O2 Level in the blood and question related to the blood quiz from thursday

[Frackingawesome]

Mark Powell's book Deco For Divers covers this question pretty well.

Ordered that book an amazon. Looks like a good read.

 

[Frackingawesome]

So does the hemoglobin get the O2 from the dissolved O2 in the plasma? Cause it sounds like there is not much 97% in the hemoglobin vs 3% in the plasma? or does it just dissolve super fast from the air to get absorbed by the hemoglobin. I know that lungs have a ton of surface area to make this process possible.

And then i know the 3% dissolved in the plasma is not much but does the hemoglobin pull that remaining 3% out as it gives its O2 molecules to other processes? and does this mean the PPO2 is lower as the blood enters the lungs vs as the blood leaves the lungs?

 

[Frackingawesome]

You need around 3 ATM of 100%O2 for it to work. I have only heard of a couple of cases years ago of it being tried, both times for CO poisonings.

that is a super interesting idea that i had not thought about... if you need about 3ATM of O2 for that to be the case does that not happen around 66fsw? isn't that about the max depth for 100% O2?

 

[Brett Hatch]

So does the hemoglobin get the O2 from the dissolved O2 in the plasma?

Background: the blood runs in a loop from the lungs to the heart through the arteries to deliver oxygen to the tissues. There the oxygen binds with carbon to create CO2; since CO2 is a lower energy state that oxygen by itself, energy is captured, which allows the tissues to do their thing (say, lift your leg). Then the blood returns toward the other side of the heart via veins, and goes back to the lungs to become re-oxygenated with freshly breathed gas, and the cycle continues.

So, both the hemoglobin and the plasma with get O2 from the gas in the lungs. Hemoglobin is really good at snagging oxygen, so it probably grabs most of it directly from the gas as the hemoglobin cruises by the fresh gas. If a hemoglobin manages to get past the lungs without acquiring oxygen, I don't know whether it can subsequently grab it from the plasma or not. Maybe. Someone with a better understanding of the process will have to answer that one.

Cause it sounds like there is not much 97% in the hemoglobin vs 3% in the plasma?

I don't know where the 3% number comes from. I smell a misconception here, let me elaborate a bit. We cannot simply take the 97% hemoglobin number and say that the "remaining 3%" must be in the plasma, because these are different numbers that represent different things. The 97% number is the percentage of how close our hemoglobin tends to be to the saturation point. Saturation is defined as the maximum amount of oxygen that the hemoglobin can hold, it's like a ceiling. To my knowledge, this point is not variable with respect to depth/pressure, it's constant.

When we are at the surface before a dive, our plasma will be at the saturation point for oxygen in a liquid, which is the same as the gas we're breathing. So at 1 atm of pressure 100% plasma saturation of 21% oxygen = .21 PPO2 . But the plasma follows fluid dynamics, so the saturation point is a function of depth. When you go down to say, 10m/33ft the ceiling increases, so the new saturation point is .42 PPO2, and our plasma will gradually approach that amount. If you're down long enough, the plasma will eventually achieve a .42 PPO2, and we could say that your plasma is saturated with O2.

So maybe when our plasma is at .21 PPO2 it just happens to be the case that the the plasma holds 3% of it and the hemoglobin holds 97%. Or it could be 60% and 40% for all I know (I don't know this number off hand). But that has absolutely nothing to do with the fact that the hemoglobin is near the saturation point, they are different quantities.

or does it just dissolve super fast from the air to get absorbed by the hemoglobin.

Sorry, I don't know how to answer this question. It does dissolve fast enough to supply our body with the O2 it needs for the metabolism to work -- is that "fast" or "slow"? I don't know.

and does this mean the PPO2 is lower as the blood enters the lungs vs as the blood leaves the lungs?

Yes, that is exactly correct. The tissues consume O2 and turn it into CO2, which is exchanged for fresh O2 in the lungs.

that is a super interesting idea that i had not thought about... if you need about 3ATM of O2 for that to be the case does that not happen around 66fsw? isn't that about the max depth for 100% O2?

I'm not a tech diver, but most of them will tell you that they do not exceed about 1.6 PPO2 in the gas they breathe. If you're breathing 100% O2, that would be 1.6 ata, or just 6m / 20 ft of water. Sometimes in hyperbaric chambers, very bent patients will breathe richer gases than this, possibly even up into the 3 atm range for short periods under supervised conditions, doctors present, etc. But under diving conditions, breathing 100% O2 at 66 feet sounds like crazytalk. Maybe you're thinking of 50% O2, which has a max depth of 21m / 70ft?

Again, not an expert here, so I hope the above helps and I really hope that I have not lied anywhere.

 

[tursiops]

that is a super interesting idea that i had not thought about... if you need about 3ATM of O2 for that to be the case does that not happen around 66fsw? isn't that about the max depth for 100% O2?

100% pure oxygen at 66 fsw would be 3 ATM x 1.0 = 3.0 PPO2. Far too much for pure O2....which is limited to 20 fsw where PPO2=1.6. That's underwater. You can get to 3 PPO2 in a dry chamber, where if you happen to tox you won't drown.

 

[GJC]

So does the hemoglobin get the O2 from the dissolved O2 in the plasma? Cause it sounds like there is not much 97% in the hemoglobin vs 3% in the plasma? or does it just dissolve super fast from the air to get absorbed by the hemoglobin. I know that lungs have a ton of surface area to make this process possible.

And then i know the 3% dissolved in the plasma is not much but does the hemoglobin pull that remaining 3% out as it gives its O2 molecules to other processes? and does this mean the PPO2 is lower as the blood enters the lungs vs as the blood leaves the lungs?

O2 has to travel through plasma to get to the hemoglobin inside the red blood cells, but it's a short trip and happens fast. The capillaries in the lungs are so small that red blood cells just fit through them one at a time, but there is a thin layer of plasma that O2 has to travel through.

As blood travels to the tissues that consume O2, O2 travels from plasma into the tissues and as plasma O2 levels drop, O2 unbinds from hemoglobin travels out of the red blood cell and replaces the O2 lost from plasma to the tissues. Hemoglobin and plasma O2 saturation drops to 60-80% of its capacity.

Of the total O2 molecules carried in the blood at any time, 3% is dissolved in plasma and 97% is attached to hemoglobin (even if you are only carrying 60% of the maximum capacity).

 

[GJC]

I don't know where the 3% number comes from. I smell a misconception here, let me elaborate a bit. We cannot simply take the 97% hemoglobin number and say that the "remaining 3%" must be in the plasma, because these are different numbers that represent different things. The 97% number is the percentage of how close our hemoglobin tends to be to the saturation point. Saturation is defined as the maximum amount of oxygen that the hemoglobin can hold, it's like a ceiling. To my knowledge, this point is not variable with respect to depth/pressure, it's constant.

When we are at the surface before a dive, our plasma will be at the saturation point for oxygen in a liquid, which is the same as the gas we're breathing. So at 1 atm of pressure 100% plasma saturation of 21% oxygen = .21 PPO2 . But the plasma follows fluid dynamics, so the saturation point is a function of depth. When you go down to say, 10m/33ft the ceiling increases, so the new saturation point is .42 PPO2, and our plasma will gradually approach that amount. If you're down long enough, the plasma will eventually achieve a .42 PPO2, and we could say that your plasma is saturated with O2.

So maybe when our plasma is at .21 PPO2 it just happens to be the case that the the plasma holds 3% of it and the hemoglobin holds 97%. Or it could be 60% and 40% for all I know (I don't know this number off hand). But that has absolutely nothing to do with the fact that the hemoglobin is near the saturation point, they are different quantities.

You're mixing up your %s. One refers to saturation and another refers to distribution.

Saturation:

Normal arterial saturation is 94-100% of the total capacity of blood to carry O2 molecules.
Normal venous saturation is 60-80%.

Distribution:

Normal distribution of O2 molecules in the blood is 3% in plasma and 97% attached to hemoglobin. Distribution pretty much stays this way regardless of whether the total saturation is 60% or 100%.

 

[tarponchik]

Of the total O2 molecules carried in the blood at any time, 3% is dissolved in plasma and 97% is attached to hemoglobin (even if you are only carrying 60% of the maximum capacity).

These numbers vary from one source to another. For example, Although oxygen dissolves in blood, only a small amount of oxygen is transported this way. Only 1.5 percent of oxygen in the blood is dissolved directly into the blood itself. Most oxygen, 98.5 percent, is bound to a protein called hemoglobin and carried to the tissues. This is quite useful reading. Also, note that gas solubility depends not only on PP, but also on the nature of gas. CO2 is more soluble than O2 which in turn is more soluble than N2.

 

[GJC]

These numbers vary from one source to another. For example, Although oxygen dissolves in blood, only a small amount of oxygen is transported this way. Only 1.5 percent of oxygen in the blood is dissolved directly into the blood itself. Most oxygen, 98.5 percent, is bound to a protein called hemoglobin and carried to the tissues. This is quite useful reading. Also, note that gas solubility depends not only on PP, but also on the nature of gas. CO2 is more soluble than O2 which in turn is more soluble than N2.

The percent distribution is going to vary slightly depending on an individual's hemoglobin level (or what you use as a normal hemoglobin level when you do your distribution calculation).

 

[Brett Hatch]

I don't know where the 3% number comes from. I smell a misconception here, let me elaborate a bit. We cannot simply take the 97% hemoglobin number and say that the "remaining 3%" must be in the plasma, because these are different numbers that represent different things. The 97% number is the percentage of how close our hemoglobin tends to be to the saturation point. Saturation is defined as the maximum amount of oxygen that the hemoglobin can hold, it's like a ceiling. To my knowledge, this point is not variable with respect to depth/pressure, it's constant.

When we are at the surface before a dive, our plasma will be at the saturation point for oxygen in a liquid, which is the same as the gas we're breathing. So at 1 atm of pressure 100% plasma saturation of 21% oxygen = .21 PPO2 . But the plasma follows fluid dynamics, so the saturation point is a function of depth. When you go down to say, 10m/33ft the ceiling increases, so the new saturation point is .42 PPO2, and our plasma will gradually approach that amount. If you're down long enough, the plasma will eventually achieve a .42 PPO2, and we could say that your plasma is saturated with O2.

So maybe when our plasma is at .21 PPO2 it just happens to be the case that the the plasma holds 3% of it and the hemoglobin holds 97%. Or it could be 60% and 40% for all I know (I don't know this number off hand). But that has absolutely nothing to do with the fact that the hemoglobin is near the saturation point, they are different quantities.

You're mixing up your %s. One refers to saturation and another refers to distribution.

Saturation:

Normal arterial saturation is 94-100% of the total capacity of blood to carry O2 molecules.
Normal venous saturation is 60-80%.

Distribution:

Normal distribution of O2 molecules in the blood is 3% in plasma and 97% attached to hemoglobin. Distribution pretty much stays this way regardless of whether the total saturation is 60% or 100%.

Interesting, this is new information for me. I may have misunderstood some of Powell's writing.

I'd like to check a concept here. One thing I took away from the early chapters of Deco for Divers is that under normal conditions (breathing air at ~ sea level): the arterial saturation of O2 in our hemoglobin is close to 100%, and the saturation point for O2 in hemoglobin is fixed with respect to pressure. Therefore increasing pressure does not substantially increase the amount of O2 in hemoglobin, since it can at most only go up a few percent, even at depth. Do I have that right?

If the above statement is correct, then it would imply that the distribution as you have described it would vary with depth and time. For example, say you begin with a normal sea-level PPO2 in the plasma (.21) and normal arterial distribution (let's say 95%). Then, you dive on air down to 20m/66ft for several hours, or however is sufficiently long for your plasma to reach an equilibrium at .63 PPO. At that time, your hemoglobin will have gone from a number close to 100% saturated to a little bit more, but not more than 100% -- negligible change. The amount of O2 dissolved in plasma however will have tripled. In this scenario, would you agree that the distribution will have changed from about 95% in hemoglobin to about 85% in hemoglobin?