Science desk
< January 17	<< Dec \| January \| Feb >>	January 19 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

January 18

Brain death and life support

Hi all. After reading the news today about Jahi McMath's body slowly deteriorating while on life support, and the fact that her brain will slowly turn into liquid, I was curious. Does the body generally function normally despite being on life support and having no brain activity? What parts of the body tend to fail first and why? Why can't she maintain her body temperature (apparently hers is always low)? Any other random information on this subject would be interesting. Thanks! Justin15w (talk) 02:00, 18 January 2014 (UTC)[reply]

I think that theoretically you could keep a person alive for the rest of their natural life on total life support. However, in practice, this is quite difficult to achieve. Consider something as simple as bed sores. A healthy person would feel the need to adjust their position, and roll over in their sleep, and the problem would be solved. Somebody brain dead doesn't roll over, and therefore their blood doesn't circulate properly, eventually causing sores, then tissue death, then gangrene and blood poisoning and death. Now if the staff constantly adjusts the patient's position, this can be avoided. And this is just one of dozens of simple problems that can happen. Add them all up and the chance of living to their normal life expectancy is quite low. (The staff would also need to use electrical stimulation to exercise all the muscles, perhaps occasionally administer a stimulant to get the heart pumping faster, then lift them out of bed to an upright position, etc.) StuRat (talk) 02:22, 18 January 2014 (UTC)[reply]

Good point. Not to mention complications from constant mainlining of medication and total parenteral nutrition. Justin15w (talk) 02:38, 18 January 2014 (UTC)[reply]

There's more going on than that. The brain controls a lot more than just breathing. It controls body temperature, salt balance, blood pressure, some digestive functions, some immune functions, etc. Once the brain dies, many other things go out of balance, and inevitably this leads to general system failure. Also the breakdown of the dead brain tissue generates toxic byproducts that damage other tissues. Looie496 (talk) 02:47, 18 January 2014 (UTC)[reply]

So how did Ariel Sharon remain alive for 8 years while in a persistent vegetative state. Look at the case of Elaine Esposito - and that was before we had "modern" technology. It would be interesting to know where the OP got the idea that Jahi McMath's brain would slowly liquify. Was that from a reputable source or press speculation, rather like we have here? Bedsores are the very least of the problems. There is plenty of technology available involving variable pressure mattresses that prevent the problem of localised pressure leading to bedsores. The idea of electrically stimulating the muscle to maintain their tone is a curious and incorrect notion. Passive exercises would be used to prevent contractures. The line "I think that theoretically you could keep a person alive for the rest of their natural life" What is natural about being kept alive in a coma? Reminds me of an incident I witnessed when an anxious patient told the consultant that he was worried about his heart and that it might stop. The consultant listend to his heart with a stethoscope and then said, "Your heart is fine, it will last you for the rest of your life". The patient was greatly reassured. There are so many variables in this question and the problem of keeping people "alive" that it is relative difficult to give a general answer. Richard Avery (talk) 08:20, 18 January 2014 (UTC)[reply]

Yes, it was an LA Times story, linked here: http://www.latimes.com/local/lanow/la-me-ln-jahi-mcmath-body-deteriorating-20140108,0,4831276.story#axzz2qrNbVpsf Justin15w (talk) 15:52, 19 January 2014 (UTC)[reply]

A Vegetative state such as Sharon's is not the same as Brain death. You may not be conscious, but your damaged brain may well be working enough to regulate your body. Rojomoke (talk) 11:08, 18 January 2014 (UTC)[reply]

I agree absolutely and I was not making comparisons between the condition of Jahi McMath and that of Ariel Sharon. I was correcting some misleading information/uninformed speculation about the nursing care of a person in a long term comatose state. Richard Avery (talk) 15:01, 18 January 2014 (UTC)[reply]

Not every facility has the equipment or staff required to prevent bed sores. And yes, they are just one of many possible problems, which is what I said. As for passive exercise (just moving the limbs periodically), that would be OK if the person is never expected to recover, but electrical stimulation of muscles will prevent muscular atrophy, which is important if they are in a coma and expected to recover. Otherwise, when they awake and can't walk, they may get discouraged and suffer from depression.

Another issue with temperature maintenance in brain dead or coma patients is that a person who is just asleep will shed covers if they overheat or snuggle under them if they get cold. These simple temperature control mechanisms no longer work for the comatose and brain dead. StuRat (talk) 15:25, 18 January 2014 (UTC)[reply]

There are very important differences between (1) a persistent vegetative state such as Sharon was in, (2) coma, and (3) brain death. In a vegetative state the brain is largely functional, but not functional enough to support consciousness. A person in this state shows substantial activity, including sleep-wake cycles, eye movements, withdrawal from painful stimuli, bowel movements, etc. What is lacking are purposeful movement and communication. In true coma, which rarely lasts for longer than five weeks, there are no sleep-wake cycles, no eye movements, etc. Only some very basic reflexes are functional. Coma almost always resolves within a month either into a vegetative state or into brain death. In brain death, all of the electrical-activity-generating tissue within the brain is dead. Not just non-functional, but actually dead. Looie496 (talk) 17:46, 18 January 2014 (UTC)[reply]

- It's also important to consider which part of the brain. The operation of basic life functions occurs in the brain stem; while most of the stuff that we consider a "person" (i.e. one's personality, emotions, memory, etc.) occur in other parts of the brain, primarily the Cerebral cortex. Thus, a body with a functioning brain stem can be kept alive almost indefinitely, but that's really not a living person if there's nothing working outside of that, it's just a bunch of tissue. --Jayron32 04:46, 19 January 2014 (UTC)[reply]

Powder beetle bite humans.

Request for medical advice

The following discussion has been closed. Please do not modify it.

Got a beetle bit a year & 5 months ago. Had Dr.' s look at it at OHSU about 20 of them and they didn't know what it is now it is eating my hand away. The VA don't even know for sure what it is.Please help I can't be the only one in the world with this. I still have a few of the bugs in a jar. — Preceding unsigned comment added by 199.15.221.104 (talk) 10:27, 18 January 2014 (UTC)[reply]

I'm sorry, but the Reference Desk is unable to offer medical advice. Rojomoke (talk) 11:11, 18 January 2014 (UTC)[reply]

Silicone Casting

Long rambling introduction of how I came to be in this position, that you can skip if you want: I originally bought a 3D printer some time ago, when they were just getting interesting, and since then have worked at producing and selling a range of different simple things, keyrings and figurines mostly, but more recently I thought to use my contacts in the costume industry to supply a few simple plastic parts there, items mass produced, strong and light weight, it seemed a good idea. Soon after, I was approached by someone that was interested in creating similar items for the same industry, out of silicon, and they asked if I would be able to produce moulds for them to cast these shapes. Initially I was a little reluctant, since it would allow them to compete with me in the same area, but I saw the value in working together and went along with it, designing a few simple moulds for them to use. However, they have since hit some issues of their own, and it is looking like they will not be able to go through with their plans at all. Which leaves me thinking, there is only a certain limited demand for printed plastic items, any chance to expand my business is helpful at this point, so perhaps I can pick up where they left off?

I am interested in casting items out of silicon (by which I mean the soft, slightly rubbery plastic stuff, I am not sure if it is related at all to the element of the same name) however, I am not entirely sure how to go about doing so, I know the basics of casting in moulds, but not the specifics for this particular material, and the internet is not being helpful, any search leads me to casting of other materials within silicon moulds, which seems more common. So, I wonder whether I might get a better answer here, from real people. Any suggestion of where I might find instructions on this method? Suggestions of good places to buy materials and equipment would also be helpful. From what I have seen, it is an area of some demand, and a wide range of possibilities, so a good opportunity for me if I can take it.

Thank you,

213.104.128.16 (talk) 22:32, 18 January 2014 (UTC)[reply]

I don't know much about casting, but the rubbery material you're considering is silicone, not the element silicon. DMacks (talk) 22:42, 18 January 2014 (UTC)[reply]

Ah, that makes sense, thanks. Still doesn't help with finding information, but it solves that little mystery. 213.104.128.16 (talk) 00:03, 19 January 2014 (UTC)[reply]

The specific subset of silicones you're looking for is silicone rubber. As for the casting process, this will depend on the viscosity of the material in its uncured state: if it's viscous, you'll have to use pressure casting (die casting), but if not, then simple permanent mold casting will do. In either case, you'll have to use the platinum-catalyzed curing system, cure-in-mold -- the other method just takes too darn long! 67.169.83.209 (talk) 06:56, 19 January 2014 (UTC)[reply]

Yes, and of course silicone contains silicon, hence the name. I've often thought that most plastics used in the kitchen should be replaced by silicone, as it doesn't absorb smells and colors like plastics do, and doesn't melt or degrade at the same low temperature as plastics. For example, I have nice glass bowls suitable for refrigerator or freezer storage, microwaving, and serving, but they have plastic covers which can't take microwaving and even warp in the dishwasher. One shortcoming of silicone seems to be that you can't get the same vibrant colors as plastics, but I could live with that. StuRat (talk) 23:10, 18 January 2014 (UTC)[reply]

In general, 3D printing is a horribly slow and expensive way to make almost anything in any reasonable quantity. Filament plastics cost between $30 and $40 per kg where granulated or pelletted plastics are around $1.50 to $2 per kg. A 3D printer can easily take an hour to make something that an injection molding machine can make in a fraction of a second. So 3D printing is a non-starter for mass-produced items.

The benefits of 3D printing only come when the quantities are small and the losses due to the expensive plastics and L-O-N-G print times are outweighed by the cost of making a mold that's only going to be used a handful of times. So (depending on your market and the nature of what you make) there is a cross-over point at which making a mold and doing some kind of casting starts to make sense.

The precise point at which that happens depends entirely on the nature of what you're making - it's volume and shape complexity being the biggest factors. Usually, when you design something that you expect to sell more than (say) a hundred of - you should design it in such a way to make molding easy.

However, the useful intersection comes sooner when you can make a mold USING a 3D printer. This gives you the convenience of going direct from CAD drawing to product - and makes creating a custom mold very cheap. The issue is making the mold resilient enough to withstand making a large enough number of finished objects. Plastic molds don't last long with any mechanically pressurized casting system - so you might find yourself needing to make many, many molds using your printer. Poured resin (for example) casts well, and a plastic mold works well for a lot of castings. Metal casting into plastic molds generally doesn't work at all because the plastic melts - but you can find low melting point alloys that will work - although you may have to do things like spinning the mold ("spincasting") to force the metal down into all of the details - and then the pressures involved will still trash your molds after not much time.

So for silicone - the issue is whether you can simply pour the stuff in (which should work) - or whether you have to force it in (which probably won't).

If you have to force it in, then you may need to make another step. 3D print the original object - take a mold from that using one of a variety of possible techniques - then use the mold for casting the finished object.

I suspect that silicone is a material right on the edge between being usable with a 3D printed mold and not...and the critical deciding factor is the shape of the object.

If you're making things like key fobs - then I'd recommend looking at other materials. SteveBaker (talk) 16:53, 20 January 2014 (UTC)[reply]

That makes sense, most of what I make is in small quantities of custom designed items, and I have made molds with the thing before, though those were sold to another company so I have no experience of exactly how the product works for casting items. the end result of the printing is a pretty tough, long lasting plastic, mine have been through some rough testing before and come out surprisingly well from it, so I suspect I'll get at least quite a few silicone parts from a single mold. And all going well, perhaps I can move on to casting other materials, to get cheaper mass produced items rather than the slow, expensive output my printer gives by itself.

The impression I'm getting from this whole discussion is that I can get the silicone rubber in more or less viscous types, the less viscous being easier to pour into the mold, of course. I am still not entirely clear on the curing process, but this is a good start. 213.104.128.16 (talk) 19:07, 20 January 2014 (UTC)[reply]

The curing process is pretty simple, as a matter of fact -- you just mix the resin and the catalyst, and then quickly pour the mixture into the mold (just like working with epoxy resin, but without the awful stench thereof). Then after filling the mold, you wait a predetermined amount of time for the mixture to set, and then open the mold and take the item out. Elementary, Dr. Watson! 67.169.83.209 (talk) 02:24, 21 January 2014 (UTC)[reply]