In patients with pulmonary embolism, what is observed in perfusion and ventilation studies?

In patients with pulmonary embolism, a perfusion study typically reveals defects, while the ventilation study remains normal. This scenario occurs because a pulmonary embolism obstructs blood flow to a region of the lung where the perfusion scan shows reduced or absent blood flow (defects) due to the blockage. However, since the ventilation is not directly affected by the embolism, the areas of the lung that are ventilated do not lose their ability to take in air, resulting in a normal ventilation scan.

This classic presentation is key for the diagnosis of pulmonary embolism. In contrast, if there were ventilation defects or both were affected, it might indicate other conditions such as pulmonary infarction or severe lung disease, which are not typical of isolated embolisms. Thus, understanding the relationship between blood flow and air exchange helps in diagnosing and differentiating pulmonary embolism from other respiratory conditions.