When you breathe, millions of small air sacs in your lungs expand as you inhale and contract when you exhale. They also support the small airways that move air through your lungs. When you have emphysema, these air sacs lose their elasticity (their ability to stretch and shrink back) and their walls eventually weaken and break. Without these sacs, the small airways collapse when you exhale so air has difficulty escaping and becomes trapped in your lungs.

Healthy lung tissue	Enlarged airways in lungs with emphysema (same magnification)

Once your lungs are filled by trapped air it becomes hard to inhale fresh air. As the amount of trapped air grows, it causes overfilling of the lung, or "hyperinflation". When the lungs are hyperinflated, your chest expands and your diaphragm (the main breathing muscle that helps the lungs work even during sleep) becomes flattened and ineffective. Your lungs are full of air but you can not exhale it effectively. This is why you feel a disabling sense of breathlessness called dyspnea. Dyspnea can make it difficult to perform your normal daily activities.

Emphysema symptoms typically develop gradually and often go unnoticed until significant lung damage has already occurred. Some common symptoms of emphysema include shortness of breath, a chronic but mild cough and limited exercise tolerance.