Postural hypoxemia in the postpneumonectomy patient.

A patient with platypnea and orthodeoxia after right pneumonectomy is described. Cardiac catheterization revealed arterial desaturation in the upright position associated with increased right to left intracardiac shunting through a patent foraman ovale. The absence of a pressure gradient between the left and right atrium in either the supine or sitting position indicated that the orthodeoxia resulted from an increase in streaming of blood from the inferior vena cava to the left atrium caused by mechanical distortion of the interatrial septum.