title: Paradoxical orthodeoxia in a patient with a large thoracic aortic aneurysm.
abstract: BACKGROUND
  Orthodeoxia is a rare clinical syndrome characterised by dyspnoea and arterial deoxygenation that accompanies a change from a supine to erect position.
  
  
  METHODS
  We describe an unusual case of "paradoxical orthodeoxia" in a 70-year-old man with a thoracic aortic aneurysm: arterial desaturation when supine that improved when erect.
  
  
  RESULTS
  Non-invasive imaging revealed compression of the left pulmonary artery by the aneurysm (thoracic computed tomography) and patent foramen ovale (transesophageal echocardiography). Nuclear studies show decreased relative left lung perfusion attributable to the former, and right-to-left atrial shunt attributable to the latter. The degree of right-to-left shunt increases in the supine position: nuclear pulmonary shunt study shows shunt extent of 21% when supine versus 10% erect.
  
  
  CONCLUSIONS
  A physioanatomical explanation is proposed.
authors: Department of Cardiothoracic Surgery, National Heart Centre, Singapore.
authors: Jia-Lin
authors: JL
authors: Soon
authors: Ru-San
authors: RS
authors: Tan
authors: David C E
authors: DC
authors: Ng
authors: Boon-Han
authors: BH
authors: Kwek
authors: Yeow-Leng
authors: YL
authors: Chua
mesh_terms: D000368:Aged; D017545:Aortic Aneurysm, Thoracic / Q000453:epidemiology*; D004417:Dyspnea / Q000209:etiology; D017548:Echocardiography, Transesophageal; D005260:Female; D006344:Heart Septal Defects, Atrial / Q000453:epidemiology; D006801:Humans; D010100:Oxygen / Q000097:blood*; D011187:Posture / Q000502:physiology*; D016683:Supine Position / Q000502:physiology
chemical_list: D010100:Oxygen