Why doesn't oxygen cause decompression sickness?

[tarponchik]

IIRC the idea was the mechanical trauma from bubbles, not the gas per se... I don't remember where I read that, though, I may have imagined it.

Autoimmune? Maybe, but this is a dark territory.

 

[Lorenzoid]

Autoimmune? Maybe, but this is a dark territory.

I recall an exchange between you two in a thread a few years ago over "immune response" versus "inflammation." Starting about here: Does the body get better at removing nitrogen?

 

[dmaziuk]

Thank you. I heard "mechanical damage" from @DDM, now I know.

(I ran computers for Life Scientists for a while, I don't really have a clue how any of it works, I only repeat what I heard from smart people.)

 

[Dr Simon Mitchell]

Does this mean that you could in theory survive for a time with saline solution instead of blood if you were at high enough pressure?

Hello Joebob,

Yes, that's exactly what it means. Indeed, it has been done with animals breathing oxygen at 3 ATA. You can see a description of this famous old experiment here.

Sound right?

Hello Smache,

Yes, pretty much. Basically, the partial pressure of oxygen in a tissue never rises enough for oxygen to actually accumulate unless we provide more than enough dissolved oxygen in the blood to meet the tissue's metabolic needs, and that won't happen unless you breathe oxygen at a very high pressure - which we cannot do in diving.

In relation to some of the other comments, if bubbles were to form from oxygen, they would probably cause harm in much the same way that bubbles from any other gas can (except that they would likely have a much shorter life). There is not much basis for believing that bubbles formed from different gases cause harm in different ways.

Bubbles don't provoke 'immune reactions' per se, but they can incite inflammatory responses which have some similar effects. For example, a bubble in a blood vessel can damage the cells lining the blood vessel walls, and this can turn on platelets, clotting, and white blood cells in a harmful clotting and inflammatory response. Just the presence of bubbles in blood seems to be able to provoke some degree of inflammatory reaction from platelets and white cells, but we don't fully understand why this spills over into symptoms in some cases but not in others. Remember it is very common for us to form nitrogen bubbles in the veins after a dive. Anyway, that's a topic for another thread.

Simon M

 

[Duke Dive Medicine]

Thank you. I heard "mechanical damage" from @DDM, now I know.

(I ran computers for Life Scientists for a while, I don't really have a clue how any of it works, I only repeat what I heard from smart people.)

Thanks for that callout. Mechanical damage is probably a bit of an oversimplification. The damage is subtle - the lining of the blood vessels is disturbed by the bubble to the point that the inflammatory cascade mentioned by @Dr Simon Mitchell is activated. This can lead to capillary leakage and obstruction.

Hyperbaric oxygen therapy leverages Henry's Law. Even at a pressure equivalent of 33 feet, with patients breathing 100% O2 we can dissolve enough oxygen in the plasma to overcome deficits in tissue oxygenation. Some examples are diabetic foot ulcers, which can happen when the microcirculation in the foot is damaged by long-term high blood sugar, central retinal artery occlusion (essentially a retinal stroke), tissue necrosis caused by therapeutic radiation, and compromised tissue flaps (surgery where skin and underlying tissue is taken from one part of the body and placed on another). The oxygen that's dissolved in the plasma can reach areas that red blood cells can't, either becaues of acute blockage or capillary damage.

Divers with decompression sickness are treated with 100% oxygen at a pressure equivalent of 60 feet, which is an inspired partial pressure of O2 of 2.82 ATA. From here it would be theoretically possible to get oxygen bends but it doesn't happen to our divers, mostly because we decompress them slowly to 30 feet after the 60-foot excursion, spend a good while at 30 feet, and then decompress them slowly from 30 feet to the surface. If a catastrophe happened and the chamber were to rapidly decompress from 60 feet with the diver on O2, we'd be much more worried about the inside tender (who breathes compressed air in the chamber), as any oxygen bubbles that would form in the diver would be rapidly metabolized and much less likely to cause symptoms.

Best regards,
DDM

 

[joebob24]

Divers with decompression sickness are treated with 100% oxygen at a pressure equivalent of 60 feet, which is an inspired partial pressure of O2 of 2.82 ATA.

What type of mask are they breathing this through? I know some of the oxygen masks used in medical settings don't always seal well enough to get the full percentage of oxygen, so do you use special masks that ensure 100 percent delivery? I have always wondered about this when comparing PPo2 from diving vs chamber PPo2. In scuba you know 100 percent of what is being inspired is coming from the tank.

 

[rjack321]

What type of mask are they breathing this through? I know some of the oxygen masks used in medical settings don't always seal well enough to get the full percentage of oxygen, so do you use special masks that ensure 100 percent delivery? I have always wondered about this when comparing PPo2 from diving vs chamber PPo2. In scuba you know 100 percent of what is being inspired is coming from the tank.

It's a not a mask it's hood. There are different brands but most look something like this with a latex neck dam. The hose delivers oxygen and vents through a one-way valve.

 

[Duke Dive Medicine]

What type of mask are they breathing this through? I know some of the oxygen masks used in medical settings don't always seal well enough to get the full percentage of oxygen, so do you use special masks that ensure 100 percent delivery? I have always wondered about this when comparing PPo2 from diving vs chamber PPo2. In scuba you know 100 percent of what is being inspired is coming from the tank.

Thanks @rjack321 for the photo. This is similar to the hoods we use. We also have Scott aviator double-hose O2 masks for the rare claustrophobic patient who doesn't tolerate the hood.

Best regards,
DDM

 

[tarponchik]

Offtopic, but interesting: is this the same as DCS?

 

[rjack321]

Offtopic, but interesting: is this the same as DCS?

Not exactly. More like a mechanical gas embolism. Fish have a swim bladder which is entirely internal, they have no way to "exhale" that gas it has to redissolve in their bloodstream and get expelled across their gills. The swim bladder is used to maintain their buoyancy and orientation.

Fish at (significant) depth that are rapidly brought to the surface faster than they can circulate and expel the rapidly expanding gas in their swim bladders generally die. The now enlarged swim bladder pushes most of their other organs every which way, their stomach often will be partly inverted through their mouth for instance. Unless returned to depth their chances of survival are very low. Even when recompressed they often die.