I am suffering from the combination of cold and bad circulation in my stump. It causes a blend of stump pain, an increase in phantom sensation and ultimately phantom limb pain .
To specialists, this is a well known issue and not a rare problem; particularly, venous drainage problems have been documented to correlate with stump and phantom pains . Vascular return is particularly a problem with longer forearm stumps [2,3], and in my instance, that issue was known and declared to me even before the amputation by the surgeon, however, having a long stump has a lot of advantages as well. Compressing the stump helps to decrease the cross section of my arm veins as all cutaneous veins are compressed and thus pressure is higher in the deeper veins - a well established observation also for legs, where a certain well balanced venous compression (but not too much of it) has been documented to increase flow [4,5 - see text cited with these references below for details about pressure]. What treats the congestion well is a relatively tight fit of a prosthetic socket, or a tight compression sock, or a tight bandage. I wouldn't just say snug, I'd really need it tight - but not too tight .
To make things worse, a vicious cycle seems to occur at the moment my poorly circulated stump is cooled down significantly. Then, circulation gets minimal rather quickly and pains of stump and phantom hand get severe and hard to bear. Normally, phantom sensations and pains as they occur daily are no big issue - one does get used to these. But that type of extreme pain is a warning signal. So I decided to take that signal serious and after getting what they call 'minor frostbite' on my stump from a skiing weekend, I went forward to research the issue of heating the prosthetic arm externally and to build such a heating from available parts. For my condition - bad venous drainage, bad vascular return, cold vicious cycle - a moderate but steady heating that would fit inside the prosthetic arm and that would last for a steady few hours and not peak over only minutes was what I needed.
Now seeing as if that is a really medical application, why not say one word about that. My arm stump has a reduced ability to sense temperature. That means if the darned thing gets too hot, there is a really good chance I will only know once it is too late. Logically I will opt for a less aggressive heating, and exclude heat pads (see below). As I am doing this completely cross label, using parts that were not designed for this application, I am doing this the usual test pilot way - test extensively, check extensively, but take a certain risk as well. If anyone was to sell such pads for prostheses you will have to get really good insurance, as stumps and prostheses in winter are a really complicated subject you may just not want to get into. This is for people that are in the position to try it out themselves and take any consequences necessary at any given point in time.
So, here we go.