or diffusion across membranes (i.e. alveolar or red cell membrane) are dependent on molecular weight, and, therefore, are associated with fractionation (Epstein and Zeiri, 1988;Schuster and Pflug, 1988). Finally, fractionation also occurs in the chemical combination of oxygen with hemoglobin (Pflug and Schuster, 1988), but whether or not this fractionation is an equilibrium or kinetic phenomenon remains unknown.…”

Section: Discussionmentioning

confidence: 99%

“…The pathways of oxygen transport to tissues include a number of processes that are likely to cause oxygen isotopic fractionation: namely, diffusion of 02 through N 2 and CO2; diffusion of 0 2 through membranes (alveolar and red cell); and chemical reactions (e.g., oxidative reactions of the respiratory chain, binding of oxygen to hemoglobin) (Epstein and Zeiri, 1988;Schuster and Pflug, 1988;Pflug and Schuster, 1988). In contrast, other steps in oxygen transport (e.g., bulk flow in the blood, convection) are less likely to result in differences between oxygen isotopes (Schuster and Pflug, 1988). The overall fractionation is determined in large part by two distinct factors: first, the fractionation that occurs at each transport step; and second, by the relative contribution of each step to tile rate of oxygen transport.…”

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confidence: 99%

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Effect of increased metabolic rate on oxygen isotopic fractionation

Zanconato

Cooper

Armon

et al. 1992

Respiration Physiology

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16O16O is preferentially used over 18O16O (a stable isotope of oxygen comprising about 0.2% of atmospheric O2) as oxygen is consumed during respiration in humans (Epstein and Zeiri, 1988, Proc. Natl. Acad. Sci. USA 85: 1727-1731). To test the hypothesis that oxygen isotopic fractionation is related to the metabolic rate, 8 healthy adults performed 5 min of constant work rate cycle ergometer exercise below and above their anaerobic threshold. Moreover, 3 subjects performed an incremental exercise to the limit of tolerance. Oxygen uptake (VO2) was measured breath by breath. Samples of the exhaled breath for oxygen isotope measurement were obtained at rest and at various times during exercise and recovery. Oxygen isotopic fractionation was determined by isotope ratio mass spectrometry and calculated as the ratio of the degree of fractionation to the oxygen consumed in the breath sample (Z value). For the constant work rate protocol, both low and high intensity exercise resulted in a significant decrease in Z compared to the rest values (P less than 0.01). However, for the high intensity exercise the reduction in fractionation was greater compared to the low intensity protocol (P less than 0.05). For the incremental test, there was a significant negative correlation between oxygen isotopic fractionation and VO2 expressed as percent of the maximal oxygen uptake (r = -0.91, P less than 0.0001). These data suggest that during exercise low-fractionating processes become more important as limiting steps for O2 transport.

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Section: Discussionsupporting

confidence: 90%