A PE starts as a clot somewhere else, usually in a deep vein in the leg (DVT). The clot breaks loose, rides the blood up through the heart, and lodges in a pulmonary artery. Air still reaches those air sacs, but no blood can get past the clot to pick it up. That wasted air is dead space. Follow the clot.
Follow the clot
The clot goes from a deep leg vein, up through the right heart, and into the lung. Watch where the blood flow stops.
Step through the trip.
The tripDVT → travels → lodges in lung
👆 Step through it
What's happening
Risk factors
Deep vein thrombosis
Not moving, or long trips
Femur fracture, surgery
Birth control pills
Smoking, obesity
Signs & symptoms
Sudden shortness of breath
Chest pain
Hemoptysis, or coughing up blood
Hypoxemia, meaning low O₂
Tachycardia, a fast heart rate
Why the O₂ drops: the blocked part of the lung still gets air, but no blood flows past it. That is classic dead space. At the same time, all the blood is pushed through the rest of the lung so fast that it cannot fully load oxygen. So the oxygen level falls.