Table 1.

Possible causes of platypnea–orthodeoxia syndrome.

Underlying Anatomical or Functional Alteration	Pathophysiologic Mechanism	Accompanying Pathologic Condition
Intracardiac shunt PFO ASD ASA with fenestration	Transient right–left shunt without elevated right–left pressure gradient	Compression of RA by aortic dilatation, elongation or aneurysm Pericardial effusion or constrictive pericarditis Postpneumectomy 1 Eosinophilic endomyocardial disease Abnormally lying Eustachian valve or Chiari network RA myxoma RA lipomatosis hypertrophy Kyphosis
	Transient right–left shunt with elevated right–left pressure gradient	Pulmonary thromboembolism Idiopathic pulmonary hypertension Right hydrothorax Long duration lung disease causing pulmonary hypertension Postpneumectomy
Pulmonary diseases with ventilation/perfusion mismatch	High V/Q ratio	Emphysema COPD Interstitial lung disease
	Low V/Q ratio	Hepatopulmonary syndrome Pulmonary arteriovenous malformations or fistulae Rendu–Osler–Weber syndrome

PFO, patent foramen ovale; ASD, atrial septal defect; ASA, atrial septal aneurysm; RA, right atrium; COPD, chronic obstructive pulmonary disease; V/Q ratio, ventilation/perfusion ratio. ¹ Postpneumectomy shunt can be present with or without elevated right atrial pressure.