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Thread: Decompression - Best Case Scenario Questions

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    Decompression - Best Case Scenario Questions

    If you were exposed to the vacuum of space under the least harsh conditions, do your lungs collapse or can they maintain their shape? Maybe something in between fully collapsed and their natural shape?

    Second, if you were intubated before hand, could enough oxygen be pushed over the surfaces of your lungs to keep you alive? I would imagine that this would be a very low pressure flow and would be completely open to the vacuum. I suspect that if your lungs partially collapse, perhaps yes, but you would do damage to the lung tissue as that O2 forced it's way out.
    Solfe

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    All you need to know about human vacuum exposure:
    https://oikofuge.com/human-exposure-to-vacuum-part-1/
    https://oikofuge.com/human-exposure-to-vacuum-part-2/

    1) You don't collapse a lung unless there's a leak between the airways and the pleural cavity. That can happen if there's air trapping within the lung during decompression. So you don't want to try to hold your breath, and you don't want to be caught at the bottom of expiration, either, when small airways close. So there's a bit of luck and a bit of preparedness involved, according to the scenario you're imagining.
    2) I don't understand the second question. Intubation keeps your upper airway open, but that's essentially irrelevant to oxygenation in this situation, where there's no oxygen.

    And I don't know what the "least harsh conditions" are for "exposed to the vacuum of space". Could you elaborate?

    Grant Hutchison

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    Quote Originally Posted by grant hutchison View Post
    And I don't know what the "least harsh conditions" are for "exposed to the vacuum of space". Could you elaborate?
    Yeah, I was puzzled by that too. Maybe Solfe meant "gradually, rather than suddenly, like through a leak in the spacesuit." But I think he will need to clarify.
    As above, so below

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    Quote Originally Posted by grant hutchison View Post
    All you need to know about human vacuum exposure:
    https://oikofuge.com/human-exposure-to-vacuum-part-1/
    https://oikofuge.com/human-exposure-to-vacuum-part-2/

    1) You don't collapse a lung unless there's a leak between the airways and the pleural cavity. That can happen if there's air trapping within the lung during decompression. So you don't want to try to hold your breath, and you don't want to be caught at the bottom of expiration, either, when small airways close. So there's a bit of luck and a bit of preparedness involved, according to the scenario you're imagining.
    2) I don't understand the second question. Intubation keeps your upper airway open, but that's essentially irrelevant to oxygenation in this situation, where there's no oxygen.

    And I don't know what the "least harsh conditions" are for "exposed to the vacuum of space". Could you elaborate?

    Grant Hutchison
    Well, the "least harsh conditions" would not be an explosive decompression, nor being ejected from a vehicle or having stuff around that could damage you in other ways and probably involve reading those two links so you don't hold your breath. I hesitate to say lab conditions because who would work in lab that exposes people to a vacuum?

    I should have noticed that intubation is upper passages only. If you could get a tube of some sort down into the lungs, would that make a difference? On further reflection, I have a feeling that a tube in the lungs would merely make you cough and heave. But theoretically if there was a source of O2 inside the lungs, could your lungs get that into your bloodstream?
    Solfe

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    Quote Originally Posted by Solfe View Post
    But theoretically if there was a source of O2 inside the lungs, could your lungs get that into your bloodstream?
    No, in a vacuum or near vacuum you lose oxygen as fast as it is introduced and the circulatory system can’t function anyway. If you try to do something to hold the pressure in the lungs without some external support, you’ll destroy the tissue. The best you could do is a mechanical counterpressure suit, or skin suit, applying mechanical pressure rather than being a full pressure suit. But there have been practical issues with them, so full pressure suits are the standard for a vacuum.

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    Quote Originally Posted by Solfe View Post
    I should have noticed that intubation is upper passages only. If you could get a tube of some sort down into the lungs, would that make a difference? On further reflection, I have a feeling that a tube in the lungs would merely make you cough and heave. But theoretically if there was a source of O2 inside the lungs, could your lungs get that into your bloodstream?
    Yes, it takes many days for people to get used to a tube in their larynx to the extent they can tolerate it without sedation--many never do, and need a trickle of cough-suppressant sedative. There are techniques involving the insufflation of oxygen through a fine catheter threaded through the larynx and into the lower trachea (I used to use this when we were retrieving foreign bodies from the airways of small children under general anaesthesia), but again a fully conscious person would cough vigorously on such a catheter.
    But setting aside the practicalities of getting the oxygen into the lower airways, the primary problem here is gas flow. You get gas into your lungs by generating a pressure gradient from outside to inside. Expanding your chest wall increases the volume of the lungs and drops the airway pressure below atmospheric. This means gas flows from the atmosphere into the lungs. Oxygen then diffuses down a concentration gradient from this fresh gas into the deoxygenated blood passing through the lungs, and carbon dioxide diffuses out. Then you breathe out, the pressure gradient reverses, and the "waste gas" is expelled.
    But in vacuum, the "atmospheric pressure" is zero. And the pressure in your alveoli is always greater than zero, because gas is diffusing out of your lung blood vessels--in particular, water vapour is pouring into your alveoli continuously, trying to reach an equilibrium pressure equal to the saturated vapour pressure of water at body temperature--47mmHg. There's no way you can reverse that net outward pressure gradient by expanding your chest wall, so any oxygen delivered to your lower airways will flow preferentially outwards, away from the alveoli.
    To get the oxygen into your circulation, you'd need a pressure gradient from outside to inside--some kind of blockage in the upper airway to stop your insufflated oxygen escaping. The trouble is, the pressure gradient required to get useful amounts of oxygen into your circulation is comparable to the operating pressures of your circulation. Venous pressures, a few mmHg; pulmonary artery pressure 25/8mmHg; systemic blood pressure, 120/80mmHg; partial pressure of oxygen in your lungs at sea level, over 100mmHg. This works fine because blood pressure is a gauge pressure but partial pressure of oxygen is an absolute pressure, so when you're surrounded by atmosphere your cardiovascular system is operating at a pressure greater than the pressure inside your lungs. In vacuum, however, your blood pressure is gauged against zero ambient pressure. The necessary partial pressure of oxygen in your lungs is then hugely higher than your venous pressure (preventing blood getting to your heart), and higher than the pressures in your pulmonary circulation (abolishing blood flow through the lungs).
    So in vacuum, to shove a useful amount of oxygen into the alveoli, you'd need pressures that will stop blood circulating through the lungs. It's a Catch-22.

    All this ignores the additional issue, raised by Van Rijn, that your lung tissue isn't designed to sustain these kinds of pressure gradient anyway--if you did manage to generate the necessary pressures, you'd immediately blow bilateral pneumothoraces, and collapse both lungs.

    Grant Hutchison

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    That was a painfully short thought experiment. Thank you for the (gruesome) details.
    Solfe

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    Quote Originally Posted by Solfe View Post
    That was a painfully short thought experiment. Thank you for the (gruesome) details.
    You think that's gruesome? I can give you gruesome.

    Grant Hutchison

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    Quote Originally Posted by grant hutchison View Post
    You think that's gruesome? I can give you gruesome.

    Grant Hutchison
    Thanks to my wife, I don't know if I need more gruesome. My wife works in an endoscopy clinic. She thought I wouldn't understand "endoscopy", so she would say "colonoscopy clinic". This left me with the impression that broccoli, chicken bones, keys, dice, candles, etc. were coming out the wrong end. Apparently, falling down and hitting your head is a great way to swallow something far too large to normally be swallowed.

    The punchline to this is always: "What were you doing?" followed by, "I don't know. I hit my head".
    Solfe

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    So, if you had advance warning and some training. Could you survive short periods of vacuum exposure? Think Dave's effort to regain entry to Discovery in 2001 Space Oddity(mis-spelled on purpose). I think the training would also have to include some effort to keep your chest cavity expanded and your throat open.

    I have seen this in other sci-fi stories, and the training included adjustments to your blink rate to minimize damage to your eyes. I actually use the blink thing when going from my basement office to bright outside conditions.

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    Quote Originally Posted by Glutomoto View Post
    So, if you had advance warning and some training. Could you survive short periods of vacuum exposure? Think Dave's effort to regain entry to Discovery in 2001 Space Oddity(mis-spelled on purpose)
    Yes, it has even happened. You have 10-20 seconds (where 20 is perhaps optimistic) conscious time and about 2 minutes time you can survive after losing consciousness if somebody helps you, but don’t try to hold your breath. Read Grant’s blog posts mentioned up thread, they cover it in detail.

    The blink rate thing, was that from a Charles Sheffield story? I remember a story from him with that idea. If I remember correctly it had people in space and conscious for a few minutes. That wouldn’t work with unmodified humans. Perhaps with some genetic engineering or implanted technology to strengthen the body, it could (for example building in the equivalent of a mechanical counter pressure suit, so you could safely hold your breath and blood circulation would continue).
    Last edited by Van Rijn; 2020-Oct-24 at 02:11 AM.

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    Thank you Van Rijn.

    I think i was on the right track, with conscious or trained reflexes. You keep your lung capacity as large as possible and do not close your throat, thus allowing air to move out freely. I still think your alveoli would suffer damage, sort of like sunburn.

    So keeping your eyes lids closed most of the time would not help limit damage? I know it helps me when I am trying to get from my office to my car. It hurts less and I can still navigate, as long as something un-expected doesn't interfere.

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    Quote Originally Posted by Glutomoto View Post
    So keeping your eyes lids closed most of the time would not help limit damage? I know it helps me when I am trying to get from my office to my car. It hurts less and I can still navigate, as long as something un-expected doesn't interfere.
    All I can say is that I havenít seen anything about damage to eyes. If I remember the Sheffield story (it has been a long time and I donít recall the title) they would briefly open their eyes, then close them for an extended time, but realistically they wouldnít be usefully conscious very long anyway, so it would largely be moot. Basically, a person will need help fast or they will die. There isnít time to do anything fancy. A prepared person might have time to do something before losing consciousness - move a handle, or whatever, as long as it isnít complicated or take a lot of physical effort, but the longer they are in vacuum the more likely they will die, with 2 minutes probably being around the practical limit to survival.

    "The problem with quotes on the Internet is that it is hard to verify their authenticity." ó Abraham Lincoln

    I say there is an invisible elf in my backyard. How do you prove that I am wrong?

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    Quote Originally Posted by Van Rijn View Post
    All I can say is that I haven’t seen anything about damage to eyes. If I remember the Sheffield story (it has been a long time and I don’t recall the title) they would briefly open their eyes, then close them for an extended time, but realistically they wouldn’t be usefully conscious very long anyway, so it would largely be moot. Basically, a person will need help fast or they will die. There isn’t time to do anything fancy. A prepared person might have time to do something before losing consciousness - move a handle, or whatever, as long as it isn’t complicated or take a lot of physical effort, but the longer they are in vacuum the more likely they will die, with 2 minutes probably being around the practical limit to survival.
    seems like we both remember the same story, but the author totally slips past me.

    thank you for reminding me about my memory limits and realty and stuff.


    and I lurk more than contribute, but wow this forum is the best.

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    I didn't deal with eye problems in my blog posts, because I'm not an ophthalmologist and they're not reported in animal experiments and human accidents.
    However, after I'd published my own little dissertation on the problem, an article discussing what might happen to your eyes at pressures below the Armstrong limit appeared in Eye News.

    Highlights are:
    -Lid swelling making it difficult to open the eyes (swelling in animal experiments was almost immediate, so this could well be a problem during the ten seconds of useful consciousness).
    -Bilateral pneumatic orbital compartment syndrome--the eyes pushed forward and compressed by water vapour forming in the sockets (again, that would happen almost immediately, judging from animal experiments).
    -Intraocular gas formation, distorting the shape of the eye from inside and causing pain. In the short term this would be limited to 47mmHg (the vapour pressure of water at body temperature), but that's a very high intraocular pressure, more than double the upper limit of normal, and at a level that would be considered an eye emergency if it was measured in someone suffering from glaucoma.
    -Cooling of the exposed cornea, conjunctiva and lids by continuous evaporation.

    All of this would be reversible if a person was able to recompress before their heart stopped, and the sparse human data we have indicates no eye injuries. But it would seem that one's ability to perform complex tasks during the brief period of consciousness in vacuum might be further degraded by steadily worsening vision.

    On a side note, I'd just mention that physicists, like Sheffield, are obviously pretty good at getting physics right in their science fiction, but are often really, really bad at physiology. They have a willingness to speculate, born of their expertise, but a limited grasp of how the human body actually works and responds to abnormal conditions. A classic example is Geoffrey Landis's popular dissertation on vacuum exposure, which ignores the low-pressure venous and pulmonary circulation, which is where the gas forms that stops your heart. The fact that he gets the conventional notation for systolic and diastolic pressures reversed ("A typical blood pressure might be 75/120") should in any case sound alarm bells about that section of his discussion.

    Grant Hutchison
    Last edited by grant hutchison; 2020-Oct-24 at 02:22 PM.

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    As we talked about before, these non-pressure skin-tight suits being pushed are just asking to cause compartment syndrome, like Miles OíBrienís own skin.

    A fasciotomy in zero gee would not be pretty

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