The Overall Fractionation Effect of Isotopic Oxygen Molecules During Oxygen Transport and Utilization in Humans
Oxygen isotopes have been used various times as a tracer to study phenomena of respiration. The tracer studies are based on the assumption that the labeled as well as the non-labeled molecules behave in a very similar manner. It is assumed that no or only slight fractionations occur between both species of molecules. Few investigations with conflicting results are known concerning fractionation effects of the oxygen molecules 16O18O and 16O2 during respiration. The fractionations measured indicate that 16O2 is consumed in preference to 16O18O by 1.8 % (Lane and Dole, 1956) or by 8 % (Muysers et al., 1963), respectively. If the latter value is correct, the effect cannot be neglected in tracer studies. One reason for determining the 16O18O/16O2 ratio during respiration was to clarify the above problem. Physiologically more interesting may be the fact that the pathways of oxygen transport to tissues include non-fractionating processes such as ventilation and blood flow and fractionating processes e.g. diffusion and chemical reactions. Measuring fractionation effects could help to differentiate between these processes when investigating respiration under varying conditions. Moreover, if one of the fractionating processes becomes limiting for oxygen transport, its fractionation power presumably determines the overall fractionating effect, and by measuring this effect its origin could be detected.
KeywordsIsotopic Oxygen Oxygen Transport Fractionation Power Fractionation Effect Fractionation Factor
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