This is a scary one.
It turns out that in older dogs of large/giant size, they can have a common condition where their vocal folds no longer open and close normally, but remain partially closed on both sides of the throat. This is called canine laryngeal paralysis, and obviously it makes it difficult for the dog to get a good full breath. Dogs start sounding wheezy and getting over-tired from mild exercise. Since panting is what cools dogs, this almost makes them less able to keep from overheating.
The other problem is that if the dog starts barking hard or trying to breathe faster, it actually closes off their airways more. You have to calm the dog down so that he can breathe, and cool him down so he doesn’t overheat. (Unless the dog is getting overly cold, which can also happen with breathing problems. So use your senses.) Sometimes vets give sedatives or cortisone to help out.
Well, it turns out that our family dog has this condition. She’s pretty old for an Irish wolfhound, and Mom took her to the vet at the first sign of weird breathing. (A lot of people don’t recognize anything wrong until the dog is in full-blown respiratory distress.) The usual treatment is a cheap, minor larynx surgery on just one side of the vocal folds. (It’s called “tieback”, so you can guess what they do; and it only takes two sutures to do it.) But wolfhounds don’t do well with anesthetics, so we will be going with non-surgical treatment for now.
So, yes, if you have a large dog and have been told not to use a choke collar — laryngeal paralysis is why you don’t. But it can still happen anyway, and nobody knows just why it happens.
If you ever hear your dog making wheezing or honking sounds, or having trouble breathing at night, have your vet check it out. Cats can also get “lar par,” and so can horses. (But horses usually get it on just one side, so it’s bad but not life-threatening.)
This page has sound videos of two dogs with severe “stridor” from laryngeal paralysis.