Cat Can't Breathe When Purring

I have a 17 year old cat who started having difficulty breathing whenever he purrs. It's like an asthma attack and has a high-pitched squeak sound at the end of each exhalation and a wet rattling sound throughout. His mouth opens on occasion and his stomach looks like a paper bag opening and closing and really appears in distress until he stops purring, then breathing returns to normal. He also seems to be alternating acting normal one day and quite listless the next. His appetite is still intact and he's still grooming. My vet has never heard of this before and he's currently undergoing tests -vitals are fine, blood/urinalysis did not produce findings, and today he's scheduled for x-rays (of which the vet said can be dicy in producing any visible signs). It's strange in that it's tied solely to his purring and I'm scared to cuddle him because then it starts again. Has anyone ever heard of this? I'm hoping to get some ideas to focus testing on as the blind guess-testing is already getting expensive.

This is totally new to me, and I've fielded a LOT of questions about odd purring. I wonder if there could possibly be polyps on his vocal cords? That might account for it.

I don't want to alarm you, so please take this as simply what I experienced, and hopefully this is not the case with you.
I had a cat who at 18, started purring louder and louder. Then his purrs started gurgling, they sounded wet. That went on for several months, but nothing else was out of the ordinary and our vet did not seemed concerned (and she is very good). He also started drooling quite a bit while he purred.
Then, seemingly out of the blue he started having difficulties breathing, and it was worse when he purred. Back to the vet, for what seemed like some sort of URI or Asthma, because it sounded like there was some sort of congestion (no snot though). Blood work was normal, urine was normal, even had an ultrasound of his chest, which showed the possibility of mild asthma because after a second opinion, they thought they could see some inflammation in his upper bronchi. We were sent home because they were going to send all of his testes to a specialist for an overview.
The next morning, I went to go find him and he was gasping for air. We immediately brought him back to the vet, and that is when they finally saw a mass in his throat. And it was only a fluke that they saw it because he happened to look back while gasping for air at the exact moment that the vet flashed a light in his mouth. It was too far down to see from the mouth in a "normal" exam, but too far up to have been caught by the ultrasound.
It turns out it was a very aggressive from of cancer, and unfortunately our attempts to remove the tumor were unsuccessful.
I'm telling you this because I would really encourage you to have your vet do an ultrasound on his throat. In your case it may not be a cancerous tumor, but it could be polyps or another type of tumor, that supposedly has something to do with the ear canal?? (that was what our vet was hoping we were dealing with), but I can't remember what this type of tumor is.
Please, please, have your vet do a thorough exam of his throat. Again, I don't mean to scare or worry you, but throat cancer is rare in cats, so your vet may not jump to that conclusion right away, until it might be too late.

Hi!
Did the xrays show anything?

granny pants said:

His mouth opens on occasion and his stomach looks like a paper bag opening and closing

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Just a thought, is your vet a cat-only vet? - be sure and select; feline only from the drop down option

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Thanks for asking. Sadly, the x-rays show a lot of bad things but still no explanation as to why he can't breathe when he purrs. He has an enlarged heart, a small murmer, and an unidentified mass that has pushed his stomach to one side. A sample of the mass was sent to the pathologist for further testing and he's been given steroid pills in the meantime. It's too soon to tell if they'll help with the breathing issue. My heart is broken. Every time I snuggle him, it sets it off so now I have to back off and let it go back to normal. There's been a lot of tears, and a lot of money spent just to keep him around (and comfortable) for as long as possible, since he is also in stage 3 renal failure. He's 17 but he looks no older than 10 and is still his sweet self besides.

What a Grand Old Man he must be! Lighting a candle for you BOTH right now.

granny pants said:

My heart is broken. There's been a lot of tears, and a lot of money spent just to keep him around (and comfortable) for as long as possible, since he is also in stage 3 renal failure.

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My heart goes out to you. No matter the age of our furry companions we cherish them and want to do everything possible to enrich their lives. I completely understand and although I have no further advice I want you to know we are here to support you. Sending special thoughts your way.