Nitrogen and Oxygen

[tursiops]

Didn't I say that my dolphin friend?

Hmmm, no, but I'm sure you meant to.
Have a Catch of the Day burger at Kite City at Te Amo for me, with lemon butter sauce please. Yum.

 

[Akimbo]

The high pressure only reduces the size of the bubbles to ease the suffering. If you take the pressure away, the bubbles will expand back.

Pressure also drives diluent back into solution. The first couple of atmospheres is a two-fer for restoring blood flow.

 

[Kevrumbo]

Goals of Oxygen Therapy in suspected DCS Syndrome case:
-Bubble Resolution through Denitrogenation (bubble contents almost pure nitrogen).
-Surround bubble with high oxygen environment
-Diffuse Nitrogen out of bubble into blood.
-Nitrogen transported to the lungs and exhaled.

Augmented with Hyperbaric Oxygen Therapy (HBO) in a Recompression Chamber, the goals are:
-Bubble size reduction (vital in suspected case of AGE).
-Hyperbaric oxygenation of hypoxic tissues.
-Reduction of tissue edema.
-Rehydration (e.g. Oral hydrating fluids or IV Normal Saline during Treatment).

Bubble size Reduction:
Decompression Sickness, small bubbles:
-Treatment starts at 2.8 ATA pressure breathing 100% Oxygen, with theoretical 70% reduction of Original Bubble Diameter.

Arterial Embolism, large gas bubbles:
-Treatment starts at 6.0 ATA pressure breathing 47% to 50% Nitrox or 50/50 Helium-Oxygen (for a ppO2 of around 2.8 to 3.0) with 55% reduction of Original Bubble Diameter.

@Kevrumbo The high pressure only reduces the size of the bubbles to ease the suffering. If you take the pressure away, the bubbles will expand back. . .

Which is why the time duration of the two pressure treatment tables for DCS and AGE are hours long (4:45 and 5:50 respectively), and in complicated cases may require an extension of a treatment session or several follow-up treatments over separate days.

TT6 starting at 2.8 ATA for DCS:

TT6A starting at 6.0 ATA for AGE:

A training run at the Catalina Hyperbaric Chamber:

 

[victorzamora]

To clarify, my question was about giving a suspected patient of DCS a 100% oxygen vs any other gas mixture.

My answer remains the same. Simply put: breathing less "inert gas" in (Nitrogen or Helium, for example) gives you the fastest way to get the inert gas you've been absorbing out of your system. So people breathe pure O2 not for the higher oxygen, but for the zero-Nitrogen and zero-Helium.

@KevinNM mentioned breathing 21% Oxygen and 79% Argon earlier. That would, essentially** do the same thing for getting the Nitrogen and Helium out of your body that you absorbed during the dive. The benefit that pure-O2 has over something like that 21-Oxy/79-Argon mixture is that Argon is still an inert gas. If you're breathing Oxygen+Inert Gas, you'll always have some inert gas you're breathing in and absorbing and needing to account for.

**Nit-Picky point that you can essentially ignore: There are some issues with that as Argon is an inert gas so you can get some counterdiffusion that may reduce the efficacy of the previously-absorbed N2 and He, but that's really getting into stuff I don't understand well enough to explain properly.

 

[Akimbo]

So people breathe pure O2 not for the higher oxygen, but for the zero-Nitrogen and zero-Helium.

Not exactly. Breathing higher (preferably pure) Oxygen also accelerates transfer of diluent in the bloodstream across the alveoli and into the lungs. That is the primary reason for beginning DCS treatment with pure O2 on deck until you can get to a chamber.

 

[tarponchik]

Pressure also drives diluent back into solution. The first couple of atmospheres is a two-fer for restoring blood flow.

True, since gas solubility increases with pressure. However, this will only work when breathing O2 since if breathing air, body liquids would be saturated by the atmospheric N2 at this pressure.

 

[victorzamora]

Not exactly. Breathing higher (preferably pure) Oxygen also accelerates transfer of diluent in the bloodstream across the alveoli and into the lungs. That is the primary reason for beginning DCS treatment with pure O2 on deck until you can get to a chamber.

I thought that was tied into the "Oxygen Window" theory that turned out to not be proven at all.

 

[Duke Dive Medicine]

There was once a belief among a very small segment of the diving community that it did do that. They called it the "oxygen window," a term that means something else by other people. The idea was that somehow very high PPO2s being converted to carbon dioxide create an "oxygen vacancy" that created more room for the nitrogen to leave. (That's the best I can explain it.)

If you think this violates both Dalton's Law and Henry's Law, that is what most people think, too.

I read the paper in which this was explained. As a non-scientist, I read carefully as it went through the observed data step by step. And then, in one magic paragraph, BAM! the idea was stated boldly, even though I could not see one iota of evidence for it in the data and discussion leading up to it. Other people were saying the same things. In Deco for Divers, Mark Powell dismissed it in a couple of sentences.

In accordance with that belief, one group of divers began to extend decompression stops when the PPO2 was at its highest, creating what they called an S-curve, in which deeper stops were longer than shallower stops. That group later decided that the theory was faulty and has dropped that practice. Another group that sprang out of that group still uses the S-curve, although I am not sure why, since I heard them admit years ago that the theory behind it was suspect.

I think what Powell dismisses is the idea that the oxygen window influences the rate of tissue inert gas washout. It does influence bubble size, and he discusses that as well.

Best regards,
DDM

 

[Akimbo]

I thought that was tied into the "Oxygen Window" theory because that turned out to not be proven at all.

It all comes back the concept of diffusion -- movement of molecules from higher to lower concentrations. The big win for divers is decreasing the concentration of diluent in the lungs -- the partial pressure matters, not the percentage. That's why Table 5 and 6 (60' on O2) often works better than Table 4 that goes to 165' on air before working back up to 60' for the switch to Oxygen.

As a US Navy Master Diver told us: Any idiot can calculate Nitrogen uptake on pure Oxygen. There ain't none.

 

[tarponchik]

@Akimbo: "It all comes back the concept of diffusion -- movement of molecules from higher to lower concentrations. The big win for divers is decreasing the concentration of diluent in the lungs -- the partial pressure matters, not the percentage" So now partial pressure and percentage are unrelated? Or did you somehow manage to decrease the concentration of diluent in the lungs w/o changing its percentage? I'm confused here.