Body's reaction to chaining

I assume you mean his arm is chained above his head/heart. I'm not in the medical profession but here's what I would guess:

If the arm is chained below his his heart, and assuming his other physical needs (food, water) are met, then he should be able to last indefinitely.

Above his heart, that's a different set of challenges. How tight are the chains? If they're cutting off the oxygen supply to the muscles (like a tourniquet), then I'd imagine he could only last a few days before he'd lose the arm.

What was his physical state before the chaining? I'd assume a physically fit individual would last longer than a couch potato.

If he can freely move his hand/fingers, I would imagine it would help to wiggle them a lot (make a fist, etc.). That would force the heart to pump blood up to those muscles.

There's a book by Aron Ralston that you might like. He is a mountain climber who was pinned against a rock wall when a large rock (like a boulder) fell on his arm. He eventually had to cut off the arm to go find help (gross, I know). If I remember correctly, he was trapped like that for a little under a week. At that point, the arm had been starved of oxygen for so long that it was just dead tissue and nothing could be done to save it.

You will have to be more specific about how the chaining was done. If he was chained to a wall the old-fashioned way, then there was enough chain so that he could move around a little. The shackle would have been the problem. His wrist would have been damaged to some degree, but he might have developed thick calluses there. People were shackled to walls for long periods of time, eo he might have survived for decades, assuming that he received adequate food and the sanitary facilities weren't too bad.

I imagine jail cell bars as vertical iron bars with only three horizontals (top, bottom, and middle). No idea how accurate that is, but if you described someone having the arm above his head because of it I'd be confused because surely the chain can slide up or down -- or he could stand up to restore circulation.

To me the scenario is getting vaguer and vaguer.

I suggest you try this! Put your arm up and keep it there for as long as you can. Observe.

If I understand the situation correctly, then he will have significant symptoms from his arm. He might cut off the circulation to his hand by letting the arm hang from the cuff, but that would simply require moving from time to time. Depending on how large his arm muscles are they might become cramped, but that would be minor. It would also depend on how the armwas extended. If he could rest it on his head, then there would be no discomfort.

Several years ago, I was taking a nap and managed to somehow cut off the circulation to one of my legs. (Normally that would cause you to have the pins-and-needles sensation and then wake up/move, but I was in the hospital and highly medicated at the time.) Right after I woke up, I decided to go to the bathroom. I didn't realize that my leg was basically completely numb due to the lack of blood flow. When I stood up, the leg just collapsed underneath me. Couldn't support any weight at all. The sensations started coming back fairly quickly - first the pins-and-needles, then a few minutes later my leg was fine - but it did manage to scare several nurses.

Of course I know that was a leg and not the arm, but... as I understand it, with all 4 limbs, you have pins-and-needles and, if you don't move, the pins-and-needles will sorta ebb away as the limb goes numb. Then once you move it's the reverse as you're getting the feeling back. So for an arm, I'd imagine he'd have limited to no fine motor ability. He could probably move his shoulder a little bit, but the arm would basically be dead weight for a few minutes.

If you want to feel it for yourself, when your body is in some kind of position where you're feeling the pins and needles (maybe laying on top of the arm?), just stay like that for a few minutes and you'll get the sensation of going numb. When you first move, you'll probably notice that you can't use it much, then you'll feel the sensation coming back. (Not that I've ever done this. Ahem.)

I think the longer his arm is in the shackel, the more weight is going to rest on where it binds to the wrist. Even if he tries to hold it up, it will get too heavy.

The first thing that he'll notice is how it's cutting and rubbing at the wrist. The circulation might be reduced, so I could definitely see some numbness and tingling. I think the fingers would be the worst, because they would not only be torqued up in the air, but the shackel at the wrist would irritate that nerve more.

When it was finally released, I think it would feel hot -- burning, and be clumbsy and just a bit of swelling from where things rubbed.

By the next day, I think the shoulder and neck would ache, but the tingling would have resolved in 30-60 minutes. Maybe the scrapes would have worn so deep as to scab up over several days.

Don't forget cold - with the blood supply decreased, it won't be around to keep the flesh warm.
I know when I've been writing too long, I get an ulnar nerve compression issue that causes pins-and-needles in my hand, and it always makes my hand terribly cold...