This is all second hand stuff told to me 20 years ago, and in German. Take it for what it is worth.... My friend and colleague, who had played 2nd trombone in one of the major West German orchestras came across a doctor who was a brass enthusiast (I think his wife was giving birth or something like that) and the doctor measured my friend's lung capacity, which proved to be slightly below normal. My friend was amazed, because he was used to playing lots of the Romantic German repertoire that called for loud playing and long phrases. The doctor explained that his informal findings (as a hobby scientist in this field he had no way of doing research that would "count" in the German scientific or medical community way) were showing that how we regulate the air is much more important than size of lungs. If it gives you joy then do it, and spread that joy to others. Don't let it be a handicap to you, show that you are "handi-capable!" Have fun!