Nu-Step is a seated elliptical and gives a fairly decent full-body workout, especially if you set the resistance to at last 4 or 5 an keep your steps at 100 per minute. It's a particularly good option for people who can't use weight-bearing machines.

100 steps per minute would be very hard to do, my lung function is at 42%

We use this at resp rehab. You sit while walking. I believe it is a pricy piece of equipment but you can see one on Amazon.