My grandmother has severe COPD, chronic obstructive pulmonary disease, thanks to forty years of cigarette smoking.
She has trouble breathing, she's always short of breath and the doctor has had to put her on oxygen therapy to treat her hypoxia. She has a portable oxygen system that she carries around with her and she completely depends on it.
Unfortunately, her COPD has gotten quite bad and there isn't much else the doctors can do for her. She just has to stick to the oxygen to prevent hypoxia and the complications it brings.