Oxygen isotope fractionation in healthy subjects and in patients with COPD

We determined the oxygen isotope fractionation degree for oxygen utilized (delta(U)) in expired alveolar gas relative to inspired air in patients with chronic obstructive lung disease (COPD) and, for comparison, in two groups of healthy subjects, old and young. In addition, we determined Delta(rel)R(vent) and Delta(rel)R(tot). These determinants of delta(U) (=Delta(rel)R(tot)-Delta(rel)R(vent)) are related to the oxygen isotope fractionation which occurs in the first part of the O(2) pathway by ventilation of alveolar gas (Delta(rel)R(vent)) and by O(2) transport and utilization in the rest of the O(2) pathway from the alveolar space (Delta(rel)R(tot)). Mean delta(U) values for the three groups of subjects were close: 9.0, 9.0 and 9.9 per thousand, respectively, with no significant differences between groups. Mean Delta(rel)R(vent) for patients with COPD was substantially larger than for young, healthy subjects, 4.0 per thousand versus 0.94 per thousand, with P<10(-3). This result indicates that the contribution of intrapulmonary gas transport by diffusion to Delta(rel)R(vent) is larger for patients with COPD than for young, healthy subjects. Mean Delta(rel)R(tot) for patients with COPD was also larger than for young, healthy subjects, 13.0 per thousand versus 10.84 per thousand, but this difference was not significant (P=0.06). Further, Delta(rel)R(tot) was much larger than Delta(rel)R(vent) for all groups of subjects (P<10(-7)).