Regional ventilation in the differential diagnosis of pulmonary embolism.

In the diagnosis of pulmonary embolism by lung scanning, clinical errors of interpretation may arise. Diseases that affect the distribution of pulmonary blood flow, such as pulmonary emphysema and bronchial asthma, may be confused with pulmonary embolism. With the addition of ventilation studies with 133xenon to the perfusion scans, distinct differences appear between patients vith emboli and those with obstructive lung disease. In patients with pulmonary emboli, ventilation is preserved in the areas of decreased perfusion, whereas patients xvith obstructive lung disease show both decreased ventilation and perfusion in the affected areas.