Anyone else with autonomic problems that are causing oxygen AND Aheart rate to drop?

My husband was diagnosed 8 years ago. Exercise is key to getting better but if he even gets up to walk much, his oxygen saturation drops but so does his heart rate. They have done every test imaginable. He has to be in a wheelchair to go anywhere. Anyone else have this or autonomic symptoms that cause a decrease in lifestyle? Not sure how to go forward. We are working with PT but it hadn’t helped.