Measuring the efficiency of pulmonary gas exchange using expired gas instead of arterial blood: Comparing the "ideal" PO2 of Riley with end-tidal PO2.

Measuring the efficiency of pulmonary gas exchange using expired gas instead of arterial blood: Comparing the "ideal" PO2 of Riley with end-tidal PO2. Am J Physiol Lung Cell Mol Physiol. 2020 Jun 03;: Authors: West JB, Liu MA, Stark PC, Prisk GK Abstract 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 PO2 and the calculated arterial PO2. The end-tidal PO2 is measured using a rapid gas analyzer, and the arterial PO2 is derived from pulse oximetry after allowing for the effect of the PCO2 on the oxygen affinity of hemoglobin. In the present report we show that the values of end-tidal PO2 and PCO2 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 PO2 difference (A-aDO2) 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 PCO2 as arterial blood, and the same respiratory exchange ratio as the whole lung. It transpires that in normal subjects, the end-tidal PO2 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...
Source: American Journal of Physiology. Lung Cellular and Molecular Physiology - Category: Cytology Authors: Tags: Am J Physiol Lung Cell Mol Physiol Source Type: research