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

[GJC]

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?

Correct, except your distribution premise is 5% in plasma and 95% hemoglobin, which is really high for plasma unless you happen to be pretty anemic. Normal distribution is more like 1.5-3% plasma and 97-98.5% hemoglobin (depending on how many hemoglobin molecules your body has). So even if you triple the amount carried by plasma, hemoglobin will still have over 90% of the distribution.

The number of O2 molecules carried by hemoglobin doesn't change much at all with pressure because amount of hemoglobin doesn't change. If all the hemoglobin receptors are full, more pressure doesn't attach any more O2 to hemoglobin.

And total blood saturation is still 94-100% (depending on your metabolic rate and breathing rate and percent of inhaled O2).

 

[Storker]

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?

Almost.

The information you seem to be missing is that binding of oxygen to hemoglobin is a chemical reaction which AFAIK isn't (much) affected by pressure. The dissolving of oxygen in body fluids is a pure dissolution process and governed by Henry's law (double the pressure, double the amount of dissolved gas)

 

[BrackaFish]

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?

A couple of terms and concepts may make this a bit easier to wrap your head around;

O2 content is the total amount of oxygen in the blood stream. It has two parts, dissolved O2 and O2 bound to hemoglobin. The two percentages will vary, but added together will always equal 100%.

Oxygen saturation or O2sat% is the percentage of hemoglobin that is carrying O2. As the hemoglobin passes through the lungs, it binds with O2.

Because the lungs are not perfect, some blood passes through them without picking up any O2. These are known as shunts. Things like collapsed or blocked airways or scarred lung tissue from injury or some anatomical issue such as a PFO will reduce the O2sat%. So in a normal situation the blood exits the lungs with a O2sat% of 94-98%.

Increasing the % of inspired O2 raises both the amount of dissolved O2 and the O2sat%. A classic example is the smoker with damaged lungs. On room air 21% their ABG might show PO2 (dissolved O2) of say 45 with an O2sat% of 78%. This person is short of breath and huffing and puffing. Place this person on 2-4 liters of 100% O2 and their ABG might improve to a PO2 of 60 and an O2sat% of 90%. They are now feeling a whole lot better.

For the relationship between dissolved O2 and saturated/unsaturated hemoglobin you can lookup O2%sat curve and dig as deep into the weeds as you would like.

Apologies for the long winded post, but there is quite a lot going on when you are breathing. It will be interesting to see how the current virus will affect diving post illness, but that is another thread. Hope this help and be safe.

 

[bubblemonkey2]

We also have learned that our metabolic rates of oxygen consumption are independent of depth, further confirming that a normally operating oxygen transport and utilization system is dominated by pressure-insensitive chemical processes. A cornerstone of rebreather diving.

Though there may still something important going on with the smaller dissolved oxygen fraction, or else we wouldn't be getting oxygen toxicity at high ppO2...?

 

[BrackaFish]

We also have learned that our metabolic rates of oxygen consumption are independent of depth, further confirming that a normally operating oxygen transport and utilization system is dominated by pressure-insensitive chemical processes. A cornerstone of rebreather diving.

Though there may still something important going on with the smaller dissolved oxygen fraction, or else we wouldn't be getting oxygen toxicity at high ppO2...?

All dissolved gases seem to cause problems for the central nervous system if there is enough of the gas present. Oxygen toxicity, nitrogen narcosis, even helium long thought to be the inert of gases will cause issues if there is enough of it present.

 

[Jcp2]

For some reason I keep on remembering “The Abyss” whenever dissolved oxygen in fluid and diving are put in the same discussion.

 

[BrackaFish]

For some reason I keep on remembering “The Abyss” whenever dissolved oxygen in fluid and diving are put in the same discussion.

Not a bad movie as diving type movies go. I seem to recall that the navy was involved in some pretty wild stuff using liquid ventilation. I bet someone like @Akimbo would know a lot about that and also the issues involving breathing strange mixes.

 

[tarponchik]

A classic example is the smoker with damaged lungs. On room air 21% their ABG might show PO2 (dissolved O2) of say 45 with an O2sat% of 78%. This person is short of breath and huffing and puffing. Place this person on 2-4 liters of 100% O2 and their ABG might improve to a PO2 of 60 and an O2sat% of 90%. They are now feeling a whole lot better.

Now I know where the legendary "better performance when on Nitrox" is coming from!

 

[Akimbo]

I seem to recall that the navy was involved in some pretty wild stuff using liquid ventilation.

This is a good resource on liquid breathing in diving: Wikipedia: Liquid breathing, Diving

This was one of the many "promising innovations" in diving when the concept was introduced to the public in the 1960s. Problems getting people "back" (on gas) has been the major showstopper. Another very difficult problem in practice would be regulating core temperature due to the high conductivity of liquids. Water is about 25x as conductive as air, HeO2 is about 6x plus as conductive depending on the mix.

 

[Frackingawesome]

Guys thank you so much for helping me understand this.

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

does this mean that as we dissolve more O2 in the blood the venous saturation is going to increase as well? i think someone else said that the metabolic rate at which we use o2 is not pressure dependent so we would use the same about no matter how much is there right?

Also as the o2 is used by the organs and is pulled out of the plasma and tin turn is replaces by the hemoglobin is this a gradient type reaction meaning as the plasma has 3ish% the hemoglobin is fine but when the plasma drops to 1.5% the o2 has a higher affinity for the plasma then the hemoglobin and disassociates? or is there some other process involved?

further more if it is a gradient (maybe not the right word) and we have 6% or 7% in the plasma at depth does not that the o2 will stay on the hemoglobin until that low point is reached?