Cotton D J, Prabhu M B, Mink J T, Graham B L
University of Saskatchewan, Saskatoon, Canada.
J Appl Physiol (1985). 1993 Aug;75(2):927-32. doi: 10.1152/jappl.1993.75.2.927.
In normal seated subjects we increased single-breath ventilation inhomogeneity by changing both the preinspiratory lung volume and breath-hold time and examined the ensuing effects on two different techniques of measuring the diffusing capacity of the lung for carbon monoxide (DLCO). We measured the mean single-breath DLCO using the three-equation method (DLCOSB-3EQ) and also measured DLCO over discrete intervals during exhalation by the "intrabreath" method (DLCOexhaled). We assessed the distribution of ventilation using the normalized phase III slope for helium (SN). DLCOSB-3EQ was unaffected by preinspiratory lung volume and breath-hold time. DLCOexhaled increased with increasing preinspiratory lung volume and decreased with increasing breath-hold time. These changes correlated with the simultaneously observed changes in ventilation inhomogeneity as measured by SN (P < 0.01). We conclude that measurements of DLCOexhaled do not accurately reflect the mean DLCO. Intrabreath methods of measuring DLCO are based on the slope of the exhaled CO concentration curve, which is affected by both ventilation and diffusion inhomogeneities. Although DLCOexhaled may theoretically provide information about the distribution of CO uptake, the concomitant effects of ventilation nonuniformity on DLCOexhaled may mimic or mask the effects of diffusion nonuniformity.
在正常坐位受试者中，我们通过改变吸气前肺容积和屏气时间来增加单次呼吸通气不均匀性，并研究其对两种不同测量肺一氧化碳弥散量（DLCO）技术的后续影响。我们使用三方程法测量平均单次呼吸DLCO（DLCOSB - 3EQ），并通过“呼气内”法在呼气的离散时间段内测量DLCO（DLCOexhaled）。我们使用氦气的标准化III期斜率（SN）评估通气分布。DLCOSB - 3EQ不受吸气前肺容积和屏气时间的影响。DLCOexhaled随吸气前肺容积增加而增加，随屏气时间增加而减少。这些变化与通过SN测量的同时观察到的通气不均匀性变化相关（P < 0.01）。我们得出结论，DLCOexhaled的测量不能准确反映平均DLCO。呼气内测量DLCO的方法基于呼出CO浓度曲线的斜率，这受到通气和弥散不均匀性的影响。尽管理论上DLCOexhaled可能提供有关CO摄取分布的信息，但通气不均匀性对DLCOexhaled的伴随影响可能模拟或掩盖弥散不均匀性的影响。
