How does air get trapped in the lungs? what would happen?

Air trapping: Air can get trapped in part of lung by obstruction to airway or bronchus. The obstruction usually acts as ball valve allowing air in but not out. The obstruction can be plug of mucus in asthma and cystic fibrosis, a foreign body such as peanut in airway, or aspiration of food when drunk or neurologically challenged. Some people with emphsema the air cells themselves are not able to empty (copd).