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To work around the space suits are SCUBA gear problem, I was wondering if it wouldn't make more sense to just bypass the lungs and their vent hole altogether and to oxygenate blood and remove CO2 (and possibly other exotic toxins) by routing it through an external machine. Maybe something light you can strap to your back or arm.

I mean... babies do this for several months before they're born, right?

Now it's self-evident that bypassing the lungs and doing away with the pressure suit won't offer any protection from heat, cold, or radiation, and you'd have to deal with those by other means or avoid those situations.

What it does offer is protection from some range of noxious atmospheres, the removal of acute vulnerability to punctures, and the freedom to talk (atmosphere permitting) and eat and poop (universe permitting) and bathe and change your clothes and generally to stay in those environments for as long as you can find fresh oxygen and power for your oxygen machine (and it may be harvesting what it needs from the local environment anyway).

It also obviates a weakness of human lungs that they only work in a restricted pressure range. A narrower range than a human might be able to endure otherwise (not a complete vacuum, but beyond 40000 ft Earth altitude).

But maybe it's not as simple as all that. Perhaps environments that seem otherwise benign are actually substantially less survivable than it would appear. The skin provides a porous interface to the local atmosphere, for example. It may allow reactions with the environment that are unhealthy or dangerous, or the local environment may obstruct reactions which are essential.

Wandering about on Wikipedia, methane and carbon dioxide atmospheres seem not uncommon, but anywhere we know that well has other serious blockers for human habitation (radiation and cold, mostly; also, wrong gravity). If not for those other problems, would they be safe environments?

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    $\begingroup$ Oxygen is needed for respiration, binding a carbon to O2 (actually quite a bit more complex) to create CO2 as the byproduct. The lungs provide the surface for gas exchange so that the balance between C02 and oxygen stays optimal. One side of the heart is dedicated to pumping blood through the lungs for this exchange, if you wanted to remove the lungs, you'd need artificial equivalents to replace them, not an oxygen pump. $\endgroup$ – XenoDwarf Jul 17 '16 at 23:54
  • $\begingroup$ I would have to agree with TunaDragon, but more importantly, I'd have to compound the problem even more. Even if you find a work around for the lungs/heart, there's still the pressure needed from our environment that keeps the gases in our bloodstream soluble. (physics.org/facts/air-atmospheric-pressure.asp) $\endgroup$ – Fayth85 Jul 18 '16 at 0:12
  • $\begingroup$ Well yes, artificial lungs is what I had in mind, although I wouldn't necessarily remove them, but bypass them (or mostly bypass them; you don't want them to die and go rotten, after all). Wasn't thinking of deep space without a pressure suit or anything. I mean, I know humans have a pressure range spanning mountaintop to shallow ocean on Earth, but perhaps it can go further when human lungs aren't a limiting factor. $\endgroup$ – sh1 Jul 18 '16 at 0:24
  • $\begingroup$ as @Fayth85 said, lungs are not the limiting factor, there are lots of reasons a space suit is necessary. There are also plenty of better ways to design them, to protect hoses. You could, in theory, attach the air supply/exchange directly to a rigid plate on the back of the suit, and pipe the air in there, possibly running hoses up inside the suit to the helmet. But you really need a pressurized air supply and something to keep the rest of you compressed. Pressurized suits are a fairly simple way to do this. $\endgroup$ – Seeds Jul 18 '16 at 15:04
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    $\begingroup$ @sh1 I think you mean resperators. $\endgroup$ – JDługosz Jul 18 '16 at 22:15
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Addressing the question at hand...

If the body was coated in latex (yes like a condom) to maintain internal pressure, and that latex was coated with silicone for insulation/protection and that silicone was coated/covered with something abrasion resistant, you could probably survive in a vacuum. But not in space because radiation would cook you and micrometeorites would perforate you, and on the top of mount Everest the cold would kill you pretty quickly unless you had more layers of insulation.

Really the most useful aspect of not having to breathe is that you can avoid inhaling asbestos, viruses, toxins, spores, pollen, farts, and bugs.

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    $\begingroup$ Especially farts. $\endgroup$ – Williham Totland Jul 18 '16 at 16:53
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If I understand your question correctly (and assuming what you described is indeed completely possible), you could go everywhere you can go now with an oxygen tank and a breathing mask.

The only potential difference (assuming that is not an issue for the device that oxygenates your blood) is that low pressure does not necessarily cause you to explode as the air in your lungs expands, but, as comments have pointed out, some pressure is still needed to keep the oxygen in your blood so I don't think you'd gain too much of a margin.

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  • $\begingroup$ At 45k feet altitude on Earth 100% oxygen isn't sufficient for human lungs to work. So if an ideal machine could do the work instead, and if that pressure isn't associated with other unavoidable hazards, then that should extend human range. Right? $\endgroup$ – sh1 Jul 18 '16 at 17:57
  • $\begingroup$ @sh1 You can go to 45k feet of altitude on earth if you have an oxygen tank and a breathing mask, so, as per my answer above, yes. $\endgroup$ – Annonymus Jul 18 '16 at 18:23
  • $\begingroup$ That would be some kind of CPAP-like breathing mask, then? $\endgroup$ – sh1 Jul 18 '16 at 18:34
  • $\begingroup$ The prime defining feature of a CPAP machine is that it pushes the air into you, but that wouldn't be necessary, you just need a direct connection to a tank that has enough O2/m3 to allow your lungs to absorb as much oxygen as they would if you were breathing at sea level $\endgroup$ – Annonymus Jul 18 '16 at 19:24
  • $\begingroup$ The problem is that human lungs don't work at 45k feet even with pure oxygen. At that altitude you need to push the oxygen into the blood. It's not recommended for long-term use, though. So that's one example environment where I'm interested in the differences. $\endgroup$ – sh1 Jul 19 '16 at 2:22
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I’ve thought about an internal oxygen store, for being able to stay underwater for long durations. It would work for space too, with a pressure suit and cooling still needed.

Consider that a day’s supply of oxygen is only about a kilogram. Super-efficient storage mechanisms would require 2 or 3 times that total. So, one lobe of a lung is replaced with a storage mechanism that can oxygenate blood from stored oxygen, and recharge when oxygen is available.

For getting rid of CO2, venting to the lung would not work via the normal mechanism once the concentration got high, but that’s just dandy if he is breathing an inert or oxygen-deficient gas.

In my underwater design, a small bladder collects the gas and is exhaled when it gets full; it's not delicate tissue like the lungs but just a bag, so it is not hurt by pressure (water depth) changes.

Or water fills the lungs when diving to prevent air pockets from existing in the body and for cooling the exchange mechanism; so the waste gas can go into the water.

On the other hand, he could have solid CO2 scrubbers that are recharged as well. This will take up more room in the body.

For a design that’s not for underwater (or extreme pressure), it’s simpler because the lungs can still do the job of gas exchange. You don’t need a new machine that directly adds oxygen to the blood; you just add fresh oxygen gas to the air in his lungs. But if he’s not actually breathing in and out it would be hard to remove the carbon dioxide from that air.


If his blood used something like respirocytes instead of red corpuscles, then the concentration of CO2 in the air held in the lung would not matter, and in could be programmed to pick up and drop off at different locations!

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Firstly you would have to teach humans to stop breathing. Breathing is considered an irrepressible reflex. From that standpoint there is no sense to engineer such a suit. Futhermore, if you were able to construct a technology that can oxygenate blood as effectively as the lung and fit it into a suit, which requires access to the bloodstream, you are quite reasonably able to create a device that oxygenates air.

That device can still be integrated into the helmet without an air hose, or if you want small enough to be put into your mouth.

For the part about the survivable surroundings just look at them individually and see what kills humans (and in what order). Usually pressure, radiation and temperature come first.

EDIT: I wanted to point out that the process of breathing is immaterial to the question.

What if? Digging Downward

So what if you're protected against the heat, pressure, and the digging process? Well, at that point, we've redefined the rules so much that I'm not sure it makes sense to try to calculate an answer.

Depending on the specs of your suit humans can survive everything. If they "dress up warm/cool/reflective as appropriate", at least if we assume appropriate means according to the surroundings.

It's a circular question, if it's too cold, hot, radioactive or the pressure is too high, the appropriate dressing up lands in a pressurized full body suit very quickly. Reaching that point there is really no point in using an external machine to do the lungs do perfectly.

Oxygenating the air in a suit of whatever model is just simpler than going directly to the blood. Unless you have a process that doesn't need input oxygen.

There seems to be no reason for anyone technically advanced enough to externally oxygenate blood to die of the stupid stuff because he forgot to suit up.

P.S. The soldiers in Scalzi's Old Men's war series have smartblood that can hold more oxygen, which enables them to do some amazing things without breathing. Still, they wear pressure suits all the time.

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  • $\begingroup$ To make this a better answer, do you have any details for the "what kills humans" part? Especially since that's basically what the question is asking for. $\endgroup$ – AndyD273 Jul 18 '16 at 20:56
  • $\begingroup$ The problem is that the question is not specified in that regard. What range of environments (not just pressures) could a human tolerate if they didn't have to use their lungs, and just had to dress up warm/cool/reflective as appropriate? If the suit is appropriate for that environment the human will survive. The usage of lungs does not affect that. $\endgroup$ – Helmar Jul 18 '16 at 21:04
  • $\begingroup$ My understanding is that the irrepressible breathing reflex is in response to CO2, which is being taken care of. If not it'd be interesting to know what babies do before they're born. Would they be in a constant state of asphyxiation panic? My intention in mentioning warm/cool/reflective was just to point out that temperature and radiation are self-evident concerns, and that they should be glossed over for the sake of finding more interesting problems, like osmosis, or the bends, etc. $\endgroup$ – sh1 Jul 19 '16 at 2:32
  • $\begingroup$ I mean... I don't presume that there's some technology that can deal with it (if there is, then as you say there's no point wondering what's possible). Just avoid those situations, or wear a sweater or whatever. $\endgroup$ – sh1 Jul 19 '16 at 2:41

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