Nitrogen... at what depth?

[northcave]

If our basic safety stops are say between 4-6m then does that mean anywhere from 1-6mm there is a net loss of nitrogen?

I'm asking relation to "don't dive when pregnant rule". I know that is a debatable subject and many people do but the scientific reason is that nitrogen in the blood has affect a Feotus. However if there is a net loss of nitrogen below 6m then one would assume a pregnant person can do shallow dives up to 6m without risk.

I'm looking for a scientific discussion, not comments like "would you risk it" or "it's not your like your messing with".

 

[Scuba J7]

DAN is going to have the most info on diving while pregnant. There not a lot of research on it for obvious reasons, but there is more concern than just nitrogen. I’ll just leave this link here, about the fifth paragraph really stands out to me.
Doesn’t really answer your question, and even though you requested to not be lambasted, you should know that you will be.
The Risks of Pregnancy and Diving — DAN | Divers Alert Network — Medical Dive Article

 

[tbone1004]

any time the ppN2 is over 0.79 *the partial pressure of nitrogen, in air, at sea level* there is nitrogen uptake. At 6m, the absolute pressure is 1.6ata, so ppN2 on air is 1.6*.79=1.26
In order to not have any inert gas uptake at 6m, the fN2=.79/1.6=49.37, so you would have to be on EAN51 or great to not have any inert gas uptake at 6m

 

[arew+4]

You are off gassing nitrogen accumulated at deeper depths during a safety stop. If you dive the whole dive at 3-6 meters you would still be accumulating nitrogen. Unless you were breathing very high O2 Nitrox.

 

[northcave]

DAN is going to have the most info on diving while pregnant. There not a lot of research on it for obvious reasons, but there is more concern than just nitrogen. I’ll just leave this link here, about the fifth paragraph really stands out to me.
Doesn’t really answer your question, and even though you requested to not be lambasted, you should know that you will be.
The Risks of Pregnancy and Diving — DAN | Divers Alert Network — Medical Dive Article

Thanks for this. I suppose one of the concluding quote says it all... "While it is possible that some diving could be completed without impact, the absolute risk of any given exposure cannot be determined from the available data."

 

[doctormike]

If our basic safety stops are say between 4-6m then does that mean anywhere from 1-6mm there is a net loss of nitrogen?

I'm asking relation to "don't dive when pregnant rule". I know that is a debatable subject and many people do but the scientific reason is that nitrogen in the blood has affect a Feotus. However if there is a net loss of nitrogen below 6m then one would assume a pregnant person can do shallow dives up to 6m without risk.

I'm looking for a scientific discussion, not comments like "would you risk it" or "it's not your like your messing with".

You will not get a scientific discussion, for the simple reason that there is no adequate human data or animal trial data to give any meaningful information one way or the other (i.e. randomized clinical trials). So no matter who you ask, you will never get an evidence based conclusion.

Certain drugs go through extensive and expensive testing to prove that they are safe during pregnancy (FDA Category A), because there is a huge market there and it's worth doing the research. But no one is going to spend millions of dollars establishing safe pregnancy diving guidelines. Even if there were funding, there are the ethical implications of risking injury to a non-consenting individual to let people pursue a fun hobby. In cases of drug testing, you consider risk vs. benefit in clearing ethics review boards before doing research - a drug might cause harm, but it also might help, so it's worth doing controlled tests. No one needs to scuba dive.

There are all sorts of possible changes to maternal-fetal circulation related to diving (cardiovascular issues, PO2 issues, ambient pressure issues, etc...). There is no data on the long term effects of diving on the developing fetus. More to your point, there is no evidence that I am aware of to imply that "the scientific reason is that nitrogen in the blood has an affect on the fetus".

So, not sure what you are looking for, but if you want an OB/GYN or a hyperbaric doc to tell you "diving while pregnant is safe within these parameters based on science", it isn't going to happen.

 

[northcave]

You will not get a scientific discussion, for the simple reason that there is no adequate human data or animal trial data to give any meaningful information one way or the other (i.e. randomized clinical trials). So no matter who you ask, you will never get an evidence based conclusion.

Certain drugs go through extensive and expensive testing to prove that they are safe during pregnancy (FDA Category A), because there is a huge market there and it's worth doing the research. But no one is going to spend millions of dollars establishing safe pregnancy diving guidelines. Even if there were funding, there are the ethical implications of risking injury to a non-consenting individual to let people pursue a fun hobby. In cases of drug testing, you consider risk vs. benefit in clearing ethics review boards before doing research - a drug might cause harm, but it also might help, so it's worth doing controlled tests. No one needs to scuba dive.

There are all sorts of possible changes to maternal-fetal circulation related to diving (cardiovascular issues, PO2 issues, ambient pressure issues, etc...). There is no data on the long term effects of diving on the developing fetus. More to your point, there is no evidence that I am aware of to imply that "the scientific reason is that nitrogen in the blood has an affect on the fetus".

So, not sure what you are looking for, but if you want an OB/GYN or a hyperbaric doc to tell you "diving while pregnant is safe within these parameters based on science", it isn't going to happen.

All fair points... thanks.

 

[stuartv]

If our basic safety stops are say between 4-6m then does that mean anywhere from 1-6mm there is a net loss of nitrogen?

No. Any time you go below the surface breathing air or Nitrox you are going to on-gas nitrogen.

Safety stops work because you are off-gassing higher pressure nitrogen that you absorbed when deeper and getting it down to a safe level - but at the end of your safety stop, you still have a higher level of nitrogen than what you had at the surface before the dive. It's just a low enough level that you can ascend and get out without significant risk of that nitrogen bubbling inside you.

If you drop into the water and only go to 1 meter, you will still on-gas a little bit of nitrogen (assuming you're breathing air or Nitrox). It's just such a small amount that you would be safe to stay there indefinitely and still get right out without any kind of safety stop.

 

[elmo]

A few years ago I was diving with a obstetrician who summed up the dangers of diving while pregnant as something along the lines of, "we know enough to say once you know you're pregnant you shouldn't risk it".
My understanding is that it's the pressure, not nitrogen that is the issue. If nitrogen were the only problem it could be solved by diving with a rich nitrox mix. That is not the case. There are air/gas pockets in the foetus that cannot be equalised, so they get crushed.

 

[tbone1004]

No. Any time you go below the surface breathing air or Nitrox you are going to on-gas nitrogen.

yes for air, no for EANx, when EAD is >0 *i.e. ppN2 is great than .79* then you will be ongassing, but if EAD<0 *which it is at some range of depths for all nitrox mixes when ppN2 is less than .79*, then you will be offgassing or neutral.
i.e. EAN51 above has a ppN2 of .79 at 20ft/6m/1.6ata so there is no inert gas pressure gradient in the tissues. EAN32 is 5.3ft/1.6m/1.16ata
anything shallower than those depths you'll be offgasing, albeit slowly