Does a portable oxygen concentrator make its own oxygen?

Can you sleep with a portable oxygen concentrator?

Is there a machine that generates oxygen?

How long can you use a portable oxygen concentrator?

Are portable oxygen concentrators effective?

What do I need to know about oxygen concentrators?

How long does Covid pneumonia last?

Is 10 liters of oxygen a lot?

How long does an oxygen concentrator last?

Is it good to sleep with oxygen?

What is normal oxygen level?

What does a oxygen concentrator do?