Mechanisms of Platypnea-Orthodeoxia: What Causes Water to Flow Uphill?

To the Editor:Platypnea-orthodeoxia is a relatively uncommon but striking clinical syndrome characterized by dyspnea and deoxygenation accompanying a change to a sitting or standing from a recumbent position. Since Burchell et al1 described this rare syndrome over half a century ago, no more than 50 cases have been reported in the literature.2Two conditions must coexist to cause platypnea-orthodeoxia: an anatomical component in the form of an interatrial communication and a functional component that produces a deformity in the atrial septum and results in a redirection of shunt flow with the …