Platypnea

Excerpt

Platypnea is a descriptive term for breathing difficulty in the upright position that improves in the supine position. Orthodeoxia has a similar meaning but emphasizes the association of breathlessness with the upright position. The diagnosis of platypnea-orthodeoxia syndrome (POS) is made when shifting from the supine to the upright position is accompanied by a reduction of oxygen saturation (SaO2) greater than 5% and of arterial oxygen partial pressure (PaO2) greater than 4 mm Hg.

POS is commonly associated with intracardiac shunting, as in cases of patent foramen ovale (PFO), atrial septal defect (ASD), atrial septal aneurysm (ASA), and congenital cardiomyopathy. Extracardiac shunting, as in pulmonary arteriovenous malformation (PAVM), hepatopulmonary syndrome (HPS), and acute respiratory distress syndrome (ARDS), is also a possible cause. Ventilation-perfusion (V/Q) mismatches, seen in conditions like pneumonectomy, chronic obstructive pulmonary disease (COPD), interstitial lung disease (ILD), and cryptogenic organizing fibrosis, can contribute to the symptoms. PFO is the most common structural anomaly associated with POS, often remaining asymptomatic for many years.

Platypnea-orthodeoxia is a clinical syndrome first observed in 1949 and originally called "orthostatic cyanosis." The terms "platypnea" and "orthodeoxia" were later introduced in 1969 and 1976, respectively, to characterize the condition in which breathlessness and SaO2 reduction worsen when upright and improve when lying down.