I have asthma and would try to appeal to him with that route? It is really scary/uncomfortable to not be able to breathe, I'd ask him if that is what he wants and/or ask him what he would do to help him if he were his child. He might have a idea of what he'd "like"/needs and would go along with; doesn't sound like you can do much if he's not going to cooperate other than sending him away to school (I had a nephew that had to have that). Not accenting "wrong" or "bad" and trying instead to listen and use "reasonable" or logical arguments and make sure he understands you want him to feel better, not to run/ruin his life, etc. seem like the only things you might be able to use. If you can get across a little of how "helpless" you feel to help because he won't let you, show you need his help to help him, etc. that might get through to him too.