Thanks for the good thoughts, Everyone! Bear is heartworm-free!
After the vet test (it wasn't a full exam, just a the heartworm test at the clinic), we took a long walk. Seems to have cleared him out, though he's still making huffing noises every now and again like his throat still has a tickle. If it develops back into the hack-with-bile-barf it had become this morning before I fed him breakfast, I'll bring him in for a proper check-up in a week after I get paid again. He's about the age that large dogs can develop enlarged hearts, and then there's the possibilities of fungal or other infections. (Though I'd be surprised if there's much fungus to be had in this arid region, even with the wet spring.)
Anyway, thank you, All. I'm so grateful to have some place to vent my worries to in the middle of the night when I'm wired and worrying about my furbabies. You are all very special humans. 
= new reply since forum marked as read
My kittehs have been sneezing and itching with allergies this spring. Hopefully, something similar is happening to Bear and it is a temporary cough due to pollen or the like. 
So good to hear 
My first two Akitas used to do that and it always scared the hell out of me. It sounds so awful. I can't remember Yoshi ever doing any schnerking though. Occasionally he gets regular hiccups that sound just like people hiccups, but now that I think about it I can't think of a single time he's ever schnerked. Actually, now I can't think of any time he's burped or farted either. Ok, maybe a couple of tiny little polite belches or super silent bitsy farts, but I just really can't think of any time he's done even that in ages.
Eeeek, my first Akita used to like to burp like a drunkard... bbbbrrrrraaggaaaadowwwwww! Boo, my second one was scared of his farts. Whenever he did it he'd jump up with this ridiculous startled look and stare at his bum with a confused yet distressed look on his face... "My God, air just leaked out of my butt!" It was really hilarious when he did it in his sleep, and he'd wake up startled and check out his bum.
Shaggy is always very dignified, looks like royalty lying around waiting for the people with palm leave to arrive to fan him. When he farts, he looks around like, "That couldn't have come from my royal butt!" Then he sniffs his butt and looks away with disdain as if disowning his butt for being so uncouth!