Heller H, Schuster K D
Department of Physiology, University of Bonn, Germany.
Am J Physiol. 1998 May;274(5):R1496-9. doi: 10.1152/ajpregu.1998.274.5.R1496.
The single-breath diffusing capacities for singly and doubly 18O-labeled CO2, DLC16O18O and DLC18O2, as well as for NO, were determined in seven anesthetized rabbits to investigate whether the theoretically predicted ratio of specific blood uptake rates of both isotopic CO2 species, theta C18O2/theta C16O18O = 2.0, can be derived from the measured values of DLC16O18O and DLC18O2. Data of DL were obtained by inflating the lungs with gas mixtures containing 0.35% C16O18O or 0.8% C18O2 or 0.05% NO in nitrogen, with breath-holding periods of 0.05-0.5 s and 2-12 s for the CO2 and NO tests, respectively. theta C18O2/theta C16O18O was calculated by applying the double-reciprocal Roughton-Forster equation to DL values obtained in each animal and by assuming that NO diffusing capacity represents the gas conductance of the alveolar-capillary membrane. The measured ratio was theta C18O2/theta C16O18O = 1.9 +/- 0.2 (mean +/- SD), thus comparing reasonably with the predicted one. Therefore, our findings provide evidence that the greater value of DLC18O2 is mainly due to the twofold higher probability (or theta value) for C18O2 than for C16O18O to disappear within red blood cells via isotopic exchange reactions.
为了研究理论预测的两种同位素二氧化碳（¹⁸O标记的二氧化碳）特定血液摄取率的比值θC¹⁸O₂/θC¹⁶O¹⁸O = 2.0是否可以从测量的DLC¹⁶O¹⁸O和DLC¹⁸O₂值中推导出来，我们测定了7只麻醉兔的¹⁶O¹⁸O和¹⁸O₂单呼吸扩散容量，以及一氧化氮（NO）的扩散容量。通过向肺内充入含0.35% C¹⁶O¹⁸O或0.8% C¹⁸O₂或0.05% NO的氮气混合气体来获取DL数据，二氧化碳测试和一氧化氮测试的屏气时间分别为0.05 - 0.5秒和2 - 12秒。通过将双倒数Roughton - Forster方程应用于每只动物获得的DL值，并假设NO扩散容量代表肺泡 - 毛细血管膜的气体传导率，计算出θC¹⁸O₂/θC¹⁶O¹⁸O。测量得到的比值为θC¹⁸O₂/θC¹⁶O¹⁸O = 1.9 ± 0.2（平均值±标准差），因此与预测值相当合理地相符。所以，我们的研究结果提供了证据，表明DLC¹⁸O₂的值更高主要是由于¹⁸O₂在红细胞内通过同位素交换反应消失的概率（或θ值）比¹⁶O¹⁸O高两倍。
