What happens if you "rebreathe" compressed air?

[Gombessa]

Help me correct my understanding:

When you're at depth and breathe compressed air, is your body is still drawing out the same amount of oxygen and releasing the same amount of CO2 as it would were you on the surface?

If so, does that mean the air you exhale and lose as bubbles in open circuit scuba has more good air "wasted" while you're at depth? And if you saved that air, could you rebreathe it, e.g., at 2ATA you could breathe the same air twice, at 3ATA three times, etc?

And I'm sure physiological reaction to CO2 comes into the equation too, but it seems like the amount of CO2 you would exhale is also proportionately smaller given a compressed volume of gas at depth?

 

[rawls]

Answer to your first question...Yes. If you are breathing compressed air at sea level then you are breathing the same percentage at depth. Blood levels of O2 and CO2 generally remain pretty constant due to regulatory mechanisms. At depth the amount of air delivered is based on pressure. If you are at 3 ata then it is taking three times the amount of air as it would take breathing compressed air at sea level in order to expand your lungs to the same capcity as it is at sea level. You are still getting 21% O2 regardless, so you are not wasting air, and there is as a result, no air to save. It simply takes more to offset the pressure pushing against you.
As far as the CO2 you would exhale at depth being less...Your lungs remain expanded with the same volume as you would have at sea level therefore you are able to exhale normally and thereby get rid of the same amount of CO2 as you do at sea level. Thing is...if you skip breathe or slow your respiratory rate and/or depth below the rate and depth which you need to expire a sufficient amount of CO2 then your blood levels will increase since you are fighting your body's instructions to breathe more deeply. The most improtant thing about CO2 is you need to breathe normally at all times in order not to allow CO2 build up...
With rebreathers CO2 is something you need to be very aware of since you are recirculating the breathing gases and the CO2 is scrubbed in the loop. If something goes wrong with the scrubbing process you can have a dangerous level of CO2 build up in your body which can be potentially fatal.

 

[Cave Diver]

Help me correct my understanding:

When you're at depth and breathe compressed air, is your body is still drawing out the same amount of oxygen and releasing the same amount of CO2 as it would were you on the surface?

If so, does that mean the air you exhale and lose as bubbles in open circuit scuba has more good air "wasted" while you're at depth? And if you saved that air, could you rebreathe it, e.g., at 2ATA you could breathe the same air twice, at 3ATA three times, etc?

And I'm sure physiological reaction to CO2 comes into the equation too, but it seems like the amount of CO2 you would exhale is also proportionately smaller given a compressed volume of gas at depth?

Your volume of air consumed changes. At 3 ATA you need 3 times the volume of gas to inflate your lungs to the same size they are on the surface. If you are breathing air, then the percentage of oxgen is .21, your body will metabolize approximately 4% of that and you will exhale approximately 4% carbon dioxide and approximately 17% oxygen.

Although the volume will change, the percentage will not.

 

[dumpsterDiver]

I'm guessing that you consume the same mass of oxygen (per unit time ) both at depth and at the surface (all other things being equal). If this is so, then the percentage of oxygen in an exhalation at depth would necessarily need to have a higher percentage of oxygen than if it occured on the surface. Yes???

Maybe you could? breath each breath twice? but I suspect that the build-up of CO2 would be the limiting factor rather than oxygen. In other words the elimination of CO2 would be more important that the intake of oxygen, at least that is my guess.

 

[Thalassamania]

I'm guessing that you consume the same mass of oxygen (per unit time ) both at depth and at the surface (all other things being equal). If this is so, then the percentage of oxygen in an exhalation at depth would necessarily need to have a higher percentage of oxygen than if it occured on the surface. Yes???

Maybe you could? breath each breath twice? but I suspect that the build-up of CO2 would be the limiting factor rather than oxygen. In other words the elimination of CO₂ would be more important that the intake of oxygen, at least that is my guess.

Yes ... you consume the same number of oxygen molecules and transform them into energy for your body (ATP), carbon dioxide and water.

Yes ... if you take a breath at the surface and exhale, in terms of percents you consume a higher percentage of oxygen and produce a higher percentage of CO₂ than you would at depth.

At a _ppO₂ of 0.10 or lower, a single breath is normally all it takes to result in immediate unconsciousness, followed by irreversible brain damage or death if the unconscious individual is not quickly revived. It is not considered advisable to expose a human being to a _ppO₂ below 0.15. Breathing a _ppCO₂ of 0.07 to 0.10 percent will result in unconsciousness in short order.

 

[SteveC]

I have wondered this same thing. When you are at 3 ata you are consuming 3 times the oxygen molecules that you would at 1 ata. While its true that the percentage of oxygen remains the same, you are breathing more oxygen with each breath. So the question remains, is your body using this extra oxygen or wasting it?

 

[Thalassamania]

I have wondered this same thing. When you are at 3 ata you are consuming 3 times the oxygen molecules that you would at 1 ata. While its true that the percentage of oxygen remains the same, you are breathing more oxygen with each breath. So the question remains, is your body using this extra oxygen or wasting it?

"Wasting" it.

Yes ... you consume the same number of oxygen molecules and transform them into energy for your body (ATP), carbon dioxide and water.

 

[SteveC]

So if the oxygen is being wasted is it not possible to reuse it somehow?

 

[pir8]

Get a rebreather

 

[Thalassamania]

Get a rebreather

Right on.