I know bassets sometimes show signs of laryngeal paralysis as they get older such as difficulty breathing. Can't be cured but not letting the dog get excited, steroids, sedative, antihistamines can help.
A lot of older dogs get congestive heart failure and have difficulty breathing. Medicine can be given to help the dog breathe easier.
I know my vet wouldn't suggest a lumpectomy on a 15 year old basset and would do whatever she could to make my dog comfortable. If you don't trust your vet to do that, find someone else.
I don't think vitamins are going to help but then none of us here are qualified to diagnose or suggest treatment.
So my suggestion is see a veterinarian-it must be scary for Glen when he's having difficulty breathing.
