The four stages of emphysema based on the GOLD emphysema staging system are mild emphysema, moderate emphysema, severe emphysema and very severe emphysema, according to WebMD. Each stage is determined by the amount of air a patient can exhale forcefully in one second.
Emphysema is a type of chronic obstructive pulmonary disease that makes breathing difficult due to a limitation in exhaling air, explains WebMD. This happens when the linings of the air sacs in the lungs are damaged, most commonly due to the toxins in cigarette smoke. Another staging system is the BODE index, which measures the impact of the disease based on the person's body mass index, airflow limitation, breathlessness and exercise capacity.