Lung Function in COPD - Topic Overview
Lung function means how well your lungs work. When you have
COPD, your lungs can't move as much air in and out as they should. And the more
serious your COPD is, the less air your lungs are able to move.
Spirometry tests are used to measure lung function.
They measure how much air you breathe out when you take long, deep breaths and
push the air out of your lungs. For people with COPD, the test measures how
well the lungs do two important jobs:
- How much air you can push out in 1 second.
- This is called forced expiratory volume in 1 second, or FEV1.
- How much air you can push out after you take a deep
breath, with no time limit.
- This is called forced vital capacity, or FVC.
When you have COPD, your FEV1 number will be lower than
normal. Just how low it is depends on what stage your COPD is—mild, moderate,
severe, or very severe. Your FVC number may also be lower than normal. These
numbers are usually stated in the form of a percentage.
glass of water. If the glass is full to the brim, it is 100% full. If it is
only half full, it is 50% full. And 33% means it is only one-third full, and so
on. Likewise, if your FEV1 is 50%, your lungs are able to handle only half as
much air as they should. If your FEV1 is 33%, your lungs are able to handle
even less—only a third as much. The lower your FEV1 percentage, the less air
your lungs are able to handle.
If you don't understand your lung
function numbers, ask your doctor to explain them for you.
the FEV1 numbers for the various stages of COPD, according to the Global
Initiative for Chronic Obstructive Lung Disease (GOLD):1
| Mild COPD (stage 1) ||80% or higher. People at this stage may
not have shortness of breath and may not know that their lungs aren't as
healthy as they should be. |
|Moderate COPD (stage 2)||50% to 79%. People at this stage may
think that their symptoms are just part of getting older.|
|Severe COPD (stage 3)||30% to 49%. At this level, the lungs are
not working well at all.|
|Very severe COPD (stage 4)||Less than 30% (or 30% to 49% plus
chronic respiratory failure, which means the lungs aren't able to get rid of
carbon dioxide). People at this stage get out of breath with just a little
activity. When symptoms get worse, they can be life-threatening.|