Platypnea

Platypnea is a clinical syndrome in which dyspnea worsens when a person assumes an upright position and improves when lying down. The associated drop in arterial oxygen saturation in the upright posture is known as orthodeoxia. Platypnea is the opposite of orthopnea.

Platypnea-orthodeoxia syndrome (POS) arises when a right-to-left shunt or marked ventilation–perfusion mismatch becomes more pronounced with standing. Common associations include intracardiac shunts such as a patent foramen ovale or other septal defects, hepatopulmonary syndrome in chronic liver disease, and pulmonary arteriovenous malformations. Less frequent contributors include diaphragmatic dysfunction, post-surgical changes, or thoracic deformities.

Pathophysiologically, upright posture can alter intrathoracic pressures, venous return, and the distribution of blood flow, increasing shunting or V/Q mismatch in susceptible individuals. This leads to desaturation and dyspnea in the erect position.

Diagnosis relies on a history of positional dyspnea with objective evidence of orthodeoxia. Assessments include pulse oximetry or arterial blood gas in supine and upright positions, and contrast-enhanced echocardiography to detect shunts. Imaging such as CT angiography or dedicated studies may identify pulmonary AVMs or other structural causes, along with evaluation for liver disease when hepatopulmonary syndrome is suspected.

Management targets the underlying condition. Treatments may include closure of intracardiac shunts, management of hepatopulmonary syndrome, or embolization of pulmonary AVMs, combined with supplemental oxygen as needed. Prognosis depends on the underlying disorder and response to therapy.