title: The mechanisms of abnormal gas exchange in acute massive pulmonary embolism.
abstract: Hypoxemia usually accompanies acute pulmonary embolism in humans, but its mechanism remains poorly understood. We studied 2 patients with acute, massive pulmonary embolism (APE) documented by pulmonary angiography. Both patients had a markedly increased alveolar-arterial oxygen difference (AaPO2). The technique of multiple inert gas elimination was used to determine the distribution of ventilation-perfusion ratios (VA/Q). An increase in VA/Q inequality was found in both patients, but this increased inequality was caused entirely by an increase in the ventilation of lung units with high VA/Q ratio. No blood flow was found perfusing lung units with a VA/Q ratio of less than 1.0. Both patients, however, had a large amount of blood flow (20 and 39% of the cardiac output) perfusing unventilated lung units (shunt), and the percent of minute ventilation to unperfused lung units as well as the VD/VT determined from the Bohr equation were increased. We conclude that in these 2 patients with APE, VA/Q inequality did not play a major role in their hypoxemia and that the widened AaPO2 is explained by the large shunts that were found.
mesh_terms: D000208:Acute Disease; D000368:Aged; D005260:Female; D006439:Hemodynamics; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology; D010313:Partial Pressure; D011655:Pulmonary Embolism / Q000503:physiopathology*; D011659:Pulmonary Gas Exchange; D014692:Ventilation-Perfusion Ratio