How to set up cardio exercise regimen

Hi,

I'm new to this forum, having recently been diagnosed with COPD. I'd like to know what kind of exercise program would have the best impact on improving my breathing and walking endurance.

I have acces to a gym; no knee problems ( already taken care of) and no oxygen. I can only walk for a few minutes on a sidewalk, mall, or indoor track without getting short of breath. Currently I can do about 10 minutes overall.

But on a treadmill, without holding on, I can do 2.5-3.0 mph for an extended time, including adjusting my speed or incline .

I'm really trying to rebuild walking endurance. Should I continue with the treadmill, even though its assisted, or stick with unassisted walking where my time walking is more limited? Or should I do a combo of both?

Thanks for taking timer to respond?responding.