Swenson E R, Robertson H T, Polissar N L, Middaugh M E, Hlastala M P
Department of Medicine, University of Washington, Seattle 98195.
J Appl Physiol (1985). 1992 Apr;72(4):1581-8. doi: 10.1152/jappl.1992.72.4.1581.
We studied CO2 and inert gas elimination in the isolated in situ trachea as a model of conducting airway gas exchange. Six inert gases with various solubilities and molecular weights (MW) were infused into the left atria of six pentobarbital-anesthetized dogs (group 1). The unidirectionally ventilated trachea behaved as a high ventilation-perfusion unit (ratio = 60) with no appreciable dead space. Excretion of higher-MW gases appeared to be depressed, suggesting a MW dependence to inert gas exchange. This was further explored in another six dogs (group 2) with three gases of nearly equal solubility but widely divergent MWs (acetylene, 26; Freon-22, 86.5; isoflurane, 184.5). Isoflurane and Freon-22 excretions were depressed 47 and 30%, respectively, relative to acetylene. In a theoretical model of airway gas exchange, neither a tissue nor a gas phase diffusion resistance predicted our results better than the standard equation for steady-state alveolar inert gas elimination. However, addition of a simple ln (MW) term reduced the remaining residual sum of squares by 40% in group 1 and by 83% in group 2. Despite this significant MW influence on tracheal gas exchange, we calculate that the quantitative gas exchange capacity of the conducting airways in total can account for less than or equal to 16% of any MW-dependent differences observed in pulmonary inert gas elimination.
我们以离体原位气管作为传导气道气体交换的模型，研究了二氧化碳和惰性气体的清除情况。将六种具有不同溶解度和分子量（MW）的惰性气体注入六只戊巴比妥麻醉犬的左心房（第1组）。单向通气的气管表现为高通气-灌注单位（比率=60），且无明显死腔。较高分子量气体的排泄似乎受到抑制，表明惰性气体交换存在分子量依赖性。在另外六只犬（第2组）中进一步探究了这一现象，这六只犬使用了三种溶解度几乎相同但分子量差异很大的气体（乙炔，26；氟利昂-22，86.5；异氟烷，184.5）。相对于乙炔，异氟烷和氟利昂-22的排泄分别降低了47%和30%。在气道气体交换的理论模型中，无论是组织扩散阻力还是气相扩散阻力，都没有比稳态肺泡惰性气体清除的标准方程能更好地预测我们的结果。然而，添加一个简单的ln（MW）项后，第1组的剩余残差平方和减少了40%，第2组减少了83%。尽管分子量对气管气体交换有显著影响，但我们计算得出，传导气道的定量气体交换能力总计占肺惰性气体清除中观察到的任何分子量依赖性差异的比例小于或等于16%。
