EFFECT OF MIXED VENOUS OXYGENATION ON ARTERIAL BLOOD IN CHRONIC OBSTRUCTIVE PULMONARY-DISEASE - BASIS FOR A CLASSIFICATION

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Abstract
Mixed venous oxygenation is an important determinant of arterial oxygenation in chronic obstructive pulmonary disease that can have a significant effect on arterial PO2 [partial oxygen pressure] even when the venous admixture is small. The effect of mixed venous oxygenation on arterial PO2 was not previously discussed with respect to the pathogenesis of the arterial hypoxia of chronic obstructive pulmonary disease. It is the effect of venous oxygenation on arterial blood that allows the prediction of mixed venous and tissue oxygenation from analysis of the arterial blood and that is the basis for a previously described classification system for chronic obstructive pulmonary disease. For a given degree of venous admixture, there is a critical range of arterial PO2 at or above which one can deduce that the mixed venous blood is normally oxygenated and below which mixed venous hypoxia can be inferred. When venous admixture is less than approximately 25% of the cardiac output, the arterial PO2 must be equal to or greater than approximately 63 mm Hg if the mixed venous PO2 is normal. Patients with venous admixtures of less than 25% can be identified by the absence of chronic hypercapnia. When venous admixture is greater than 24%, recognizable by the presence of chronic hypercapnia, the critical range of arterial PO2 that indicates normal mixed venous oxygenation is approximately 50 mm Hg or more. These relationships are based on direct measurements of arterial and mixed venous blood in 55 patients with chronic obstructive pulmonary disease and form the basis of a useful classification system for this disease.

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