Does Oxygen REALLY not contribute to DCS

[do it easy]

To get O2 bends you need to saturate O2 binding to hemoglobin in order to produce free O2 which can then dissolve into tissues. That happens only at levels above 1.6 ppO2 so it isn't relevant to diving.

Under pressure, O2 will also dissolve into the plasma.

 

[rjack321]

To get O2 bends you need to saturate O2 binding to hemoglobin in order to produce free O2 which can then dissolve into tissues. That happens only at levels above 1.6 ppO2 so it isn't relevant to diving.

O2 almost always saturates hemoglobin in healthy people at 0.21 ppO2

 

[rjack321]

My guess is that the high PPO2 results in oxygen generating free radicals in tissue that in turn cause cellular damage. Seems to me I remember that free radicals are regularly generated in cells from 02 but there are enough biochemical buffers to keep those free radicals at acceptable levels.

My toxicology professor's voice is rattling around in my head, I think epoxides are somehow involved in the whole entire free radical generation process . . . but that class was long ago.

]

That's about it. OTUs were developed to limit oxidative damage, which you can tolerate up to a point.

I inquired elsewhere if people who are exposed to high pp02s on a regular basis - like someone needign regular hyperbaric treatments for diabetes related issues, wound healing, etc. might be at greater risk of cancer or other side effects of oxidative damage. Nobody's knows. If someone has a paper or more on this issue I'm all ears.

 

[rjack321]

That sounds like nonsense. I don't know what the answer is but it's not that. I'll take a wild guess although I don't really care about the mechanism as much as prevention. My WAG, oxygen interferes with cholinesterase in some way.

Pescy do you even know what the Krebs cycle is?

 

[lamont]

Back on topic, I believe, the OP was asking about DCS. I believe Haldane did some experiments with goats breathing pure oxygen under pressure and then released the pressure to simulate an ascent. They exhibited DCS like symptoms which cleared relatively quickly. I think this was effectively oxygen DCS, so it might be possible in humans.

That was at ppO2s of >= 2.0

 

[pescador775]

Pescy do you even know what the Krebs cycle is?

Yes, do you?

.....................

 

[lamont]

O2 almost always saturates hemoglobin in healthy people at 0.21 ppO2

i'm official confused... that seems to be entirely correct... yet we also don't metabolise most O2... so, why is O2 not considered a dissovled gas? what is it if it is not dissolved gas?

 

[pescador775]

Lamont, most O2 is exhaled. The small remaining amount in the plasma is taken up by the cells, or more properly, converted into a chemical chain by the mitochondria and turned into fuel for the cells. In other words, the oxygen is metabolized.

 

[dsteding]

i'm official confused... that seems to be entirely correct... yet we also don't metabolise most O2... so, why is O2 not considered a dissovled gas? what is it if it is not dissolved gas?

Lamont-my point exactly. It seems to me that we could saturate tissues, but my guess is that it is PPO2 limited, and symptoms would resolve themselves quickly as the O2 was metabolized. However, we must metabolize O2 at a fairly high rate, based on the fact that we go hypoxic when not, uh, breathing. So, maybe we just can't get there at scuba PPO2s.

Where is Lynne anyways? I bet she is off diving. Inexcusable.

 

[dsteding]

Lamont, most O2 is exhaled. The small remaining amount in the plasma is taken up by the cells, or more properly, converted into a chemical chain which is fuel for the mitochondria, small organelles which are the "furnaces" for vertebrate cells. In other words, the oxygen is metabolized.

Yeah, but, given Henry's Law, not all O2 in solution is going to be "taken up" by cells, and metabolized. If what you are refering to when you say "most O2 is exhaled" is offgassing of excess O2 in solution through the lungs, the same goes for N2 and other inert gases.

My point, and maybe I am not being clear, is that metabolism of oxygen is going to have a rate-limiting step. That step is either (1) supply of carbon or ATP in the Krebs cycle or (2) supply of oxygen. If the metabolism of oxygen is rate limited by (1) then you will, if you put enough oxygen into the system, in theory, saturate tissues. The oxygen then should obey Henry's Law and offgas as pressure is reduced. Reduce pressure fast enough, and you will get bent.

If, however, it is limited by (2) you'd never get DCS from oxygen. To loop this all back--this is what I assumed the OP was asking, namely, can you get DCS from too much oxygen in your tissues?