[CliffordK]

That is interesting about liquid breathing.  So, can an ordinary fish withstand higher G-Forces than a human?

It might be possible to put a person on a heart/lung bypass machine, then fill the lungs with water or some other liquid.  No doubt it would generate a strong cough reaction, so one would probably have to heavily sedate the person.

One might be able to artificially change the blood pressure too.

I'm sure there is still an acceleration limit, as nothing is completely homogeneous for density.

[WildRose]

That is interesting about liquid breathing.  So, can an ordinary fish withstand higher G-Forces than a human?

It might be possible to put a person on a heart/lung bypass machine, then fill the lungs with water or some other liquid.  No doubt it would generate a strong cough reaction, so one would probably have to heavily sedate the person.

One might be able to artificially change the blood pressure too.

I'm sure there is still an acceleration limit, as nothing is completely homogeneous for density.

They've actually been working on liquid breathing since the fifties. 


Reaserch has produced some success with lower mammals and very premature babies but they have yet to come up with a fluid capable of the necessary exchange rates of oxygen and CO2 to support an adult human more than briefly and adult lungs then react badly to being flooded when the fluid is removed.


As you can imagine it's also a very controversial field of experimentation with very few people even being willing to participate.


Fortunately science and tech have both advanced to the point that most of what's left to be worked out can probably be done via computer simulations once an acceptable fluid can be identified.


It just seemed to me that immersion plus pressurization should increase resistance to G Forces even more than immersion alone since it would help (or should help) to prevent organs from tearing loose due to those G's.


We could conceivably intubate pilots and crews long enough to get them through launch/acceleration phases to keep the lungs working even without them being able to fully inflate due to the internally pressurized suits.  As long as you have the proper balance of gasses circulating through the lungs exchange will happen with or without inflation/deflation.


That would also be much less invasive than a heart lung machine which might not be able to function properly anyhow at high G's.

[Colin2B]

Reaserch has produced some success with lower mammals and very premature babies but they have yet to come up with a fluid capable of the necessary exchange rates of oxygen and CO2 to support an adult human more than briefly and adult lungs then react badly to being flooded when the fluid is removed.

Perfluorocarbon seems to be used with some success. Reports I've read indicate one problem is higher viscosity than air which means breathing is hard work and rib stress fractures have been reported.

[CliffordK]

Perfluorocarbon seems to be used with some success. Reports I've read indicate one problem is higher viscosity than air which means breathing is hard work and rib stress fractures have been reported.

It is quite possible that with high G-Forces, one wouldn't be able to expand and contract the rib cage anyway.  One could, of course, aid breathing with a pump, perhaps driven by natural nerve/electrical impulses to the diaphragm.

How would extreme G-Forces affect the heart?  Blood vessels?  Could the shape of the major heart valves change enough to cause problems?

Looking at deep SCUBA dives, the body seems to tolerate the pressures reasonably well, other than correcting for breathing (and various breathing and gas related issues).  Perhaps that would be another thing one could try.

So, with the tank idea, what would happen if one pressurized it to say 50 ATMs while accelerating?  Would that improve the ability for breathing and gas exchange?

[WildRose]

Perfluorocarbon seems to be used with some success. Reports I've read indicate one problem is higher viscosity than air which means breathing is hard work and rib stress fractures have been reported.

It is quite possible that with high G-Forces, one wouldn't be able to expand and contract the rib cage anyway.  One could, of course, aid breathing with a pump, perhaps driven by natural nerve/electrical impulses to the diaphragm.

How would extreme G-Forces affect the heart?  Blood vessels?  Could the shape of the major heart valves change enough to cause problems?

Looking at deep SCUBA dives, the body seems to tolerate the pressures reasonably well, other than correcting for breathing (and various breathing and gas related issues).  Perhaps that would be another thing one could try.

So, with the tank idea, what would happen if one pressurized it to say 50 ATMs while accelerating?  Would that improve the ability for breathing and gas exchange?

You're on the same track I am.  Presumably just like with saturation diving if they stay under pressure long enough there will be a decompression period necessary after such long exposures.


I was thinking more in terms of something like a rigid dive suit for pressurization rather than flooding say the entire cabin of a plane or space vessel.


More particularly I'm thinking of long periods at high G acceleration which would be necessary to reach the speeds necessary for exploration in deep space or beyond Mars in our own solar system.


The distances become so vast that the need to accelerate to at least near light speed to reduce travel time is going to be necessary for manned missions.

[Colin2B]

Presumably just like with saturation diving if they stay under pressure long enough there will be a decompression period necessary after such long exposures.

As you probably know one of the limitations for scuba diving is nitrogen which saturates body tissues which then comes out of solution on ascent to form damaging bubbles. Also at depths below 40m in sea water nitrogen becomes a narcotic causing hallucinations and risk of death due to disorientation. Perfluorocarbon avoids nitrogen narcosis as it replaces nitrogen as the carrier of O2 and CO2, this also means there should be no need for extended decompression other than to equalise pressure in body cavities.
Unfortunately at partial pressures of >0.45ata O2 becomes toxic, although it might require exposures of many hours to a few days, but for pO2 > 1.6ata brain toxicity can occur within minutes to hours and this occurs at a depth of 66m in sea water which is a pressure of 7.6ata with a breathing gas containing 21% O2. If I remember correctly the toxicity is due to the compressed O2 molecules now being so close together that they collide with each other forming oxygen radicals which do the actual damage. Fluids are relatively incompressible so the O2 molecules should not be forced closer together, but I'm not sure whether this is true when the O2 is in tissue subject to the higher pressure
The other problem might be air in various body cavities e.g. stomach and gut, this gets compressed and could cause surrounding tissue to stretch. It's certainly an issue if the pressure doesn't equalise slowly on ascent.

[jeffreyH]

Probably a better way to get decent acceleration is to get into an elliptic orbit. Accelerate into and out of perihelion each time round until the desired momentum is obtained. I have no idea if this is feasible BTW. Since you feel no acceleration due to gravity you limit exposure to harmful effects. If it is at all possible to carry out.

[WildRose]

Presumably just like with saturation diving if they stay under pressure long enough there will be a decompression period necessary after such long exposures.

As you probably know one of the limitations for scuba diving is nitrogen which saturates body tissues which then comes out of solution on ascent to form damaging bubbles. Also at depths below 40m in sea water nitrogen becomes a narcotic causing hallucinations and risk of death due to disorientation. Perfluorocarbon avoids nitrogen narcosis as it replaces nitrogen as the carrier of O2 and CO2, this also means there should be no need for extended decompression other than to equalise pressure in body cavities.
Unfortunately at partial pressures of >0.45ata O2 becomes toxic, although it might require exposures of many hours to a few days, but for pO2 > 1.6ata brain toxicity can occur within minutes to hours and this occurs at a depth of 66m in sea water which is a pressure of 7.6ata with a breathing gas containing 21% O2. If I remember correctly the toxicity is due to the compressed O2 molecules now being so close together that they collide with each other forming oxygen radicals which do the actual damage. Fluids are relatively incompressible so the O2 molecules should not be forced closer together, but I'm not sure whether this is true when the O2 is in tissue subject to the higher pressure
The other problem might be air in various body cavities e.g. stomach and gut, this gets compressed and could cause surrounding tissue to stretch. It's certainly an issue if the pressure doesn't equalise slowly on ascent.

Good thoughts.  For deep dives though particularly those requiring many hours at depth the work around is to us a mixture of Oxygen, Nitrogen, and Helium.  Used in the right mix and divers can remain at work hundreds of feet below the surface particularly if they have a capsue, or modern version of the old diving bell.   This is done pretty much on a daily basis around the world on offshore rigs and military divers.

We start here with the following: If one atmosphere equals about 14.6 pounds per square inch pressure, and the pressure increases 1 atmosphere for every 10 meters of depth. How many atmospheres are forcing the nitrogen into the blood stream at 30 meters (about 100 feet) and at 75 meters (about 250 feet)?

S0 using my proposed 250' dive  14.6g (Pressure of water force against the body) For units here I'll say as the diver goes down he's adding 1atm.

Therefore upon reaching the 250m depth we have 14.6*250'=We arrive at pretty much the max pressure the human can tolerate for any length of time and still function absent one of the hard suits made for the deeper depths and provide the wearer wit protection against the pressures as they go deeper.

This is where I come to my question.   Propose that using such a suit and pressuring it from the inside as Gforces build upon acceration then providing the astronauts the ability to survive the pressure.  The fluid could be water or water combind with some soluables to help reduce the direct pressure on the wearer hiving them the ability to suvive the kinds of burns necessary to reach our neighbors as we keep reaching further out into space.

Realistically we need to build a ship that is capable of approaching near light speed or the trips would have to be either generational or at least one way with everyone knowing that even if they reach their objectives at the site they are sent to, they would most likely never live to return to earth essentially just dying of old age on the trip.

To achieve that kind of speed it's going to require a rocket to just continually accelerate slowly up to whatever "cruising speed" is set.

There is another probable benefit to the heavy suits filled with fluid is that in the event of an emergency such as a small meteoroid turning up in their path requiring quick maneuvers to avoid it, the crew are well dressed to deal with the lateral turns, twists and even dives or acceleration as the fluid will just contain you in your pressure bubble one benefit of which is that as it builds pressure, it "shrinks" you from the outside in and in doing so reduce or eliminate organ tearing loose which can quickly lead to death.

Free floating in a pressurized "flooded" cabin I think posses more risk than rewards due to the expense and difficulty in attempting to make sure everything is dry and tight.

Thanks for chiming back in. Hard to find a crowd in which you can have such a conversation at all.

Best to all. WR

[PmbPhy]

Humans cannot, in general withstand high acceleration very well. The main problem is that the blood tends accumulate in the direction opposite to that of the acceleration. This is for instance the limiting factor when designing fighter jets, in that there is no use making one that can turn so sharply that the pilot would black out due to the acceleration.

However, it a person is submerged in a tank of water (or some other liquid with a density close to that of human tissue) accelerating the whole tank would not put a lot of strain of the person inside, since the force would be evenly distributed as a pressure gradient in the liquid. The blood would no longer tend accumulate in the direction opposite to that of the acceleration.

So, how many “G-forces” (how many times the Earth’s gravitational acceleration) could a person in a water tank withstand?

Ten times Earth gravity? A hundred times Earth gravity? Could you envisage shooting someone into space using a cannon, as Jules Verne proposed for going to the moon?


The limiting factor is likely to be forces on the air we have in our lungs, nose, ears etc. - that like air bubbles will want to rise up through the pressure gradient. If the gradient is too strong they could rip through human tissue. But the question is how high the acceleration would have to be for this (or some other damage) to happen...

There is a limit to the usefulness of accelerating in a water tank. The pressure can't be distributed evenly throughout the brain since its encased in a hard shell, i.e. the skull. So that brain will become squashed in the direction parallel to the acceleration. It's also harder for the heart to pump blood in in the direction parallel to the acceleration. My guess is that under extreme acceleration this may become a problem.

[jeffreyH]

This then raises a question. In free-fall a human undergoes acceleration but does not feel the force. Therefore both brain and blood flow would only become a problem due to extreme tidal forces. We can only overcome the problem if we could apply a force globally throughout an object rather than locally at a surface.

[Colin2B]

We can only overcome the problem if we could apply a force globally throughout an object rather than locally at a surface.

Yes, that's the problem, you can accelerate a rigid seat pushing the astronaut but brain, blood etc will try to stay at their previous speed.

[PmbPhy]

This then raises a question. In free-fall a human undergoes acceleration but does not feel the force. Therefore both brain and blood flow would only become a problem due to extreme tidal forces. We can only overcome the problem if we could apply a force globally throughout an object rather than locally at a surface.

Indeed, for a body in free-fall which is not subject to tidal forces or a body whose extent in spacetime is local , i.e. so small that the tidal forces can be ignored then there's no problem. If there's no tidal forces present, e.g. in a uniform gravitational field, then the body experience nothing different than being at rest in an inertial frame of reference in flat spacetime.

However the only force that acts globally, i.e. causes all parts of the body at the same rate relative to an inertial frame, is the gravitational force. Exceptions to this rule are when the force field is uniform and charge per unit mass is uniform throughout the body.