Breathing pure oxygen

leroyjenkens

I've heard that breathing pure oxygen is bad for you, but I can't find any information about it online. Is it bad?

Do scuba divers and astronauts breathe pure oxygen or is it diluted with other gases?

Borek

Oxygen poisoning.

Too high partial pressure in the air leads to seizures and blackouts, together with uncontrolled cotractions of muscles.

You can still breathe pure oxygen, just its pressure must be low enough.

jamesb-uk

Even when a patient is put 'on oxygen', the gas they are breathing is not pure oxygen, it just has a higher % in it. The lungs are generally very efficient at getting oxygen out of the air and into the blood;I heard that the red blood cells leaving the lungs are about 98% saturated with it, so breathing more oxygen is not going to do a huge deal of good to a healthy person.

Andy Resnick

I've asked a few docs about this at work, it does seem counterintuitive that too high a percentage oxygen is just as bad as too low a percentage. We decided that the problem is that a too-high O2 concentration displaces CO2 in the blood and tissues; this changes the pH- and that is the problem: an off-nominal pH.

Borek

Could be - no idea what the physiological mechanism is, but I have seen results at work.

In fact it is enough to hyperventillate for a few minutes to start to feel uncontrolled contractions of muscles - lips at first.

Moonbear

I never gave it considerable thought before, but that makes sense. I was thinking along the lines that Borek was, that without a CO₂ signal, hyperventillation would be a problem.

Since the OP also asked about divers, I think the O₂ is displaced with nitrogen for divers as they head into deeper depths.

Borek

When you go deeper nitrogen becomes dangerous as well (see nitrogen narcosis) - thus you don't use nitrogen to dilute oxygen, rather other gases with lower molecular mass (these times in form of mixtures, like trimix or heliox).

Moonbear

Oh, right, helium is definitely in the mix for very deep sea diving. I was watching some show where they had guys working pretty deep to repair oil rigs at sea, and as they communicated with the people on the platform, their voices were all squeaky. It was pretty hilarious, because they were all these big, burly, oil rig working, deep sea diving, manly men type people and talking in these funny, squeaky, high-pitched voices from the helium.

Mech_Engineer

Yeah Nitrogen narcolepsy kicks in at around 120-150 ft (3.5-4.5 atmospheres) depending on the person's physiology, so it can't be used for depths below that. I've personally gotten nitrogen narcolepsy at 140 ft before, it felt kind of like being drunk and giddy at the same time.

mgb_phys

You only need a partial pressure 0.2atm oxygen to function normally.
You are supposed to only use 100% O2 for a maximum of 24hours, but this is mainly because it irritates the lungs. Most hospital masks are designed to also allow some room air in so you aren't breathing 100% O2
Medical and aircraft bottled oxygen is often 70% O2 (the rest nitrogen) but that's mainly for fire prevention, there are a bunch of plastics and grease/oil that combust in 100% O2.

Higher oxygen partial pressures cause entertaining central nervous system toxicity effects, like convulsions. The limit for O2 in dangerous situations (like underwater) is generally 1.6atm but you can use upto around 3.2atm on the surface in a chamber for short periods.

In diving, down to normal recreational depths (40m) the best thing to use it Nitrox - air with enhanced O2 either 32 or 38% O2. Below 40m Nitrogen narcosis becomes a problem which is why it's the limit for recreational scuba.
Below that you have to remove the nitrogen and replace it with helium = Heliox.

As you go deeper to the point that 21% oxygen would get above 1.6atm you also have to remove some of the oxygen. That gets dangerous because you then have a mix that doesn't have enough oxygen to breathe at shallower depths, so as you descend you have to swap systems. It's a bit safer in commercial diving where someone at the surface (who hopefully isn't as stressed, disorientated and narced) is handling the mixes.

Then as you get much deeper (below 2-300m) helium starts to cause the same CNS symptoms as O2 and you have to replace some of the helium with hydrogen = trimix. With this you can work at 800m!

ps. guess who used to be a diving instructor

mgb_phys

I'm not sure that concentration of CO2 triggers breathing, I think it's just partial pressure. There are some people with a low sensitivity to CO2 who need a high concentration to trigger a breath - when you give them oxygen they pass out !