Clots most commonly travel to the lungs as a result of a blood clot, typically a deep vein thrombosis (DVT) in the leg, breaking loose and traveling through the bloodstream. This blockage of a lung artery is known as a pulmonary embolism (PE).
The Process Explained:
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Clot Formation (DVT): Deep vein thrombosis (DVT) often forms in the deep veins of the legs. Several factors can contribute to DVT, including prolonged inactivity (such as during long flights or bed rest), surgery, certain medical conditions, and some medications.
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Clot Detachment: A portion of the DVT can break off and enter the bloodstream. This detached clot is now called an embolus.
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Journey to the Heart: The embolus travels through progressively larger veins towards the heart. It passes through the inferior vena cava (the large vein that carries blood from the lower body to the heart) and enters the right atrium.
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Passage to the Lungs: From the right atrium, the embolus travels to the right ventricle and then into the pulmonary artery, which carries blood to the lungs.
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Lodging in the Lungs (PE): As the pulmonary artery branches into smaller and smaller vessels within the lungs, the embolus eventually becomes lodged in a vessel that is too narrow for it to pass through. This blockage restricts blood flow to that portion of the lung, causing a pulmonary embolism.
Alternative Causes of Pulmonary Embolism:
While DVT is the most common cause, other materials can also travel to the lungs and cause a pulmonary embolism. These include:
- Air bubbles: Can enter the bloodstream during certain medical procedures.
- Fat emboli: Can occur after a fracture, particularly of a long bone.
- Tumor fragments: Rare, but possible if a tumor sheds cells into the bloodstream.
Summary:
A pulmonary embolism typically occurs when a blood clot (most often originating as a DVT in the leg) breaks free and travels through the bloodstream to the lungs, where it blocks an artery and restricts blood flow. While blood clots are the most common cause, other materials like air, fat, or tumor fragments can also cause a PE.
