Platypnea-orthodeoxia syndrome (POS) is a cause of positional dyspnea and hypoxemia that worsens in the upright position and improves with recumbency. It is proposed that the mechanism is due to increased right-to-left shunting, commonly through a patent foramen ovale (PFO). We hypothesized that the upright position leads to an increase in the PFO height facilitating orthodeoxia.
Elisarraras et al. (Wed,) studied this question.