increased PO2 at depth

[cruiser]

This may not be the correct forum but it was the closest I could find so here goes.

Let's say when we dive to 4 atmospheres, we are filling our lungs with 4 times as many gas molecules as at the surface. Are our alveoli absorbing all these extra gas molecules or is there a lot of waste?

And if we are processing all these extra molecules, wouldn't that indicate that our alveoli are woefully underutilized at the surface?

 

[PatW]

Oxygen gets into you blood by two means: one is by simply dissolving in the blood. That is a trivial amount. Remember the ability of water to hold dissolved gas increases with decreasing temperature. That is why cold soda pop in a glass stays "fizzy" longer than warm soda pop in a glass.

The whole point of the lungs is to transfer oxygen to the hemoglobin in our blood. At sea level in normal air, the hemoglobin in the blood leaving the lung's capillary bed is already over 99% saturated in a normal person. So increasing the pressure of oxygen will increase the saturation of the hemoglobin but there just is not any clinically significant extra oxygen carrying capacity available. So any increase would be insignificant.

I recall that it was popular for winded football players to suck on oxygen on the side lines. The whole thing would have no physiological effect. It was all placebo.

 

[bleeb]

To expand on this and try to put a few numbers on things, you're typically consuming only about 0.04-0.05 ata of the O2 in your breathing gas. This is a metabolic requirement and independent of depth. At the surface, that means you breathe in 20.9% O2, and breathe out somewhere in the vicinity of 16.5%. Since the ppO2 you consume is not affected by depth, at 4 ata (99 fsw/30 msw) you are indeed breathing out something close to 20% O2. IIRC, as a broad generalization, people without hypoxic adaptations don't start to pass out until the ppO2 is down to 0.10-0.13.

 

[Peter Guy]

Let's say when we dive to 4 atmospheres, we are filling our lungs with 4 times as many gas molecules as at the surface. Are our alveoli absorbing all these extra gas molecules or is there a lot of waste?

The comments regarding oxygen are, as far as I know, correct. The increased number of O2 molecules is pretty much irrelevant.

OTOH, the increased number of N2 molecules is NOT irrelevant and, in fact, your body will be absorbing more and more N2 as a result of the increased number of N2 molecules which is the result of the increased pressure.

 

[NC Wreck Diver]

Hey Cruiser:

Are you Nitrox Certified? I looked at your Public Profile, but it is not listed. Review Boyles Law of compressed gases at depth. With Nitrox, you do uptake more O2 than typical air (79%N - 21%O2). But your body metabolizes SOME of this. That is why we have an MOD (Max Operatating Depth) for the different percentages of enriched O2 we breathe. All Nitrox computers have a CNS Clock (Central Nervous System Clock) to monitor the extra O2 breathed. Before I list a few other things, let me know if you are Nitrox Certified. If you are, reviewing your text will help you.

Safe diving to you.

 

[cruiser]

Oxygen gets into you blood by two means: one is by simply dissolving in the blood. That is a trivial amount. Remember the ability of water to hold dissolved gas increases with decreasing temperature. That is why cold soda pop in a glass stays "fizzy" longer than warm soda pop in a glass.

The whole point of the lungs is to transfer oxygen to the hemoglobin in our blood. At sea level in normal air, the hemoglobin in the blood leaving the lung's capillary bed is already over 99% saturated in a normal person. So increasing the pressure of oxygen will increase the saturation of the hemoglobin but there just is not any clinically significant extra oxygen carrying capacity available. So any increase would be insignificant.

I recall that it was popular for winded football players to suck on oxygen on the side lines. The whole thing would have no physiological effect. It was all placebo.

PatW--

This was very helpful, thanks.

Is it also placebo to feel more energized after diving enriched air nitrox?

 

[PatW]

PatW--

This was very helpful, thanks.

Is it also placebo to feel more energized after diving enriched air nitrox?

I don't recall having this effect. But remember as mentioned above, you have 2 gases affecting your body under pressure. You have the oxygen. The effects of increased oxygen should not be much until you start to deal with oxygen toxicity.

The other thing you have is the increased nitrogen.

When you dive with nitrox, the increased oxygen probably has almost no effect unless you go deep enough to get into oxygen toxicity.

But when you dive at depth, you have increased nitrogen uptake and the narcotic effects of nitrogen under pressure.

So with the oxygen, no I don't see any positive benefits to using nitrox. But there may be a real physiological benefit to nitrox based on less nitrogen exposure.

Now I haven't noticed such an effect. But it could be something like a hangover. Different people have radically different symptoms.

 

[cruiser]

To expand on this and try to put a few numbers on things, you're typically consuming only about 0.04-0.05 ata of the O2 in your breathing gas. This is a metabolic requirement and independent of depth. At the surface, that means you breathe in 20.9% O2, and breathe out somewhere in the vicinity of 16.5%. Since the ppO2 you consume is not affected by depth, at 4 ata (99 fsw/30 msw) you are indeed breathing out something close to 20% O2. IIRC, as a broad generalization, people without hypoxic adaptations don't start to pass out until the ppO2 is down to 0.10-0.13.

I didn't realize we had so much oxygen left in our exhale (especially at 4 ata). Is this what makes rebreathers more efficient, that the O2 being exhaled is captured for reuse?

 

[bleeb]

I didn't realize we had so much oxygen left in our exhale (especially at 4 ata). Is this what makes rebreathers more efficient, that the O2 being exhaled is captured for reuse?

Pretty much, yes.

It's also the reason why, if you unexpectedly suffer an OOA emergency at depth, your lungs still have enough O2 for you to keep even the most novice diver healthy enough to dive going for at least another minute or two. It's not the drop in O2 that makes you feel like you need to breathe. It's the buildup of CO2, which you can ignore (or learn to ignore more) for brief periods.

 

[cruiser]

The comments regarding oxygen are, as far as I know, correct. The increased number of O2 molecules is pretty much irrelevant.

OTOH, the increased number of N2 molecules is NOT irrelevant and, in fact, your body will be absorbing more and more N2 as a result of the increased number of N2 molecules which is the result of the increased pressure.

So the N2 keeps being absorbed until the blood is saturated or you start to ascend?