As a lung disease, emphysema has several stages, including "mild", "moderate", "severe" and "very severe".
To tell the severity of the disease, a patient may have a test that examines the function of lungs. The test is forced expiratory volume in 1 second (FEV1), which tells how much air the patient can blow out of the lungs in one second.
According to Global Initiative for Chronic Obstructive Lung Disease staging system, when the result of FEV1 is between 30% and 50%, it refers to severe emphysema.
Key word: severe emphysema