[Platypnea-orthodeoxia syndrome]

Platypnea-orthodeoxia is an uncommon syndrome of dyspnea and hypoxemia induced by upright posture, which is subsequently relieved by recumbency. Traditionally, this condition has been reported in association with pulmonary, hepatic and cardiac diseases, but the mechanism is different in each situation. In presence of an atrial septal defect, a right to left cardiac shunt resulting as a consequence of redirection of the inferior vena cava flow towards the atrial septum and results in postural hypoxemia. In pulmonary shunts, as in hepatopulmonary syndrome and a-v pulmonary fistulas, the mechanism of hypoxemia is related to the preferential circulation to basal areas of both lungs in the upright position. On the other hand, lung diseases affecting basal areas and increasing the alveolar pressure are related to the development of parenchimal pulmonary shunts with hypoxemia during postural changes, since the dead space, the functional shunt and the hypoxic vascular pulmonary constriction are affected. The autonomic neuropathy may attenuate normal sympathetic vasoconstrictor responses during postural changes, resulting in ventilation-perfusion mismatching and hypoxemia. Clinical and therapeutic aspects of this sindrome are provided.