In a pulmonary embolism, which region is ventilated but not perfused, i.e., dead space?

In a pulmonary embolism, which region is ventilated but not perfused, i.e., dead space?

• A. Normal ventilation and perfusion
• B. Perfused but not ventilated (shunt)
• C. Ventilated but not perfused (dead space)
• D. Neither ventilated nor perfused

Answer: (C)

In a pulmonary embolism, a clot blocks blood flow to a portion of the lung, so the alveoli in that region still receive air but have no blood reaching them to pick up oxygen or release carbon dioxide. This creates ventilation without perfusion, which is what we call physiologic dead space (alveolar dead space). This differs from a shunt, where blood is flowing through regions that are not ventilated (perfusion without ventilation). Normal regions have both ventilation and perfusion, and areas with neither ventilation nor perfusion are not the typical scenario in a PE. Therefore, the region described as ventilated but not perfused corresponds to dead space.

In a pulmonary embolism, a clot blocks blood flow to a portion of the lung, so the alveoli in that region still receive air but have no blood reaching them to pick up oxygen or release carbon dioxide. This creates ventilation without perfusion, which is what we call physiologic dead space (alveolar dead space).

This differs from a shunt, where blood is flowing through regions that are not ventilated (perfusion without ventilation). Normal regions have both ventilation and perfusion, and areas with neither ventilation nor perfusion are not the typical scenario in a PE. Therefore, the region described as ventilated but not perfused corresponds to dead space.