If you have COPD any other chronic lung condition, you probably know what it means to have a lower than normal blood oxygen saturation level. Chronic Obstructive Pulmonary Disease is just one example, but it means that your lungs' ability to bring in enough oxygen is compromised. The tiny air sacks in your lungs have been damaged, so you can't absorb enough oxygen through these sacks into your bloodstream.
It's important to have a certain level of oxygen, versus a certain level of carbon dioxide in your blood at one time. The carbon dioxide is carried back to your lungs, where it is breathed out when you exhale. The oxygen you breathed in gets delivered to every part of your body, as part of the fuel you need to keep your body working properly.