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What is COPD?

The airways of the lungs branch out like an upside-down tree. At the end of each branch are many small, balloon-like air sacs. In healthy people, each airway is clear and open and the air sacs are small, elastic, and springy. When you breathe in, each air sac fills up with air, like a small balloon, and when you breathe out, the balloon deflates and the air goes out.