Partial pressure of oxygen is lower in the left upper pulmonary vein than in the right in adults with atrial septal defect - Difference in Po-2 between the right and left pulmonary veins

Background: The right-to-left shunt at the atrial level is responsible for arterial hypoxemia in patients with atrial septal defect. Objectives: This study investigated the mechanism of arterial hypoxemia in patients with atrial septal defect by measuring the Po-2 in both the right and left upper pulmonary veins. Subjects and method: We prospectively measured the Po-2 in the femoral arte ry and the right and left upper pulmonary veins during cardiac catheterizat ion in 13 adults (median age, 53 years) and 7 children (median age, 7 years ) with secundum atrial septal defect, The adults and children were studied consecutively. Contrast echocardiography was performed to evaluate right-to -left shunt in all adults. Results: Among the children, there were no patients showing arterial hypoxe mia, and there was no difference in the Po-2 (+/-SD) between the right and left upper pulmonary veins (right, 100 +/- 3.8 mm Hg vs left, 100 +/- 7.8 m m Hg; p = 0.92), However, arterial hypoxemia was present in 11 of the 13 ad ult patients, although contrast echocardiography showed more than a moderat e degree of right-to-left shunt in only four adults. The Po, was lower in t he left upper pulmonary vein than it was in the right upper pulmonary vein in all adult patients (right, 91.6 +/- 13.8 mm Hg vs left, 73.0 +/- 11.5 mm Hg; p < 0.0001). Conclusion: The Po-2 was lower in the left upper pulmonary vein than it was in the right upper pulmonary vein in adults with atrial septal defect. Car e must be taken in measuring pulmonary blood now if the Po-2 in the left up per pulmonary vein is low enough to influence oxygen content. The decreased Po-2 in the left upper pulmonary vein may contribute to arterial hypoxemia in addition to light-to-left shunt at the atrial level in adults with atri al septal defect.