Orthodeoxia: a new finding in interstitial fibrosis.

Orthodeoxia--arterial desaturation accentuated by the upright position and improved by recumbency--has been described earlier with true pulmonary vascular shunts and intracardiac shunts. This phenomenon has been described in some parenchymal lung diseases, but has not been reported with interstitial fibrosis. We describe 2 patients with predominantly basal interstitial fibrosis, disabling dyspnea, and severe hypoxemia who demonstrated this positional oxygenation change. Large or surgically correctable arteriovenous malformations (AVM), or intracardiac shunts, were not demonstrated in either patient. This finding has important implications for oxygen prescription and the explanation of positional dyspnea.