COPD usually caused by smoking. COPD = chronic obstructive pulmonary disease. Chronic means >6mo. Obstructive means there's a blockage. Pulmonary means the lungs. So, COPD is the obstructive dz of the lungs. We used to call it emphysema = damage of the alveoli, they are very thin. They don't have much air exchange. They kinda thin out and they get bigger. Lungs is like sponge = tiny little holes and pockets for air to move around. It looks like sponge. It should look like a sponge. COPD lungs are mostly air. And, that's bad. We don't want lungs to be full of air. The lungs should be a sponge. COPD lungs and chest x-ray, it's much more overinflated and clear. U should be able to see it on CXRAY. It's going to look more black.
They also used to be chronic bronchitis. Chronic inflammation of the bronchi. They get narrowed and they get full of junk and they get narrower and they get infxn. They can have some phlegm and coughing and can be like asthma.
When the pt is having a very difficulty time breathing and they try to exhale, it doesn't work. And, that doesn't work. You'll see pt trying to breathe out slowly. They have prolonged expiratory phase. They breathe out very long and slowly with their mouth closed. That's what they call purse lip breathing. They do this to compensate for obstructive bronchi.
Now we know that it's not one thing or another. Most pt have emphysema or chronic bronchitis. Most ppl have features of both. So, hyper-inflated lungs, difficulty breathing, coughing, more infxn, chronic. Do their lungs get oxygen better or worse? Worse? Because damage of alveoli and obstructive bronchi. What's their pulse ox going to be ? Less than normal.

PE: no fluid sounds in lungs (no crackles). but hyper-resonating sounds (egophony).