Electric heating for my prosthetic arm [tech build / instructions]
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.
Solutions that I looked into and discarded
Heating pads are plastic bags that contain chemicals. A heat emitting reaction is trigged by shaking the bag and after that, a temperature of 75 to 85 degrees C is achieved over a time of 20 minutes to 2 hours. While a heating pad may be the right thing to place in a pocket, I cannot afford a skin burn. The pads are usually to large to fit inside a prosthetic socket. The pads are awkward to fix to the outside of a prosthetic socket and no determined and predictable relief is to be expected at the inside while the outside of the prosthetic gets heated rather significantly. Besides, time course of the temperature was not in line with my outdoors activity schedules - usually, like, skiing for a day or so.
Insulation of the arm.
While I already use ample isolation in terms of preserving heat (underwear, woolen pullovers, high tech jacket) these never really worked. Isolation is a good concept generally, but here I am dealing with a clear medical insufficiency of circulation. I really exhausted regular ways of insulation so I was now looking for an external heat source as my internal heat source - the stump - also is insufficient to heat my arm at 25 degrees C environmental temperature. It simply is not enough.
Electrical heating of prosthetic arm - prototype December 25th 2010
First, I got myself a set of insoles and a set of battery backs together with a recharger from the Austrian company Therm-ic.
You can order the parts from Amazon USA as a complete package:
Alternatively, a more affordable way would be to order soles and batteries separately, here soles off US Amazon:
... and some battery packs to start with:
The insoles have a shape that is rather rigid and are not useful to be used inside my prosthetic arm. However, I turned them around and after heating it up for a few minutes found that only a small part of that sole actually contains heated elements - the part that is gray, that contains a big white X, at the tip of the sole. The rest of the sole is just rubber and I found it would be best to cut it off and discard it.
So I first carefully pulled off the black plastic sole to expose the flat cable.
Then I cut around the heated elements that are contained in that gray area marked with a big white X. These guys made their soles already knowing their customers wanted to cut them up! Great people :) At any rate, two soles were cut up and I ended up with small flat pads that just about fit into my old socket that is slightly too wide. Ironically, my prosthetic technician already used shoe inlays / commercial sole pads to fix my sockets that were too wide, so using soles again - even if heated - would be exactly what my technician would do to make that old socket fit a bit better anyway.
This is my stump wearing a liner (gray fabric on the outside, white silicone on the inside) and what you see here is my stump lying flat on the table, with one pad on the op, one on the bottom - and that is exactly the position I was using to maneuver my arm plus heating pads into the prosthetic socket until I got the pin (which you see to the left top in the image) lock inside the pinlock of my prosthetic arm.
Again, the same image - I marked the location of the two heating pads. Right now I only "placed" them loosely on the outside of the liner, but they could be taped there or held in place by some plastic or aluminum foil. I just did not feel it would be necessary as after sliding the stump plus all parts inside the socket, all parts were squeezed in location anyway and could not move away any more.
As I slide that setup into the socket, you can see how neat all parts fit. The battery packs contain a slightly rounded shape and flat and comfortable brackets that I use to clip them onto the prosthetic socket.
This is the final result: liner plus heating pads locked in place, flat cables (that are part of the soles) running out of the socket, and plugged into the battery packs. These are located close to the elbow rather than more outward towards the wrist - because of the center of gravity. Like this, the weight is not an issue.
A closeup view shows how the flat cable runs well between liner and socket and is of no concern at all.
This view shows the brackets of the batteries. As my old socket here really is too wide at its narrowest circumference (that'd be at the end of the stump, all the way down into the socket) and as it is absolutely too wide up at the entrance / edge, that you see here, fixing some brackets to it is of no concern inasmuch as comfort is concerned. My plan is to later wear another layer of compressive sock over the stump so all that extra space I have now will then be used up.
Yeah, and I actually tested the heating. Great stuff so far. I will keep working on this, so far this is a first prototype - and report back once there are any news, problems, injuries, further improvements or success. A nice thing to follow up with would be a six hour temperature curve or so.
And remember. You read that here first. Here is where cool ideas get born, discussed, played with, prototyped and published. This is as Open European Design as it ever gets. Cheers to Therm-ic for these cool soles they are making.
With this instruction, I only describe what I did and I tried to explain exactly why I did it. I make no claim as to this being useful to you or anyone else. If you try this, you are definitely on your own. In fact, you should be only allowed to do what your doctor or prosthetic technician allows you to. If you do modify your prosthetic socket, you are well advised to get technical advice, technical support and possibly your prosthetic technician to do this for you.
 Gillis Leon (1964) The management of the painful amputation stump and a new theory for the phantom phenomena. Brit J Surg 51(2):87. - - This is a very interesting paper, whose claims correlate rather well with my personal experiences. The author then states: "I feel that diminished blood-flow to the tissues may be the common denominator in all the various mechanisms that may initiate pain. Diminished bloodflow leads to local oxygen deficiency relative to the momentary function of the tissues concerned, and this local hypoxia may set off the pain impulses. This aspect should form the basis for future research work, and the solution to the problem may well lie here." I do not believe there to be "the" solution to "the" problem as phantom pain is indeed a complex issue - but vascular problems are definitely at the root of my own stump and phantom pains as I am mostly able to cope with these by compression or muscular activity or both, and at the same time not by any other means.
 The Major Amputations - John R. Glover - The American Journal of Nursing - Vol. 50, No. 9 (Sep., 1950), pp. 544-550 - Published by: Lippincott Williams & Wilkins Stable URL: http://www.jstor.org/stable/3459301 -----From the text: "Excessive length of the stump is often a definite disadvantage since it may cause disturbance of circulation, swelling, and enduration with distortion of the stump's shape".
 Henry H. Kessler (1939) Amputations and prosthesis. The American Journal of Surgery, Volume 43, Issue 2, February 1939, Pages 560-572, ISSN 0002-9610, DOI: 10.1016/S0002-9610(39)90880-9. http://www.sciencedirect.com/science/article/B6VHS-4C00KP1-33H/2/5bc2eec2a1375c85c953ff92acf2030f)v ..... "Circulation of the stump of the lower third of the forearm is very poor ..."
 Bernard Sigel, MD; Annette L. Edelstein; Lane Savitch; James H. Hasty, PhD; W. Robert Felix, Jr, MD (1975) Type of Compression for Reducing Venous Stasis - Study of Lower Extremities During Inactive Recumbency - - Arch Surg. 1975;110(2):171-175. Abstract: Determination of the optimal compression to reduce venous stasis was studied in terms of the amount of pressure and manner of application (graded or uniform pressure). Both lower extremities of seven inactive recumbent subjects were tested using transcutaneous Doppler ultrasonic measurement of femoral vein blood flow velocity. Optimal compression was defined as the externally applied pressure that produced the greatest increase in femoral vein flow velocity consistent with safety and the practicality of hospital use of elastic stockings. Optimal compression for elastic stockings to be used by hospitalized patients who spend substantial time in bed should be 18 to 8 mm Hg (ankle to midthigh). At this compression, average femoral vein blood flow velocity is increased to 138.4% of base line. Gradient compression at this level was found to produce a greater femoral vein flow velocity than the same amount of compression distributed uniformly over the lower extremity.
 The effect of compression on venous stasis - P.M. GAYLARDE, I. SARKANY, H.J. DODD
Article first published online: 29 JUL 2006 - DOI: 10.1111/j.1365-2133.1993.tb00167.x British Journal of Dermatology - Volume 128, Issue 3, pages 255258, March 1993 -
Summary -- Skin blood flow in the lower leg is increased by external compression in standing subjects. This prevents the hypoxia induced by standing. The maximum increase in oxygen tension is seen when the external pressure is 4050 mmHg. Pressures in the range of those produced by lightweight elastic stockings were found to be ineffective. Our results uphold the commonly held clinical opinion that only compression bandages or strong stockings are effective in the treatment of venous ulcers. External compression when the subject is recumbent causes skin oxygen tension to fall. Uniform external pressure exceeding 10 mmHg should therefore be avoided in the prophylactic treatment of post-operative deep-vein thrombosis. This observation suggests that when the patient is confined to bed, only lightweight stockings are safe in the prophylaxis of post-operative deep-vein thrombosis.
 Thanks to Sue Webb for clarifying this.