In COPD, less air flows in and out of the airways because of one or more of the following:

The airways and air sacs lose their elasticity. Elasticity is the stretchiness your lungs need to fill up with and push out air. In COPD, these sacs act less like a balloon and more like a lead pipe.

The airways make more mucus than usual, which clog them and make breathing more difficult. The inflammation caused by smoke and other irritants produce mucus. It’s not a good thing when instead of breathing air, you’re attempting to breathe a smoke-filled swamp of snot-like material.

The walls of the airways become thick and inflamed. Over time, inflammation can cause permanent changes in the walls of the airways to compensate for the environment you’ve created.

The walls between many of the air sacs are destroyed. Ongoing inflammation overwhelms the body’s ability to repair itself, and eventually sheets of tissue in your airways are destroyed beyond repair, providing you with less tissue to exchange oxygen from the lungs to the blood vessels that carry oxygen through the body.