Accumulated 02 following a large number of repetitive Nitrox dives over 3 days.

[jgttrey]

If someone hands me a tank and says the pressure is PO2=100 bars, I need to know if he means it is 100% O2, and half full, or full but only half of the gas is O2.

Who does that? Maybe at the fill station someone might say "this one's got 100 bar of O2 in it" but if someone said here's a cylinder with a "PO2 of 100bar" I think we'd look at him like he had rocks in his head.

 

[jgttrey]

Obviously not!

I think they are used interchangeably by divers who actually use those terms on regular basis.

Yes, I get that some posters have wondered if there is a difference, but in actual practice I've never, ever heard someone use "PO2" to mean anything other than PPO2.

 

[BlueTrin]

I think they are used interchangeably by divers who actually use those terms on regular basis.

Yes, I get that some posters have wondered if there is a difference, but in actual practice I've never, ever heard someone use "PO2" to mean anything other than PPO2.

When I try to google it, PO2 seems to be used for partial pressure of O2 but in your blood (for medical sources)

 

[GJC]

I have a suggestion.

Because the p's mean different things to different people and because the p's by themselves don't provide enough information on exactly what you are referring to, let's eliminate the p's.

You can say O2 percent
You can say O2 pressure using whatever pressure measurement you prefer.
But you can't use p by itself anymore.

I might even remove the p from my keyboard to prevent me from using p's in the future.

 

[doctormike]

No not tank pressure, pressure delivered. Like PO2 1.4 ATM. Maybe the exact definition is wrong, but it just helps me to think of it this way....

Because the p's mean different things to different people and because the p's by themselves don't provide enough information on exactly what you are referring to, let's eliminate the p's.

Science doesn't work if "the p's mean different things to different people", and neither does scuba training.

PO2 1.4 means that the partial pressure of oxygen in the gas that you are breathing is 1.4 ATA. It is the product of the percentage of O2 in the gas (FiO2) and the depth in atmosphere.

Not sure what you mean by "pressure delivered", but PO2 is a partial pressure of O2. It's on a scale where 100% O2 at sea level is PO2 of 1.0. For the purposes of scuba physiology, we assume that we are always breathing gas at pretty close to ambient pressure, because otherwise you get pulmonary barotrauma.

"O2 percent" is FiO2, which is the percentage of all of the gas molecules in the mix that are O2

"O2 pressure" is a non-standard term, so I don't know what it means. "Tank pressure" - I know what that means, no matter what is in the tank

"P" means nothing in the context of this discussion. Pt or Ptotal are used to mean total gas pressure (i.e ambient pressure).

PO2 is used pretty widely in diving. I occasionally see PPO2 but I'm not sure what you are getting for the extra letter, since PO2 is such a standard usage. Insisting on PPO2 because it's more descriptive begs the question why we don't insist on writing out "Partial Pressure of Oxygen". We don't. We use PO2.

 

[BlueTrin]

I have a suggestion.

Because the p's mean different things to different people and because the p's by themselves don't provide enough information on exactly what you are referring to, let's eliminate the p's.

You can say O2 percent
You can say O2 pressure using whatever pressure measurement you prefer.
But you can't use p by itself anymore.

I might even remove the p from my keyboard to prevent me from using p's in the future.

Let’s hope someone does make his own definition of O then

 

[Madacub]

High O2 affect all cells, not just pulmonary. The pulmonary symptoms just show up first. Your cells need time to recover from an exposure. Time and pressure affect your exposure. Recovery time is not an exact science at this point.

What is pretty clear is that short term exposure at high pressure causes seizures, thus the 1.4 limit.

That's the simple version.

We were typing at the same time. See my previous post for a little more detail.

Hi GJC, thanks for your response. I don't understand part of it. You say "The pulmonary symptoms just show up first". I think it depends. If you go straight to 140 feet on EAN32, CNS will show up first. Of course you know that. So I don't understand what you wrote.

 

[uncfnp]

I don’t believe the definition or abbreviation for partial pressure changes just because it is at depth.

Virtually every medical text or scientific article I can find uses PO2 for partial pressure of oxygen. It seems that the diving community has adopted ppO2. And yes, in that context, they do seem to be used interchangably.

 

[Madacub]

Yeah, that confused me as well... I have always used them interchangeably. Ambient pressure is the total pressure of all gasses, and it is made up of the sum of the partial pressures of each individual gas (Dalton's law). So by specifying PO2, PN2, etc... I thought that meant by definition a partial pressure.



That was the controversy discussed upthread. But the half life does refer to CNS toxicity. For example, from the Shearwater manual:

During a dive the CNS never decreases. When back at the surface, a half-life of elimination of 90 minutes is used. So for example, if at the end of the dive the CNS was 80%, then 90 minutes later it will be 40%. In 90 more minutes it will be 20%, etc. Typically after about 6 half-life times (9 hours), everything is back close to equilibrium (0%).

I don't remember reading about half life with respect to pulmonary toxicity, but time with a lower PO2 is definitely protective - this is one of the reasons for air breaks during chamber treatments and long decompressions on rich gas.




The clock refers to CNS toxicity, pulmonary toxicity is tracked with OTUs. Check out that Dive Rite article, and the Shearwater blog post.


No. CNS toxicity is depth, mix and time. If you stay long enough at 1.4, you will go over your maximum single dive limits (150 minutes on the NOAA table). And, of course, there is a huge amount of individual variation.

Hi doctormike, thanks for your response. Let me digest those bits regarding the Shearwater manual and the Shearwater blog post for a bit. (I had read the manual earlier, as well as the Shearwater blog post).

I think going down the path of OTUs is not going to add clarity at this time.

The Diverite article says "Note that these air breaks are intended to forestall symptoms of pulmonary oxygen toxicity; there is no risk of seizure or other CNS manifestations in these circumstances.". This seems to buttress what I am saying (?).

 

[Madacub]

Or it could just be a troll that is seeing how long it takes to get bounced out of the board again. May be put a poll togather, or a thread to enumerate the names used. The threads involved have been very informative, yet annoying.



Bob

I really don't think he was trolling. It seems a long, long, long way to go for that purpose. But maybe I am too naive in the ways of the interwebs......(Or maybe there was more going on behind the scenes)