Wikipedia:Reference desk/Archives/Science/2014 October 17

= October 17 =

Giving blood to lose weight
If you give blood, will your body burn more fat in response to replace the lost blood? ScienceApe (talk) 02:26, 17 October 2014 (UTC)


 * Yes, indeed. Replacing a pint consumes about 650 calories. Not much, but every little bit helps. Dominus Vobisdu (talk) 02:30, 17 October 2014 (UTC)


 * Cody McKenzie recently did that to make weight for a fight. According to a doctor, it's not recommended, but not a terrible idea, in the very short-term. Of course, in that case, it had little to do with burning fat, just that a pint of blood weighs a little over a pound. InedibleHulk (talk) 13:23, 17 October 2014 (UTC)


 * Right, runners and wrestlers also sometimes also use more conventional excretion (defecation, urination) to reduce weight before a race or a match. BTW, Dominus, your claim makes sense, but do you have a reference for that? SemanticMantis (talk) 14:53, 17 October 2014 (UTC)
 * In general one should not assume that "uses calories" is the same as "helps you lose weight". For example, in winter, you use more calories just staying alive than in summer, because you need to generate more heat.  However, most people gain rather than lose weight in the winter, presumably because they also eat more.  Unless both your caloric income and outgo are otherwise rigorously controlled (which is almost never the case) it is very difficult to predit the effect of a single change. --Trovatore (talk) 14:57, 17 October 2014 (UTC)


 * And don't forget the downside. Giving blood causes you to lose iron, and possibly other nutrients.  There is a limit to how quickly your body can absorb iron from your diet, so this imposes a limit on how much blood you can give.  (You can also have iron infusions (IV's), but this has it's own negatives.)  Also, blood cells can only be rebuilt at a certain rate, even if enough iron is present.  And if you happened to suffer an injury and bleed right after having given lots of blood, you might well bleed to death sooner.
 * The doctor in that McKenzie article says it's about eight weeks for red blood cells to come back. For what it's worth, he looked weak and slow in that fight, though that may have had more to do with fishing instead of training. InedibleHulk (talk) 15:45, 17 October 2014 (UTC)


 * Something I've thought of, for the morbidly obese, is something like hemodialysis, but where they remove unhealthy nutrients from the blood, like bad fats, bad cholesterol, & excess sodium and sugar, and perhaps increase good fats, good cholesterol, and other needed nutrients. If the person was already on dialysis for kidney failure, this wouldn't pose much additional risk, and could offer quite a benefit, part of which would be losing weight.   I think I will ask a Q about this.  StuRat (talk) 14:56, 17 October 2014 (UTC)

Effect of oxygen percentage vs. partial pressure on flammability
I have always assumed that the flammability of a give material was a function of the partial pressure of oxygen in the atmosphere it was exposed to and not the strict percentage of oxygen. For instance, I would have thought that a material would be more or less equally flammable in a 21% O2 1.0 atm environment as it would be in a 10.5% O2 2.0 atm hyperbaric one or a 42% O2 0.5 hypobaric one.

But this NASA document, Recommendations for Exploration Spacecraft Internal Atmospheres (Lang, et. al., 2005) says:
 * By contrast with human respiration that depends primarily on oxygen partial pressure in the atmosphere, materials flammability depends strongly on oxygen concentration (volume percent) and to a lesser extent on total pressure. (pg 11)

but doesn't appear to go any further into the subject.

Where can I learn more about this? I'd like to read about the physics behind this and see some "Constant Flammability Curves" showing pO2 vs. %O2 for various materials.

Oxygen states:
 * The fire that killed the Apollo 1 crew in a launch pad test spread so rapidly because the capsule was pressurized with pure O2 but at slightly more than atmospheric pressure, instead of the 1⁄3 normal pressure that would be used in a mission.

which supports my earlier understanding.

thanks fireman stow -- 190.58.249.28 (talk) 04:38, 17 October 2014 (UTC)
 * Actually, it does not support your previous understanding, it's just consistent with it. In that case, both partial pressure and concentration were much higher than in normal air. I suspect one reason why concentration is important is because all of the gases in the mixture help dissipate the heat. So adding e.g. more nitrogen will make the flame burn, effectively, colder, since there is more gas available to carry away heat from the flame. Chemical reaction are highly dependent on temperature. Also, the oxygen must be able to come into contact with the fuel. If there is more inert filler gas, that may happen less frequently. To use a mechanical analogy, it's a lot harder to get to the buffet if the room is full of people, even if most just stand and talk. --Stephan Schulz (talk) 14:51, 17 October 2014 (UTC)


 * Yes, "consistent with" is what I should have said. And the Apollo 1 statement is not inconsistent with the NASA document either, as while the latter says that percentage is the stronger effect, it does mention that the partial pressure does have an effect, albeit a lesser one.
 * Your temperature effect makes a lot of sense to me.
 * Your crowded room analogy is an interesting one. In a steady state situation where the oxygen is not being consumed, the rate at which a particular type of gas molecule impinges on a unit area is strictly a function of the partial pressure of that species, and fully independent of the partial pressures of other gas species.  It might take you longer to get to the buffet, but it will take longer to get away once you are there.  But things change when a significant fraction of the local oxygen is consumed and must be replaced.  The the additional inert gasses will affect the mean free path and diffusion rate of the oxygen, and thus the rate at which it can feed the fire. Very interesting!  I wonder how strong this effect is, and if it might be more pronounced in micro-gravity where convection is not in play.
 * Thanks, Stephan, for two promising mechanisms. I wonder what their relative strengths are, and I would still love to see some numbers or a graph showing the magnitude of the effect on flammability of pO2 compared to %O2. -- 190.58.249.8 (talk) 01:07, 18 October 2014 (UTC)

Dialysis plus
Something I've thought of is something like hemodialysis, but where they remove unhealthy nutrients from the blood, like bad fats, bad cholesterol, & excess sodium and sugar, and perhaps increase good fats, good cholesterol, and other needed nutrients. If the person was already on dialysis for kidney failure, this wouldn't pose much additional risk, and could offer quite a benefit.

So:

1) Is this possible ?

2) Which baddies could be removed ?

3) Is anyone doing it ?

4) Is anyone researching it ?

Thanks, StuRat (talk) 14:56, 17 October 2014 (UTC)


 * Loyola Medical Center has actually developed a procedure called "LDLapheresis" for patients whose "bad cholesterol" won't respond to diet, exercise, the statin drugs or harsh language. Once every two weeks, a patient spends two to four hours connected to an apheresis unit that removes 70-to-80 percent of the patient's LDL (bad) cholesterol, then returns the blood to the body. The good HDL cholesterol is not removed. here's the Science Daily article loupgarous (talk) 16:37, 17 October 2014 (UTC)


 * Excellent, but the risk of sepsis might outweigh the benefits, if that's the only baddie they remove and the patient wasn't already on dialysis (although they seem to restrict it to people with extremely high bad cholesterol and/or who have had heart attacks). StuRat (talk) 17:16, 17 October 2014 (UTC)

Plasmapheresis would seem to be one method to remove the baddies:

1) Remove the blood.

2) Separate out the plasma from the cells, by centrifuge.

3) Discard the plasma, which contains most of the baddies.

4) Mix replacement plasma, with the proper level of nutrients, with the cells removed in step 2.

5) Return the remixed blood to the body.

Now I realize there are a lot of risks involved, so this might not be practical for everyone, but perhaps just for current hemodialysis patients. Also, are we able to synthetically manufacture blood plasma, or must we rely on donors ? StuRat (talk)


 * Blood_plasma -> Simulated_body_fluid, googling /synthetic plasma/ led me to Blood substitute, as well as . The answer seems to be we can synthesize materials with many properties of plasma, but it's not plasma. /Plasma extender/ and /plasma volume expander/ are other key phrases. SemanticMantis (talk) 18:39, 17 October 2014 (UTC)


 * This sounds like an incredibly expensive way to damage red blood cells and waste plasma that could better be used for saving the lives of trauma victims. It reminds me of various world leaders who have tried to extend their lives by consuming the blood of virgins, in one way or another.  If, of course, someone like Bill Gates, who has never stolen money from anyone, wants to buy blood to address some hypothetical problem, a laissez-faire system wouldn't stop him. μηδείς (talk) 20:47, 17 October 2014 (UTC)


 * Doesn't sound very expensive under my scenario, where they are already in for hemodialysis. It would just be one more machine hooked in.  It might even save money, if this method replaces, and is cheaper than, the current methods used to filter out waste products.  The current methods also miss some toxins, like one you get from eating star fruit. StuRat (talk) 21:08, 17 October 2014 (UTC)


 * My understanding is that dialysis costs several (i.e., more than $4) thousand a month. Even insulin treatment costs a tenth of that.  I won't argue, we'll simply have to settle for sources on this one. μηδείς (talk) 23:54, 17 October 2014 (UTC)


 * Yes, dialysis is expensive, but you seem to be ignoring the fact that I've repeatedly said I'm talking about patients who are ALREADY HAVING DIALYSIS for kidney failure. Thus, there would be minimal added cost to doing this in addition to, or perhaps in place of, filtering the blood for waste.  In fact, the more expensive it is now, the more opportunity for savings there would be by doing it a new way. StuRat (talk) 00:24, 18 October 2014 (UTC)


 * Stu, all I can say is I sincerely hope you and no one you know are so bad off as to need dialysis, and if so, ask your doctor. μηδείς (talk) 03:05, 18 October 2014 (UTC)


 * LOL. I can't believe you're still arguing this when a reference for LDLapheresis was given above.  However, since dialysis, like the kidneys, already does filter out bulk fluid including any small molecular weight wastes, this isn't actually a great leap forward, unless you specifically remove particular problems (like LDL) or unless you know all the mid-molecular-weight substances and can re-extract the ones you want from the waste or provide from an external source and then increase your pore size a bit.  (Note dialysis implies a choice of pore size, so your argument amounts to an argument over what pore size to use and how then to compensate for problems of dialysis)  But aside from targeted, extraordinary interventions against recognized disease states, it's hard to believe any technology we devise soon can outdo a well-evolved kidney in this department. Wnt (talk) 16:06, 18 October 2014 (UTC)


 * Kidneys seem to do a good job of filtering waste, but don't do such a good job of filtering out trans fats, saturated fat, bad cholesterol, excess sodium, etc. As for excess sugar, the pancreas gets rid of that by producing insulin, but that results in it being transformed from sugar into fat, which isn't a good thing unless you happen to be at risk of starvation or at least underweight.  And most of human evolution took place at a time when the current baddies were in such short supply that removing them from the body wasn't much of a concern. StuRat (talk) 16:21, 18 October 2014 (UTC)


 * Removing just saturated fat or just trans fat or just cholesterol is not really feasible by any sort of dialysis, since they're in the large LDL particles. The sugar can be eliminated with a kidney tweak (SGLT2 inhibitors dapagliflozin and canagliflozin).  I'd have to think more about the sodium. Wnt (talk) 19:38, 18 October 2014 (UTC)


 * Removing saturated fat and trans fats with LDL cholesterol would be good. Also, how about my idea of removing all the plasma, which presumably contains most of the baddies, then replacing it with an artificial plasma ? StuRat (talk) 14:36, 19 October 2014 (UTC)


 * Well, the point is you have plasma proteins. Losing too much of this stuff is one problem in diabetic nephropathy.  To restore all the appropriate protein, including, say, all the unique circulating antibodies in the plasma, is, well... beyond our technology.  You have to have an upper limit to the dialysis. Wnt (talk) 22:11, 19 October 2014 (UTC)


 * Thanks. I suppose the only way around that limit, with current technology, is to use plasma from a live donor with good numbers (fats, cholesterol, sodium, etc.) to replace the bad plasma in the dialysis patient.  Hopefully, as technology improves, artificial plasma will become better and be used for this purpose instead. StuRat (talk) 17:58, 20 October 2014 (UTC)
 * I definitely don't know (and I doubt that many experiments have been done) but I'd speculate there might be a risk of "autoimmune" (actually, plasma-vs-host immune, or vice versa) reactions due to differences in the self antigens of the individuals. Maybe there's some data from parabiosis experiments in animals, except.. in practice, that's such a .. dramatic technique I suspect there should be a random background of problems that might swamp the data.  Hemophilia patients used to receive many plasma transfusions over a long period, so I suppose the risk can't be too extreme; yet clearly they were willing to tolerate a risk of viral infections that we're even known about at the time... which could still be an issue today for all we know ... anyway, for now I can't even guess.  But the idea definitely doesn't feel right. Wnt (talk) 04:52, 21 October 2014 (UTC)