Most pulmonary arteriovenous malformations are in the base of the lungs; thus, while upright, blood flow is redistributed to the lung base causing more shunting. While supine, less shunting occurs ...

It is due to vasodilation and angiogenesis in the pulmonary vascular bed, which leads to ventilation-perfusion mismatching, diffusion limitation to oxygen exchange, and arteriovenous shunting.