Department of Medicine, University of California, San Diego, La Jolla, California.
Am J Physiol Lung Cell Mol Physiol. 2020 Aug 1;319(2):L289-L293. doi: 10.1152/ajplung.00150.2020. Epub 2020 Jun 3.
When using a new noninvasive method for measuring the efficiency of pulmonary gas exchange, a key measurement is the oxygen deficit, defined as the difference between the end-tidal alveolar Po and the calculated arterial Po. The end-tidal Po is measured using a rapid gas analyzer, and the arterial Po is derived from pulse oximetry after allowing for the effect of the Pco on the oxygen affinity of hemoglobin. In the present report we show that the values of end-tidal Po and Pco are highly reproducible, providing a solid foundation for the measurement of the oxygen deficit. We compare the oxygen deficit with the classical ideal alveolar-arterial Po difference (A-aDO) as originally proposed by Riley, and now extensively used in clinical practice. This assumes Riley's criteria for ideal alveolar gas, namely no ventilation-perfusion inequality, the same Pco as arterial blood, and the same respiratory exchange ratio as the whole lung. It transpires that, in normal subjects, the end-tidal Po is essentially the same as the ideal value. This conclusion is consistent with the very small oxygen deficit that we have reported in young normal subjects, the significantly higher values seen in older normal subjects, and the much larger values in patients with lung disease. We conclude that this noninvasive measurement of the efficiency of pulmonary exchange is identical in many respects to that based on the ideal alveolar Po, but that it is easier to obtain.
当使用新的非侵入性方法来测量肺气体交换效率时，一个关键的测量指标是氧亏，定义为终末肺泡 Po 和计算的动脉 Po 之间的差值。终末肺泡 Po 使用快速气体分析仪测量，而动脉 Po 则通过脉搏血氧饱和度测量得出，同时考虑了 Pco 对血红蛋白氧亲和力的影响。在本报告中，我们表明终末肺泡 Po 和 Pco 的值具有高度可重复性，为氧亏的测量提供了坚实的基础。我们将氧亏与经典的理想肺泡-动脉 Po 差（A-aDO）进行了比较，该差由 Riley 最初提出，现在已广泛应用于临床实践中。这假设了 Riley 对理想肺泡气体的标准，即没有通气-灌注不等、与动脉血相同的 Pco，以及与整个肺相同的呼吸交换率。事实证明，在正常受试者中，终末肺泡 Po 基本上与理想值相同。这一结论与我们在年轻正常受试者中报告的非常小的氧亏、在年龄较大的正常受试者中看到的明显较高的值以及在肺部疾病患者中看到的更高的值是一致的。我们得出结论，这种非侵入性的肺交换效率测量在许多方面与基于理想肺泡 Po 的测量相同，但更容易获得。
