I just googled "fast breathing dogs" and came up with thesehttp://pets.webmd.com/dogs/dog-wheezing ... g-problemshttp://www.petmd.com/dog/conditions/res ... ea_panting
I really don't know, either. I would encourage you to keep an eye on the gums, pale, white gums are a sign of IMHA, which warrants an immediete trip to the vet, and which some of us have unfortunately experienced. I remember when my dog had it and was on pred his breathing was what you were describing, but that was from the prednisone. Sending good thoughts that you get answers. It is very difficult when you do the right things(get immediete care for your dog) and they have no answers. I would google and google and read and see if you can come up with something that the vet can test for.