How Do I Help My Dog?

My dog Duke (he's about 75 lbs) has been coughing, gagging, and hacking for a few days now. There isn't anything coming up but it sounds awful. We did not own him as a puppy but we do think that his windpipe was slightly damaged from being on a choker collar because he tends to hyperventilate after he gets excited or runs around outside. He has taken heart worm medication and has not been put into a kennel at any point since we have had him so heart worms and kennel cough would be out. Does anyone have any ideas to help him until we can get him to the vet? I just want to soothe his coughing a little bit if I can.