ANP decreases arterial oxygen partial pressure by increasing shunt flow in pulmonary circulation

This study was designed to clarify the decreased arterial oxygen partial pressure (PaO2) mechanism induced by atrial natriuretic peptide (ANP) infusion. In order to examine the effects of ANP on gas exchange across the normal lungs, ANP was infused to eight anesthetized dogs, ventilated with mixed gases of oxygen and nitrogen. PaO2 and venous oxygen partial pressure (PvO2), ventilation-perfusion ratio (VA/Q), shunt-total blood flow ratio (QS/QT) were measured before and during ANP infusion under ventilation with 10, 20, 30% oxygen. In this study ANP decreased PaO2 from 89.0 +/- 4.2 to 85.4 +/- 5.4 mmHg during 20% oxygen ventilation, and from 138.1 +/- 3.6 to 132.5 +/- 4.1 mmHg during 30% oxygen ventilation. ANP increased VA/Q and QS/QT. We conclude that the decrease in PaO2 caused by ANP infusion was mainly due to the increased venous admixture.