Schuster K D
Respir Physiol. 1985 Apr;60(1):21-37. doi: 10.1016/0034-5687(85)90037-4.
The kinetics of alveolar-capillary CO2 transfer was investigated, using 18O-labeled carbon dioxide (C16O18O), in 21 experiments on 2 resting human subjects. Single-breath experiments were performed. After the subjects expired to residual volume, they inspired a gas mixture containing 20% O2 and 2.8% CO2 - a quarter of CO2 was labeled with 18O. The breath-hold time ranged between 0.5 and 20 sec. After expiration the gas mixture was analysed by mass spectrometry. The C16O18O concentration of the end-expiratory gas decreased with the increasing breath-hold time. The relationship of both showed a biexponential characteristic with the two time constants 0.4 and 16 sec. The lower time constant characterizes the CO2 transfer from the alveolar space to the capillary blood, as well as the isotopic equilibration of the 18O within the blood. The higher time constant could result from small admixtures of the label from the dead spaces or the lung tissues. The diffusing capacity of C16O18O was calculated by using the first part of the indicator clearance curve. The derived mean value of 862 ml X mm Hg-1 X min-1 is considered to be a lower limit of the 'membrane diffusing capacity' for CO2 (DMCO2).
利用18O标记的二氧化碳（C16O18O），在21次针对2名静息人体受试者的实验中，研究了肺泡-毛细血管二氧化碳转移的动力学。进行了单次呼吸实验。受试者呼气至残气量后，吸入一种含有20%氧气和2.8%二氧化碳的混合气体，其中四分之一的二氧化碳用18O标记。屏气时间在0.5至20秒之间。呼气后，通过质谱分析混合气体。呼气末气体的C16O18O浓度随屏气时间的增加而降低。两者的关系呈现双指数特征，时间常数分别为0.4秒和16秒。较低的时间常数表征了二氧化碳从肺泡腔向毛细血管血液的转移，以及血液中18O的同位素平衡。较高的时间常数可能是由于死腔或肺组织中少量标记物的混入所致。通过使用指示剂清除曲线的第一部分来计算C16O18O的扩散容量。得出的平均值862 ml·mmHg-1·min-1被认为是二氧化碳“膜扩散容量”（DMCO2）的下限。
